Soft magnetic powder, magnetic core, and magnetic device

Abstract

To provide a magnetic core and a magnetic device with excellent DC superimposition characteristics, and also to provide soft magnetic powder suitable for the magnetic core and the magnetic device.SOLUTION: There is provided soft magnetic powder including a soft magnetic particle 2 containing at least one selected from Fe and Co. The soft magnetic powder satisfies the relation of σFeCo(S)-σFeCo(C)≥0.005, where an element distribution obtained by analyzing a surface layer part S of the soft magnetic particle using a 3D atom probe (3DAP) method is divided into a plurality of grids to calculate a sum of a content ratio of Fe and a content ratio of Co in each grid and a standard deviation of the sum of the content ratio of Fe and the content ratio of Co is represented by σFeCo(S) where a population is the plurality of grids, and an element distribution obtained by analyzing a center part C of the soft magnetic particle using the 3DAP method is divided into a plurality of grids to calculate the sum of the content ratio of Fe and the content ratio of Co in each grid and a standard deviation of the sum of the content ratio of Fe and the content ratio of Co is represented by σFeCo(C) where the population is the plurality of grids.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a soft magnetic powder, a magnetic core, and a magnetic device. [Background technology]

[0002] In recent years, power supplies have been required to be smaller and have higher output, and accordingly, magnetic devices used in power supply circuits are also required to be smaller and support higher currents. One effective way to miniaturize magnetic devices is to use magnetic cores with high magnetic permeability. However, when the magnetic permeability is improved, the magnetization of the magnetic core is saturated even in a small magnetic field, which results in a decrease in the limit value of the DC superimposition current, and the device tends to be unable to support higher currents.

[0003] As a method for simultaneously solving the problems of miniaturization and high current, Patent Document 1 discloses a method of molding a magnetic core by densely packing magnetic powder with high saturation magnetic flux density, while Patent Document 2 discloses a method of placing an insulator between magnetic powder particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-75721 A [Patent Document 2] JP 2002-33211 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetic core and a magnetic device having excellent DC bias characteristics, and a soft magnetic powder suitable for the magnetic core and the magnetic device. [Means for solving the problem]

[0006] The aspects of the present invention are as follows.

[0007] [1] A soft magnetic powder comprising soft magnetic particles containing at least one selected from iron and cobalt, The surface layer of the soft magnetic particles is analyzed by the 3D atom probe method to obtain an element distribution, which is divided into multiple grids. The sum of the iron content and cobalt content in each grid is calculated, and the standard deviation of the sum of the iron content and cobalt content when the multiple grids are considered as a population is expressed as σ FeCo (S) The element distribution obtained by analyzing the center of a soft magnetic particle using the 3D atom probe method is divided into multiple grids, and the sum of the iron content and cobalt content in each grid is calculated. The standard deviation of the sum of the iron content and cobalt content when the multiple grids are considered as a population is σ FeCo When it is expressed as (C), σ FeCo (S)-σ FeCo (C) A soft magnetic powder that satisfies the relationship of ≧0.005.

[0008] [2] A magnetic core comprising the soft magnetic powder according to [1].

[0009] [3] A magnetic device comprising the magnetic core described in [2]. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of the soft magnetic powder according to this embodiment. [Diagram 2] FIG. 2 is a schematic diagram for explaining the range observed by 3DAP in a soft magnetic particle. [Diagram 3] FIG. 3 is a schematic cross-sectional view of the magnetic core according to the present embodiment. [Figure 4A] FIG. 4A shows the results of observing the distribution of iron in a sample according to an embodiment by 3DAP. [Figure 4B] FIG. 4B shows the results of observing the distribution of cobalt in the sample according to the example by 3DAP. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (1. Soft magnetic powder) As shown in Fig. 1, the soft magnetic powder 1 according to this embodiment includes a plurality of soft magnetic particles 2. In the soft magnetic powder 1, the position of each soft magnetic particle 2 is not fixed, and the soft magnetic powder 1 has fluidity.

[0012] The average particle diameter (D50) of the soft magnetic powder according to this embodiment can be selected depending on the application, etc. For example, the average particle diameter (D50) may be within a range of 3 to 100 μm. The average particle diameter may be controlled by the powder production conditions, or may be controlled by classification processing, etc. In this specification, the particle diameter of the soft magnetic particles is a particle diameter measured by a laser diffraction scattering method.

[0013] The shape of the soft magnetic particles may be spherical or close to spherical. For example, the average circularity of the cross section of the soft magnetic particles may be 0.7 or more, preferably 0.85 or more, and more preferably 0.9 or more. For example, Wadell's circularity may be used as the circularity.

[0014] The soft magnetic powder may contain only soft magnetic particles of the same material, or may contain soft magnetic particles of different materials, as long as the relationship described below is satisfied. Examples of different materials include soft magnetic metals made of different elements, and soft magnetic metals made of the same elements but with different compositions.

[0015] In this embodiment, an insulating coating may be formed so as to cover at least a part of the surface of the soft magnetic particle. The insulating coating may be, for example, an oxide film formed by oxidation of the surface of the soft magnetic particle, or a coating formed on the surface of the soft magnetic particle using an insulating material. The insulating material is preferably an inorganic material such as an oxide, nitride, or carbide. Examples of oxides include SiO2, MgO, Al2O3, phosphates, silicates, borosilicates, and bismuthates, which may be crystalline or may be glass. Examples of oxide glass include phosphate-based glass, bismuthate-based glass, and borosilicate glass. The coating may be composed of a plurality of coatings. For example, a coating may be formed using an insulating material on an oxide film formed by oxidation of the surface of the soft magnetic particle.

[0016] The average thickness of the coating portion is preferably 1 nm or more and 250 nm or less, and more preferably 20 nm or more and 250 nm or less.

[0017] The soft magnetic powder according to this embodiment may contain only soft magnetic particles that do not have a coating formed thereon, may contain both soft magnetic particles that do not have a coating formed thereon and soft magnetic particles that have a coating formed thereon, or may contain only soft magnetic particles that have a coating formed thereon.

[0018] In this embodiment, the soft magnetic particles are made of a soft magnetic metal containing at least one element selected from iron (Fe) and cobalt (Co). That is, the soft magnetic particles may be made of a soft magnetic metal containing iron, may be made of a soft magnetic metal containing cobalt, or may be made of a soft magnetic metal containing iron and cobalt. In this embodiment, the soft magnetic metal is preferably a soft magnetic metal containing iron or a soft magnetic metal containing iron and cobalt.

[0019] The soft magnetic metal containing at least one element selected from iron and cobalt may have a crystalline structure, an amorphous structure, or a nanocrystalline structure.

[0020] The soft magnetic metal containing at least one element selected from iron and cobalt may contain elements other than iron and cobalt. The soft magnetic metal may further contain element X, chromium (Cr), nickel (Ni), or element M.

[0021] The element X is at least one element selected from the group consisting of B (boron), Si (silicon), P (phosphorus) and C (carbon). By including the element X, the crystal magnetic anisotropy can be reduced, and therefore the coercive force can be reduced.

[0022] The element M is at least one element selected from Al (aluminum), S (sulfur), Ti (titanium), V (vanadium), Mn (manganese), Cu (copper), Zr (zirconium), Nb (niobium), Mo (molybdenum), Zn (zinc), Ga (gallium), As (arsenic), Ag (silver), Sn (tin), Sb (antimony), Au (gold), Bi (bismuth), Y (yttrium), La (lanthanum), Pt (platinum), Mg (magnesium), Ca (calcium), N (nitrogen), O (oxygen), Hf (hafnium), Ta (tantalum) and W (tungsten). By incorporating the element M and changing the content, it is possible to control the amorphous structure and nanocrystalline structure, and a structure that provides good soft magnetic properties can be obtained.

[0023] In this embodiment, when Cr is contained, a powder with high corrosion resistance can be obtained.

[0024] In this embodiment, the composition of the soft magnetic metal containing at least one element selected from iron and cobalt is expressed by the composition formula (Fe 1- αCoα) 100-w-x-y-z Ni w X x Cr y Mz In the above composition formula, X is the above-mentioned element X, which is at least one element selected from B, Si, P, and C. M is the above-mentioned element M, which is at least one element selected from Al, S, Ti, V, Mn, Cu, Zr, Nb, Mo, Zn, Ga, As, Ag, Sn, Sb, Au, Bi, Y, La, Pt, Mg, Ca, N, O, Hf, Ta, and W.

[0025] In the above composition formula, it is preferable that "α", "w", "x", "y" and "z" satisfy the relationships: 0≦α≦1, 0≦w≦80, 3≦x≦30, 0≦y≦8, 0≦z≦11.

[0026] The soft magnetic metal may contain elements other than the above-mentioned elements as unavoidable impurities. For example, the total content of elements other than the above-mentioned elements in 100% by mass of the soft magnetic metal may be 0.1% by mass or less, and preferably 0.05% by mass or less.

[0027] In this embodiment, elemental analysis is performed on the surface layer and center of the soft magnetic particle by the three-dimensional atom probe method. As shown in FIG. 2, the surface layer S is a region from the surface of the soft magnetic particle 2 to 500 nm in the direction from the surface to the center. The surface of the soft magnetic particle is the outermost surface 2a of the region in which the above-mentioned soft magnetic metal composition is maintained in the particle. Therefore, when a coating portion (including a natural oxide film) 3 is formed on the soft magnetic particle, the outermost surface 2a of the region in which the above-mentioned soft magnetic metal composition is maintained is not the outermost surface 3a of such coating portion 3 but the outermost surface 2a of the region in which the above-mentioned soft magnetic metal composition is maintained.

[0028] 2, the center C is a region extending up to 300 nm from the center 2b of the soft magnetic particle 2 in the direction from the center toward the surface. When the soft magnetic particle has a shape other than a sphere, the center C is set to the center of gravity of the soft magnetic particle.

[0029] The three-dimensional atom probe (3DAP) method applies a high electric field to the tip of a needle-shaped sample, ionizes the atoms on the sample surface, and causes them to desorb from the sample, and detects the desorbed ions with a detector. The distribution of the elements that make up the sample can be observed three-dimensionally based on the flight time to the detector and the detection position.

[0030] The observation range A of the element distribution shown in FIG. 2 may be a range in which the standard deviation of the total content ratio of iron and cobalt, which will be described later, can be calculated. In this embodiment, the observation range is 3200 nm 3 Above 20000nm 3 The shape of the observation range may be set arbitrarily, taking into consideration the shape of the grid formed by dividing the observation range. For example, the shape of the observation range is a rectangular parallelepiped.

[0031] The observation range is divided into a plurality of grids. The shape of the grids can be, for example, a cube. The size of the grids can be set according to the number of grids. The number of grids is the number of populations for calculating the standard deviation of the total content ratio of iron and cobalt, and is therefore preferably a number that allows the standard deviation to be calculated with high accuracy. In this embodiment, the number of grids is set to 400 or more.

[0032] Therefore, when the observation range is set to, for example, a rectangular parallelepiped of 10 nm×10 nm×200 nm, the rectangular parallelepiped is divided into 2,500 cubic grids of 2 nm×2 nm×2 nm.

[0033] Next, the iron content (concentration) and the cobalt content (concentration) are calculated for each divided grid, and the sum of the iron content and the cobalt content for each grid is calculated. Although the soft magnetic metal has a uniform composition as a whole, the iron content and the sum of the cobalt content in a micro-localized region such as a grid may vary from grid to grid (each grid may show variation). Such variation for each grid is expressed as the standard deviation of the sum of the iron content and the cobalt content. In other words, the sum of the iron content and the cobalt content in the divided grids, for example, 2500 grids, is used as the population, and the standard deviation of the sum of the iron content and the cobalt content is calculated.

[0034] In this embodiment, the standard deviation of the sum of the iron content and the cobalt content in the surface layer of the soft magnetic particles is σ FeCo (S), and the standard deviation of the sum of the iron content and cobalt content in the center of the soft magnetic particle is σ FeCo When (C) is used, σ FeCo (S) and σ FeCo (C) is σ FeCo (S)-σ FeCo (C) ≧ 0.005. In other words, this indicates that the variation in the sum of the iron content and the cobalt content in the surface layer is somewhat greater than the variation in the sum of the iron content and the cobalt content in the center portion.

[0035] The large variation in the sum of the iron content rate and the cobalt content rate in the surface layer is considered to mean that the uniformity of the interatomic distance of the constituent elements is low near the surface of the soft magnetic particle, and strain and stress remain near the surface of the soft magnetic particle. On the other hand, the uniformity of the interatomic distance of the constituent elements is relatively high near the center of the soft magnetic particle compared to near the surface, so the residual stress near the center is considered to be low. Since such residual stress leads to a decrease in magnetic permeability, it is presumed that in soft magnetic particles that satisfy the above standard deviation relationship, the magnetic permeability is low only near the surface.

[0036] Here, in a magnetic core formed by filling magnetic powder, the close magnetic gap between particles strongly affects the DC bias characteristics. Therefore, the DC bias characteristics are improved by reducing the areas where the interparticle magnetic gap is extremely narrow (narrow gap areas between particles), such as areas where particles are in contact with each other. Reducing the narrow gap areas between particles is equivalent to forming areas of low magnetic permeability between particles. Therefore, a magnetic core obtained by using a soft magnetic powder containing soft magnetic particles whose standard deviation satisfies the above relationship has improved DC bias characteristics.

[0037] Furthermore, since there is lattice distortion due to residual stress near the surface, it is presumed that the continuous slip surface during deformation when pressure is applied from the outside tends to decrease. Also, the area of ​​the narrow gap between particles increases due to the deformation of the particles by pressing when filling and molding the magnetic material, which also causes the DC superposition characteristics of the magnetic core to deteriorate. Therefore, by using a soft magnetic powder containing soft magnetic particles whose standard deviation satisfies the above relationship, the particles can move in the direction of filling the gap without deformation during pressing, thereby reducing the volume. As a result, it is presumed that the area of ​​the narrow gap between particles can be reduced, improving the DC superposition characteristics.

[0038] σ FeCo (S)-σ FeCo The lower limit of (C) may be 0.005, 0.01, or 0.019. FeCo (S)-σ FeCo The upper limit of (C) is not particularly limited, but may be 1.024 from the viewpoint of the production method.

[0039] σ FeCo (S) and σ FeCo The measurement of (C) is performed at one point on one particle, and the measured value is expressed as σ FeCo (S) and σ FeCo The above measurement is performed for a plurality of soft magnetic particles. In this embodiment, when the number ratio of the measured plurality of soft magnetic particles is set to 100%, σ FeCo (S)-σFeCo The percentage by number of soft magnetic particles satisfying the above relationship in (C) is preferably 50% or more, and more preferably 65% ​​or more.

[0040] (2. Manufacturing method of soft magnetic powder) As a method for producing the soft magnetic powder according to the present embodiment, the above σ FeCo Any method may be used as long as it can produce soft magnetic particles that satisfy the relationship of In this embodiment, after the soft magnetic powder is produced by a known method for producing soft magnetic powder, the soft magnetic powder is subjected to post-treatment.

[0041] Examples of known methods for producing soft magnetic powder include the carbonyl method, spray pyrolysis method, CVD method, PVD method, gas atomization method, water atomization method, and rotating disk method. Another example is a method in which a ribbon obtained by a single roll method is pulverized to obtain a powder. In order to control the average particle size of the obtained powder, classification treatment such as air classification, wet classification, and dry classification may be performed. In this embodiment, atomization methods such as gas atomization and water atomization are preferred.

[0042] As a post-treatment for the soft magnetic powder, the soft magnetic powder is subjected to a heat treatment and then quenching treatment, which involves rapid cooling. The heat treatment conditions vary depending on the composition, but the heat treatment temperature may be 300°C or higher, 500°C or higher, or 800°C or higher. The upper limit of the heat treatment temperature may be set according to the composition of the soft magnetic metal, etc. Also, the holding time at the heat treatment temperature may be 1 minute to 1 hour. The atmosphere in the heat treatment may be an inert atmosphere. Examples of the inert atmosphere include a nitrogen atmosphere and an argon atmosphere. Also, this heat treatment may also serve as a heat treatment for precipitating nanocrystals.

[0043] After the heat treatment, the soft magnetic powder is quenched. An example of a method for quenching is to immediately put the soft magnetic powder after the heat treatment into running water. The temperature of the running water is preferably 0 to 30°C. The flow rate of the running water may be 50 L / min or more, 100 L / min or more, or 300 L / min or more. If the flow rate is high, the above σFeCo Therefore, it becomes easy to manufacture soft magnetic particles that satisfy the relationship.

[0044] By quenching after the heat treatment in this way, the surface layer of the soft magnetic particles is easily distorted, whereas the center is not quenched to the extent that distortion is easily generated. FeCo (S) is σ FeCo (C) tends to be larger than the above σ FeCo It is easy to be satisfied with the relationship.

[0045] In addition, in the case of cooling the soft magnetic powder by air cooling after the heat treatment, the above σ FeCo It is difficult to manufacture soft magnetic particles that satisfy the above σ relationship. FeCo However, it is difficult to manufacture soft magnetic particles that satisfy the above relationship.

[0046] The powder after quenching is collected to obtain the soft magnetic powder according to this embodiment.

[0047] (3. Magnetic core) The magnetic core according to the present embodiment is formed to have a predetermined shape by including the soft magnetic powder described above. In such a magnetic core, the soft magnetic powder loses fluidity, and the soft magnetic particles contained in the soft magnetic powder are fixed at predetermined positions, and become one of the components of the magnetic core. By including the soft magnetic powder described above in the magnetic core according to the present embodiment, the DC superposition characteristics of the magnetic core are improved.

[0048] The magnetic core according to the present embodiment may contain a powder other than the soft magnetic powder described above. That is, the magnetic core may contain only the soft magnetic powder described above, or may contain multiple types of soft magnetic powder including the soft magnetic powder described above.

[0049] When the magnetic core contains multiple types of soft magnetic powder, the composition of the particles contained in each powder may be the same or different. Also, the average particle diameter of each powder may be the same or different. For example, the magnetic core may contain two types of powder, a large diameter powder with a large average particle diameter and a small diameter powder with a small average particle diameter, or may contain three types of powder (large diameter powder, medium diameter powder, small diameter powder) with different average particle diameters. The mass ratio of the large diameter powder to the small diameter powder, or the mass ratio of the large diameter powder to the medium diameter powder to the small diameter powder may be set in consideration of the magnetic properties to be obtained. The mass ratio of the large diameter powder to the small diameter powder may be, for example, 20 to 100 mass% for the large diameter powder and 0 to 80 mass% for the small diameter powder. Also, the mass ratio of the large diameter powder to the medium diameter powder to the small diameter powder may be, for example, 20 to 80 mass% for the medium diameter powder, and the remainder may be distributed between the large diameter powder and the small diameter powder, and the distribution ratio is not particularly limited and may be, for example, 10 to 90%.

[0050] When the magnetic core contains multiple types of soft magnetic powder, the soft magnetic powder is preferably contained as a powder with a relatively large average particle size (large diameter powder, medium diameter powder). In addition, the soft magnetic powder is preferably contained in an amount of 20% by mass or more, more preferably 30% by mass or more and 100% by mass or less, out of 100% by mass of the powder contained in the magnetic core.

[0051] The magnetic core may contain a binder that bonds the particles in the powder together, in addition to the powder. Examples of binders include thermosetting resins such as epoxy resin, phenol resin, and silicone resin. By containing the resin, the soft magnetic particles (large diameter particles 21 of the large diameter powder and small diameter particles 22 of the small diameter powder) in the magnetic core 10 are bonded together via the resin 5 as shown in FIG. 3, and fixed into a predetermined shape.

[0052] The proportion of the soft magnetic particles in the magnetic core (filling rate) may be 70 to 90%.

[0053] A known method can be used to manufacture the magnetic core. First, a powder containing at least the soft magnetic powder described above is mixed with a binder (for example, a thermosetting resin) to obtain a mixture. If necessary, the mixture obtained may be made into a granulated powder. The amount of the binder to be blended may be 1 to 5 parts by mass with respect to 100 parts by mass of the powder.

[0054] Next, the mixture or granulated powder is filled into a mold and compressed to obtain a green body having the shape of a magnetic core. The filling rate can be controlled by the pressure during compression molding.

[0055] The resulting molded body is subjected to a curing treatment at, for example, 50 to 200° C., whereby the resin is cured and the soft magnetic particles are fixed via the resin, thereby obtaining a magnetic core.

[0056] (4. Magnetic Devices) The magnetic device according to the present embodiment has the above-mentioned magnetic core. The magnetic device may have a configuration in which a coil is embedded inside the magnetic core, or a configuration in which a wire is wound around the surface of the magnetic core. Examples of such magnetic devices include inductors, transformers, and choke coils.

[0057] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and may be modified in various aspects within the scope of the present invention. EXAMPLES

[0058] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0059] (Experiment 1) In experiment 1, magnetic cores of sample numbers 1a to 13d were manufactured using mixed powders obtained by mixing the large-diameter powder made of the soft magnetic powder described above and the small-diameter powder made of pure iron (Fe) powder. The average particle diameter (D50) of the small-diameter powder was 1 μm.

[0060] The soft magnetic powder (large diameter powder) was produced as follows. First, the atomic ratio of (Fe 0.75 Co 0.25 ) 90 S 10 The raw metals were weighed out so as to obtain the composition and placed in a crucible placed in an atomizing device. Next, after the chamber of the atomizing device was evacuated, the crucible was heated by high-frequency induction using a work coil installed outside the crucible, and the raw metals in the crucible were melted and mixed to obtain a molten metal (molten metal) at 1500°C.

[0061] The obtained molten metal was fed into the chamber as a linear continuous fluid through a nozzle provided at the bottom of the crucible, and water was sprayed onto the fed molten metal to obtain soft magnetic powder. The obtained soft magnetic powder had a crystalline structure, and its average particle size (D50) was 20 μm. Inductively Coupled Plasma (ICP) analysis confirmed that the composition of the soft magnetic powder was consistent with the composition of the weighed raw metal.

[0062] The obtained soft magnetic powders were subjected to the following post-treatment, except for sample numbers 1a to 1d. For sample numbers 2a to 13d, the obtained soft magnetic powders were filled into a heat treatment furnace and subjected to heat treatment. The heat treatment atmosphere was a nitrogen atmosphere, the heating temperature during the heat treatment was the temperature shown in Table 1, and the holding time was 1 hour.

[0063] For samples 2a to 2d, after the heat treatment, the soft magnetic powder was allowed to cool in the furnace, and when the temperature inside the furnace had decreased to room temperature, the soft magnetic powder was recovered from the heat treatment furnace.

[0064] For samples 3a to 12d, immediately after the heat treatment, the soft magnetic powder was dropped into running water at a temperature of 25° C. and a flow rate shown in Table 1 to be quenched, and the soft magnetic powder was collected.

[0065] For samples 13a to 13d, immediately after the heat treatment, the soft magnetic powder was dropped into still water at a temperature of 25° C. to be quenched, and the soft magnetic powder was collected.

[0066] For sample numbers 1a to 13d, needle-shaped samples were prepared from the surface and center portions of multiple particles in the collected soft magnetic powder, and observed by the 3DAP method to obtain the distribution of elements contained in the particles. In this example, the surface portion of the particle was defined as the region located 200 nm from the surface in the direction from the surface to the center of the particle when the oxide film formed on the particle was excluded, and the center portion of the particle was defined as the region located ±100 nm from the center in the direction from the center to the surface of the particle.

[0067] The observation range of the 3DAP was 10 nm × 10 nm × 200 nm. The observation range was divided into 2500 cubic grids of 2 nm × 2 nm × 2 nm, and the content ratio of iron (Fe) and cobalt (Co) in each grid was calculated. The results of the observation of the distribution of iron by 3DAP for the surface layer of sample number 7a are shown in Figure 4A, and the results of the observation of the distribution of cobalt by 3DAP are shown in Figure 4B.

[0068] From the calculated iron and cobalt content ratios, the sum of the iron content ratio and the cobalt content ratio in each grid (total content ratio) was calculated. The calculated 2,500 data were used as the population, and the standard deviation σ FeCo The surface layer σ FeCo σ FeCo (S) and σ at the center FeCo σ FeCo This is indicated as (C). The obtained σ FeCo (S) to σ FeCo By subtracting (C), σ FeCo (S)-σ FeCo (C) was calculated, and the results are shown in Table 1.

[0069] In addition, σ FeCo (S)-σ FeCo The percentage of the number of particles in which (C) is within the above range was 65% or more in all samples of sample numbers 3a to 12d. In addition, in the samples of odd numbers among sample numbers 15 to 421 described later, σ FeCo (S)-σ FeCo The percentage of particles having (C) within the above range was 65% or more.

[0070] In the samples 1a to 13d, the obtained soft magnetic powder (large diameter powder) and the pure iron powder (small diameter powder) were mixed so that the ratio of the large diameter powder was 80 mass% and the ratio of the small diameter powder was 20 mass% to obtain a mixed powder. The obtained mixed powder was kneaded with an epoxy resin to prepare a mixture. The amount of the epoxy resin to be mixed with respect to 100 mass parts of the mixed powder was 2.5 mass parts.

[0071] For samples 1a to 1d, the mixture obtained was filled into a mold of a given toroidal shape, and the molding pressure was changed to obtain molded bodies with different filling rates of the mixed powder. The epoxy resin contained in the obtained molded body was thermally cured at 180°C for 60 minutes to produce a toroidal core (outer diameter 11 mm, inner diameter 6.5 mm, thickness 2.5 mm). The filling rate of the mixed powder in the obtained toroidal core is shown in Table 1. The filling rate of the mixed powder in the toroidal core was calculated by dividing the density of the toroidal core calculated from the dimensions and mass of the toroidal core by the theoretical density of the toroidal core calculated from the specific gravities of various materials.

[0072] A copper wire was wound around each sample of the toroidal core of sample numbers 1a to 1d, and the inductance of the toroidal core at a frequency of 1 MHz was measured using an LCR meter without applying a DC superimposed current, i.e., when the DC superimposed current was 0 A. The relative permeability was calculated from the obtained inductance, and this value was taken as the initial relative permeability μi. The results are shown in Table 1.

[0073] Next, the DC superimposed current was gradually increased from 0 A for each of the toroidal core samples of sample numbers 1a to 1d in which copper wire was wound. The DC superimposed current value was measured when μi decreased by 10% from when the DC superimposed current was 0 A, and this current value was designated as Isat (unit: A). The results are shown in Table 1.

[0074] From μi and Isat of the toroidal cores of sample numbers 1a to 1d, an approximate straight line showing the relationship between μi and Isat was calculated, and Isat when μi was 30 on the approximate straight line was defined as "Isat at μi=30" (A). The results are shown in Table 1.

[0075] For each group of sample numbers 2a to 2d, 3a to 3d, 4a to 4d, 5a to 5d, 6a to 6d, 7a to 7d, 8a to 8d, 9a to 9d, 10a to 10d, 11a to 11d, 12a to 12d, and 13a to 13d, the obtained soft magnetic powder was used to prepare mixed powders and toroidal cores in the same manner as for sample numbers 1a to 1d, and the magnetic properties of the toroidal cores were evaluated in the same manner as for sample numbers 1a to 1d, and "Isat at μi=30" was calculated. The value of "Isat at μi=30" calculated for sample numbers 1a to 1d was taken as the Isat improvement rate (%) when "Isat at μi=30" calculated for sample numbers 1a to 1d was taken as 100%. The higher the Isat improvement rate, the better the DC superposition characteristics. In this example, samples with an Isat improvement rate of 110% or more were judged to be good. The results are shown in Table 1.

[0076] [Table 1]

[0077] From Table 1, σ FeCo (S)-σ FeCo It was confirmed that when (C) is within the above-mentioned range, the improvement rate of Isat is large, and a magnetic core having excellent DC bias characteristics can be obtained.

[0078] (Experiment 2) For the even-numbered sample numbers, except that the composition of the soft magnetic powder (large diameter powder) was the composition shown in Tables 2 to 12, mixed powders and toroidal cores were produced in the same manner as for sample numbers 1a to 1d, and the magnetic properties of the toroidal cores were evaluated in the same manner as for sample numbers 1a to 1d, and Isat was calculated at μi shown in Tables 2 to 12. That is, for each sample number, a predetermined μi was set as a representative value from the magnetic properties of the four samples, as in Experiment 1, and Isat was calculated at the set μi. The results are shown in Tables 2 to 12.

[0079] For the odd-numbered sample numbers shown in Tables 2 to 6, the mixed powder was prepared by the same method as sample numbers 8a to 8d, except that the composition of the soft magnetic powder (large diameter powder) was the composition shown in Tables 2 to 6. For the odd-numbered sample numbers shown in Tables 7 to 12, the mixed powder was prepared by the same method as sample numbers 8a to 8d, except that the composition of the soft magnetic powder (large diameter powder) was the composition shown in Tables 7 to 12 and the quenching treatment conditions were the conditions shown in Tables 7 to 12. Using the prepared mixed powder, a toroidal core was prepared by the same method as sample numbers 8a to 8d, and the magnetic properties of the toroidal core were evaluated by the same method as sample numbers 8a to 8d, and the Isat at μi shown in Tables 2 to 12 was calculated. From the calculated Isat, the Isat improvement rate was calculated relative to the Isat of the sample number having the same composition. For example, the Isat improvement rate of sample number 15 is a value when the Isat of sample number 14 having the same composition is set to 100%. The results are shown in Tables 2 to 12.

[0080] [Table 2]

[0081] [Table 3]

[0082] [Table 4]

[0083] [Table 5]

[0084] [Table 6]

[0085] [Table 7]

[0086] [Table 8]

[0087] [Table 9]

[0088] [Table 10]

[0089] [Table 11]

[0090] [Table 12]

[0091] From Tables 2 to 12, σ FeCo (S)-σ FeCo It was confirmed that when (C) is within the above-mentioned range, the improvement rate of Isat is large, and a magnetic core having excellent DC bias characteristics can be obtained.

[0092] (Experiment 3) For the even-numbered sample numbers, soft magnetic powder was produced by the same method as for sample numbers 1a to 1d, and a coating was formed on the surface of the soft magnetic particles of the obtained soft magnetic powder using a mechanofusion device. For sample numbers 388, 390, and 392, P-Zn-Al-O oxide glass was formed as the coating, for sample number 394, Bi-Zn-B-Si-O oxide glass was formed as the coating, and for sample number 396, Ba-Zn-B-Si-Al-O oxide glass was formed as the coating. The thickness of the coating was controlled by the amount of coating material added to form the coating.

[0093] A mixed powder was obtained using soft magnetic powder containing soft magnetic particles with a coating portion formed thereon, and a toroidal core was manufactured using the same method as for sample numbers 1a to 1d. The magnetic properties of the toroidal core were evaluated using the same method as for sample numbers 1a to 1d, and Isat was calculated for μi shown in Table 13. That is, for each sample number, a predetermined μi was set as a representative value from the magnetic properties of the four samples, as in Experiment 1, and Isat was calculated for the set μi. The results are shown in Table 13.

[0094] For the odd-numbered sample numbers, soft magnetic powder was produced by the same method as for sample numbers 8a to 8d, and a coating was formed on the surface of the soft magnetic particles of the obtained soft magnetic powder using a mechanofusion device. For sample numbers 389, 391, and 393, P-Zn-Al-O oxide glass was formed as the coating, for sample number 395, Bi-Zn-B-Si-O oxide glass was formed as the coating, and for sample number 397, Ba-Zn-B-Si-Al-O oxide glass was formed as the coating. The thickness of the coating was controlled by the amount of coating material added to form the coating.

[0095] A mixed powder was obtained using soft magnetic powder containing soft magnetic particles forming a coating portion, and a toroidal core was produced by the same method as for sample numbers 8a to 8d. The magnetic properties of the toroidal core were evaluated by the same method as for sample numbers 8a to 8d, and Isat at μi shown in Table 13 was calculated. From the calculated Isat, the Isat improvement rate was calculated relative to the Isat of sample numbers having the same composition and thickness of the oxide glass constituting the coating portion. For example, the Isat improvement rate of sample number 389 is a value when the Isat of sample number 388 having the same composition and thickness of the oxide glass is taken as 100%. The results are shown in Table 13.

[0096] [Table 13]

[0097] From Table 13, for soft magnetic particles with a coating on the surface, σ FeCo (S)-σ FeCoIt was confirmed that when (C) is within the above-mentioned range, the improvement rate of Isat is large, and a magnetic core having excellent DC bias characteristics can be obtained.

[0098] (Experiment 4) For the even-numbered sample numbers, soft magnetic powder was manufactured by the same method as for sample numbers 1a to 1d, and the obtained soft magnetic powder (large diameter powder) and pure iron powder (small diameter powder) were mixed in the ratio shown in Table 14 to obtain a mixed powder. Using the obtained mixed powder, a toroidal core was manufactured by the same method as for sample numbers 1a to 1d, and the magnetic properties of the toroidal core were evaluated by the same method as for sample numbers 1a to 1d, and Isat was calculated at μi shown in Table 14. That is, for each sample number, a predetermined μi was set as a representative value from the magnetic properties of the four samples as in Experiment 1, and Isat was calculated at the set μi. The results are shown in Table 14.

[0099] For the odd-numbered sample numbers, soft magnetic powder was manufactured by the same method as sample numbers 8a to 8d, and the obtained soft magnetic powder (large diameter powder) and pure iron powder (small diameter powder) were mixed in the ratio shown in Table 14 to obtain a mixed powder. Using the obtained mixed powder, a toroidal core was manufactured by the same method as sample numbers 8a to 8d, and the magnetic properties of the toroidal core were evaluated by the same method as sample numbers 8a to 8d, and the Isat at μi shown in Table 14 was calculated. From the calculated Isat, the Isat improvement rate was calculated relative to the Isat of the sample number having the same mixing ratio of the large diameter powder and the small diameter powder. For example, the Isat improvement rate of sample number 399 is a value when the Isat of sample number 398 having the same mixing ratio of the large diameter powder and the small diameter powder is set to 100%. The results are shown in Table 14.

[0100] [Table 14]

[0101] From Table 14, even if the mixing ratio of the soft magnetic powder containing the above-mentioned soft magnetic particles is changed, σ FeCo (S)-σ FeCoIt was confirmed that when (C) is within the above-mentioned range, the improvement rate of Isat is large, and a magnetic core having excellent DC bias characteristics can be obtained.

[0102] (Experiment 5) For the even-numbered sample numbers, soft magnetic powders were manufactured in the same manner as sample numbers 1a to 1d, except that the average particle size was set to 3 μm by classification. The Fe-Co-BP-Si-Cr alloy powder having an amorphous structure was used as the large-diameter powder, the obtained soft magnetic powder was used as the medium-diameter powder, and the pure iron powder used in experiment 1 was used as the small-diameter powder. The average particle size of the large-diameter powder was 20 μm.

[0103] Large diameter powder, medium diameter powder, and small diameter powder were mixed in the ratio shown in Table 15 to obtain a mixed powder. Using the obtained mixed powder, a toroidal core was manufactured by the same method as for sample numbers 1a to 1d, and the magnetic properties of the toroidal core were evaluated by the same method as for sample numbers 1a to 1d, and Isat was calculated at μi shown in Table 15. That is, for each sample number, a predetermined μi was set as a representative value from the magnetic properties of the four samples, as in Experiment 1, and Isat was calculated at the set μi. The results are shown in Table 15.

[0104] For the odd-numbered sample numbers, soft magnetic powders were produced in the same manner as sample numbers 8a to 8d, except that the average particle diameter was set to 3 μm by classification. The Fe-Co-BP-Si-Cr alloy powder having an amorphous structure was used as the large-diameter powder, the obtained soft magnetic powder was used as the medium-diameter powder, and the pure iron powder used in experiment 1 was used as the small-diameter powder. The average particle diameter of the large-diameter powder was 20 μm.

[0105] The large diameter powder, the medium diameter powder, and the small diameter powder were mixed in the ratio shown in Table 15 to obtain a mixed powder. The obtained mixed powder was used to manufacture a toroidal core by the same method as sample numbers 8a to 8d, and the magnetic properties of the toroidal core were evaluated by the same method as sample numbers 8a to 8d to calculate the Isat at μi shown in Table 15. From the calculated Isat, the Isat improvement rate was calculated relative to the Isat of the sample number having the same mixing ratio of the large diameter powder, the medium diameter powder, and the small diameter powder. For example, the Isat improvement rate of sample number 407 is a value when the Isat of sample number 406 having the same mixing ratio of the large diameter powder, the medium diameter powder, and the small diameter powder is set to 100%. The results are shown in Table 15.

[0106] [Table 15]

[0107] From Table 15, even if the soft magnetic powder containing the above-mentioned soft magnetic particles is used as the medium-sized powder and the mixing ratio is changed, σ FeCo (S)-σ FeCo It was confirmed that when (C) is within the above-mentioned range, the improvement rate of Isat is large, and a magnetic core having excellent DC bias characteristics can be obtained.

[0108] (Experiment 6) For the even-numbered sample numbers, soft magnetic powders were manufactured in the same manner as sample numbers 1a to 1d, except that the average particle diameter was set to the value shown in Table 16 by classification processing. Toroidal cores were manufactured using only the manufactured soft magnetic powder in the same manner as sample numbers 1a to 1d, and the magnetic properties of the toroidal cores were evaluated in the same manner as sample numbers 1a to 1d, and Isat was calculated at μi shown in Table 16. That is, for each sample number, a predetermined μi was set as a representative value from the magnetic properties of the four samples, as in Experiment 1, and Isat was calculated at the set μi. The results are shown in Table 16.

[0109] For the odd-numbered sample numbers, soft magnetic powders were produced in the same manner as sample numbers 8a to 8d, except that the average particle diameter was set to the value shown in Table 16 by classification processing. Toroidal cores were produced using only the produced soft magnetic powder in the same manner as sample numbers 8a to 8d, and the magnetic properties of the toroidal cores were evaluated in the same manner as sample numbers 8a to 8d, and Isat at μi shown in Table 16 was calculated. From the calculated Isat, the Isat improvement rate was calculated relative to the Isat of sample numbers having the same average particle diameter. For example, the Isat improvement rate of sample number 415 is a value when the Isat of sample number 414 having the same average particle diameter is set to 100%. The results are shown in Table 16.

[0110] [Table 16]

[0111] From Table 16, when only the soft magnetic powder containing the above-mentioned soft magnetic particles is used and the average particle diameter is changed, σ FeCo (S)-σ FeCo It was confirmed that when (C) is within the above-mentioned range, the improvement rate of Isat is large, and a magnetic core having excellent DC bias characteristics can be obtained. [Explanation of symbols]

[0112] 1...Soft magnetic powder 2...Soft magnetic particles 3…Coating 10…Magnetic core 21...Large particles 22...Small particles 5…Resin

Claims

1. A soft magnetic powder comprising soft magnetic particles containing at least one selected from iron and cobalt, The element distribution obtained by analyzing the surface layer of the soft magnetic particle by a three-dimensional atom probe method is divided into a plurality of grids, the sum of the iron content rate and the cobalt content rate in each grid is calculated, and the standard deviation of the sum of the iron content rate and the cobalt content rate when the plurality of grids are used as a population is defined as σ FeCo (S), The element distribution obtained by analyzing the center portion of the soft magnetic particle by a three-dimensional atom probe method is divided into a plurality of grids, the sum of the iron content rate and the cobalt content rate in each grid is calculated, and the standard deviation of the sum of the iron content rate and the cobalt content rate when the plurality of grids are used as a population is defined as σ FeCo When expressed as (C), σ FeCo (S)-σ FeCo (C) A soft magnetic powder satisfying the relationship: ≧0.

005.

2. A magnetic core comprising the soft magnetic powder according to claim 1.

3. A magnetic device comprising the magnetic core according to claim 2.

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