Soft magnetic nanoparticle aggregate and method for producing same

Abstract

A soft magnetic nanoparticle aggregate (1) comprises a plurality of soft magnetic nanoparticles (2) that are in close contact with each other, and a non-magnetic layer (3) that is filled in a grain boundary phase between the soft magnetic nanoparticles, the soft magnetic nanoparticles having an average particle diameter of 50 nm or less as observed by a transmission electron microscope, the thickness of the non-magnetic layer being 4.9 nm or less, and the coercive force of the soft magnetic nanoparticle aggregate (1) is 71±7.1 [A / m] or less as measured by a vibration sample magnetometer.

Description

Soft magnetic nanoparticle assembly and method for producing same

[0001] The present disclosure relates to soft magnetic nanoparticle assemblies and methods for producing the same.

[0002] Patent Document 1 proposes a soft magnetic metal film made of an alloy primarily composed of iron (Fe) and deposited with magnetically isotropic nanoparticles with a particle diameter of 3 nm to 10 nm. This soft magnetic metal film has a thickness of 0.1 to 500 μm, which allows for a saturation magnetization per unit mass of 215 emu / g and a coercive force of 100 A / m or less, i.e., 1.2 Oe or less, thereby achieving excellent soft magnetic properties such as a high saturation magnetic flux density and low coercive force.

[0003] JP 2011-171495 A

[0004] In a soft magnetic nanoparticle assembly, the saturation magnetic flux density can be increased by packing soft magnetic nanoparticles at a high density, and the coercive force can be reduced, thereby improving the soft magnetic properties.

[0005] However, due to the large specific surface area of ​​nanoparticles, friction and static electricity occur between particles, preventing adhesion between particles and making it difficult to form a high-density soft magnetic nanoparticle aggregate. Although heat treatment can be used to increase the density, heat treatment at high temperatures coarsens the particle size and reduces the soft magnetic properties, making it impossible to obtain a high-density soft magnetic nanoparticle aggregate while maintaining excellent soft magnetic properties.

[0006] On the other hand, simply increasing the density of soft magnetic nanoparticles results in increased eddy currents in proportion to the particle size if there is electrical contact between the particles, resulting in eddy current loss. It is known that eddy current loss can be reduced by providing a non-magnetic layer on the surface of soft magnetic nanoparticles, but this results in a structure in which a thick non-magnetic layer covers the entire surface of the soft magnetic nanoparticles. This reduces the proportion of the soft magnetic material in the soft magnetic nanoparticles, making it impossible to increase the density of the soft magnetic material and resulting in a decrease in magnetic flux density per unit volume. Therefore, it is difficult to obtain excellent soft magnetic properties.

[0007] An object of the present disclosure is to provide a soft magnetic nanoparticle assembly having excellent soft magnetic properties and a method for producing the same.

[0008] A soft magnetic nanoparticle assembly in one aspect of the present disclosure comprises a plurality of soft magnetic nanoparticles (2) closely attached to one another, and a non-magnetic layer (3) filled in the grain boundary phase between the soft magnetic nanoparticles, wherein the average particle diameter of the soft magnetic nanoparticles observed with a transmission electron microscope is 50 nm or less, the thickness of the non-magnetic layer is 4.9 nm or less, and the coercive force measured with a vibrating sample magnetometer is 71±7.1 [A / m] or less.

[0009] Thus, because the particle diameter of the soft magnetic nanoparticles is 50 nm or less, an increase in coercivity is suppressed. Furthermore, because the thickness of the nonmagnetic layer is thin, at 4.9 nm or less, even if the soft magnetic nanoparticles are partially covered with the nonmagnetic layer, adjacent soft magnetic nanoparticles are in close contact with each other in the uncovered portions, and even if the nonmagnetic layer is present, the density of the soft magnetic nanoparticles in the soft magnetic nanoparticle assembly is high. This allows for a high saturation magnetic flux density. Furthermore, this configuration makes it possible to achieve a low coercivity of 71 [A / m] or less, resulting in a soft magnetic nanoparticle assembly with excellent soft magnetic properties, namely, a high saturation magnetic flux density and a low coercive force.

[0010] In addition, a manufacturing method of a soft magnetic nanoparticle assembly according to another aspect of the present disclosure includes: preparing a plurality of soft magnetic nanoparticles (2); forming composite soft magnetic nanoparticles (20) in which the surface of each of the plurality of soft magnetic nanoparticles is coated with a non-magnetic material (10); amorphizing the soft magnetic nanoparticles contained in the composite soft magnetic nanoparticles to form an amorphous bulk body (40); and thermally decomposing the non-magnetic material contained in the amorphous bulk body by heat treatment to release a portion of the non-magnetic material, thereby manufacturing a soft magnetic nanoparticle assembly (1) in which adjacent soft magnetic nanoparticles are adhered to each other and a non-magnetic layer (3) composed of the pyrolyzed non-magnetic material is disposed in the grain boundary phase between the soft magnetic nanoparticles.

[0011] This manufacturing method allows for the production of soft magnetic nanoparticle aggregates. The soft magnetic nanoparticle aggregates obtained in this manner have soft magnetic nanoparticles densely packed together, with only a thin nonmagnetic layer formed in the grain boundary phase between the soft magnetic nanoparticles. Therefore, it is possible to achieve both high saturation magnetic flux density and low coercive force, making it possible to produce soft magnetic nanoparticle aggregates with excellent soft magnetic properties.

[0012] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below.

[0013] 1 is a cross-sectional view of a soft magnetic nanoparticle assembly according to a first embodiment of the present disclosure. FIG. 2 is a flowchart showing a method for manufacturing a soft magnetic nanoparticle assembly. FIG. 3 is a cross-sectional view of one particle of soft magnetic nanoparticle. FIG. 4 is a cross-sectional view of one particle of soft magnetic nanoparticle, the surface of which is covered with a non-magnetic material. FIG. 5 is a cross-sectional view of a granulated body. FIG. 6 is a cross-sectional view of an amorphous bulk body formed on a substrate. FIG. 7 is a cross-sectional view of a soft magnetic nanoparticle assembly formed on a substrate. FIG. 8 is a transmission electron microscope (TEM) image of soft magnetic nanoparticles, the surface of which is covered with a non-magnetic material. FIG. 9 is a diagram showing the formation of an amorphous bulk body using a cold spray (hereinafter referred to as CS) device. FIG. 10 is a photograph of the appearance of a soft magnetic nanoparticle assembly. FIG. 11 is a magnetic characteristic diagram showing the change in saturation magnetic flux density with respect to a change in magnetic field. FIG. 12 is a graph showing coercive force. FIG. 13 is a diagram showing the relationship between hydrogen heat treatment temperature and coercive force. FIG. 14 is a table showing TEM images.

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the following, including other embodiments described below, identical or equivalent parts will be denoted by the same reference numerals.

[0015] First Embodiment A soft magnetic nanoparticle assembly according to this embodiment will be described. First, the structure of the soft magnetic nanoparticle assembly will be described.

[0016] <Structure of Soft Magnetic Nanoparticle Assembly> The soft magnetic nanoparticle assembly 1 shown in Fig. 1 is an assembly formed by densely packing a plurality of soft magnetic nanoparticles 2, that is, fine particles of a soft magnetic material with a nano-sized particle size. More specifically, the soft magnetic nanoparticle assembly 1 has a structure in which the soft magnetic nanoparticles 2 are densely packed, adjacent soft magnetic nanoparticles 2 are in close contact with each other, and a non-magnetic layer 3 is filled in the gaps between the soft magnetic nanoparticles 2. In other words, the non-magnetic layer 3 is disposed in the grain boundary phase that forms the boundary between each soft magnetic nanoparticle 2. Because each soft magnetic nanoparticle 2 is in a state of close contact with each other at a high density, the gaps between the soft magnetic nanoparticles 2 are small, and the non-magnetic layer 3 is disposed in those small gaps.

[0017] The soft magnetic nanoparticles 2 may be made of any soft magnetic material, but are preferably made of a material with excellent soft magnetic properties, such as pure iron nanoparticles made only of Fe (iron). Pure iron refers to high-purity iron made of highly pure iron, and the higher the purity, the better. In particular, it is preferable for the soft magnetic nanoparticles 2 to be made of pure iron of about 99.9% or more made only of Fe, which is called high-purity iron. As shown in FIG. 1, although the soft magnetic nanoparticles 2 have a random crystal shape, adjacent particles in the soft magnetic nanoparticle assembly 1 are densely packed in a state of close contact with each other.

[0018] The particle diameter of the soft magnetic nanoparticles 2 is 4 to 50 nm, preferably 6 to 20 nm. When the soft magnetic nanoparticles 2 are single magnetic domain particles, the coercive force tends to increase with the particle size, so the smaller the particle diameter, the better. On the other hand, from the perspective of practical use, the larger the particle diameter, the better.

[0019] Furthermore, when soft magnetic nanoparticle assemblies 1 are manufactured using the manufacturing method described below, the particle diameter of the soft magnetic nanoparticles 2 contained therein can be 20 nm or less. Soft magnetic nanoparticles 2 with a particle diameter of 20 nm or less have a low coercive force, and the coercive force can be 71 ± 7.1 [A / m], i.e., 0.9 ± 0.09 [Oe] or less. The coercive force is a value measured using a vibrating sample magnetometer. A coercive force of 71 [A / m], i.e., 0.9 [Oe] or less can be obtained, but since a measurement error of 10% can occur, the value is expressed as an estimate taking into account the measurement error. On the other hand, the smaller the particle diameter of the soft magnetic nanoparticles 2, the lower the coercive force can be, but in experiments, the minimum particle diameter was approximately 4 ± 0.5 nm. However, it is difficult to uniformly set the particle diameter to approximately 4 nm, and soft magnetic nanoparticles 2 including those with a particle diameter of 6 ± 0.5 nm or more can be obtained relatively easily. The particle diameter is the average particle diameter observed by a transmission electron microscope, but since a measurement error can occur within a range of about 0.5 nm, the value is expressed taking into account the measurement error.

[0020] The preferred particle diameter range for the soft magnetic nanoparticles 2 is 6 to 20 nm. This range is more preferable if all soft magnetic nanoparticles 2 have a particle diameter of 6 to 20 nm, but does not necessarily mean that particle diameters of less than 6 nm or more than 20 nm are excluded. It is sufficient that the average particle diameter is within the range of 6 to 20 nm. However, it is preferable that the maximum particle diameter of the soft magnetic nanoparticles 2 contained in the soft magnetic nanoparticle assembly 1 is 50 nm or less, and that only soft magnetic nanoparticles 2 of 20 nm or less are included.

[0021] The higher the density of the soft magnetic nanoparticles 2 in the soft magnetic nanoparticle assembly 1, that is, the higher the ratio of the volume of the soft magnetic nanoparticles 2 to the volume of the soft magnetic nanoparticle assembly 1, the better. As described above, when the soft magnetic nanoparticles 2 are pure iron nanoparticles and the non-magnetic layer 3 is an organic substance, particularly oleylamine or a decomposition product produced by thermally decomposing oleylamine, the density of the soft magnetic nanoparticles 2 in the soft magnetic nanoparticle assembly 1 can be made as high as 97%, for example.

[0022] The non-magnetic layer 3 is provided so as to penetrate into the gaps between the soft magnetic nanoparticles 2 and cover the surfaces of the soft magnetic nanoparticles 2, in other words so as to cover the surfaces of the parts of the soft magnetic nanoparticles 2 that are not in close contact with adjacent soft magnetic nanoparticles 2. The non-magnetic layer 3 may be disposed so as to cover all of the gaps between the soft magnetic nanoparticles 2, or may be disposed so as to cover the surfaces of the soft magnetic nanoparticles 2 within the gaps while leaving gaps inside the non-magnetic layer 3.

[0023] The non-magnetic layer 3 is composed of an organic substance or a carbide, which is a decomposition product. For example, when the non-magnetic layer 3 is a carbide, it is formed by thermally decomposing the non-magnetic material 10, which will be described later. As an example, the non-magnetic layer 3 can be formed by preparing a liquid containing the non-magnetic material 10, which is composed of an organic substance such as a resin, mixing the soft magnetic nanoparticles 2 into the solution, drying the solution, and then thermally decomposing the non-magnetic material 10. In this case, the organic substance that constitutes the non-magnetic material 10 is thermally decomposed to form a carbide, and the non-magnetic layer 3 is formed from the carbide.

[0024] As described above, the soft magnetic nanoparticles 2 are densely packed together, so the gaps between the soft magnetic nanoparticles 2 are small, and the thickness of the non-magnetic layer 3 is thin, at 4.9 nm or less, for example 1.1 nm. Therefore, even if the soft magnetic nanoparticles 2 are partially covered with the non-magnetic layer 3, the density of the non-magnetic layer 3 in the soft magnetic nanoparticle assembly 1 is low, and the density of the soft magnetic nanoparticles 2 is high.

[0025] As described above, the soft magnetic nanoparticle assembly 1 of this embodiment is composed of an assembly of numerous soft magnetic nanoparticles 2 and non-magnetic layers 3 disposed in the gaps between them. Although the soft magnetic nanoparticles 2 have random crystal shapes, they are densely packed adjacent to each other in the soft magnetic nanoparticle assembly 1. This allows for a high saturation magnetic flux density to be obtained.

[0026] Furthermore, by packing the soft magnetic nanoparticles 2 at a high density, direct interactions between the particles are promoted, making it possible to reduce the substantial magnetic anisotropy and further reduce the coercive force.

[0027] The coercive force is a value that indicates the efficiency or loss in the soft magnetic properties, and the smaller the value, the better the soft magnetic properties. The saturation magnetic flux density is the magnetic flux density when the soft magnetic nanoparticles 2 are magnetically saturated, and the higher the value, the better the soft magnetic properties. The saturation magnetic flux density is measured, for example, using a vibrating sample magnetometer. The more densely the soft magnetic nanoparticles 2 are packed, the higher the saturation magnetic flux density per unit volume can be.

[0028] Furthermore, the soft magnetic nanoparticle assembly 1 of this embodiment has a structure in which soft magnetic nanoparticles 2 are packed at high density, but the surfaces thereof are covered with a non-magnetic layer 3. This suppresses electrical contact between the particles, making it possible to reduce eddy current loss.

[0029] On the other hand, when the surface of the soft magnetic nanoparticles 2 is covered with a non-magnetic layer 3, if the non-magnetic layer 3 is thick, the soft magnetic nanoparticles 2 cannot be densified, and the magnetic flux density per unit volume decreases. Therefore, there is a trade-off between trying to reduce eddy current loss and decreasing the soft magnetic properties of the soft magnetic nanoparticle assembly 1. In particular, in the case of nanoparticles, the large specific surface area results in a significant decrease in magnetic flux density.

[0030] However, in the soft magnetic nanoparticle assembly 1 of this embodiment, the nonmagnetic layer 3 can be thinned to 4.9 nm or less, for example 1.1 nm, and the density of the nonmagnetic layer 3 can be reduced, thereby increasing the density of the soft magnetic nanoparticles 2 and suppressing a decrease in the magnetic flux density per unit volume. Therefore, it is possible to achieve both a high saturation magnetic flux density and a low coercive force, and to obtain a soft magnetic nanoparticle assembly 1 with excellent soft magnetic properties.

[0031] <Method for manufacturing soft magnetic nanoparticle assembly 1> Next, a method for manufacturing the soft magnetic nanoparticle assembly 1 described above will be described. The soft magnetic nanoparticle assembly 1 of this embodiment is manufactured through the steps shown in the manufacturing flow of Figure 2. Specifically, in Figure 2, the steps include a soft magnetic nanoparticle precursor synthesis step of step S0, a soft magnetic nanoparticle synthesis step of step S1, a nonmagnetic material coating step of step S2, a granulation step of step S3, an amorphous bulk formation step of step S4, a separation step of step S5, and a peeling step of step S6. The steps shown in steps S0 to S6 will be described as steps (1) to (7) below.

[0032] (1) Soft Magnetic Nanoparticle Precursor Synthesis Step In this step, a precursor that will be the raw material for the soft magnetic nanoparticles 2 is synthesized. The raw material for the soft magnetic nanoparticles 2 and the raw material for the non-magnetic material 10 are mixed. Specifically, Fe(CO) ５ The mixing ratio of the soft magnetic nanoparticles 2 to oleylamine is arbitrary, but for example, the molar ratio of oleylamine to the soft magnetic nanoparticles 2 is set to 1:2.5.

[0033] (2) Soft Magnetic Nanoparticle Synthesis Step In this step, soft magnetic nanoparticles 2 are produced by heating the precursor. Fe(CO) ５ is iron pentacarbonyl, a precursor of iron compounds that exist in liquid form under standard conditions, and is synthesized, for example, from carbon monoxide and fine iron powder. ５When this liquid is heated, pure iron nanoparticles that constitute the soft magnetic nanoparticles 2 are generated. The soft magnetic nanoparticles 2 at this stage have a crystalline shape, for example, a sphere as shown in FIG. 3A, and a particle diameter of approximately 2 to 10 nm. The stirring temperature is arbitrary, but is controlled to a temperature above 30°C, at which thermal decomposition begins, and below 200°C, which does not cause particle growth of the soft magnetic nanoparticles 2, and more preferably below 130°C. It has been confirmed that the saturation magnetic flux density of the soft magnetic nanoparticles 2 does not change significantly with temperature changes up to 200°C, but the coercive force increases above 200°C (see M. Kamata et al., J. Magn. Soc. Jpn, 36, 309 (2012)). Therefore, by setting the stirring temperature below 200°C, for example at 70±3°C, the saturation magnetic flux density is maintained high while the increase in coercive force is suppressed.

[0034] In this specification, the particle diameter is the average value of 30 particles observed by TEM, and if the particles are spherical, the diameter is calculated; if the particles are spindle-shaped having a major axis and a minor axis, or amorphous, the area is calculated by image processing, and the diameter of a circle with the same area is calculated as the particle diameter. As described above, if the soft magnetic nanoparticles 2 in this process are pure iron nanoparticles, they will be spherical, and their diameter will be the particle.

[0035] (3) Non-magnetic Material Coating Step As shown in FIG. 3B, composite soft magnetic nanoparticles 20 are formed by coating the surfaces of soft magnetic nanoparticles 2 with non-magnetic material 10. Specifically, as shown in FIG. 4, soft magnetic nanoparticles 2 are mixed into a liquid containing non-magnetic material 10. As a result, the non-magnetic material 10 adheres to the surfaces of the soft magnetic nanoparticles 2, and the non-magnetic material 10 is arranged in the "grain boundary phase" at the boundaries between the particles of the soft magnetic nanoparticles 2. At this time, the thickness of the non-magnetic material 10 is about 1 to 3 nm, and preferably about 1 to 2 nm.

[0036] The liquid containing the non-magnetic material 10 may be a solution in which the non-magnetic material 10 is dissolved in a solvent, or if the non-magnetic material 10 is liquid, the non-magnetic material 10 itself may be used. Of course, even if the non-magnetic material 10 is liquid, a solution in which the non-magnetic material 10 is dissolved in a solvent may be used as the liquid containing the non-magnetic material 10. By dissolving the non-magnetic material 10 in a solvent, the concentration of the non-magnetic material 10 in the solution can be adjusted. When using a solution in which the non-magnetic material 10 is dissolved in a solvent, for example, a solvent is used that has a boiling point lower than the temperature at which the non-magnetic material 10 is thermally decomposed (hereinafter referred to as the thermal decomposition temperature) at normal pressure or a specific atmospheric pressure.

[0037] For example, oleylamine (CH3(CH2)7CH:CH(CH2)8NH2), a surfactant, is used as the nonmagnetic material 10. As oleylamine itself is a liquid, it is possible to use oleylamine as is for the liquid containing the nonmagnetic material 10, but a solution in which oleylamine is dissolved in toluene, a solvent, is used. A solution in which this oleylamine is dissolved in toluene is prepared, and soft magnetic nanoparticles 2 are mixed into this solution and heated. As a result, oleylamine adheres to the surface of the soft magnetic nanoparticles 2 as the nonmagnetic material 10, resulting in a structure in which the surface of the soft magnetic nanoparticles 2 is coated with oleylamine. Because toluene is volatile, it volatilizes at this time, but it may be completely volatilized and removed, or some of it may remain.

[0038] The soft magnetic nanoparticles 2 and oleylamine, etc. are also mixed while stirring with a propeller, and the heating temperature is set to 200° C. or less, for example, 70±1° C. The mixing ratio of the soft magnetic nanoparticles 2 and oleylamine is arbitrary, but for example, the molar ratio of oleylamine to the volume of the soft magnetic nanoparticles 2 is set to 1:2.5.

[0039] The thickness of the non-magnetic material 10 is determined by the volume of the soft magnetic nanoparticles 2, in other words, the volume of oleylamine relative to the surface area of ​​the soft magnetic nanoparticles 2. Therefore, by appropriately adjusting the mixing ratio of the soft magnetic nanoparticles 2 and oleylamine, the non-magnetic material 10 can be made to have a desired thickness. If the non-magnetic material 10 is too thick, the density of the soft magnetic nanoparticles 2 in the soft magnetic nanoparticle assembly 1 that is finally formed will be hindered, so it is preferable that the thickness of the non-magnetic material 10 in this step be about 1 to 2 nm, as described above.

[0040] (4) Granulation Step After drying the composite soft-magnetic nanoparticles 20 in which the surfaces of the soft magnetic nanoparticles 2 are covered with the non-magnetic material 10, the composite soft-magnetic nanoparticles 20 are granulated to form granules 30 which are aggregates of the composite soft-magnetic nanoparticles 20 as shown in Fig. 3C. At this time, the size of the granules 30 is arbitrary, but it is preferable to set the size to one that is easy to handle in subsequent steps.

[0041] Heat treatment is performed to promote drying when drying the composite soft-magnetic nanoparticles 20. For the heat treatment, the composite soft-magnetic nanoparticles 20 are placed in a heat treatment device, and vacuum heat treatment is preferably performed in which the composite soft-magnetic nanoparticles 20 are heated in a reduced pressure atmosphere, preferably in a vacuum state, and hydrogen heat treatment is preferably performed in which the composite soft-magnetic nanoparticles 20 are heated in a hydrogen atmosphere.

[0042] For example, the heat treatment is performed using a tubular furnace as the heat treatment device. For the vacuum heat treatment, the degree of vacuum is set to 1.0×10 Pa. For the hydrogen heat treatment, H ２ The flow rate of hydrogen (H2) was set to 400 cc / min. The heating temperature for both the vacuum heat treatment and the hydrogen heat treatment was set to 200°C or less, and here both were set to 170°C, but different temperatures may be used depending on the Fe particle size. The duration of the vacuum heat treatment and the hydrogen heat treatment may be determined arbitrarily depending on the degree of dryness, but here both were performed for 5 hours.

[0043] Furthermore, when forming granules 30 of a uniform size, the dried composite soft-magnetic nanoparticles 20 are formed into small lumps, which are then broken down to form granules 30 of the desired size. Specifically, the dried composite soft-magnetic nanoparticles 20 are pressed with a hand press to form pellets, i.e., small lumps. These pellets are made up of a large number of densely packed soft magnetic nanoparticles 2, each of which is surrounded by the non-magnetic material 10. The size of the pellets is arbitrary, but is set to be larger than the size of the granules 30 that is ultimately desired to be obtained.

[0044] The pellets are then crushed in a mortar (not shown) to produce granules 30 of uniform size, for example, with particle diameters of about 20 to 200 μm, which are easy to handle in subsequent processes.

[0045] (5) Amorphous Bulk Forming Step The granules 30 are plastically deformed to make the crystals of the soft magnetic nanoparticles 2 in the granules 30 amorphous. For example, the crystals of the soft magnetic nanoparticles 2 can be made amorphous using a CS device based on the CS method.

[0046] As shown in FIG. 5, the CS device includes a high-pressure gas source 100 , a powder supply source 101 , a preheater 102 , and a CS gun 103 .

[0047] The high-pressure gas source 100 supplies a carrier gas 100a at high pressure. In this example, an inert atmosphere CS apparatus is used, and the carrier gas 100a is, for example, N 2 O 3 with a gas purity of 99.999% or more. ２ Nitrogen gas is used, with a gas temperature of 100°C and a gas pressure of 0.5 MPa. A gas supply line 104 is connected to the high-pressure gas source 100, and the supply and stop of carrier gas 100a is adjusted by controlling a valve 105 provided on the gas supply line 104. The gas supply line 104 branches into two, one branch line 104a connected to the CS gun 103 and the other branch line 104b connected to the powder supply source 101.

[0048] The powder supply source 101 contains granulated material 30 whose size has been made uniform in the granulation process, and is connected to the high-pressure gas source 100 via a branch path 104b, and is also connected to the CS gun 103 via a discharge path 106. The powder supply source 101 extrudes the particles of the contained granulated material 30 into the discharge path 106 based on the high-pressure carrier gas 100a supplied from the branch path 104b, and supplies them to the CS gun 103.

[0049] The preheater 102 heats the carrier gas 100a to a predetermined temperature, for example, 100° C. The preheater 102 is provided in the CS gun 103 and heats the gas supply path 104, but may be disposed outside the CS gun 103.

[0050] The CS gun 103 accelerates the granules 30 to a supersonic speed range by mixing them with a gas flow of high-pressure carrier gas 100a supplied from a branch path 104a, and sprays the granules 30 in a solid state onto a substrate 110 installed at the end of the outlet 103a of the CS gun 103. As a result, the granules 30 are caused to collide with the substrate 110, and an impact force is applied to the granules 30. The carrier gas 100a is mixed with N ２ When the gas was used, the gas purity, gas temperature, and gas pressure were set under the above conditions, the material of the soft magnetic nanoparticles 2 was Fe, and the particle size of the granules 30 was set to 20 to 200 μm, the granules 30 were accelerated to approximately several hundred m / sec and ejected.

[0051] As a result, the granules 30 collide with the substrate 110, generating a large impact force on the particles, causing the crystalline state of the soft magnetic nanoparticles 2 in the composite soft magnetic nanoparticles 20 to become amorphous, resulting in the amorphous bulk body 40 shown in Fig. 3D. The material of the substrate 110 is arbitrary, but it is advisable to use a material different from the constituent material of the soft magnetic nanoparticles 2 in the soft magnetic nanoparticle assembly 1 to be produced, preferably a material with a different linear expansion coefficient. Here, the substrate 110 is made of Cu (copper).

[0052] The magnitude of the impact force at this time is determined by parameters such as the size of the granules 30, the gas flow rate, the side chain length of the surfactant constituting the non-magnetic material 10, and the surfactant coverage. For this reason, the parameters that determine the impact force are adjusted so that an impact force that will cause the crystals of the soft magnetic nanoparticles 2 to become amorphous can be generated.

[0053] (6) Release Process: The amorphous bulk body 40 is subjected to a vacuum heat treatment in which the amorphous bulk body 40 is heated at least in a reduced pressure atmosphere, preferably in a vacuum state, to thermally decompose the nonmagnetic material 10 and release some of the components of the nonmagnetic material 10. In addition to the heating in the reduced pressure atmosphere, it is preferable to perform a hydrogen heat treatment in which the amorphous bulk body 40 is heated in a hydrogen atmosphere. This thermal decomposition reduces the amount of nonmagnetic material 10 between the soft magnetic nanoparticles 2 contained in the amorphous bulk body 40, as shown in FIG. 3E . The crystal shape of the soft magnetic nanoparticles 2 then becomes random, forming a soft magnetic nanoparticle assembly 1, and the soft magnetic nanoparticles 2 are densely packed and adjacent to each other within the soft magnetic nanoparticle assembly 1.

[0054] For example, a tubular furnace is used as the heat treatment device, and the vacuum heat treatment is performed at a vacuum level of 1.0×10 Pa. The hydrogen heat treatment is performed using H ２ The flow rate of the vacuum heat treatment was 400 cc / min. The temperature for both the vacuum heat treatment and the hydrogen heat treatment was 200°C or less, and here both were set to 170°C, but different temperatures may be used depending on the particle size. The duration of the vacuum heat treatment and the hydrogen heat treatment can be determined depending on the degree of release of the non-magnetic material 10, as long as it is equal to or longer than the time required for crystallization of the magnetic nanoparticles, and is arbitrary. Here, both were performed for 48 hours.

[0055] Furthermore, when some of the components of the nonmagnetic material 10 are desorbed by thermal decomposition in this manner, a nonmagnetic layer 3 is formed. The thickness of the nonmagnetic layer 3 can be made as thin as 4.9 nm or less. The thickness of this nonmagnetic layer 3 can be adjusted as desired, depending on the heat treatment time and the thickness of the nonmagnetic material 10 before desorption, but experiments have shown that it is possible to make it as thin as at least 1.1 nm. Because the thickness of the nonmagnetic layer 3 can be made thin in this way, the soft magnetic nanoparticles 2 can be densified even when the nonmagnetic layer 3 is filled in the grain boundary phase in the gaps between the soft magnetic nanoparticles 2.

[0056] (7) Peeling Step Since the soft magnetic nanoparticle assembly 1 remains attached to the surface of the substrate 110, the soft magnetic nanoparticle assembly 1 is peeled off from the substrate 110. For example, the substrate 110 and the soft magnetic nanoparticle assembly 1 are placed in a cooling device and cooled. Here, the substrate 110 and the soft magnetic nanoparticle assembly 1 are cooled to about 5°C. This allows the soft magnetic nanoparticle assembly 1 to be peeled off from the substrate 110 due to thermal stress generated based on the difference in linear expansion coefficient between the substrate 110 and the constituent material of the soft magnetic nanoparticles 2 in the soft magnetic nanoparticle assembly 1. This allows a mass of soft magnetic nanoparticle assembly 1 to be obtained, as shown in FIG. 6. The soft magnetic nanoparticle assembly 1 obtained in this manner is a large mass of about several mm, for example, about 25 mm as shown in FIG. 6.

[0057] The manufacturing method described above makes it possible to obtain a soft magnetic nanoparticle assembly 1. In the soft magnetic nanoparticle assembly 1 obtained in this manner, the soft magnetic nanoparticles 2 are in a state of being closely packed together at a high density, with only a thin nonmagnetic layer 3 formed in the grain boundary phase between the soft magnetic nanoparticles 2. Therefore, it is possible to achieve both a high saturation magnetic flux density and a low coercive force, making it possible to obtain a soft magnetic nanoparticle assembly 1 with excellent soft magnetic properties.

[0058] Furthermore, the soft magnetic nanoparticle assembly 1 is not composed only of soft magnetic nanoparticles 2, but has a structure in which the grain boundary phase is filled with a nonmagnetic layer 3. This makes it possible to reduce the heat generated when the nonmagnetic layer 3 applies a magnetic field to the soft magnetic nanoparticle assembly 1 at high frequency.

[0059] Furthermore, the soft magnetic nanoparticle assembly 1 produced through the peeling process is obtained by colliding the granules 30 onto the substrate 110, depositing the granules, and then thermally decomposing the deposited material. Therefore, by simply adjusting the thickness of the deposition on the substrate 110, the soft magnetic nanoparticle assembly 1 can be formed thick, with a thickness of several hundred μm or more, preferably 1000 μm or more. Experiments have shown that soft magnetic nanoparticle assembly 1 with a thickness of 1500 μm or more can be obtained. In this way, since the thickness can be increased, the practicality of the soft magnetic nanoparticle assembly 1 can be improved. Furthermore, since the soft magnetic nanoparticle assembly 1 can be obtained as large-sized agglomerates, the practicality can be further improved.

[0060] For reference, comparative experiments were conducted on a soft magnetic nanoparticle aggregate 1 manufactured using the CS method as in this embodiment, Comparative Example 1 manufactured by press molding and then heat-treated, and Comparative Example 2 in which pure iron nanoparticles were heat-treated.

[0061] Specifically, for this embodiment and Comparative Example 1, the same steps were performed up to (1) the soft magnetic nanoparticle synthesis step, (2) the nonmagnetic material coating step, and (3) the granulation step, but the subsequent steps were different to produce the soft magnetic nanoparticle assembly 1. For this embodiment, after each of steps (1) to (3), the soft magnetic nanoparticle assembly 1 was produced by performing (4) the amorphous bulk formation step, (5) the release step, and (6) the peeling step, as described above. Furthermore, for Comparative Example 1, after each of steps (1) to (3), press molding was performed at a molding pressure of 196 kgf, in an inert atmosphere, and at room temperature of approximately 27°C to form granules 30, and then the nonmagnetic material 10 was thermally decomposed to produce the soft magnetic nanoparticle assembly 1. For Comparative Example 2, pure iron nanoparticles were produced via step (1), and then a heat treatment similar to the thermal decomposition of the nonmagnetic material 10 was performed.

[0062] Then, the soft magnetic nanoparticles 2 were evaluated for each sample of this embodiment and comparative examples 1 and 2. For this embodiment and comparative example 1, the density, magnetic properties, and texture were evaluated. For comparative example 2, only the magnetic properties were evaluated. The density was evaluated by a liquid weighing method. The magnetic properties were evaluated using a VSM (Vibrating Sample Magnetometer). The texture was evaluated using a TEM.

[0063] Regarding density, in Comparative Example 1, the density before pyrolysis of the nonmagnetic material 10 was 35%, but after pyrolysis it was 73%. Furthermore, in this embodiment, the density before pyrolysis of the nonmagnetic material 10 was 32%, but after pyrolysis it was 97%. From these results, it can be seen that the soft magnetic nanoparticle assembly 1 of this embodiment was able to increase the density of the soft magnetic nanoparticles 2, and the density was improved by 60% or more compared to Comparative Example 1.

[0064] Furthermore, among the magnetic properties, the change in saturation magnetic flux density with respect to changes in magnetic field was investigated for each of the present embodiment and comparative examples 1 and 2. FIG. 7A shows the results. As shown in FIG. 7A, in the case of the present embodiment, the saturation magnetic flux density was 216 [emu / g] per unit mass. A value of 180 [emu / g] or higher can be considered a high saturation magnetic flux density, and in the case of the present embodiment, it was 180 [emu / g] or higher. Furthermore, comparative example 2 uses pure iron nanoparticles, which result in a high saturation magnetic flux density. However, the present embodiment also achieved a saturation magnetic flux density equivalent to that of comparative example 2. Meanwhile, the coercivity, among the magnetic properties, was also investigated for each of the present embodiment and comparative examples 1 and 2. FIG. 7B shows the results. As shown in FIG. 7B, the coercivity was 24 [Oe], i.e., 1900 [A / m], for comparative example 2, 13 [Oe], i.e., 1000 [A / m], for comparative example 1, and 0.9 [Oe], i.e., 71 [A / m], for the present embodiment. As described above, it can be seen that the soft magnetic nanoparticle assembly 1 of this embodiment has a high saturation magnetic flux density and low coercive force, and thus has excellent magnetic properties. Note that the coercive force is a value measured with a vibrating sample magnetometer, but since a measurement error of 10% can occur, in the case of a measured value of 71 [A / m], the value taking into account the measurement error is 71±7.1 [A / m].

[0065] Furthermore, multiple samples of this embodiment and Comparative Example 1 that underwent the same steps up to the debonding step were prepared, and the coercivity was examined at different hydrogen heat treatment temperatures. Figure 8 shows the results. Here, the change in coercivity was examined when the hydrogen heat treatment temperature was set to four different temperatures: 130°C, 150°C, 170°C, and 190°C. As shown in Figure 8, the coercivity of the sample of this embodiment was lower than that of the sample of Comparative Example 1 at all hydrogen heat treatment temperatures. In particular, at 170°C and 190°C, the coercivity of the sample of this embodiment was lower than that of the sample of Comparative Example 1. Based on these results, if the coercivity at each temperature is approximated by a straight line, it can be said that performing hydrogen heat treatment at a temperature above 150°C is effective in achieving a low coercivity.

[0066] The structural structures of this embodiment and Comparative Example 1 are as shown in the TEM image of the structural image in Figure 9. As shown in this figure, it can be seen that in the case of press molding, the grain boundary phase between the soft magnetic nanoparticles 2 is large. This indicates that the soft magnetic nanoparticles 2 cannot be densified in the case of press molding. Furthermore, in the case of this embodiment, the grain boundary phase between the soft magnetic nanoparticles 2 is small, and the soft magnetic nanoparticles 2 can be densified.

[0067] When the soft magnetic nanoparticles 2 are not densely packed and there is a large grain boundary phase between each particle, as in Comparative Example 1 shown in Figure 9, the coercivity does not decrease due to the averaging of the magnetic anisotropy.

[0068] In contrast, in the soft magnetic nanoparticle assembly 1 of this embodiment shown in Fig. 9, the soft magnetic nanoparticles 2 are densely packed adjacent to each other in the soft magnetic nanoparticle assembly 1. In this state, it is possible to reduce the substantial magnetic anisotropy of the soft magnetic nanoparticle assembly 1, and it is possible to further reduce the coercive force.

[0069] While the present disclosure has been described based on the above-described embodiment, it is not limited to the embodiment and encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

[0070] For example, in the above embodiment, the amorphous bulk formation process was performed based on the CS method, but any other method may be used as long as it generates an impact force that causes the crystals of the soft magnetic nanoparticles 2 to become amorphous.

[0071] Furthermore, a granulation step was carried out to form granules 30 that are aggregates of composite soft-magnetic nanoparticles 20. This is also merely one example, and if the aggregates of composite soft-magnetic nanoparticles 20 obtained in the non-magnetic material coating step have a size that is easy to handle in subsequent steps, the granulation step does not need to be carried out.

[0072] Furthermore, although the peeling step utilizes the difference in linear expansion coefficient between the substrate 110 and the soft magnetic nanoparticles 2, the soft magnetic nanoparticle assembly 1 may also be mechanically peeled off from the substrate 110 using a tool such as a scraper.

[0073] It goes without saying that in each of the above embodiments, the elements constituting the embodiment are not necessarily essential unless they are particularly clearly stated as essential or are considered to be clearly essential in principle, etc. Furthermore, in each of the above embodiments, when numerical values ​​such as the number, value, amount, range, etc. of the components of the embodiment are mentioned, they are not limited to that specific number unless they are particularly clearly stated as essential or are clearly limited to a specific number in principle, etc.

[0074] (Viewpoints of the Present Disclosure) The above-described present disclosure can be understood from the following viewpoints, for example.

[0075] [First Aspect] A soft magnetic nanoparticle assembly comprising: a plurality of soft magnetic nanoparticles (2) closely contacting each other; and a non-magnetic layer (3) filling a grain boundary phase between the soft magnetic nanoparticles, wherein the soft magnetic nanoparticles have an average particle diameter of 50 nm or less as observed with a transmission electron microscope; the non-magnetic layer has a thickness of 4.9 nm or less; and the coercive force measured with a vibrating sample magnetometer is 71±7.1 [A / m] or less.

[0076] [Second Aspect] The soft magnetic nanoparticle assembly according to the first aspect, wherein the soft magnetic nanoparticles are pure iron nanoparticles composed only of Fe, and the non-magnetic layer is composed of a carbide.

[0077] [Third Aspect] A soft magnetic nanoparticle assembly according to the first or second aspect, which has a saturation magnetic flux density of 180 [emu / g] or more as measured with a vibrating sample magnetometer.

[0078] [Fourth Aspect] A soft magnetic nanoparticle assembly according to any one of the first to third aspects, wherein the soft magnetic nanoparticles have an average particle size of 4 nm or more as observed by a transmission electron microscope.

[0079] [Fifth Aspect] A soft magnetic nanoparticle assembly according to any one of the first to third aspects, wherein the soft magnetic nanoparticles have a particle diameter of 6 to 20 nm as observed by a transmission electron microscope.

[0080] [Sixth Aspect] A method for producing a soft magnetic nanoparticle assembly, comprising: preparing a plurality of soft magnetic nanoparticles (2); forming composite soft magnetic nanoparticles (20) by coating the surface of each of the plurality of soft magnetic nanoparticles with a non-magnetic material (10); amorphizing the soft magnetic nanoparticles contained in the composite soft magnetic nanoparticles to form an amorphous bulk body (40); and thermally decomposing the non-magnetic material contained in the amorphous bulk body by heat treatment to remove a portion of the non-magnetic material, thereby producing a soft magnetic nanoparticle assembly (1) in which adjacent soft magnetic nanoparticles are adhered to each other and a non-magnetic layer (3) composed of the thermally decomposed non-magnetic material is disposed in the grain boundary phase between the soft magnetic nanoparticles.

[0081] [Seventh Aspect] The method for producing a soft magnetic nanoparticle assembly according to the sixth aspect, which includes forming the composite soft magnetic nanoparticles and then forming a granule (30) that is an aggregate of the composite soft magnetic nanoparticles, wherein forming the amorphous bulk body plastically deforms the granules to make the soft magnetic nanoparticles amorphous.

[0082] [Eighth Aspect] The method for producing a soft magnetic nanoparticle aggregate according to the seventh aspect, wherein the amorphous bulk body is formed by using a cold spray device to eject the granules onto the surface of a substrate (110) and causing the granules to collide with the substrate, thereby plastically deforming the granules.

[0083] [Ninth Aspect] A method for producing a soft magnetic nanoparticle aggregate described in any one of the sixth to eighth aspects, wherein the temperature of the thermal treatment for thermal decomposition of the non-magnetic material is 200°C or less when producing the soft magnetic nanoparticle aggregate.

Claims

1. A soft magnetic nanoparticle assembly comprising: a plurality of soft magnetic nanoparticles (2) closely attached to each other; and a non-magnetic layer (3) filled in the grain boundary phase between the soft magnetic nanoparticles; wherein the average particle diameter of the soft magnetic nanoparticles observed with a transmission electron microscope is 50 nm or less; the thickness of the non-magnetic layer is 4.9 nm or less; and the coercive force measured with a vibrating sample magnetometer is 71±7.1 [A / m] or less.

2. The soft magnetic nanoparticle assembly according to claim 1, wherein the soft magnetic nanoparticles are pure iron nanoparticles composed only of Fe, and the non-magnetic layer is composed of a carbide.

3. A soft magnetic nanoparticle assembly according to claim 1 or 2, having a saturation magnetic flux density of 180 [emu / g] or more as measured by a vibrating sample magnetometer.

4. A soft magnetic nanoparticle assembly according to claim 1 or 2, wherein the soft magnetic nanoparticles have an average particle diameter of 4 nm or more as observed by a transmission electron microscope.

5. A soft magnetic nanoparticle assembly according to claim 1 or 2, wherein the particle diameter of the soft magnetic nanoparticles observed by a transmission electron microscope is 6 to 20 nm.

6. A method for producing a soft magnetic nanoparticle assembly, comprising: preparing a plurality of soft magnetic nanoparticles (2); forming composite soft magnetic nanoparticles (20) in which the surface of each of the plurality of soft magnetic nanoparticles is coated with a nonmagnetic material (10); amorphizing the soft magnetic nanoparticles contained in the composite soft magnetic nanoparticles to form an amorphous bulk body (40); and producing a soft magnetic nanoparticle assembly (1) in which adjacent soft magnetic nanoparticles are adhered to each other and a nonmagnetic layer (3) composed of the pyrolyzed nonmagnetic material is disposed in the grain boundary phase between the soft magnetic nanoparticles by thermally decomposing the nonmagnetic material contained in the amorphous bulk body through heat treatment to remove a portion of the nonmagnetic material.

7. A method for producing a soft magnetic nanoparticle aggregate as described in claim 6, which includes forming a granule (30) that is an aggregate of the composite soft magnetic nanoparticles after forming the composite soft magnetic nanoparticles, and in forming the amorphous bulk body, the granule is plastically deformed to make the soft magnetic nanoparticles amorphous.

8. A method for producing a soft magnetic nanoparticle aggregate as described in claim 7, in which the amorphous bulk body is formed by using a cold spray device to spray the granules onto the surface of a substrate (110) and causing the granules to collide with the substrate, thereby causing plastic deformation.

9. A method for producing a soft magnetic nanoparticle aggregate described in any one of claims 6 to 8, wherein, in producing the soft magnetic nanoparticle aggregate, the heat treatment temperature for thermal decomposition of the non-magnetic material is carried out at 200°C or less.