Soft magnetic powder, magnetic core, and magnetic device

Abstract

Provided are a magnetic core and a magnetic device having excellent DC superposition characteristics, and a soft magnetic powder suitable for the magnetic core and the magnetic device. The soft magnetic powder contains soft magnetic particles containing at least one selected from the group consisting of Fe and Co, the element distribution obtained by the 3DAP method in the surface layer part of the soft magnetic particles is divided into a plurality of grids, and the sum of the Fe content ratio and the Co content ratio in each grid is calculated. The standard deviation of the sum of the Fe content ratio and the Co content ratio when a plurality of grids are taken as a whole is expressed as [sigma] FeCo (S), the element distribution obtained by the 3DAP method for the central part of the soft magnetic particles is divided into a plurality of grids, and the sum of the Fe content ratio and the Co content ratio in each grid is calculated. When the standard deviation of the sum of the Fe content ratio and the Co content ratio when a plurality of grids are taken as a whole is expressed as sigma FeCo (C), sigma FeCo (S)-sigma FeCo (C) > = 0.005.

Description

Technical Field

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

[0002] In recent years, there has been a trend of miniaturization and high output requirements for power supplies, and there has been a trend of miniaturization and high current requirements for magnetic components used in power supply circuits. As a method of miniaturizing magnetic components, it is effective to use a magnetic core with high magnetic permeability to form the component. However, if the magnetic permeability is increased, the magnetic core will be saturated even in a small magnetic field, so the result is that the limit value of the DC superposition current is reduced, and there is a trend that it cannot cope with high currents.

[0003] As a method for simultaneously solving the problems of miniaturization and high current, Patent Document 1 discloses a method of densely filling magnetic powder with high saturation magnetic flux density to form a magnetic core. Patent Document 2 discloses a method of interposing an insulating material between particles of magnetic powder.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2002-75721

[0007] Patent Document 2: Japanese Patent Application Publication No. 2002-33211 Summary of the invention

[0008] Technical problem to be solved by the invention

[0009] The present invention has been made in view of such actual circumstances, and an object of the present invention is to provide a magnetic core and a magnetic device having excellent DC superposition characteristics, and a soft magnetic powder suitable for the magnetic core and the magnetic device.

[0010] Solutions for solving technical problems

[0011] The aspects of the present invention are as follows.

[0012] [1] A soft magnetic powder comprising soft magnetic particles containing at least one selected from iron and cobalt,

[0013] The element distribution obtained by analyzing the surface of the soft magnetic particles by the three-dimensional atom probe method is divided into a plurality of grids, and the sum of the iron content ratio and the cobalt content ratio in each grid is calculated. The standard deviation of the sum of the iron content ratio and the cobalt content ratio when the plurality of grids are taken as a whole is expressed as σ FeCo (S),

[0014] The element distribution obtained by analyzing the center of the soft magnetic particles by the three-dimensional atom probe method is divided into multiple grids, and the sum of the iron content ratio and the cobalt content ratio in each grid is calculated. The standard deviation of the sum of the iron content ratio and the cobalt content ratio when the multiple grids are taken as a whole is expressed as σ FeCo (C)

[0015] Satisfy σ FeCo (S)-σ FeCo (C)≥0.005.

[0016] [2] A magnetic core comprising the soft magnetic powder described in [1].

[0017] [3] A magnetic device comprising the magnetic core described in [2]. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic cross-sectional view of the soft magnetic powder according to the present embodiment.

[0019] Figure 2 This is a schematic diagram for explaining the range observed by 3DAP in soft magnetic particles.

[0020] Figure 3 It is a schematic cross-sectional view of the magnetic core of this embodiment.

[0021] Figure 4A These are the results of observing the distribution of iron by 3DAP for the samples of the examples.

[0022] Figure 4B These are the results of observing the distribution of cobalt by 3DAP for the samples of the examples.

[0023] Explanation of symbols:

[0024] 1…soft magnetic powder; 2…soft magnetic particles; 3…coating; 10…magnetic core; 21…large diameter particles; 22…small diameter particles; 5…resin DETAILED DESCRIPTION

[0025] (1. Soft magnetic powder)

[0026] like Figure 1 As shown, the soft magnetic powder 1 of the present embodiment includes a plurality of soft magnetic particles 2. In the soft magnetic powder 1, the positions of the soft magnetic particles 2 are not fixed, and the soft magnetic powder 1 has fluidity.

[0027] The average particle size (D50) of the soft magnetic powder of this embodiment can be selected according to the application, etc. For example, the average particle size (D50) can also be in the range of 3 to 100 μm. The average particle size can be controlled by powder manufacturing conditions or by classification treatment, etc. In this specification, the particle size of the soft magnetic particles is the particle size measured by the laser diffraction scattering method.

[0028] In addition, as the shape of the soft magnetic particles, a spherical or nearly spherical shape is exemplified. For example, the average circularity of the cross section of the soft magnetic particles can be 0.7 or more, preferably 0.85 or more, and more preferably 0.9 or more. As the circularity, for example, Wadell's circularity can be used.

[0029] As long as the soft magnetic powder satisfies the relationship described below, it can only contain soft magnetic particles of the same material, or it can mix soft magnetic particles of different materials. In addition, different materials are exemplified by different elements constituting the soft magnetic metal, or different compositions even if the elements constituting the soft magnetic metal are the same.

[0030] In the present embodiment, an insulating coating may be formed in a manner that covers at least a portion of the surface of the soft magnetic particles. As the insulating coating, for example, it may be an oxide film formed by oxidation of the surface of the soft magnetic particles, or it may be a coating formed on the surface of the soft magnetic particles using an insulating material. As the insulating material, inorganic materials such as oxides, nitrides, and carbides are preferred. As oxides, SiO2, MgO, Al2O3, phosphates, silicates, borosilicates, bismuthates, etc. are exemplified, and they may be crystalline or glass. As oxide glass, phosphate-based glass, bismuth-based glass, borosilicate-based glass, etc. are exemplified. The coating may also be composed of a plurality of coatings. For example, it is also possible to form a coating using an insulating material on an oxide film formed by oxidation of the surface of the soft magnetic particles.

[0031] The average thickness of the coating portion is preferably from 1 nm to 250 nm, and more preferably from 20 nm to 250 nm.

[0032] The soft magnetic powder of the present embodiment may include only soft magnetic particles without a coating, may include both soft magnetic particles without a coating and soft magnetic particles with a coating, or may include only soft magnetic particles with a coating.

[0033] In the present embodiment, the soft magnetic particles are composed of a soft magnetic metal containing at least one element selected from iron (Fe) and cobalt (Co). That is, the soft magnetic particles can be composed of a soft magnetic metal containing iron, a soft magnetic metal containing cobalt, or a soft magnetic metal containing iron and cobalt. In the present embodiment, the soft magnetic metal is preferably a soft magnetic metal containing iron, or a soft magnetic metal containing iron and cobalt.

[0034] 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.

[0035] The soft magnetic metal containing at least one element selected from iron and cobalt may contain elements other than iron and cobalt. Furthermore, the soft magnetic metal may contain element X, chromium (Cr), nickel (Ni), or element M.

[0036] The element X is at least one element selected from B (boron), Si (silicon), P (phosphorus), and C (carbon). By including the element X, the crystal magnetoanisotropy can be reduced, and thus the coercive force can be reduced.

[0037] 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 containing the element M and changing the content, the amorphous structure and the nanocrystalline structure can be controlled, and a structure that can obtain good soft magnetic properties can be obtained.

[0038] In the present embodiment, when Cr is contained, a powder having high corrosion resistance can be obtained.

[0039] In the present embodiment, the composition of the soft magnetic metal containing at least one element selected from iron and cobalt can be represented by a composition formula based on the number of atoms: 1-α Co α ) 100-w-x-y-z Ni w X x Cr y M zIn the above composition formula, X is the above element X and is at least one element selected from B, Si, P and C. M is the above element M and 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.

[0040] In the above composition formula, "α", "w", "x", "y" and "z" preferably satisfy the relationship of 0≤α≤1, 0≤w≤80, 3≤x≤30, 0≤y≤8, and 0≤z≤11.

[0041] The soft magnetic metal may contain elements other than the above elements as inevitable impurities. For example, the content of the elements other than the above elements in 100 mass % of the soft magnetic metal may be 0.1 mass % or less, preferably 0.05 mass % or less.

[0042] In this embodiment, elemental analysis is performed on the surface and center of the soft magnetic particles by a three-dimensional atom probe method. Figure 2 As shown, the surface layer S is a region from the surface to 500 nm in the direction from the surface of the soft magnetic particle 2 toward the center. The surface of the soft magnetic particle is the outermost surface 2a of the region in which the composition of the soft magnetic metal is maintained in the particle. Therefore, in the case where a coating (including a natural oxide film) 3 is formed on the soft magnetic particle, the outermost surface 2a of the region in which the composition of the soft magnetic metal is maintained is the surface of the soft magnetic particle, not the outermost surface 3a of such a coating 3.

[0043] like Figure 2 As shown, the center portion C is a region extending from the center 2b of the soft magnetic particle 2 to 300 nm in the direction toward the surface. When the soft magnetic particle has a shape other than a sphere, the center of gravity of the soft magnetic particle is taken as the center.

[0044] The three-dimensional atom probe (3DAP) method is a method in which a high electric field is applied to the tip of a needle-shaped sample, atoms present on the sample surface are ionized and released from the sample, and the released ions are detected by a detector. The distribution of elements constituting the sample can be observed three-dimensionally by the flight time to the detector and the detected position.

[0045] As Figure 2 The observation range A of the element distribution shown in FIG. 1 may be any range as long as the standard deviation of the total content ratio of iron and cobalt described later can be calculated. In the present embodiment, the observation range is set to 3200 nm. 3 Above, preferably 20000nm 3The shape of the observation range may be arbitrarily set in consideration of the shape of the grid formed by dividing the observation range. For example, the shape of the observation range is a rectangular parallelepiped.

[0046] The observation range is divided into a plurality of grids. The shape of the grid can be set to a cube, for example. The size of the grid can be set according to the number of grids. The number of grids becomes the total number of standard deviations of the total content ratio of iron and cobalt for calculation, and therefore, it is preferably the number of the degree of the standard deviation that can be calculated with high accuracy. In the present embodiment, the number of grids is set to 400 or more.

[0047] Therefore, when the observation range is set to a rectangular parallelepiped of, for example, 10 nm×10 nm×200 nm, the rectangular parallelepiped is divided into 2500 cubes of 2 nm×2 nm×2 nm.

[0048] Next, in each divided grid, the iron content ratio (concentration) and the cobalt content ratio (concentration) are calculated, and the sum of the iron content ratio and the cobalt content ratio in each grid is calculated. As a whole, the soft magnetic metal has a uniform composition, but the sum of the iron content ratio and the cobalt content ratio in a tiny local area such as a grid sometimes changes for each grid (sometimes a deviation is shown for each grid). Such a deviation of each grid is expressed as the standard deviation of the sum of the iron content ratio and the cobalt content ratio. That is, the sum of the iron content ratio and the cobalt content ratio in the divided grid, for example, 2500 grids, is used as a whole, and the standard deviation of the sum of the iron content ratio and the cobalt content ratio is calculated.

[0049] In the present embodiment, the standard deviation of the sum of the content ratio of iron and the content ratio of cobalt in the surface layer of the soft magnetic particles is σ FeCo (S), the standard deviation of the sum of the iron content and the cobalt content in the center of the soft magnetic particles is σ FeCo (C), σ FeCo (S) and σ FeCo (C) satisfies σ FeCo (S)-σ FeCo (C) ≥ 0.005. That is, the deviation of the sum of the iron content and the cobalt content in the surface layer is somewhat greater than the deviation of the sum of the iron content and the cobalt content in the center portion.

[0050] It is believed that the deviation of the sum of the ratio of the iron content and the ratio of the cobalt content in the surface portion is large, which means that near the surface of the soft magnetic particles, the uniformity of the interatomic distance of the constituent elements is reduced, and deformation and stress remain near the surface of the soft magnetic particles. On the other hand, near the center of the soft magnetic particles, compared with the surface, the uniformity of the interatomic distance of the constituent elements is higher, and therefore, it is believed that the residual stress near the center is reduced. Such residual stress causes the reduction of magnetic permeability, and therefore, in the soft magnetic particles that meet the relationship of the above-mentioned standard deviation, it is inferred that only the magnetic permeability near the surface is reduced.

[0051] Here, in a magnetic core filled with magnetic powder, the close magnetic gap between particles has a strong influence on the DC superposition characteristics. Therefore, by reducing the extremely narrow magnetic gap between particles such as the part where the particles are in contact with each other (the narrow gap part between particles), the DC superposition characteristics are improved. Reducing the narrow gap part between particles is synonymous with forming a region with low magnetic permeability between particles. Therefore, the DC superposition characteristics of the magnetic core obtained using soft magnetic powder containing soft magnetic particles whose standard deviation satisfies the above relationship are improved.

[0052] Furthermore, because there is lattice distortion accompanied by residual stress near the surface, it is inferred that there is a trend of reduction in the continuous sliding surface when deforming when pressure is applied from the outside. In addition, the area of ​​the narrow gap between particles increases due to the deformation of the particles caused by the punching when the magnetic body is filled and formed, which also becomes the reason for reducing the DC superposition characteristics of the magnetic core. Therefore, by using a soft magnetic powder containing soft magnetic particles whose standard deviation satisfies the above-mentioned relationship, the particles can be deformed without being pressed, and the particles move in the direction of filling the gaps to reduce the volume. As a result, it is inferred that the area of ​​the narrow gap between particles can be reduced, and the DC superposition characteristics can be improved.

[0053] 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 value of (C) is not particularly limited, but may be 1.024 from the viewpoint of the production method.

[0054] σ FeCo (S) and σ FeCo The measurement of (C) is performed at one point in one particle, and its measured value can be set as σ in the particle. FeCo (S) and σ FeCo (C) The above measurement is performed on a plurality of soft magnetic particles. In this embodiment, when the ratio of the number of the plurality of soft magnetic particles measured is set to 100%, σ FeCo (S)-σ FeCo(C) The number ratio of the soft magnetic particles satisfying the above relationship is preferably 50% or more, more preferably 65% ​​or more.

[0055] (2. Method for producing soft magnetic powder)

[0056] As a method for producing the soft magnetic powder of the present embodiment, any method that can produce the soft magnetic powder satisfying the above-mentioned σ FeCo In this embodiment, after the soft magnetic powder is produced by a known method for producing a soft magnetic powder, the soft magnetic powder is post-processed.

[0057] As known methods for producing soft magnetic powder, carbonyl method, spray pyrolysis method, CVD method, PVD method, gas atomization method, water atomization method, rotating disk method, etc. are exemplified. In addition, a method of obtaining powder by crushing a thin ribbon obtained by a single roller method is exemplified. In order to control the average particle size of the obtained powder, classification treatments such as air flow classification, wet classification, and dry classification may also be performed. In this embodiment, atomization methods such as gas atomization method and water atomization method are preferred.

[0058] As a post-treatment of the soft magnetic powder, a quenching treatment is performed in which the soft magnetic powder is rapidly cooled after being heat-treated. The heat treatment conditions vary depending on the composition, and the heat treatment temperature can be above 300°C, above 500°C, or above 800°C. The upper limit of the heat treatment temperature can be set according to the composition of the soft magnetic metal, etc. In addition, the holding time of the heat treatment temperature can be set to 1 minute to 1 hour. The atmosphere during the heat treatment can be set to an inert atmosphere. As an inert atmosphere, a nitrogen atmosphere, an argon atmosphere, etc. are exemplified. In addition, the heat treatment can also serve as a heat treatment for precipitating nanocrystals.

[0059] After the heat treatment, the soft magnetic powder is quenched. As a method of quenching, a method of immediately putting the soft magnetic powder after the heat treatment into running water is exemplified. The temperature of the running water is preferably 0 to 30°C. In addition, 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 large, it is easy to manufacture a material that satisfies the above-mentioned σ FeCo The relationship between soft magnetic particles.

[0060] By performing rapid cooling after the heat treatment, the surface layer of the soft magnetic particles is more likely to be deformed. On the other hand, the center portion is more likely to be deformed and less likely to be rapidly cooled. Therefore, σ FeCo (S) is easier than σ FeCo (C) is large, which easily satisfies the above σ FeCo relationship.

[0061] In addition, it is not easy to produce a soft magnetic powder that satisfies the above-mentioned σ by cooling the soft magnetic powder by air cooling or other cooling methods after the heat treatment. FeCo In addition, even if the cooling method of the soft magnetic powder after the heat treatment is not in running water but in still water, it is not easy to produce soft magnetic particles that meet the above σ FeCo The relationship between soft magnetic particles.

[0062] The powder after rapid cooling is recovered to obtain the soft magnetic powder of the present embodiment.

[0063] (3. Magnetic core)

[0064] The magnetic core of this embodiment is formed to include the above-mentioned soft magnetic powder and have a predetermined shape. 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, becoming one of the components of the magnetic core. Since the magnetic core of this embodiment includes the above-mentioned soft magnetic powder, the DC superposition characteristics of the magnetic core are improved.

[0065] The magnetic core of the present embodiment may contain powders 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 a plurality of soft magnetic powders including the soft magnetic powder described above.

[0066] In the case where the magnetic core contains a plurality of soft magnetic powders, the composition of the particles contained in each powder may be the same or different. In addition, the average particle size of each powder may be the same or different. For example, in the magnetic core, two types of powders, large-diameter powder with a large average particle size and small-diameter powder with a small average particle size, may be included, or three types of powders with different average particle sizes (large-diameter powder, medium-diameter powder, and small-diameter powder) may be included. The mass ratio of large-diameter powder and small-diameter powder, or the mass ratio of large-diameter powder, medium-diameter powder, and small-diameter powder can be set as long as the magnetic properties obtained are taken into consideration. With respect to the mass ratio of large-diameter powder and small-diameter powder, for example, large-diameter powder can be set to 20 to 100 mass%, and small-diameter powder can be set to 0 to 80 mass%. In addition, with respect to the mass ratio of large-diameter powder, medium-diameter powder, and small-diameter powder, for example, medium-diameter powder is set to 20 to 80 mass%, and the remaining part can be distributed according to large-diameter powder and small-diameter powder. There is no particular limitation on the distribution ratio, for example, it can be set to 10 to 90%.

[0067] When the magnetic core contains multiple soft magnetic powders, the soft magnetic powder is preferably contained as a powder with a larger average particle size (large diameter powder, medium diameter powder). In addition, the soft magnetic powder is preferably contained in 100% by mass of the powder contained in the magnetic core, and more preferably contains 30% by mass to 100% by mass.

[0068] The magnetic core may contain a binder for bonding the particles in the powder to each other in addition to the powder. Examples of the binder include thermosetting resins such as epoxy resins, phenolic resins, and silicone resins. By including a resin such as Figure 3 As shown, in the magnetic core 10 , the soft magnetic particles (large diameter particles 21 of large diameter powder and small diameter particles 22 of small diameter powder) are bonded to each other via the resin 5 and fixed in a predetermined shape.

[0069] The ratio of the soft magnetic particles in the magnetic core (filling rate) may be 70 to 90%.

[0070] The manufacturing method of the magnetic core can adopt a known method. First, a powder containing at least the above-mentioned soft magnetic powder and a binder (for example, a thermosetting resin) are mixed to obtain a mixture. In addition, the obtained mixture can also be made into granulated powder as needed. The amount of the binder can be set to 1 to 5 parts by mass relative to 100 parts by mass of the powder.

[0071] Next, the mixture or granulated powder is filled into a mold and compression-molded to obtain a molded body having the shape of a magnetic core. The filling rate can be controlled by the pressure during compression molding.

[0072] The obtained 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.

[0073] (4. Magnetic devices)

[0074] The magnetic device of this embodiment has the above-mentioned magnetic core. The magnetic device may have a structure in which a coil is buried inside the magnetic core, or may have a structure in which a wire is wound on the surface of the magnetic core. Examples of such magnetic devices include inductors, transformers, choke coils, and the like.

[0075] As mentioned above, although embodiment of this invention was demonstrated, this invention is not limited to any embodiment mentioned above, It can also be changed in various aspects within the scope of this invention.

[0076] Example

[0077] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples.

[0078] (Experiment 1)

[0079] In Experiment 1, magnetic cores of Sample Nos. 1a to 13d were produced using a mixed powder obtained by mixing large-diameter powder composed of the above-mentioned soft magnetic powder and small-diameter powder composed of pure iron (Fe) powder. The average particle size (D50) of the small-diameter powder was 1 μm.

[0080] The soft magnetic powder (large diameter powder) is prepared as follows. First, the atomic ratio is (Fe 0.75 Co 0.25 ) 90 Si 10 The raw metals are weighed in the form of a composition and placed in a crucible disposed in an atomizing device. Next, the chamber of the atomizing device is evacuated, and the crucible is heated by high-frequency induction using a working coil disposed outside the crucible, so that the raw metals in the crucible are melted and mixed to obtain a melt (molten metal) at 1500°C.

[0081] The obtained molten metal is passed through a nozzle provided at the bottom of the crucible, and supplied into the chamber as a linear continuous fluid, and water is sprayed on the supplied molten metal to obtain a soft magnetic powder. The obtained soft magnetic powder has a crystalline structure, and its average particle size (D50) is 20 μm. In addition, ICP analysis confirms that the composition of the soft magnetic powder is consistent with the composition of the weighed raw metal.

[0082] The obtained soft magnetic powders were subjected to the following post-treatment except for sample numbers 1a to 1d. In 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 set to a nitrogen atmosphere, the heating temperature during the heat treatment was set to the temperature shown in Table 1, and the holding time was set to 1 hour.

[0083] In sample numbers 2a to 2d, after the heat treatment was completed, the soft magnetic powder was left to cool in the furnace, and the soft magnetic powder was recovered from the heat treatment furnace when the temperature in the furnace dropped to room temperature.

[0084] In sample numbers 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 for rapid cooling, and the soft magnetic powder was recovered.

[0085] In sample numbers 13a to 13d, immediately after the heat treatment, the soft magnetic powder was dropped into still water at a temperature of 25°C for rapid cooling, and the soft magnetic powder was recovered.

[0086] In sample numbers 1a to 13d, needle-shaped samples were prepared at the surface and center of a plurality of particles in the recovered soft magnetic powder, and observed by the 3DAP method to obtain the distribution of elements contained in the particles. In this embodiment, the surface of the particle is set to be a 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 is removed, and the center of the particle is set to be a region located ±100 nm from the center in the direction from the center of the particle to the surface.

[0087] The observation range of 3DAP was set to 10nm×10nm×200nm. The observation range was divided into 2500 cubic grids of 2nm×2nm×2nm, and the content ratio of iron (Fe) and cobalt (Co) in each grid was calculated. Figure 4A The results of observing the distribution of iron by 3DAP are shown in Figure 4B The results of observing the distribution of cobalt by 3DAP are shown in FIG.

[0088] Based on the calculated iron and cobalt content ratios, calculate the sum of the iron content ratio and the cobalt content ratio in each grid (total content ratio). Calculate the standard deviation σ of the sum of the iron and cobalt content ratios based on the calculated 2500 data as a whole. FeCo . The surface part of σ FeCo Denoted as σ FeCo (S), the center part σ FeCo Denoted as σ FeCo (C). By obtaining σ FeCo Subtract σ from (S) FeCo (C), calculate σ FeCo (S)-σ FeCo (C) The results are shown in Table 1.

[0089] In addition, σ FeCo (S)-σ FeCo (C) The number ratio of particles within the above range is 65% or more in all samples with sample numbers 3a to 12d. In addition, in the odd-numbered samples among the sample numbers 15 to 421 described later, σ FeCo (S)-σ FeCo (C) The number ratio of particles within the above range is 65% or more.

[0090] In sample numbers 1a to 13d, the obtained soft magnetic powder (large diameter powder) and pure iron powder (small diameter powder) were mixed in such a manner that the ratio of the large diameter powder was 80 mass % and the ratio of the small diameter powder was 20 mass %, thereby obtaining a mixed powder. The obtained mixed powder was kneaded with an epoxy resin to prepare a mixture. The amount of the epoxy resin was set to 2.5 mass parts relative to 100 mass parts of the mixed powder.

[0091] In sample numbers 1a to 1d, the obtained mixture is filled into a mold of a specified annular shape, and the molding pressure is changed to obtain a molded body with different filling rates of the mixed powder. The epoxy resin contained in the obtained molded body is thermally cured at 180°C for 60 minutes to produce an annular core (outer diameter 11 mm, inner diameter 6.5 mm, thickness 2.5 mm). The filling rate of the mixed powder in the obtained annular core is shown in Table 1. In addition, the filling rate of the mixed powder in the annular core is calculated by dividing the density of the annular core calculated based on the size and mass of the annular core by the theoretical density of the annular core calculated based on the specific gravity of various materials.

[0092] Copper wire was wound around each sample of the toroidal core of sample number 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 superposition current, that is, when the DC superposition current was 0 A. The relative magnetic permeability was calculated from the obtained inductance, and this value was set as the initial relative magnetic permeability μi. The results are shown in Table 1.

[0093] Next, the DC superimposed current was gradually increased from 0 A for each sample of the toroidal core of sample number 1a to 1d wound with copper wire. The DC superimposed current value when the DC superimposed current decreased by 10% from μi at 0 A was measured and the current value was defined as Isat (unit: A). The results are shown in Table 1.

[0094] Based on 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 was defined as “Isat at μi=30” (A).

[0095] For each group of sample numbers 2a to 2d, sample numbers 3a to 3d, sample numbers 4a to 4d, sample numbers 5a to 5d, sample numbers 6a to 6d, sample numbers 7a to 7d, sample numbers 8a to 8d, sample numbers 9a to 9d, sample numbers 10a to 10d, sample numbers 11a to 11d, sample numbers 12a to 12d, and sample numbers 13a to 13d, the obtained soft magnetic powder was also used to prepare a mixed powder and a ring core by the same method as sample numbers 1a to 1d, and the magnetic properties of the ring core were evaluated by the same method as sample numbers 1a to 1d, and "Isat atμi=30" was calculated. The value of "Isat atμi=30" when "Isat atμi=30" calculated in sample numbers 1a to 1d was 100% was set as the Isat improvement rate (%). The larger the Isat improvement rate, the better the DC superposition characteristics. In this embodiment, samples with an Isat improvement rate of 110% or more were judged to be good. Table 1 shows the results.

[0096] [Table 1]

[0097]

[0098] It can be confirmed from Table 1 that FeCo (S)-σ FeCo (C) In the case where the value is within the above range, the Isat improvement rate becomes large, and a magnetic core having excellent DC superposition characteristics is obtained.

[0099] (Experiment 2)

[0100] For even-numbered sample numbers, except that the composition of the soft magnetic powder (large diameter powder) is set to the composition shown in Tables 2 to 12, the mixed powder and the ring core are prepared by the same method as sample numbers 1a to 1d, the magnetic properties of the ring core are evaluated by the same method as sample numbers 1a to 1d, and Isat under μi shown in Tables 2 to 12 is calculated. That is, in each sample number, as in Experiment 1, the specified μi is set as a representative value based on the magnetic properties of the four samples, and Isat under the set μi is calculated. The results are shown in Tables 2 to 12.

[0101] For the odd-numbered sample numbers shown in Tables 2 to 6, mixed powders were prepared by the same method as sample numbers 8a to 8d, except that the composition of the soft magnetic powder (large diameter powder) was set to the composition shown in Tables 2 to 6. In addition, for the odd-numbered sample numbers shown in Tables 7 to 12, mixed powders were prepared by the same method as sample numbers 8a to 8d, except that the composition of the soft magnetic powder (large diameter powder) was set to the composition shown in Tables 7 to 12 and the quenching treatment conditions were set to the conditions shown in Tables 7 to 12. Using the prepared mixed powders, an annular core was prepared by the same method as sample numbers 8a to 8d, and the magnetic properties of the annular core were evaluated by the same method as sample numbers 8a to 8d, and Isat under μi shown in Tables 2 to 12 was calculated. Based on the calculated Isat, the Isat improvement rate relative to the Isat of the sample number with the same composition was calculated. For example, the Isat improvement rate of sample number 15 is the value when the Isat of sample number 14 with the same composition is 100%. The results are shown in Tables 2 to 12.

[0102] [Table 2]

[0103]

[0104] [Table 3]

[0105]

[0106] [Table 4]

[0107]

[0108] [Table 5]

[0109]

[0110] [Table 6]

[0111]

[0112] [Table 7]

[0113]

[0114] [Table 8]

[0115]

[0116] [Table 9]

[0117]

[0118] [Table 10]

[0119]

[0120] [Table 11]

[0121]

[0122] [Table 12]

[0123]

[0124] It can be confirmed from Tables 2 to 12 that FeCo (S)-σ FeCo (C) In the case where the value is within the above range, the Isat improvement rate becomes large, and a magnetic core having excellent DC superposition characteristics is obtained.

[0125] (Experiment 3)

[0126] For even-numbered sample numbers, soft magnetic powders were manufactured by the same method as sample numbers 1a to 1d, and a coating was formed on the surface of the soft magnetic particles by a mechanical fusion 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. In addition, the thickness of the coating was controlled by the amount of coating material added to form the coating.

[0127] A mixed powder was obtained using soft magnetic powder containing soft magnetic particles with a coating formed thereon, and a toroidal core was manufactured by the same method as sample numbers 1a to 1d. The magnetic properties of the toroidal core were evaluated by the same method as sample numbers 1a to 1d, and Isat under μi shown in Table 13 was calculated. That is, in each sample number, as in Experiment 1, a specified μi was set as a representative value based on the magnetic properties of four samples, and Isat under the set μi was calculated. The results are shown in Table 13.

[0128] For the odd-numbered sample numbers, soft magnetic powders were manufactured by the same method as sample numbers 8a to 8d, and a coating was formed on the surface of the soft magnetic particles by a mechanical fusion 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. In addition, the thickness of the coating was controlled by the amount of coating material added to form the coating.

[0129] A mixed powder was obtained using soft magnetic powder containing soft magnetic particles with a coating formed thereon, and a toroidal core was prepared by the same method as sample numbers 8a to 8d. The magnetic properties of the toroidal core were evaluated by the same method as sample numbers 8a to 8d, and Isat under μi shown in Table 13 was calculated. Based on the calculated Isat, the Isat improvement rate was calculated relative to the Isat of the sample number with the same composition and thickness of the oxide glass constituting the coating. For example, the Isat improvement rate of sample number 389 is the value when the Isat of sample number 388 with the same composition and thickness of the oxide glass is 100%. The results are shown in Table 13.

[0130] [Table 13]

[0131]

[0132] It can be confirmed from Table 13 that for the soft magnetic particles having a coating formed on the surface, FeCo (S)-σ FeCo (C) In the case where the value is within the above range, the Isat improvement rate becomes large, and a magnetic core having excellent DC superposition characteristics is obtained.

[0133] (Experiment 4)

[0134] For even-numbered sample numbers, soft magnetic powder was manufactured by the same method as 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 ring core was manufactured by the same method as sample numbers 1a to 1d, and the magnetic properties of the ring core were evaluated by the same method as sample numbers 1a to 1d, and Isat under μi shown in Table 14 was calculated. That is, in each sample number, as in Experiment 1, the specified μi was set as a representative value based on the magnetic properties of the four samples, and Isat under the set μi was calculated. The results are shown in Table 14.

[0135] For odd-numbered sample numbers, soft magnetic powder is 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) are mixed in the ratio shown in Table 14 to obtain a mixed powder. Using the obtained mixed powder, a ring core is manufactured by the same method as sample numbers 8a to 8d, and the magnetic properties of the ring core are evaluated by the same method as sample numbers 8a to 8d, and Isat under μi shown in Table 14 is calculated. Based on the calculated Isat, the Isat improvement rate is calculated relative to the Isat obtained by the sample number with the same mixing ratio of large diameter powder and small diameter powder. For example, the Isat improvement rate of sample number 399 is the value when the Isat of sample number 398 with the same mixing ratio of large diameter powder and small diameter powder is 100%. The results are shown in Table 14.

[0136] [Table 14]

[0137]

[0138] It can be confirmed from Table 14 that even if the mixing ratio of the soft magnetic powder containing the above-mentioned soft magnetic particles is changed, FeCo (S)-σ FeCo (C) In the case where the value is within the above range, the Isat improvement rate is also large, and a magnetic core having excellent DC superposition characteristics is obtained.

[0139] (Experiment 5)

[0140] For even-numbered sample numbers, soft magnetic powders were produced by the same method 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 set as the large-diameter powder, the obtained soft magnetic powder was set as the medium-diameter powder, and the pure iron powder used in Experiment 1 was set as the small-diameter powder. The average particle size of the large-diameter powder was 20 μm.

[0141] 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 ring core by the same method as sample numbers 1a to 1d, and the magnetic properties of the ring core were evaluated by the same method as sample numbers 1a to 1d, and Isat under μi shown in Table 15 was calculated. That is, in each sample number, as in Experiment 1, the specified μi was set as a representative value based on the magnetic properties of the four samples, and Isat under the set μi was calculated. The results are shown in Table 15.

[0142] For the odd-numbered sample numbers, soft magnetic powders were produced by the same method as sample numbers 8a to 8d, 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 set as the large-diameter powder, the obtained soft magnetic powder was set as the medium-diameter powder, and the pure iron powder used in Experiment 1 was set as the small-diameter powder. The average particle size of the large-diameter powder was 20 μm.

[0143] A large diameter powder, a medium diameter powder, and a small diameter powder are mixed in the ratio shown in Table 15 to obtain a mixed powder. Using the obtained mixed powder, a ring core is made by the same method as sample numbers 8a to 8d, and the magnetic properties of the ring core are evaluated by the same method as sample numbers 8a to 8d, and Isat under μi shown in Table 15 is calculated. Based on the calculated Isat, the Isat improvement rate is calculated relative to the Isat of the sample number with the same mixing ratio of large diameter powder, medium diameter powder, and small diameter powder. For example, the Isat improvement rate of sample number 407 is the value when the Isat of sample number 406 with the same mixing ratio of large diameter powder, medium diameter powder, and small diameter powder is 100%. The results are shown in Table 15.

[0144] [Table 15]

[0145]

[0146] It can be confirmed from Table 15 that when the soft magnetic powder containing the above-mentioned soft magnetic particles is set as the medium diameter powder, even if the mixing ratio is changed, the FeCo (S)-σ FeCo (C) In the case where the value is within the above range, the Isat improvement rate becomes large, and a magnetic core having excellent DC superposition characteristics is obtained.

[0147] (Experiment 6)

[0148] For even-numbered sample numbers, soft magnetic powders were manufactured by the same method as sample numbers 1a to 1d, except that the average particle size was set to the value shown in Table 16 by classification. Ring cores were manufactured by the same method as sample numbers 1a to 1d using only the manufactured soft magnetic powders, and the magnetic properties of the ring cores were evaluated by the same method as sample numbers 1a to 1d, and Isat at μi shown in Table 16 was calculated. That is, in each sample number, the specified μi was set as a representative value based on the magnetic properties of the four samples, and Isat at the set μi was calculated, as in Experiment 1. The results are shown in Table 16.

[0149] For odd-numbered sample numbers, soft magnetic powders were manufactured by the same method as sample numbers 8a to 8d, except that the average particle size was set to the value shown in Table 16 by classification. Using only the manufactured soft magnetic powder, an annular core was manufactured by the same method as sample numbers 8a to 8d, and the magnetic properties of the annular core were evaluated by the same method as sample numbers 8a to 8d, and Isat under μi shown in Table 16 was calculated. Based on the calculated Isat, the Isat improvement rate relative to the Isat of the sample number with the same average particle size was calculated. For example, the Isat improvement rate of sample number 415 is the value when the Isat of sample number 414 with the same average particle size is 100%. The results are shown in Table 16.

[0150] [Table 16]

[0151]

[0152] It can be confirmed from Table 16 that if only the soft magnetic powder containing the above-mentioned soft magnetic particles is used and the average particle size is changed, FeCo (S)-σ FeCo (C) In the case where the value is within the above range, the Isat improvement rate becomes large, and a magnetic core having excellent DC superposition characteristics is obtained.

Claims

1. A soft magnetic powder, wherein: The soft magnetic powder comprises soft magnetic particles containing at least one selected from iron and cobalt, The element distribution obtained by analyzing the surface of the soft magnetic particles by a three-dimensional atom probe method is divided into a plurality of grids, the sum of the iron content ratio and the cobalt content ratio in each grid is calculated, and the standard deviation of the sum of the iron content ratio and the cobalt content ratio when the plurality of grids are taken as a whole is expressed as σ FeCo (S), The element distribution obtained by analyzing the central part of the soft magnetic particles by the three-dimensional atom probe method is divided into a plurality of grids, and the sum of the iron content ratio and the cobalt content ratio in each grid is calculated. The standard deviation of the sum of the iron content ratio and the cobalt content ratio when the plurality of grids are taken as a whole is expressed as σ FeCo (C) Satisfy σ FeCo (S)-σ FeCo (C)≥0.

005.

2. A magnetic core, wherein: Contains the soft magnetic powder according to claim 1.

3. A magnetic device, wherein: A magnetic core according to claim 2 is provided.

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