Method for producing soft magnetic powder, soft magnetic powder, powder core, magnetic element, and electronic device

Abstract

To provide a soft magnetic powder capable of producing a powder magnetic core realizing a high magnetic permeability and a low iron loss under a high frequency, a powder magnetic core and a magnetic element comprising the soft magnetic powder, and an electronic apparatus capable of miniaturization and high output characteristics.SOLUTION: A soft magnetic powder comprises grains having a composition of FexCuaNbb(Si1-yBy)100-x-a-b [a, b, x satisfy 0.3≤a≤2.0, 2.0≤b≤4.0, 72.5≤x<75.5. Further, y is a number satisfying f(x)≤y≤0.99, and f(x)=(4×10-34)x17.56.]. Each grain comprises: crystal grains with a grain size of 1.0 to 30.0 nm; Cu segregated parts; and crystal grain boundaries. The content ratio of the crystal grains is 30% or more, and provided that the ones located at a surface layer part and having a grain size of 1.0 to 5.0 nm are defined as first Cu segregated parts and the ones located at an inside and having a grain size of 3.0 to 10.0 nm are defined as second Cu segregated parts, these number ratios are 80% or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention provides A method for producing soft magnetic powder, The present invention relates to soft magnetic powders, dust cores, magnetic elements, and electronic devices. [Background technology]

[0002] In order to achieve miniaturization and high output in various mobile devices equipped with magnetic elements containing powder magnetic cores, the switching power supply must be able to handle high frequencies and high currents. Accordingly, the soft magnetic powder contained in powder magnetic cores must also be able to handle high frequencies and high currents.

[0003] Patent Document 1 describes Fe x Cu a Nb b (Si 1-y B y ) 100-x-a-b [where a, b, and x are atomic percent and are numbers that satisfy 0.3≦a≦2.0, 2.0≦b≦4.0, and 73.0≦x≦79.5. Also, y is a number that satisfies f(x)≦y<0.99. Note that f(x)=(4×10 -34 )x 17.56 The soft magnetic powder has a composition represented by the formula: and contains 30% by volume or more of a crystalline structure having a particle size of 1.0 nm or more and 30.0 nm or less. By including minute crystals in such a soft magnetic powder, it is possible to reduce iron loss at high frequencies. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-189928 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the soft magnetic powder described in Patent Document 1 still has room for improvement in terms of stably realizing excellent soft magnetism even at high frequencies and increasing electromagnetic conversion efficiency at high frequencies. Specifically, the challenge is to further increase the magnetic permeability at high frequencies and further reduce losses (iron losses) at high frequencies in soft magnetic powders. [Means for solving the problem]

[0006] Soft magnetic powder according to an application example of the present invention Manufacturing method teeth, a step of melting the raw material to obtain a molten metal; a step of obtaining soft magnetic powder by atomizing the molten metal and cooling and solidifying the same; and The soft magnetic powder is Fe x Cu a Nb b (Si 1-y B y ) 100-x-a-b [a, b, x are each a number expressed in atomic percent, 0.3≦a≦2.0, 2.0≦b≦4.0, 72.5≦x<75.5 Meet the following. Also, y is a number that satisfies f(x)≦y≦0.99, and f(x)=(4×10 -34 )x 17.56 ] The particles have a composition represented by The particles are Crystal grains having a grain size of 1.0 nm or more and 30.0 nm or less and containing Fe-Si crystals; A Cu segregation portion where Cu is segregated, Grain boundaries and and a particle size D50 at which a cumulative 50% of the particle size distribution from the small diameter side in a volumetric basis of the particles is 5 μm or more and 50 μm or less; The content ratio of the crystal grains in the particles is 30 volume % or more, of the particles The cross section is a 200 nm square area centered at a depth of 1 μm from the surface.The Cu segregation portion located in the surface layer portion and having a grain size of 1.0 nm or more and 5.0 nm or less is defined as a first Cu segregation portion, of the particles The area is 200 nm square and is set at the center of the cross section. When the Cu segregation portion located inside and having a grain size of 3.0 nm or more and 10.0 nm or less is defined as a second Cu segregation portion, a number ratio of the first Cu segregation portions to the Cu segregation portions located in the surface layer portion is 80% or more, The ratio of the number of the second Cu segregation portions to the number of the Cu segregation portions located inside is 80% or more. The soft magnetic powder according to the application example of the present invention is Fe x Cu a Nb b (Si 1-y B y ) 100-x-a-b [a, b, x are each a number expressed in atomic percent, 0.3≦a≦2.0、 2.0≦b≦4.0、 72.5≦x<75.5 Meet the following. Also, y is a number that satisfies f(x)≦y≦0.99, and f(x)=(4×10 -34 )x 17.56 ] The particles have a composition represented by The particles are Crystal grains having a grain size of 1.0 nm or more and 30.0 nm or less and containing Fe-Si crystals; A Cu segregation portion where Cu is segregated, Grain boundaries and and a particle size D50 at which a cumulative 50% of the particle size distribution from the small diameter side in a volumetric basis of the particles is 5 μm or more and 50 μm or less; The content ratio of the crystal grains in the particles is 30% by volume or more, The Cu segregation portion is located in a surface layer portion of the cross section of the particle, which is within a 200 nm square range centered at a position 1 μm deep from the surface, and has a particle size of 1.0 nm or more and 5.0 nm or less, and is defined as a first Cu segregation portion; When the Cu segregation portion, which is located within a 200 nm square range set at the center of the cross section of the particle and has a particle size of 3.0 nm or more and 10.0 nm or less, is defined as a second Cu segregation portion, a number ratio of the first Cu segregation portions to the Cu segregation portions located in the surface layer portion is 80% or more, The ratio of the number of the second Cu segregation portions to the number of the Cu segregation portions located inside is 80% or more.

[0007] A powder magnetic core according to an application example of the present invention is The soft magnetic powder according to the application example of the present invention is included.

[0008] The magnetic element according to the application example of the present invention includes: The present invention is characterized by including a powder magnetic core according to an application example of the present invention.

[0009] The electronic device according to the application example of the present invention includes: The magnetic element according to the application example of the present invention is included. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a diagram schematically showing a cross section of one particle contained in the soft magnetic powder according to the embodiment. [Figure 2] FIG. 2 is a schematic diagram of a portion of the surface layer shown in FIG. 1, observed under an electron microscope at an enlarged scale. [Figure 3] FIG. 2 is a schematic diagram of a portion of the interior shown in FIG. 1, observed enlarged with an electron microscope. [Figure 4] FIG. 2 is a diagram showing a region in a two-axis orthogonal coordinate system in which x is the horizontal axis and y is the vertical axis, where the range of x and the range of y in the composition formula of the soft magnetic powder according to the embodiment overlap. [Figure 5] FIG. 1 is a vertical cross-sectional view showing an example of an apparatus for producing metal powder by a rotary water jet atomization method. [Figure 6] FIG. 1 is a plan view schematically showing a toroidal type coil component. [Figure 7] FIG. 1 is a transparent perspective view schematically showing a closed magnetic circuit type coil component. [Figure 8] FIG. 1 is a perspective view showing a mobile personal computer, which is an electronic device including a magnetic element according to an embodiment. [Figure 9] FIG. 1 is a plan view showing a smartphone as an electronic device including a magnetic element according to an embodiment. [Figure 10] FIG. 1 is a perspective view showing a digital still camera, which is an electronic device including a magnetic element according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The soft magnetic powder, dust core, magnetic element, and electronic device of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings.

[0012] 1. Soft magnetic powder The soft magnetic powder according to the embodiment is a metal powder exhibiting soft magnetism. This soft magnetic powder can be used for any purpose, but for example, the particles are bound together with a binder and used to produce various compacts such as dust cores and electromagnetic wave absorbers.

[0013] The soft magnetic powder according to the embodiment contains Fe x Cu a Nb b (Si 1-y B y ) 100-x-a-b The particle has a composition represented by the formula: This formula represents the ratio of the five elements Fe, Cu, Nb, Si, and B in the composition.

[0014] a, b, and x are each a number expressed in atomic percent, where a satisfies 0.3≦a≦2.0, b satisfies 2.0≦b≦4.0, and x satisfies 72.5≦x<75.5.

[0015] Also, y satisfies f(x)≦y≦0.99, and f(x), which is a function of x, is f(x)=(4×10 -34 )x 17.56 is.

[0016] FIG. 1 is a diagram schematically showing a cross section of one particle 6 contained in the soft magnetic powder according to the embodiment.

[0017] In this embodiment, a 200 nm square range centered at a position 1 μm deep from the surface 600 in the cross section of the particle 6 shown in Fig. 1 is referred to as a "surface layer portion 601." Also, a 200 nm square range set at a position 2 μm to 25 μm deep from the surface 600, preferably at the center of the cross section of the particle 6, is referred to as an "interior portion 602."

[0018] Fig. 2 is a schematic diagram of a portion of the surface layer 601 shown in Fig. 1, observed under an enlarged microscope using an electron microscope. Fig. 3 is a schematic diagram of a portion of the interior 602 shown in Fig. 1, observed under an enlarged microscope using an electron microscope.

[0019] The particle 6 shown in FIG. 1 has a crystal grain 61, a Cu segregation portion 62, and a crystal grain boundary 63, which are shown in FIGS. 2 and 3, respectively.

[0020] The crystal grains 61 are regions containing Fe—Si crystals, and have a grain size of 1.0 nm or more and 30.0 nm or less.

[0021] The Cu segregation portion 62 is a region where Cu is segregated. Of these, the Cu segregation portion 62 located in the surface layer portion 601 shown in FIG. 2 and having a particle size of 1.0 nm or more and 5.0 nm or less is referred to as a "first Cu segregation portion 621." Furthermore, the Cu segregation portion 62 located in the interior portion 602 shown in FIG. 3 and having a particle size of 3.0 nm or more and 10.0 nm or less is referred to as a "second Cu segregation portion 622." In the soft magnetic powder according to this embodiment, the state of the Cu segregation portion 62, for example, the particle size, is different between the surface layer portion 601 and the interior portion 602.

[0022] The content ratio of crystal grains 61 in the particle 6 is 30% or more. Furthermore, among the Cu segregation portions 62 located in the surface layer portion 601, the number ratio of first Cu segregation portions 621 is 80% or more. Furthermore, among the Cu segregation portions 62 located in the interior 602, the number ratio of second Cu segregation portions 622 is 80% or more.

[0023] As will be described in detail later, such soft magnetic powder can be used to produce a dust core that achieves high magnetic permeability and low iron loss at high frequencies, thereby realizing a magnetic element that has excellent DC bias characteristics and high electromagnetic conversion efficiency at high frequencies.

[0024] The composition of the particles 6 will be described below. 1.1.Composition Fe (iron) is an element that has a significant effect on the basic magnetic properties and mechanical properties of the particles 6 .

[0025] The Fe content x is set to 72.5 atomic % or more and less than 75.5 atomic %, preferably 72.8 atomic % or more and 75.0 atomic % or less, and more preferably 73.0 atomic % or more and 74.5 atomic % or less. If the Fe content x is below the lower limit, the saturation magnetic flux density of the soft magnetic powder may decrease. On the other hand, if the Fe content x is above the upper limit, an amorphous structure cannot be stably formed during the production of the soft magnetic powder, and it may be difficult to form the crystal grains 61 having the fine grain size described above.

[0026] When the soft magnetic powder according to the embodiment is produced from raw materials, Cu (copper) tends to separate from Fe. Therefore, the inclusion of Cu causes fluctuations in the composition, resulting in regions in the particles 6 that are easily crystallized. As a result, precipitation of the body-centered cubic Fe phase, which is relatively easily crystallized, is promoted, making it easier to form the crystal grains 61.

[0027] The Cu content a is set to 0.3 atomic % or more and 2.0 atomic % or less, preferably 0.5 atomic % or more and 1.5 atomic % or less, and more preferably 0.7 atomic % or more and 1.3 atomic % or less. If the Cu content a is below the lower limit, the crystal grains 61 may not be refined, and it may be impossible to form crystal grains 61 with a particle size within the aforementioned range. On the other hand, if the Cu content a is above the upper limit, the mechanical properties of the particles 6 may be reduced and they may become brittle.

[0028] When heat treatment is performed, Nb (niobium) contributes to the refinement of the crystal grains 61 together with Cu. Therefore, it is possible to easily form the crystal grains 61 having the above-mentioned fine grain size.

[0029] The Nb content b is 2.0 atomic % or more and 4.0 atomic % or less, preferably 2.5 atomic % or more and 3.5 atomic % or less, and more preferably 2.7 atomic % or more and 3.3 atomic % or less. If the Nb content b is below the lower limit, the crystal grains 61 may not be refined, and crystal grains 61 with a particle size within the aforementioned range may not be formed. On the other hand, if the Nb content b is above the upper limit, the mechanical properties of the particles 6 may be reduced, and the particles 6 may become brittle. Furthermore, the magnetic permeability of the soft magnetic powder may be reduced.

[0030] Silicon (Si) promotes amorphization when the soft magnetic powder according to the embodiment is produced from raw materials. Therefore, when producing the soft magnetic powder according to the embodiment, a homogeneous amorphous structure is first formed, and then crystallization of the amorphous structure facilitates the formation of crystal grains 61 with a more uniform grain size. The uniform grain size contributes to averaging the magnetocrystalline anisotropy in each crystal grain 61, thereby reducing the coercive force and increasing the magnetic permeability, thereby improving the soft magnetic properties.

[0031] B (boron) promotes amorphization when the soft magnetic powder according to the embodiment is produced from raw materials. Therefore, when producing the soft magnetic powder according to the embodiment, a homogeneous amorphous structure is first formed, and then crystallization of the amorphous structure makes it easier to form crystal grains 61 with a more uniform grain size. The uniform grain size contributes to averaging the magnetocrystalline anisotropy in each crystal grain 61, thereby reducing the coercive force and increasing the magnetic permeability, thereby improving the soft magnetic properties. Furthermore, by using Si and B in combination, the difference in atomic radii of the two elements can synergistically promote amorphization.

[0032] Here, when the sum of the contents of Si and B is 1 and the ratio of the content of B to this total is y, the ratio of the content of Si to the total is 1-y.

[0033] This y is a number that satisfies f(x)≦y≦0.99. And, f(x), which is a function of x, is f(x)=(4×10 -34 )x17.56 is.

[0034] FIG. 4 is a diagram showing a region in a two-axis orthogonal coordinate system in which x is the horizontal axis and y is the vertical axis, where the range of x and the range of y in the composition formula of the soft magnetic powder according to the embodiment overlap.

[0035] In FIG. 4, an area A where the x range and the y range overlap is inside the solid line drawn on the Cartesian coordinate system.

[0036] Specifically, when the (x, y) coordinates that satisfy the four equations x=72.5, x=75.5, y=f(x), and y=0.99 are plotted on a Cartesian coordinate system, region A is a closed region enclosed by three lines and one curve, but does not include the line at x=75.5.

[0037] Furthermore, y is preferably a number that satisfies f'(x)≦y≦0.97. And, f'(x), which is a function of x, is expressed as f'(x)=(4×10 -29 )x 14.93 is.

[0038] The dashed line in FIG. 4 indicates a region B where the above-mentioned preferable range of x and the above-mentioned preferable range of y overlap.

[0039] Specifically, region B is a closed region surrounded by three straight lines and one curve when the (x, y) coordinates that satisfy the four equations x=72.8, x=75.0, y=f'(x), and y=0.97 are plotted on a Cartesian coordinate system.

[0040] Furthermore, y is more preferably a number that satisfies f"(x)≦y≦0.95. And, f"(x), which is a function of x, is expressed as f"(x)=(4×10 -29 )x 14.93 It is +0.05.

[0041] The dashed dotted line in FIG. 4 indicates a region C where the more preferable range of x and the more preferable range of y overlap.

[0042] Specifically, when the (x, y) coordinates that satisfy the four equations x = 73.0, x = 74.5, y = f"(x), and y = 0.95 are plotted on a Cartesian coordinate system, region C corresponds to the closed region enclosed by three straight lines and one curve.

[0043] When soft magnetic powders in which x and y are at least within region A are manufactured, they are highly likely to form a homogeneous amorphous structure. Therefore, by crystallizing the soft magnetic powders, it is possible to form crystal grains 61 with particularly uniform and fine grain sizes. This results in soft magnetic powders with sufficiently reduced coercive force and increased magnetic permeability. Furthermore, the use of this soft magnetic powder increases the electrical resistance between the crystal grains 61, allowing the iron loss of the powder magnetic core to be kept sufficiently low.

[0044] Furthermore, soft magnetic powders in which x and y are included in at least region A can form uniform crystal grains 61 even when the Fe content is sufficiently increased. This allows for soft magnetic powders with sufficiently increased magnetic permeability and saturation magnetic flux density to be obtained. As a result, a powder magnetic core can be obtained that has high magnetic permeability and saturation magnetic flux density while achieving sufficiently low iron loss.

[0045] If the value of y is smaller than that of region A, the balance between the Si content and the B content is lost, making it difficult to form a homogeneous amorphous structure when producing the soft magnetic powder. As a result, crystal grains 61 with a small particle size cannot be formed, and the coercive force cannot be reduced sufficiently.

[0046] On the other hand, when the value of y is larger than that of region A, the balance between the Si content and the B content is lost, making it difficult to form a homogeneous amorphous structure when producing the soft magnetic powder. As a result, crystal grains 61 with a small particle size cannot be formed, and the coercive force cannot be reduced sufficiently.

[0047] The lower limit of y is determined by the function of x as described above, but is preferably 0.30 or more, more preferably 0.45 or more, and even more preferably 0.55 or more, which allows the soft magnetic powder to have a higher saturation magnetic flux density and a higher magnetic permeability.

[0048] Furthermore, particularly in regions B and C, by reducing the Fe content, it is possible to achieve a low coercive force while suppressing a decrease in the magnetic permeability of the soft magnetic powder.

[0049] Furthermore, the sum of the Si content and the B content, (100-xab), is not particularly limited, but is preferably 15.0 atomic % or more and 24.0 atomic % or less, more preferably 18.0 atomic % or more and 23.5 atomic % or less, and even more preferably 20.0 atomic % or more and 23.0 atomic % or less. When (100-xab) is within the above range, crystal grains 61 with a particularly uniform particle size can be formed in the soft magnetic powder.

[0050] Here, y(100-xab) corresponds to the content of B in the soft magnetic powder. y(100-xab) is appropriately set in consideration of the coercive force and saturation magnetic flux density as described above, and preferably satisfies 5.0≦y(100-xab)≦17.0, more preferably 7.0≦y(100-xab)≦16.0, and even more preferably 8.0≦y(100-xab)≦15.0.

[0051] This results in a soft magnetic powder containing a relatively high concentration of B (boron). Even if such soft magnetic powder has a high Fe content, it is possible to form a homogeneous amorphous structure during production. Therefore, subsequent heat treatment can form crystal grains 61 with small and relatively uniform grain sizes, achieving high magnetic flux density and high magnetic permeability while sufficiently reducing coercivity. Furthermore, the electrical resistance between the crystal grains 61 is high, allowing the iron loss of the powder magnetic core to be kept sufficiently low.

[0052] If y(100-xab) is below the lower limit, the B content will be small, which may make it difficult to achieve amorphousness during the production of soft magnetic powder, depending on the overall composition. This may hinder the achievement of low coercivity and high electrical resistance. On the other hand, if y(100-xab) is above the upper limit, the B content will be high and the Si content will be relatively low, which may reduce the magnetic permeability and saturation magnetic flux density of the soft magnetic powder.

[0053] In addition, the soft magnetic powder according to the embodiment contains the above-mentioned Fe x Cu a Nb b (Si 1-y B y ) 100-x-a-b In addition to the composition represented by the formula (I), impurities may be contained. Examples of impurities include any elements other than those mentioned above, but it is preferable that the total content of impurities is 0.50 atomic % or less. Within this range, impurities are unlikely to impair the effects of the present invention, so their inclusion is permitted.

[0054] The content of each impurity element is preferably 0.05 atomic % or less, and within this range, the impurities are not likely to impair the effects of the present invention, so their inclusion is permissible.

[0055] The composition of the soft magnetic powder according to the embodiment has been described above, but the composition and impurities are identified by the following analytical method.

[0056] Examples of analytical methods include iron and steel - atomic absorption spectrometry specified in JIS G 1257:2000, iron and steel - inductively coupled plasma (ICP) atomic emission spectrometry specified in JIS G 1258:2007, iron and steel - spark discharge atomic emission spectrometry specified in JIS G 1253:2002, iron and steel - X-ray fluorescence analysis specified in JIS G 1256:1997, and gravimetric / titration / absorptiometry specified in JIS G 1211 to G 1237.

[0057] Specific examples include a solid-state optical emission spectrometer manufactured by SPECTRO, in particular a spark discharge optical emission spectrometer, model: SPECTROLAB, type: LAVMB08A, and an ICP device, model CIROS120 manufactured by Rigaku Corporation.

[0058] In particular, when identifying carbon (C) and sulfur (S), the oxygen flow combustion (high-frequency induction heating furnace combustion)-infrared absorption method specified in JIS G 1211:2011 is also used. Specifically, the LECO CS-200 carbon / sulfur analyzer can be used.

[0059] In particular, when specifying N (nitrogen) and O (oxygen), the nitrogen determination method for iron and steel specified in JIS G 1228:1997 and the oxygen determination method for metallic materials specified in JIS Z 2613:2006 are also used. Specific examples include the LECO oxygen and nitrogen analyzer TC-300 / EF-300.

[0060] 1.2.Crystal Grains As described above, the particles 6 of the soft magnetic powder according to the embodiment contain Fe—Si crystals and have crystal grains 61 with a grain size of 1.0 nm or more and 30.0 nm or less.

[0061] Fe-Si crystals have a characteristic of high saturation magnetic flux density, which is specific to Fe-Si-based compositions. Furthermore, by miniaturizing the crystal grains 61 containing Fe-Si crystals and making the grain size uniform, the number density of the crystal grains 61 increases, and therefore the saturation magnetic flux density of the crystal grains 61 is less likely to decrease even when they are miniaturized. Therefore, the particles 6 can achieve a high saturation magnetic flux density.

[0062] In addition, since the crystal grains 61 in the particles 6 are made fine, the magnetocrystalline anisotropy in the crystal grains 61 is easily averaged. Therefore, even if the Fe concentration is high, an increase in coercive force can be suppressed. Therefore, the particles 6 can have a low coercive force. Furthermore, when many crystal grains 61 with such a grain size are included, the magnetic permeability of the particles 6 becomes high.

[0063] From the above, it is possible to increase the saturation magnetic flux density and magnetic permeability of the particles 6 while also achieving a low coercive force.

[0064] Furthermore, since the grain size of the crystal grains 61 is within the above range, the electrical resistance between the particles 6 increases. This is thought to be because the crystal grains 61 are fine and have a uniform grain size, which increases the number density of the grain boundaries between the crystal grains 61. When the electrical resistance between the particles 6 increases, eddy currents become less likely to flow, which reduces eddy current loss in the powder core. For this reason, soft magnetic powder composed of particles 6 containing crystal grains 61 contributes to the realization of a powder core with low iron loss.

[0065] In the particles 6, the content of crystal grains 61 is preferably 55% or more, more preferably 55% to 99%, and even more preferably 70% to 95%. If the content of crystal grains 61 is below the lower limit, the proportion of crystal grains 61 decreases, resulting in insufficient averaging of the magnetic crystal anisotropy, which may result in a decrease in the magnetic permeability of the soft magnetic powder and an increase in the coercive force. Furthermore, the saturation magnetic flux density may decrease and the iron loss of the powder magnetic core may increase. On the other hand, the content of crystal grains 61 may exceed the upper limit, but this is thought to result in a decrease in the content of crystal grain boundaries 63 (described later). This creates a situation in which the crystal grains 61 are prone to rapid growth, and slight variations in the heat treatment temperature may lead to the crystal grains 61 becoming coarse. This may result in a decrease in the magnetic permeability of the soft magnetic powder and an increase in the coercive force.

[0066] The content ratio of the crystal grains 61 is a volume ratio, but since it is considered to be approximately equal to the area ratio occupied by the crystal grains 61 with respect to the area of ​​the cut surface, the area ratio may also be regarded as the content ratio. Therefore, the content ratio of the crystal grains 61 can be found as the ratio of the area occupied by the crystal grains 61 with respect to the total area of ​​the range described above in the observed image.

[0067] The grain size of the crystal grain 61 is determined by observing a cut surface of the particle 6 with an electron microscope and reading the image from a 200 nm square range centered at a depth of 5 μm from the surface. In this method, a perfect circle having the same area as the crystal grain 61 is assumed, and the diameter of the perfect circle, i.e., the equivalent circle diameter, can be taken as the grain size of the crystal grain 61. For example, a STEM (scanning transmission electron microscope) is used as the electron microscope.

[0068] The average grain size is calculated by averaging the grain sizes of the read crystal grains 61. The average grain size of the crystal grains 61 is preferably 2.0 nm or more and 25.0 nm or less, and more preferably 5.0 nm or more and 20.0 nm or less. This makes the above-mentioned effects, i.e., low coercivity and high magnetic permeability, and high saturation magnetic flux density and low iron loss of the powder magnetic core, more pronounced. The average grain size of the crystal grains 61 is calculated from the grain sizes of 10 or more grains.

[0069] The particles 6 may include crystal grains with a particle size outside the above-mentioned range, that is, crystal grains with a particle size of less than 1.0 nm or more than 30.0 nm.

[0070] Furthermore, the fact that the crystal grains 61 contain Fe-Si crystals can be identified by EDX (energy dispersive X-ray spectroscopy) analysis using a STEM. Specifically, first, an observation image of the cross section of the particle 6 is obtained using a STEM. The crystal grains 61 are identified from this observation image. Next, an EDX analysis using a STEM is performed, and quantitative analysis of each element is performed from the analysis results using a quantification method. If the Fe concentration is highest in the crystal grain 61 in terms of atomic ratio, followed by the Si concentration, it can be said that the crystal grains 61 contain Fe-Si crystals.

[0071] For example, a JEM-ARM200F manufactured by JEOL Ltd. can be used as the STEM. Furthermore, an NSS7 manufactured by Thermo Fisher Scientific can be used as the EDX analyzer. The accelerating voltage during analysis is 120 kV, and Cliff-Lorimer (MBTS) quantification without absorption correction is used as the quantification method using the EDX spectrum.

[0072] 1.3.1st Cu segregation part As described above, the particle 6 has the first Cu segregation portion 621. The first Cu segregation portion 621 is located in the surface layer portion 601 of the particle 6, where Cu is locally segregated, and has a grain size of 1.0 nm or more and 5.0 nm or less. The presence of such fine first Cu segregation portions 621 in the surface layer portion 601 indirectly supports the fact that the Cu segregation portions 62 are distributed throughout almost the entire particle 6. The surface layer portion 601 dissipates heat more easily than the interior portion 602 during heat treatment performed during the production of the particle 6. Therefore, the presence of the fine first Cu segregation portions 621 in the surface layer portion 601 indicates that the Cu segregation portions 62 are distributed throughout the entire particle 6 with a high probability. As a result, the Cu segregation portions 62 serve as nucleation sites, resulting in finer crystal grains 61 and more uniform grain sizes, thereby achieving high magnetic permeability and low coercive force. Furthermore, the electrical resistance between the crystal grains 61 increases, and the iron loss of the powder magnetic core can be further reduced.

[0073] The grain size of the first Cu segregation portion 621 is measured as follows. First, EDX analysis using STEM is performed on the cross section of particle 6. Next, a surface analysis image showing the Cu concentration distribution is obtained from the analysis results using a quantification method.

[0074] Next, in the obtained area analysis image, the number of Cu segregation portions 62 is counted for each particle size within a 200 nm square range (surface layer portion 601) centered at a position 1 μm deep from the surface of the particle 6. Specifically, first, binarization image processing is performed on the area analysis image representing the Cu concentration distribution, and particles with a particle size of 1 nm or more are extracted as Cu segregation portions 62. The particle size is the maximum length that can be taken in the area where Cu is segregated. Of the particle sizes thus determined, those within the above range are defined as the particle sizes of the first Cu segregation portions 621.

[0075] Furthermore, the ratio of the number of the first Cu segregation portions 621 to the extracted Cu segregation portions 62 is set to 80% or more, and preferably 90% or more, thereby making it possible to realize the effect of miniaturizing the crystal grains 61 and making the grain size uniform.

[0076] If the number ratio of the first Cu segregation portions 621 is below the lower limit, there is a risk of a decrease in the dispersibility of the first Cu segregation portions 621. As a result, there is a risk that the region benefiting from the effects of miniaturizing the crystal grains 61 and making the grain size uniform may be limited to a part of the particle 6.

[0077] On the other hand, the particle 6 may include, in the surface layer 601, a Cu segregation portion 62 having a particle size outside the above-mentioned range, that is, a Cu segregation portion 62 that does not correspond to the first Cu segregation portion 621.

[0078] Furthermore, the average grain size of the first Cu segregation portion 621 is preferably 1.5 nm or more and 4.5 nm or less, and more preferably 2.0 nm or more and 4.0 nm or less. When the average grain size of the first Cu segregation portion 621 is within this range, crystal grains 61 having a sufficiently fine and more uniform grain size can be formed by heat treatment. As a result, the skin effect suppresses eddy currents flowing in the surface layer portion 601, and the soft magnetic powder can have a lower iron loss and a further lower coercive force.

[0079] The average grain size of the first Cu segregation portions 621 is calculated by counting the number of the first Cu segregation portions 621 for each grain size and calculating the average grain size from the counting results of 10 or more.

[0080] The maximum value of the Cu concentration in the first Cu segregation portions 621 is not particularly limited, but is preferably greater than 6.0 atomic %. By including the first Cu segregation portions 621 in which Cu is segregated at a high concentration, the function of the first Cu segregation portions 621 as nucleation sites is strengthened during heat treatment.

[0081] The maximum value of the Cu concentration in the first Cu segregation portion 621 is set to more than 6.0 atomic % as described above, but is preferably set to 10.0 atomic % or more, and more preferably set to 16.0 atomic % or more.

[0082] On the other hand, from the viewpoint of avoiding uneven distribution of the first Cu segregation portions 621, the maximum value of the Cu concentration is preferably 70.0 atomic % or less, and more preferably 60.0 atomic % or less.

[0083] Furthermore, the Cu concentration of the first Cu segregation portions 621 is preferably 2.0 times or more, more preferably 5.0 times or more and 50 times or less, and even more preferably 7.0 times or more and 30 times or less, the Cu concentration of the grain boundaries 63. As a result, the first Cu segregation portions 621 favorably generate crystal planes that promote the growth of the crystal grains 61, thereby fully functioning as nucleation sites. Furthermore, the Cu concentration of the crystal grain boundaries 63 is sufficiently reduced, and a decrease in the crystallization temperature of the crystal grain boundaries 63 is suppressed. Note that the Cu concentration of the first Cu segregation portions 621 may exceed the upper limit, but this may cause the first Cu segregation portions 621 to coarsen, adversely affecting the crystal grains 61 and the crystal grain boundaries 63.

[0084] Furthermore, the Cu concentration of the first Cu segregation portions 621 is preferably 2.0 times or more, more preferably 5.0 times or more and 50 times or less, and even more preferably 7.0 times or more and 30 times or less, the Cu concentration of the crystal grains 61. This allows the first Cu segregation portions 621 to favorably generate crystal planes that promote the growth of the crystal grains 61, thereby fully functioning as nucleation sites. Furthermore, the first Cu segregation portions 621 exist without being incorporated into the crystal grains 61, thereby suppressing coarsening of the crystal grains 61. Furthermore, the Cu concentration of the crystal grains 61 is sufficiently reduced, suppressing a decrease in the saturation magnetic flux density and an increase in the coercive force of the crystal grains 61 due to Cu. The Cu concentration of the first Cu segregation portions 621 may exceed the upper limit, but this may result in coarsening of the first Cu segregation portions 621.

[0085] The Cu concentration of the first Cu segregation portion 621 and the Cu concentration of the crystal grains 61 are determined by EDX analysis using STEM on the central portion of the first Cu segregation portion 621 and the central portion of the crystal grains 61, and then quantitatively determined from the analysis results.

[0086] The Cu concentration in the grain boundary 63 is determined by subjecting the midpoint between two adjacent first Cu segregation portions 621 in the grain boundary 63 to EDX analysis using STEM, and then determining the concentration of Cu in the grain boundary 63 by a quantification method from the analysis results.

[0087] The Cu concentration in the surface layer portion 601 is preferably 1.1 times or more, and more preferably 1.2 to 3.0 times, the Cu concentration in the interior portion 602. This provides the effect of suppressing the enlargement of the crystal grains 61, even in the surface layer portion 601 where the crystal grains 61 are likely to enlarge, by the first Cu segregation portion 621 where Cu is segregated at a high concentration. This makes it possible to sufficiently increase the content ratio of the crystal grains 61 having the above-mentioned particle size in the entire particle 6.

[0088] The Cu concentration in the surface layer portion 601 is measured within the aforementioned 200 nm square range, that is, within the range including all of the crystal grains 61, the first Cu segregation portions 621, and the crystal grain boundaries 63.

[0089] The Cu concentration in the interior 602 is measured within the aforementioned 200 nm square range, that is, the range including all of the crystal grains 61, the second Cu segregation portions 622, and the crystal grain boundaries 63.

[0090] 1.4.Second Cu segregation part As described above, the particle 6 has a second Cu segregation region 622. The second Cu segregation region 622 is located in the interior 602 of the particle 6, where Cu is locally segregated. The region has a particle size of 3.0 nm or more and 10.0 nm or less. The presence of the second Cu segregation region 622 with such a particle size in the interior 602 indicates that the second Cu segregation region 622 is prevented from enlarging in the interior 602, where heat dissipation is more difficult than in the surface layer 601. Therefore, the presence of the second Cu segregation region 622 remaining relatively fine in the interior 602 indicates that the Cu segregation region 62 is distributed throughout the particle 6 with a high probability. This allows the Cu segregation region 62 to function as a nucleation site, resulting in finer crystal grains 61 with uniform particle size, thereby achieving high magnetic permeability and low coercivity. Furthermore, the electrical resistance between the crystal grains 61 is increased, further reducing the iron loss of the powder magnetic core.

[0091] The grain size of the second Cu segregation portion 622 is measured as follows. First, EDX analysis using STEM is performed on the cross section of particle 6. Next, a surface analysis image showing the Cu concentration distribution is obtained from the analysis results using a quantification method.

[0092] Next, in the obtained area analysis image, the number of Cu segregation regions 62 is counted for each particle size at a position between 2 μm and 25 μm deep from the surface of the particle 6, preferably within a 200 nm square range (interior 602) set at the center of the cross section of the particle 6. Specifically, first, binarization image processing is performed on the area analysis image representing the Cu concentration distribution, and those with a particle size of 1 nm or more are extracted as Cu segregation regions 62. The particle size is the maximum length that can be taken at the site where Cu is segregated. Of the particle sizes thus determined, those within the above range are defined as the particle sizes of the second Cu segregation regions 622.

[0093] Furthermore, the ratio of the number of the second Cu segregation portions 622 to the extracted Cu segregation portions 62 is set to 80% or more, and preferably 90% or more, thereby making it possible to realize the effect of miniaturizing the crystal grains 61 and making the grain size uniform.

[0094] If the number ratio of the second Cu segregation portions 622 is below the lower limit, there is a risk of a decrease in the dispersibility of the second Cu segregation portions 622. As a result, there is a risk that the region benefiting from the effects of miniaturizing the crystal grains 61 and making the grain size uniform may be limited to a part of the particle 6.

[0095] On the other hand, the particle 6 may include, in the interior 602, a Cu segregation portion 62 having a particle size outside the above-mentioned range, that is, a Cu segregation portion 62 that does not fall under the second Cu segregation portion 622.

[0096] Furthermore, the average grain size of the second Cu segregation portion 622 is preferably larger than the average grain size of the first Cu segregation portion 621, more preferably 1.2 times or more, and even more preferably 1.5 times or more and 2.5 times or less, of the average grain size of the first Cu segregation portion 621. Specifically, the average grain size of the second Cu segregation portion 622 is preferably 3.5 nm or more and 8.0 nm or less, and more preferably 4.0 nm or more and 6.0 nm or less. When the average grain size of the second Cu segregation portion 622 is within the above range, it is possible to form, by heat treatment, crystal grains 61 having a grain size that is slightly larger than that of the crystal grains 61 contained in the surface layer portion 601 but is sufficiently fine and more uniform. As a result, it is possible to achieve both high magnetic permeability and low coercivity of the soft magnetic powder.

[0097] The average grain size of the second Cu segregation portions 622 is calculated by counting the number of the second Cu segregation portions 622 for each grain size and calculating the average grain size from the counting results of 10 or more.

[0098] The maximum Cu concentration of the second Cu segregation regions 622 is not particularly limited, but is preferably greater than 6.0 atomic percent. By including the second Cu segregation regions 622 in which Cu is segregated at a high concentration, the function of the second Cu segregation regions 622 as nucleation sites is strengthened during heat treatment. This allows crystal grains 61 of uniform size to be efficiently generated from the surface to deep positions of the particles 6. As a result, it is possible to achieve both averaging of the magnetocrystalline anisotropy and an increase in the proportion of crystal grains 61 of uniform size, thereby more effectively achieving both low coercivity and high magnetic permeability.

[0099] The maximum value of the Cu concentration in the second Cu segregation portion 622 is set to more than 6.0 atomic % as described above, but is preferably set to 10.0 atomic % or more, and more preferably set to 16.0 atomic % or more.

[0100] On the other hand, from the viewpoint of avoiding uneven distribution of the second Cu segregation portions 622, the maximum value of the Cu concentration is preferably 70.0 atomic % or less, and more preferably 60.0 atomic % or less.

[0101] 1.5. Grain Boundaries As described above, the particle 6 has a crystal grain boundary 63. The crystal grain boundary 63 is a region having an amorphous structure adjacent to the crystal grain 61, and is preferably a region having higher Nb and B concentrations than the crystal grain 61. Therefore, the crystal grain boundary 63 can be identified based on the structure, Nb concentration distribution, and B concentration distribution. Since the crystallization temperature is high at such a crystal grain boundary 63, the amorphous state is likely to be maintained even after heat treatment. Therefore, the crystal grain boundary 63 has the effect of suppressing the crystal grain 61 from coarsening. This makes it easier to maintain the grain size of the crystal grain 61 finer and more uniform.

[0102] The content ratio of the crystal grain boundaries 63 in the particles 6 is preferably 5.0 times or less, more preferably 0.02 times or more and 2.0 times or less, and even more preferably 0.10 times or more and less than 1.0 times, of the content ratio of the crystal grains 61. This optimizes the balance of the ratio between the crystal grains 61 and the crystal grain boundaries 63. As a result, the crystal grains 61 are made finer and the grain size is made more uniform.

[0103] The Nb concentration of the crystal grain boundaries 63 is preferably higher than the Nb concentration of the crystal grains 61, more preferably at least 1.3 times, and even more preferably at least 1.5 times and no more than 6.0 times. This sufficiently increases the crystallization temperature of the crystal grain boundaries 63. Therefore, when the soft magnetic powder is heat-treated, crystallization of the crystal grain boundaries 63 is suppressed. As a result, the crystal grain boundaries 63 suppress coarsening of the crystal grains 61. Note that the Nb concentration of the crystal grain boundaries 63 may exceed the upper limit, but depending on the composition ratio, this may actually lower the crystallization temperature of the crystal grain boundaries 63.

[0104] The B concentration of the crystal grain boundaries 63 is preferably higher than the B concentration of the crystal grains 61, more preferably at least 1.1 times, and even more preferably at least 1.2 times and no more than 5.0 times. This sufficiently increases the crystallization temperature of the crystal grain boundaries 63. Therefore, when the soft magnetic powder is heat-treated, crystallization of the crystal grain boundaries 63 is suppressed. As a result, the crystal grain boundaries 63 suppress coarsening of the crystal grains 61. Note that the B concentration of the crystal grain boundaries 63 may exceed the upper limit, but depending on the composition ratio, this may actually lower the crystallization temperature of the crystal grain boundaries 63.

[0105] The Nb concentration and B concentration at the grain boundary 63 are determined by subjecting the grain boundary 63 to an EDX analysis using a STEM at the midpoint between two adjacent grains 61, and then quantifying the analysis results.

[0106] The Nb concentration and B concentration of the crystal grain 61 are determined by subjecting the central portion of the crystal grain 61 to EDX analysis using STEM, and then quantifying the analysis results.

[0107] 1.6. Effects of the embodiment As described above, the soft magnetic powder according to this embodiment contains Fe x Cu a Nb b (Si 1-y B y ) 100-x-a-b The particles 6 have a composition expressed by the formula: a, b, and x are each a number expressed in atomic percent. a satisfies 0.3≦a≦2.0, b satisfies 2.0≦b≦4.0, and x satisfies 72.5≦x<75.5. y is a number that satisfies f(x)≦y≦0.99, and f(x)=(4×10 -34 )x 17.56 is.

[0108] The particle 6 has a crystal grain 61, a Cu segregation portion 62, and a crystal grain boundary 63. The crystal grain 61 has a grain size of 1.0 nm or more and 30.0 nm or less and is a region containing Fe—Si crystals. The Cu segregation portion 62 is a region where Cu is segregated.

[0109] The Cu segregation portion 62 located in the surface layer portion 601 of the particle 6 and having a particle size of 1.0 nm or more and 5.0 nm or less is referred to as the first Cu segregation portion 621. The Cu segregation portion 62 located in the interior 602 of the particle 6 and having a particle size of 3.0 nm or more and 10.0 nm or less is referred to as the second Cu segregation portion 622. The content ratio of crystal grains 61 in the particle 6 is 30% or more. Furthermore, among the Cu segregation portions 62 located in the surface layer portion 601, the number ratio of the first Cu segregation portions 621 is 80% or more. Furthermore, among the Cu segregation portions 62 located in the interior 602, the number ratio of the second Cu segregation portions 622 is 80% or more.

[0110] This configuration allows the fine Cu segregation portions 62 to be dispersed evenly within the particles 6, thereby enabling the crystal grains 61 to be refined and have a uniform particle size. This results in a soft magnetic powder that combines low coercivity with high magnetic permeability at high frequencies. Furthermore, the particles 6 have high internal electrical resistance, making it difficult for eddy currents to flow. As a result, a powder magnetic core with low iron loss and high magnetic permeability can be realized. This also allows for the realization of a magnetic element with excellent electromagnetic conversion efficiency at high frequencies.

[0111] In addition, it is not necessary for all particles in the soft magnetic powder according to the embodiment to have the above-described structure, and it may contain particles that do not have the above-described structure, but it is preferable that 95% by mass or more of the particles have the above-described structure.

[0112] Furthermore, the soft magnetic powder according to the embodiment may be mixed with other soft magnetic powders or non-soft magnetic powders, and the mixed powder may be used for producing a powder core or the like.

[0113] 1.7.Si segregation area Although not shown, the particle 6 may include a Si segregation portion where Si is segregated. This Si segregation portion exists near the surface of the particle 6. In other words, the Si segregation portion exists between the Cu segregation portion 62 and the surface of the particle 6. By including the Si segregation portion existing at such a position, the insulating properties of the particle 6 are improved. This makes it possible to suppress the generation of eddy currents that pass through the paths between the particles 6.

[0114] The Si segregated portion can be identified from an area analysis image obtained by EDX analysis using a STEM on the cross section of the particle 6. Specifically, elemental analysis is performed on a 250 nm square area including the surface of the cross section of the particle 6, and the Si segregated portion is identified as a region where the Si concentration is locally high. In this case, it is preferable that the image shows a range of 200 nm or more deep from the surface of the particle.

[0115] The Si concentration in the Si segregated portion is preferably 10.0 atomic % or more, more preferably 15.0 atomic % to 60.0 atomic % or less, and even more preferably 20.0 atomic % to 50.0 atomic % or less. If the Si concentration exceeds the upper limit, the amount of Si distributed to the crystal grains 61 will relatively decrease, and the high saturation magnetic flux density derived from the crystal grains 61 may be impaired. The Si concentration in the Si segregated portion is determined as the maximum value when the Si concentration in the range shown in the image is measured by elemental analysis using EDX.

[0116] Furthermore, such Si segregation portions are likely to be formed when the particles 6 have the composition described above, particularly when the relationship between x and y is within the region shown in FIG.

[0117] 1.8.Fe concentration distribution In the particles 6, the Fe concentration at a position 12 nm from the surface is preferably higher than the O concentration in terms of atomic concentration ratio. This makes it possible to realize particles 6 in which the oxide film, whose main component is an oxide such as SiO2, is prevented from becoming thicker than necessary. In other words, by minimizing the thickness of the oxide film and reducing the amount of Si in the oxide film, the amount of Si distributed in the crystal grains 61 can be ensured, and the content ratio occupied by the crystal grains 61 can be sufficiently ensured. As a result, a soft magnetic powder with higher saturation magnetic flux density and magnetic permeability can be obtained.

[0118] The Fe concentration and O concentration can be determined from a surface analysis image (mapping image) and a line analysis result (line scan result) obtained by EDX analysis using a STEM on a cross section of the particle 6.

[0119] The difference between the Fe concentration and the O concentration is not particularly limited, but is preferably 10 atomic % or more, and more preferably 30 atomic % or more. The upper limit of the difference between the Fe concentration and the O concentration is not particularly limited, but is preferably 80 atomic % or less, and more preferably 60 atomic % or less.

[0120] 1.9.Various characteristics In the soft magnetic powder according to the embodiment, the Vickers hardness of the particles 6 is preferably 1000 or more and 3000 or less, and more preferably 1200 or more and 2500 or less. When the soft magnetic powder containing particles 6 with such hardness is compression-molded into a powder core, deformation at the contact points between the particles 6 is minimized. This keeps the contact area small, and improves the insulation between the particles 6 in the powder core.

[0121] If the Vickers hardness is below the lower limit, depending on the average particle size of the soft magnetic powder, the particles 6 may be easily crushed at the contact points between them when the soft magnetic powder is compression-molded. This increases the contact area, which may reduce the insulation between the particles 6 in the powder core. On the other hand, if the Vickers hardness is above the upper limit, depending on the average particle size of the soft magnetic powder, the powder compactibility may decrease, reducing the density of the resulting powder core, which may reduce the saturation magnetic flux density and magnetic permeability of the powder core.

[0122] The Vickers hardness of the particle 6 is measured by a micro Vickers hardness tester at the center of the cross section of the particle 6. The center of the cross section of the particle 6 is the position corresponding to the midpoint of the long axis on the cut surface when the particle 6 is cut. The pressing load of the indenter during the test is 1.96 N.

[0123] The average particle size D50 of the soft magnetic powder is not particularly limited, but is preferably 1 μm to 50 μm, more preferably 5 μm to 45 μm, and even more preferably 10 μm to 30 μm. By using soft magnetic powder with such an average particle size, the path along which eddy currents flow can be shortened, making it possible to manufacture a powder magnetic core that can sufficiently suppress eddy current loss generated within the particles 6.

[0124] Furthermore, when the soft magnetic powder has an average particle size of 10 μm or more, it can be mixed with a soft magnetic powder having a smaller average particle size than the soft magnetic powder according to the embodiment to produce a mixed powder that can achieve a high green density. This mixed powder is also one embodiment of the soft magnetic powder according to the present invention. With such a mixed powder, the particle size distribution can be easily adjusted, making it easier to increase the packing density of the powder core, and the saturation magnetic flux density and magnetic permeability of the powder core can be increased.

[0125] The average particle size D50 of the soft magnetic powder is determined as the particle size at which the cumulative 50% from the smallest diameter side is reached in the volume-based particle size distribution obtained by laser diffraction.

[0126] If the average particle size of the soft magnetic powder is below the lower limit, the soft magnetic powder may become too fine, which may reduce the packing ability of the soft magnetic powder. This reduces the compaction density of the powder core, which is an example of a powder compact. Depending on the material composition and mechanical properties of the soft magnetic powder, the saturation magnetic flux density and magnetic permeability of the powder core may decrease. On the other hand, if the average particle size of the soft magnetic powder is above the upper limit, depending on the material composition and mechanical properties of the soft magnetic powder, the eddy current loss generated within the particles 6 may not be sufficiently suppressed, which may increase the iron loss of the powder core.

[0127] For soft magnetic powders, when the volume-based particle size distribution obtained by laser diffraction is measured, the particle size at the 10% cumulative size from the smallest diameter side is defined as D10, and the particle size at the 90% cumulative size from the smallest diameter side is defined as D90. (D90-D10) / D50 is preferably 1.0 to 2.5, more preferably 1.2 to 2.3. (D90-D10) / D50 is an index indicating the degree of spread of the particle size distribution. By keeping this index within the above range, the packing properties of the soft magnetic powder are improved. This results in a compact with particularly high magnetic properties, such as magnetic permeability and saturation magnetic flux density.

[0128] The coercive force of the soft magnetic powder is not particularly limited, but is preferably less than 2.0 Oe (less than 160 A / m), and more preferably 0.1 Oe to 1.5 Oe (39.9 A / m to 120 A / m). By using soft magnetic powder with such a low coercive force, it is possible to produce a powder magnetic core in which hysteresis loss is sufficiently suppressed even at high frequencies.

[0129] The coercive force of the soft magnetic powder can be measured using a vibrating sample magnetometer such as TM-VSM1230-MHHL manufactured by Tamagawa Seisakusho Co., Ltd.

[0130] The maximum magnetization of the soft magnetic powder is Mm [emu / g], and the true density of particle 6 is ρ [g / cm 3], the saturation magnetic flux density Bs [T] calculated by 4π / 10000 × ρ × Mm = Bs is preferably 1.0 [T] or more, and more preferably 1.1 [T] or more. By using soft magnetic powder with such a high saturation magnetic flux density, it is possible to realize a powder magnetic core that is less likely to saturate even at high currents.

[0131] The true density ρ of the soft magnetic powder is measured using a fully automatic gas displacement densitometer, AccuPyc1330, manufactured by Micromeritics, Inc. The maximum magnetization Mm of the soft magnetic powder is measured using a vibrating sample magnetometer, VSM system, TM-VSM1230-MHHL, manufactured by Tamagawa Seisakusho Co., Ltd.

[0132] Furthermore, when the soft magnetic powder is formed into a cylindrical compact with an inner diameter of 8 mm and a mass of 0.7 g, and this compact is compressed axially with a load of 20 kgf, the resistance of the compact in the axial direction is preferably 0.3 kΩ or more, and more preferably 1.0 kΩ or more. Soft magnetic powders that can produce compacts with such resistance values ​​have sufficient insulation between particles. Therefore, such soft magnetic powders contribute to the realization of magnetic elements that can suppress eddy current loss.

[0133] The upper limit of the resistance value is not particularly limited, but in consideration of suppressing variations, it is preferably 30.0 kΩ or less, and more preferably 9.0 kΩ or less.

[0134] 2. Manufacturing method of soft magnetic powder Next, a method for producing the soft magnetic powder will be described.

[0135] The soft magnetic powder may be produced by any manufacturing method, for example, by subjecting metal powder produced through various powdering methods such as atomization methods such as water atomization, gas atomization, and rotary water flow atomization, reduction methods, carbonyl methods, and pulverization methods to a crystallization treatment.

[0136] Atomization methods include water atomization, gas atomization, and rotary water atomization, depending on the type of coolant and the device configuration. The soft magnetic powder is preferably produced via atomization, more preferably via water atomization or rotary water atomization, and even more preferably via rotary water atomization. Atomization is a method of producing powder by pulverizing and cooling molten metal by colliding it with a fluid such as a liquid or gas sprayed at high speed. Using such atomization methods, a high cooling rate can be achieved, thereby promoting amorphization. As a result, crystal grains with a more uniform particle size can be formed by heat treatment.

[0137] In this specification, the term "water atomization" refers to a method of producing metal powder by using a liquid such as water or oil as a coolant, spraying it in an inverted cone shape that converges to one point, and then causing molten metal to flow down and collide with the converging point, thereby pulverizing the molten metal.

[0138] Furthermore, the rotary water jet atomization method allows the molten metal to be cooled extremely rapidly, so that the disordered atomic arrangement of the molten metal can be maintained to a high degree during solidification. Therefore, by carrying out a crystallization treatment after that, it is possible to efficiently produce metal powder having crystal grains with a uniform particle size.

[0139] The method for producing metal powder by the rotary water jet atomization method will be further described below. In the rotary water atomization method, a coolant is sprayed along the inner surface of a cooling cylinder and rotated along the inner surface of the cooling cylinder, forming a coolant layer on the inner surface. Meanwhile, raw metal powder is melted, and the resulting molten metal is allowed to fall naturally while a liquid or gas jet is sprayed onto it. This causes the molten metal to splash and become entrained in the coolant layer. As a result, the splashed, finely divided molten metal is rapidly cooled and solidified, yielding metal powder.

[0140] FIG. 5 is a vertical cross-sectional view showing an example of an apparatus for producing metal powder by the rotary water jet atomization method.

[0141] The powder manufacturing apparatus 30 shown in FIG. 5 includes a cooling cylinder 1, a crucible 15, a pump 7, and a jet nozzle 24. The cooling cylinder 1 is a cylinder for forming a cooling liquid layer 9 on its inner circumferential surface. The crucible 15 is a supply container for supplying molten metal 25 so that it flows down into a space 23 inside the cooling liquid layer 9. The pump 7 supplies the cooling liquid to the cooling cylinder 1. The jet nozzle 24 sprays a gas jet 26 that breaks the flowing molten metal 25 into droplets. The molten metal 25 is prepared according to the composition of the soft magnetic powder.

[0142] The cooling cylinder 1 has a cylindrical shape and is installed so that the axis of the cylinder is aligned vertically or tilted at an angle of 30° or less relative to the vertical.

[0143] The upper opening of the cooling cylinder 1 is closed by a lid 2. The lid 2 is formed with an opening 3 for supplying the flowing molten metal 25 to the space 23 of the cooling cylinder 1.

[0144] A cooling liquid ejection pipe 4 is provided at the top of the cooling cylinder 1 to eject cooling liquid onto the inner circumferential surface of the cooling cylinder 1. A plurality of ejection ports 5 of the cooling liquid ejection pipe 4 are provided at equal intervals along the circumferential direction of the cooling cylinder 1.

[0145] The coolant jetting pipe 4 is connected to a tank 8 via a pipe connected to a pump 7, and the coolant in the tank 8 is pumped up by the pump 7 and jetted into the cooling cylinder 1 via the coolant jetting pipe 4. As a result, the coolant gradually flows down while rotating along the inner surface of the cooling cylinder 1, forming a coolant layer 9 along the inner surface. Note that a cooler may be interposed in the tank 8 or along the circulation flow path as needed. In addition to water, oils such as silicone oil may be used as the coolant, and various additives may also be added. Furthermore, by removing dissolved oxygen from the coolant in advance, oxidation of the powder produced during cooling can be suppressed.

[0146] In addition, a layer thickness adjusting ring 16 for adjusting the thickness of the coolant layer 9 is detachably provided on the lower part of the inner circumferential surface of the cooling cylinder 1. By providing this layer thickness adjusting ring 16, the flow rate of the coolant is reduced, and the thickness of the coolant layer 9 can be ensured and made uniform.

[0147] Furthermore, a cylindrical draining mesh 17 is connected to the bottom of the cooling cylinder 1, and a funnel-shaped powder collection container 18 is provided below this draining mesh 17. A coolant collection cover 13 is provided around the draining mesh 17 so as to cover it, and a drain port 14 formed at the bottom of this coolant collection cover 13 is connected to the tank 8 via piping.

[0148] Jet nozzle 24 is provided in space 23. Jet nozzle 24 is attached to the tip of gas supply pipe 27 inserted through opening 3 of lid 2, and is positioned so that its nozzle is directed toward molten metal 25 in the form of a thin stream.

[0149] To produce metal powder in such powder production apparatus 30, first, pump 7 is operated to form a coolant layer 9 on the inner circumferential surface of cooling cylinder 1. Next, molten metal 25 in crucible 15 is caused to flow down into space 23. When gas jet 26 is blown onto the flowing molten metal 25, molten metal 25 is scattered, and the finely pulverized molten metal 25 is caught in coolant layer 9. As a result, the finely pulverized molten metal 25 cools and solidifies, and metal powder is obtained.

[0150] In the rotary water jet atomization method, a continuous supply of cooling liquid allows for a stable, extremely high cooling rate, which stabilizes the amorphous state of the metal powder produced before heat treatment. As a result, by carrying out a subsequent crystallization treatment, soft magnetic powder with crystal grains of uniform size can be efficiently produced.

[0151] Furthermore, the molten metal 25 atomized to a certain size by the gas jet 26 falls by inertia until it is caught in the cooling liquid layer 9, and at that time the droplets are made spherical.

[0152] For example, the flow rate of molten metal 25 flowing down from crucible 15 varies depending on the size of the apparatus and is not particularly limited, but is preferably kept to 1 kg per minute or less. This ensures that molten metal 25 scatters as droplets of appropriate size, resulting in soft magnetic powder with the average particle size described above. Furthermore, by limiting the amount of molten metal 25 supplied per unit time to a certain extent, a sufficient cooling rate can be achieved. Note that, for example, by reducing the flow rate of molten metal 25 within the above range, adjustments can be made to reduce the average particle size of the metal powder.

[0153] On the other hand, the outer diameter of the thin stream of molten metal 25 flowing down from crucible 15, i.e., the inner diameter of the outlet of crucible 15, is not particularly limited, but is preferably 1 mm or less. This makes it easier to uniformly apply gas jet 26 to the thin stream of molten metal 25, making it easier to uniformly scatter droplets of an appropriate size. As a result, metal powder with the average particle size described above is obtained. Furthermore, since the amount of molten metal 25 supplied per unit time is reduced, the cooling rate is increased.

[0154] The flow velocity of the gas jet 26 is not particularly limited, but is preferably set to 100 m / s or more and 1000 m / s or less. This also allows the molten metal 25 to be scattered as droplets of appropriate size, thereby obtaining metal powder with the average particle size described above. Furthermore, since the gas jet 26 has sufficient velocity, the scattered droplets are also given sufficient velocity, making the droplets finer and shortening the time it takes for the droplets to become entrained in the cooling liquid layer 9. As a result, the droplets can be sphericalized in a short time and cooled in a short time. Note that, for example, by increasing the flow velocity of the gas jet 26 within the above range, the average particle size of the metal powder can be reduced.

[0155] As other conditions, for example, it is preferable to set the pressure of the coolant supplied to the cooling cylinder 1 at the time of ejection to about 50 MPa or more and 200 MPa or less, and the liquid temperature to about -10°C or more and 40°C or less. This optimizes the flow rate of the coolant layer 9, and allows the pulverized molten metal 25 to be cooled appropriately and evenly.

[0156] Furthermore, the temperature of molten metal 25 is preferably set to about Tm+20°C or more and Tm+200°C or less, where Tm is the melting point of the metal powder to be produced, and more preferably set to about Tm+50°C or more and Tm+150°C or less. This makes it possible to minimize variations in properties among particles when molten metal 25 is pulverized by gas jet 26, and more reliably make the produced metal powder amorphous before heat treatment. The gas jet 26 can be replaced with a liquid jet if necessary.

[0157] In addition, the cooling rate when cooling the molten metal 25 in the atomization method is 1×10 4 °C / s or more, and 1 × 10 5 °C / s or more is more preferable, and 1 × 10 6 It is more preferable that the cooling rate is 100°C / s or higher. Such rapid cooling allows for particularly stable amorphization, ultimately resulting in soft magnetic powder with crystal grains of uniform size. It also reduces variations in the composition ratio between particles of the soft magnetic powder. Furthermore, by increasing the cooling rate, the Fe concentration can be made higher than the O concentration.

[0158] The metal powder produced as described above is subjected to a crystallization treatment, whereby at least a portion of the amorphous structure is crystallized to form crystal grains.

[0159] The crystallization treatment can be carried out by subjecting a metal powder containing an amorphous structure to a heat treatment. The heat treatment temperature is not particularly limited, but is preferably 520°C to 640°C, more preferably 530°C to 630°C, and even more preferably 540°C to 620°C. Furthermore, the heat treatment time is preferably maintained at the temperature for 1 minute to 180 minutes, more preferably 3 minutes to 120 minutes, and even more preferably 5 minutes to 60 minutes. By setting the heat treatment temperature and time within the above ranges, crystal grains with a more uniform particle size can be produced.

[0160] If the heat treatment temperature or time is below the lower limit, crystallization may be insufficient and the particle size may be less uniform, depending on the composition of the metal powder. On the other hand, if the heat treatment temperature or time is above the upper limit, crystallization may be excessive and the particle size may be less uniform, depending on the composition of the metal powder.

[0161] The heating and cooling rates in the crystallization treatment affect the grain size and uniformity of the crystal grains generated by the heat treatment, the distribution, grain size, and Cu concentration of Cu segregated areas, and the Nb and B concentrations at the grain boundaries.

[0162] The heating rate is preferably 10°C / min or more and 35°C / min or less, more preferably 10°C / min or more and 30°C / min or less, and even more preferably 15°C / min or more and 25°C / min or less. By setting the heating rate within the above range, the distribution and grain size of the Cu segregation region and the Cu concentration can be kept within the above range, and the Nb concentration and B concentration at the grain boundary can be kept within the above range. This also allows the grain size and content ratio of the crystal grains to be kept within the above range. Note that if the heating rate is below the above lower limit, the time exposed to high temperature will be extended, but the grain size of the Cu segregation region will not increase, and the Nb concentration and B concentration at the grain boundary may not increase sufficiently. As a result, the content ratio of the crystal grains will increase and the grain size of the crystal grains may become too large. If the heating rate exceeds the upper limit, the time exposed to high temperatures will be shortened, but the grain size of the Cu segregated portion will increase, and the Nb and B concentrations at the grain boundaries may increase more than necessary. This may result in a decrease in the content of crystal grains. Furthermore, the distribution of the Cu segregated portion may become too shallow, and the Cu concentration may become too low.

[0163] The temperature drop rate is preferably 40°C / min to 80°C / min, more preferably 50°C / min to 70°C / min, and even more preferably 55°C / min to 65°C / min. By setting the temperature drop rate within the above range, the distribution and grain size of the Cu segregation region and the Cu concentration can be kept within the above ranges, and the Nb and B concentrations at the grain boundaries can also be kept within the above ranges. This allows the grain size and content ratio of the crystal grains to be kept within the above ranges. If the temperature drop rate is below the lower limit, the time exposed to high temperatures will be extended, but the grain size of the Cu segregation region will be small, and the Nb and B concentrations at the grain boundaries may not be sufficiently increased. Therefore, the content ratio of the crystal grains will increase and the grain size of the crystal grains may become too large. If the temperature drop rate exceeds the upper limit, the time exposed to high temperatures will be shortened, but the grain size of the Cu segregated portion will increase, and the Nb and B concentrations at the grain boundaries may increase more than necessary. This may result in a decrease in the content of crystal grains. Furthermore, the distribution of the Cu segregated portion may become too shallow, and the Cu concentration may become too low.

[0164] The atmosphere for the crystallization treatment is not particularly limited, but is preferably an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere such as hydrogen or ammonia decomposition gas, or a reduced pressure atmosphere thereof, which allows crystallization while suppressing oxidation of the metal, and results in a soft magnetic powder with excellent magnetic properties. In this manner, the soft magnetic powder according to this embodiment can be manufactured.

[0165] The soft magnetic powder thus obtained may be classified as necessary. Examples of classification methods include dry classification such as sieving classification, inertial classification, centrifugal classification, and air classification, and wet classification such as sedimentation classification.

[0166] If necessary, an insulating film may be formed on the surface of each particle of the obtained soft magnetic powder. Examples of materials constituting this insulating film include inorganic materials such as phosphates such as magnesium phosphate, calcium phosphate, zinc phosphate, manganese phosphate, and cadmium phosphate, and silicates such as sodium silicate. Alternatively, the insulating film may be appropriately selected from the organic materials listed as constituent materials of the binder described below.

[0167] 3. Powder cores and magnetic elements Next, the powder magnetic core and the magnetic element according to the embodiment will be described.

[0168] The magnetic element according to the embodiment can be applied to various magnetic elements having a magnetic core, such as a choke coil, an inductor, a noise filter, a reactor, a transformer, a motor, an actuator, a solenoid valve, a generator, etc. Furthermore, the powder magnetic core according to the embodiment can be applied to the magnetic cores provided in these magnetic elements.

[0169] Two types of coil components will be described below as representative examples of magnetic elements. 3.1.Toroidal type First, a toroidal type coil component will be described as an example of a magnetic element according to the embodiment.

[0170] FIG. 6 is a plan view schematically showing a toroidal type coil component. 6 has a ring-shaped powder magnetic core 11 and a conductive wire 12 wound around this powder magnetic core 11. Such a coil component 10 is generally called a toroidal coil.

[0171] The powder magnetic core 11 is obtained by mixing the soft magnetic powder according to the embodiment with a binder, feeding the resulting mixture into a molding die, and then pressurizing and molding it. That is, the powder magnetic core 11 is a compact containing the soft magnetic powder according to the embodiment. Such a powder magnetic core 11 has high saturation magnetic flux density and magnetic permeability, and low iron loss. As a result, when the powder magnetic core 11 is installed in an electronic device or the like, it is possible to reduce the power consumption of the electronic device or the like and improve its performance, thereby contributing to improving the reliability of the electronic device or the like. The binder may be added as needed, or may be omitted.

[0172] Furthermore, the magnetic permeability of the powder magnetic core 11 measured at a measurement frequency of 100 MHz is preferably 18.0 or more, and more preferably 19.5 or more. Such a powder magnetic core 11 can realize a magnetic element with excellent DC bias characteristics and high electromagnetic conversion efficiency at high frequencies. Note that, when measuring the magnetic permeability, the powder magnetic core 11 is prepared by compacting soft magnetic powder at a compaction pressure of 294 MPa (3 t / cm). 2 ) to form a ring-shaped powder core 11 having an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm, and the magnetic permeability is measured in this state with a conductor having a wire diameter of 0.6 mm wound seven times around the powder core 11.

[0173] The magnetic permeability of the powder magnetic core 11 is the relative magnetic permeability calculated from the self-inductance of the closed magnetic circuit magnetic core coil, i.e., the effective magnetic permeability. To measure the magnetic permeability, an impedance analyzer such as the 4194A manufactured by Agilent Technologies, Inc. is used. The number of turns of the winding is 7, and the wire diameter of the winding is 0.6 mm.

[0174] The iron loss of the powder magnetic core 11 measured at a maximum magnetic flux density of 50 mT and a measurement frequency of 900 kHz was 9000 [kW / m 3 ] or less, and 7000 [kW / m 3 ] or less, and 6500 [kW / m 3] or less. With such a powder magnetic core 11, a magnetic element with high electromagnetic conversion efficiency at high frequencies can be realized. Note that, for the powder magnetic core 11 used when measuring the iron loss, soft magnetic powder was compacted under a compacting pressure of 294 MPa (3 t / cm 2 ) to form a ring-shaped powder core 11 with an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm, and iron loss is measured in this state with a conductor with a wire diameter of 0.5 mm wound 36 times around each of the primary and secondary sides of this powder core 11.

[0175] Furthermore, the coil component 10 including such a powder magnetic core 11 has low iron loss and high performance.

[0176] Examples of materials constituting the binder used to fabricate the powder magnetic core 11 include organic materials such as silicone resins, epoxy resins, phenolic resins, polyamide resins, polyimide resins, and polyphenylene sulfide resins, and inorganic materials such as phosphates such as magnesium phosphate, calcium phosphate, zinc phosphate, manganese phosphate, and cadmium phosphate, and silicates such as sodium silicate. Thermosetting polyimide or epoxy resins are particularly preferred. These resin materials are easily cured by heating and have excellent heat resistance. This improves the ease of manufacturing and heat resistance of the powder magnetic core 11.

[0177] The ratio of binder to soft magnetic powder varies slightly depending on the target magnetic flux density, mechanical properties, allowable eddy current loss, etc. of the powder core 11 to be produced, but is preferably about 0.5% by mass to 5% by mass, and more preferably about 1% by mass to 3% by mass. This allows the particles of the soft magnetic powder to be sufficiently bound together, and enables the production of powder core 11 with excellent magnetic properties such as magnetic flux density and magnetic permeability. If necessary, various additives may be added to the mixture for any purpose.

[0178] The conductive wire 12 may be made of a highly conductive material, such as a metal material containing Cu, Al, Ag, Au, Ni, etc. If necessary, an insulating film may be provided on the surface of the conductive wire 12.

[0179] The shape of the powder magnetic core 11 is not limited to the ring shape shown in FIG. 6, but may be, for example, a shape in which a part of the ring is missing, or a shape in which the longitudinal direction is linear.

[0180] Furthermore, the powder magnetic core 11 may contain soft magnetic powder other than the soft magnetic powder according to the embodiment described above or non-magnetic powder, as needed.

[0181] 3.2.Closed magnetic circuit type Next, a closed magnetic circuit type coil component, which is an example of a magnetic element according to the embodiment, will be described.

[0182] FIG. 7 is a see-through perspective view that schematically shows a closed magnetic circuit type coil component. The closed magnetic circuit type coil component will be described below, but the following description will focus on the differences from the toroidal type coil component, and a description of similar points will be omitted.

[0183] 7, the coil component 20 according to this embodiment is formed by embedding a conductor wire 22 formed into a coil shape inside a powder magnetic core 21. That is, the coil component 20 is formed by molding the conductor wire 22 with the powder magnetic core 21. This powder magnetic core 21 has a configuration similar to that of the powder magnetic core 11 described above.

[0184] It is easy to obtain a relatively small coil component 20 having this configuration. In manufacturing such a small coil component 20, by using a powder magnetic core 21 that has high magnetic flux density and permeability and low loss (core loss), it is possible to obtain a coil component 20 that is small in size, yet has low loss and low heat generation and is capable of handling a large current.

[0185] Furthermore, because the conductive wire 22 is embedded inside the powder core 21, gaps are unlikely to occur between the conductive wire 22 and the powder core 21. This makes it possible to suppress vibrations caused by magnetostriction of the powder core 21, and also to suppress the generation of noise associated with this vibration.

[0186] When manufacturing the coil device 20 according to the present embodiment as described above, first, the conductive wire 22 is placed in the cavity of a molding die, and the cavity is filled with granulated powder containing the soft magnetic powder according to the embodiment. That is, the granulated powder is filled so as to encompass the conductive wire 22.

[0187] Next, the granulated powder is pressed together with the conductive wire 22 to obtain a compact. Next, similarly to the above embodiment, the compact is subjected to a heat treatment, thereby hardening the binder and obtaining the powder magnetic core 21 and the coil component 20.

[0188] The powder magnetic core 21 may contain soft magnetic powder other than the soft magnetic powder according to the embodiment described above or non-magnetic powder, as needed.

[0189] 4.Electronic equipment Next, an electronic device including the magnetic element according to the embodiment will be described with reference to FIGS.

[0190] Fig. 8 is a perspective view showing a mobile personal computer, which is an electronic device including the magnetic element according to the embodiment. The personal computer 1100 shown in Fig. 8 includes a main body 1104 including a keyboard 1102, and a display unit 1106 including a display unit 100. The display unit 1106 is rotatably supported on the main body 1104 via a hinge structure. Such a personal computer 1100 includes a magnetic element 1000, such as a choke coil or inductor for a switching power supply, or a motor.

[0191] Fig. 9 is a plan view showing a smartphone, which is an electronic device including the magnetic element according to the embodiment. The smartphone 1200 shown in Fig. 9 includes a plurality of operation buttons 1202, an earpiece 1204, and a mouthpiece 1206. A display unit 100 is disposed between the operation buttons 1202 and the earpiece 1204. Such a smartphone 1200 includes a magnetic element 1000, such as an inductor, a noise filter, or a motor, built in.

[0192] 10 is a perspective view showing a digital still camera, which is an electronic device including the magnetic element according to the embodiment. The digital still camera 1300 photoelectrically converts an optical image of a subject using an imaging element such as a CCD (Charge Coupled Device) to generate an imaging signal.

[0193] 10 includes a display unit 100 provided on the back of a case 1302. The display unit 100 functions as a viewfinder that displays an object as an electronic image. A light receiving unit 1304 including an optical lens, a CCD, etc. is provided on the front side of the case 1302, i.e., the back side in the figure.

[0194] When the photographer checks the subject image displayed on the display unit 100 and presses the shutter button 1306, the image signal from the CCD at that time is transferred to and stored in memory 1308. This digital still camera 1300 also incorporates magnetic elements 1000 such as inductors and noise filters.

[0195] Examples of electronic devices according to the embodiments include the personal computer of FIG. 8, the smartphone of FIG. 9, and the digital still camera of FIG. 10, as well as mobile phones, tablet terminals, watches, inkjet ejection devices such as inkjet printers, laptop personal computers, televisions, video cameras, video tape recorders, car navigation devices, pagers, electronic organizers, electronic dictionaries, calculators, electronic game devices, word processors, workstations, videophones, security television monitors, electronic binoculars, POS terminals, medical devices such as electronic thermometers, blood pressure monitors, blood glucose meters, electrocardiogram measuring devices, ultrasound diagnostic devices, and electronic endoscopes, fish finders, various measuring devices, instruments for vehicles, aircraft, and ships, mobile object control devices such as automobile control devices, aircraft control devices, railway vehicle control devices, and ship control devices, and flight simulators.

[0196] As described above, such electronic devices include the magnetic element 1000 according to the embodiment, which provides the effects of the magnetic element, such as low coercive force and high saturation magnetic flux density, and allows for miniaturization and increased output of the electronic devices.

[0197] The soft magnetic powder, dust core, magnetic element, and electronic device of the present invention have been described above based on preferred embodiments, but the present invention is not limited to these.

[0198] For example, in the above embodiment, a compacted powder such as a dust core has been described as an example of an application of the soft magnetic powder of the present invention, but the application examples are not limited to this and may also be, for example, a magnetic fluid, a magnetorheological elastomer composition, a magnetic head, an electromagnetic wave shielding member, or other magnetic devices. Furthermore, the shapes of the powder magnetic core and the magnetic element are not limited to those shown in the drawings, and may be any shape. [Example]

[0199] Next, specific examples of the present invention will be described. 5. Manufacturing of powder magnetic cores 5.1. Sample No. 1 First, the raw materials were melted in a high-frequency induction furnace and pulverized by a rotary water jet atomization method to obtain metal powder. The flow rate of the molten metal from the crucible was 0.5 kg / min, the inner diameter of the crucible's outlet was 1 mm, and the gas jet flow rate was 900 m / s. The metal powder was then classified using a wind classifier. The composition of the resulting metal powder is shown in Table 1. The composition was determined using a SPECTRO solid-state optical emission spectrometer, model SPECTROLAB, type LAVMB08A. The total impurity content was found to be 0.50 atomic % or less.

[0200] Next, the particle size distribution of the obtained metal powder was measured. This measurement was performed using a laser diffraction particle size distribution measuring device, Microtrac HRA9320-X100 manufactured by Nikkiso Co., Ltd. The average particle size D50 of the metal powder was determined from the particle size distribution and was found to be 20 μm. Furthermore, the obtained metal powder was evaluated using an X-ray diffractometer to determine whether the structure before heat treatment was amorphous.

[0201] The obtained metal powder was then heated in a nitrogen atmosphere under the heating conditions shown in Table 1 to obtain a soft magnetic powder.

[0202] Next, the obtained soft magnetic powder was mixed with an epoxy resin as a binder to obtain a mixture, where the amount of epoxy resin added was 2 parts by mass per 100 parts by mass of the metal powder.

[0203] The resulting mixture was then stirred and dried for a short time to obtain a dried mass. The dried mass was then sieved through a 400 μm mesh sieve and pulverized to obtain a granulated powder. The resulting granulated powder was dried at 50° C. for 1 hour.

[0204] Next, the obtained granulated powder was filled into a molding die, and a molded body was obtained under the following molding conditions.

[0205] <Molding conditions> Molding method: Press molding Shape of molding: Ring-shaped - Dimensions of the molded body: outer diameter 14mm, inner diameter 8mm, thickness 3mm ·Molding pressure: 3t / cm 2 (294MPa)

[0206] Next, the compact was heated in an air atmosphere at a temperature of 150°C for 0.5 hours to harden the binder, thereby obtaining a powder magnetic core.

[0207] 5.2. Samples No. 2 to 16 A dust core was obtained in the same manner as Sample No. 1, except that the production conditions for the soft magnetic powder and the production conditions for the dust core were changed as shown in Table 1.

[0208] [Table 1]

[0209] In Table 1, among the soft magnetic powders of each sample number, those that correspond to the present invention are indicated as "Examples," and those that do not correspond to the present invention are indicated as "Comparative Examples."

[0210] Furthermore, when x and y in the composition of the soft magnetic powder of each sample number were located inside region C, they were entered as "C" in the region column, when they were located outside region C but inside region B, they were entered as "B" in the region column, and when they were located outside region B but inside region A, they were entered as "A" in the region column. When they were located outside region A, they were entered as "-" in the region column.

[0211] 6. Evaluation of soft magnetic powders and dust cores 6.1.Evaluation of soft magnetic powder particles The soft magnetic powder particles obtained in each of the examples and comparative examples were processed into thin pieces using a focused ion beam device to obtain test pieces.

[0212] Next, the obtained test piece was observed using a scanning transmission electron microscope, and an elemental analysis was carried out to obtain an area analysis image.

[0213] Next, the grain size of the crystal grains containing Fe—Si crystals was measured from the observed image, and the content ratio of crystal grains falling within the range of 1.0 nm to 30.0 nm was calculated. The calculation results are shown in Table 2.

[0214] Furthermore, by analyzing the surface analysis images, the various indices shown in Table 2 or Table 3 were obtained for the first Cu segregation area, the second Cu segregation area, the Cu concentration ratio between the surface and the interior, the Si segregation area, the Fe concentration distribution, and the O concentration distribution.

[0215] The "number ratio of first Cu segregation portions" shown in Table 2 refers to the number ratio of first Cu segregation portions to the total number of Cu segregation portions counted in the surface layer portion of the particle. Also, the "Cu concentration ratio (1) of first Cu segregation portions" shown in Table 2 refers to the ratio (multiple) of the Cu concentration of the first Cu segregation portions to the Cu concentration of the crystal grains, and the "Cu concentration ratio (2) of first Cu segregation portions" refers to the ratio (multiple) of the Cu concentration of the first Cu segregation portions to the Cu concentration of the crystal grain boundaries.

[0216] Furthermore, the "number ratio of second Cu segregation portions" shown in Table 2 indicates the number ratio of second Cu segregation portions to the total number of Cu segregation portions counted inside a particle.

[0217] Furthermore, the "Nb concentration ratio" shown in Table 2 refers to the ratio (multiple) of the Nb concentration at the grain boundary to the Nb concentration in the crystal grains, and the "B concentration ratio" refers to the ratio (multiple) of the B concentration at the grain boundary to the B concentration in the crystal grains.

[0218] Furthermore, the "ratio of Cu concentration in the surface layer to the interior" shown in Table 2 is the ratio of the Cu concentration in the surface layer to the Cu concentration in the interior expressed as a multiple.

[0219] Furthermore, the Fe concentration and O concentration at a position 12 nm from the particle surface were compared, and if the Fe concentration was higher, it was indicated as "Fe>O," and if the O concentration was higher, it was indicated as "O>Fe," as shown in Table 3. The presence or absence of Si segregation was also evaluated.

[0220] 6.2. Resistivity of Compacted Soft Magnetic Powder The electric resistance value of the compacted powder of the soft magnetic powder obtained in each of the Examples and Comparative Examples was measured by the method described below.

[0221] First, a lower punch electrode was set at the bottom of a cylindrical mold cavity with an inner diameter of 8 mm. Next, 0.7 g of soft magnetic powder was filled into the cavity. Next, an upper punch electrode was set at the top of the cavity. The mold, lower punch electrode, and upper punch electrode were then set in a load application device. Next, a digital force gauge was used to apply a load of 20 kgf in the direction that would reduce the distance between the lower punch electrode and the upper punch electrode. Then, with the load applied, the electrical resistance between the lower punch electrode and the upper punch electrode was measured. The measured resistance values ​​were then evaluated according to the following evaluation criteria.

[0222] A: Resistance value is 5.0kΩ or more B: Resistance is 3.0kΩ or more and less than 5.0kΩ C: Resistance is 0.3 kΩ or more and less than 3.0 kΩ D: Resistance less than 0.3 kΩ The evaluation results are shown in Table 3.

[0223] 6.3. Measurement of coercive force of soft magnetic powder The coercive force of each of the soft magnetic powders obtained in each of the Examples and Comparative Examples was measured, and the measured coercive force was evaluated in accordance with the following evaluation criteria.

[0224] A: Coercive force less than 0.90 Oe B: Coercive force is 0.90 Oe or more and less than 1.33 Oe C: Coercive force is 1.33 Oe or more and less than 1.67 Oe D: Coercive force is 1.67 Oe or more and less than 2.00 Oe E: Coercive force is 2.00 Oe or more and less than 2.33 Oe F: Coercive force is 2.33 Oe or more The evaluation results are shown in Table 3.

[0225] 6.4. Calculation of saturation magnetic flux density of soft magnetic powder The saturation magnetic flux density of each of the soft magnetic powders obtained in the examples and comparative examples was calculated from the results of measuring the maximum magnetization. The calculation results are shown in Table 3.

[0226] 6.5.Measuring the magnetic permeability of powder cores The magnetic permeability of each of the powder magnetic cores obtained in the examples and comparative examples was measured. The measurement results are shown in Table 3.

[0227] 6.6.Measuring Iron Loss in Powder Cores The iron loss of each of the powder magnetic cores obtained in the examples and comparative examples was measured under the following measurement conditions.

[0228] Measurement equipment: BH analyzer, Iwasaki Electric Co., Ltd. SY-8258 Measurement frequency: 900kHz Number of winding turns: Primary 36, Secondary 36 Winding wire diameter: 0.5mm Maximum magnetic flux density: 50mT The measurement results are shown in Table 3.

[0229] [Table 2]

[0230] [Table 3]

[0231] As is clear from Table 3, the soft magnetic powders obtained in each example had both low coercivity and high magnetic permeability. Furthermore, the powder cores containing the soft magnetic powders obtained in each example had high magnetic permeability and low iron loss. [Explanation of symbols]

[0232] 1...cooling cylinder, 2...lid, 3...opening, 4...coolant jet pipe, 5...discharge port, 6...particles, 7...pump, 8...tank, 9...coolant layer, 10...coil component, 11...powder core, 12...conductor, 13...coolant recovery cover, 14...drain port, 15...crucible, 16...layer thickness adjusting ring, 17...liquid draining mesh, 18...powder recovery container, 20...coil component, 21...powder core, 22...conductor, 23...space, 24...jet nozzle, 25...molten metal, 26...gas jet, 27...gas supply pipe, 30...powder manufacturing apparatus, 61...crystal grain, 62...Cu segregation portion, 63...crystal Grain boundary, 600...surface, 601...surface layer, 602...interior, 621...first Cu segregation portion, 622...second Cu segregation portion, 100...display portion, 1000...magnetic element, 1100...personal computer, 1102...keyboard, 1104...main body portion, 1106...display unit, 1200...smartphone, 1202...operation button, 1204...earpiece, 1206...mouthpiece, 1300...digital still camera, 1302...case, 1304...light receiving unit, 1306...shutter button, 1308...memory, A...area A, B...area B, C...area C

Claims

1. A process of melting raw materials to obtain molten metal; a step of obtaining soft magnetic powder by atomizing the molten metal and cooling and solidifying the same; and The soft magnetic powder is Fe ｘ Cổ ａ Nｺ ｂ (Yes) １－ｙ B ｙ ) １００－ｘ－ａ－ｂ [a, b, and x are each a number expressed in atomic %; 0.3≦a≦2.0, 2.0≦b≦4.0, 72.5≦x<75.5 Meet the following. Furthermore, y is a number that satisfies f(x)≦y≦0.99, and f(x)=(4×10 －３４ ) x １７．５６ It is.] The particles have a composition represented by The particles are crystal grains having a grain size of 1.0 nm or more and 30.0 nm or less and containing Fe—Si crystals; a Cu segregation portion in which Cu is segregated; Grain boundaries and and a particle size D50, at which a cumulative 50% of the particles from the small diameter side in a volume-based particle size distribution of the particles is 5 μm or more and 50 μm or less; The content ratio of the crystal grains in the particles is 30% by volume or more, the Cu segregation portion, which is located in a surface layer portion of the cross section of the particle within a range of 200 nm square centered at a position 1 μm deep from the surface, and has a particle size of 1.0 nm or more and 5.0 nm or less, is defined as a first Cu segregation portion; When the Cu segregation portion, which is located within a 200 nm square range set at the center of the cross section of the particle and has a particle size of 3.0 nm or more and 10.0 nm or less, is defined as a second Cu segregation portion, a number ratio of the first Cu segregation portions to the Cu segregation portions located in the surface layer portion is 80% or more, a number ratio of the second Cu segregation portions to the internally located Cu segregation portions is 80% or more.

2. The method for producing soft magnetic powder according to claim 1 , wherein the Cu concentration in the surface layer is 1.1 times or more the Cu concentration in the interior.

3. The method for producing soft magnetic powder according to claim 1 or 2, wherein the Cu concentration of the second Cu segregation portion is more than 6.0 atomic %.

4. The method for producing soft magnetic powder according to claim 1 , wherein the content of the crystal grains in the particles is 55% by volume or more.

5. Fe ｘ Cổ ａ Nｺ ｂ (Yes) １－ｙ B ｙ ) １００－ｘ－ａ－ｂ [a, b, and x are each a number expressed in atomic %; 0.3≦a≦2.0, 2.0≦b≦4.0, 72.5≦x<75.5 Meet the following. Furthermore, y is a number that satisfies f(x)≦y≦0.99, and f(x)=(4×10 －３４ ) x １７．５６ It is.] The particles have a composition represented by The particles are crystal grains having a grain size of 1.0 nm or more and 30.0 nm or less and containing Fe—Si crystals; a Cu segregation portion in which Cu is segregated; Grain boundaries and and a particle size D50, at which a cumulative 50% of the particles from the small diameter side in a volume-based particle size distribution of the particles is 5 μm or more and 50 μm or less; The content ratio of the crystal grains in the particles is 30% by volume or more, the Cu segregation portion, which is located in a surface layer portion of the cross section of the particle within a range of 200 nm square centered at a position 1 μm deep from the surface, and has a particle size of 1.0 nm or more and 5.0 nm or less, is defined as a first Cu segregation portion; When the Cu segregation portion, which is located within a 200 nm square range set at the center of the cross section of the particle and has a particle size of 3.0 nm or more and 10.0 nm or less, is defined as a second Cu segregation portion, a number ratio of the first Cu segregation portions to the Cu segregation portions located in the surface layer portion is 80% or more, A soft magnetic powder characterized in that the number ratio of the second Cu segregation portions to the Cu segregation portions located inside is 80% or more.

6. A dust core comprising the soft magnetic powder according to claim 5 .

7. It is ring-shaped with an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm. When the magnetic permeability was measured at a frequency of 100 MHz using a conductor with a wire diameter of 0.6 mm wound seven times, The powder magnetic core according to claim 6 , wherein the magnetic permeability is 18.0 or more.

8. It is ring-shaped with an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm. When iron loss was measured using a 0.5 mm diameter conductor wound 36 times on each of the primary and secondary sides at a maximum magnetic flux density of 50 mT and a measurement frequency of 900 kHz, The iron loss is 9000 [kW / m ３ 8. The powder magnetic core according to claim 6, wherein the average particle size is 100 μm or less.

9. A magnetic element comprising the powder magnetic core according to any one of claims 6 to 8.

10. An electronic device comprising the magnetic element according to claim 9.

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