Α -fe-containing rare earth-iron-based magnetic powder, method for producing the same, magnetic material for magnetic field amplification, and magnetic material for microwave absorption

Abstract

To provide magnetic powder having excellent responsiveness to a magnetic field, and to provide a method for producing the same.SOLUTION: An α - Fe-containing rare earth-iron-based magnetic powder including a core region containing a rare earth R (R is at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe, an α - Fe-containing region containing α - Fe and at least one selected from the group consisting of an oxide, a nitride, and an oxynitride of the rare earth R outside the core region, and an iron oxide-containing region containing magnetite or maghemite outside the α - Fe-containing region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an α-Fe-containing rare earth-iron-based magnetic powder, a method for producing the same, a magnetic material for magnetic field amplification, and a magnetic material for ultra-high frequency absorption. [Background technology]

[0002] In recent years, the trend toward smaller, more multifunctional devices and faster computing speeds has led to higher drive frequencies, and the widespread use of high-frequency and ultra-high-frequency devices is steadily expanding. Particularly noteworthy is the development of power devices used in the high-frequency range (1 MHz to less than 1 GHz). For example, GaN electronic devices are expected to see significant market growth in the future as high-frequency, high-power wireless and power electronics devices. Increasing the frequency of GaN circuits for power electronics requires not only GaN devices but also higher-frequency passive components. For example, GaN wireless power transfer operates at frequencies exceeding 10 MHz, necessitating coils with magnetic core materials capable of operating at high frequencies. Furthermore, there is an increasing demand for inductors, reactors, transformers, and antennas that function in the high-frequency range (20 MHz to less than 1 GHz). However, due to the lack of magnetic core materials with excellent high-frequency characteristics, air-core coils are unavoidable. Even if the use of GaN can increase frequency and reduce device size, the overall circuit size increases. As an example of a conventional high frequency magnetic material, a rare earth-iron-nitrogen magnetic material in which the powder surface is coated with a ferrite magnetic material has been known (Patent Document 1).

[0003] The next area of ​​interest is the development of information infrastructure in the ultra-high frequency range from 1 GHz to 1 THz. There are various needs for high frequency properties of materials that absorb spurious signals and their harmonics in the range of 1 GHz to less than 10 GHz for 5G, 10 GHz to less than 100 GHz for 5G+, and 100 GHz to less than 1 THz for 6G, and the need for such materials has been increasing recently. In particular, there are currently no materials that can absorb wide-band ultra-high frequencies above 1 GHz, even above 10 GHz, and there are high hopes for the emergence of ultra-wide frequency band ultra-high frequency absorbing materials that can be used widely in the range of 1 GHz to less than 1 THz. One example of a magnetic material for high frequencies that has been known to date is a rare earth-iron-nitrogen magnetic material in which the powder surface is coated with a ferrite magnetic material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2008 / 136391 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a magnetic powder that is highly responsive to a magnetic field, and a method for producing the same. [Means for solving the problem]

[0006] An α-Fe-containing rare earth-iron magnetic powder according to one embodiment of the present disclosure has a core region containing a rare earth element R (R is at least one element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe, an α-Fe-containing region outside the core region containing α-Fe and at least one element selected from the group consisting of oxides, nitrides, and oxynitrides of the rare earth element R, and an iron oxide-containing region outside the α-Fe-containing region containing magnetite or maghemite.

[0007] Furthermore, a method for producing an α-Fe-containing rare earth-iron-based magnetic powder according to one embodiment of the present disclosure includes a phosphorus treatment step of adding an inorganic acid to a slurry containing a rare earth-iron-based magnetic powder containing a rare earth R (R is at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe, water, and a phosphorus-containing substance, thereby forming a phosphorus compound coating portion on the magnetic powder, thereby obtaining a rare earth-iron-based magnetic powder having a phosphorus compound coating portion; an oxidation step of heat-treating the rare earth-iron-based magnetic powder having the phosphorus compound coating portion in an oxygen-containing atmosphere at 350°C or higher and 600°C or lower; The method includes an annealing step of heat-treating the rare earth-iron magnetic powder having an oxidized phosphorus compound coating portion in an atmosphere of an inert gas or a reducing gas not containing nitrogen atoms at 200° C. to 600° C. After the annealing step, a further step of heat-treating the α-Fe-containing rare earth-iron magnetic powder in an oxygen-containing atmosphere at 200° C. to 600° C. may be included. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a magnetic powder that is excellent in response to a magnetic field, and a method for producing the same. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows the frequency dependence of the complex relative permeability of the magnetic materials using the magnetic powders produced in Examples 1 to 3 and Comparative Examples 1 to 4. [Figure 2] 1 shows XRD patterns of the magnetic powders produced in Examples 1 and 3 and Comparative Examples 1 and 2. [Figure 3] This shows a STEM-DF image of the surface vicinity of a cross section of the magnetic powder produced in Comparative Example 2. The EDS analysis points listed in Table 3 are shown in the figure. [Figure 4] 1 shows a STEM-DF image of the surface vicinity of a cross section of the magnetic powder produced in Example 1. The EDS analysis points listed in Table 4 are shown in the figure. [Figure 5]1 shows a STEM-DF image of the surface vicinity of a cross section of the magnetic powder produced in Example 3. The EDS analysis points listed in Table 5 are shown in the figure. [Figure 6] 1 shows a STEM-EDS mapping image of Fe in a cross section of the magnetic powder produced in Comparative Example 2. [Figure 7] 1 shows a STEM-EDS mapping image of Fe in a cross section of the magnetic powder produced in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiments of the present disclosure are described in detail below. However, the embodiments described below are examples for embodying the technical ideas of the present disclosure, and the present disclosure is not limited to the following. In this specification, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0011] In this specification, "high frequency" refers to electromagnetic waves having a high frequency, and in this disclosure, unless otherwise specified, particularly refers to electromagnetic waves of 1 MHz or more and less than 1 GHz. In this specification, "ultra-high frequency" refers to electromagnetic waves having a frequency higher than high frequency, and in this disclosure, unless otherwise specified, particularly refers to electromagnetic waves of 1 GHz or more and less than 1 THz.

[0012] In this specification, "excellent efficiency" means that at a certain frequency f, the ratio of the imaginary term (μ") to the real term (μ') of the complex relative permeability (μ) of a magnetic material, i.e., tan δ = μ" / μ' (also called the loss coefficient), takes a small value. δ is called the phase difference. Also, the value of (90° - δ) is called the phase angle θ. Therefore, "excellent efficiency" means that the phase angle θ, opposite to δ, takes a large value close to 90°. When tan δ and δ are small, or when the phase angle θ is large and approaches 90°, electromagnetic waves of frequency f can be amplified while reducing loss. In terms of magnetic field amplification characteristics, an increase in the value of the phase angle θ (a decrease in the values ​​of tan δ and δ) is said to be "an improvement in the phase angle θ (tan δ)," while a decrease in the value of the phase angle θ (an increase in the values ​​of tan δ and δ) is said to be "a deterioration in the phase angle θ (tan δ)."

[0013] In this specification, "excellent response to a magnetic field" means (1) that at a frequency f in the high frequency range, the magnetic moment of the magnetic material follows the magnetic field and the complex relative permeability (μ r ) takes a large value and the imaginary term (μ") takes a small value, and therefore tanδ also takes a small value, or (2) in the ultra-high frequency range f, it responds to magnetic fields by resonating with electromagnetic waves, and the imaginary term (μ") takes a large value. Materials with little delay or loss in magnetization in the high frequency range have high μ' and low μ", have excellent response to magnetic fields, and function as magnetic field amplification materials. Materials that can follow magnetic fields but experience delay in magnetization in the ultra-high frequency range, but do not cause loss, have high μ", have excellent response to magnetic fields, and function as electromagnetic wave absorption materials. The complex relative permeability of a material that does not respond to magnetic fields is the complex relative permeability of a vacuum (μ'=1, μ"=0, μ r =1) and does not function as a high-frequency magnetic material.

[0014] In this specification, the "magnetic field amplification" property refers to a property in which the real term (μ') of the complex relative magnetic permeability of a magnetic material is greater than 1, which is the real term of the relative magnetic permeability of a vacuum, and the magnetic field in the space in which the magnetic material is placed is increased compared to that in a vacuum (or atmosphere). Good or high magnetic field amplification properties refer to a high μ', and a material with a μ' of greater than 2 at a certain frequency f is called a "magnetic material for magnetic field amplification" (at frequency f). When simply referring to relative magnetic permeability, this refers collectively to the absolute value of the real term and the absolute value of the imaginary term of the complex relative magnetic permeability. Unless otherwise specified, high relative magnetic permeability or high magnetic permeability refers to a high real term of the relative magnetic permeability.

[0015] <<Rare earth-iron magnetic powder containing α-Fe>> The α-Fe-containing rare earth-iron magnetic powder of this embodiment is characterized by having a core region containing a rare earth element R (R is at least one element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe, an α-Fe-containing region outside the core region containing α-Fe and at least one element selected from the group consisting of oxides, nitrides, and oxynitrides of the rare earth element R, and an iron oxide-containing region outside the α-Fe-containing region containing magnetite or maghemite.

[0016] <Core Areas> The core region contains rare earth elements R (R is at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe. R is at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm, and among these, Nd, Sm, and Ce are preferred in terms of achieving high magnetic permeability.

[0017] Sm may account for more than 50 atomic %, 70 atomic % or more, or even 90 atomic % or more of the total rare earth R component. When the core region is made of a rare earth-iron-nitrogen-based magnetic material containing nitrogen and is crystalline and has a tetragonal crystal structure containing Sm, it is suitable as a magnetic material for magnetic field amplification, offering the advantages of high μ' and a low phase angle θ in the 10 MHz range or higher. Materials with small crystallite sizes are suitable for use as both magnetic materials for ultra-high frequency absorption and magnetic field amplification. Furthermore, rare earth-iron-nitrogen-based magnetic materials containing Sm with a tetragonal or small crystallite structure are also highly practical, being inexpensive. However, when using rare earth-iron-nitrogen-based magnetic materials containing Sm for applications requiring high relative permeability, it is preferable that the Sm content be less than 50 atomic %. In this case, Sm may be less than 50 atomic %, 25 atomic % or less, or 5 atomic % or less of the total rare earth R component. Moreover, the core region preferably further contains N (nitrogen) in order to provide excellent efficiency in the high frequency range.

[0018] The composition of the core region is represented by the general formula 1 below: R x X 100-x-y N y (1) Examples of such rare earth-iron-nitrogen magnetic materials include those composed of a rare earth element R, a ferromagnetic component (X), and nitrogen (N), as represented by the formula: where x and y are the atomic percentages of R and N, respectively. x is preferably 3 to 30, more preferably 3 to 15. y is preferably 2 to 30, more preferably 2 to 25. X is at least one selected from the group consisting of Fe, Co, and Ni, and the total amount of Co and Ni relative to the total amount of Fe, Co, and Ni is preferably 50 atomic % or less, and may be 1 atomic % or less. When Co is contained at 1 atomic % or more, the Curie point tends to be higher and thermal properties tend to be improved. When Ni is contained at 1 atomic % or more, oxidation resistance tends to be improved. In this specification, Fe, Co, and Ni are sometimes collectively referred to as the X component.

[0019] The composition of the core region is represented by the general formula 2 below: Rx X 100-x-y-z M y N z (2) Examples of such rare earth-iron-nitrogen magnetic materials include those composed of a rare earth element R, a ferromagnetic component (X), an M component, and nitrogen (N), as represented by the formula (1). Here, x, y, and z are the atomic percentages of R, M, and N, respectively. x is preferably 2 to 24, and more preferably 2 to 15. y is preferably 0.0001 to 25, and more preferably 0.5 to 25. z is preferably 2 to 50, and more preferably 3 to 50. X is the same as in formula 1 above, and M is at least one element selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr. When a rare earth-iron-nitrogen magnetic material having a tetragonal crystal structure contains such an M component, it becomes a material with in-plane magnetic anisotropy.

[0020] When the nitrogen atom content is within the ranges described in the above formulas 1 and 2, there are advantages in that the real term of the relative magnetic permeability is high and tan δ is low. The crystal structure of the core region of the rare earth-iron-nitrogen based magnetic material having the composition of the above formulas 1 and 2 is Th2Zn 17 type, Th2Ni 17 Type, ThMn 12 In either case, in-plane anisotropic materials are preferred because they have a high μ' and can absorb a wide range of frequencies in the ultra-high frequency range. From this perspective, the preferred rare earth components for each crystal structure are rhombohedral Th2Zn 17 In the type Ce, Pr, Nd, Eu, Gd, and Tb, hexagonal Th2Ni 17 In the type Y, Dy, Ho, Er, Tm, and Lu, tetragonal ThMn 12 Examples of rare earth-iron-nitrogen-based magnetic materials include Sm, Er, Tm, Y, Ce, Eu, Gd, and Lu. Furthermore, rare earth-iron-nitrogen-based magnetic materials containing nitrogen can achieve high-frequency magnetic materials with high permeability and high efficiency in the high-frequency range, even in an amorphous state. In this case, light and medium rare earth elements such as La, Ce, Pr, Nd, and Sm are preferred as rare earth components.

[0021] The composition of the core region is represented by the general formula 3 below: R x X100-x (3) Examples of rare earth-iron magnetic materials include those consisting of a rare earth element R and a ferromagnetic component (X), expressed as follows: where x is the atomic percentage of R. x is preferably 2 or more and 33 or less, more preferably 5 or more and 15 or less. X is the same as above. In the case of a "rare earth-iron" magnetic material, which is a rare earth-iron magnetic material that does not contain nitrogen, boron (B), or carbon (C), the crystal structure of the core region is Th2Zn 17 type, Th2Ni 17 Type, ThMn 12 In other words, the rare earth component preferable for each crystal structure is rhombohedral ThZn 17 In the type Ce, Pr, Nd, Eu, Gd, Tb and Sm, hexagonal Th2Ni 17 In the type Y, Dy, Ho, Er, Tm, and Lu, tetragonal ThMn 12 The types include Tb, Y, Ce, Eu, Gd, and Lu, respectively.

[0022] The composition of the core region is represented by the general formula 4 below: R x X 100-x-y B y (4) Examples of such rare earth-iron magnetic materials include those composed of a rare earth element R, a ferromagnetic component (X), and boron (B), as represented by the formula: where x and y are the atomic percentages of R and B, respectively. x is preferably 2 to 30, and more preferably 3 to 15. y is preferably 2 to 30, and more preferably 3 to 15. X is the same as above, but X may be substituted with the above-mentioned M component in a range of 0.0001 atomic percent to less than 50 atomic percent. When a rare earth-iron magnetic material having a tetragonal crystal structure contains these M components, it becomes a material with high magnetic permeability.

[0023] In the case of rare earth-iron based magnetic materials containing mainly boron, it is also preferable that the materials have in-plane anisotropy in terms of having a high μ', such as tetragonal NdFe 14 Preferred rare earth elements in the B type include Sm, Er, and Tm.

[0024] The composition of the core region is represented by the general formula 5 below: R x X 100-x-y-z N y C z (5) Examples of suitable rare earth-iron magnetic materials include those composed of a rare earth element R, a ferromagnetic component (X), and carbon (C), as represented by the formula (5). These rare earth-iron magnetic materials may also be rare earth-iron-nitrogen magnetic materials containing nitrogen (N). Here, x, y, and z are each in atomic percent. x is preferably 3 to 30, more preferably 3 to 15. y + z is preferably 2 to 30, more preferably 2 to 25. y / z is preferably 0 to 10,000, more preferably 0 to 1,000. X is the same as above, but X may be substituted with an M component in a range of 0.0001 to less than 50 atomic percent. When the rare earth-iron magnetic material or rare earth-iron-nitrogen magnetic material represented by the formula (5) has a tetragonal crystal structure and contains these M components, the material exhibits in-plane magnetic anisotropy. When the nitrogen and carbon atom contents are within the ranges specified in formula 5, the real term of the relative magnetic permeability is high and tan δ is low, which is an advantage. The preferred rare earth components for each crystal structure are the same as those for rare earth-iron-nitrogen magnetic materials. As more nitrogen is replaced by carbon, the magnetic permeability and Curie point deteriorate, but heat resistance improves slightly.

[0025] However, although the core region of the present disclosure can be formed using any of the magnetic materials represented by the above formulas 1 to 5, it is particularly preferable that the rare earth-iron-based magnetic material contains nitrogen as a component. When a rare earth-iron-nitrogen-based magnetic material is selected for the core region of the present disclosure, high magnetic permeability and high responsiveness to magnetic fields are exhibited.

[0026] The average particle size of the core region is not particularly limited as long as it is within a particle size range that can achieve excellent efficiency in the target frequency band, but is preferably 0.05 μm to 1000 μm, more preferably 0.1 μm to 500 μm, even more preferably 0.5 μm to 161 μm, and particularly preferably 0.5 μm to 50 μm. Here, the average particle size refers to the median diameter measured under dry conditions using a laser diffraction particle size distribution analyzer. In other words, the average particle size is expressed as D50, which is the particle size at which the integrated value of the particle size distribution on a volume basis corresponds to 50%.

[0027] The core region contains a rare earth-iron-nitrogen compound, and in an XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity (I) of the (110) plane of α-Fe to the peak intensity (II) of the strongest line of the rare earth-iron-nitrogen compound is preferably 0.01 or more and less than 100, more preferably 0.1 or more and 10 or less. Within this range, there is an effect of improving μ' while maintaining a low tan δ around 100 MHz.

[0028] The core region contains a rare earth-iron-nitrogen compound, and in an XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity (I) of the (511) plane of magnetite or maghemite to the peak intensity (II) of the strongest line of the rare earth-iron-nitrogen compound is preferably 0.01 or more and less than 100, more preferably 0.1 or more and less than 100. Within this range, there is an effect of improving μ' while maintaining a low tan δ.

[0029] The core region contains a rare earth-iron-nitrogen compound, and in an XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity (I) of the (104) plane of hematite to the diffraction peak intensity (II) of the (511) plane of the magnetite or maghemite is preferably 0 or more and less than 10, and more preferably 0 or more and less than 5. Within this range, loss due to the electrical insulating effect of hematite is improved, and furthermore, the magnetic coupling effect of maghemite and / or magnetite can be obtained, resulting in a dramatic improvement in magnetic permeability.

[0030] <Method of manufacturing the core region> There are no particular limitations on the method for producing the rare earth-iron magnetic powder that constitutes the core region, and examples of production methods using the solid phase method or precipitation method will be described in detail below.

[0031] (solid phase method) The method for producing rare earth-iron magnetic powder by the solid phase method is as follows: A step of mixing R oxide powder, Fe raw material, and Ca powder (mixing step); The method includes a step of reducing the resulting mixture (reduction step). The method for producing rare earth-iron based magnetic powder by the solid phase method preferably further comprises a step of nitriding the alloy particles obtained in the reduction step (nitriding step).

[0032] [Mixing process] In the mixing step, alloy particles are obtained by mixing rare earth R oxide powder, an Fe raw material, and Ca powder. In the mixing step, not only metallic Fe but also Fe2O3 and / or Fe3O4 can be used as the Fe raw material. When Fe2O3 and / or Fe3O4 are used, the content (total number of moles of Fe contained in Fe2O3 and / or Fe3O4 relative to the total number of moles of Fe contained in metallic Fe, Fe2O3, and / or Fe3O4) is preferably 30 atomic % or less. The reaction heat generated when these iron oxides are reduced by Ca promotes a uniform reaction overall, leading to savings in external energy and improved yield. The amount of granular Ca mixed must be sufficient to reduce the oxide of the R oxide and the selectively mixed metal oxide. The amount of granular Ca mixed may be 0.5 to 3 times, preferably 1 to 2 times, the equivalent of oxygen atoms contained in the R oxide and the selectively mixed Fe2O3 and / or Fe3O4.

[0033] [Reduction process] The mixed powder obtained in the mixing step is placed in a heating vessel capable of being evacuated. After evacuating the heating vessel, the mixture is heated to 600°C to 1300°C, preferably 700°C to 1200°C, and more preferably 800°C to 1100°C while passing argon gas through the vessel. At a heating temperature below 600°C, the reduction reaction of the oxides does not proceed. At a heating temperature above 1300°C, the rare earth and Fe may melt and form clumps. Furthermore, at a heating temperature of 700°C or higher, the reduction time can be shortened, which tends to improve productivity. At a heating temperature of 1200°C or lower, Ca scattering can be reduced, which tends to further reduce variation during reduction. The heat treatment time may be 4 hours or less, preferably less than 120 minutes, more preferably less than 90 minutes, from the viewpoint of conducting the reduction reaction more uniformly. The lower limit of the heat treatment time is preferably 10 minutes or more, more preferably 30 minutes or more. If the mixed powder contains an appropriate amount of Fe2O3 and / or Fe3O4 in addition to metallic Fe, self-heating occurs during the temperature rise, allowing for an efficient and uniform reaction. On the other hand, if Fe2O3 and / or Fe3O4 is mixed in an amount exceeding 30 atomic % relative to metallic Fe, as in the mixing process described above, the excessive heat generated may cause an explosion or scattering. Furthermore, the particle size of the resulting rare earth-iron magnetic powder can be controlled by controlling the reduction temperature. Generally, the higher the reduction temperature, the larger the powder particle size.

[0034] [Nitriding process] To obtain a core region containing N (nitrogen), the alloy particles obtained in the reduction step are subjected to a nitriding process (nitriding process). In the nitriding process, the particles are cooled in argon gas to a temperature range of preferably 250°C to 800°C, more preferably 300°C to 600°C, and even more preferably 400°C to 550°C. The heating vessel is then evacuated again, and nitrogen gas is introduced. The gas introduced is not limited to nitrogen, but may also be a gas containing nitrogen atoms, such as ammonia. The particles are heated at a pressure above atmospheric pressure while passing nitrogen gas for several hours, preferably about 5 hours, after which the heating is stopped and the particles are allowed to cool.

[0035] The product obtained after the reduction or nitriding process may contain, in addition to the rare earth-iron-based magnetic powder, by-product CaO, unreacted metallic calcium, and other components, forming a composite sintered mass. In this case, a water-washing process can be performed by placing the product in ion-exchange water to separate calcium oxide (CaO) and other calcium-containing components from the magnetic powder as a calcium hydroxide (Ca(OH)2) suspension. This water-washing process may involve several cycles of stirring in water, leaving the product to stand, and removing the supernatant. Residual calcium hydroxide may also be thoroughly removed by washing the magnetic powder with acetic acid or the like. Since the remaining unreacted Ca becomes calcium nitride (Ca3N2), which makes removal easier, a water-washing process is preferably performed after the heat treatment in the nitriding process. The rare earth-iron-based magnetic powder obtained in this manner tends to have a sharper particle size distribution.

[0036] (precipitation method) The method for producing rare earth-iron magnetic powder by precipitation is as follows: a step of mixing a solution containing R and Fe with a precipitant to obtain a precipitate containing R and Fe (precipitation step); a step of calcining the precipitate to obtain an oxide containing R and Fe (oxidation step); A step of heat-treating the oxide in a reducing gas-containing atmosphere to obtain a partial oxide (pretreatment step); A process of reducing the partial oxide (reduction process) The method includes: The method for producing rare earth-iron based magnetic powder by the precipitation method preferably further comprises a step of nitriding the alloy particles obtained in the reduction step (nitriding step).

[0037] [Precipitation process] In the precipitation step, an R raw material containing rare earth element R and an Fe raw material containing iron Fe are dissolved in a strongly acidic solution to prepare a solution containing R and Fe. The R raw material and the Fe raw material are not limited as long as they can be dissolved in a strongly acidic solution. For example, in terms of ease of availability, an R raw material can be an R oxide, and an Fe raw material can be iron sulfate (FeSO4). The concentration of the solution containing R and Fe can be adjusted appropriately within a range in which the R raw material and the Fe raw material are substantially soluble in the acidic solution. In terms of solubility, an example of the acidic solution is sulfuric acid.

[0038] An insoluble precipitate containing R and Fe is obtained by reacting a solution containing R and Fe with a precipitant. The solution containing R and Fe is sufficient as long as it becomes a solution containing R and Fe upon reaction with the precipitant. For example, a raw material containing R and a raw material containing Fe may be prepared as separate solutions, and each solution may be added dropwise to react with the precipitant. Even when prepared as separate solutions, the concentrations of each raw material are appropriately adjusted so that they are substantially soluble in the acidic solution. The precipitant is not limited as long as it is an alkaline solution that reacts with the solution containing R and Fe to produce a precipitate, and examples include ammonia water and caustic soda, with caustic soda being preferred.

[0039] After separating the precipitate, it is preferable to remove the solvent from the separated material in order to prevent the precipitate from redissolving in the remaining solvent during the heat treatment in the subsequent oxidation step, causing aggregation of the precipitate when the solvent evaporates, or changes in particle size distribution, powder particle size, etc. Specific examples of the method for removing the solvent include drying in an oven at 70°C or higher and 200°C or lower for 5 hours to 12 hours when water is used as the solvent.

[0040] The precipitation step may be followed by a step of separating and washing the resulting precipitate. The washing step is appropriately carried out until the conductivity of the supernatant solution becomes 50 μS / cm or less. The step of separating the precipitate may involve, for example, adding a solvent (preferably water) to the resulting precipitate and mixing, followed by filtration, decantation, or the like.

[0041] [Oxidation process] The oxidation step is a step in which the precipitate formed in the precipitation step is fired to obtain an oxide containing R and Fe. For example, the precipitate can be converted to an oxide by heat treatment. When the precipitate is heat-treated, it must be performed in the presence of oxygen, for example, in an air atmosphere. Furthermore, since it must be performed in the presence of oxygen, it is preferable that the non-metallic portion of the precipitate contains oxygen atoms. The heat treatment temperature in the oxidation step (hereinafter referred to as the oxidation temperature) is not particularly limited, but is preferably 700°C to 1300°C, and more preferably 900°C to 1200°C. If the temperature is less than 700°C, oxidation will be insufficient, and if the temperature exceeds 1300°C, the desired shape, average particle size, and particle size distribution of the rare earth-iron magnetic powder will tend not to be obtained. The heat treatment time is also not particularly limited, but may be 0.5 to 4 hours, and preferably 1 to 3 hours.

[0042] [Pretreatment process] The pretreatment step is a step in which an oxide containing R and Fe is heat-treated in an atmosphere containing a reducing gas to obtain a partial oxide in which part of the oxide is reduced.

[0043] [Reduction process] The reduction process involves heating the partial oxide in the presence of a reducing agent at a temperature between 600°C and 1300°C, preferably between 700°C and 1200°C, and more preferably between 800°C and 1100°C, to obtain alloy particles. At a heating temperature below 600°C, the reduction reaction of the oxide does not proceed. At a heating temperature above 1300°C, R and Fe may melt and form clumps. Furthermore, a heating temperature of 700°C or higher tends to shorten the reduction time, improving productivity. A temperature of 1200°C or lower tends to reduce the scattering of the reducing agent, Ca, and further reduce variation during reduction. Controlling the reduction temperature allows for control of the particle size of the rare earth-iron magnetic powder; generally, the higher the reduction temperature, the larger the powder particle size. The heat treatment time is preferably less than 120 minutes, more preferably less than 90 minutes, from the viewpoint of achieving a more uniform reduction reaction. The lower limit of the heat treatment time is preferably 10 minutes or more, more preferably 30 minutes or more.

[0044] [Nitriding process] To obtain a core region containing N (nitrogen), the alloy particles obtained in the reduction process are nitrided (nitriding process). The nitriding process produces high-frequency magnetic powder with higher magnetic permeability. Because the particulate precipitate obtained in the precipitation process is used, porous, agglomerated alloy particles are obtained in the reduction process. This allows for immediate nitriding by heat treatment in a nitrogen atmosphere without pulverization, ensuring uniform nitriding.

[0045] The heat treatment temperature in the nitriding treatment of the alloy particles (hereinafter referred to as the nitriding temperature) is preferably 250°C or higher and 800°C or lower, more preferably 300°C or higher and 600°C or lower. In order to suppress decomposition of the nitriding reaction product in the subsequent nitriding step and increase the reaction efficiency, the temperature is particularly preferably 400°C or higher and 550°C or lower, and the atmosphere is replaced with a nitrogen atmosphere within this temperature range. The heat treatment time may be set to a value that allows the nitriding of the alloy particles to be carried out sufficiently uniformly.

[0046] <α-Fe containing region> The α-Fe-containing region is present outside the core region and contains at least one selected from the group consisting of α-Fe and oxides, nitrides, and oxynitrides of rare earth elements R. The α-Fe-containing region enhances the insulation between adjacent magnetic powder particles and suppresses efficiency degradation due to eddy currents across grains. As a result, the use of the magnetic powder of the present disclosure improves tan δ and phase angle θ in the high-frequency range, resulting in a more efficient magnetic material for magnetic field amplification. The α-Fe-containing region also magnetically connects adjacent magnetic powder particles and reduces demagnetizing fields. As a result, the use of the magnetic powder of the present disclosure tends to further improve the real term μ' of the magnetic permeability of the magnetic material for magnetic field amplification. The α-Fe-containing region can be formed, for example, by forming a phosphorus compound coating on the surface of the magnetic powder and then heat-treating it in an oxygen-containing atmosphere.

[0047] The α-Fe-containing region preferably contains at least one compound selected from the group consisting of oxides, nitrides, and oxynitrides of rare earth element R, as well as nanocrystals of the α-Fe phase. The α-Fe-containing region more preferably contains at least one nanocrystal selected from the group consisting of oxides, nitrides, and oxynitrides of rare earth element R. The presence of at least one nanocrystal selected from the group consisting of oxides, nitrides, and oxynitrides of rare earth element R can be confirmed, for example, by observing a halo near the strongest diffraction line of the compound (e.g., a diffraction angle 2θ of approximately 20 to 30°) in XRD using a CuKα radiation source, or by observing a ring inside the ring pattern indicating the α-Fe phase in electron diffraction measurements of the α-Fe-containing region. For example, when R is Sm, the oxide, nitride, and oxynitride of rare earth element R are samarium oxide, samarium nitride, and samarium oxynitride, respectively. The α-Fe-containing region may further contain carbon-containing substances, such as double oxides, double nitrides, double oxynitrides, and carbonitrides containing rare earth elements R and iron, and boron-containing substances, such as borides, to the extent that magnetic coupling is not impaired. Among these, the double oxides, double nitrides, and double oxynitrides may have a perovskite structure or a spinel structure. A structure containing nanocrystals of α-Fe and at least one compound selected from the group consisting of oxides, nitrides, and oxynitrides containing R can be formed, for example, by forming a phosphorus compound coating on the surface of a magnetic powder and then heat-treating it in an oxygen-containing atmosphere, or by nitriding the magnetic powder and then annealing it.

[0048] The "α-Fe phase" is a cubic crystal with a bcc structure, and its main component is Fe. The α-Fe phase can also contain ferromagnetic components such as Co and Ni, with the total content of the ferromagnetic components preferably being 50 atomic % or less. The α-Fe phase can also contain M components, such as metals like Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr, and nitrogen, but to preserve the ferromagnetism of the α-Fe phase, it is preferable to use an amount that does not disrupt the bcc structure. For example, when Si is included, it is preferably 10 atomic % or less. When nitrogen is included, it is preferably 5 atomic % or less. Furthermore, when boron is included, it is preferably 12 atomic % or less, more preferably 5 atomic % or less. When carbon is included, it is preferably 12 atomic % or less, more preferably 5 atomic % or less.

[0049] The α-Fe-containing region is believed to contain at least one compound selected from the group consisting of rare-earth oxides, nitrides, and oxynitrides, as well as nanocrystals composed of α-Fe, thereby enhancing the electrical insulation and magnetic coupling effects of the α-Fe-containing region. Here, "electrical insulation" refers to the presence of highly resistive α-Fe-containing regions on the surface of the magnetic powder, which blocks electrical conduction between the core regions of adjacent magnetic powders and prevents the generation of eddy currents across the core regions. This electrical insulation reduces eddy current loss, achieving "excellent efficiency." Furthermore, "magnetic coupling" refers to the presence of highly resistive but ferromagnetic α-Fe-containing regions on the surface of the magnetic powder, which creates ferromagnetic and magnetostatic coupling between adjacent core regions. This magnetic coupling reduces local demagnetizing fields and weakens the demagnetizing fields acting on the core regions, thereby achieving high relative permeability.

[0050] The average particle size of at least one compound selected from the group consisting of oxides, nitrides, and oxynitrides of rare earth elements R contained in the α-Fe-containing region is preferably 1 nm or more but less than 1000 nm, more preferably 1 nm or more but less than 100 nm, even more preferably 1 nm or more but less than 20 nm, and particularly preferably 1 nm or more but less than 10 nm. The average particle size of Fe-based nanocrystals having a bcc structure is preferably 1 nm or more but less than 1000 nm, more preferably 1 nm or more but less than 100 nm, even more preferably 1 nm or more but less than 20 nm, and particularly preferably greater than 1.5 nm but less than 10 nm. These particle sizes can be measured by TEM (transmission electron microscope) or STEM (scanning transmission electron microscope) or EDS (energy dispersive X-ray analysis) attached to these microscopes on the cross section of the α-Fe-containing rare earth-iron magnetic powder.

[0051] Furthermore, the crystallite diameter of Fe-based nanocrystals with a bcc structure can sometimes be calculated using the half-width of the peak on the (110) plane measured by powder X-ray diffraction (when the crystallite diameter is between 1 nm and 100 nm and can be separated from the core peak) using the Scherrer equation D = Kλ / β cosθ (K: Scherrer constant 0.9, λ: X-ray wavelength (nm), β: half-width of the diffraction peak (radians), θ: Bragg angle (radians)). For example, the half-width of the α-Fe phase crystals can be determined by measuring with a CuKα X-ray source at 40 kV and 15 mA, with a step width of 2θ = 0.01 between diffraction angles 10 < 2θ < 90. For example, the half-width of the α-Fe phase crystals can be determined using a wavelength where λ is 0.154 nm. Alternatively, the half-width of the crystals consisting of the α-Fe phase can be determined by measuring with an X-ray source of CoKα, 40 kV, 135 mA, and a step width of 2θ = 0.01 between diffraction angles of 20 < 2θ < 110. For example, measurements are made at a wavelength where λ is 0.179 nm. In this case, the crystallite size determined by the Scherrer equation is preferably 1 nm or more and 100 nm or less, more preferably 1 nm or more and 20 nm or less, even more preferably 1 nm or more and 15 nm or less, and particularly preferably greater than 1.5 nm and 10 nm or less.

[0052] The atomic concentration (atomic %) of Fe in the entire α-Fe-containing region is preferably 25 atomic % or more, more preferably 40 atomic % or more. The upper limit of the atomic concentration of Fe is not particularly limited, but may be 80 atomic % or less. When the atomic concentration of Fe is 25 atomic % or more, magnetic coupling is maintained, which tends to reduce the demagnetizing field and increase the magnetic permeability.

[0053] The atomic concentration (atomic %) of rare earth R in the entire α-Fe-containing region is preferably 1 atomic % or more and 50 atomic % or less, and more preferably 2 atomic % or more and 30 atomic % or less. The atomic concentration (atomic %) of nitrogen in the entire α-Fe-containing region is preferably 0 atomic % or more and 50 atomic % or less, and more preferably 0.01 atomic % or more and 30 atomic % or less. The atomic concentration (atomic %) of oxygen in the entire α-Fe-containing region is preferably 0 atomic % or more and 55 atomic % or less, and more preferably 0.01 atomic % or more and 40 atomic % or less. The atomic concentration of each element in the α-Fe-containing region is determined by averaging the atomic concentration in each region in STEM-EDS line analysis.

[0054] The average atomic concentration (atomic %) of oxygen (O) in the entire α-Fe-containing region is preferably higher than the average atomic concentration (atomic %) of oxygen (O) in the core region. The average atomic concentration of oxygen (O) in the α-Fe-containing region is preferably at least 1.05 times, more preferably at least 1.5 times, even more preferably at least 2 times, and particularly preferably at least 2.5 times, the average atomic concentration of oxygen (O) in the core region. The average atomic concentration of rare earth (R) in the α-Fe-containing region is at most 2 times, preferably at most 1.9 times, and more preferably at most 1.8 times, the average atomic concentration of rare earth (R) in the core region. The average atomic concentration of rare earth (R) in the α-Fe-containing region may be at least 0.1 times, preferably at least 0.5 times, the average atomic concentration of rare earth (R) in the core region. The "average atomic concentration" of a specific element here refers to the atomic concentration obtained by performing STEM-EDS line analysis on one or more lines that penetrate the α-Fe-containing rare earth-iron magnetic powder in the thickness direction from the core region to the outermost surface of the α-Fe-containing region, obtaining measured values ​​of the atomic concentration of the element at 10 or more points, and averaging these values.

[0055] The thickness of the α-Fe-containing region is preferably 0.001% or more and less than 50% of the average particle size of the α-Fe-containing rare earth-iron magnetic powder, more preferably 0.002% or more and 45% or less, even more preferably 0.003% or more and 35% or less, and particularly preferably 0.01% or more and 20% or less. A thickness of 0.001% or more tends to improve electrical insulation. If the thickness is less than 50%, the presence of the core region tends to increase μ'.

[0056] The thickness of the α-Fe-containing region is preferably 1 nm to 80 μm, more preferably 2 nm to 80 μm, even more preferably 3 nm to 20 μm, even more preferably 3 nm to 10 μm, and particularly preferably 5 nm to 5 μm. From the perspective of improving μ' in the high-frequency region, the thickness may be 100 nm or more, 300 nm or more, or 1 μm or less. A thickness of 1 nm or more tends to improve electrical insulation. If the thickness is 10 μm or less, the presence of the core region tends to increase μ'. The thickness of the α-Fe-containing region can be measured by performing compositional analysis using TEM, STEM, or SEM observation images of the cross section of the α-Fe-containing rare earth-iron-based magnetic powder, using TEM images and secondary electron / backscattered electron images, or EDS line analysis, area analysis, or point analysis.

[0057] The surface coverage of the core region by the α-Fe-containing region is preferably 10% or more, more preferably 50% or more, even more preferably 80% or more, and particularly preferably 100%. Increasing the surface coverage of the core region has the effect of increasing electrical insulation and improving tan δ and phase angle θ. In particular, a surface coverage of 100% promotes electrical isolation of the magnetic powder, further enhancing the above effects. The surface coverage of the core region by the α-Fe-containing region can be measured by observing the cross-section of the powder using a TEM, STEM, or SEM equipped with EDS. The ratio of the length of the contact area between the α-Fe-containing region and the core region to the entire perimeter of the observed core region is defined as the "surface coverage." In this case, it is preferable to measure the cross-sections of 20 to 50 magnetic powders from the images observed using the above method and average the value to determine the surface coverage.

[0058] The α-Fe-containing region may have a so-called sea (oxide, nitride, or oxynitride phase containing at least one of the rare earth elements R or M)-island (nano α-Fe phase) structure in which ferromagnetic α-Fe phase nanocrystals are isolated in an oxide, nitride, or oxynitride phase containing at least one of the rare earth elements R or M. The α-Fe-containing region may have a sea (oxide, nitride, or oxynitride phase containing at least one of the rare earth elements R or M)-island (nano α-Fe phase) structure, in which the metallic α-Fe phase is isolated in the "sea" matrix phase of oxide, nitride, or oxynitride containing at least one of the rare earth elements R or M, thereby preventing electron percolation and maintaining electrical insulation. The α-Fe phase in the α-Fe-containing region may also be regularly arranged. When the α-Fe phases in the α-Fe-containing region are regularly arranged, the α-Fe phases are composed of crystalline grains and can be regularly arranged at high density. This allows the α-Fe phases to be ferromagnetically or magnetostatically coupled, making it easier for magnetic flux to pass through the α-Fe-containing region, and this tends to make the magnetic coupling more stable.

[0059] The α-Fe-containing region may have a sea-island structure including sea regions and island regions, in which the atomic concentration (%) of X is higher in the island regions than in the sea regions, and the atomic concentrations (%) of rare earth element R and oxygen O are lower in the island regions than in the sea regions. The atomic concentration (%) of X in the island regions is preferably 10 points or more higher, more preferably 20 points or more higher, than the atomic concentration (%) of X in the sea regions. The atomic concentrations (%) of rare earth element R and oxygen O in the sea regions are preferably 2 points or more higher, more preferably 5 points or more higher, than the atomic concentrations (%) of rare earth element R and oxygen O in the island regions, respectively. The atomic concentrations (%) of each element in the island regions and sea regions are determined by averaging the atomic concentrations in each region in STEM-EDS line analysis.

[0060] The presence or absence of oriented crystalline phases, as well as their size and volume fraction, can be measured by observing STEM images of α-Fe-containing rare earth-iron-based magnetic powders or by using an ED (electron diffraction) device attached to a TEM. For example, in cross-sectional STEM images of α-Fe-containing rare earth-iron-based magnetic powders, regions containing both the α-Fe phase and oxide, nitride, or oxynitride phases containing at least one of the rare earth R or M components, with unidirectional lattice fringes, are considered "oriented regions." Image analysis is then performed. Using a scanning transmission electron microscope (STEM), five regions containing the α-Fe-containing regions of the α-Fe-containing rare earth-iron-based magnetic powder (multiple fields may be used if the α-Fe-containing region is thick) are photographed. The size and volume fraction of the oriented crystalline phase can be confirmed by comparing the "oriented regions" with non-oriented regions within the photographed regions. The presence or absence of oriented crystals can also be confirmed by examining the electron diffraction pattern of the TEM-ED image.

[0061] <Phosphorus compound coated part> The α-Fe-containing rare earth-iron-based magnetic powder preferably has a phosphorus compound coating portion, particularly from the viewpoint of improving oxidation resistance. The phosphorus compound coating portion is preferably present outside the α-Fe-containing region, i.e., on the opposite side of the core region across the α-Fe-containing region.

[0062] The thickness of the phosphorus compound coating portion is preferably 1 nm to 200 nm, more preferably 2 nm to 50 nm, from the viewpoint of improving the tangent δ and phase angle θ of the magnetic material in the high-frequency range. The thickness of the coating portion can be measured by performing composition analysis on the cross-section of the α-Fe-containing rare earth-iron-based magnetic powder using line analysis, area analysis, or point analysis with EDS in a TEM, STEM, or SEM observation image. When measuring by line analysis, for example, the range in which the atomic concentration of phosphorus (P) is observed as 1 atomic % or more may be considered to be the phosphorus compound coating portion. One example is a structure in which the phosphorus compound coating portion completely covers the surface of the α-Fe-containing rare earth-iron-based magnetic powder (surface coverage rate: 100%). In this case, adjacent magnetic powders are considered to be completely electrically insulated. That is, with this structure, the phosphorus compound coating portion has the effect of reducing iron loss due to eddy currents across the grains, thereby further improving the tangent δ and phase angle θ in the high-frequency range and obtaining a more efficient magnetic material for magnetic field amplification. Furthermore, when the thickness of the phosphorus compound coating is 10 nm or less, the α-Fe-containing region and the iron oxide-containing region (including magnetite or maghemite) sandwiching this layer are ferromagnetically coupled. This magnetic coupling reduces the local demagnetizing field and further weakens the demagnetizing field acting on the core region, thereby achieving a high relative permeability.

[0063] Examples of phosphorus compounds constituting the phosphorus compound coating portion include inorganic phosphoric acids such as orthophosphoric acid, pyrophosphoric acid, and polyphosphoric acid, and phosphates of these with Na, Ca, Pb, Zn, Fe, R, ammonium, Mo, W, V, and Cr (these metal elements and atomic groups are sometimes referred to as phosphate-forming components in this disclosure), as well as "phosphorus-containing amorphous compounds" and "phosphorus-containing nanocrystalline compounds" containing at least one selected from the rare earth element X component R, Fe, Co, or Ni, a phosphate-forming component, and N, and a P and / or phosphorus-containing substance. Among these, phosphates, "phosphorus-containing amorphous compounds," and "phosphorus-containing nanocrystalline compounds" are preferred in terms of providing a dense surface coating for the powder composed of the core region and the α-Fe-containing region. The "phosphorus-containing nanocrystalline material" may be a rare earth phosphate, or may be in the form of a eutectic or mixed crystal containing a rare earth phosphate and at least one selected from the group consisting of phosphates of an X component (Fe, Co, or Ni) and phosphates formed by the bonding of a phosphate-forming component with phosphoric acid. The inclusion of a "phosphorus-containing nanocrystalline compound" further improves thermal stability, tending to prevent degradation of the high-frequency characteristics of the magnetic material even after the high-temperature kneading and thermal curing processes (described later) that are applied during the bonded magnetic material production process after phosphorus treatment. This also contributes to the high thermal stability and excellent efficiency of the final molded product. The term "nanocrystalline compound" refers to a compound with fine crystals measuring 1 nm or more but less than 1 μm. Phosphorus compounds containing crystals smaller than 1 nm are considered to be compounds with an amorphous structure that lacks a nanocrystalline structure. The crystallinity of the phosphorus compound coating and the diameter of the fine crystals in the phosphorus compound coating can be confirmed by lattice image observation using TEM or analysis using an electron diffraction (ED) device attached to the TEM.

[0064] The content of the phosphorus compound in the α-Fe-containing rare earth-iron-based magnetic powder having a phosphorus compound coating, assuming that the phosphorus compound exists as a rare earth phosphate, is preferably 0.001% by mass to 4.5% by mass, more preferably 0.05% by mass to 2.5% by mass, and most preferably 0.1% by mass to 2% by mass. A content of 4.5% by mass or less can reduce aggregation of the rare earth-iron-based magnetic powder, suppressing a decrease in relative permeability while also tending to reduce deterioration of tan δ and phase angle θ in the high-frequency range. A content of 0.001% by mass or more further improves the electrical insulation of the phosphorus compound coating, which similarly suppresses a decrease in relative permeability and tends to reduce deterioration of tan δ and phase angle θ in the high-frequency range.

[0065] The phosphorus (P) content in the α-Fe-containing rare earth-iron magnetic powder is preferably 0.0005% by mass or more, more preferably 0.001% by mass or more, and even more preferably 0.05% by mass or more. The phosphorus content in the α-Fe-containing rare earth-iron magnetic powder is preferably 4% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less.

[0066] The phosphorus compound preferably coats at least a portion of the surface of the powder comprising the core region and the α-Fe-containing region, in order to prevent a decrease in efficiency due to eddy currents, i.e., a deterioration in tan δ and phase angle θ. In magnetic powders, a surface coverage of 10% or more is effective in reducing eddy currents to a certain extent, but a surface coverage of 50% or more is preferred, and 80% or more is more preferred. A surface coverage of 10% or more tends to suppress eddy currents generated between particles and reduce the deterioration of tan δ and phase angle θ. α-Fe-containing rare earth-iron-based magnetic powders with a 100% coverage by the phosphorus compound coating have high insulation properties, depending on the composition, crystal structure, and powder particle size of the magnetic powder, and therefore can achieve low tan δ and a high phase angle θ at high frequencies.

[0067] The coverage of the surface of the magnetic powder with the phosphorus compound coating can be estimated by observing the cross section of the magnetic powder using a TEM, STEM, or SEM equipped with EDS, and the ratio of the length of the contact area of ​​the phosphorus-containing coating to the entire perimeter of the observed surface of the α-Fe-containing rare earth-iron-based magnetic powder is defined as the "surface coverage." In this case, it is preferable to measure the cross sections of 20 to 50 magnetic powders from the images observed using the above method and take the average value as the surface coverage.

[0068] The phosphorus compound coating portion present on the surface of the α-Fe-containing rare earth-iron-based magnetic powder may have a region (R-high concentration region) in which the atomic concentration of rare earth (R) is higher than the atomic concentration of rare earth R in the rare earth-iron-based magnetic powder (core region). The atomic concentration of rare earth R in the R-high concentration region can be 1.05 times or more, preferably 1.1 times or more, more preferably 1.2 times or more, and even more preferably 1.4 times or more, of the atomic concentration of rare earth R in the core region. Furthermore, the atomic concentration of rare earth R in the R-high concentration region can be, for example, 4 times or less than the atomic concentration of rare earth R in the core region. Here, the R-high concentration region is a region including a layer that exhibits the maximum P (phosphorus) peak in STEM-EDS line analysis of the α-Fe-containing rare earth-iron-based magnetic powder. The thickness of the R-high concentration region can be, for example, 1 nm or more, preferably 3 nm to 150 nm, more preferably 5 nm to 100 nm, and even more preferably 7 nm to 80 nm. When the atomic concentration of rare earth R in the R-rich region is within the above range relative to the R atomic concentration in the core region, the electrical resistivity tends to be high and the relative permeability tends to be high. The atomic concentration (atomic %) of each element in the R-rich region is determined by averaging the atomic concentrations in the phosphorus compound coating in STEM-EDS line analysis.

[0069] The atomic concentration ratio R / X of the total amount of rare earth R and X component Fe, Co, or Ni in the R-high concentration region may be 0.05 or more, preferably 0.1 or more, and more preferably 0.2 or more. The upper limit of R / X in the R-high concentration region may be 100 or less, 20 or less, or even 10 or less. Furthermore, R / X in the R-high concentration region may have a higher value than R / X in the core region. R / X in the R-high concentration region may be 1 time or more of R / X in the core region, preferably 1.5 times or more, more preferably 2 times or more, and even more preferably 2.5 times or more. When R / X in the R-high concentration region is within the above range, the X atomic concentration near the core region is lowered, which tends to further improve water resistance.

[0070] The α-Fe-containing rare earth-iron magnetic powder may further have a high-Mo concentration layer. In the high-Mo concentration layer, the Mo used to form the phosphorus compound coating portion is present in a higher concentration than in the iron oxide layer and the α-Fe-containing region described below. The high-Mo concentration layer is preferably located outside the α-Fe-containing region. In some cases, having a high-Mo concentration layer can increase the strength of the coating layer and improve corrosion resistance.

[0071] When the α-Fe-containing rare earth-iron magnetic powder includes a Mo-rich layer, the thickness of the Mo-rich layer is preferably 0.01% to 10% of the average particle size of the α-Fe-containing rare earth-iron magnetic powder, more preferably 0.02% to 1%. The thickness of the Mo-rich layer is preferably 1 nm to 1 μm, more preferably 2 nm to 100 nm.

[0072] <Iron oxide-containing area> The α-Fe-containing rare earth-iron magnetic powder further has an iron oxide-containing region. The iron oxide-containing region exists outside the α-Fe-containing region, but may exist outside the phosphorus compound coating portion or outside the Mo-rich layer. The iron oxide-containing region is mainly composed of an iron oxide phase containing magnetite or maghemite. The presence of an iron oxide-containing region containing magnetite (Fe3O4) or maghemite (γ-Fe2O3), which are ferromagnetic materials, outside the α-Fe-containing region tends to improve the magnetic permeability of the α-Fe-containing rare earth-iron magnetic powder.

[0073] The presence of iron oxide-containing regions in α-Fe-containing rare earth-iron magnetic powders can be confirmed by, for example, XRD using a CuKα radiation source, observing peaks in regions of strong magnetite diffraction lines that do not overlap with the diffraction lines of the core region (e.g., diffraction angle 2θ of the (220) plane is around 29-31°, and diffraction angle 2θ of the (511) plane is around 56-58°), or near the strongest diffraction lines of maghemite (e.g., diffraction angle 2θ of the (220) plane is around 29-31°, and diffraction angle 2θ of the (511) plane is around 56-58°). Maghemite and magnetite have the same tetragonal spinel crystal structure, and their lattice constants a are almost the same (0.835 nm for the former and 0.840 nm for the latter), making it difficult to distinguish between nano-sized phases by XRD. Therefore, to distinguish between maghemite and magnetite, it is necessary to (1) measure the Fe valence using XPS (X-ray photoelectron spectroscopy), or (2) compare the radial distribution functions obtained by extracting and Fourier-transforming EXAFS (extended X-ray absorption fine structure) vibrations from XAFS (X-ray absorption fine structure) spectra. When comparing the electromagnetic properties of maghemite and magnetite, the former has a volume resistivity of 10 6 Ωm and magnetization 0.42 T, while the latter has a volume resistivity of 4 × 10 -5Ωm, and magnetization 0.60 T, so although maghemite has slightly lower magnetization than magnetite, it has high electrical resistance, with magnetite being superior in magnetic coupling and maghemite being advantageous in electrical insulation. Therefore, if you want to achieve better efficiency rather than high magnetic permeability, you can oxidize and convert magnetite that has already formed outside the α-Fe-containing region into maghemite by heat treating it at 200°C to 600°C in an oxygen-containing atmosphere using methods such as annealing in hydrogen.

[0074] The iron oxide-containing region preferably contains maghemite and / or magnetite as its primary component. That is, hematite is preferably not contained, or if present, is not the primary component. For example, when the core region contains a rare earth-iron-nitrogen-based compound, if the ratio (I) / (II) of the diffraction peak intensity (I) of the (104) plane of hematite to the diffraction peak intensity (II) of the (511) plane of the magnetite or maghemite in the XRD diffraction pattern is 0 or greater but less than 10, not only is loss improved due to the electrical insulating effect of hematite, but the magnetic coupling effect of maghemite and / or magnetite is also expected, resulting in a dramatic improvement in magnetic permeability. If the individual peaks cannot be distinguished by XRD, the presence and composition ratio of iron oxide may be calculated from quantitative values ​​obtained by EDS in TEM, STEM, or SEM observation images of the cross section of the α-Fe-containing rare earth-iron-based magnetic powder.

[0075] The iron oxide-containing region may contain metal phases or intermetallic compound phases with high electrical conductivity, such as α-Fe, cementite, or Fe3B phase, but it is preferable that they are not present on the outermost surface. Their presence on the outermost surface is undesirable because they generate eddy currents throughout the material, significantly reducing efficiency. In this case, the thickness is preferably 0.2 nm to 10 μm, more preferably 1 nm to 1 μm, and even more preferably 1 nm to 100 nm. By keeping the thickness within the above range, it is possible to suppress a decrease in efficiency due to eddy currents.

[0076] The thickness of the iron oxide-containing region is preferably 0.01% to 10% of the average particle size of the α-Fe-containing rare earth-iron-based magnetic powder, and more preferably 0.05% to 2%. Within these ranges, the ferromagnetic coupling between the magnetic powder particles becomes stronger, the demagnetizing field decreases, and μ' tends to increase. Furthermore, the thickness of the iron oxide-containing region is preferably greater than 0 nm and less than 1 μm, and more preferably 1 nm to 100 nm. Setting the thickness of the iron oxide-containing region to 1 μm or less tends to suppress a decrease in μ'. The thickness of the iron oxide-containing region can be measured by performing compositional analysis using EDS line analysis, area analysis, or point analysis on a TEM, STEM, or SEM image of a cross section of the α-Fe-containing rare earth-iron-based magnetic powder.

[0077] The content of magnetite or maghemite in the α-Fe-containing rare earth-iron magnetic powder is preferably 0.005% by mass to 0.15% by mass, more preferably 0.01% by mass to 0.1% by mass, in which case iron oxide-containing regions tend to be uniformly formed on the surface of the α-Fe-containing rare earth-iron magnetic powder.

[0078] The iron oxide-containing region covers at least a portion of the surface of the powder, which is composed of the core region and the α-Fe-containing region. In the magnetic powder, the surface coverage of the iron oxide-containing region is preferably 25% or more, more preferably 75% or more. Within these ranges, improvements in both tan δ and μ' tend to be achieved. An α-Fe-containing rare earth-iron-based magnetic powder with a 100% coverage of the iron oxide-containing region can achieve complete electrical insulation and magnetic coupling, achieving higher magnetic permeability and efficiency than a coating that does not include the iron oxide-containing region, such as a hematite-iron oxide coating. The surface coverage of the magnetic powder with the iron oxide-containing region can be estimated by observing the cross-section of the magnetic powder using a TEM, STEM, or SEM equipped with EDS. The "surface coverage" is defined as the ratio of the length of the contact area of ​​the magnetite or maghemite-containing coating to the total perimeter of the observed α-Fe-containing rare earth-iron-based magnetic powder surface. In this case, it is preferable to measure the cross sections of 20 to 50 magnetic powder particles from the image observed by the above-mentioned method and take the average value as the surface coverage rate.

[0079] In addition to magnetite or maghemite, the iron oxide-containing region may contain Ni, Co, or M elements (at least one element selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr) derived from the core region or additives added during phosphorus treatment, or Na, Mg, Ca, K, Cu, Pb, Zn, Zr, Mo, Ba, Hf, Ta, La, Y, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Lu, or Sm added during phosphorus treatment. In this case, a substance having the spinel structure of magnetite is called "M-ferrite" depending on the content of the M element. However, in this disclosure, since the amount of the M element is low (less than 16.5 atomic %), it is considered to be a substance that falls within the category of magnetite. Maghemite also has the same crystalline structure as magnetite, that of a spinel, and maghemite has a structure in which 1 / 6 of the octahedral volume (octahedral site) of the spinel-type crystal structure is vacant. Therefore, the crystal structure of the intermediate between magnetite and maghemite shown in N. Imaoka, E. Kakimoto, K. Takagi, K. Ozaki, M. Tada, T. Nakagawa, M. Abe, Jounal of Magnetism and Magnetic Materials, vol. 476, pp. 613-621 (2019) is also spinel-type, and in the present disclosure, this intermediate is also considered to be a type of magnetite. Furthermore, the iron oxide-containing region may contain carbon and boron derived from the core region or the like.

[0080] The method for producing the α-Fe-containing rare earth-iron-based magnetic powder having an iron oxide-containing region is not particularly limited. For example, as described below, the powder can be produced by a method including an annealing step in which a rare earth-iron-based magnetic powder having an oxidized phosphorus compound coating portion is heat-treated at 350°C or higher and 600°C or lower in an atmosphere of an inert gas or a reducing gas that does not contain nitrogen atoms.

[0081] <Particle size of magnetic powder> The average particle size of the α-Fe-containing rare earth-iron-based magnetic powder is preferably 0.1 μm to 100 μm, more preferably 0.5 μm to 50 μm. If the particle size is less than 0.1 μm, the filling amount of the magnetic powder in the compact is small, which may reduce the real term of the relative magnetic permeability in the high-frequency range. As a result, the properties of the magnetic material tend to be extremely poor. If the particle size exceeds 50 μm, the μ" of the compact tends to decrease, and this tendency becomes even more pronounced if the particle size exceeds 100 μm. Here, the average particle size refers to the median diameter measured under dry conditions using a laser diffraction particle size analyzer. In other words, the average particle size of the magnetic powder of the present disclosure is expressed as D50, which is the particle size at which the integrated value of the particle size distribution based on volume of the α-Fe-containing rare earth-iron-based magnetic powder corresponds to 50%.

[0082] As the particle size of the core region of an α-Fe-containing rare earth-iron-based magnetic powder increases, eddy currents begin to occur within the grains at low frequencies due to the skin effect. Therefore, the larger the particle size, the lower the relative permeability real term begins to decrease. Therefore, reducing the particle size of the magnetic powder tends to maintain high magnetic field amplification characteristics up to high frequencies. It is preferable for magnetic materials for magnetic field amplification to have an upper limit on the particle size of the magnetic powder corresponding to the frequency f0 (Hz) at which the real term of the relative permeability begins to decrease. On the other hand, as the particle size decreases, the filling amount of the magnetic powder in the compact decreases and the specific surface area increases. For example, in the case of a phosphorus compound coating with a thickness of 10 nm, if the particle size of the powder is 0.1 μm, the relative permeability decreases by only about 50%, but if the particle size is 0.05 μm, the relative permeability will be approximately 6%. Therefore, the lower limit of the particle size of the core region of the α-Fe-containing rare earth-iron-based magnetic powder of the present disclosure is around 0.1 μm, regardless of frequency. Because of the above trade-off, it is preferable to set the particle size range of the magnetic powder to be more suitable for the target frequency band.

[0083] <<Magnetic materials for magnetic field amplification>> The magnetic material for magnetic field amplification of this embodiment is characterized by containing α-Fe-containing rare earth-iron-based magnetic powder. By containing α-Fe-containing rare earth-iron-based magnetic powder, it is preferable that the magnetic material for magnetic field amplification has a high relative permeability μ' of 11 or more in the range of 1 MHz or more and less than 10 MHz.

[0084] The particle size of the α-Fe-containing rare earth-iron-based magnetic powder is preferably 0.1 μm to 100 μm. The reason for this is, as mentioned above, that when powder larger than 100 μm is used as a magnetic material for amplifying magnetic fields above 1 MHz, the relative permeability tends to decrease due to the skin effect. Furthermore, when using powders larger than 10 μm as magnetic material for amplifying magnetic fields, a large pressure of 0.5 GPa or more is usually applied to increase the volume fraction. This causes the powder particles to come into contact with each other, resulting in large eddy current losses and a significant decrease in the real term of the relative permeability. Therefore, it is preferable for a fine, moderately soft material such as a phosphorus compound, which is not as hard as ferrite or transition metal oxides but not too soft like resins, to cover the α-Fe-containing rare earth-iron-based magnetic powder or to be present between the particles. This prevents deterioration of the magnetic powder's inherent properties, such as relative permeability.

[0085] The magnetic material for magnetic field amplification is preferably used at frequencies of 1 MHz or more and less than 1 GHz. Therefore, depending on the composition and particle size distribution of the α-Fe-containing rare earth-iron-based magnetic powder, the imaginary term of the relative permeability may begin to increase in the frequency range of 0.5 GHz or more and less than 1 GHz. The magnetic material for magnetic field amplification of this embodiment may be used in the frequency range of 1 MHz or more and less than 0.5 GHz, and is preferably used in the frequency range of 1 MHz or more and less than 0.1 GHz. When used as a magnetic material for magnetic field amplification within the above range, powder of 3 μm to 100 μm in size is used without using a fine pulverizing device such as a jet mill, and magnetic field orientation, which reduces throughput, is not necessary, which is preferable from the perspective of balancing cost and properties.

[0086] More specific applications of magnetic field amplification magnetic materials include wireless power supply coils operating in the 6 MHz to 6 GHz range, magnetic field amplification magnetic materials used in antennas and couplers, magnetic field absorption magnetic materials for RFID (Radio Frequency Identification) tags operating at frequencies above 10 MHz but below 1 GHz, particularly at 920 MHz, and transformers, inductors, and reactors for high-frequency circuits above 20 MHz. For example, they can be used as thin sheets attached to the back of antennas or transmitters to concentrate magnetic flux within the sheet due to their magnetic field amplification properties, inserted inside cylindrical or rectangular coils, or wrapped around a donut-shaped or yoke-equipped magnetic core to improve the real term of the coil's relative permeability. They can also be used as magnetic inks to form magnetic circuits such as coils by coating or injecting them onto or into electronic circuits.

[0087] <Magnetic metals and / or metal oxides> The magnetic material for magnetic field amplification of this embodiment preferably contains a magnetic metal and / or metal oxide in addition to the α-Fe-containing rare earth-iron magnetic powder. Here, the magnetic metal may be an alloy, and the magnetic metal oxide may be a composite oxide. The magnetic metal and / or metal oxide is usually contained in the magnetic material for magnetic field amplification in the form of powder or particles.

[0088] By introducing magnetic metals and / or metal oxides into the gaps between the α-Fe-containing rare earth-iron-based magnetic powder while maintaining electrical insulation between the rare earth-iron-based soft magnetic material (the core region of the α-Fe-containing rare earth-iron-based magnetic powder) and the magnetic metals and / or metal oxides, the demagnetizing field of the soft magnetic material powder is reduced, thereby increasing the real term μ' of the complex relative permeability. The presence of magnetic metals and / or metal oxides increases the volume fraction of the magnetic components, thereby improving the relative permeability. However, the rate of improvement (the rate of increase in relative permeability) is not directly proportional to the volume fraction of the magnetic components, but rather increases hyperbolically. This is thought to be due to a decrease in the demagnetizing field. As the volume fraction of the magnetic components, including the magnetic metals and / or metal oxides, increases, i.e., as it approaches 1, the rate of improvement in relative permeability due to this demagnetizing field tends to increase rapidly.

[0089] Examples of magnetic metals include Fe (preferably carbonyl iron), Ni, Co, Fe-Ni alloys, Fe-Ni-Si alloys, sendust, Fe-Si-Al alloys, Fe-Si-Cr alloys, Fe-Cu-Nb-Si alloys, and amorphous alloys. Examples of magnetic metal oxides include spinel ferrites such as maghemite, magnetite, Ni-ferrite, Zn-ferrite, Mn-Zn ferrite, Ni-Zn ferrite, and Ni-Mn ferrite, as well as garnet ferrite and magnetoplumbite ferrite. In order to further improve the magnetic field amplification properties of the magnetic material, the magnetic metal and / or metal oxide added to the magnetic material for magnetic field amplification is preferably one or more of Ni, Fe (preferably carbonyl iron), and magnetite (Fe3O4).

[0090] When used as a magnetic material for magnetic field amplification, the average particle size of the magnetic metal and / or metal oxide is not particularly limited, but is preferably 1 nm to 100 μm, more preferably 2 nm to 50 μm, and even more preferably 3 nm to 20 μm. If the average particle size of the magnetic metal and / or metal oxide exceeds 100 μm, eddy current loss increases in the high-frequency range, potentially resulting in reduced magnetic field amplification characteristics. If the average particle size of the magnetic metal and / or metal oxide is less than 1 nm, compactibility may deteriorate and aggregation of the metal and / or metal oxide may occur, potentially hindering the inherent affinity and functional effects of small particle size metal and / or metal oxide powders, such as improving the dispersibility of rare earth-iron-based soft magnetic powders. Note that the average particle size of 0.1 μm or more refers to the median diameter measured under dry conditions using a laser diffraction particle size analyzer. An average particle size of less than 0.1 μm is the median diameter measured under wet conditions using a dynamic light scattering particle size distribution analyzer. For magnetic materials (compounds, compacts, etc.), another method is to measure the particle sizes of 20 or more, preferably 50 or more, particles of a powder that are sufficiently representative of the entire material from a micrograph such as TEM, STEM, or SEM, determine the volumetric particle size distribution, and then obtain the median diameter. In the above, the average particle size can be expressed as D50, which is the particle size at which the integrated value of the particle size distribution on a volume basis of magnetic metal and / or metal oxide powder is 50%.

[0091] The shape of the magnetic metal and / or metal oxide is not particularly limited, and may be any shape such as spherical, plate-like, flat, scaly, needle-like, fibrous, or irregular, but a spherical shape is usually preferred in order to ensure that the metal and / or metal oxide is uniformly present in the grain boundaries of the rare earth-iron-based soft magnetic powder and is magnetically isotropic.

[0092] It is desirable for magnetic metals and / or metal oxides to be as close as possible to each other, even if a thin insulating layer is present on the surface, in which case the demagnetizing field is low and the real term μ' of the complex relative magnetic permeability can be increased. Therefore, when a magnetic metal and / or metal oxide is bonded to other non-magnetic components (e.g., an insulating layer), the ratio of the magnetic metal and / or metal oxide to the total is preferably 10% by volume or more, and to achieve a higher real term μ' of the complex relative magnetic permeability, it is more preferably 25% by volume or more, even more preferably 50% by volume or more, and may even be 100% by volume.

[0093] In the magnetic material for magnetic field amplification, the content (total content) of the magnetic metal and / or metal oxide is preferably 0.1 to 100 parts by mass, more preferably 0.2 to 50 parts by mass, and even more preferably 0.5 to 25 parts by mass, per 100 parts by mass of the rare earth-iron-based soft magnetic powder (the entire rare earth-iron-based soft magnetic powder, including the core region, the phosphorus compound coating portion, and the iron oxide-containing surface region). When the content of the magnetic metal and / or metal oxide is 0.1 part by mass or more per 100 parts by mass of the rare earth-iron-based soft magnetic powder, the addition of the magnetic metal and / or metal oxide can improve the packing density of the magnetic component per unit volume and reduce the demagnetizing field, thereby sufficiently increasing the real term μ' of the complex relative permeability. Furthermore, if the content of magnetic metal and / or metal oxide is 100 parts by mass or less per 100 parts by mass of rare earth-iron based soft magnetic powder, the content of rare earth-iron based soft magnetic powder in the composition is sufficiently ensured, resulting in a composition with better magnetic field amplification characteristics, particularly better efficiency, which can be suitably used in applications requiring high efficiency as well as high magnetic permeability, such as transformers and inductors used in high frequency ranges.

[0094] The magnetic material for magnetic field amplification of this embodiment is characterized by a high real term of relative permeability even in the high frequency range. For example, the real term of relative permeability at a frequency of 1 MHz or more and 30 MHz or less is preferably 2 or more, more preferably 5 or more, and even more preferably 10 or more. Furthermore, the real term of relative permeability at a frequency of more than 30 MHz and less than 1 GHz is preferably 2 or more, and even more preferably 4 or more. Furthermore, the magnetic material for magnetic field amplification of this embodiment can have a real term μ' of relative permeability at a frequency of, for example, 30 MHz of 2.1 or more, preferably 5.5 or more, more preferably 10 or more, and even more preferably 10.5 or more. The magnetic material for magnetic field amplification of this embodiment can have a real term μ' of relative permeability at a frequency of 20 MHz of 500 or less, for example, and may have a real term μ' of relative permeability at a frequency of 20 MHz of 200 or less.

[0095] In the magnetic material for magnetic field amplification of this embodiment, the real term μ' of the relative permeability at 10 MHz is preferably 11 or more. Furthermore, the tan δ(μ" / μ') and phase angle θ at 10 MHz are preferably 0.1 or less and 84° or more, more preferably 0.05 or less and 87° or more, and even more preferably 0.02 or less and 88° or more.

[0096] Furthermore, the magnetic material for magnetic field amplification of this embodiment preferably has a real term of relative magnetic permeability at 50 MHz of 11 or more. Furthermore, tan δ and phase angle θ at 50 MHz may be 0.2 or less and 78° or more, respectively. If the real term of relative magnetic permeability at 50 MHz, tan δ, and phase angle θ are within the above ranges, the magnetic material for magnetic field amplification has a high magnetic field amplification effect, is highly efficient, and is low-cost, particularly when used at frequencies around this range (for example, 20 MHz or more and 80 MHz or less), and this is preferable. If tan δ (μ" / μ') and phase angle θ are 0.05 or less and 87° or more, heat generation can be reduced when incorporated into an element or system, and the temperature of components can be lowered, which tends to improve stability.

[0097] Furthermore, the magnetic material for magnetic field amplification of this embodiment preferably has a real term of relative permeability at 100 MHz of 11 or more. Furthermore, tan δ and phase angle θ at 100 MHz may be 0.3 or less and 73° or more, respectively. If the real term of relative permeability at 100 MHz, tan δ, and phase angle θ are within the above ranges, the magnetic material for magnetic field amplification will have a high magnetic field amplification effect, is highly efficient, and is low-cost, particularly when used at frequencies around this range (e.g., 80 MHz or more and 120 MHz or less), and this is preferable. If tan δ (μ" / μ') and phase angle θ are 0.2 or less and 78° or more, respectively, heat generation can be reduced when incorporated into an element or system, and the temperature of components can be lowered, which tends to improve stability.

[0098] Here, the complex relative permeability, tan δ, and phase angle θ can be measured by measuring the impedance of a toroidal sample using an impedance analyzer, (vector) network analyzer, or BH analyzer and converting the results into complex relative permeability, tan δ, and phase angle θ. Depending on the frequency range (e.g., when measuring using a network analyzer at frequencies above 500 MHz), the S-parameter method can also be used. Specifically, magnetic powder and a thermosetting epoxy resin are mixed so that the magnetic powder content is 97% by mass, and then kneaded to produce a resin compound. This resin compound is placed in a mold with an inner diameter of 3.1 mm and an outer diameter of 8 mm, molded under a pressure of 0.8 GPa, and then thermally cured in vacuum at 150°C for 2 hours to produce a toroidal compact. Using this sample, the complex relative permeability over the frequency range from 1 MHz to 1 GHz is evaluated from the inductance value determined using a single-turn inductor test fixture using an impedance analyzer (E4991B, Keysight).

[0099] The magnetic material for magnetic field amplification of this embodiment also has the characteristic that the frequency dependence of the relative permeability is small. For example, in applications such as wireless power supply, power is supplied at a frequency of 13.56 MHz, so a magnetic material with small change in the real term μ' of the relative permeability in the range of 2 MHz to 20 MHz, which includes that frequency, has excellent efficiency and is therefore preferably used. Furthermore, there are many materials whose relative permeability changes significantly even at 5 MHz or less, so even in applications in this frequency range, materials whose real term of the relative permeability is stable in the range of 2 MHz to 20 MHz are preferably used. In these applications, materials with large change in μ' in the above frequency range also have a tendency for μ" to deviate greatly from 0, which also tends to deteriorate tan δ and phase angle θ.

[0100] The magnetic material for magnetic field amplification of this embodiment may contain a resin. A composite material of a magnetic material and a resin is called a bonded magnetic material, and the resin contained in this bonded magnetic material may be a thermosetting resin or a thermoplastic resin. Examples of thermoplastic resins include polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), polyamide (PA), polypropylene (PP), polyethylene (PE), and thermoplastic elastomers. Examples of thermosetting resins include epoxy resin, phenolic resin, urea resin, melamine resin, guanamine resin, unsaturated polyester resin, vinyl ester resin, diallyl phthalate resin, polyurethane resin, silicone resin, polyimide resin, alkyd resin, furan resin, dicyclopentadiene resin, acrylic resin, allyl carbonate resin, and thermosetting elastomers commonly known as rubber.

[0101] The resin content in the bonded magnetic material is preferably 0.1% by mass or more and 95% by mass or less. A resin content of 0.1% by mass or more further improves impact resistance, while a resin content of 95% by mass or less can suppress extreme decreases in relative permeability and magnetization. Furthermore, for applications requiring both high relative permeability and impact resistance, for the same reasons as above, the resin content in the bonded magnetic material is more preferably 0.5% by mass or more and 50% by mass or less. When used as a transformer for a high-frequency circuit with particularly excellent efficiency, a resin content of 1% by mass or more and 15% by mass or less is most preferable. Furthermore, since the real term of the relative permeability of the magnetic field amplification magnetic material of this embodiment is particularly high, a resin content of 15% by mass or less is also preferable, although this varies somewhat depending on the application. Compacts that do not undergo sintering and do not contain resin, such as compacts using auxiliary agents such as volatile organic solvents, are very brittle and extremely difficult to use in magnetic field amplification magnetic materials such as magnetic cores for wireless power transmission coils and inductors, which are subject to loads. Furthermore, molded bodies containing many interpenetrating air spaces, such as green compacts molded under a pressure of 1.5 GPa or less, tend to be unsuitable for high-temperature applications because they are susceptible to oxidation degradation and extreme embrittlement, resulting in poor impact resistance, when exposed to temperatures of 50°C or higher for long periods of time. Therefore, in molded bodies for the above-mentioned applications, the resin content is preferably 0.1% by mass or more and 95% by mass or less, more preferably 0.5% by mass or more and 50% by mass or less, and even more preferably 1% by mass or more and 15% by mass or less.

[0102] The resin compound for bonded magnetic materials can be obtained, for example, by using a kneader to mix and / or knead an α-Fe-containing rare earth-iron-based magnetic powder with a resin at 180° C. to 300° C. For example, the α-Fe-containing rare earth-iron-based magnetic powder and a resin are mixed in a mixer, then kneaded and extruded in a twin-screw extruder. The extruded strands are air-cooled and then cut into pieces several millimeters in size using a pelletizer, thereby obtaining pelletized resin compounds for bonded magnetic materials.

[0103] A bonded magnetic material can be produced by molding a resin compound using an appropriate molding machine. Specifically, for example, a resin compound melted in the barrel of the molding machine is injection-molded into a mold to which a magnetic field is applied, aligning the axis of easy magnetization (orientation process), thereby obtaining a magnetically oriented molded bonded magnetic material. Furthermore, a sheet-shaped bonded magnetic material sheet for magnetic field amplification or for ultra-high frequency absorption can be produced by calendaring or hot-press molding a pelletized resin compound. By rolling this to a thickness of 20 μm to 200 μm, a magnetic material for magnetic field amplification with a high real term of relative magnetic permeability can be obtained, and it is suitable for use, for example, as a magnetic material compact for magnetic field amplification in RFID tags.

[0104] <Magnetic materials for ultra-high frequency absorption> The magnetic material for absorbing ultra-high frequencies of this embodiment is characterized by containing a rare earth-iron-nitrogen magnetic powder containing a phosphorus compound, R (R is at least one element selected from Y, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Lu, and Sm, and when Sm is contained, Sm accounts for less than 50 atomic % of the total R component), Fe, and N.

[0105] The magnetic material for absorbing ultra-high frequency waves of this embodiment contains a rare earth-iron-nitrogen based magnetic powder and a phosphorus compound, and therefore has a high imaginary term of relative permeability, with μ" being 0.2 or more in the range of 1 GHz or more and 0.11 THz or less, and as a magnetic material for magnetic field amplification, the majority of the region has μ" being 0.1 or more in the range of 1 MHz or more and less than 1 GHz. The magnetic material for absorbing ultra-high frequency waves of this embodiment is not particularly limited as long as it contains a phosphorus compound and a rare earth-iron-nitrogen based magnetic powder containing R (R is at least one selected from Y, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Lu, and Sm, and when Sm is contained, Sm accounts for less than 50 atomic % of the total R component), Fe, and N, but for example, the magnetic powder of the above-mentioned embodiment can be used.

[0106] The average particle size of rare earth-iron-nitrogen magnetic powders used in ultra-high frequency absorption magnetic materials is preferably 0.1 μm or more and 10 μm or less. As mentioned above, in the ultra-high frequency range above 1 GHz, powders with a particle size of 3 μm or more tend to have a reduced relative permeability due to the skin effect. Therefore, the particle size must be 0.1 μm or more, and direct contact between magnetic particles must be avoided as much as possible. For example, even if a 30 μm rare earth-iron-nitrogen magnetic powder is crushed to 5 μm or less to be used in ultra-high frequency absorption magnetic materials, the magnetic powder particles may come into contact with each other and become conductive when compacted, resulting in an average size of 30 μm for the conductive agglomerates. In this case, the effect of particle size on high frequency characteristics will be the same as when the powder is used before crushing, defeating the purpose of crushing. In particular, when producing magnetic sheets, molding methods that simultaneously apply heat and pressure, such as hot pressing and calendering, are often used, and in this case, it is preferable that an insulating film such as a phosphorus compound firmly adheres to the surface of the magnetic particles so that even if the magnetic particles aggregate within the molded body matrix, the magnetic particles are electrically insulated from each other.By coating the surface of magnetic powder that tends to aggregate with a fine and moderately soft phosphorus compound that is not as hard as ferrite or transition metal oxides, a high-density, high-frequency magnetic material with high relative permeability can be obtained by simultaneously applying heat and pressure.

[0107] The magnetic material for absorbing ultra-high frequencies of this embodiment is characterized by a high imaginary term μ" of relative permeability even at ultra-high frequencies. For example, the imaginary term μ" of relative permeability at a frequency of 1 GHz or higher but lower than 20 GHz is preferably 0.2 or higher, and more preferably 0.3 or higher. Furthermore, the imaginary term μ" of relative permeability at a frequency of 20 GHz or higher but lower than 1 THz is preferably 0.1 or higher, and even more preferably 0.2 or higher. Furthermore, the magnetic material for absorbing ultra-high frequencies of this embodiment can have the imaginary term μ" of relative permeability at a frequency of 10 GHz be 0.2 or higher, and is preferably 0.47 or higher, more preferably 0.5 or higher, and even more preferably 0.55 or higher. In the magnetic material for absorbing ultra-high frequency waves of this embodiment, the imaginary term μ″ of the relative permeability at a frequency of 10 GHz can be 5 or less, and may be 4 or less. In addition, in the magnetic material for absorbing ultra-high frequency waves of this embodiment, the imaginary term μ″ of the relative permeability at a frequency of 0.11 THz, for example, can be 0.02 or more, preferably 0.05 or more, more preferably 0.1 or more, and even more preferably 0.2 or more. In the magnetic material for absorbing ultrahigh frequencies of this embodiment, the imaginary term μ" of the relative permeability at a frequency of 0.11 THz can be 2 or less, and may be 1.5 or less. In addition, in the magnetic material for absorbing ultrahigh frequencies of this embodiment, the ratio of the imaginary term μ" of the relative permeability at 0.11 THz to the imaginary term μ" of the relative permeability at a frequency of 10 GHz is preferably 0.03 or more, and more preferably 0.1 or more. In the magnetic material for absorbing ultrahigh frequencies of this embodiment, the ratio of the imaginary term μ" of the relative permeability at 0.11 THz to the imaginary term μ" of the relative permeability at a frequency of 10 GHz is preferably 5 or less, and more preferably 1 or less. When the ratio of the imaginary term μ" of the relative permeability at 0.11 THz to the imaginary term μ" of the relative permeability at a frequency of 10 GHz of the magnetic material for absorbing ultrahigh frequencies is in the above range, better absorption characteristics can be exhibited over a wide frequency band.

[0108] The magnetic material for ultra-high frequency absorption of this embodiment contains a rare earth-iron-nitrogen magnetic powder and a phosphorus compound, enabling ultra-wide frequency band ultra-high frequency absorption from 1 GHz to 1 THz, and is distinct from magnetic materials with low relative permeability in a narrow band of about 10 GHz, such as uniaxial magnetocrystalline anisotropy materials expected to be used at such ultra-high frequencies, such as hexagonal ferrite, borides, and epsilon iron oxide. For in-plane magnetocrystalline anisotropy materials, which have lower electrical resistivity than oxide materials but higher resistance than metal-based materials and maintain high-frequency characteristics up to 1 THz, the inclusion of a phosphorus compound with high electrical resistivity in the magnetic powder is a major feature.

[0109] <Magnetic metals and / or metal oxides> The magnetic material for absorbing ultra-high frequency waves of this embodiment may contain, in addition to the α-Fe-containing rare earth-iron magnetic powder, a magnetic metal and / or metal oxide. Here, the magnetic metal may be an alloy, and the magnetic metal oxide may be a composite oxide. The magnetic metal and / or metal oxide is usually contained in the magnetic material for absorbing ultra-high frequency waves in the form of powder or particles.

[0110] In the magnetic material for absorbing ultra-high frequencies, the content (total content) of the magnetic metal and / or metal oxide is preferably 0.1 to 100 parts by mass, more preferably 0.2 to 50 parts by mass, and even more preferably 0.5 to 30 parts by mass, relative to 100 parts by mass of the rare earth-iron-based soft magnetic powder (the entire rare earth-iron-based soft magnetic powder including the core region, the phosphorus compound coating portion, and the iron oxide-containing surface region). When the content of the magnetic metal and / or metal oxide is 0.1 parts by mass or more per 100 parts by mass of the rare earth-iron based soft magnetic powder, the addition of the magnetic metal and / or metal oxide can improve the filling rate of the magnetic component per unit volume and reduce the demagnetizing field, thereby sufficiently achieving the effects of increasing the real term μ' of the complex relative permeability and improving the imaginary term μ" of the complex relative permeability. Furthermore, when the content of the magnetic metal and / or metal oxide is 100 parts by mass or less per 100 parts by mass of the rare earth-iron based soft magnetic powder, the content of the rare earth-iron based soft magnetic powder in the composition is sufficiently ensured, resulting in a composition with better ultra-high frequency absorption properties.

[0111] Examples of magnetic metals include Fe (preferably carbonyl iron), Ni, Co, Fe-Ni alloys, Fe-Ni-Si alloys, sendust, Fe-Si-Al alloys, Fe-Si-Cr alloys, Fe-Cu-Nb-Si alloys, and amorphous alloys. Examples of magnetic metal oxides include spinel ferrites such as maghemite, magnetite, Ni-ferrite, Zn-ferrite, Mn-Zn ferrite, Ni-Zn ferrite, and Ni-Mn ferrite, as well as garnet ferrite and magnetoplumbite ferrite. In order to further improve the magnetic field amplification properties of the magnetic material, the magnetic metal and / or metal oxide added to the magnetic material for magnetic field amplification is preferably one or more of Ni, Fe (preferably carbonyl iron), and magnetite (Fe3O4).

[0112] More specific applications of magnetic materials for absorbing ultra-high frequencies include components for absorbing ultra-high frequency signals and spurious emissions in mobile communication devices, small mobile phone base stations, and cloud base stations applicable to 5G (5th Generation Mobile Communication System), 5G+ (5th Generation Plus Mobile Communication System), and 6G (6th Generation Mobile Communication System), as well as infrastructure equipment such as their equipment, devices, and antennas; components for absorbing ultra-high frequency signals and spurious emissions in equipment and devices used in ITS (Intelligent Transport Systems), Wireless HDMI (registered trademark) (Wireless High-Definition Multimedia Interface), Wireless LAN (Wireless Local Area Network), satellite broadcasting (Ka-band), etc.; and electromagnetic noise absorption components that remove mainly the second to seventh harmonics from personal computers.

[0113] The magnetic material for ultra-high frequency absorption of this embodiment may contain a resin. A composite material of a magnetic material and a resin is called a bonded magnetic material, and the resin contained in this bonded magnetic material may be a thermosetting resin or a thermoplastic resin. Examples of thermoplastic resins include polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), polyamide (PA), polypropylene (PP), polyethylene (PE), and thermoplastic elastomers. Examples of thermosetting resins include epoxy resin, phenolic resin, urea resin, melamine resin, guanamine resin, unsaturated polyester resin, vinyl ester resin, diallyl phthalate resin, polyurethane resin, silicone resin, polyimide resin, alkyd resin, furan resin, dicyclopentadiene resin, acrylic resin, allyl carbonate resin, and thermosetting elastomers commonly known as rubber.

[0114] The resin content in the bonded magnetic material is preferably 0.1% by mass or more and 95% by mass or less. A resin content of 0.1% by mass or more further improves impact resistance, while a resin content of 95% by mass or less can prevent extreme decreases in relative permeability and magnetization. Furthermore, for the bonded magnetic material of this embodiment, in applications requiring both high relative permeability and impact resistance, a range of 0.5% by mass or more and 50% by mass or less is more preferable for the same reasons as above. When used as a transformer for a high-frequency circuit with particularly excellent efficiency, a range of 1% by mass or more and 15% by mass or less is even more preferable. Furthermore, in order to achieve a particularly high real term of relative permeability as a magnetic field amplification magnetic material of this embodiment and particularly improve absorption characteristics as an ultrahigh-frequency absorption material, a content of 15% by mass or less is also preferable, although this varies somewhat depending on the application. Compacts that do not undergo sintering and do not contain resin, such as compacts made using additives such as volatile organic solvents, are extremely brittle and are extremely difficult to use as magnetic field amplification materials, such as cores for wireless power transmission coils and inductors, which are subject to heavy loads, or as ultra-high frequency absorption materials for 5G+ and 6G mobile devices, which are frequently carried and subjected to shocks. Furthermore, compacts containing many air gaps, such as compacts pressed at pressures of 1.5 GPa or less, tend to be unsuitable for high-temperature applications because they suffer from oxidation degradation, extreme embrittlement, and reduced impact resistance when exposed to temperatures above 50°C for long periods of time. Therefore, in compacts for such applications, the resin content is preferably 0.1% to 95% by mass, more preferably 0.5% to 50% by mass, and even more preferably 1% to 15% by mass.

[0115] The resin compound for the bonded magnetic material can be obtained, for example, by mixing and / or kneading a phosphorus compound with a rare earth-iron-nitrogen-based magnetic powder and a resin, or by mixing and / or kneading an α-Fe-containing rare earth-iron-based magnetic powder and a resin, using a kneader at 180° C. to 300° C. For example, the α-Fe-containing rare earth-iron-based magnetic powder and a resin can be mixed in a mixer, and then kneaded and extruded in a twin-screw extruder. The extruded strands are air-cooled and then cut into pieces several millimeters in size using a pelletizer, thereby obtaining the resin compound for the bonded magnetic material of this embodiment in pellet form.

[0116] The bonded magnetic material of this embodiment can be produced by molding the resin compound using an appropriate molding machine. Specifically, for example, the resin compound melted in the barrel of the molding machine is injection-molded into a mold to which a magnetic field is applied, aligning the easy axis of magnetization (orientation process), thereby obtaining a magnetically oriented molded bonded magnetic material. Furthermore, sheet-shaped bonded magnetic material sheets for magnetic field amplification or for ultra-high frequency absorption can be produced by calendering or hot-press molding the pellet-shaped resin compound. By rolling this to a thickness of 20 μm to 200 μm, a magnetic material for magnetic field amplification with a high real term of relative magnetic permeability can be obtained. For example, this can be used as a magnetic material compact for magnetic field amplification in RFID tags or as a magnetic material compact for ultra-high frequency absorption in mobile devices.

[0117] The other components and additives added to the magnetic material for absorbing ultra-high frequencies as needed may be, for example, those listed as the other components and additives added to the magnetic material for amplifying magnetic fields described above. The preferred ranges of the contents of these other components and additives in the magnetic material for absorbing ultra-high frequencies are also the same as the preferred ranges of the contents in the magnetic material for amplifying magnetic fields.

[0118] <<Method for manufacturing α-Fe-containing rare earth-iron magnetic powder>> The method for producing the α-Fe-containing rare earth-iron-based magnetic powder of this embodiment is as follows: a phosphorus treatment step in which an inorganic acid is added to a slurry containing a rare earth-iron-based magnetic powder containing a rare earth R (R is at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe, water, and a phosphorus-containing substance, thereby forming a phosphorus compound coating on the magnetic powder and obtaining a rare earth-iron-based magnetic powder having a phosphorus compound coating; an oxidation step of heat-treating the rare earth-iron-based magnetic powder having the phosphorus compound coating portion in an oxygen-containing atmosphere at 350°C or higher and 600°C or lower; An annealing process in which the rare earth-iron magnetic powder having an oxidized phosphorus compound coating is heat-treated at 200°C to 600°C in an atmosphere of an inert gas or a reducing gas that does not contain nitrogen atoms. The present invention is characterized by comprising:

[0119] In this embodiment, an annealing step is included in which a rare earth-iron based magnetic powder having an oxidized phosphorus compound coating portion is heat-treated at 200°C or higher and 600°C or lower in an atmosphere consisting of an inert gas or a reducing gas not containing nitrogen atoms, thereby making it possible to obtain an α-Fe-containing rare earth-iron based magnetic powder having a core region, an α-Fe-containing region, and an iron oxide-containing region containing magnetite or maghemite outside the α-Fe-containing region.

[0120] Heat-treating the rare earth-iron magnetic powder with the phosphorus compound coating in an oxygen-containing atmosphere at 350°C to 600°C results in the formation of an α-Fe-containing region, with a surface structure in which a phosphorus compound coating is further laminated on the outer surface. This structure combines the aforementioned electrical insulation and magnetic coupling, achieving high permeability and excellent loss characteristics. It also creates a hematite layer on the outer surface. While this layer is effective in further strengthening electrical insulation, it increases the volume fraction of the low-magnetic region and increases the overall demagnetizing field of the magnetic powder, potentially limiting the full potential of the high permeability. Heat-treating this powder at 200°C to 600°C in an atmosphere of an inert gas or a reducing gas containing no nitrogen atoms converts the weakly magnetic hematite into magnetite or maghemite, imparting strong magnetism to the outermost layer and significantly reducing the overall demagnetizing field of the magnetic powder.

[0121] Both magnetite and maghemite exhibit ferromagnetism, and ferromagnetic bonding occurs with the α-Fe-containing phase through the phosphorus compound coating, greatly reducing the demagnetizing field in the magnetic part, while electrical insulation is generated by the phosphorus compound coating and the α-Fe-containing phase (this effect is greater in maghemite than in magnetite, as will be described later), resulting in unexpectedly high magnetic permeability and sufficient efficiency.

[0122] [Phosphorus treatment process] In the phosphorus treatment step, an inorganic acid is added to a slurry containing rare earth-iron-based magnetic powder, water, and a phosphorus-containing substance to form a phosphorus compound coating on the magnetic powder, thereby obtaining a rare earth-iron-based magnetic powder having a phosphorus compound coating. The rare earth-iron-based magnetic powder having a phosphorus compound coating is formed by the reaction of a metal component (e.g., X or a rare earth element) contained in the rare earth-iron-based magnetic powder with a phosphorus component (e.g., phosphoric acid) contained in the phosphorus-containing substance, resulting in the precipitation of a phosphorus compound (e.g., iron phosphate, samarium phosphate, cerium phosphate, etc.). Furthermore, by precipitating the phosphorus compound on the surface of the rare earth-iron-based magnetic powder, the phosphorus compound preferably coats at least a portion of the surface of the rare earth-iron-based magnetic powder (such a coating is referred to as a "phosphorus compound coating" or "phosphorus coating"; the portion formed by such a coating is referred to as a "phosphorus compound coating").

[0123] In the phosphorus treatment process, by using water as the solvent, phosphorus compounds such as phosphates with smaller particle sizes are precipitated compared to when an organic solvent is used, which results in a magnetic powder with a dense phosphorus compound coating, and tends to provide excellent efficiency in the high frequency range.

[0124] The method for preparing a slurry containing a rare earth-iron magnetic powder, water, and a phosphorus-containing material is not particularly limited. For example, the slurry can be prepared by mixing the rare earth-iron magnetic powder with a phosphorus-containing material solution containing the phosphorus-containing material in water as a solvent. The content of the rare earth-iron magnetic powder in the slurry is preferably 1% to 50% by mass, and more preferably 5% to 20% by mass from the viewpoint of productivity. The content of the phosphorus-containing material in the slurry is not particularly limited. However, when the phosphorus-containing material is phosphoric acid and is composed only of hydrogen and a phosphoric acid component (PO), the content is, for example, 0.01% to 10% by mass in terms of PO, and preferably 0.05% to 5% by mass from the viewpoints of reactivity between the metal component and the phosphoric acid component and productivity.

[0125] Examples of phosphorus-containing substances include elemental phosphorus and compositions thereof, phosphate compounds such as orthophosphoric acid, heteropolyacid compounds such as phosphotungstic acid and phosphomolybdic acid, salts of phosphorus-containing acid compounds such as phosphate compounds and heteropolyacid compounds with metal ions or ammonium ions, organic phosphorus compounds such as phosphate esters, phosphite esters, and phosphine oxides, and phosphorus-containing metals such as iron phosphide, phosphor bronze, and Fe-BP-Cu and Fe-Nb-BP-based alloys.

[0126] When the phosphorus-containing substance is a phosphoric acid compound, the phosphoric acid aqueous solution can be obtained by mixing the phosphoric acid compound with water. Examples of phosphoric acid compounds include phosphates such as orthophosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, zinc phosphate, and calcium phosphate; inorganic phosphoric acids such as hypophosphorous acid, hypophosphite, pyrophosphate, and polyphosphoric acid; and organic phosphoric acids and their salts. These compounds may be used alone or in combination. In addition, additives such as oxoacid salts (e.g., molybdate, tungstate, vanadate, and chromate), oxidizers (e.g., sodium nitrate and sodium nitrite), and chelating agents (e.g., EDTA) can be used to improve the water resistance and corrosion resistance of the coating and the magnetic properties of the magnetic powder. Among the phosphorus-containing substances, from the viewpoint of reaction control and coating amount control, inorganic phosphoric acids such as orthophosphoric acid, pyrophosphoric acid, and polyphosphoric acid, and phosphoric acid compounds such as phosphates of these with Na, Mg, Al, Ca, K, Ti, V, Cr, Mn, Ni, Cu, Pb, Zn, Fe, Zr, Mo, Ba, Hf, Ta, La, Y, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Lu, Sm, ammonium, and the like are preferred.

[0127] The phosphoric acid concentration (PO4 equivalent) in the phosphoric acid aqueous solution is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, from the viewpoints of the solubility of the phosphoric acid compound, storage stability, and ease of chemical conversion treatment. The pH of the phosphoric acid aqueous solution is preferably 1 to 4.5, and more preferably 1.5 to 4, from the viewpoint of ease of control of the precipitation rate of phosphate. The pH can be adjusted with dilute hydrochloric acid, dilute sulfuric acid, etc.

[0128] In the phosphorus treatment process, adjusting the pH of the slurry by adding an inorganic acid can increase the amount of phosphorus compound precipitation compared to when no inorganic acid is added. This results in a magnetic powder with a thick coating (also referred to as film thickness), improved tan δ and phase angle θ, and improved magnetic field amplification characteristics. The pH of the slurry is preferably adjusted to 1 or more and 4.5 or less, more preferably 1.6 or more and 3.9 or less, and even more preferably 2 or more and 3 or less. At a pH of less than 1, the rare earth-iron magnetic powder tends to aggregate from locally precipitated large amounts of phosphorus compounds, resulting in a deterioration in tan δ and phase angle θ in the high-frequency range. At a pH of more than 4.5, the amount of precipitation of phosphorus compounds such as phosphates decreases, resulting in a deterioration in tan δ and phase angle θ in the high-frequency range. Examples of inorganic acids that can be added include hydrochloric acid, nitric acid, sulfuric acid, boric acid, and hydrofluoric acid. During the phosphorus treatment process, it is preferable to add an inorganic acid as needed to maintain the pH within the above range. While inorganic acids are used from the perspective of wastewater treatment, organic acids can also be used in combination depending on the purpose. Examples of organic acids include acetic acid, formic acid, and tartaric acid.

[0129] The phosphorus treatment step can also be performed so that the phosphorus content in the resulting magnetic powder is 0.0005% by mass or more. The phosphorus content in the magnetic powder obtained in the phosphorus treatment step is preferably 0.001% by mass or more, more preferably 0.05% by mass or more. The phosphorus content in the magnetic powder obtained in the phosphorus treatment step is preferably 4% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. A phosphorus content of 0.0005% by mass or more tends to enhance the effect of coating with the phosphorus compound, while a phosphorus content of 4% by mass or less tends to suppress the aggregation of magnetic powder particles originating from the phosphorus compound, which may cause deterioration of tan δ and phase angle θ in the high-frequency range. When producing a magnetic material for magnetic field amplification with particularly excellent efficiency, the phosphorus content is preferably 0.05% by mass or more and 1% by mass or less. The bulk phosphorus content of the entire magnetic powder can be measured using ICP-AES (inductively coupled plasma atomic emission spectroscopy). The local phosphorus content of the magnetic powder phase in the phosphorus compound-coated powder and the phosphorus compound coating portion can be measured using STEM-EDS line analysis. The phosphorus (P) atomic concentration in the phosphorus compound coating portion is preferably 0.1 atomic % or more, more preferably 0.3 atomic % or more. The P atomic concentration in the phosphorus compound coating portion may be 25 atomic % or less, preferably 15 atomic % or less. If the phosphorus content in the phosphorus compound coating portion is less than 0.1 atomic %, the electrical insulation properties of the phosphorus compound tend to be poor, while if it exceeds 25 atomic %, not only does the real term of the relative permeability in the high frequency range decrease, but corrosion resistance also tends to decrease.

[0130] The phosphorus treatment step may be carried out so that the phosphorus compound coating portion present on the surface of the obtained magnetic powder has a region (R-rich region) in which the rare earth (R) atomic concentration is higher than the R atomic concentration in the rare earth (R)-iron-based magnetic powder. An example of the rare earth element (R) is Sm, and in this case, the Sm-rich region can be evaluated based on the Sm atomic concentration.

[0131] The pH of the slurry containing the rare earth-iron magnetic powder, water, and phosphorus-containing material is adjusted to a range of 1 to 4.5, preferably for 10 minutes or more, and more preferably for 30 minutes or more in order to reduce areas where the coating is thin. In the early stages of pH maintenance, the pH rises quickly, so the intervals between additions of inorganic acid for pH control are short, but as coating progresses, the pH fluctuations gradually slow down and the intervals between additions of inorganic acid become longer, allowing the reaction endpoint to be determined.

[0132] [Oxidation process after phosphorus treatment] In this process, the rare earth-iron magnetic powder having a phosphorus compound coating is heat-treated at 350°C to 600°C in an oxygen-containing atmosphere. The oxidation treatment is thought to oxidize the surface of the rare earth-iron magnetic powder from the interface between the phosphorus compound coating and the rare earth-iron magnetic powder, forming an α-Fe-containing region disproportionated into an α-Fe phase and at least one phase selected from the group consisting of oxides, nitrides, and oxynitrides of rare earth R. As a result, a magnetic material for magnetic field amplification with improved tan δ and phase angle θ in the high-frequency range can be obtained.

[0133] In this process, an iron oxide layer is deposited on the surface of the α-Fe-containing rare earth-iron magnetic powder from the phosphorus compound coating. This iron oxide is often primarily hematite. The iron oxide layer may be either bound or free on the surface of the α-Fe-containing rare earth-iron magnetic powder. For applications requiring higher efficiency, it is preferable to leave this iron oxide layer bound. This iron oxide layer is then reduced in a subsequent annealing process to form an iron oxide-containing region primarily composed of maghemite and / or magnetite, resulting in high magnetic permeability and high efficiency. The iron oxide layer may contain at least one of Ni, Co, and M component elements.

[0134] The oxidation treatment is carried out by heat treating the phosphorus-treated magnetic powder in an oxygen-containing atmosphere. The reaction atmosphere preferably contains oxygen in an inert gas such as nitrogen or argon. The oxygen concentration is preferably 3% to 25% by volume, more preferably 3.5% to 21% by volume. During the oxidation reaction, the gas is preferably exchanged at a flow rate of 2 L / min to 10 L / min per 1 kg of magnetic powder.

[0135] The temperature during the oxidation treatment varies depending on the composition of the core region and the surface coverage of the core region, and is 300°C or higher and 600°C or lower, preferably 320°C or higher and 580°C or lower, more preferably 350°C or higher and 550°C or lower, and even more preferably 400°C or higher and 500°C or lower. If the temperature is lower than 300°C, the real term of the relative permeability in the high frequency range tends to decrease. If the temperature exceeds 600°C, the magnetic powder tends to decompose excessively. The reaction time may be 30 minutes or longer, 1 hour or longer, or 3 hours or longer. The reaction time may be 20 hours or shorter, or 10 hours or longer.

[0136] By undergoing an oxidation process after the phosphorus treatment process, it is thought that excessive thermal decomposition in the core region can be avoided, and the α-Fe phase can be gradually separated and dispersed from the matrix at the nano-level through a disproportionation reaction starting from the surface of the rare earth-iron magnetic powder beneath the phosphorus compound coating.

[0137] [Annealing process] In this step, the rare earth-iron based magnetic powder having an oxidized phosphorus compound coating is heat-treated at 200°C to 600°C in an atmosphere of an inert gas or a reducing gas not containing nitrogen atoms. It is believed that this step reduces at least a portion of the hematite formed on the surface of the α-Fe-containing rare earth-iron based magnetic powder in the oxidation step, and forms an iron oxide-containing region containing magnetite or maghemite outside the α-Fe-containing region.

[0138] Examples of inert gases used during heat treatment include Ar gas, N2 gas, Ne gas, and He gas. Examples of reducing gases that do not contain nitrogen atoms used during heat treatment include H2 gas and CO gas. A mixed gas of these gases may also be used. The oxygen concentration in the atmosphere during heat treatment is preferably 0.1% by volume or less, and more preferably 0.01% by volume or less.

[0139] The temperature during heat treatment varies depending on the composition of the core region and the surface coverage of the core region, and is 350°C or higher and 600°C or lower, preferably 380°C or higher and 550°C or lower, and more preferably 400°C or higher and 480°C or lower. If the temperature is lower than 350°C, the treatment time tends to be very long. If the temperature exceeds 600°C, the coating film made of the phosphorus compound tends to deteriorate. The reaction time may be 10 minutes or longer, 1 hour or longer, or 3 hours or longer. The reaction time may be 20 hours or shorter, or 6 hours or shorter.

[0140] After an annealing step of heat-treating at 200°C to 600°C in an atmosphere of an inert gas or a reducing gas not containing nitrogen atoms, a heat-treatment step of heat-treating at 200°C to 600°C in an oxygen-containing atmosphere may be carried out. This heat-treatment step can also oxidize magnetite generated outside the α-Fe-containing region to maghemite. The heat-treatment temperature is preferably 200°C to 600°C, more preferably 200°C to 500°C, and even more preferably 200°C to 300°C.

[0141] [Silica treatment process] The magnetic powder that has undergone the annealing process may be subjected to silica treatment as needed. Forming a silica thin film on the magnetic powder can improve oxidation resistance. The silica thin film can be formed, for example, by mixing alkyl silicate, magnetic powder, and an alkaline solution.

[0142] [Silane coupling treatment process] The magnetic powder after silica treatment may be further treated with a silane coupling agent. By subjecting the magnetic powder on which a thin silica film has been formed to a silane coupling treatment, a silane coupling agent film is formed on the thin silica film, improving the magnetic properties of the magnetic powder, as well as improving wettability with resin and the strength of the molded product.The silane coupling agent may be selected according to the type of resin and is not particularly limited. Examples of the silane coupling agent include γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, hexamethylenedisilazane, γ-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, vinyltrichlorosilane, Vinyltris(β-methoxyethoxy)silane, vinyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, oleidopropyltriethoxysilane, γ-isocyanatopropyltriethoxysilane, Examples of silane coupling agents include polyethoxydimethylsiloxane, polyethoxymethylsiloxane, bis(trimethoxysilylpropyl)amine, bis(3-triethoxysilylpropyl)tetrasulfane, γ-isocyanatepropyltrimethoxysilane, vinylmethyldimethoxysilane, 1,3,5-N-tris(3-trimethoxysilylpropyl)isocyanurate, t-butylcarbamatetrialkoxysilane, and N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine. These silane coupling agents may be used alone or in combination of two or more.The amount of silane coupling agent added is preferably 0.2 to 0.8 parts by mass, more preferably 0.25 to 0.6 parts by mass, per 100 parts by mass of magnetic powder. If the amount is less than 0.2 parts by mass, the effect of the silane coupling agent is small, but if the amount exceeds 0.8 parts by mass, aggregation of the magnetic powder tends to deteriorate the magnetic properties of the magnetic powder and the compact.

[0143] In addition, without carrying out the silica treatment step and / or the silane coupling treatment step, or after these treatment steps, isopropyl triisostearoyl titanate, isopropyl tri(N-aminoethyl-aminoethyl) titanate, isopropyl tris(dioctyl pyrophosphate) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraoctyl bis(ditridecyl phosphite) titanate, isopropyl trioctanoyl titanate, isopropyl tridodecyl benzene sulfonate, Magnetic powders can be surface-treated using titanium-based coupling agents such as bis(dioctylpyrophosphate)ethylene titanate, isopropyl dimethacryl isostearoyl titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecylphosphite) titanate, and isopropyl tricumylphenyl titanate, or aluminum-based, zirconium-based, chromium-based, iron-based, or tin-based coupling agents such as acetoalkoxyaluminum diisopropylate. When this surface treatment is used to produce bonded magnetic materials, the magnetic powder exhibits improved affinity with the resin to be added, resulting in significant isolated dispersion of the α-Fe-containing rare earth-iron magnetic powder, improved electrical insulation between the powders, and potentially superior efficiency at high frequencies.

[0144] After the phosphorus treatment step, oxidation step, annealing step, silica treatment step, or silane coupling treatment step, the magnetic powder can be filtered, dehydrated, and dried by conventional methods.

[0145] The real term of the relative magnetic permeability of α-Fe-containing rare earth-iron magnetic powder can be improved by uniformizing the particle size distribution. Uniformization of the particle size distribution can be achieved by a typical dry classification method or wet classification method. Uniformization of the particle size distribution can be performed at any time: before the phosphoric acid treatment, after the phosphorus treatment process, after the oxidation process, after the annealing process, after the silica treatment process, or after the silane coupling treatment process. [Example]

[0146] The present disclosure will be explained in more detail with reference to the following examples, but the present disclosure is not limited to these examples in any way.

[0147] The evaluation methods used in the examples are as follows.

[0148] (1) XRD and α-Fe peak intensity ratio and half-width The XRD pattern of the magnetic powder was measured using a powder X-ray crystal diffractometer (Rigaku Minflex 600C, X-ray wavelength: CuKα) under the following conditions: acceleration voltage 40 kV, tube current 15 mA, step width 2θ = 0.01 between 10 < 2θ < 90.

[0149] (2) Average particle size The average particle size of the magnetic powder was measured using a laser diffraction particle size distribution analyzer (MALVERN Inst. MASTERSIZER 2000).

[0150] (3) Complex relative permeability measurement (1MHz to 1GHz) The magnetic powder and epoxy resin, a thermosetting resin, were mixed so that the magnetic powder content was 97% by mass, and then kneaded to produce a resin compound. This resin compound was placed in a mold with an inner diameter of 3.1 mm and an outer diameter of 8 mm and molded at a pressure of 0.8 GPa. It was then thermally cured in a vacuum at 150°C for 2 hours to produce a toroidal compact. Using this sample, the complex relative permeability in the frequency range of 1 MHz to 1 GHz was evaluated using an impedance analyzer (E4991B, Keysight) from the inductance value obtained using a single-turn inductor test fixture.

[0151] (4) STEM-EDS analysis and TEM-ED analysis STEM analysis of the magnetic powder surface was performed as follows. First, the obtained magnetic powder was carbon-coated and then cross-sectioned and thinned using a focused ion beam (FIB). The obtained sample was measured using a STEM (manufactured by JEOL Ltd., model number JEM-F200; accelerating voltage 200 kV) and an EDS (system: manufactured by JEOL Ltd., model number SD100HR; detector: JEOL Ltd. dry SD detector) attached to the STEM.

[0152] Comparative Example 1 NdFe with an average particle size of approximately 15 μm was prepared by the precipitation method using iron sulfate and neodymium sulfate as raw materials as follows: 17 N3 magnetic powder was prepared.

[0153] [Preparation of Nd-Fe sulfate solution] 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. 0.45 kg of Nd2O3 powder and 0.70 kg of 70% sulfuric acid were then added and stirred thoroughly until completely dissolved. Next, pure water was added to the resulting solution, and the final Fe concentration was adjusted to 0.726 mol / L and the Nd concentration to 0.106 mol / L, creating a Nd-Fe sulfuric acid solution.

[0154] [Precipitation process] The entire Nd-Fe sulfate solution was added dropwise to 20 kg of pure water maintained at 40°C over a period of 70 minutes while stirring. At the same time, 15% aqueous ammonia was added dropwise to adjust the pH to 7-8. This yielded a slurry containing Nd-Fe hydroxide. The resulting slurry was washed with pure water by decantation, and the hydroxide was subjected to solid-liquid separation. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0155] [Oxidation process] The hydroxide obtained in the precipitation process was calcined in air at 1030°C for 1 hour. After cooling, red Nd-Fe oxide was obtained as raw powder.

[0156] [Pretreatment process] 100 g of Nd-Fe oxide was placed in a steel container with a bulk thickness of 10 mm. The container was placed in a furnace, and the pressure was reduced to 100 Pa. Then, while introducing hydrogen gas, the temperature was raised to the pretreatment temperature of 850°C and maintained at that temperature for 15 hours to obtain a black powder partial oxide.

[0157] [Reduction process] 60 g of the partial oxide obtained in the pretreatment process and 19.2 g of metallic calcium with an average particle size of approximately 6 mm were mixed and placed in a furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The temperature was raised to 1045°C and held for 45 minutes to obtain Fe-Nd alloy particles.

[0158] [Nitriding process] Subsequently, the temperature inside the furnace was cooled to 100°C, and then the furnace was evacuated and the temperature was raised to 450°C while introducing nitrogen gas, and maintained at that temperature for 23 hours to obtain a bulk product containing magnetic powder.

[0159] [Water washing process] The aggregated product obtained in the nitriding process was poured into 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was poured into the product and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated twice, followed by dehydration and drying, followed by mechanical crushing to obtain Nd2Fe 17 N3 magnetic powder (average particle size approximately 15 μm) was obtained.

[0160] [Phosphorus treatment process] The phosphate treatment solution was prepared by mixing 85% orthophosphoric acid, sodium dihydrogen phosphate, and sodium molybdate dihydrate in a mass ratio of 1:6:1, and adjusting the pH to 2 and the PO concentration to 20 mass% with pure water and dilute hydrochloric acid. 17The N3 magnetic powder was stirred for 1 minute in a dilute hydrochloric acid solution (1000 g water:70 g hydrogen chloride) to remove surface oxide films and contaminants. The solution was then repeatedly drained and refilled until the conductivity of the supernatant liquid reached 100 μS / cm or less, yielding a slurry containing 10% by mass of Nd-Fe-N magnetic powder. While stirring the resulting slurry, 100 g of the prepared phosphate treatment solution was poured into the treatment tank. Then, 6% by mass of hydrochloric acid was added periodically to control the pH of the phosphate treatment reaction slurry within a range of 2.0±0.1, which was maintained for 40 minutes. The resulting slurry was then suction filtered, dehydrated, and vacuum dried to obtain the Nd-Fe-N magnetic powder according to Comparative Example 1, which had a phosphorus compound coating.

[0161] Comparative Example 2 [Preparation of Nd-Fe sulfate solution] 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. 0.45 kg of Nd2O3 powder and 0.70 kg of 70% sulfuric acid were then added and stirred thoroughly until completely dissolved. Next, pure water was added to the resulting solution, and the final Fe concentration was adjusted to 0.726 mol / L and the Nd concentration to 0.106 mol / L, creating a Nd-Fe sulfuric acid solution.

[0162] [Precipitation process] The entire Nd-Fe sulfate solution was added dropwise to 20 kg of pure water maintained at 40°C over a period of 70 minutes while stirring. At the same time, 15% aqueous ammonia was added dropwise to adjust the pH to 7-8. This yielded a slurry containing Nd-Fe hydroxide. The resulting slurry was washed with pure water by decantation, and the hydroxide was subjected to solid-liquid separation. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0163] [Oxidation process] The hydroxide obtained in the precipitation process was calcined in air at 1030°C for 1 hour. After cooling, red Nd-Fe oxide was obtained as raw powder.

[0164] [Pretreatment process] 100 g of Nd-Fe oxide was placed in a steel container with a bulk thickness of 10 mm. The container was placed in a furnace, and the pressure was reduced to 100 Pa. Then, while introducing hydrogen gas, the temperature was raised to the pretreatment temperature of 850°C and maintained at that temperature for 15 hours to obtain a black powder partial oxide.

[0165] [Reduction process] 60 g of the partial oxide obtained in the pretreatment process and 19.2 g of metallic calcium with an average particle size of approximately 6 mm were mixed and placed in a furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The temperature was raised to 1045°C and held for 45 minutes to obtain Fe-Nd alloy particles.

[0166] [Nitriding process] Subsequently, the temperature inside the furnace was cooled to 100°C, and then the furnace was evacuated and the temperature was raised to 450°C while introducing nitrogen gas, and maintained at that temperature for 23 hours to obtain a bulk product containing magnetic powder.

[0167] [Water washing process] The aggregated product obtained in the nitriding process was poured into 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was poured into the product and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated twice, followed by dehydration and drying, followed by mechanical crushing to obtain Nd2Fe 17 N3 magnetic powder (average particle size approximately 15 μm) was obtained.

[0168] [Phosphorus treatment process] The phosphate treatment solution was prepared by mixing 85% orthophosphoric acid, sodium dihydrogen phosphate, and sodium molybdate dihydrate in a mass ratio of 1:6:1, and adjusting the pH to 2 and the PO concentration to 20 mass% with pure water and dilute hydrochloric acid. 17The N3 magnetic powder was stirred for 1 minute in a dilute hydrochloric acid solution (1000g water:70g hydrogen chloride) to remove surface oxide films and contaminants. The solution was then repeatedly drained and refilled until the supernatant's conductivity reached 100μS / cm or less, yielding a slurry containing 10% by mass of Nd-Fe-N magnetic powder. While stirring the resulting slurry, 100g of the prepared phosphate treatment solution was poured into the treatment tank. Then, 6% by mass of hydrochloric acid was added periodically to control the pH of the phosphate treatment reaction slurry within the range of 2.0±0.1, which was maintained for 40 minutes. The resulting solution was then suction filtered, dehydrated, and vacuum dried to yield Nd-Fe-N magnetic powder with a phosphorus compound coating.

[0169] 300 g of Nd-Fe-N magnetic powder having a phosphorus compound coating was gradually heated from room temperature in an atmosphere of a mixed gas of nitrogen and air (oxygen concentration 4 vol%, 5 L / min), and heat-treated at 465°C for 4 hours to obtain oxidized Nd-Fe-N magnetic powder (average particle size approximately 8 μm) according to Comparative Example 2.

[0170] Example 1 The oxidized Nd-Fe-N magnetic powder of Comparative Example 2 was further heated gradually from room temperature in an argon atmosphere to 420°C for 4 hours, thereby obtaining the Nd-Fe-N magnetic powder of Example 1 (average particle size approximately 8 μm).

[0171] Example 2 The oxidation-treated Nd-Fe-N magnetic powder of Comparative Example 2 was subjected to the same treatment as in Example 1, except that the heat treatment atmosphere was changed from an argon atmosphere to a nitrogen atmosphere and the heat treatment time was changed from 4 hours to 30 minutes, thereby obtaining Nd-Fe-N magnetic powder (average particle size approximately 8 μm) according to Example 2.

[0172] Example 3 The oxidation-treated Nd-Fe-N magnetic powder of Comparative Example 2 was subjected to the same treatment as in Example 1, except that the heat treatment atmosphere was changed from an argon atmosphere to a hydrogen atmosphere and the heat treatment time was changed from 4 hours to 15 minutes, to obtain Nd-Fe-N magnetic powder (average particle size approximately 8 μm) of Example 3.

[0173] Comparative Example 3 The oxidation-treated Nd-Fe-N magnetic powder of Comparative Example 2 was subjected to the same treatment as in Example 1, except that the heat treatment atmosphere was changed from an argon atmosphere to an ammonia atmosphere and the heat treatment time was changed from 4 hours to 15 minutes, thereby obtaining Nd-Fe-N magnetic powder (average particle size approximately 8 μm) according to Comparative Example 3.

[0174] Comparative Example 4 300 g of the Nd-Fe-N magnetic powder having the phosphorus compound coating portion of Comparative Example 1 was gradually heated from room temperature in an argon gas atmosphere and subjected to heat treatment at 420°C for 4 hours to obtain the Nd-Fe-N magnetic powder (average particle size approximately 8 μm) of Comparative Example 4.

[0175] Table 1 shows the heat treatment conditions for the magnetic powders according to Examples 1 to 3 and Comparative Examples 1 to 4. [Table 1]

[0176] The frequency dependence of the complex relative permeability of the magnetic powders according to Examples 1 to 3 and Comparative Examples 1 to 4 was measured in the range of 1 MHz to 1 GHz using the method described above, and the results are shown in Figure 1. Furthermore, the frequency characteristics at 2 MHz, 10 MHz, 50 MHz and 100 MHz are shown in Table 2.

[0177] [Table 2]

[0178] In Table 2, Examples 1 to 3 showed high μ' and low μ" at 2 MHz compared to Comparative Examples 1 to 4. This is thought to be because the weakly magnetic α-Fe2O3 formed on the particle surface was converted to magnetite (Fe3O4) or maghemite (γ-Fe2O3) (Example 1) by heat treatment in an Ar atmosphere, and to α-Fe or Fe3O4 (Example 3) by heat treatment in an H2 atmosphere.

[0179] 1, the μ' at 12 MHz of all the α-Fe-containing rare earth-iron magnetic materials of the examples was 11 or more. In addition, the tan δ at 10 MHz was extremely excellent at 0.02 or less, demonstrating high magnetic permeability and high efficiency.

[0180] Figure 2 shows the XRD patterns obtained under the aforementioned conditions for the magnetic powders of Example 1, Example 3, Comparative Example 1, and Comparative Example 2. The peaks of hematite (α-Fe2O3) near 2θ = 33° and 49.7° that were generated in Comparative Example 2 by oxidation treatment disappeared in Example 1. Furthermore, new peaks appeared in Example 1 near 2θ = 30° and 56°. These are thought to be peaks of magnetite or maghemite. Furthermore, a broad peak was observed near 2θ = 44° to 45° for the magnetic powders of all Examples and Comparative Examples 2 and 3. This confirmed the presence of α-Fe-containing regions composed of nanocrystals. The peak was observed at a lower angle than that of typical α-Fe, but this is thought to be due to the lattice distortion of α-Fe itself as it tries to lattice match with rare earth oxides, nitrides, or oxynitrides, resulting in a shift to the lower angle. In the XRD patterns of Examples 1 and 3, the ratios (I) / (II) of the diffraction peak intensity (I) of the (110) plane of α-Fe to the peak intensity (II) of the strongest line of the rare earth-iron-nitrogen compound were 2.9 and 4.4, respectively, and were in the range of 0.01 or more and less than 100.

[0181] In the XRD diffraction pattern of Example 1, the ratio (I) / (II) of the diffraction peak intensity (I) of the (511) plane of magnetite or maghemite to the peak intensity (II) of the strongest line of the rare earth-iron-nitrogen compound was 0.3, which was in the range of 0.01 or more and less than 100.

[0182] Furthermore, in the XRD diffraction pattern of Example 1, the ratio (I) / (II) of the diffraction peak intensity (I) of the (104) plane of hematite to the diffraction peak intensity (II) of the (511) plane of the magnetite or maghemite was 0, and was in the range of 0 or more and less than 10. Although no diffraction lines of magnetite or maghemite were observed in the XRD diffraction pattern of Example 3, their presence was confirmed by STEM-EDS.

[0183] The surfaces of the magnetic powders of Comparative Example 1, Comparative Example 2, Example 1, and Example 3 were observed using a STEM (manufactured by JEOL Ltd., model number JEM-F200; accelerating voltage 200 kV) and an EDS system (system: manufactured by JEOL Ltd., model number SD100HR; detector: JEOL Ltd. dry SD detector) attached to the STEM. For STEM and STEM-EDS, observations were made at 1 million magnification for Figures 3, 4, and 5, respectively, and at 4 million magnification for Figures 6 and 7.

[0184] The STEM-DF image of Comparative Example 2 is shown in FIG. 3, and the quantitative results (atomic %) of EDS at p1, p2, and p3 in FIG. [Table 3]

[0185] The STEM-DF image of Example 1 is shown in FIG. 4, and the quantitative results (atomic %) of EDS at p4, p5, and p6 in FIG. [Table 4]

[0186] The STEM-DF image of Example 3 is shown in FIG. 5, and the quantitative results (atomic %) of EDS at p7, p8, and p9 in FIG. [Table 5]

[0187] Observations were made at magnifications of 1 million times (Fig. 3), 1 million times (Fig. 4), and 1 million times (Fig. 5) for STEM and EDS, respectively.

[0188] For Comparative Example 2, Table 3 and Figure 3 show that the composition of p1 is almost identical to Fe2O3, and when combined with the XRD measurement results, it is believed that hematite is present in most of p1. It is believed that p3 contains a phosphorus compound coating consisting of Nd, Fe, P, and O. Since p2 exhibits a composition between p1 and p3, it is believed that the above compounds are mixed.

[0189] For Example 1, Table 4 and Figure 4 show that the composition of p4 is nearly identical to Fe2O3, and when combined with the XRD measurement results, it is believed that magnetite or maghemite is present in most of p4. p6 is believed to contain a phosphorus compound-coated microcrystalline portion centered on a solid solution of neodymium phosphate and iron phosphate, which are composed of Nd, Fe, P, and O. p5 exhibits a composition between p4 and p6, and is therefore believed to contain a mixture of the above compounds.

[0190] 5 for Example 3, the composition of p8 is mostly Fe, and therefore α-Fe, which was generated by hydrogen reduction of hematite seen in p1 of Comparative Example 2, is considered to be the main component of p8. The oxygen ratio in p7 is higher than that in p8, and therefore it is considered that only the outermost surface portion has been reoxidized, and that a mixture of hematite, magnetite, and maghemite is present in p7.

[0191] Fig. 6 shows a STEM-EDS image of Fe observed for Comparative Example 2. In Fig. 6, three types of regions were identified based on the shade of color, and in correspondence with Fig. 3, these were identified as, from top to bottom, an iron oxide-containing region including hematite, a phosphorus compound coating region, and an α-Fe-containing region, and the proportion of Fe present also matched.

[0192] Figure 7 shows a STEM-EDS image of Fe observed for Example 1. As in Figure 6, the presence of an α-Fe-containing region was confirmed below the phosphorus compound coating.

[0193] In Comparative Example 2, the film thicknesses of the iron oxide-containing region, the phosphorus compound-coated portion, and the α-Fe-containing region were 70 nm, 10 nm, and 470 nm, respectively. In Example 1, the film thicknesses of the iron oxide-containing region, the phosphorus compound-coated portion, and the α-Fe-containing region were 90 nm, 10 nm, and 870 nm, respectively. The film thicknesses of the iron oxide-containing region, the phosphorus compound coating portion, and the α-Fe-containing region in Comparative Example 3 were 45 nm, 11 nm, and 240 nm, respectively. The film thickness of the α-Fe region included in the iron oxide-containing region was 42 nm.

[0194] Example 4 Phosphorus compound-coated NdFe prepared in Example 1 17 The N3 soft magnetic powder was mixed with epoxy resin, a thermosetting resin, and then kneaded to prepare a compound. 17 The content of N3 soft magnetic powder was 96% by mass. The resulting compound was placed in a mold and molded under a pressure of 1.4 GPa, after which it was heat-cured in a vacuum at 150°C for 2 hours to produce a toroidal compact with an inner diameter of 3.1 mm, an outer diameter of 8 mm, and a thickness of 1.30 mm.

[0195] Example 5 Phosphorus compound-coated NdFe prepared in Example 1 17 Nd3 soft magnetic powder, magnetite (Fe3O4) (average particle size 0.1 μm), and epoxy resin, a thermosetting resin, were mixed and kneaded to prepare a compound. 17 The N3 soft magnetic powder content was 93.5% by mass, and the magnetite content was 2.5% by mass. The resulting compound was placed in a mold and molded under a pressure of 1.4 GPa, then heat-cured in a vacuum at 150°C for 2 hours to produce a toroidal compact with an inner diameter of 3.1 mm, an outer diameter of 8 mm, and a thickness of 1.28 mm.

[0196] Using the molded bodies of Examples 4 and 5, the complex relative permeability in the frequency range of 1 MHz to 1 GHz was evaluated using an impedance analyzer (E4991B, manufactured by Keysight) from the inductance value determined using a single-turn inductor test fixture. In addition, tan δ=μ" / μ' was calculated from the determined μ' and μ" values. Table 6 shows the frequency characteristics at 10 MHz, 50 MHz, and 100 MHz.

[0197] [Table 6]

[0198] From the comparison between Example 4 and Example 5, it is clear that the phosphorus compound-coated NdFe 17 By adding magnetic metal oxide (Fe3O4: magnetite) to the N3 soft magnetic powder, μ' becomes higher in the range of 10 MHz to 100 MHz, and tan δ is equal to or greater than that, resulting in higher efficiency.

[0199] The invention according to the present disclosure may include, for example, the following aspects. [1] a core region including rare earth R (R is at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe; an α-Fe-containing region outside the core region, the α-Fe-containing region including α-Fe and at least one selected from the group consisting of an oxide, a nitride, and an oxynitride of a rare earth element R; The α-Fe-containing rare earth-iron magnetic powder has an iron oxide-containing region containing magnetite or maghemite outside the α-Fe-containing region. [2] When the rare earth element R contains Sm, the content of Sm is less than 50 atomic % of the total R component. Item 1. The α-Fe-containing rare earth-iron magnetic powder according to item 1. [3] The core region further comprises N. Item 1 or 2. The α-Fe-containing rare earth-iron magnetic powder according to item 1 or 2. [4] The α-Fe containing region is nanocrystals consisting of at least one selected from the group consisting of oxides, nitrides, and oxynitrides of the rare earth R; and containing nanocrystals made of α-Fe, Item 4. The α-Fe-containing rare earth-iron magnetic powder according to any one of Items 1 to 3. [5] Item 5. The α-Fe-containing rare earth-iron magnetic powder according to any one of items 1 to 4, having a phosphorus compound coating portion between the α-Fe-containing region and the iron oxide-containing region. [6] Item 6. The α-Fe-containing rare earth-iron-based magnetic powder according to any one of Items 1 to 5, wherein the thickness of the α-Fe-containing region is 0.01% or more and less than 50% of the average particle size of the α-Fe-containing rare earth-iron-based magnetic powder. [7] 7. The α-Fe-containing rare earth-iron magnetic powder according to any one of items 1 to 6, wherein the thickness of the α-Fe-containing region is 1 nm or more and 80 μm or less. [8] the core region includes a rare earth-iron-nitrogen compound; Item 8. The α-Fe-containing rare earth-iron magnetic powder according to any one of Items 1 to 7, wherein in an XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity (I) of the (110) plane of α-Fe to the peak intensity (II) of the strongest line of the rare earth-iron-nitrogen compound is 0.01 or more and less than 100. [9] the core region includes a rare earth-iron-nitrogen compound; Item 9. The α-Fe-containing rare earth-iron magnetic powder according to any one of Items 1 to 8, wherein in an XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity (I) of the (511) plane of magnetite or maghemite to the peak intensity (II) of the strongest line of the rare earth-iron-nitrogen compound is 0.01 or more and less than 100.

[10] the core region includes a rare earth-iron-nitrogen compound; Item 10. The α-Fe-containing rare earth-iron magnetic powder according to any one of Items 1 to 9, wherein in an XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity (I) of the (104) plane of hematite to the diffraction peak intensity (II) of the (511) plane of the magnetite or maghemite is 0 or more and less than 10.

[11] Item 11. The α-Fe-containing rare earth-iron magnetic powder according to any one of items 1 to 10, having a tan δ of 0.1 or less and μ′ of 11 or more at 10 MHz.

[12] Item 12. The α-Fe-containing rare earth-iron magnetic powder according to any one of items 1 to 11, having a tan δ of 0.2 or less and μ′ of 11 or more at 50 MHz.

[13] Item 13. The α-Fe-containing rare earth-iron magnetic powder according to any one of items 1 to 12, having a tan δ of 0.3 or less and μ′ of 11 or more at 100 MHz.

[14] Item 14. A magnetic material for magnetic field amplification, comprising the α-Fe-containing rare earth-iron magnetic powder according to any one of Items 1 to 13.

[15] Item 15. The magnetic material for magnetic field amplification according to item 14, further comprising a resin.

[16] Item 16. The magnetic material for magnetic field amplification according to item 14 or 15, which is used for wireless power supply.

[17] Item 16. The magnetic material for magnetic field amplification according to item 14 or 15, for use in a transformer, inductor, or reactor for a high-frequency circuit exceeding 20 MHz.

[18] Item 14. A magnetic material for absorbing ultra-high frequencies, comprising the α-Fe-containing rare earth-iron magnetic powder according to any one of items 1 to 13.

[19] a phosphorus treatment step in which an inorganic acid is added to a slurry containing a rare earth-iron-based magnetic powder containing a rare earth R (R is at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe, water, and a phosphorus-containing substance, thereby forming a phosphorus compound coating on the magnetic powder and obtaining a rare earth-iron-based magnetic powder having a phosphorus compound coating; an oxidation step of heat-treating the rare earth-iron-based magnetic powder having the phosphorus compound coating portion in an oxygen-containing atmosphere at 350°C or higher and 600°C or lower; An annealing process in which rare earth-iron magnetic powder having an oxidized phosphorus compound coating is heat-treated at 200°C to 600°C in an atmosphere consisting of an inert gas or a reducing gas that does not contain nitrogen atoms. A method for producing an α-Fe-containing rare earth-iron magnetic powder, comprising:

[20] Item 20. The method for producing an α-Fe-containing rare earth-iron-based magnetic powder according to Item 19, wherein the inert gas is Ar gas or N2 gas. [twenty one] Item 19 or 20, the method for producing an α-Fe-containing rare earth-iron-based magnetic powder according to Item 20, wherein the reducing gas not containing nitrogen atoms is H2 gas. [twenty two] 22. The method for producing an α-Fe-containing rare earth-iron-based magnetic powder according to any one of items 19 to 21, wherein in the phosphorus treatment step, the inorganic acid is added to adjust the pH of the slurry to 1 or more and 4.5 or less. [twenty three] Item 23. The method for producing an α-Fe-containing rare earth-iron-based magnetic powder according to any one of items 19 to 22, further comprising a step of heat-treating the α-Fe-containing rare earth-iron-based magnetic powder in an oxygen-containing atmosphere at 200 ° C. or more and 600 ° C. or less after the annealing step. [twenty four] Item 16. The magnetic material for magnetic field amplification according to item 15, further comprising a magnetic metal and / or metal oxide. [twenty five] Item 25. The magnetic material for magnetic field amplification according to Item 24, wherein the metal oxide is magnetite.

Claims

1. a core region including a rare earth element R (R is at least one element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe; an α-Fe-containing region outside the core region, the α-Fe-containing region including at least one selected from the group consisting of α-Fe and an oxide, nitride, and oxynitride of a rare earth element R; The α-Fe-containing rare earth-iron magnetic powder has an iron oxide-containing region containing magnetite or maghemite outside the α-Fe-containing region.

2. When the rare earth element R contains Sm, the content of Sm is less than 50 atomic % of the total R component.

2. The α-Fe-containing rare earth-iron magnetic powder according to claim 1.

3. The core region further comprises N.

3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1.

4. The α-Fe containing region is Nanocrystals consisting of at least one selected from the group consisting of oxides, nitrides, and oxynitrides of the rare earth R; and Contains nanocrystals made of α-Fe, 3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1.

5. 3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1, further comprising a phosphorus compound coating portion between the α-Fe-containing region and the iron oxide-containing region.

6. 3. The α-Fe-containing rare earth-iron-based magnetic powder according to claim 1, wherein the thickness of the α-Fe-containing region is 0.01% or more and less than 50% of the average particle size of the α-Fe-containing rare earth-iron-based magnetic powder.

7. 3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1, wherein the thickness of the α-Fe-containing region is 1 nm or more and 80 μm or less.

8. the core region includes a rare earth-iron-nitrogen compound; 3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1, wherein in an XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity (I) of the (110) plane of α-Fe to the peak intensity (II) of the strongest line of the rare earth-iron-nitrogen compound is 0.01 or more and less than 100.

9. the core region includes a rare earth-iron-nitrogen compound; 3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1, wherein in an XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity (I) of the (511) plane of magnetite or maghemite to the peak intensity (II) of the strongest line of the rare earth-iron-nitrogen compound is 0.01 or more and less than 100.

10. the core region includes a rare earth-iron-nitrogen compound; 3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1, wherein in an XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity (I) of the (104) plane of hematite to the diffraction peak intensity (II) of the (511) plane of the magnetite or maghemite is 0 or more and less than 10.

11. 3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1, wherein tan δ at 10 MHz is 0.1 or less and μ′ is 11 or more.

12. 3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1, wherein tan δ at 50 MHz is 0.2 or less and μ′ is 11 or more.

13. 3. The α-Fe-containing rare earth-iron magnetic powder according to claim 1, wherein tan δ at 100 MHz is 0.3 or less and μ′ is 11 or more.

14. A magnetic material for magnetic field amplification, comprising the α-Fe-containing rare earth-iron magnetic powder according to claim 1 or 2.

15. The magnetic material for magnetic field amplification according to claim 14 , further comprising a resin.

16. The magnetic material for magnetic field amplification according to claim 14, which is used for wireless power supply.

17. 15. The magnetic material for magnetic field amplification according to claim 14, for use in a transformer, inductor or reactor for a high frequency circuit exceeding 20 MHz.

18. A magnetic material for absorbing ultra-high frequency waves, comprising the α-Fe-containing rare earth-iron magnetic powder according to claim 1 or 2.

19. a phosphorus treatment step in which an inorganic acid is added to a slurry containing a rare earth-iron based magnetic powder containing a rare earth R (R is at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sm) and Fe, water, and a phosphorus-containing substance, thereby forming a phosphorus compound coating on the magnetic powder, thereby obtaining a rare earth-iron based magnetic powder having a phosphorus compound coating; an oxidation step of heat-treating the rare earth-iron magnetic powder having the phosphorus compound coating portion in an oxygen-containing atmosphere at 350° C. or higher and 600° C. or lower; An annealing step in which the rare earth-iron magnetic powder having the oxidized phosphorus compound coating portion is heat-treated at 200°C or higher and 600°C or lower in an atmosphere consisting of an inert gas or a reducing gas not containing nitrogen atoms. A method for producing an α-Fe-containing rare earth-iron based magnetic powder, comprising:

20. The inert gas is Ar gas or N ２ The method for producing α-Fe-containing rare earth-iron-based magnetic powder according to claim 19, wherein the magnetic powder is a gas.

21. The reducing gas containing no nitrogen atoms is H ２ The method for producing α-Fe-containing rare earth-iron-based magnetic powder according to claim 19, wherein the magnetic powder is a gas.

22. 21. The method for producing an α-Fe-containing rare earth-iron-based magnetic powder according to claim 19, wherein in the phosphorus treatment step, the inorganic acid is added to adjust the pH of the slurry to 1 or more and 4.5 or less.

23. The method for producing an α-Fe-containing rare earth-iron-based magnetic powder according to claim 19 or 20, further comprising a step of heat-treating the α-Fe-containing rare earth-iron-based magnetic powder at 200°C or higher and 600°C or lower in an oxygen-containing atmosphere after the annealing step.

24. The magnetic material for magnetic field amplification according to claim 15, further comprising a magnetic metal and / or metal oxide.

25. 25. The magnetic material for magnetic field amplification according to claim 24, wherein the metal oxide is magnetite.

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