Soft magnetic powder and magnetic cores

Abstract

To provide soft magnetic powder used for the production of a magnetic substance core having a high relative magnetic permeability and high DC superposition properties.SOLUTION: Soft magnetic powder comprises Fe and Co. The total content of Fe and Co with respect to the whole of the soft magnetic powder is 90 mass% or more. The content of Fe with respect to the total content of Fe and Co is 30 or more to 95 or less mass%. The average particle diameter of the soft magnetic powder is 0.10 μm or more to 5.0 μm or less. An oxygen content in the surface of the soft magnetic powder is 0.010 g / m2 or less. The true density of the soft magnetic powder with respect to the theoretical density of the soft magnetic powder is 90 or more to 99% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 describes an invention relating to an Fe—Co alloy powder having an average particle size of 0.25 to 0.80 μm. This Fe—Co alloy powder can achieve high μ′ in the high frequency band and has good heat resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019-142610 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a soft magnetic powder that can be used to produce a magnetic core having high relative permeability and excellent DC bias characteristics. [Means for solving the problem]

[0005] In order to achieve the above object, the soft magnetic alloy of the present invention comprises: A soft magnetic powder containing Fe and Co, The total content of Fe and Co relative to the entire soft magnetic powder is 90% by mass or more, The content of Fe relative to the total content of Fe and Co is 30% by mass or more and 95% by mass or less, The average particle size of the soft magnetic powder is 0.10 μm or more and 5.0 μm or less, The amount of oxygen on the surface of the soft magnetic powder is 0.010 g / m 2 is as follows: The true density of the soft magnetic powder is 90% or more and 99% or less of the theoretical density of the soft magnetic powder.

[0006] The soft magnetic powder may further contain an accessory component, and the content of the accessory component relative to the entire soft magnetic powder may be 5% by mass or less.

[0007] The auxiliary component may be one or more selected from B, Si, P, Cu, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Ni, Al, Mn, Ag, Zn, S, Sn, As, Sb, Bi, N, O, and rare earth elements.

[0008] The soft magnetic powder may have an average particle size of 0.1 μm or more and 1.0 μm or less.

[0009] The magnetic core of the present invention contains the soft magnetic powder described above. [Brief explanation of the drawings]

[0010] [Figure 1] This is an example of a chart obtained by X-ray crystal structure analysis. [Figure 2] 2 is an example of a pattern obtained by profile fitting the chart of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described below based on embodiments.

[0012] (magnetic core) The magnetic core according to this embodiment contains the soft magnetic powder according to this embodiment, which will be described later. Furthermore, the magnetic core according to this embodiment is made using a powder obtained by mixing large-diameter and small-diameter powders, with the large-diameter soft magnetic powder having an average particle size of more than 5.0 μm and the small-diameter soft magnetic powder according to this embodiment, which will be described later, having an average particle size of 5.0 μm or less. Furthermore, the soft magnetic particles contained in the large-diameter powder and / or the small-diameter powder may be insulatingly coated.

[0013] When a magnetic core is produced using a powder in which large-diameter powder and small-diameter powder are mixed, the packing density of the magnetic core is more likely to be improved and the relative permeability is more likely to be improved than when a magnetic core is produced using only large-diameter powder or only small-diameter powder, because the gaps between the soft magnetic particles derived from the large-diameter powder can be filled with the soft magnetic particles derived from the small-diameter powder.

[0014] There are no particular restrictions on the composition and microstructure of the large-diameter powder. They can be selected appropriately depending on the application of the magnetic core. The microstructure of the large-diameter powder can be confirmed by XRD. It can also be confirmed using TEM.

[0015] When the large-diameter powder has an amorphous structure, and when the large-diameter powder has a nanocrystalline structure, the relative permeability of the magnetic core is likely to improve, and core loss is likely to be reduced.

[0016] An amorphous structure is a structure having only amorphous or a heteroamorphous structure. A heteroamorphous structure is a structure in which primary microcrystals exist in an amorphous material. The average crystal grain size of the primary microcrystals is not particularly limited, but may be 0.3 nm or more and 10 nm or less. An amorphous structure has an amorphization rate of 85% or more as confirmed by XRD. Whether a structure has only amorphous or is heteroamorphous can be confirmed by TEM. A nanocrystalline structure is a structure mainly containing nanocrystals. In a structure consisting of crystals (nanocrystals), the amorphization rate as confirmed by XRD is less than 85%. In a nanocrystalline structure, the average crystal grain size of the nanocrystals is 5 nm or more and 100 nm or less.

[0017] In this embodiment, soft magnetic metal powders having an amorphization rate X of 85% or more, as shown in the following formula (1), have a structure containing only amorphous matter or a heteroamorphous structure, and soft magnetic metal powders having an amorphization rate X of less than 85% have a structure consisting of crystals. X = 100 - (Ic / (Ic + Ia) × 100) ... (1) Ic: Crystalline scattering integrated intensity Ia: Amorphous scattering integrated intensity

[0018] The amorphous ratio X is calculated by performing X-ray crystal structure analysis on the soft magnetic metal powder by XRD, identifying the phase, reading the peaks of crystallized Fe or a compound (Ic: crystalline scattering integrated intensity, Ia: amorphous scattering integrated intensity), determining the crystallization ratio from the peak intensity, and then calculating the amorphous ratio X using the above formula (1). The calculation method will be explained in more detail below.

[0019] The soft magnetic metal powder according to this embodiment is subjected to X-ray crystal structure analysis by XRD to obtain a chart as shown in Fig. 1. This is subjected to profile fitting using the Lorentz function of the following formula (2), and a crystalline component pattern α showing the crystalline scattering integrated intensity as shown in Fig. 2 is obtained. c , amorphous component pattern α showing amorphous scattering integrated intensity a , and the combined pattern α c+a The amorphization rate X is calculated from the crystalline scattering integrated intensity and amorphous scattering integrated intensity of the obtained pattern using the above formula (1). The measurement range is set to a diffraction angle 2θ of 30° to 60°, where a halo derived from amorphous matter can be confirmed. Within this range, the error between the integrated intensity actually measured by XRD and the integrated intensity calculated using the Lorentz function is set to within 1%.

[0020]

number

[0021] When the soft magnetic alloy powder of this embodiment contains nanocrystals, each particle contains a large number of nanocrystals. That is, the particle size of the soft magnetic alloy powder, which will be described later, is different from the crystal grain size of the nanocrystals.

[0022] By observing the cross section of the magnetic core using SEM-EDS or the like, it is possible to distinguish between soft magnetic particles derived from large-diameter powder and soft magnetic particles derived from small-diameter powder. Specifically, soft magnetic particles derived from large-diameter powder and soft magnetic particles derived from small-diameter powder can be distinguished by the difference in particle size in SEM images. Also, soft magnetic particles derived from large-diameter powder and soft magnetic particles derived from small-diameter powder may not be distinguishable in SEM images. This is because the particle size ranges of large-diameter powder and small-diameter powder may overlap. In such cases, soft magnetic particles that cannot be distinguished in SEM images can be distinguished by performing composition analysis using EDS or the like.

[0023] In the cross section, the average equivalent circular diameter of the soft magnetic particles derived from the large diameter powder is preferably greater than 5 μm and less than 50 μm. Furthermore, the average equivalent circular diameter of the soft magnetic particles derived from the small diameter powder is preferably between 0.1 μm and 5 μm. Furthermore, the average equivalent circular diameter of the soft magnetic particles derived from the large diameter powder is preferably between 2.0 and 100 times the average equivalent circular diameter of the soft magnetic particles derived from the small diameter powder.

[0024] By having each of the average equivalent circular diameters within the above range, the gaps between the soft magnetic particles derived from the large-diameter powder can be effectively filled with the soft magnetic particles derived from the small-diameter powder, which makes it easier to further improve the filling rate of the magnetic core and the relative permeability.

[0025] The coil component according to this embodiment has the magnetic core according to this embodiment. There are no particular limitations on the shape of the coil component. By having the magnetic core according to this embodiment, the coil component according to this embodiment can satisfy both high inductance and good DC bias characteristics.

[0026] (Soft magnetic powder) The soft magnetic powder according to this embodiment (the small diameter powder) is A soft magnetic powder containing Fe and Co, The total content of Fe and Co in the entire soft magnetic powder is 90% by mass or more, The content of Fe relative to the total content of Fe and Co is 30 mass% or more and 95 mass% or less, The average particle size of the soft magnetic powder is 0.10 μm or more and 5.0 μm or less, The amount of oxygen on the surface of the soft magnetic powder is 0.010g / m 2 is as follows: The true density of the soft magnetic powder is 90% or more and 99% or less of the theoretical density of the soft magnetic powder.

[0027] The soft magnetic powder according to this embodiment can be used to produce a magnetic core having a high relative magnetic permeability and excellent DC bias characteristics. Specifically, the soft magnetic powder according to this embodiment can be used as the large-diameter powder, and the soft magnetic powder according to this embodiment, having an average particle diameter of 5.0 μm or less, can be used as the small-diameter powder, and the characteristics of the magnetic core produced using this powder can be improved.

[0028] As described above, the soft magnetic powder according to this embodiment has a total Fe and Co content of 90% by mass or more relative to the entire soft magnetic powder, and an Fe content of 30% by mass or more and 95% by mass or less relative to the total Fe and Co content. That is, the soft magnetic powder according to this embodiment mainly contains Fe and Co. The soft magnetic powder according to this embodiment has high saturation magnetization due to the main inclusion of Fe and Co. Furthermore, the DC bias characteristics of a magnetic core produced using a powder obtained by mixing large-diameter powder and small-diameter powder (the soft magnetic powder according to this embodiment) can be improved.

[0029] If the Fe content is too low or too high, the saturation magnetization tends to be low, and the DC bias characteristics of a magnetic core made using a powder in which large-diameter powder and small-diameter powder (soft magnetic powder with an Fe content outside the above range) are mixed will be degraded.

[0030] The soft magnetic powder according to this embodiment may further contain auxiliary components in addition to Fe and Co. The auxiliary components may be one or more selected from B, Si, P, Cu, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Ni, Al, Mn, Ag, Zn, S, Sn, As, Sb, Bi, N, O, and rare earth elements, or one or more selected from V, Cr, Ni, and Sm. Rare earth elements refer to Sc, Y, and lanthanides. The inclusion of the above auxiliary components can control the processability, corrosion resistance, and saturation magnetization of the soft magnetic powder according to this embodiment. When considering processability, the total content of the above auxiliary components is preferably 2% by mass or more. Furthermore, when considering the magnetic properties and corrosion resistance of the soft magnetic powder, the total content of the auxiliary components is preferably 10% by mass or less with respect to the entire soft magnetic powder. Furthermore, when considering the saturation magnetization of the soft magnetic powder, the total content of the auxiliary components is preferably 5% by mass or less with respect to the entire soft magnetic powder.

[0031] The soft magnetic powder according to this embodiment may contain elements other than the above elements (Fe, Co, B, Si, P, Cu, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Ni, Al, Mn, Ag, Zn, S, Sn, As, Sb, Bi, N, O, and rare earth elements) as inevitable impurities. The content of the inevitable impurities may be 1% by mass or less, with the entire soft magnetic powder being 100% by mass. Furthermore, the total content of the accessory components and the inevitable impurities may be 10% by mass or less.

[0032] The soft magnetic powder according to this embodiment has an oxygen content of 0.010 g / m on the surface. 2 The amount of oxygen per unit area on the surface varies depending on the degree of oxidation of the surface of the soft magnetic powder. If the amount of oxygen on the surface is too high, the DC bias characteristics of a magnetic core made using a powder in which large-diameter powder and small-diameter powder (soft magnetic powder according to this embodiment) are mixed are likely to deteriorate.

[0033] The soft magnetic powder according to the present embodiment may have an average particle size of 0.10 μm or more and 1.0 μm or less. When the average particle size of the soft magnetic powder according to the present embodiment is 0.10 μm or more and 1.0 μm or less, it becomes easier to improve the filling rate of the magnetic core produced using a powder obtained by mixing large-diameter powder and small-diameter powder (the soft magnetic powder according to the present embodiment), and it becomes easier to improve the relative permeability.

[0034] (Method of manufacturing soft magnetic powder) The soft magnetic powder according to this embodiment can be produced by producing a soft magnetic powder by a known method and then reducing the soft magnetic powder by a mechanochemical reduction method.

[0035] There are no particular limitations on the method for producing the soft magnetic powder before reduction by mechanochemical reduction. For example, the soft magnetic powder may be produced by atomization methods such as water atomization and gas atomization. Alternatively, the soft magnetic powder may be produced by synthesis methods such as CVD using at least one of evaporation, reduction, and thermal decomposition of metal salts. Alternatively, the soft magnetic powder may be produced by electrolysis or carbonyl method.

[0036] By changing the soft magnetic powder manufacturing conditions in the soft magnetic powder manufacturing method described above, some of the powder particles contained in the soft magnetic powder become hollow particles. Hollow particles are particles with a hollow interior. Because some of the powder particles contained in the soft magnetic powder become hollow particles, the true density of the soft magnetic powder is 99% or less of its theoretical density. Hollow particles can be destroyed after powder manufacturing. Soft magnetic powder with destroyed hollow particles has a true density approaching 100% of its theoretical density. However, magnetic cores made using soft magnetic powder with destroyed hollow particles have reduced uniformity. Furthermore, magnetic cores made using soft magnetic powder with destroyed hollow particles have poor DC bias characteristics due to the reduced uniformity. Furthermore, magnetic cores containing hollow particles tend to have good DC bias characteristics.

[0037] Among the above-mentioned methods for producing soft magnetic powder, for example, when soft magnetic powder is produced by atomization, the number of hollow particles varies depending on the atomization conditions, particularly the water pressure and gas pressure during atomization. The higher the water pressure and gas pressure during atomization, the greater the number of hollow particles. This results in a decrease in the true density of the soft magnetic powder relative to its theoretical density. When soft magnetic powder is produced by atomization under unsuitable atomization conditions, such as when the water pressure or gas pressure during atomization is too high, the true density of the soft magnetic powder relative to its theoretical density becomes less than 90%. When the true density of the soft magnetic powder relative to its theoretical density becomes less than 90%, the magnetic permeability decreases. This is because when the true density of the soft magnetic powder relative to its theoretical density becomes less than 90%, the flow of magnetic flux in the magnetic core is hindered.

[0038] At this stage, the soft magnetic powder may be classified to control the average particle size of the soft magnetic powder to a desired value. There are no particular limitations on the classification method, but swirling air classification is preferably used when the average particle size is approximately 0.3 μm or more. Differential electrostatic classification is preferably used when the average particle size is approximately less than 0.3 μm.

[0039] The soft magnetic powder according to this embodiment can be produced by reducing the obtained soft magnetic powder by mechanochemical reduction.

[0040] The mechanochemical reduction method will be described below.

[0041] A known method for reducing soft magnetic powder is a hydrogen reduction heat treatment method.

[0042] However, when soft magnetic powder is reduced by hydrogen reduction heat treatment, the soft magnetic powder tends to aggregate. This excessive aggregation results in a lower true density than the theoretical density of the soft magnetic powder. As a result, even if a magnetic core is made using soft magnetic powder reduced by hydrogen reduction heat treatment, the filling factor and relative permeability are not sufficiently high.

[0043] The mechanochemical reduction method is a reduction method that applies a mechanofusion device to the reduction of soft magnetic powder. Mechanofusion devices have traditionally been used for coating various powders. The inventors have discovered that by using a mechanofusion device to reduce soft magnetic powder, it is possible to prevent the soft magnetic powder from agglomerating and to proceed with the reduction in an optimal manner.

[0044] In the mechanochemical reduction method, first, a hydrogen atmosphere is created inside the mechanofusion device. Next, the soft magnetic powder before reduction is introduced into the rotating rotor. Then, the rotor is rotated while controlling the gap between the inner wall surface of the rotating rotor and the press head and the rotation speed of the rotating rotor.

[0045] As the rotor rotates, friction between the soft magnetic powder and the inner wall surface of the rotor causes the soft magnetic powder to locally heat up. The soft magnetic powder is then reduced while being locally heated. As a result, in the reduction process using the mechanochemical reduction method, the agglomerated soft magnetic powder is crushed and reduced simultaneously. Therefore, the reduction can be carried out efficiently while preventing the agglomeration of the soft magnetic powder.

[0046] The lower the rotation speed of the rotor, the more difficult it is for the reduction of the soft magnetic powder to proceed smoothly. As a result, the amount of oxygen on the surface of the soft magnetic powder increases. Furthermore, if the rotation speed of the rotor is too high, the hollow particles contained in the soft magnetic powder are more likely to be destroyed.

[0047] The smaller the gap between the inner wall surface of the rotating rotor and the press head, the less likely the soft magnetic powder is to agglomerate, reducing the amount of oxygen on the surface of the soft magnetic powder. However, the smaller the gap between the inner wall surface of the rotating rotor and the press head, the more likely the powder particles of the soft magnetic powder, especially the hollow particles, are to be destroyed. As a result, the true density of the soft magnetic powder becomes too high relative to its theoretical density. Furthermore, the destruction of hollow particles increases the proportion of elongated powder particles. As a result, the DC bias characteristics of magnetic cores made using a powder mixture of large-diameter powder and small-diameter powder (soft magnetic powder with a true density too high relative to its theoretical density) tend to deteriorate.

[0048] The larger the gap between the inner wall surface of the rotating rotor and the press head, the more likely the soft magnetic powder is to agglomerate. This is because the agglomerated soft magnetic powder is less likely to be broken down. As a result, the agglomerated soft magnetic powder is not sufficiently broken down. This leaves voids between the powder particles, making the soft magnetic powder's true density too low relative to its theoretical density. Furthermore, the DC bias characteristics of magnetic cores made using a powder that is a mixture of large-diameter powder and small-diameter powder (soft magnetic powder whose true density is too low relative to its theoretical density) are likely to deteriorate.

[0049] (Magnetic core manufacturing method) There are no particular limitations on the manufacturing method of the magnetic core according to this embodiment. It is sufficient that the method includes a step of mixing large-diameter powder and small-diameter powder (the soft magnetic powder according to this embodiment). After mixing the large-diameter powder and small-diameter powder, the magnetic core according to this embodiment may be manufactured by a known method. For example, the large-diameter powder and small-diameter powder may be mixed and then kneaded with a thermosetting resin to manufacture a resin compound, which may then be filled into a mold, pressure-molded, and the resin may be thermally cured to manufacture the magnetic core (dust core) according to this embodiment.

[0050] There are no particular limitations on the applications of the magnetic core according to this embodiment. Examples include coil components such as inductors, choke coils, and transformers. In particular, when the magnetic core according to this embodiment is used in a coil component, a coil component that satisfies both high inductance and good DC bias characteristics can be obtained. [Example]

[0051] The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

[0052] First, the pure metal materials of Fe, Co, and the subcomponents were weighed out so as to obtain master alloys having the compositions shown in Tables 1 to 5. After evacuating the chamber, the contents were melted by high-frequency heating to produce master alloys.

[0053] The produced master alloy was then heated to 1500°C and melted. Soft magnetic powders having the compositions shown in Tables 1 to 5 were then produced by high-pressure water atomization. Next, the powders were classified to obtain powders with the average particle sizes shown in Tables 1 to 5. To obtain powders with an average particle size of 0.30 μm or more, a swirling air classifier (Aero Fine Classifier, manufactured by Nisshin Engineering Inc.) was used for classification. To obtain powders with an average particle size of less than 0.30 μm, a differential electrostatic classifier (Model 3082, manufactured by TSI Inc.) was used for classification.

[0054] Next, mechanochemical reduction was performed on the classified soft magnetic powder. A mechanofusion device (AMS-Lab manufactured by Hosokawa Micron) was prepared. Next, a hydrogen atmosphere was created inside the mechanofusion device. Next, the classified soft magnetic powder was introduced into the rotating rotor of the mechanofusion device, and the rotating rotor was rotated. At this time, the rotation speed of the rotating rotor and the gap between the inner wall surface of the rotating rotor and the press head were set to the values ​​shown in Tables 1 to 5.

[0055] It was confirmed that the average particle size (D50) of the obtained soft magnetic powder was the value shown in Tables 1 to 5 using a laser diffraction particle size distribution measuring device (HELOS&RODOS, Sympatec).

[0056] The amount of oxygen per unit area on the surface of the obtained soft magnetic powder was measured using TC6600 manufactured by LECO.

[0057] The saturation magnetization of the obtained soft magnetic powder was measured in an external magnetic field of 795.8 kA / m (10 kOe) using a vibrating sample magnetometer (VSM-3S-15 manufactured by Toei Kogyo Co., Ltd.) A saturation magnetization of 1.80 T or more is good, and 2.20 T or more is particularly good.

[0058] The reason why a saturation magnetization of 2.20 T or more is considered particularly favorable is that the saturation magnetization of pure iron powder and permalloy powder, which have traditionally been used as small-diameter powders, both have an upper limit of about 2.15 T.

[0059] The true density of the obtained soft magnetic powder was measured by the Archimedes method using a Wardon pycnometer. The theoretical density of the obtained soft magnetic powder was calculated from the composition of the soft magnetic powder. Then, the ratio of the true density to the theoretical density was calculated.

[0060] Next, the obtained soft magnetic powder (small diameter powder) was mixed with other soft magnetic powder (large diameter powder) to prepare a magnetic core.

[0061] As another soft magnetic powder (large diameter powder) described above, an Fe-Si-Cr-BC soft magnetic powder (KUAMET 6B2 manufactured by Epson Atmix Corporation) was prepared. The soft magnetic powder had an average particle size (D50) of 23 μm and an amorphous structure.

[0062] Next, the large-diameter powder and the small-diameter powder were mixed in a mass ratio of 80:20. The soft magnetic powder obtained by mixing was then kneaded with epoxy resin to prepare a resin compound. The mass ratio of the soft magnetic powder in the resin compound was adjusted to 2.5 mass%. YSLV-80XY manufactured by Nippon Steel Chemical & Material Co., Ltd. was used as the epoxy resin.

[0063] The obtained resin compound was filled into a mold of a predetermined toroidal shape. Then, the molding pressure was controlled so that the filling rate of the final toroidal core was about 80%, and a molded body was obtained. Specifically, the molding pressure was 1 to 10 ton / cm. 2 The resin contained in the obtained molded body was then 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).

[0064] The filling rate η of the soft magnetic 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.

[0065] The relative permeability of the toroidal core was calculated from the inductance measured at a frequency of 100 kHz using an LCR meter (Agilent Technologies 4284A) and a DC bias power supply (Agilent Technologies 42841A). The relative permeability when the DC superimposed magnetic field was 0 A / m was defined as μ0, and the relative permeability when the DC superimposed magnetic field was 8000 A / m was defined as μ8k. A μ0 of 40 or higher was considered good. A μ8k of 30 or higher was considered good. Then, μ8k / μ0 was calculated. The higher the μ8k / μ0, the better the DC superimposed characteristics.

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3]

[0069] [Table 4]

[0070] [Table 5]

[0071] Table 1 shows examples and comparative examples carried out under the same conditions except for varying the Fe content. The soft magnetic powders (small diameter powders) of the examples, in which the Fe content relative to the total content of Fe and Co was 30% by mass or more and 95% by mass or less, had high saturation magnetization and high true density relative to the theoretical density. Furthermore, when a core was made by mixing the small diameter powder with the large diameter powder, a core with high μ8k and excellent DC bias characteristics was obtained. In contrast, the soft magnetic powders (small diameter powders) of the comparative examples, in which the Fe content was too low, had lower saturation magnetization than the other examples. Furthermore, when a core was made by mixing the small diameter powder with the large diameter powder, a core with low μ8k and poor DC bias characteristics was obtained. Furthermore, the soft magnetic powders (small diameter powders) of the comparative examples, in which the Fe content was too high, had lower saturation magnetization than the other examples. Furthermore, when a core was made by mixing the small diameter powder with the large diameter powder, a core with low μ8k and poor DC bias characteristics was obtained.

[0072] Table 2 shows examples and comparative examples of sample No. 4 in Table 1, carried out under the same conditions except for varying the gap between the inner wall surface of the rotor and the press head. The smaller the gap between the inner wall surface of the rotor and the press head, the higher the true density of the soft magnetic powder relative to its theoretical density, and the lower the amount of oxygen on the surface. Furthermore, when a core was produced by mixing a soft magnetic powder (small-diameter powder) whose true density relative to the theoretical density was within a predetermined range with a large-diameter powder, a core with good relative permeability and DC bias characteristics was obtained. In contrast, in the comparative example, in which the true density was too high relative to the theoretical density, the μ8k of the core decreased, resulting in poor DC bias characteristics. Furthermore, in the comparative example, in which the true density was too low relative to the theoretical density, the μ0 of the core decreased.

[0073] Table 3 shows examples and comparative examples performed under the same conditions as Sample No. 4 in Table 1, except that the average particle size of the soft magnetic powder was changed and the gap between the inner wall surface of the rotor and the press head was changed so that the amount of oxygen on the surface of the soft magnetic powder would not change even if the average particle size was changed. When a core was produced by mixing soft magnetic powder (small-diameter powder) with a specified average particle size range with large-diameter powder, a core with a high packing density and good relative permeability and DC bias characteristics was obtained. In contrast, whether the average particle size was small or large, the true density of the soft magnetic powder relative to the theoretical density decreased. The packing density and relative permeability of the core also decreased.

[0074] Table 4 shows examples and comparative examples of sample No. 4 in Table 1, carried out under the same conditions except for varying the rotor speed. The lower the rotor speed, the greater the amount of oxygen on the surface of the soft magnetic powder, and the lower the saturation magnetization. Furthermore, when a core was produced by mixing soft magnetic powder (small-diameter powder) with a surface oxygen content within a predetermined range with large-diameter powder, a core with good relative permeability and DC bias characteristics was obtained. In contrast, in the comparative example, where the surface oxygen content was too high, the μ8k of the core decreased, resulting in poor DC bias characteristics.

[0075] Table 5 shows examples of samples 2a, 3, or 4 in Table 1, which were produced under the same conditions except for the addition of minor components. When a soft magnetic powder (small-diameter powder) with a composition, average particle size, surface oxygen content, and true density relative to theoretical density within a specified range was mixed with a large-diameter powder to produce a core, a core with good relative permeability and DC bias characteristics was obtained. Furthermore, soft magnetic powders (small-diameter powders) containing 5% or less minor components had higher saturation magnetization than soft magnetic powders (small-diameter powders) produced under substantially the same conditions except for the minor component content exceeding 5% by mass.

Claims

1. A soft magnetic powder containing Fe and Co, The total content of Fe and Co relative to the entire soft magnetic powder is 90 mass% or more, The content of Fe relative to the total content of Fe and Co is 30% by mass or more and 95% by mass or less, The average particle size of the soft magnetic powder is 0.10 μm or more and 5.0 μm or less, The amount of oxygen on the surface of the soft magnetic powder is 0.010 g / m 2 is as follows: The true density of the soft magnetic powder is 90% or more and 99% or less of the theoretical density of the soft magnetic powder, The content of the subcomponent relative to the entire soft magnetic powder is 0% by mass or more and 10% by mass or less, the auxiliary component is one or more selected from V, Cr, Ni, and Sm, A soft magnetic powder in which the content of unavoidable impurities other than the above elements is 0% by mass or more and 1% by mass or less, with the total amount of the soft magnetic powder being 100% by mass.

2. 2. The soft magnetic powder according to claim 1, further comprising an accessory component, the content of the accessory component being 5% by mass or less relative to the entire soft magnetic powder.

3. 3. The soft magnetic powder according to claim 1, wherein the average particle size of the soft magnetic powder is 0.1 μm or more and 1.0 μm or less.

4. A magnetic core comprising the soft magnetic powder according to any one of claims 1 to 3.

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