Soft magnetic powder, powder magnetic core, magnetic element and electronic apparatus

Abstract

To provide soft magnetic powder capable of producing green compact excellent in oxidation resistance, density, coercive force and DC superposition property, a powder magnetic core containing the soft magnetic powder, a magnetic element provided with the powder magnetic core, and an electronic apparatus provided with the magnetic element.SOLUTION: A soft magnetic powder is composed of the composition and impurities of the formula FexCuaNbb(Si1-y(B1-zCrz)y)100-x-a-b [where a, b, x, y, and z satisfy 0.3≤a≤2.0, 2.0≤b≤4.0, 75.5≤x≤79.5, 0.55≤y≤0.91, 0.015≤z≤0.185], and has an average particle size of 5.0 μm to 45.0 μm, a crystallite size measured by X-ray diffraction of 5.0 nm to 20.0 nm, and a permeability reduction rate d defined by the following equation of 3.0% or less. d=|μ1-μ100| / μ1×100 [In the above equation, μ1 is the permeability measured at 1 MHz, and μ100 is the permeability measured at 100 MHz.]SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to soft magnetic powder, compacted magnetic cores, magnetic elements, and electronic devices.

Background Art

[0002] Patent Document 1 discloses soft magnetic powder containing amorphous metal particles having a composition represented by the compositional formula: Fe 100-a-b-c-d-e-f-g Cr a Si b B c C d Al e Ti f Co g [where a, b, c, d, e, f, and g are numbers representing atomic percentages, and satisfy 0 < a ≤ 3.0, 5.0 ≤ b ≤ 15.0, 7.0 ≤ c ≤ 15.0, 0.1 ≤ d ≤ 3.0, 0 < e ≤ 0.016, 0 < f ≤ 0.009, 0 ≤ g ≤ 0.025.] According to such a configuration, soft magnetic powder having good magnetic properties due to the amorphous alloy and low coercive magnetization can be obtained.

[0003] [[ID=三十二]]

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the method for producing soft magnetic powder described in Patent Document 1 still has room for improvement in terms of ensuring a further reduction in coercivity. For example, even after heat treatment, the coercivity of some particles may not be sufficiently reduced. Therefore, it is a challenge to realize a soft magnetic powder that reliably achieves a low coercivity.

[0006] Furthermore, the reduction in the green compact density and the deterioration in the DC bias characteristics due to oxidation cause a reduction in the operational stability of a magnetic element using the green compact.

[0007] Therefore, the realization of a soft magnetic powder that can be used to produce a green compact that has excellent oxidation resistance, density, coercive force, and DC bias characteristics is an issue. [Means for solving the problem]

[0008] The soft magnetic powder according to the application example of the present invention is Composition formula expressed as atomic ratio: Fe x Cu a Nb b (Si 1-y (B 1-z Cr z ) y ) 100-x-a-b [a, b, x, y, z are 0.3≦a≦2.0, 2.0≦b≦4.0, 75.5≦x≦79.5, 0.55≦y≦0.91, 0.015≦z≦0.185, Satisfy.] It is composed of the following composition and impurities: The average particle size is 5.0 μm or more and 45.0 μm or less, The crystallite size measured by X-ray diffraction is 5.0 nm or more and 20.0 nm or less, It was mixed with 2.0% by mass of epoxy resin, and the resulting mixture was subjected to a pressure of 294.2 MPa (3 t / cm 2) to obtain a ring-shaped first compact having an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm. When a conductor having a wire diameter of 0.6 mm is wound seven times around the first compact to produce a first specimen, the reduction rate d of magnetic permeability, expressed by the following formula, is 3.0% or less. d=|μ1-μ 100 | / μ1×100 [where μ1 is the magnetic permeability of the first object measured at a frequency of 1 MHz, and μ 100 is the magnetic permeability of the first object measured at a frequency of 100 MHz.]

[0009] 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.

[0010] The magnetic element according to the application example of the present invention includes: The dust core according to the application example of the present invention is provided.

[0011] 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 provided. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an example of a DSC curve obtained from a metal powder according to an embodiment. [Figure 2] FIG. 1 is a plan view schematically showing a toroidal type coil component. [Figure 3] FIG. 1 is a transparent perspective view schematically showing a closed magnetic circuit type coil component. [Figure 4] 1 is a perspective view showing a configuration of a mobile personal computer as an electronic device according to an embodiment. [Figure 5] FIG. 1 is a plan view illustrating a configuration of a smartphone as an electronic device according to an embodiment. [Figure 6] 1 is a perspective view showing a configuration of a digital still camera which is an electronic device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] The soft magnetic powder, metal 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.

[0014] 1. Soft magnetic powder The soft magnetic powder according to the embodiment is a metal powder exhibiting soft magnetism. Such soft magnetic powder can be used for any purpose, but for example, the particles are bound together via a binder and used to produce various compacts such as dust cores and electromagnetic wave absorbers.

[0015] The soft magnetic powder according to the embodiment has a composition formula Fe x Cu a Nb b (Si 1-y (B 1-z Cr z ) y ) 100-x-a-b [a, b, x, y, z are 0.3≦a≦2.0, 2.0≦b≦4.0, 75.5≦x≦79.5, 0.55≦y≦0.91, 0.015≦z≦0.185, Satisfy.] It is composed of the composition and impurities represented by the formula:

[0016] Moreover, the soft magnetic powder according to the embodiment has an average particle size of 5.0 μm or more and 45.0 μm or less.

[0017] Furthermore, the soft magnetic powder according to the embodiment has a crystallite diameter of 5.0 nm or more and 20.0 nm or less as measured by X-ray diffraction.

[0018] In such soft magnetic powders, the oxidation resistance of the soft magnetic powder is enhanced by adding an optimal amount of Cr (chromium). As a result, when the soft magnetic powder is compacted, it is possible to prevent the density of the compact from decreasing due to oxides. Furthermore, by optimizing the amount of each element added, the crystallite size of the soft magnetic powder is controlled so that it does not become too small or too large. As a result, it is possible to prevent an increase in the coercive force of the soft magnetic powder.

[0019] Furthermore, when the soft magnetic powder according to the embodiment is molded together with a binder to produce a ring-shaped first compact, the magnetic permeability of the first compact satisfies a predetermined value. This magnetic permeability is evaluated as follows.

[0020] First, an epoxy resin in an amount equivalent to 2.0% by mass of the soft magnetic powder according to the embodiment was mixed with the soft magnetic powder, and the resulting mixture was subjected to a pressure of 294.2 MPa (3 t / cm 2 ) pressure. This produces a ring-shaped first compact with an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm, and a relative density of 66%. The relative density is a relative value obtained by dividing the density obtained by dividing the mass of the first compact by the volume by the true density of the soft magnetic powder. Next, a conductor with a wire diameter of 0.6 mm is wound seven times around the obtained first compact to produce a first specimen. Next, the magnetic permeability of the first specimen is measured at a frequency of 1 MHz and a frequency of 100 MHz. The soft magnetic powder according to the embodiment has a permeability reduction rate d, expressed by the following formula, of 3.0% or less.

[0021] d=|μ1-μ 100 | / μ1×100 [where μ1 is the magnetic permeability of the first object measured at a frequency of 1 MHz, and μ 100 is the magnetic permeability of the first object measured at a frequency of 100 MHz.]

[0022] According to this configuration, in a magnetic element manufactured using the soft magnetic powder, magnetic saturation is unlikely to occur even when a DC current is superimposed on the coil. Therefore, by using the soft magnetic powder according to the embodiment, a magnetic element having good DC superimposition characteristics and excellent operational stability can be manufactured.

[0023] The soft magnetic powder according to the embodiment will be described in detail below. 1.1.Composition Fe (iron) has a significant effect on the basic magnetic properties and mechanical properties of the soft magnetic powder according to the embodiment.

[0024] The Fe content x is 75.5 atomic % or more and 79.5 atomic % or less, preferably 76.0 atomic % or more and 78.5 atomic % or less, and more preferably 76.5 atomic % or more and 78.0 atomic % or less. If the Fe content x is below the lower limit, the saturation magnetic flux density of the soft magnetic powder decreases. 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, resulting in an excessively large crystallite size and an increase in coercive force.

[0025] 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 within the particles that are prone to crystallization. As a result, the precipitation of the body-centered cubic Fe phase, which is relatively prone to crystallization, is promoted, and crystal grains having the aforementioned crystallite size are more likely to form.

[0026] The Cu content a is 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 are not refined, and crystal grains with a crystallite size within the aforementioned range cannot be formed. On the other hand, if the Cu content a is above the upper limit, the mechanical properties of the soft magnetic powder deteriorate and it becomes brittle.

[0027] When a material containing a large amount of amorphous structure is subjected to heat treatment, Nb (niobium) contributes to the refinement of crystal grains together with Cu, which makes it easier to form crystal grains with the above-mentioned crystallite size.

[0028] 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 refinement of the crystal grains is impaired, and it is not possible to form crystal grains with a crystallite size within the aforementioned range. On the other hand, if the Nb content b is above the upper limit, the mechanical properties of the soft magnetic powder are reduced and the powder becomes brittle. In addition, the magnetic permeability of the soft magnetic powder is reduced.

[0029] 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 with a more uniform crystallite size. The uniform crystallite size contributes to averaging the magnetocrystalline anisotropy of each crystal grain, thereby reducing the coercive force and increasing the magnetic permeability, thereby contributing to improved soft magnetic properties.

[0030] 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 this structure facilitates the formation of crystal grains with a more uniform crystallite size. As a result, the coercive force can be reduced and the magnetic permeability can be increased, thereby improving the soft magnetic properties. Furthermore, by using Si and B together, the difference in atomic radii of the two elements can synergistically promote amorphization.

[0031] Cr (chromium) improves the oxidation resistance of soft magnetic powder. This prevents oxides from reducing the density of the compacted powder when the soft magnetic powder is compacted. As a result, the effect of oxides on magnetic properties can be reduced. Optimizing the Cr content also allows the crystallite size of the soft magnetic powder to be controlled so that it is neither too small nor too large. As a result, the increase in coercivity of the soft magnetic powder can be suppressed. The addition of Cr also reduces the Si content relatively, stabilizing magnetic permeability over a wide frequency range. This improves DC bias characteristics.

[0032] The total content of Si, B, and Cr (Si+B+Cr) is set to 1, and the ratio of the total content of B and Cr (B+Cr) to this total content (Si+B+Cr) is set to y.

[0033] The value of y satisfies 0.55≦y≦0.91, preferably 0.60≦y≦0.90, and more preferably 0.65≦y≦0.80. This allows the amounts of Si, B, and Cr to be balanced. As a result, the oxidation resistance and magnetic permeability of the soft magnetic powder can both be improved in a balanced manner.

[0034] If y is below the lower limit, the oxidation resistance decreases and the crystallite diameter becomes too small, resulting in a decrease in magnetic permeability, whereas if y is above the upper limit, the crystallite diameter becomes too large, resulting in an increase in coercivity.

[0035] Also, the ratio of the Cr content to the total content (B+Cr) is defined as z. The value of z satisfies 0.015≦z≦0.185, preferably 0.030≦z≦0.150, and more preferably 0.045≦z≦0.120. This allows the amounts of B and Cr to be balanced. As a result, the oxidation resistance and magnetic permeability of the soft magnetic powder can both be improved in a balanced manner.

[0036] If z is below the lower limit, the oxidation resistance decreases and the crystallite diameter becomes too small, resulting in a decrease in magnetic permeability, whereas if z is above the upper limit, the crystallite diameter becomes too large, resulting in an increase in coercivity.

[0037] The Si content is preferably 1.5 atomic % or more and 14.0 atomic % or less, more preferably 3.0 atomic % or more and 10.0 atomic % or less, and even more preferably 4.0 atomic % or more and 8.0 atomic % or less, thereby obtaining a soft magnetic powder from which a green compact having a lower coercive force and better DC bias characteristics can be produced.

[0038] The B content is preferably 5.0 atomic % or more and 17.0 atomic % or less, more preferably 7.0 atomic % or more and 16.0 atomic % or less, and even more preferably 9.0 atomic % or more and 13.5 atomic % or less, thereby obtaining a soft magnetic powder from which a green compact having a lower coercive force and better DC bias characteristics can be produced.

[0039] The Cr content is preferably 0.3 atomic % or more and 2.7 atomic % or less, more preferably 0.5 atomic % or more and 2.2 atomic % or less, and even more preferably 0.8 atomic % or more and 1.8 atomic % or less. This can further improve the oxidation resistance of the soft magnetic powder and further reduce the generation of oxides. As a result, the crystallite size of the crystal grains contained in each particle can be appropriately controlled.

[0040] The soft magnetic powder according to the embodiment has the above composition formula Fe x Cu a Nb b (Si 1-y (B 1-z Cr z ) y ) 100-x-a-b In addition to the composition represented by the formula (1), impurities may be contained. 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, even if impurities are mixed in, they are unlikely to impair the above-mentioned effects, so their inclusion is permitted.

[0041] The content of each element contained in the impurities is preferably 0.05 atomic % or less, and within this range, the impurities are not likely to impair the above-mentioned effects, so their inclusion is permissible.

[0042] Furthermore, among the impurities, the oxygen content is preferably 1500 ppm or less, and more preferably 800 ppm or less. If the oxygen content is within the above range, the generation of oxides that cause a decrease in the density of the compact can be particularly suppressed.

[0043] The soft magnetic powder according to the embodiment has been described above, and the composition and impurities are identified by the following analytical method.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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 general method for oxygen determination 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 and the LECO oxygen, nitrogen and hydrogen analyzer ONH836.

[0048] 1.2.Particle size The average particle size of the soft magnetic powder according to the embodiment is 5.0 μm or more and 45.0 μm or less, preferably 7.0 μm or more and 30.0 μm or less, and more preferably 10.0 μm or more and 20.0 μm or less.

[0049] By using soft magnetic powder with such an average particle size, the path through which eddy currents flow can be shortened, making it possible to manufacture a magnetic element in which eddy current loss can be sufficiently suppressed.Furthermore, the filling rate of the soft magnetic powder in the compact can be increased, making it easier to increase the magnetic permeability and saturation magnetic flux density of the powder core.

[0050] Furthermore, when the soft magnetic powder has an average particle size of 10 μm or more, it can achieve a higher compact density when mixed with a soft magnetic powder having a smaller average particle size than the soft magnetic powder according to the embodiment, which makes it easier to increase the saturation magnetic flux density and magnetic permeability of the powder magnetic core.

[0051] The average particle size of the soft magnetic powder refers to the particle size D50 at which the cumulative frequency is 50% from the smallest diameter side in the cumulative particle size distribution on a volume basis of the soft magnetic powder obtained using a laser diffraction particle size distribution analyzer.

[0052] 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 may reduce the magnetic permeability and saturation magnetic flux density of the powder core depending on the composition and mechanical properties of the soft magnetic powder. On the other hand, if the average particle size of the soft magnetic powder is above the upper limit, depending on the composition and mechanical properties of the soft magnetic powder, it may not be possible to sufficiently suppress eddy current loss generated within the particles, which may increase the iron loss of the magnetic element.

[0053] 1.3.Crystallite size The soft magnetic powder according to the embodiment has a crystallite diameter of 5.0 nm or more and 20.0 nm or less, as measured by X-ray diffraction. If the crystallite diameter is within this range, the crystallite diameter of the soft magnetic powder is optimized, and even if the content of Si, which has the effect of increasing magnetic permeability, is relatively low, the decrease in magnetic permeability is suppressed. Furthermore, the magnetic crystal anisotropy of each crystal grain is easily averaged, resulting in a soft magnetic powder with low coercivity. Furthermore, a soft magnetic powder with stable magnetic permeability over a wide frequency range can be realized. This reduces the likelihood of magnetic saturation, resulting in a soft magnetic powder that can realize magnetic elements with good DC bias characteristics and excellent operational stability.

[0054] The crystallite diameter of the soft magnetic powder is preferably 6.0 nm or more and 13.0 nm or less, and more preferably 8.0 nm or more and 11.0 nm or less.

[0055] The crystallite size is measured by X-ray diffraction by obtaining X-ray diffraction patterns for the soft magnetic powder and a standard sample, estimating the Fe-derived diffraction line width, and then calculating the crystallite size using the Scherrer method. The X-ray diffraction pattern obtained for the standard sample is used to estimate the diffraction line width derived from the instrument. This diffraction line width can be used to correct the crystallite size calculated from the soft magnetic powder.

[0056] Each particle constituting the soft magnetic powder according to the embodiment contains crystal grains satisfying the above-mentioned crystallite diameter, but may also contain an amorphous structure. The coexistence of crystal grains and an amorphous structure can further reduce the magnetostriction of the soft magnetic powder. As a result, a soft magnetic powder whose magnetic permeability is less likely to decrease even with a low Si content can be obtained.

[0057] 1.4.Magnetic permeability In the soft magnetic powder according to the embodiment, when the magnetic permeability of the first specimen described above is measured at a frequency of 1 MHz, the magnetic permeability is preferably 15 or more and less than 21, more preferably 16 or more and less than 20, and even more preferably 17 or more and less than 20.

[0058] With this configuration, it is believed that magnetic saturation is less likely to occur over a wide frequency range because the Si content in the soft magnetic powder is optimized. Therefore, when a DC current is superimposed on the coil in a magnetic element manufactured using the soft magnetic powder, a magnetic element with good DC superimposition characteristics can be realized.

[0059] The magnetic permeability is measured using an impedance analyzer (Keysight Technologies, 4294A) or the like.

[0060] Furthermore, in the soft magnetic powder according to the embodiment, when the magnetic permeability of the first specimen described above is measured at a frequency of 100 MHz, the magnetic permeability is preferably 15 or more and less than 21, more preferably 16 or more and less than 20, and even more preferably 17 or more and less than 20.

[0061] According to this configuration, a soft magnetic powder can be obtained that can be used over a wide frequency range and that can realize a magnetic element that is miniaturized.

[0062] Furthermore, in the soft magnetic powder according to the embodiment, the rate of decrease in magnetic permeability when the frequency is increased from 1 MHz to 100 MHz is 3.0% or less as mentioned above, but is preferably 2.5% or less, and more preferably 2.0% or less.

[0063] 1.5. DC Superimposition Characteristics When the soft magnetic powder according to the embodiment is molded together with a binder to produce a ring-shaped second compact, the DC bias characteristics of the second compact preferably satisfy predetermined conditions. The DC bias characteristics are evaluated as follows.

[0064] First, an epoxy resin in an amount equivalent to 2.0% by mass of the soft magnetic powder according to the embodiment was mixed with the soft magnetic powder, and the resulting mixture was subjected to a pressure of 294.2 MPa (3 t / cm 2 ) pressure. This results in a ring-shaped second molded body with an outer diameter of 28 mm, an inner diameter of 14 mm, and a thickness of 5 mm. Next, the obtained second molded body is placed in a resin case, and a 1.25 mm diameter wire is wound 50 times around the case to create a second test piece. Next, an AC signal with a frequency of 10 kHz is applied to the second test piece, and the inductance when no DC bias current is superimposed is used as the reference value. Next, the inductance is measured while gradually increasing the DC bias current superimposed on the second test piece. Then, when the measured value falls to 80% of the reference value (when the measured value falls to 80% assuming the reference value to be 100%), the DC bias current superimposed on the second test piece is measured. In this specification, the DC bias current at this time is referred to as the "DC bias allowable current" and is used as an index for evaluating DC bias characteristics.

[0065] In the soft magnetic powder according to the embodiment, the DC bias current is preferably 17 A or more, more preferably 18 A to 24 A, and even more preferably 19 A to 22 A. If the DC bias current is within the above range, it can be considered that the superposition of a sufficiently high DC bias current is acceptable. Therefore, soft magnetic powders having a DC bias current within the above range can realize magnetic elements with sufficiently high DC bias characteristics and excellent operational stability.

[0066] The DC bias allowable current may exceed the upper limit, but in that case, the manufacturing difficulty of the soft magnetic powder increases, which may lead to an increase in manufacturing costs and a decrease in manufacturing yield.

[0067] The DC power supply uses two parallel-connected DC stabilized power supplies (Takasago Manufacturing Co., Ltd., EX-1500H), and the inductance measurement device uses an impedance analyzer (Keysight Technologies, Inc., 4294A).

[0068] 1.6.Coercive force The coercive force of the soft magnetic powder according to the embodiment is not particularly limited, but is preferably less than 2.00 [Oe] (less than 160 [A / m]), and more preferably 0.10 [Oe] or more and 1.67 [Oe] or less (39.9 [A / m] or more and 133 [A / m] or less). By using such a soft magnetic powder with a low coercive force, it is possible to manufacture a magnetic element that can sufficiently suppress hysteresis loss even at high frequencies.

[0069] 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.

[0070] 1.7.Saturation magnetic flux density The saturation magnetic flux density of the soft magnetic powder according to the embodiment is preferably 1.20 T or more, more preferably 1.25 T or more, even more preferably 1.28 T or more, and particularly preferably 1.30 T or more, thereby making it possible to obtain a magnetic element that is less likely to saturate even at high currents.

[0071] The saturation magnetic flux density of the soft magnetic powder is measured, for example, by the following method. First, the true specific gravity ρ of the soft magnetic powder is measured using a fully automatic gas displacement density meter, AccuPyc1330, manufactured by Micromeritics. Next, 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. Then, the saturation magnetic flux density Bs is calculated using the following formula. Bs=4π / 10000×ρ×Mm

[0072] 1.8. Molded body density The soft magnetic powder according to the embodiment is mixed with an epoxy resin in an amount equivalent to 2.0 mass % of the soft magnetic powder, and the obtained mixture is subjected to a compressive strength of 294.2 MPa (3 t / cm 2 ) the density of the third compact obtained by press molding at a pressure of 4.99 g / cm 3 It is preferable that the density is 5.01 g / cm or more. 3 More than 5.20g / cm 3 It is more preferable that the density of the third compact is within the above range. If the density of the third compact is within the above range, the oxide occupancy rate in the third compact can be sufficiently reduced, and as a result, the alloy occupancy rate can be sufficiently secured. This allows the magnetic permeability and saturation magnetic flux density of the magnetic element to be further increased.

[0073] 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 various purposes.

[0074] 2. Manufacturing method of soft magnetic powder Next, an example of a method for producing the soft magnetic powder according to the embodiment will be described.

[0075] The soft magnetic powder may be a powder produced by any method. Examples of production methods include various atomization methods such as water atomization, rotary water flow atomization, and gas atomization, as well as pulverization. Of these, atomization is preferably used. By using atomization, it is possible to efficiently produce high-quality metal powder with particle shapes closer to perfect spheres and with less formation of oxides, etc. Therefore, by using atomization, it is possible to produce metal powder with a smaller specific surface area.

[0076] Atomization is a method for producing metal powder by colliding molten metal with a high-speed jet of liquid or gas, thereby pulverizing and cooling the molten metal. After pulverizing the molten metal, the particles become more spherical during the solidification process, making it possible to produce particles that are closer to perfect spheres.

[0077] Of these, the water atomization method uses a liquid such as water as a coolant, sprays it in an inverted cone shape that converges to one point, and causes molten metal to flow down toward this convergence point and collide with it, thereby producing metal powder from molten metal.

[0078] In addition, the rotary water jet atomization method is a method for producing metal powder by supplying a cooling liquid along the inner surface of a cooling cylinder and rotating it along the inner surface, while spraying a liquid or gas jet onto molten metal and incorporating the scattered molten metal into the cooling liquid.

[0079] Furthermore, the gas atomization method is a method of producing metal powder from molten metal by using a gas as a cooling medium, spraying it in an inverted cone shape that converges to one point, and causing molten metal to flow down and collide toward this convergence point.

[0080] Each particle of the metal powder obtained in this manner is composed of an amorphous structure. By subjecting this metal powder to a crystallization treatment (heat treatment) described below, the soft magnetic powder according to the embodiment can be obtained.

[0081] The metal powder according to the embodiment is a metal powder intended to be subjected to a crystallization treatment, and is composed of the same composition and impurities as the soft magnetic powder described above.

[0082] A DSC (Differential Scanning Calorimeter) curve is obtained for such metal powder by differential scanning calorimetry, where the mass of the sample is 20 mg and the measurement atmosphere is a nitrogen atmosphere.

[0083] FIG. 1 is an example of a DSC curve obtained from a metal powder used to manufacture a soft magnetic powder according to an embodiment.

[0084] Each of the DSC curves L1 to L5 shown in FIG. 1 has a first exothermic peak P1 and a second exothermic peak P2. The second exothermic peak P2 is located at a higher temperature than the first exothermic peak P1. The DSC curves L1 to L5 were obtained from metal powders with varying Cr contents as shown in FIG. 1. Specifically, the DSC curves L1, L2, L3, L4, and L5 were obtained from metal powders with compositions containing Cr contents of 0.0 atomic %, 0.5 atomic %, 1.0 atomic %, 1.5 atomic %, and 2.0 atomic %. The Fe contents of these metal powders were 77.0 atomic %, Cu contents 1.0 atomic %, and Nb contents 3.0 atomic %. The B contents were adjusted so that the sum of the B contents and the Cr contents was 13.3 atomic %.

[0085] The first exothermic peak P1 is a peak whose peak top temperature Tx1 is in the range of 450°C or higher and 550°C or lower. The first exothermic peak P1 is a peak associated with heat generated when the crystal grains of the soft magnetic powder described above are generated. Therefore, this first exothermic peak P1 can be said to be a peak due to crystallization necessary in the production of soft magnetic powder. This crystallization generates crystal grains having, for example, a body-centered cubic lattice (Bcc-Fe) structure. Hereinafter, these will also be simply referred to as "crystal grains."

[0086] The second exothermic peak P2 is a peak whose peak top temperature Tx2 is in the range of 600°C to 700°C. The second exothermic peak P2 is a peak associated with heat generation that occurs when a crystalline structure different from the crystal grains of the soft magnetic powder described above is formed. This crystalline structure, which is mainly composed of, for example, an Fe-B alloy, deteriorates the soft magnetic properties of the soft magnetic powder. Therefore, the second exothermic peak P2 can be said to be a peak due to a crystalline structure that is unnecessary in the production of the soft magnetic powder. Hereinafter, this will also be referred to as an "unnecessary crystalline structure."

[0087] In the metal powder according to the embodiment, the temperature difference Tx2-Tx1 between the first exothermic peak P1 and the second exothermic peak P2 is 125°C or more and 180°C or less. This ensures a sufficient temperature difference, making it easier to apply the heat required to generate the crystal grains described above when the metal powder is heat-treated between the temperatures of the first exothermic peak P1 and the second exothermic peak P2. This allows the crystallization process to be performed at a higher temperature, allowing the crystal grains to grow appropriately while avoiding the formation of unnecessary crystalline structures. As a result, it becomes easier to produce soft magnetic powders with crystallite sizes controlled within the aforementioned range.

[0088] The temperature difference Tx2-Tx1 between the first exothermic peak P1 and the second exothermic peak P2 is preferably 130°C or higher and 165°C or lower, and more preferably 135°C or higher and 155°C or lower.

[0089] If this temperature difference is below the lower limit, when attempting to sufficiently generate crystal grains within the aforementioned range of crystallite diameters, that is, when performing heat treatment at a temperature sufficiently higher than the temperature of the first exothermic peak P1, there is a risk of unintentional crystallization corresponding to the second exothermic peak P2. On the other hand, although this temperature difference may exceed the upper limit, depending on the temperature of the second exothermic peak P2, the temperature of the first exothermic peak P1 may become too low, which may result in variations in the grain size and the crystallite diameter of the generated crystal grains being likely to fall outside the aforementioned range.

[0090] This temperature difference depends on the composition of the metal powder, particularly the Cr content. As shown in Figure 1, the temperature difference tends to increase as the Cr content changes from 0 atomic % to 2.0 atomic %. It is also thought to be affected by the state of the amorphous structure in the metal powder. For example, if the cooling rate during the formation of the amorphous structure is slow, the temperature difference tends to narrow. For this reason, when producing metal powder, a production method that allows for a fast cooling rate from molten metal, such as the rotary water jet atomization method, is preferably used.

[0091] The metal powder as described above is subjected to a crystallization treatment (heat treatment), whereby at least a part of the amorphous structure is crystallized to form crystal grains.

[0092] The crystallization treatment can be carried out by subjecting the soft magnetic 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 appropriate and uniform crystallite size can be produced.

[0093] If the heat treatment temperature or time is below the lower limit, depending on the composition of the soft magnetic powder, crystallization may be insufficient, resulting in an excessively small crystallite diameter or poor uniformity of the crystallite diameter. On the other hand, if the heat treatment temperature or time is above the upper limit, depending on the composition of the soft magnetic powder, crystallization may proceed too far, resulting in an excessively large crystallite diameter or poor uniformity of the crystallite diameter.

[0094] 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.

[0095] The oxygen concentration in the atmosphere during the crystallization treatment affects the amount of oxides produced. Therefore, the oxygen concentration in the atmosphere during the crystallization treatment is preferably 1000 ppm or less by volume, more preferably 5 ppm or more to 500 ppm or less, and even more preferably 10 ppm or more to 200 ppm or less. This suppresses the production of oxides, resulting in a soft magnetic powder that can be used to produce high-density green compacts.

[0096] The temperature drop rate in the crystallization treatment is preferably 1°C / min or more and 100°C / min or less, more preferably 2°C / min or more and 30°C / min or less, and even more preferably 4°C / min or more and 20°C / min or less. By setting the temperature drop rate within the above range, it becomes easier to control the crystallite diameter of the soft magnetic powder within the above range. It is also possible to suppress variation in the crystallite diameter. Note that if the temperature drop rate is below the lower limit, the crystallite diameter of the soft magnetic powder is likely to become excessively large, while if the temperature drop rate is above the upper limit, variation in the crystallite diameter of the soft magnetic powder may become large. In this manner, the soft magnetic powder according to this embodiment can be manufactured.

[0097] The produced soft magnetic powder may be classified as needed. Examples of classification methods include dry classification such as sieving classification, inertial classification, and centrifugal classification, and wet classification such as sedimentation classification.

[0098] 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, ceramic materials such as silica, alumina, magnesia, zirconia, and titania, and glass materials such as borosilicate glass and silica glass.

[0099] 3. Powder cores and magnetic elements Next, the powder magnetic core and the magnetic element according to the embodiment will be described.

[0100] 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.

[0101] 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, which is a magnetic element according to the embodiment, will be described.

[0102] Fig. 2 is a plan view schematically showing a toroidal-type coil component 10. The coil component 10 shown in Fig. 2 has a ring-shaped powder core 11 and a conductive wire 12 wound around the powder core 11.

[0103] The powder magnetic core 11 is obtained by mixing the soft magnetic powder according to the embodiment with a binder and compacting the resulting mixture. Because the powder magnetic core 11 is a compact containing the soft magnetic powder according to the embodiment, it has a high compact density and excellent coercive force and DC bias characteristics. Therefore, when a coil component 10 including the powder magnetic core 11 is installed in an electronic device or the like, it is possible to improve the performance and miniaturize the electronic device or the like.

[0104] Examples of materials constituting the binder used in producing 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.

[0105] 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.

[0106] The shape of the powder magnetic core 11 is not limited to the ring shape shown in FIG. 2, 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.

[0107] 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.

[0108] 3.2.Closed magnetic circuit type Next, a closed magnetic circuit type coil component, which is a magnetic element according to the embodiment, will be described. FIG. 3 is a see-through perspective view that schematically shows a coil component 20 of a closed magnetic circuit type.

[0109] The closed magnetic circuit type coil component 20 will be described below, but the following description will focus on the differences from the toroidal type coil component 10, and a description of similar points will be omitted.

[0110] 3 is formed by embedding a coil-shaped conductive wire 22 inside a powder magnetic core 21. Because the powder magnetic core 21 is a compact containing the soft magnetic powder according to the embodiment, it has a high molding density and excellent coercive force, magnetic permeability, and DC bias characteristics. Therefore, when the coil component 20 including the powder magnetic core 21 is installed in an electronic device or the like, it is possible to improve the performance and miniaturize the electronic device or the like.

[0111] 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.

[0112] 4.Electronic equipment Next, an electronic device including the magnetic element according to the embodiment will be described with reference to FIGS.

[0113] Fig. 4 is a perspective view showing the configuration of a mobile personal computer 1100, which is an electronic device according to an embodiment. The personal computer 1100 shown in Fig. 4 includes a main body 1104 having a keyboard 1102, and a display unit 1106 having 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.

[0114] Fig. 5 is a plan view showing the configuration of a smartphone 1200, which is an electronic device according to an embodiment. The smartphone 1200 shown in Fig. 5 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 built-in magnetic element 1000, such as an inductor, a noise filter, or a motor.

[0115] 6 is a perspective view showing the configuration of a digital still camera 1300, which is an electronic device according to an 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.

[0116] The digital still camera 1300 shown in Fig. 6 has 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.

[0117] 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.

[0118] Examples of electronic devices according to the embodiments include a personal computer 1100 in FIG. 4, a smartphone 1200 in FIG. 5, and a digital still camera 1300 in FIG. 6, 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.

[0119] Such electronic devices include the magnetic element according to the embodiment, thereby enjoying the effects of the magnetic element and achieving high performance and miniaturization of the electronic devices.

[0120] 5. Effects of the embodiment As described above, the soft magnetic powder according to the embodiment has the composition formula Fe x Cu a Nb b (Si 1-y (B 1-z Cr z ) y ) 100-x-a-b[where a, b, x, y, and z satisfy 0.3≦a≦2.0, 2.0≦b≦4.0, 75.5≦x≦79.5, 0.55≦y≦0.91, and 0.015≦z≦0.185.] and impurities, and the average particle size is 5.0 μm or more and 45.0 μm or less, and the crystallite diameter measured by X-ray diffraction is 5.0 nm or more and 20.0 nm or less.

[0121] In addition, the soft magnetic powder according to the embodiment is mixed with an epoxy resin having a mass ratio of 2.0 mass %, and the obtained mixture has a compressive strength of 294.2 MPa (3 t / cm 2 ) to obtain a ring-shaped first compact having an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm. When a conductor having a wire diameter of 0.6 mm is wound seven times around the first compact to produce a first specimen, the reduction rate d of magnetic permeability, expressed by the following formula, is 3.0% or less.

[0122] d=|μ1-μ 100 | / μ1×100 [where μ1 is the magnetic permeability of the first object measured at a frequency of 1 MHz, and μ 100 is the magnetic permeability of the first object measured at a frequency of 100 MHz.]

[0123] According to this configuration, a soft magnetic powder is obtained that can be used to produce a green compact having excellent oxidation resistance, density, coercive force, and DC bias characteristics.

[0124] In the soft magnetic powder according to the embodiment, the magnetic permeability μ1 is 15 or more and less than 21. This configuration is believed to make magnetic saturation less likely to occur due to the optimized Si content in the soft magnetic powder, resulting in a soft magnetic powder that can realize a magnetic element with excellent DC bias characteristics.

[0125] The soft magnetic powder according to the embodiment was mixed with 2.0 mass % of epoxy resin, and the obtained mixture had a compressive strength of 294.2 MPa (3 t / cm 2), to obtain a ring-shaped second compact with an outer diameter of 28 mm, an inner diameter of 14 mm, and a thickness of 5 mm. A second specimen is then produced by winding a 1.25 mm diameter wire around the second compact 50 times. The DC bias current measured for the second specimen is 17 A or more. This DC bias current is the DC bias current superimposed on the second specimen when an AC signal with a frequency of 10 kHz is passed through the second specimen and, assuming the inductance when no DC bias current is superimposed is the reference value, the DC bias current superimposed on the second specimen is gradually increased and the measured inductance drops to 80% of the reference value.

[0126] According to this configuration, a soft magnetic powder can be obtained that can realize a magnetic element having sufficiently high DC bias characteristics and excellent operational stability.

[0127] In the soft magnetic powder according to the embodiment, the Si content is 4.0 atomic % or more and 8.0 atomic % or less, the B content is 9.0 atomic % or more and 13.5 atomic % or less, and the Cr content is 0.5 atomic % or more and 2.2 atomic % or less.

[0128] This configuration allows for the production of soft magnetic powders that can be used to produce compacts with lower coercivity and better DC bias characteristics. Furthermore, the oxidation resistance of the soft magnetic powder can be further improved, minimizing the generation of oxides. As a result, the crystallite size of each particle can be appropriately controlled.

[0129] In the soft magnetic powder according to the embodiment, the oxygen content is 1500 ppm or less. According to this configuration, it is possible to particularly suppress the generation of oxides that cause a decrease in the density of the compact.

[0130] In the soft magnetic powder according to the embodiment, the maximum magnetization measured using a vibrating sample magnetometer is defined as Mm [emu / g], and the true density is defined as ρ [g / cm 3 ], the saturation magnetic flux density Bs [T] calculated by 4π / 10000 × ρ × Mm = Bs is 1.20 [T] or more. With this configuration, a magnetic element that is less likely to saturate even with a high current can be obtained.

[0131] The powder magnetic core according to the embodiment contains the soft magnetic powder according to the embodiment. With this configuration, a powder magnetic core having good density, coercive force, and DC bias characteristics can be obtained.

[0132] The magnetic element according to the embodiment includes the powder magnetic core according to the embodiment. According to this configuration, a magnetic element can be obtained that can improve the performance and reduce the size of electronic devices and the like that incorporate the magnetic element.

[0133] The electronic device according to the embodiment includes the magnetic element according to the embodiment. With this configuration, an electronic device with high performance and small size can be obtained.

[0134] The soft magnetic powder, metal 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.

[0135] For example, in the above embodiment, a powder compact such as a powder core has been described as an example of an application of the soft magnetic powder of the present invention, but the application is not limited to this and may be, for example, a magnetic fluid, a magnetic head, or other magnetic device. Furthermore, the shapes of the powder core and the magnetic element are not limited to those shown in the drawings and may be any shape. [Example]

[0136] Next, specific examples of the present invention will be described. 6. Preparation of Soft Magnetic Powder 6.1. 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.

[0137] Next, the obtained metal powder was subjected to a crystallization treatment by heating in a nitrogen atmosphere. The heating temperatures in the heat treatment are as shown in Table 1. The temperature drop rate after heating was 10°C / min, and the oxygen concentration in the atmosphere for the crystallization treatment was 100 ppm. The heating temperatures shown in Table 1 were determined in advance by searching for the heating temperature at which the coercive force of the soft magnetic powder becomes minimum.

[0138] The mixture was then classified using an air classifier, thereby obtaining soft magnetic powder Sample No. 1. Table 1 shows the composition of the obtained soft magnetic powder, the structure of the metal powder before heat treatment, the crystallization temperature of the metal powder, and the heating temperature of the heat treatment.

[0139] 6.2. Samples No. 2 to 16 A soft magnetic powder was obtained in the same manner as Sample No. 1, except that the production conditions for the soft magnetic powder were changed as shown in Table 1. The soft magnetic powder of sample No. 16 was not subjected to heat treatment.

[0140] [Table 1]

[0141] In Table 1 and Table 2 described later, among the soft magnetic powders of each sample number, those that correspond to the present invention are designated as "Examples," and those that do not correspond to the present invention are designated as "Comparative Examples."

[0142] 7. Evaluation of soft magnetic powder and compacts 7.1.Average particle size of soft magnetic powder The average particle size of the soft magnetic powder of each example and comparative example was measured. The measurement results are shown in Table 2.

[0143] 7.2. Crystallite size of soft magnetic powder The crystallite diameter of each of the soft magnetic powders of the examples and comparative examples was measured by X-ray diffraction. The measurement results are shown in Table 2.

[0144] 7.3.Oxygen content of soft magnetic powder The oxygen content of the soft magnetic powders of each example and comparative example was measured. The oxygen content was measured using an ONH836 oxygen / nitrogen / hydrogen analyzer manufactured by LECO. The measurement results are shown in Table 2.

[0145] 7.4. Coercive force of soft magnetic powder The coercive force of the soft magnetic powders of each example and each comparative example was measured by the method described above. The measured coercive force was then evaluated in accordance with the following evaluation criteria. The evaluation results are shown in Table 2.

[0146] 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

[0147] 7.5. Saturation magnetic flux density of soft magnetic powder The saturation magnetic flux density of the soft magnetic powder obtained in each example and comparative example was calculated by the method described above. The calculation results are shown in Table 2.

[0148] 7.6. Molded body density The density of the compacts manufactured using the soft magnetic powders of each Example and Comparative Example was measured by the method described above. The measured density of the compacts was evaluated according to the following evaluation criteria. The measurement results are shown in Table 2.

[0149] A: Density of compact is 5.01 g / cm 3 That's all B: Density of compact is 4.99 g / cm 3 More than 5.01g / cm 3 is less than C: Density of compact is 4.99 g / cm 3 is less than

[0150] 7.7. Magnetic permeability of compact For the compacts manufactured using the soft magnetic powders obtained in each Example and Comparative Example, the magnetic permeability was measured at frequencies of 1 MHz and 100 MHz using the method described above. In addition, the rate of decrease in magnetic permeability when the frequency was increased from 1 MHz to 100 MHz was calculated. The measurement results and calculation results are shown in Table 2.

[0151] 7.8. DC Superimposition Characteristics of Molded Products The DC bias allowable current of the compacts manufactured using the soft magnetic powders obtained in each Example and Comparative Example was measured using the method described above.The DC bias characteristics were evaluated based on the measurement results and the following evaluation criteria.The evaluation results are shown in Table 2.

[0152] A: DC bias characteristics are particularly good (DC bias allowable current is 19A or more and 22A or less) B: Good DC bias characteristics (DC bias allowable current is 18A or more but less than 19A, or 22A or more but less than 24A) C: DC bias characteristics are fairly good (DC bias allowable current is 17A or more but less than 18A or more than 24A) D: Poor DC bias characteristics (DC bias allowable current is less than 17A)

[0153] [Table 2]

[0154] As shown in Table 2, the soft magnetic powders of each example had good oxidation resistance and a relatively low oxygen content, even though they had a high Fe content. It was also confirmed that the soft magnetic powders of each example had low coercive force. Furthermore, the compacts manufactured using the soft magnetic powders of each example had good density and DC bias characteristics. [Explanation of symbols]

[0155] 10...coil component, 11...powder magnetic core, 12...conductor, 20...coil component, 21...powder magnetic core, 22...conductor, 100...display unit, 1000...magnetic element, 1100...personal computer, 1102...keyboard, 1104...main body, 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, L1...DSC curve, L2...DSC curve, L3...DSC curve, L4...DSC curve, L5...DSC curve, P1...first heat generation peak, P2...second heat generation peak, Tx1...temperature, Tx2...temperature

Claims

1. Composition formula expressed in atomic ratio: Fe ｘ Cu ａ Nb ｂ (Si １－ｙ (B １－ｚ Cr ｚ ) ｙ ) １００－ｘ－ａ－ｂ [a, b, x, y, z are 0.3≦a≦2.0, 2.0≦b≦4.0, 75.5≦x≦79.5, 0.55≦y≦0.91, 0.015≦z≦0.185, Satisfy the above.] It is composed of the following composition and impurities: The average particle size is 5.0 μm or more and 45.0 μm or less, The crystallite diameter measured by X-ray diffraction is 5.0 nm or more and 20.0 nm or less, The mixture was mixed with an epoxy resin having a mass ratio of 2.0 mass%, and the resulting mixture had a pressure of 294.2 MPa (3 t / cm ２ ) to obtain a ring-shaped first compact having an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm, and then winding a conductor having a wire diameter of 0.6 mm seven times around the first compact to produce a first specimen, the soft magnetic powder characterized in that the reduction rate d of magnetic permeability, expressed by the following formula, is 3.0% or less. d=|μ １ -m １００ | / μ １ ×100 [In the above formula, μ １ is the magnetic permeability of the first object measured at a frequency of 1 MHz, and μ １００ is the magnetic permeability of the first subject measured at a frequency of 100 MHz.]

2. The magnetic permeability μ １ 2. The soft magnetic powder according to claim 1, wherein the ρ is 15 or more and less than 21.

3. 2.0 mass% of epoxy resin, and the resulting mixture was subjected to a pressure of 294.2 MPa (3 t / cm ２ 3. The soft magnetic powder according to claim 1, wherein the second compact is press-molded at a pressure of 100 MPa to obtain a ring-shaped second compact having an outer diameter of 28 mm, an inner diameter of 14 mm, and a thickness of 5 mm. Then, a conductor having a wire diameter of 1.25 mm is wound 50 times around the second compact to prepare a second test piece. An AC signal having a frequency of 10 kHz is passed through the second test piece, and when the inductance when no DC bias current is superimposed is taken as a reference value, the DC bias current superimposed on the second test piece is gradually increased and the measured inductance drops to 80% of the reference value, the DC bias current superimposed on the second test piece is 17 A or more.

4. The Si content is 4.0 atomic % or more and 8.0 atomic % or less, The content of B is 9.0 atomic % or more and 13.5 atomic % or less, 3. The soft magnetic powder according to claim 1, wherein the Cr content is 0.5 atomic % or more and 2.2 atomic % or less.

5. 3. The soft magnetic powder according to claim 1, wherein the oxygen content is 1500 ppm or less.

6. The maximum magnetization measured using a vibrating sample magnetometer is defined as Mm [emu / g]. True density is ρ [g / cm ３ ], 3. The soft magnetic powder according to claim 1, wherein the saturation magnetic flux density Bs [T] calculated by 4π / 10000×ρ×Mm=Bs is 1.20 [T] or more.

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

8. A magnetic element comprising the powder magnetic core according to claim 7.

9. An electronic device comprising the magnetic element according to claim 8.

Images