α-Fe PHASE-CONTAINING RARE EARTH-IRON-NITROGEN BASED MAGNETIC POWDER, MANUFACTURING METHOD OF THE SAME, AND MANUFACTURING METHOD OF α-Fe PHASE-CONTAINING RARE EARTH-IRON-NITROGEN BASED MAGNETIC POWDER

Abstract

To provide a magnetic powder excellent in a high-frequency characteristic having high magnetic permeability, low iron loss, and excellent efficiency even when a high frequency is applied, and provide a manufacturing method of the same.SOLUTION: An α-Fe phase-containing rare earth-iron-nitrogen-based magnetic powder has a core region, and an α-Fe phase-containing region present outside the core region. The core region has a latent crystal structure represented by the following formula 1 that 1: RxX(100-x-y-z)MyNz...Formula 1. In the Formula 1, R is a rare-earth element, and X includes at least Fe, M is at least one selected from a group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr, N is a nitrogen atom, and x, y, and z are 2≤x≤15, 0.5≤y≤25, and 3≤z≤50, respectively, in atom%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an α-Fe phase-containing rare earth-iron-nitrogen based magnetic powder, a method for producing the same, and a method for producing the α-Fe phase-containing rare earth-iron-nitrogen based magnetic powder. [Background technology]

[0002] In recent years, with the miniaturization and multifunctionality of devices and the increasing speed of computing processes, drive frequencies have become increasingly higher, and the 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, the market for GaN electronic devices is predicted to grow significantly 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, requiring coils with magnetic core materials capable of operating at high frequencies. However, due to the lack of magnetic core materials with excellent high-frequency characteristics, air-core coils are unavoidable. While the use of GaN can increase frequency and reduce the device size, the overall circuit size increases. One example of a conventional high-frequency magnetic material is a rare-earth-iron-nitrogen-based magnetic material in which the powder surface is coated with a ferrite-based magnetic material (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2008 / 136391 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the material disclosed in Patent Document 1 is not efficient enough to be used as a magnetic field amplification material in the above-mentioned range of 1 MHz to 1 THz, and in particular, its efficiency is insufficient when used as a highly efficient magnetic field amplification material in the range of 10 MHz to less than 1 GHz.

[0005] The present disclosure aims to provide a magnetic powder with excellent high-frequency characteristics, which has high magnetic permeability even when subjected to high frequency, low iron loss, and excellent efficiency, and a method for manufacturing the same. [Means for solving the problem]

[0006] An α-Fe phase-containing rare earth-iron-nitrogen based magnetic powder according to one embodiment of the present disclosure is an α-Fe phase-containing rare earth-iron-nitrogen based magnetic powder having a core region and an α-Fe phase-containing region located outside the core region, The core region has Formula 1: R x X (100-x-y-z) M y N z (Formula 1) (In formula 1, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; N is a nitrogen atom, x, y, and z are in atomic percent, and are 2≦x≦15, 0.5≦y≦25, and 3≦z≦50. is a rare earth-iron-nitrogen magnetic powder having a cryptocrystalline structure represented by The α-Fe phase-containing region includes an α-Fe phase and at least one selected from the group consisting of an oxide, a nitride, and an oxynitride containing at least one of R and M.

[0007] Furthermore, a method for producing an α-Fe phase-containing rare earth-iron-nitrogen-based magnetic powder according to one embodiment of the present disclosure comprises reacting a compound represented by the following formula 2: R x X(100-x-y) M y (Formula 2) (In formula 2, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; x and y are atomic percent, 2.06≦x≦30, 0.515≦y≦50. A step of heat-treating the rare earth-iron magnetic powder represented by the formula (I) in ammonia gas to obtain a rare earth-iron-nitrogen compound; heat-treating the rare earth-iron-nitrogen compound in an atmosphere containing at least one gas selected from the group consisting of an inert gas, a hydrogen gas, and a nitrogen gas; Includes:

[0008] Furthermore, a method for producing an α-Fe phase-containing rare earth-iron-nitrogen-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-nitrogen-based magnetic powder, water, and a phosphorus-containing substance to obtain a rare earth-iron-nitrogen-based magnetic powder having a phosphorus compound coating portion; an oxidation step of heat-treating the rare earth-iron-nitrogen magnetic powder having the phosphorus compound coating portion in an oxygen-containing atmosphere at 300°C or higher and 600°C or lower; Including, the rare earth-iron-nitrogen magnetic powder has a core region and an α-Fe phase-containing region located outside the core region, The core region has formula 3: R x X (100-x-y-z) M y N z (Formula 3) (In formula 3, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; N is a nitrogen atom, x, y, and z are in atomic percent, and are 2≦x≦15, 0.5≦y≦25, and 3≦z≦50. is a rare earth-iron-nitrogen magnetic powder having a cryptocrystalline structure represented by The α-Fe phase-containing region includes an α-Fe phase and at least one selected from the group consisting of an oxide, a nitride, and an oxynitride containing at least one of R and M. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a magnetic powder having excellent high-frequency characteristics, including high magnetic permeability even when subjected to high frequency, low iron loss, and excellent efficiency, as well as a method for manufacturing the same. [Brief explanation of the drawings]

[0010] [Figure 1] 1 shows XRD patterns (Co-Kα) of the magnetic powders of Example 1 and Comparative Examples 1 and 2. [Figure 2a] 1 shows a STEM-EDS image of the surface vicinity of a cross section of the magnetic powder of Example 1. [Figure 2b] 1 shows a STEM-EDS image of the vicinity of an α-Fe phase-containing region in a cross section of the magnetic powder of Example 1. [Figure 3] 1 shows a STEM-EDS line profile near the surface of a cross section of the magnetic powder of Example 1. [Figure 4a] 1 shows a TEM-ED image of an α-Fe phase-containing region of the magnetic powder of Example 1. [Figure 4b] 1 shows a TEM-ED image of the core region of the magnetic powder of Example 1. [Figure 5] 1 shows a TEM image of the core region of the magnetic powder of Example 1. [Figure 6] 1 shows XRD patterns of Examples 2 and 3 and Comparative Examples 3 and 4. [Figure 7a] 10 shows a STEM-EDS mapping image of the vicinity of the surface of a cross section of the magnetic powder of Example 3. [Figure 7b] 1 shows a STEM-EDS image of the vicinity of an α-Fe phase-containing region in a cross section of the magnetic powder of Example 3. [Figure 8] 10 shows a STEM-EDS line profile near the surface of a cross section of the magnetic powder of Example 3. [Figure 9a] 1 shows a TEM-ED image of an α-Fe phase-containing region of the magnetic powder of Example 3. [Figure 9b] 1 shows a TEM-ED image of the core region of the magnetic powder of Example 3. [Figure 10] 1 shows a TEM image of the core region of the magnetic powder of Example 3. [Figure 11] 1 shows the frequency dependence of the complex relative permeability of the magnetic materials using the magnetic powders produced in Example 1 and Comparative Examples 1 and 2. [Figure 12] 1 shows the frequency dependence of the complex relative permeability of the magnetic materials using the magnetic powders produced in Examples 2 and 3 and Comparative Examples 3 and 4. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] In this specification, "high frequency" refers to electromagnetic waves having a high frequency, and in this disclosure, unless otherwise specified, it particularly refers to electromagnetic waves of 1 MHz or more and less than 1 GHz.

[0013] 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°, and by having small tan δ and δ, or by having a phase angle θ that is large and close to 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)."

[0014] In this specification, the "magnetic field amplification" characteristic refers to a characteristic 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 of a vacuum (or atmosphere). Good or high magnetic field amplification characteristics 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 refers to a high real term of the relative magnetic permeability.

[0015] <<α-Fe phase containing rare earth-iron-nitrogen magnetic powder>> The α-Fe phase-containing rare earth-iron-nitrogen-nitrogen based magnetic powder of this embodiment is an α-Fe phase-containing rare earth-iron-nitrogen based magnetic powder having a core region and an α-Fe phase-containing region located outside the core region, The core region has Formula 1: R x X (100-x-y-z) M y N z (Formula 1) (In formula 1, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; N is a nitrogen atom, x, y, and z are in atomic percent, and are 2≦x≦15, 0.5≦y≦25, and 3≦z≦50. is a rare earth-iron-nitrogen magnetic powder having a cryptocrystalline structure represented by The α-Fe phase-containing region is characterized by including an α-Fe phase and at least one selected from the group consisting of oxides, nitrides, and oxynitrides containing at least one of R and M.

[0016] <Core Areas> The core region is a rare earth-iron-nitrogen magnetic powder having a cryptocrystalline structure, represented by the following formula 1. R x X (100-x-y-z) M y N z (Formula 1) (In formula 1, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; N is a nitrogen atom, x, y, and z are in atomic percent, and are 2≦x≦15, 0.5≦y≦25, and 3≦z≦50.

[0017] In Formula 1, R is a rare earth element. Examples of rare earth elements include Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. The core region may contain two or more of these rare earth elements. Among these, light rare earth elements are preferred from the viewpoint of relative permeability, and Sm, Ce, Nd, and Pr are preferred because of the stable supply of raw materials. However, when Nd, which is expensive as a rare earth element, is included, the Nd content of the entire R component is preferably less than 50 atomic %, more preferably 25 atomic % or less, and even more preferably 5 atomic % or less.

[0018] X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe. By containing Fe, the material tends to exhibit strong ferromagnetism at room temperature. Furthermore, X may contain Co or Ni in addition to Fe. With respect to the entire X component, Fe is preferably 50 atomic % or more, and may be 99 atomic % or more. With respect to the entire X component, the total amount of 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 high and thermal properties tend to be improved. When Ni is contained at 1 atomic % or more, the oxidation resistance tends to be high.

[0019] M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr, and by including any of these, the rare earth-iron-nitrogen magnetic powder becomes a material with magnetic anisotropy. When M is Ti, V, Mo, Nb, or W, this is preferable because the crystalline rare earth-iron magnetic powder is easily converted to a cryptocrystalline state by nitriding with ammonia gas.

[0020] One of the features of the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder of the present invention is that the crystal structure of the rare earth-iron magnetic powder, which primarily has in-plane magnetic anisotropy, is disrupted by over-nitriding, resulting in a cryptocrystalline material with medium-range order, which is the source of magnetic anisotropy. This results in both high efficiency and a large μ'. Crystalline materials with long-range order, such as tetragonal, have high magnetic anisotropy and a high resonant frequency. While these materials are suitable for use as ultrahigh-frequency absorption materials in the 1 GHz to 1 THz range, μ' in the high-frequency range, particularly in the 10 MHz to 1 GHz range, remains small because the crystal lattice limits spin motion. Conversely, amorphous (non-crystalline) materials with only short-range order have a high degree of freedom for spin motion to follow changes in the magnetic field direction of electromagnetic waves, resulting in a large μ'. However, μ'' also increases, which tends to increase tan δ (lower phase angle θ) and reduce efficiency. In this specification, a material that has only short-range order and cannot be considered an aggregate of microcrystals, for example, a material whose Scherrer diameter (described later) is approximately 0.1 nm or less, which is the lattice spacing of the 220 plane of the α-Fe structure, is considered amorphous.

[0021] In formula 1, x, y, and z are, in atomic percent, 2≦x≦15, 0.5≦y≦25, and 3≦z≦50, respectively. x is preferably 3≦x≦10. y is preferably 3≦y≦15. z is preferably 9≦z≦42, and more preferably 15≦z≦36.

[0022] Sm may account for more than 50 atomic %, 70 atomic % or more, or 90 atomic % or more of the entire R component in formula 1. When the Sm content is within these ranges, not only are there the advantages of high μ' and a low phase angle θ in the region of 10 MHz or more, but there is also excellent practicality in that the cost is low.

[0023] The rare earth-iron-nitrogen magnetic powder of the present invention has cryptocrystalline characteristics and only has medium-range order, so its XRD diffraction lines are observed as a large halo pattern. The maximum intensity position of the halo pattern is determined by the fact that the raw material of each rare earth-iron magnetic powder is Th2Zn17 type crystal (rhombohedral system), Th2Ni 17 type crystal (hexagonal system), ThMn 12 If the core region is a tetragonal crystal, it will be located near the diffraction peak position of the strongest line. The core region can be made into a homogeneous cryptocrystalline state when a rare earth-iron based magnetic powder having a homogeneous crystalline structure is nitrided. Because the crystal structure loses its long-range order, it cannot be identified even by XRD, and can only be determined to have a "cryptocrystalline" structure, which is an aggregate of very fine crystals. In this specification, this cryptocrystalline state and the aforementioned amorphous state are collectively referred to as amorphous.

[0024] The core region has a cryptocrystalline structure. A cryptocrystalline structure is an aggregate having not only short-range order but also medium-range order, and is an aggregate of nanoscale microcrystals. In the present invention, whether the core region has a cryptocrystalline structure can be evaluated by the following method (1) or (2). (1) In the diffraction pattern of the magnetic powder measured by X-ray diffraction (XRD) using a CoKα radiation source, the half-width based on the baseline is 7° or more and 13° or less at a diffraction angle 2θ. (2) (a) In an electron diffraction image of a sample surface with a thickness of 100 nm or less, using an electron beam with a beam diameter of approximately 1 to 200 nm, a ring pattern is observed in the region corresponding to a lattice spacing of 0.15 to 0.3 nm, or (b) four or more diffraction points can be identified, and a lattice image showing an orderly structure of 1 to 10 nm is observed in the transmission electron beam image, or (c) the Scherrer diameter calculated from the strongest line measured by XRD is 1.5 nm or less.

[0025] The half-width is measured at the position corresponding to the peak of the strongest line of the raw material. As mentioned above, the cryptocrystalline structure of the core region offers the advantage of both high efficiency and a large μ'. The half-width of the core region measured by X-ray diffraction (XRD) based on the baseline of the peak is preferably 7° to 13°, more preferably 8° to 12°, in terms of diffraction angle 2θ. An angle of less than 7° tends to make the magnetic powder more crystalline and μ' lower. An angle of more than 13° tends to make the magnetic powder more amorphous, resulting in a lower phase angle θ and a higher tan δ. If the peak is adjacent to the diffraction line of the α-Fe phase and cannot be separated, the half-width may be estimated slightly broader. In any case, an angle of more than 13° tends to make the magnetic powder more amorphous, resulting in a lower phase angle θ and a higher tan δ. A ring pattern observed in the electron diffraction image of the core region in the region corresponding to a lattice spacing of 0.15 nm to 0.3 nm confirms that the core region is cryptocrystalline. Alternatively, even if the Scherrer diameter calculated when the peak of the α-Fe phase can be separated from the strongest line measured by XRD is 1.5 nm or less, it is confirmed that the material is cryptocrystalline.

[0026] The core region preferably contains 3 atomic % or more of nitrogen atoms, more preferably 9 atomic % or more, and even more preferably 15 atomic % or more. When the nitrogen atom content is within these ranges, the real term of the relative magnetic permeability is high and tan δ is low, which is advantageous.

[0027] 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%.

[0028] <Method of manufacturing the core region> Examples of methods for producing the rare earth-iron-nitrogen magnetic powder that constitutes the core region will be described below, but the method is not particularly limited to these. (1) Preparation process of rare earth-iron master alloy Methods for producing master alloys of rare earth-iron magnetic powder include: (I) high-frequency melting, in which the R, X, and M metal components are melted by high frequency and cast into a mold; (II) arc melting (also known as the arc button method), in which the metal components are placed in a copper boat or other container and melted by arc discharge; (III) drop casting or suction casting, in which the arc-melted molten metal is dropped into a water-cooled mold in one go and quenched; (IV) ultra-rapid cooling, in which high-frequency melted molten metal is dropped onto a rotating copper roll to obtain a ribbon-shaped alloy; (V) gas atomization, in which high-frequency melted molten metal is atomized with gas to obtain alloy powder; and (VI) powder of the X and / or M components. Alternatively, any of the following methods may be used: (VII) a reduction-diffusion method in which XM alloy powder, oxide powder of R and / or M components, and a reducing agent are reacted at high temperature to reduce R or R and M components while diffusing R or R and M components into X component and / or XM alloy powder; (VII) a mechanical alloying method in which each metal component and / or alloy is reacted while being finely pulverized using a ball mill or the like; or (VIII) a hydrogenation decomposition desorption recombination (HDDR) method in which an alloy obtained by any of the above methods is heated in a hydrogen atmosphere to decompose into R and / or M hydrides and X component and / or M components or XM alloy, and then recombined and alloyed under high temperature and low pressure while expelling hydrogen.

[0029] When using high-frequency melting or arc melting, large impurity phases of 1 μm or larger, mainly composed of X components, tend to precipitate when the alloy solidifies from the molten state. This increases the volume fraction of components with resonant frequencies in the low-frequency range, even after the nitriding process, leading to reduced efficiency in the high-frequency range. Therefore, to eliminate these large X components and increase the amount of the rare earth-iron master alloy (main raw material phase) with a tetragonal, rhombohedral, or hexagonal (especially tetragonal) crystal structure that serves as the raw material for the rare earth-iron-nitrogen-based magnetic powder, annealing is effective in a gas containing at least one of an inert gas (e.g., argon, helium), and hydrogen gas, or in a vacuum, at a temperature range of 200°C to 1300°C, preferably 600°C to 1185°C. Alloys produced by this method have larger grain sizes and better crystallinity than alloys produced by methods such as rapid cooling. Therefore, this alloy contains a large amount of homogeneous main raw material phase, making it preferable as a master alloy for obtaining the magnetic powder of the present invention. On the other hand, master alloys obtained by the rapid cooling method or mechanical alloying method have the advantage that their fine metal structure allows for homogenization with short annealing times. The most preferable method for producing rare earth-iron alloys, taking advantage of both of these advantages, is the suction casting method. The alloy melting method is the same as arc melting, but the cooling rate is faster than the conventional arc button method, resulting in finer phase separation and generally requiring a shorter annealing time.

[0030] (2) Coarse crushing and classification process Although it is possible to directly nitride the rare earth-iron alloy ingot or R / D or HDDR alloy powder produced by the above method, if the crystal grain size is larger than 2000 μm, the nitriding time will be long, and it is more efficient to perform coarse pulverization before nitriding. Coarse pulverization to 200 μm or less is particularly preferred because it further improves the nitriding efficiency.

[0031] Coarse pulverization is carried out using a jaw crusher, hammer, stamp mill, rotor mill, pin mill, cutter mill, etc. Alternatively, alloy powder suitable for nitriding can be prepared using a pulverizer such as a ball mill or jet mill, depending on the conditions. A method of absorbing hydrogen into the master alloy and then pulverizing it with the above-mentioned pulverizer, or a method of repeatedly absorbing and releasing hydrogen to pulverize the alloy may also be used.

[0032] Furthermore, after coarse grinding, adjusting the particle size using a classifier such as a sieve, vibrating or ultrasonic classifier, air sieve, or cyclone is also effective in achieving more uniform nitriding. After coarse grinding and classification, annealing in an inert gas or hydrogen can sometimes remove structural defects. The above is the method for preparing the powder or ingot raw material of the rare earth-iron master alloy used in the manufacturing method of the core region, but the optimal conditions for nitriding, as shown below, vary depending on the crystal grain size, crushed grain size, surface condition, etc. of these raw materials.

[0033] (3) Nitriding and annealing process Nitriding is a process in which a gas containing a nitrogen source, such as ammonia gas or nitrogen gas, is brought into contact with the rare earth-iron magnetic powder or ingot with a homogeneous composition obtained in the above step (1) or steps (1) and (2), thereby introducing nitrogen into the crystal structure.

[0034] In this case, it is preferable to have hydrogen present in the nitriding atmosphere gas, as this not only increases nitriding efficiency but also allows nitriding without destroying the cryptocrystalline structure of the core region. Furthermore, to control the reaction, an inert gas such as argon, helium, or neon may also be present. The most preferable nitriding atmosphere is a mixed gas of ammonia and hydrogen, and controlling the ammonia partial pressure ratio to within the range of 0.1 to 0.7 not more than 0.7 not only increases nitriding efficiency but also allows the production of magnetic powders that satisfy the nitrogen content range of the rare earth-iron-nitrogen magnetic powder used in the present invention.

[0035] The nitriding reaction can be controlled by the gas composition, heating temperature, heat treatment time, and pressure. The heating temperature varies depending on the mother alloy composition and nitriding atmosphere, but is preferably between 100°C and 600°C. Below 100°C, the nitriding rate tends to be very slow. Above 600°C, the main raw material phase undergoes thermal decomposition, resulting in significant phase separation, resulting in the formation of a crystalline X component-based phase of 1 μm or larger, or the material becoming amorphous. To increase the nitriding efficiency and the main phase content, a more preferable temperature range is between 250°C and 500°C. The nitriding time is optional, but is selected between 1 minute and 100 hours, with longer times being generally set at lower temperatures and shorter times at higher temperatures. The nitriding temperature and time are selected taking into account industrial efficiency and cost.

[0036] Furthermore, after nitriding, annealing in an atmosphere containing at least one selected from the group consisting of inert gas, hydrogen gas, and nitrogen gas can improve magnetic properties. In particular, producing rare earth-iron-nitrogen magnetic powder in a high-nitridation region with a nitrogen content of 25 atomic % to 50 atomic % and then annealing in an atmosphere containing hydrogen gas and / or nitrogen gas is highly preferable in terms of adjusting the composition and improving the homogeneity of the nitrogen-containing magnetic powder and increasing the magnetic permeability and magnetization. Annealing in a gas flow containing nitrogen gas after the nitriding, phosphorus treatment, and oxidation processes is particularly preferable, as it can form an α-Fe phase-containing region and adjust the nitrogen content of the cryptocrystalline core region, thereby improving magnetic properties.

[0037] It is recommended that the annealing temperature be approximately the same as the nitriding temperature, but μ' and tan δ tend to improve when the temperature is 350° C. or higher and 500° C. or lower. The annealing time is preferably 1 minute or longer and 24 hours or shorter.

[0038] Nitriding and annealing equipment includes horizontal and vertical tubular furnaces, rotary reactors, and sealed reactors. While any of these devices can be used to prepare the magnetic powder of the present invention, rotary reactors are preferred for obtaining powders with a uniform nitrogen composition distribution. The gas used in the reaction can be supplied by a gas flow method, in which a gas flow of 1 atmosphere or more is fed into the reactor while maintaining a constant gas composition; a sealed gas method, in which the gas is sealed in a container at a pressure between 0.01 and 70 atmospheres; or a combination of these. Only after going through the above nitriding and annealing process can the rare earth-iron-nitrogen magnetic powder be produced.

[0039] (4) Fine grinding process The fine pulverization step is carried out for the purpose of pulverizing the rare earth-iron-nitrogen magnetic powder into an even finer powder. As the fine pulverization method, in addition to the methods mentioned in step (2) above, dry or wet fine pulverization equipment such as a rotary ball mill, a vibration ball mill, a planetary ball mill, a wet mill, a jet mill, a cutter mill, a pin mill, an automatic mortar, or a combination thereof can be used.

[0040] A preferred method for producing the rare earth-iron-nitrogen magnetic powder of the present invention involves preparing a rare earth-iron master alloy by the method exemplified in step (1) or steps (1) and (2), nitriding it by the method shown in step (3), and then finely pulverizing it by the method shown in step (4). In particular, if the raw alloy obtained in step (1) or the raw alloy obtained by pulverizing and classifying it by the method shown in step (2) is heat-treated at 600°C to 1300°C in an atmosphere containing inert gas and / or hydrogen gas, then nitrided by heat-treatment at 100 to 600°C in an atmosphere containing ammonia gas, and then annealed, a magnetic powder can be obtained with extremely little deterioration in magnetic properties due to oxidation inside the powder.

[0041] <α-Fe phase containing region> The α-Fe phase-containing region is present outside the core region and contains at least one selected from the group consisting of an α-Fe phase and an oxide, nitride, and oxynitride containing at least one of R and M. The α-Fe phase-containing region enhances the insulation between adjacent magnetic powder particles and suppresses efficiency loss due to eddy currents across grains. As a result, use of the magnetic powder of the present invention further improves tan δ and phase angle θ in the high-frequency range, resulting in a more efficient magnetic powder for magnetic field amplification. Furthermore, the α-Fe phase-containing region magnetically connects adjacent magnetic powder particles and reduces demagnetizing fields. As a result, use of the magnetic powder of the present invention tends to further improve the real term μ' of the magnetic permeability of the magnetic material for magnetic field amplification. The α-Fe phase-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.

[0042] The α-Fe phase-containing region preferably contains at least one compound selected from the group consisting of oxides, nitrides, and oxynitrides containing at least one of the R and M elements, and nanocrystals of the α-Fe phase. The α-Fe phase-containing region more preferably contains nanocrystals of oxides, nitrides, or oxynitrides containing at least one of the R and M elements. That at least one of the oxides, nitrides, or oxynitrides containing R or M, or both R and M, is a nanocrystal 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 CoKα radiation source, or by observing a ring inside the ring pattern representing the α-Fe phase in electron diffraction measured on the α-Fe phase-containing region. Oxides, nitrides, and oxynitrides containing R or M, or both R and M, for example, when R is Sm and M is Ti, are samarium oxide, titanium oxide, samarium-titanium composite oxide, samarium nitride, titanium nitride, samarium-titanium composite nitride, samarium oxynitride, titanium oxynitride, and samarium-titanium composite oxynitride, respectively. The α-Fe phase-containing region may further contain a double oxide, double nitride, or double oxynitride containing rare earth elements R, M, and iron, to the extent that magnetic coupling is not impaired. These double oxides, double nitrides, and double oxynitrides may have a perovskite structure or a spinel structure. A structure containing at least one compound selected from the group consisting of oxides, nitrides, and oxynitrides containing at least one of R and M, and nanocrystals consisting of the α-Fe phase, 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.

[0043] The "α-Fe phase" is a cubic crystal with a bcc structure, and its main component is Fe. Ferromagnetic components such as Co and Ni can be substituted for up to 50 atomic % of Co and Ni combined. M components and nitrogen can also be contained, but in order not to impair the ferromagnetic properties of the α-Fe phase, it is preferable to use amounts that do not disrupt the bcc structure. For example, when Si is included as an M component, it is preferable that it be 10 atomic % or less. When nitrogen is included, it is preferable that it be 5 atomic % or less.

[0044] The α-Fe phase-containing region is believed to contain at least one compound selected from the group consisting of oxides, nitrides, and oxynitrides containing at least one of R and M, as well as nanocrystals composed of the α-Fe phase, thereby enhancing the electrical insulation and magnetic coupling effects of the α-Fe phase-containing region. Here, "electrical insulation" refers to the presence of highly resistive α-Fe phase-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 phase-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.

[0045] The α-Fe phase-containing region contains at least one compound selected from the group consisting of oxides, nitrides, and oxynitrides containing at least one of R and M. The average particle size of the 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 1 nm or more but less than 10 nm. The average particle size of the 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 1.5 nm or more but less than 10 nm. These particle sizes can be measured by TEM (transmission electron microscope) or STEM (scanning transmission electron microscope), or by EDS (energy dispersive X-ray analysis) attached to these microscopes, of the cross section of the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder.

[0046] 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 crystals consisting of the α-Fe phase can be determined by measuring with a CuKα X-ray source at 40 kV and 20 mA, with a step width of 2θ = 0.02 between diffraction angles 10 < 2θ < 90. For example, the half-width of crystals consisting of the α-Fe phase can be determined by measuring at 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.

[0047] The atomic concentration (atomic %) of Fe in the entire α-Fe phase-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 it 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.

[0048] The atomic concentration (atomic %) of R in the entire α-Fe phase-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 phase-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 phase-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 phase-containing region is determined by averaging the atomic concentration in each region in STEM-EDS line analysis.

[0049] The average atomic concentration of oxygen (O) (atomic %) in the entire α-Fe phase-containing region is preferably higher than the average atomic concentration of oxygen (O) (atomic %) in the core region. The average atomic concentration of oxygen (O) in the α-Fe phase-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 R in the α-Fe phase-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 R in the core region. The average atomic concentration of R in the α-Fe phase-containing region may be at least 0.1 times, preferably at least 0.5 times, the average atomic concentration of 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 phase-containing rare earth-iron-nitrogen magnetic powder in the thickness direction from the core region to the outermost surface of the α-Fe phase-containing region, obtaining measured values ​​of the atomic concentration of element X at 10 or more points, and averaging these measured values.

[0050] The thickness of the α-Fe phase-containing region is preferably 0.001% or more and less than 50% of the average grain size of the core region, 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'.

[0051] The thickness of the α-Fe phase-containing region is preferably 2 nm to 80 μm, more preferably 3 nm to 20 μm, and even more preferably 5 nm to 5 μm. From the perspective of improving μ' in the high-frequency region, a thickness of 5 nm to 1 μm is even more preferable. A thickness of 2 nm or more tends to improve electrical insulation. A thickness of 10 μm or less tends to increase μ' due to the presence of the core region. The thickness of the α-Fe phase-containing region can be measured by performing compositional analysis using TEM, STEM, or SEM observation images of the cross section of the α-Fe phase-containing rare earth-iron-nitrogen-based magnetic powder, line analysis or area analysis using TEM images, secondary electron and backscattered electron images, or EDS, or point analysis with a sufficient number of measurement points, for example, point analysis at 10 or more points.

[0052] The surface coverage of the core region by the α-Fe phase-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 phase-containing region can be measured by observing the cross section of the 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 between the α-Fe phase-containing region and the core region to the entire perimeter of the observed core region. 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.

[0053] The α-Fe phase-containing region may have a structure in which nanocrystals of the ferromagnetic α-Fe phase are isolated in an oxide phase, nitride phase, or oxynitride phase containing at least one of R and M, i.e., a so-called sea (oxide phase, nitride phase, or oxynitride phase containing at least one of R and M)-island (nano α-Fe phase) structure. When the α-Fe phase-containing region has a sea (oxide phase, nitride phase, or oxynitride phase containing at least one of R and M)-island (nano α-Fe phase) structure, the metallic α-Fe phase is isolated in the "sea" matrix phase of oxide, nitride, or oxynitride containing at least one of R and M, preventing electron percolation and maintaining electrical insulation. The α-Fe phase in the α-Fe phase-containing region may also be regularly arranged. When the α-Fe phase in the α-Fe phase-containing region is regularly arranged, the α-Fe phase is composed of crystalline particles, 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 phase-containing region, and this tends to make the magnetic coupling more stable.

[0054] The α-Fe phase-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.

[0055] 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-nitrogen 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-nitrogen magnetic powders, regions containing both the α-Fe phase and oxide, nitride, or oxynitride phases containing at least one of R and M and exhibiting unidirectional lattice fringes are defined as "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-nitrogen magnetic powder (or multiple regions if the α-Fe-containing regions are thick) can be 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.

[0056] <Phosphorus compound coated part> The α-Fe phase-containing rare earth-iron-nitrogen 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 phase-containing region, i.e., on the opposite side of the core region with the α-Fe phase-containing region in between.

[0057] 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 tan 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 phase-containing rare earth-iron-nitrogen-based magnetic powder by line or area analysis using EDS in TEM, STEM, or SEM observation images, or by point analysis using a sufficient number of measurement points. When measuring by line analysis or the like, 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 phase-containing rare earth-iron-nitrogen-based magnetic powder (surface coverage rate: 100%). In this case, adjacent magnetic powder particles are considered to be completely electrically insulated. In other words, with this structure, the phosphorus compound coating portion has the effect of reducing iron loss due to eddy currents across the particles, thereby further improving the tan δ and phase angle θ in the high-frequency range and obtaining a more efficient magnetic powder for magnetic field amplification.

[0058] Examples of phosphorus compounds constituting the phosphorus compound coating include inorganic phosphoric acids such as orthophosphoric acid, pyrophosphoric acid, and polyphosphoric acid, as well as phosphates of these compounds 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). These compounds also include "phosphorus-containing amorphous compounds" and "phosphorus-containing nanocrystalline compounds" containing at least one element selected from R, X, a phosphate-forming component, and N, and P and / or a phosphorus-containing material. Among these, phosphates, "phosphorus-containing amorphous compounds," and "phosphorus-containing nanocrystalline compounds" are preferred in terms of achieving a dense surface coating on the powder composed of the core region and the α-Fe phase-containing region. The "phosphorus-containing nanocrystalline-containing 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 element selected from a phosphate of the X component and a phosphate formed by bonding a phosphate-forming component with phosphoric acid. The inclusion of a "phosphorus-containing nanocrystalline compound" further improves thermal stability, meaning that the high-frequency characteristics of the magnetic material tend not to deteriorate even after the high-temperature mixing and heat-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 fine crystals less than 1 nm are considered to be in the category of compounds with an amorphous structure that does not have a nano-sized microcrystalline 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.

[0059] The content of the phosphorus compound in the α-Fe phase-containing rare earth-iron-nitrogen 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-nitrogen 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.

[0060] The phosphorus (P) content in the α-Fe phase-containing rare earth-iron-nitrogen 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 phase-containing rare earth-iron-nitrogen 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.

[0061] The phosphorus compound preferably coats at least a portion of the surface of the powder comprising the core region and the α-Fe phase-containing region, since this prevents 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 phase-containing rare earth-iron-nitrogen 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 can therefore achieve a tan δ of 0.05 or less at 20 MHz and a high phase angle θ.

[0062] 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 phase-containing rare earth-iron-nitrogen-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.

[0063] The phosphorus compound coating portion present on the surface of the α-Fe phase-containing rare earth-iron-nitrogen-based magnetic powder may have a region (R-rich region) in which the rare earth (R) atomic concentration is higher than the R atomic concentration in the rare earth-iron-nitrogen-based magnetic powder (core region). The R atomic concentration in the R-rich region may 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 R atomic concentration in the core region. The R atomic concentration in the R-rich region may be, for example, 4 times or less of the R atomic concentration in the core region. Here, the R-rich region is a region encompassing a layer that exhibits the maximum P (phosphorus) peak in STEM-EDS line analysis of the α-Fe phase-containing rare earth-iron-nitrogen-based magnetic powder. The thickness of the R-rich region may 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 R atomic concentration 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.

[0064] The atomic concentration ratio R / X of the R component to the X component 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 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.

[0065] The α-Fe phase-containing rare earth-iron-nitrogen 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 phase-containing region described below. The high-Mo concentration layer is preferably located outside the α-Fe phase-containing region. In some cases, having a high-Mo concentration layer has the effect of increasing the strength of the coating layer and improving corrosion resistance.

[0066] When the α-Fe phase-containing rare earth-iron-nitrogen 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 phase-containing rare earth-iron-nitrogen magnetic powder, and more preferably 0.02% to 1%. The thickness of the Mo-rich layer is preferably 1 nm to 1 μm, and more preferably 2 nm to 100 nm.

[0067] The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder may further have an iron oxide layer. The iron oxide layer is primarily composed of an iron oxide phase containing an α-Fe2O3 phase. It may be a ferrite phase, a maghemite phase, or an iron oxide phase containing M, but the non-magnetic or weakly magnetic α-Fe2O3 phase is preferred because it has electrical insulation properties and improves tan δ. The iron oxide layer is preferably present outside the α-Fe phase-containing region, more preferably outside the phosphorus compound coating, and even more preferably outside the Mo-rich layer. The iron oxide layer may also contain Co or Ni. The presence of an iron oxide layer or a rare earth phosphate precipitate layer outside the phosphorus compound coating tends to provide thermodynamic stability to the α-Fe phase-containing region, improving insulation properties and tan δ.

[0068] When the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder has an iron oxide layer, the thickness of the iron oxide layer is preferably greater than 0% and less than 20% of the average particle size of the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder, and more preferably 0.001% to 5%. By making the thickness 20% or less, a decrease in μ' tends to be suppressed. Furthermore, the thickness of the iron oxide layer is preferably greater than 0 nm and less than 1 μm, and more preferably 1 nm to 100 nm. By making the thickness of the iron oxide layer 1 μm or less, a decrease in μ' tends to be suppressed.

[0069] <Particle size of magnetic powder> The average particle size of the α-Fe phase-containing rare earth-iron-nitrogen 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 and the imaginary term of the relative magnetic permeability in the ultra-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 phase-containing rare earth-iron-nitrogen magnetic powder corresponds to 50%.

[0070] As the particle size of the core region of an Fe-phase-containing rare earth-iron-nitrogen-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 of the particle size corresponding to the frequency f0 (Hz) at which the relative permeability real term begins to decrease. On the other hand, as the particle size decreases, the loading amount of magnetic powder in the compact decreases and the specific surface area increases. For example, in the case of a 10-nm-thick phosphorus compound coating, while a powder particle size of 0.1 μm reduces the relative permeability by only about 50%, a particle size of 0.05 μm reduces the relative permeability to about 6%. Therefore, the lower limit of the core region of the α-Fe-phase-containing rare earth-iron-nitrogen-based magnetic powder of the present disclosure is approximately 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.

[0071] The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder preferably has a relative permeability real term (μ') of 5 or more at 30 MHz and a tan δ of 0.2 or less at 30 MHz, and more preferably a relative permeability real term (μ') of 10 or more at 30 MHz and a tan δ of 0.1 or less at 30 MHz. A powder with a relative permeability real term of 5 or more at 30 MHz and a tan δ of 0.2 or less is preferably used for transformer cores. The relative permeability and tan δ of a magnetic material using the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder can be measured as follows. The magnetic powder and a thermosetting epoxy resin are mixed so that the magnetic powder content is 92% by mass or more, 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 7.9 mm, or an inner diameter of 10 mm and an outer diameter of 14 mm, and molded at a pressure of 0.8 GPa. It is then heat-cured in air at 180°C for 40 minutes to produce a toroidal compact. The relative permeability of the produced compact is measured using an impedance analyzer (Keysight E4991B or Agilent E4991A). Below, evaluations of μ', μ", δ, and phase angle θ at frequencies above 1 MHz and below 1 GHz can be performed by preparing similar magnetic materials for evaluation.

[0072] <<Magnetic materials for magnetic field amplification>> The magnetic material for magnetic field amplification of this embodiment is characterized by containing an α-Fe phase-containing rare earth-iron-nitrogen magnetic powder. By containing the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder, it is preferable that the magnetic material for magnetic field amplification has a high relative permeability μ' of 2 or more in the range of 1 MHz or more but less than 1 GHz, and also has excellent efficiency such that the phase angle θ is higher in the range of 1 MHz or more but less than 1 GHz.

[0073] The particle size of the α-Fe phase-containing rare earth-iron-nitrogen 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 at 1 MHz or higher, 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 contact between the powder particles, 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 phase-containing rare earth-iron-nitrogen magnetic powder or to be present between the particles, thereby preventing deterioration of the magnetic powder's inherent properties, such as relative permeability.

[0074] 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 phase-containing rare earth-iron-nitrogen-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.

[0075] More specific applications of magnetic field amplification materials include wireless power supply coils, magnetic field amplification materials for RFID (Radio Frequency Identification) tags, 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 into cylindrical or rectangular coils, or wound 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.

[0076] 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.

[0077] In the magnetic material for magnetic field amplification of this embodiment, the real term of the relative magnetic permeability at 30 MHz is preferably 10 or more. Furthermore, tan δ (μ" / μ') and phase angle θ at 30 MHz are preferably 0.19 or less and 79° or more, more preferably 0.12 or less and 83° or more, and even more preferably 0.09 or less and 85° or more. Furthermore, tan δ and phase angle θ at 30 MHz may be 0.03 or less and 88° or more. If the real term of the relative magnetic permeability at 30 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 (for example, 10 MHz to 40 MHz). If tan δ (μ" / μ') and phase angle θ are 79° or more, heat generation can be reduced when the material is incorporated into an element or system, and the temperature of components can be lowered, which tends to improve stability. Here, the complex relative permeability tan δ and the phase angle θ can be measured by measuring the impedance of a toroidal sample using an impedance analyzer, a (vector) network analyzer, or a BH analyzer and converting the results into complex relative permeability tan δ and the phase angle θ, or by using the S-parameter method depending on the frequency range (for example, when measuring using a network analyzer at 500 MHz or higher).

[0078] 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.

[0079] 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.

[0080] 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 perforated 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.

[0081] The resin compound for bonded magnetic materials can be obtained, for example, by using a kneader to mix and / or knead an α-Fe phase-containing rare earth-iron-nitrogen magnetic powder with a resin at 180° C. to 300° C. For example, the α-Fe phase-containing rare earth-iron-nitrogen 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.

[0082] 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.

[0083] <<Method for manufacturing α-Fe phase-containing rare earth-iron-nitrogen magnetic powder>> The method for producing the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder of this embodiment is a method for producing a rare earth-iron-nitrogen magnetic powder by reacting a compound of the formula 2 below: R x X (100-x-y) M y (Formula 2) The method includes the steps of: heat-treating a rare earth-iron-based magnetic powder represented by the formula (2), where R is a rare earth element; X is at least one element selected from the group consisting of Fe, Co, and Ni, including at least Fe; M is at least one element selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; and x and y are, in atomic percent, 2.06≦x≦30 and 0.515≦y≦50, respectively, in ammonia gas to obtain a rare earth-iron-nitrogen compound; and heat-treating the rare earth-iron-nitrogen compound in an atmosphere containing at least one element selected from the group consisting of inert gas, hydrogen gas, and nitrogen gas. In this embodiment, the rare earth-iron-based magnetic powder is heat-treated in ammonia gas and then in an inert atmosphere, thereby forming an α-Fe phase-containing region on the surface of the magnetic powder. In formula 2, R, X, and M are as defined for formula 1. In formula 2, x is 2.06≦x≦30 in atomic %, preferably 3.3≦x≦17.2, and more preferably 3.5≦x≦15.6. In formula 2, y is 0.515≦y≦50 in atomic %, preferably 3.3≦y≦25.9, and more preferably 3.5≦y≦23.4.

[0084] [Process of heat treating rare earth-iron magnetic powder in ammonia gas] The rare earth-iron magnetic powder to be subjected to heat treatment in ammonia gas in this process can be, for example, that which has undergone step (1) the preparation of a rare earth-iron master alloy and step (2) the coarse crushing and classification process described above as the method for manufacturing the core region.

[0085] The average particle size of the rare earth-iron magnetic powder is preferably 0.2 μm to 200 μm, more preferably 1 μm to 100 μm, and even more preferably 2 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 is 50%.

[0086] In this process, the heat treatment temperature is preferably 100°C or higher and 600°C or lower, and more preferably 300°C or higher and 450°C or lower. Below 100°C, the nitriding rate tends to be very slow, while above 600°C, the main raw material phase tends to decompose into rare earth nitrides, iron nitrides, and nitrides of the M component. The heat treatment time is preferably 1 minute or longer, more preferably 0.1 hours or longer, even more preferably 1 hour or longer, and particularly preferably 2 hours or longer. The heat treatment time is preferably 100 hours or shorter, more preferably 24 hours or shorter, and even more preferably 10 hours or shorter. The heat treatment time tends to be longer when the heat treatment temperature is low, and can be adjusted appropriately depending on the desired properties of the magnetic powder.

[0087] Heat-treating rare earth-iron-nitrogen magnetic powder in ammonia gas can nitride the powder to produce a rare earth-iron-nitrogen compound. The gas used for heat treatment may contain H2 gas, Ar gas, or other gases in addition to ammonia. The inclusion of these gases improves nitriding efficiency and facilitates reaction control. When gases other than ammonia gas are included, the mole fraction of ammonia gas is preferably 10% or greater, more preferably 30% or greater. The nitriding conditions used in step (3) of the nitriding and annealing process described above for the core region production method may also be used as processing conditions. The rare earth-iron-nitrogen compound obtained in this process contains cryptocrystalline phases. The structure and evaluation of the cryptocrystalline phases are as described above for the core region.

[0088] [Process for heat treating rare earth-iron-nitrogen compound in an inert atmosphere] Following the heat treatment in ammonia gas, the rare earth-iron-nitrogen compound is heat-treated in an atmosphere containing at least one gas selected from the group consisting of inert gas, hydrogen gas, and nitrogen gas. In this process, an α-Fe phase-containing region is formed on the surface of the magnetic powder. Gases contained in the inert atmosphere include argon, helium, and neon. The heat treatment temperature is preferably 400°C to 600°C, and more preferably 450°C to 550°C. Temperatures below 400°C tend to result in insufficient α-Fe phase-containing regions on the surface of the magnetic powder, while temperatures above 600°C tend to decompose the main raw material phase into rare earth nitride, iron nitride, and nitrides of the M component. The heat treatment time is preferably 0.1 hours or more, more preferably 1 hour or more, and even more preferably 2 hours or more. The heat treatment time is preferably 100 hours or less, more preferably 30 hours or less, and even more preferably 20 hours or less. The heat treatment time tends to be longer when the heat treatment temperature is low, but can be adjusted appropriately depending on the desired magnetic powder properties. As the treatment conditions, the annealing conditions in the step (3) nitriding and annealing step described above in the method for producing the core region may be adopted.

[0089] <<Method for manufacturing rare earth-iron-nitrogen magnetic powder containing phosphorus-coated α-Fe phase>> The method for producing the phosphorus-coated α-Fe phase-containing rare earth-iron-nitrogen-based magnetic powder of this embodiment includes a phosphorus treatment step of adding an inorganic acid to a slurry containing a rare earth-iron-nitrogen-based magnetic powder, water, and a phosphorus-containing substance to obtain a rare earth-iron-nitrogen-based magnetic powder having a phosphorus compound coating portion, and an oxidation step of heat-treating the rare earth-iron-nitrogen-based magnetic powder having the phosphorus compound coating portion at 300° C. or more and 600° C. or less in an oxygen-containing atmosphere, wherein the rare earth-iron-nitrogen-based magnetic powder has a core region and an α-Fe phase-containing region present outside the core region, and the core region satisfies the following formula 3: R x X (100-x-y-z) M y N z (Formula 3) (in Formula 3, R is a rare earth element; X is at least one element selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one element selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; N is a nitrogen atom; and x, y, and z are, in atomic percent, 2≦x≦15, 0.5≦y≦25, and 3≦z≦50, respectively), characterized in that the α-Fe phase-containing region contains at least one element selected from the group consisting of an α-Fe phase and an oxide, nitride, and oxynitride containing at least either R or M. In Formula 3, R, X, M, x, y, and z are as defined for Formula 1, respectively.

[0090] [Phosphorus treatment process] In the phosphorus treatment step, an inorganic acid is added to a slurry containing a rare earth-iron-nitrogen-based magnetic powder, water, and a phosphorus-containing substance to obtain a rare earth-iron-nitrogen-based magnetic powder having a phosphorus compound coating. The rare earth-iron-nitrogen-based magnetic powder having a phosphorus compound coating is formed by the precipitation of a phosphorus compound (e.g., iron phosphate, samarium phosphate, cerium phosphate, etc.) through a reaction between a metal component (e.g., X or a rare earth element) contained in the rare earth-iron-nitrogen-based magnetic powder and a phosphorus component (e.g., phosphoric acid) contained in the phosphorus-containing substance. Furthermore, it is preferable that the phosphorus compound precipitates on the surface of the rare earth-iron-nitrogen-based magnetic powder, thereby coating at least a portion of the surface of the rare earth-iron-nitrogen-based magnetic powder with the phosphorus compound (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 portion").

[0091] In the phosphorus treatment process, by adjusting the pH of the slurry by adding an inorganic acid, the amount of phosphorus compound precipitated can be increased compared to when no inorganic acid is added. This results in a magnetic powder with a thick coating (also called film thickness), which improves tan δ and phase angle θ and improves magnetic field amplification characteristics. Furthermore, 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, resulting in a magnetic powder with a dense phosphorus compound coating, which tends to provide excellent efficiency in the high frequency range.

[0092] The method for preparing a slurry containing a rare earth-iron-nitrogen 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-nitrogen 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-nitrogen 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.

[0093] 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.

[0094] 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 phosphate-based compounds 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. 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, Ca, Pb, Zn, Fe, Y, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Lu, Sm, ammonium, etc. are preferred.

[0095] 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.

[0096] In the phosphorus treatment process, the slurry is acidified by adding an inorganic acid. The pH is preferably adjusted to 1 to 4.5, more preferably 1.6 to 3.9, and even more preferably 2 to 3. If the pH is less than 1, the rare earth-iron-nitrogen 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. If the pH is greater than 4.5, the amount of precipitated 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 be used in combination depending on the purpose. Examples of organic acids include acetic acid, formic acid, and tartaric acid.

[0097] 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.

[0098] 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-nitrogen 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.

[0099] The pH of the slurry containing the rare earth-iron-nitrogen 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.

[0100] [Oxidation process after phosphorus treatment] In this process, the magnetic powder obtained in the phosphorus treatment process is oxidized by heat treatment at 300°C to 600°C in an oxygen-containing atmosphere. The oxidation process is thought to oxidize the surface of the rare earth-iron-nitrogen magnetic powder from the interface between the phosphorus compound coating and the rare earth-iron-nitrogen magnetic powder, forming an α-Fe phase-containing region disproportionated into an α-Fe phase and at least one phase selected from the group consisting of oxides, nitrides, and oxynitrides containing R or M, or both R and M. As a result, a magnetic material for magnetic field amplification with improved tangent δ and phase angle θ in the high-frequency range can be obtained.

[0101] During this process, an iron oxide layer may be deposited on the surface of the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder from the phosphorus compound coating. This phenomenon occurs when the phosphorus compound coating transitions from a eutectic or mixed crystal of iron phosphate and / or M phosphate and rare earth phosphate to a rare earth phosphate single phase during the "oxidation process after phosphorus treatment," resulting in the release of excess iron components from the first coating. This iron oxide layer may be one or more of hematite, magnetite, ferrite, and wüstite, but is often hematite. The iron oxide layer may be either bound or free on the surface of the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder. For applications requiring higher efficiency, it is preferable to keep this iron oxide phase bound, while for applications requiring a higher μ', it is better to free it. Methods for freeing the iron oxide layer include mechanically knocking it off by tumbling or dissolving only the iron oxide layer by reaction with acid. The hematite, magnetite, ferrite, and wustite layers may contain at least one of Ni, Co, and M component elements.

[0102] 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.

[0103] 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 550°C or lower, more preferably 330°C or higher and 500°C or lower, and even more preferably 350°C or higher and 480°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.

[0104] The thermal decomposition temperature of rare earth-iron-nitrogen magnetic powder in the core region is known to be approximately 550 to 650°C. It is also known that in oxygen-containing atmospheres, oxidation degradation occurs above 200°C. It was previously unknown to use magnetic powder that has been heated to a temperature close to its thermal decomposition temperature in an oxygen-containing atmosphere as an excellent α-Fe phase-containing rare earth-iron-nitrogen magnetic material. It is believed that by undergoing the phosphorus treatment and oxidation processes, excessive thermal decomposition of the core region can be avoided, while the α-Fe phase is gradually separated and dispersed from the matrix at the nano-level through a disproportionation reaction starting from the surface of the rare earth-iron-nitrogen magnetic powder beneath the phosphorus compound coating.

[0105] [Silica treatment process] The magnetic powder that has undergone the phosphorus treatment and oxidation processes 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.

[0106] [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.

[0107] 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 phase-containing rare earth-iron-nitrogen magnetic powder, improved electrical insulation between the powders, and potentially superior efficiency at high frequencies.

[0108] After the phosphorus treatment step, oxidation step, silica treatment step, or silane coupling treatment step, the magnetic powder can be filtered, dehydrated, and dried by conventional methods.

[0109] The real term of the relative magnetic permeability of phosphorus-coated α-Fe phase-containing rare earth-iron-nitrogen magnetic powder can be improved by homogenizing the particle size distribution. The particle size distribution can be homogenized by a typical dry classification method or wet classification method. The particle size distribution can be homogenized at any time: before the phosphoric acid treatment, after the phosphoric acid treatment step, after the oxidation step, after the silica treatment step, or after the silane coupling treatment step. [Example]

[0110] 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.

[0111] (1) The evaluation methods used in the examples are as follows. (1-1) Element content The concentrations of P and Mo in the magnetic powder were measured using ICP atomic emission spectroscopy (ICP-AES, Hitachi High-Tech Science SPS3500). The concentration of N in the magnetic powder was measured using inert gas fusion (Horiba EMGA-820).

[0112] (1-2) XRD, α-Fe phase peak intensity ratio, and half-width The XRD pattern of the magnetic powder was measured using a powder X-ray crystal diffractometer (Rigaku SmartLab, X-ray wavelength: CoKα) under the following conditions: acceleration voltage 40 kV, tube current 135 mA, diffraction angle 20°<2θ<110°, step width 2θ=0.01°, scan rate 5° / min.

[0113] (1-3) Average particle size The average particle size of the magnetic powder was measured using a laser diffraction particle size distribution analyzer (HELOS&RODOS manufactured by Nippon Laser Co., Ltd.).

[0114] (1-4) Complex relative permeability measurement (1MHz~1GHz) The magnetic powder and epoxy resin, a thermosetting resin, were mixed and kneaded to produce a resin compound, with the magnetic powder content being 92% or 97.5% by mass. This resin compound was placed in a mold with an inner diameter of 3.1 mm and an outer diameter of 7.9 mm, or a mold with an inner diameter of 10 mm and an outer diameter of 14 mm, and molded at a pressure of 0.8 GPa. The toroidal compact was then thermally cured in air at 180°C for 40 minutes to produce a toroidal compact. The complex relative permeability of this sample was evaluated in the frequency range of 1 MHz to 1 GHz using an impedance analyzer (Keysight E4991B, Agilent E4991A) based on the inductance value measured using a single-turn inductor test fixture.

[0115] (1-5) 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 thin-sectioned using a focused ion beam (FIB). The obtained samples were measured using a STEM (FEI, model Talos F200X, accelerating voltage 200 kV or JEOL, model JEM-F200, accelerating voltage 200 kV) and a STEM-EDS system (FEI, model SuperX, detector: Bruker SDD detector, or JEOL, model SD100HR, dry SD detector) attached to the STEM. Line analysis was performed from the exterior to the interior of the magnetic powder using the step width described below to observe the continuous change in atomic concentration of each constituent element. During this analysis, there was a risk that high levels of carbon (C) from the resin used to prepare the cross-sectional sample might be detected at some measurement locations, so the atomic concentration was calculated as the sum of the elements excluding C. The crystallinity and orientation of the α-Fe phase-containing regions of the magnetic powder were evaluated using TEM-ED.

[0116] (2) SmFeTiN magnetic powder [Example 1] The ingots produced by the suction casting method were annealed at 1000°C for 2 hours in an Ar atmosphere to produce Sm as a raw material for rare earth-iron-nitrogen magnetic powder. 8.0 Fe 84.4 Ti7.6 A raw material alloy having the following composition was prepared. 12 The alloy had a high Sm content and low Fe and Ti content compared to the Sm:Fe:Ti = 1:11:1 type crystal structure. After pulverizing this raw alloy with a cutter mill in an argon atmosphere, it was classified to allow for the introduction of a large amount of nitrogen by heat treatment. 8.0 Fe 84.4 Ti 7.6 A raw alloy powder was obtained.

[0117] 6.0 g of this raw alloy powder was placed in a horizontal tubular furnace, heated to 390°C at a rate of 7.4°C / min in ammonia gas and hydrogen gas flows of 1.5 L / min, and then heat-treated for 30 minutes (nitriding step). 5.7 Fe 60.1 Ti 5.4 N 28.8 A magnetic powder having the following composition was prepared.

[0118] This Sm 5.7 Fe 60.1 Ti 5.4 N 28.8Magnetic powder with the above composition was subjected to phosphate treatment as follows. 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 with pure water and dilute hydrochloric acid to a PO concentration of 20% by mass. The magnetic powder was stirred for 1 minute in dilute hydrochloric acid with a pH of 1 or less to remove surface oxide films and contaminants. After this, draining and adding water repeatedly until the conductivity of the supernatant liquid reached 100 μS / cm or less, yielding a slurry containing 10% by mass of magnetic powder. While stirring the resulting slurry, 100 g of the prepared phosphate treatment solution was poured into a treatment tank. The pH of the phosphate treatment reaction slurry was maintained at 2.5±0.3 for 40 minutes by periodically adding 6% by mass hydrochloric acid. The resulting slurry was then suction filtered, dehydrated, and vacuum dried to obtain magnetic powder coated with a phosphorus compound. The magnetic powder having this phosphorus compound coating was gradually heated from room temperature in an air atmosphere and heat-treated at 475°C for 4 hours to obtain an oxidized phosphorus-coated α-Fe phase-containing rare earth-iron-nitrogen magnetic powder. The D50 of the obtained magnetic powder was 12 μm.

[0119] When this magnetic powder was analyzed by XRD using a CoKα radiation source, the half-width of the strongest peak, which is the core region of the cryptocrystalline phase relative to the baseline in the diffraction pattern, was 2θ = 10.3°. Furthermore, in an electron diffraction image obtained from a 100 nm beam diameter area on the surface of a sample less than 100 nm thick, a ring pattern was observed within a radius of 0.20 to 0.27 nm from the center, with a range of 0.15 to 0.3 nm. Four or more diffraction spots were distinguishable, and a lattice image showing an ordered structure of 1 to 5 nm was observed in the transmission electron image. The Scherrer diameter calculated from the strongest peak, which is the core region of the cryptocrystalline phase, was 1 nm.

[0120] [Comparative Example 1] Sm as a raw material for rare earth-iron alloys 6.9 Fe 86.4 Ti 6.7 The raw alloy of the composition was prepared by suction casting. This raw alloy was further crushed in a cutter mill in an argon atmosphere, and then classified to obtain Sm particles with a particle size of approximately 25 μm or less. 6.9 Fe86.4 Ti 6.7 A raw alloy powder was obtained. 3.1 g of this raw alloy powder was placed in a horizontal tubular furnace, heated to 450°C at a rate of 10°C / min in a nitrogen gas flow rate of 3 L / min, and heat-treated for 20 hours. After that, it was rapidly cooled to room temperature. 5.4 Fe 67.3 Ti 5.2 N 22.1 The magnetic powder thus obtained had a D50 of 20 μm. The thickness of the magnetic powder measured by XRD using a CoKα radiation source was 1 μm. 12 The half-width of the strongest line due to the structure was 2θ=0.4°, and the Scherrer diameter was 20 nm.

[0121] Comparative Example 2 Sm in Comparative Example 1 5.4 Fe 67.3 Ti 5.2 N 22.1 A rare earth-iron-nitrogen-based magnetic powder coated with a phosphorus compound of Comparative Example 2 was obtained by oxidation treatment in the same manner as in Example 1, except that a magnetic powder of the composition was used and the oxidation treatment temperature of the magnetic powder having a phosphorus compound coating portion was changed to 450°C. The D50 of the obtained magnetic powder was 19.8 μm ... 12 The half-width of the strongest line due to the structure was 2θ=0.5°, and the Scherrer diameter was 20 nm.

[0122] (3)CeFeTiN magnetic powder [Example 2] The ingots produced by the suction casting method were annealed in an Ar atmosphere at 1000°C for 2 hours to produce Ce as a raw material for rare earth-iron magnetic powder. 7.9 Fe 84.4 Ti 7.7 This raw alloy was further pulverized in a cutter mill in an argon atmosphere, and then classified to obtain Ce alloys with a particle size of approximately 25 μm or less. 7.1 Fe 85.1 Ti 7.8The raw alloy powder was obtained. This raw alloy powder was placed in a horizontal tubular furnace, heated to 390°C at a rate of 7.4°C / min in ammonia gas and hydrogen gas flows of 1.5 L / min and 3 L / min, and then heat-treated for 30 minutes (nitriding step). Then, it was heat-treated at 500°C for 2 hours in a nitrogen atmosphere to obtain Ce. 5.9 Fe 62.4 Ti 5.7 N 26.0 An α-Fe phase-containing rare earth-iron-nitrogen magnetic powder was prepared with the following composition: The obtained magnetic powder had a D50 of 12 μm.

[0123] The half-width of the strongest line originating from the cryptocrystalline phase, which is the core region of the diffraction pattern of the magnetic powder measured by XRD using a CoKα radiation source, was 2θ = 11.9°, based on the baseline. The Scherrer diameter calculated from the strongest line originating from the cryptocrystalline phase, which is the core region of the XRD, was 0.9 nm.

[0124] [Example 3] The ingots produced by the suction casting method were annealed at 1000°C for 2 hours in an Ar gas atmosphere to produce Ce as a raw material for rare earth-iron-nitrogen magnetic powder. 7.1 Fe 85.1 Ti 7.8 A raw material alloy having the following composition was prepared. 12 CeFe with a crystal structure of type 11 Compared to Ti1, it had a composition with less Ce and more Fe and Ti.

[0125] This raw alloy is further crushed in a cutter mill in an argon atmosphere, and then classified to obtain Ce particles with a particle size of approximately 25 μm or less. 7.1 Fe 85.1 Ti 7.8 A raw alloy powder was obtained. 11.6 g of this raw alloy powder was placed in a horizontal tubular furnace, heated to 390°C at a rate of 7.4°C / min in ammonia gas at a flow rate of 1.5 L / min and hydrogen gas at a flow rate of 3 L / min, and heat-treated for 60 minutes (nitriding step). After this, it was rapidly cooled to room temperature and the Ce 4.9 Fe 59.2 Ti 5.4 N 30.5 A magnetic powder having the following composition was prepared.

[0126] Except for using this powder and changing the oxidation treatment temperature of the magnetic powder having a phosphorus compound coating portion to 350° C., an oxidized phosphorus compound-coated α-Fe phase-containing rare earth-iron-nitrogen-based magnetic powder was obtained in the same manner as in Example 1. The D50 of the obtained magnetic powder was 12 μm.

[0127] When magnetic powder was analyzed by XRD using a CoKα radiation source, the half-width of the strongest peak originating from the cryptocrystalline phase, which is the core region of the diffraction pattern based on the baseline, was 2θ = 11.0°. Furthermore, in an electron diffraction image obtained from a beam diameter of 80 nm on the surface of a sample less than 100 nm thick, a ring pattern was observed within a radius of 0.18 to 0.27 nm from the center, which was found to be in the range of 0.15 to 0.3 nm. A lattice image indicating an ordered structure of 1 to 2 nm was observed in the transmission electron image. The Scherrer diameter calculated from the strongest peak originating from the cryptocrystalline phase, which is the core region of the XRD, was 1 nm.

[0128] Comparative Example 3 The ingots produced by the suction casting method were annealed at 1000°C for 2 hours to obtain Ce as a raw material for rare earth-iron-nitrogen magnetic powder. 7.7 Fe 84.6 Ti 7.7 A raw material alloy having the following composition was prepared.

[0129] This raw alloy is further crushed in a cutter mill in an argon atmosphere, and then classified to obtain Ce particles with a particle size of approximately 100 μm or less. 7.7 Fe 84.6 Ti 7.7 A raw alloy powder was obtained. 4.5 g of this raw alloy powder was placed in a horizontal tubular furnace, heated to 450°C at a rate of 10°C / min in a nitrogen gas flow rate of 3 L / min, and heat-treated for 20 hours (nitriding step). After that, it was rapidly cooled to room temperature, and Ce was removed. 6.0 Fe 66.0 Ti 6.0 N 22.0 The magnetic powder was prepared with the following composition. The D50 of the obtained magnetic powder was 43.6 μm. The thickness of the ThMn12 The half-width of the strongest line due to the structure was 2θ=0.6°, and the Scherrer diameter was 20 nm.

[0130] Comparative Example 4 Ce in Comparative Example 3 6.0 Fe 66.0 Ti 6.0 N 22.0 An oxidized phosphorus-coated rare earth-iron-nitrogen magnetic powder was obtained in the same manner as in Example 1, except that a magnetic powder of the following composition was used and the oxidation temperature of the R-Fe-Mn anisotropic magnetic powder having a phosphorus compound coating was changed to 440°C. The D50 of the obtained magnetic powder was 43.6 μm. This magnetic powder was measured by XRD using a CoKα radiation source, and the ThMn 12 The half-width of the strongest line due to the structure was 2θ=0.3°, and the Scherrer diameter was 30 nm.

[0131] (4) Microstructure of SmFeTiN magnetic powder Figure 1 shows the XRD patterns of Example 1 and Comparative Examples 1 and 2, Figure 2a shows a STEM-EDS mapping image near the surface of Example 1, Figure 2b shows a STEM-EDS mapping image near the α-Fe phase-containing region of Example 1, Figure 3 shows a STEM-EDS line profile measured with a step width of 0.717 nm near the surface of Example 1, and Figure 4 shows TEM-ED images of the α-Fe phase-containing region and core region of Example 1. Figure 5 shows a TEM image of the core region of Example 1.

[0132] In Example 1, a halo pattern (half-width at 2θ = 10.3°) and an α-Fe2O3 peak (half-width at 2θ = 0.2°) due to the cryptocrystalline structure were present. The peak could not be separated from the α-Fe phase-containing region. In the TEM-EDS image, a ring pattern and four diffraction spots were observed in the region showing a diffraction pattern of 0.20 to 0.27 nm, ranging from 0.15 to 0.3 nm. The TEM image also showed a region where lattice patterns of approximately 1 to 5 nm were observed, which, together with the Scherrer diameter (1 nm), supports the idea that the core region is cryptocrystalline. The STEM-EDS mapping image revealed an α-Fe phase-containing region approximately 150 nm thick around the periphery of the core region, and a fine α-Fe phase and samarium oxide, samarium titanium composite oxide, samarium oxynitride, samarium titanium composite oxynitride, samarium nitride, or samarium titanium composite nitride phases of approximately 4 nm were observed (see Figure 2b). TEM-ED images of the α-Fe phase-containing region revealed thin spots and ring patterns at positions roughly corresponding to the (110) bond length of the α-Fe phase with a bcc structure. Furthermore, an inner ring pattern was observed within the longer bond lengths (0.30–0.35 nm) outside the 0.15–0.3 nm range, which is presumed to represent samarium oxide, samarium titanium composite oxide, samarium oxynitride, samarium titanium composite oxynitride, samarium nitride, or samarium titanium composite nitride phases. Mapping and line profiles confirmed the presence of an Fe-O-rich layer and an Sm-Ti-P-rich layer from the periphery of the coating. The Fe-O-rich layer was presumed to be the hematite layer identified by XRD. ICP-MS revealed P and Mo concentrations of 2600 ppm and 4700 ppm, respectively, presumably resulting from phosphorus treatment. Measurement by inert gas fusion revealed a N concentration of 8.2 wt%.

[0133] In Comparative Example 1, XRD showed that ThMn 12 SmFe with structure 11Peaks attributed to TiN and the α-Fe phase were present. The peak half-widths of the strongest lines were 2θ = 0.4° and 0.3°, respectively, and the Scherrer diameter was 20 nm or more, indicating crystalline. SEM observation of the particle cross section revealed that this α-Fe phase peak was due to an internal impurity phase exceeding 1 μm in size. ICP-MS showed that P and Mo were below the detection limit (P: <100 ppm, Mo: <30 ppm). Measurement by inert gas fusion method revealed that the N concentration was 6.0 wt%.

[0134] In Comparative Example 2, XRD showed that ThMn 12 SmFe with structure 11 Peaks were present for TiN, hematite, and the α-Fe phase. The half-widths of the respective strongest lines were 2θ = 0.5°, 0.6°, and 1.2°. The SmFeTiN phase was crystalline with a Scherrer diameter of 20 nm or more. An α-Fe phase-containing region was present, with an α-Fe phase having a Scherrer diameter of approximately 8 nm. ICP-MS revealed that the sample contained 560 ppm and 2700 ppm of P and Mo, respectively, which were presumed to be due to phosphorus treatment. Measurement by inert gas fusion revealed that the N concentration was 4.3 wt%.

[0135] (5) Microstructure of CeFeTiN magnetic powder Figure 6 shows the XRD patterns of Examples 2 and 3 and Comparative Examples 3 and 4, Figure 7a shows a STEM-EDS mapping image near the surface of Example 3, Figure 7b shows a STEM-EDS mapping image near the α-Fe phase-containing region of Example 3, Figure 8 shows a STEM-EDS line profile measured with a step width of 0.478 nm for Example 3, and Figure 9 shows TEM-EDS images of the α-Fe phase-containing region and core region of Example 3. Figure 10 shows a TEM image of the core region of Example 3.

[0136] In Example 2, the XRD pattern showed a broad peak pattern due to the ThMn12 structure, indicating cryptocrystalline in the core region. The half-width of the strongest line was 2θ = 12°, and the Scherrer diameter was 0.9 nm. It was not possible to separate the peak from the α-Fe phase-containing region. TEM observation confirmed the presence of the α-Fe-containing region.

[0137] In Example 3, a halo pattern (half-width at 2θ = 11.0°) due to the cryptocrystalline structure of the core region and a peak (half-width at 2θ = 1.0°) due to the iron oxide layer, α-Fe2O3, were present. The peak could not be separated from the α-Fe phase-containing region. In the TEM-EDS image, a ring pattern was observed in the region showing a peak size of 0.18 to 0.27 nm, ranging from 0.15 to 0.3 nm. The TEM image also showed a region where a lattice pattern of approximately 1 to 2 nm was observed, which, together with the Scherrer diameter (1 nm), supports the idea that the core region is cryptocrystalline. In the STEM-EDS mapping image, an α-Fe phase-containing region approximately 5 nm thick was present around the periphery of the core region, and fine α-Fe phases approximately 2 nm thick, as well as cerium oxide, cerium titanium composite oxide, cerium oxynitride, cerium titanium composite oxynitride, cerium nitride, or cerium titanium nitride phases, were observed (see Figure 7b). TEM-ED images of the α-Fe phase-containing region revealed thin spots and ring patterns at positions roughly corresponding to the (110) bond length of the α-Fe phase with a bcc structure. Furthermore, within these, at positions with longer bond lengths (0.26–0.38 nm), a ring pattern was observed extending beyond the 0.15–0.3 nm range, which is presumed to be cerium oxide, cerium titanium composite oxide, cerium oxynitride, cerium titanium composite oxynitride, cerium nitride, or cerium titanium nitride phase. Mapping and line profiles confirmed, from the periphery, a needle-shaped cerium phosphate precipitate layer, an Fe-O-rich layer, and a Ce-Ti-P-rich layer. The Fe-O-rich layer was presumed to be the hematite layer identified by XRD. ICP-MS revealed P and Mo concentrations of 620 ppm and 1700 ppm, respectively, presumably resulting from phosphorus treatment. Measurement by inert gas fusion revealed a nitrogen concentration of 9.3 wt%.

[0138] In Comparative Example 3, XRD showed that ThMn 12 CeFe with structure 11Peaks attributed to TiN and the α-Fe phase were present. The peak half-widths of the strongest lines were 2θ = 0.6° and 0.2°, respectively, and the Scherrer diameter was 20 nm or more, indicating crystalline. SEM observation of the particle cross section revealed that this α-Fe phase peak was due to an internal impurity phase exceeding 1 μm in size. ICP-MS showed that P and Mo were below the detection limit (P: <100 ppm, Mo: <30 ppm). Measurement by inert gas fusion method revealed that the N concentration was 6.0 wt%.

[0139] In Comparative Example 4, XRD showed that ThMn 12 CeFe with structure 11 Peaks were present for TiN, hematite, and the α-Fe phase. The half-widths of the respective strongest lines were 2θ = 0.3°, 0.3°, and 2.6°. The CeFeTiN phase was crystalline with a Scherrer diameter of 20 nm or more. An α-Fe phase-containing region was present, with an α-Fe phase having a Scherrer diameter of approximately 4 nm. ICP-MS revealed that the sample contained 1100 ppm and 2400 ppm of P and Mo, respectively, which were presumed to be due to phosphorus treatment. Measurement by inert gas fusion revealed that the N concentration was 6.0 wt%.

[0140] (6) Complex relative permeability of compacts of SmFeTiN magnetic powder Using the magnetic powders of Comparative Examples 1 and 2 and Example 1, samples for measuring complex relative magnetic permeability at 1 MHz to 1 GHz were prepared by the method described above (toroidal compacts (resin added amount 2.5 mass%) with densities of 6.02 (Comparative Example 1), 5.57 (Comparative Example 2), and 5.15 (Example 1). The frequency dependence of complex relative magnetic permeability at 1 MHz to 100 MHz was measured using the method described above, and the results are shown in FIG. 11, and the evaluation results of the high-frequency characteristics are shown in Tables 1 and 2.

[0141] [Table 1] [Table 2]

[0142] In Comparative Example 1, tan δ at 30 MHz was 0.1 or more, and in Comparative Example 2, tan δ at 30 MHz was less than 0.1, but μ' was 3.7, which was very small. In contrast, in Example 1, tan δ at 30 MHz was less than 0.1, and μ' was 10 or more. The magnetic powder of Example 1 has an α-Fe phase-containing region and a cryptocrystalline structure in the core region, so μ' was higher than in Comparative Examples 1 and 2, exceeding 5, and tan δ was lower than 0.2, at 0.073.

[0143] (7) Complex relative permeability of compacts of CeFeTiN-based magnetic powder Using the magnetic powders of Comparative Examples 3 and 4 and Examples 2 and 3, samples for measuring complex relative permeability at 1 MHz to 1 GHz were prepared by the method described above (toroidal compacts with densities of 4.72 (Example 2) (resin addition amount 8 mass%), 4.96 (Example 3), and 5.61 (Comparative Example 3), 5.43 (Comparative Example 4) (resin addition amount 2.5 mass%)). The frequency dependence of complex relative permeability at 1 MHz to 100 MHz was measured using the method described above, and the results are shown in FIG. 12, and the evaluation results of the high-frequency characteristics are shown in Tables 3 and 4.

[0144] [Table 3] [Table 4]

[0145] In Comparative Examples 3 and 4, tan δ at 30 MHz was 0.2 or more, and μ' was less than 10. On the other hand, in Examples 2 and 3, tan δ at 30 MHz was less than 0.1, and μ' was 11 or more. Since Examples 2 and 3 have an α-Fe phase-containing region and the core region has a cryptocrystalline structure, μ' was higher than in Comparative Examples 3 and 4, exceeding 5 and being 10 or more, and tan δ was lower than 0.2, being 0.069 and 0.083, respectively.

[0146] The invention according to the present disclosure may include, for example, the following aspects. <1> An α-Fe phase-containing rare earth-iron-nitrogen magnetic powder having a core region and an α-Fe phase-containing region located outside the core region, The core region has Formula 1: R x X (100-x-y-z) M y N z (Formula 1) (In formula 1, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; N is a nitrogen atom, x, y, and z are in atomic percent, and are 2≦x≦15, 0.5≦y≦25, and 3≦z≦50. is a rare earth-iron-nitrogen magnetic powder having a cryptocrystalline structure represented by the α-Fe phase-containing region includes an α-Fe phase and at least one selected from the group consisting of an oxide, a nitride, and an oxynitride containing at least one of R and M; Rare earth-iron-nitrogen magnetic powder containing α-Fe phase. <2> R is at least one selected from the group consisting of Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu; Item 1. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to Item 1. <3> R is at least one selected from the group consisting of Ce, Pr, Nd, and Sm. Item 1 or 2. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder. <4> Sm is more than 50 atomic % relative to the total R components in the formula 1. Item 4. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to any one of Items 1 to 3. <5> The total amount of Co and Ni is 50 atomic % or less relative to the entire X component. Item 5. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to any one of Items 1 to 4. <6> The α-Fe phase containing region is nanocrystals consisting of at least one selected from the group consisting of oxides, nitrides, and oxynitrides containing at least one of R and M; and Contains nanocrystals consisting of the α-Fe phase. Item 6. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to any one of Items 1 to 5. <7> the thickness of the α-Fe phase-containing region is 0.001% or more and less than 50% of the average grain size of the core region; Item 7. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to any one of Items 1 to 6. <8> The thickness of the α-Fe phase-containing region is 2 nm or more and 80 μm or less. Item 8. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to any one of Items 1 to 7. <9> A phosphorus compound coating portion is provided on the outside of the α-Fe phase-containing region. Item 9. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to any one of Items 1 to 8. <10> Formula 2 below: R x X (100-x-y) M y (Formula 2) (In formula 2, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; x and y are atomic percent, 2.06≦x≦30, 0.515≦y≦50. A step of heat-treating the rare earth-iron magnetic powder represented by the formula (I) in ammonia gas to obtain a rare earth-iron-nitrogen compound; heat-treating the rare earth-iron-nitrogen compound in an atmosphere containing at least one gas selected from the group consisting of an inert gas, a hydrogen gas, and a nitrogen gas; A method for producing an α-Fe phase-containing rare earth-iron-nitrogen magnetic powder, comprising: <11> a phosphorus treatment step in which an inorganic acid is added to a slurry containing a rare earth-iron-nitrogen-based magnetic powder, water, and a phosphorus-containing substance to obtain a rare earth-iron-nitrogen-based magnetic powder having a phosphorus compound coating portion; an oxidation step of heat-treating the rare earth-iron-nitrogen magnetic powder having the phosphorus compound coating portion in an oxygen-containing atmosphere at 300°C or higher and 600°C or lower; Including, the rare earth-iron-nitrogen magnetic powder has a core region and an α-Fe phase-containing region located outside the core region, The core region has formula 3: R x X (100-x-y-z) M y N z (Formula 3) (In formula 3, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; N is a nitrogen atom, x, y, and z are in atomic percent, and are 2≦x≦15, 0.5≦y≦25, and 3≦z≦50. is a rare earth-iron-nitrogen magnetic powder having a cryptocrystalline structure represented by the α-Fe phase-containing region includes an α-Fe phase and at least one selected from the group consisting of an oxide, a nitride, and an oxynitride containing at least one of R and M; A method for producing rare earth-iron-nitrogen magnetic powder containing α-Fe phase. <12> Item 12. A method for producing an α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to Item 11, 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. <13> Item 13. A method for producing an α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to Item 11 or 12, wherein the phosphorus content in the rare earth-iron-nitrogen magnetic powder having a phosphorus compound coating portion is 0.0005% by mass or more and 4% by mass or less. <14> Item 10. A magnetic material for magnetic field amplification, comprising the α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to any one of Items 1 to 9. <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, for use in wireless power supply. <17> Item 16. The magnetic material for magnetic field amplification according to item 14 or 15, for use in an inductor core. <18> Item 16. The magnetic material for magnetic field amplification according to item 14 or 15, for use in an RFID tag. <19> 19. The magnetic material for magnetic field amplification according to any one of items 14 to 18, wherein the real term of the relative permeability at 30 MHz is 5 or more, and tan δ at 30 MHz is 0.2 or less. [Industrial Applicability]

[0147] According to the present disclosure, an α-Fe phase-containing rare earth-iron-nitrogen magnetic powder having excellent magnetic field amplification properties can be obtained. This magnetic powder can be suitably used as a magnetic material for magnetic field amplification. This magnetic material for magnetic field amplification can be used in a variety of applications, including transformers, heads, inductors, reactors, cores, yokes, and other devices used in high-frequency or ultra-high-frequency ranges, primarily in power equipment and information and communications-related devices; materials for elements and antennas that transmit and receive high-frequency or ultra-high-frequency signals, such as RFID tags and wireless power supplies; microwave elements, magnetostrictive elements, magnetoacoustic elements, and magnetic recording elements; and magnetic materials for sensors that use magnetic fields, such as Hall elements, magnetic sensors, current sensors, rotation sensors, and electronic compasses.

Claims

1. An α-Fe phase-containing rare earth-iron-nitrogen magnetic powder having a core region and an α-Fe phase-containing region located outside the core region, The core region has the following formula 1: R ｘ X （１００－ｘ－ｙ－ｚ） M ｙ N ｚ (Formula 1) (In formula 1, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; N is a nitrogen atom, x, y, and z are in atomic percent, and are 2≦x≦15, 0.5≦y≦25, and 3≦z≦50. It is a rare earth-iron-nitrogen magnetic powder having a cryptocrystalline structure represented by the α-Fe phase-containing region includes an α-Fe phase and at least one selected from the group consisting of an oxide, a nitride, and an oxynitride containing at least one of R and M; Rare earth-iron-nitrogen magnetic powder containing α-Fe phase.

2. R is at least one selected from the group consisting of Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu; 2. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to claim 1.

3. R is at least one selected from the group consisting of Ce, Pr, Nd, and Sm; 3. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to claim 1.

4. Sm is more than 50 atomic % relative to the total R component in the formula 1.

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

5. The total amount of Co and Ni is 50 atomic % or less based on the entire X component.

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

6. The α-Fe phase containing region is a compound consisting of at least one selected from the group consisting of oxides, nitrides, and oxynitrides containing at least either R or M; and Contains nanocrystals consisting of an α-Fe phase, 3. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to claim 1.

7. the thickness of the α-Fe phase-containing region is 0.001% or more and less than 50% of the average grain size of the core region; 3. The α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to claim 1.

8. The thickness of the α-Fe phase-containing region is 2 nm or more and 80 μm or less.

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

9. A phosphorus compound coating portion is provided on the outside of the α-Fe phase-containing region.

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

10. Formula 2 below: R ｘ X （１００－ｘ－ｙ） M ｙ (Formula 2) (In formula 2, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; x and y are, in atomic percent, 2.06≦x≦30 and 0.515≦y≦50, respectively. a step of heat-treating the rare earth-iron magnetic powder represented by the formula (I) in ammonia gas to obtain a rare earth-iron-nitrogen compound; heat-treating the rare earth-iron-nitrogen compound in an atmosphere containing at least one gas selected from the group consisting of an inert gas, a hydrogen gas, and a nitrogen gas; A method for producing an α-Fe phase-containing rare earth-iron-nitrogen magnetic powder, comprising:

11. a phosphorus treatment step in which an inorganic acid is added to a slurry containing a rare earth-iron-nitrogen-based magnetic powder, water, and a phosphorus-containing substance to obtain a rare earth-iron-nitrogen-based magnetic powder having a phosphorus compound coating portion; an oxidation step of heat-treating the rare earth-iron-nitrogen magnetic powder having the phosphorus compound coating portion in an oxygen-containing atmosphere at 300° C. or higher and 600° C. or lower; Including, the rare earth-iron-nitrogen magnetic powder has a core region and an α-Fe phase-containing region located outside the core region, The core region has the following formula 3: R ｘ X （１００－ｘ－ｙ－ｚ） M ｙ N ｚ (Formula 3) (In formula 3, R is a rare earth element, X is at least one selected from the group consisting of Fe, Co, and Ni, and contains at least Fe; M is at least one selected from the group consisting of Ti, V, Mo, Nb, W, Si, Al, Mn, and Cr; N is a nitrogen atom, x, y, and z are in atomic percent, and are 2≦x≦15, 0.5≦y≦25, and 3≦z≦50. It is a rare earth-iron-nitrogen magnetic powder having a cryptocrystalline structure represented by the α-Fe phase-containing region includes an α-Fe phase and at least one selected from the group consisting of an oxide, a nitride, and an oxynitride containing at least one of R and M; A method for producing rare earth-iron-nitrogen magnetic powder containing α-Fe phase.

12. 12. The method for producing an α-Fe phase-containing rare earth-iron-nitrogen magnetic powder according to claim 11, 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.

13. The method for producing an α-Fe phase-containing rare earth-iron-nitrogen-based magnetic powder according to claim 11 or 12, wherein the phosphorus content in the rare earth-iron-nitrogen-based magnetic powder having a phosphorus compound coating portion is 0.0005 mass% or more and 4 mass% or less.

14. A magnetic material for magnetic field amplification, comprising the α-Fe phase-containing rare earth-iron-nitrogen 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, for use in wireless power supply.

17. The magnetic material for magnetic field amplification according to claim 14 for use in an inductor core.

18. The magnetic material for magnetic field amplification according to claim 14, for use in an RFID tag.

19. 15. The magnetic material for magnetic field amplification according to claim 14, wherein the real term of the relative permeability at 30 MHz is 5 or more and tan δ at 30 MHz is 0.2 or less.

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