JP2002093607A - Manetic multilayer fine particle, its manufacturing method, and magnetic multilayer fine particle dispersion medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain magnetic fine particles of multilayer structure and a method of manufacturing the same, and to improve a magnetic multilayer fine particle dispersion medium formed by the use of the magnetic fine particles in high-frequency magnetic field absorption properties and magneto-optical properties. SOLUTION: A multilayer magnetic fine particle is composed of a fine particle serving as a center nucleus and a single-layered or multilayered coating layer covering the center nucleus. A ferromagnetic layer, formed by plating ferrite, is made to serve as the coating layer for the formation of magnetic multilayer fine particles, the magnetic multilayer fine particles are dispersed in a binder, the binder, where the magnetic multilayere fine particles are dispersed, is molded into a magnetic multilayer fine particle medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic multilayer fine particle, a method for producing the same, and a magnetic multilayer fine particle dispersion medium in which the magnetic multilayer fine particle is dispersed. The present invention relates to a magnetic fine particle having improved properties, a method for producing the same, and a magnetic fine particle dispersion medium.

[0002]

2. Description of the Related Art Magnetic fine particles such as ferromagnetic metal fine particles and ferrite fine particles are dispersed in a binder to form a composite.
In the form of a magnetic fine particle dispersion medium, it is widely used as a radio wave absorber, used as a magnetic recording medium such as a magnetic tape and a floppy disk, and further applied to a magneto-optical effect element. Are also being considered.

[0003] In such a dispersion medium, in addition to the magnetic fine particles used as they are dispersed in a resin or the like, the magnetic fine particles can be easily dispersed by applying a surface treating agent to the surface of the magnetic fine particles. Alternatively, there is a method in which when the magnetic fine particles are ferromagnetic metals, insulation between particles is obtained by providing a thin layer such as an oxide film on the surface thereof.

[0004] The surface layer of these magnetic fine particles merely plays a role of improving the dispersibility of the particles and a role of weakening the magnetic or electrical coupling between the magnetic particles. Therefore, any of these magnetic fine particles may be regarded as substantially a single-layer magnetic fine particle.

Accordingly, the present inventors have focused on new possibilities for electromagnetic field response, such as improving the high-frequency microwave complex permeability characteristics and magneto-optical effect by imparting a multilayer structure to magnetic particles. Researched.

[0006] As the magnetic particles having a layered structure, particles having a ferrite plating layer provided on the surface of a polyacryl sphere have already been developed by the present inventors. However, these are particles mainly used for medical use, and do not improve high-frequency microwave complex permeability characteristics or magneto-optical effects.

[0007] Further, as fine particles having a multilayer structure, multilayer particles formed by using reverse micelles, so-called nano-onion fine particles, have recently been recently announced and attracted attention. In these particles, the particle size is limited to the possible range of reverse micelles. Therefore, the average particle size is 20 to 30
The upper limit is about nm. Since nano-onion fine particles produced by using reverse micelles are limited to very small ones, the fine particles have a giant magnetoresistive effect (a micro-size is essentially an important phenomenon). GMR) is only being researched.

[0008]

SUMMARY OF THE INVENTION The present invention is based on the above-mentioned conventional technology. By changing the magnetic fine particles from a conventional single-layer structure to a multi-layer structure and forming a multi-layer structure, the magneto-optical effect and the high-frequency or microwave We found the necessity of improving the complex permeability characteristics and proceeded with research. In conducting the research, the present inventors analyzed the response of the dispersed magnetic particles to the electromagnetic field from multiple angles, and used a plating method such as ferrite plating as a means to actually form magnetic particles having a multilayer structure. Was used as the means. The ferrite plating method is a method of forming a ferrite layer on a substrate in an aqueous solution, and has been developed by one of the present inventors. Its applicability has been greatly expanded.

One of the applications of the ferrite plating technique is that it can be applied to the magnetic particles having a multilayer structure of the present invention, that is, the magnetic multilayer fine particles, thereby enabling a new development of ferrite plating. It is.

[0010]

SUMMARY OF THE INVENTION The present invention is directed to a magnetic multilayer fine particle, a method for producing the same, and a dispersion medium in which the magnetic multilayer fine particle is dispersed. Improving the electromagnetic field characteristics of the magnetic fine particle dispersion medium, for example, improving the magneto-optical effect,
Alternatively, it is possible to increase the complex magnetic permeability and the complex permittivity at a high frequency or a microwave.

The first magnetic multilayer fine particle of the present invention has a center core having ferromagnetism and one or more coating layers covering the center core, and the coating layer is formed by plating. It has a ferromagnetic layer. The thickness of the coating layer is not particularly limited. In order to sufficiently obtain the effect of the multilayer structure, for example, it is preferable to have an average thickness of about 1/10 or more of the average diameter of the central core.

In the magnetic multilayer fine particles of the present invention, ferromagnetic metal fine particles such as metallic iron can be used as the core having ferromagnetism. By using a ferromagnetic metal particle having a large saturation magnetization as a central nucleus of the magnetic multilayer fine particle and providing a coating of a ferrite layer which is a high-resistance magnetic substance, the magnetic multilayer fine particle has a high saturation magnetization,
A high specific resistance can be provided between particles. In the magnetic multilayer fine particles of the present invention, the ferromagnetic core may be ferrite fine particles such as spinel type,
Garnet-type ferrite fine particles and hexagonal ferrite fine particles may also be used.

As the central nucleus of the magnetic multilayer fine particles of the present invention,
Using garnet type ferrite with excellent magneto-optical properties,
By coating this with, for example, spinel ferrite, it is possible to obtain magnetic multilayer fine particles whose magneto-optical properties are appropriately controlled. If hexagonal ferrite fine particles are used as the central nucleus, by utilizing their strong anisotropy,
Magnetic multilayer fine particles with easy particle orientation can be obtained, and the unique complex magnetic permeability characteristics of the hexagonal ferrite fine particles due to a strong anisotropic magnetic field can be controlled and used by the multilayer structure. Further, even when spinel ferrite is used for the central core and the core is coated with spinel ferrite, the magneto-optical characteristics or the complex magnetic permeability characteristics can be appropriately controlled by selecting the respective compositions.

The second magnetic multilayer fine particle of the present invention has a central core having ferroelectricity and one or more coating layers covering the central core, and the coating layer is formed by plating. It has a ferromagnetic layer.

In the present invention, the central core having ferroelectricity includes, in addition to the central core having a ferroelectric substance, the central core having a dielectric constant as high as that of the ferroelectric substance. The magnitude of the dielectric constant is preferably 100 or more, more preferably 500 or more, in order to obtain the effect of a high dielectric constant.

By having such a central nucleus, magnetic multilayer fine particles having a high complex magnetic permeability and a high complex dielectric constant can be obtained. Conventionally, it has been desired that radio wave absorbers have a high complex permittivity as well as a high complex magnetic permeability.However, since a practical material having ferromagnetism and ferroelectricity cannot be obtained at the same time, Could not respond to. The magnetic multilayer fine particles of this configuration according to the present invention can meet such demands.

In the magnetic multilayer fine particles of the present invention, at least one of the coating layers is preferably a ferrite layer, and the ferrite layer is preferably a layer formed by ferrite plating.

In ferrite plating, temperature and pH in aqueous solution
Each of them has a feature that a high-quality film can be formed under relatively mild conditions. For this reason, it is possible to provide a coating layer having a good quality and excellent magnetic properties with a well-adjusted film thickness without deteriorating the central nucleus when forming the coating layer.

In the magnetic multilayer fine particles of the present invention,
At least one of the coating layers can be a metal layer.
In this case, the metal layer can be formed by electroless plating. By using electroless plating, treatment in an aqueous solution is possible, as with ferrite plating.

In the magnetic multilayer fine particles of the present invention,
Particles having an isotropic particle shape, such as a central core having a spherical shape or a cubic symmetry, can be used. If the central nucleus is a fine particle having an isotropic shape, it is easy to make the shape of the magnetic multilayer fine particle medium isotropic. By using the magnetic multilayer fine particles having an isotropic shape, it is easy to manufacture a magnetic particle dispersion medium having no directivity.

In the magnetic multilayer fine particles of the present invention,
The shape of the central nucleus may be a flat particle shape such as a plate shape. Further, in the magnetic multilayer fine particles of the present invention, those having a shape in which a central core has a shape extending in one direction such as a needle shape, a rod shape, a spinning shape, or the like can be used. When the central nucleus has the fine particles having such a shape, the obtained magnetic multilayer fine particles can have the same particle shape.

By using the magnetic multilayer fine particles having a flat particle shape or the magnetic multilayer fine particles having a long particle shape in one direction, it is easy to orient these particles and produce a magnetic particle dispersion medium having directionality. become. Giving the dispersion medium directionality in this way, that is, imparting anisotropy, is useful when used as a radio wave absorber,
It is also useful when used as a magneto-optical material.

The magnetic multilayer fine particle dispersion medium of the present invention is characterized in that the above magnetic multilayer fine particles are dispersed in a binder + binder. The magnetic multilayer fine particles of the present invention are dispersed in a binder to form a magnetic multilayer fine particle dispersion medium, so that the characteristics of the magnetic multilayer fine particles with respect to high frequency, microwave electromagnetic field, and light can be utilized, and a wide range of applications can be obtained. Can be

The magnetic multilayer fine particle dispersion medium of the present invention can be used as a radio wave absorber. In particular, when used as a radio wave absorber in the quasi-microwave and microwave regions, a large amount of attenuation can be obtained as compared with a conventional radio wave absorber. When used as a radio wave absorber, it is preferable that the magnetic multilayer fine particle dispersion medium is formed in a plate shape, for example, and a metal end plate is provided on one surface thereof. In order to obtain sufficient radio wave absorption when used as a radio wave absorber,
The average particle size of the magnetic multilayer fine particles is preferably 0.1 μm
To 1 mm, more preferably 1 μm to 100 μm.

Further, the magnetic multilayer fine particle dispersion medium of the present invention comprises:
It can be used as a magneto-optical effect material. In the medium in which the magnetic fine particles are dispersed, the value of the off-diagonal term of the refractive index tensor can be increased due to the dispersion effect of the magnetic fine particles, and the Faraday rotation angle and the like can be increased. It is possible to further increase the value by the conversion. In this case, the average particle size of the magnetic multilayer fine particles is preferably 0.05 μm to 1 μm, which is a large average particle size range having a large interaction with light, and 0.1 μm to 0.3 μm.
Is more preferred.

According to the method for producing magnetic multilayer fine particles of the present invention, the magnetic layer is coated on the surface of the fine particles functional with respect to an electromagnetic field by at least one of ferrite plating and electroless plating. It is for producing fine particles. In the present invention, the fine particles functional with respect to an electromagnetic field in the present invention are fine particles having ferromagnetism, fine particles having ferroelectricity, or fine particles having a dielectric constant as high as a ferroelectric substance.

In the ferrite plating method, fine particles are dispersed, a reaction solution having ferrous iron ions is added thereto, and the reaction proceeds by oxidizing the ferrous iron ions and adjusting the pH to form a ferrite plating layer on the surfaces of the fine particles. Form.

According to this method, a well-fixed ferrite layer is formed at a temperature near room temperature as described above, and good crystallinity and good magnetic properties can be obtained. Here, if the ferrite plating layer is formed while applying ultrasonic waves to the reaction solution, ferrite plating can be performed more uniformly, and crystallinity can be further improved.

According to the method for producing magnetic multilayer fine particles of the present invention, the surfaces of the particles are plated in a state in which the fine particles are dispersed in a plating solution, so that the periphery of the particles can be coated.
In addition, the shape and size of the central nucleus and the thickness of the coating layer can be arbitrarily selected, and magnetic multilayer fine particles well suited to the purpose can be manufactured.

[0030]

FIG. 1 shows a magnetic multilayer fine particle 11 according to the present invention.
It is sectional drawing which showed typically several examples of Embodiment of this invention. Figure 1
In (a), the periphery of the central nucleus 12 is covered with a covering layer 13a, (b) is the periphery of the central nucleus covered with the covering layers 13a and 13b, and (c) is the periphery of the central nucleus. Is coated in three layers of coating layers 13a, 13b and 13c. (d) is a diagram in which the periphery of the central nucleus is covered four times with coating layers 13a, 13b, 13c and 13d. FIG. 1 shows an example in which the central core is coated with up to four layers, but the coating layer may be further multilayered as necessary.

The particle shape of the central core 12 may be isotropic, such as a spherical shape or a shape close to a sphere as shown in FIG. 1, a shape close to a regular polyhedron such as a cube, or the like. Anisotropic central nucleus, such as a flat shape such as the flat plate shape shown in the schematic cross-sectional view of Fig. 2 (a), the rod shape shown in the schematic cross-sectional view of Fig. 2 (b), and the shape of particles long in one direction close to them Magnetic multilayer fine particles 21 provided with a coating layer 23 on 22 may be used.

The central nucleus can have a spherical or nearly spherical shape or a shape close to a regular polyhedron such as a cube, and magnetic multilayer fine particles using these can have the same shape as the central nucleus. When such magnetic multilayer fine particles are dispersed in a binder resin and molded, it is easy to provide an isotropic dispersion medium as shown in the schematic cross-sectional view of FIG. In FIG. 3 (a),
The magnetic multilayer fine particles 31 are dispersed in a binder resin and molded to form a plate-like magnetic multilayer fine particle dispersion medium.

The binder used here is not particularly limited, and can be selected from known materials according to the application. For example, a resin such as a silicone resin containing siloxane as a main component can be selected and used.

Further, by forming the central core into a flat shape such as a flat plate shape or a unidirectionally long particle shape such as a rod shape, the magnetic multilayer fine particles can be formed into a flat shape or a unidirectionally long particle shape. As described above, the magnetic multilayer fine particles may be formed into a plate shape or a rod shape so as to give an appropriate directionality to the demagnetizing field in the magnetic material particles. When the magnetic multilayer fine particles have a dielectric such as a ferroelectric substance in the center nucleus, for example, the shape of the center nucleus is made to be flat or long in one direction, so that a suitable directional property can be applied to the demagnetizing field inside the dielectric. May be given.

In each of the above figures, the case where each layer covering the central core is covered with a uniform thickness is shown. However, the covering layer is not necessarily required to be uniform, and the effect of the multilayer structure of the present invention is not required. The layer may be a layer having a nonuniform coating shape or a layer having a partial coating layer, as long as it is possible to obtain.

By dispersing and orienting these particles in a binder, anisotropic dispersion of flat and rod-like particles shown in the schematic cross-sectional views of FIGS. 3 (b) and 3 (c), respectively. A dispersion medium having a property can be obtained.
Here, a mechanical method or a magnetic method can be used for the orientation of the particles.

As shown in the schematic cross-sectional view of FIG. 4, the magnetic multilayer fine particles of the present invention use ferromagnetic metal fine particles such as metallic iron or metallic cobalt for the central core 42, and surround the central core 42 with, for example, ferrite plating. And may be covered with the ferrite layer 43.

With such a configuration, the magnetic particles 41 having high resistance and a larger saturation magnetization than ferrite are formed.
In the frequency spectrum characteristic of the complex magnetic permeability shown in 5, the limit in the case of ferrite (Snoek limit) can be exceeded.

As shown in the schematic cross-sectional view of FIG. 6A, the core of the magnetic multilayer fine particles of the present invention is made of a material having a high dielectric constant, for example, ferroelectric particles 62 such as barium titanate.
By coating the periphery with ferrite plating 63a, magnetic multilayer fine particles 61 having high magnetic permeability and high dielectric constant are obtained. Further, as shown in a schematic cross-sectional view of FIG. 6B, a material 62 having such a high dielectric constant was used for the central core, and a layer 63b of metallic cobalt metal nickel was provided around the periphery by electroless plating. After that, it may be covered with ferrite plating 63a.

As shown in the schematic sectional view of FIG. 7, when ferrite fine particles are used for the core 72 of the magnetic multilayer fine particles of the present invention, garnet type ferrite or hexagonal ferrite besides spinel type ferrite is used. Can be. The coating layer covering the core of ferrite is provided with a coating layer formed by ferrite plating or a coating layer 73 formed by electroless plating. In addition, a multilayered layer obtained by laminating these coating layers can also be used. By such a composite, the magnetic multilayer fine particles 71 having composite characteristics that cannot be obtained by a single ferrite particle are obtained.

In the production of the magnetic multilayer fine particles of the present invention, first, the fine particles forming the central nucleus are immersed in a reaction solution (ferrite plating solution or electroless plating solution) for coating the particle surface, and the fine particles are dispersed as uniformly as possible. . Next, the reaction liquid is reacted to coat the surface of the dispersed fine particles. Magnetic fine particles having a multilayer coating layer can be obtained by changing the reaction solution and further coating the coated particles.

As a specific example, a process in which fine particles are coated by ferrite plating will be described with reference to a ferrite plating apparatus shown in FIG. Fine particles that form the central nucleus
82, for example, barium titanate fine particles are dispersed in water, and in a glass vessel 86 immersed in a hot bath 80, a divalent iron ion salt such as FeCl ₂ , a divalent metal ion salt such as MCl ₂ and, if necessary, Then, ferrite plating is performed using a ferrite plating reaction solution 87 containing trivalent iron ions such as FeCl ₃ .
Ferrite plating is performed by ultrasonic (1
9.5 kHz, 600 w) while adding an oxidizing agent such as NaNO ₂ nitrite gradually to oxidize,
The controller 89 adjusts the pH with NH ₄ OH or the like.

Here, divalent Fe ions and M ions are adsorbed to OH groups, which are adsorption sites on the surface of the barium titanate fine particles, and hydrogen ions are released. Next, when a reaction in which a part of divalent Fe becomes trivalent by oxidation is performed, divalent Fe ions and M ions are again adsorbed on this surface. Then, oxidation
A reaction in which a part of Fe becomes trivalent is performed, and by such repetition, a plating layer of spinel ferrite is formed on the particle surface. The same applies to the case where the central core is made of another material, for example, metallic iron, which is an adsorption site present on the oxidized surface.
A divalent Fe ion or M ion is adsorbed on the OH group, and a ferrite plating layer can be formed in the same manner.

Here, when the ferrite generation reaction proceeds while irradiating the liquid with ultrasonic waves, it is easy to form a ferrite layer on the entire surface of the fine particles, and it is possible to form a ferrite plating layer having good crystallinity. it can. Here, the thickness of the coating layer can be easily controlled by adjusting the progress rate and the time of the reaction by oxidation.

Next, an embodiment of the present invention will be described.

(Example 1) (The central core is metallic iron, which is coated with ferrite plating, and a radio wave absorber is prepared using the same.) An average particle diameter of 0.2 μm and an oxide layer on the surface Using metal iron particles as the central core, the average thickness is applied to the surface using ferrite plating.
A ferrite layer of 0.1 μm was formed to obtain magnetic fine particles having a composite structure of metallic iron and NiZnFe ferrite.

Here, the ferrite plating was performed under the following conditions using a glass vessel (capacity: 500 ml) shown in FIG. 9 and applying ultrasonic waves. Reaction solution: FeCl ₂ (12 g / l) + NiCl ₂ (4 g / l) + ZnCl ₂ (0.5 g
/ l), pH = 6.0 Temperature: 80 ℃ Ultrasonic: Frequency 19.5kHz, Power 600w Plating time: 6 minutes

Next, the magnetic fine particles were subjected to a surface treatment with a silane coupling agent, dispersed in a silicone resin, molded and cured to prepare a magnetic multilayer fine particle dispersion medium. The ratio between the fine particles and the nonvolatile resin was 5: 1 by weight, and the volume filling ratio of the fine particles was 57%.

The frequency characteristics of the complex magnetic permeability of the magnetic multilayer fine particle dispersion medium were measured. As a result, frequency characteristics of complex magnetic permeability exceeding the limit of Snoek were obtained.

(Example 2) (Barium titanate particles are used as a central nucleus, which are coated with ferrite plating, and a radio wave absorber is prepared using the particles.) Barium titanate having an average particle size of 0.5 μm Using the particles as the central nucleus and using ferrite plating on the surface
A NiZnFe ferrite layer was formed with an average thickness of 0.2 μm to obtain magnetic fine particles having a composite structure of barium titanate and ferrite.

Here, the ferrite plating was performed under the following conditions. Reaction solution: FeCl ₂ (12 g / l) + NiCl ₂ (4 g / l) + ZnCl ₂ (0.5 g
/ l), pH = 6.0 Temperature: 80 ℃ Ultrasonic: Frequency 19.5kHz, Power 600w Plating time: 12 minutes

Next, the prepared magnetic fine particles were surface-treated with a silane coupling agent, dispersed in a silicone resin, molded and cured to prepare a magnetic multilayer fine particle dispersion medium. The ratio of the fine particles to the nonvolatile resin was 6: 1 by weight, and the volume filling ratio of the fine particles was 60%.

The frequency characteristics of the complex magnetic permeability of this magnetic multilayer fine particle dispersion medium were measured. As a result, frequency characteristics of complex magnetic permeability exceeding the limit of Snoek were obtained.

(Example 3) (Ferrite plating is applied to bismuth yttrium iron garnet particles, and a dispersion for magneto-optics is produced using the same.) Bismuth yttrium iron garnet particles having an average particle size of 0.2 μm are used as a central nucleus. Then, a CoFe ferrite layer was formed on the surface by using a ferrite plating method to obtain magnetic fine particles having a composite structure of bismuth yttrium garnet and CoFe ferrite.

Here, ferrite plating was performed under the following conditions. Reaction solution: FeCl ₂ (12 g / l) + CoCl ₂ (6 g / l), pH = 6.2 Temperature: 80 ° C Ultrasonic: frequency 19.5 kHz, power 600 w Plating time: 12 minutes

Next, the magnetic fine particles were subjected to a surface treatment with a silane coupling agent, and then dispersed in an acrylic resin at a content of about 10% to obtain a light-transmitting magnetic multilayer fine particle dispersion.

As a result of measuring the magneto-optical properties of the obtained magnetic multilayer fine particle dispersion, an increase in the Faraday effect was observed. This is presumably because the localization effect of light was emphasized by the multilayering of the magnetic particles.

(Example 4) (Ferrite plating is performed on the central core of metallic iron, then electroless plating of Co is performed, and ferrite plating is performed, and a radio wave absorber using the same is produced.) Reaction solution: FeCl ₂ (12 g / l) + NiCl ₂ (4 g / l) + ZnCl ₂ (0.5 g) on the surface of 1 μm metal iron fine particles by ferrite plating.
/ l), pH = 6.0 Temperature: 80 ° C Ultrasound: Frequency 19.5 kHz, Power 600w Plating time: 24 minutes A NiZnFe ferrite layer of about 0.4 μm was formed and covered. Subsequently, a Ni base was first formed on the surface of the obtained fine particle powder by electroless plating, and a buffer solution containing a cobalt sulfate solution and having a pH value of 9 was set thereon.
At 0 ° C., a Co film of about 0.1 μm was formed.

After that, the surface of the fine particle powder was again applied to the surface by the ferrite plating method under the same conditions as above for about 0.4 mm.
Coating was performed with a μm NiZnFe ferrite layer to obtain magnetic multilayer fine particles composed of a metal iron core, a ferrite layer, and a metal layer and a ferrite layer.

Next, the magnetic fine particles were subjected to a surface treatment with a silane coupling agent, then dispersed in a silicone resin, molded and cured to prepare a magnetic multilayer fine particle dispersion medium. The ratio between the fine particles and the nonvolatile resin was 5: 1 by weight, and the volume filling ratio of the fine particles was 57%.

The frequency characteristics of the complex magnetic permeability of the magnetic multilayer fine particle dispersion medium were measured. As a result, frequency characteristics of complex magnetic permeability exceeding the limit of Snoek were obtained.

(Example 5) (Barium titanate / ferrite / Co layer / ferrite layer) (Production of radio wave absorber using this) Ferrite plating method on the surface of titanium oxide having a rutile structure with an average particle size of about 1 μm Reaction solution: FeCl ₂ (12 g / l) + NiCl ₂ (4 g / l) + ZnCl ₂ (0.5 g
/ l), pH = 6.0 Temperature: 80 ° C. Ultrasonic: frequency 19.5 kHz, power 600 w Plating time: 48 minutes, and formed and covered a NiZnFe ferrite layer of about 0.8 μm in thickness. Subsequently, a Ni base was first formed on the surface of the obtained fine particle powder by electroless plating, and a buffer solution containing a cobalt sulfate solution and having a pH value of 9 was set thereon.
At 0 ° C., a Co film of about 0.1 μm was formed.

Thereafter, the surface of the fine particle powder is coated with a NiZnFe ferrite layer of about 0.8 μm by another ferrite plating method, and magnetic multilayer fine particles comprising a dielectric core, a ferrite layer, a metal layer and a ferrite layer are formed. Obtained.

Next, the magnetic fine particles were subjected to a surface treatment with a silane coupling agent, then dispersed in a silicone resin, molded and cured to prepare a magnetic multilayer fine particle dispersion medium. The ratio between the fine particles and the nonvolatile resin was 6.5: 1 by weight, and the volume filling ratio of the fine particles was 62%.

The frequency characteristics of the complex magnetic permeability of the magnetic multilayer fine particle dispersion medium were measured. As a result, frequency characteristics of complex magnetic permeability exceeding the limit of Snoek were obtained.

[0066]

According to the magnetic multilayer fine particles of the present invention and the method for producing the same, the material and shape and size of the central core and the thickness of the coating layer can be arbitrarily selected. You can choose variously.

For this reason, in the dispersion medium in which the magnetic multilayer fine particles of the present invention are dispersed, it is possible to enhance the magneto-optical characteristics such as the Faraday rotation angle and its figure of merit by selecting the center nucleus and the coating layer. Therefore, an excellent magneto-optical material can be obtained, and an elongation exceeding a snake limit line can be obtained in the frequency characteristic of the complex magnetic permeability, so that, for example, an excellent characteristic as a radio wave absorber can be obtained.

Further, according to the method for producing magnetic multilayer fine particles of the present invention, the production of magnetic tank fine particles can be carried out in an aqueous solution without using a vacuum, and at a temperature close to normal temperature and normal pressure. Therefore, the production can be performed with high productivity without requiring a large-scale production apparatus.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing an embodiment of a magnetic multilayer fine particle of the present invention.

FIG. 2 is a cross-sectional view schematically showing magnetic multilayer fine particles having an anisotropic particle shape such as a flat shape and a rod shape according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view schematically showing an embodiment of a dispersion medium in which the magnetic multilayer fine particles of the present invention are dispersed in a binder resin and molded.

FIG. 4 is a schematic cross-sectional view showing magnetic multilayer fine particles of one embodiment of the present invention in which ferromagnetic metal fine particles are used as a central nucleus and the periphery thereof is covered with a ferrite layer.

FIG. 5 is a diagram showing a frequency spectrum of a complex magnetic permeability.

FIG. 6: Ferroelectric particles having a high dielectric constant are used for the central core,
FIG. 4 is a schematic cross-sectional view showing magnetic multilayer fine particles according to an embodiment of the present invention constituted by coating the periphery with ferrite plating 63.

FIG. 7 is a schematic cross-sectional view showing magnetic multilayer fine particles of the embodiment of the present invention using ferrite fine particles as a central nucleus.

FIG. 8 is a diagram schematically illustrating an example of a ferrite plating tank for forming a ferrite plating layer according to the embodiment of the magnetic multilayer fine particles of the present invention.

[Explanation of symbols]

 11,21,31,41,61,71: Magnetic multilayer fine particles, 12,22,32,42,62,72 ... Central core, 13a, 13b, 13c, 13d, 23,43,63a, 63b, 73 ... Coating layer, 34 ... Binder resin, 35 ... Magnetic multilayer fine particle dispersion medium, 80 ... Hot bath, 86 ... Glass vessel, 87 ... Reaction liquid, 88 ... Ultrasonic horn, 89 ... pH controller

Claims (9)

[Claims] 1. A magnetic multilayer having a ferromagnetic center core and one or more coating layers covering the center core, wherein the coating layer has a ferromagnetic layer formed by plating. Fine particles. 2. The magnetic multilayer fine particles according to claim 1, wherein the central nucleus is a ferromagnetic metal fine particle. 3. The magnetic multilayer fine particle according to claim 1, wherein the central nucleus is a ferrite fine particle. 4. A magnetic multilayer comprising: a core having ferroelectricity; and one or more coating layers covering the core, wherein the coating layer has a ferromagnetic layer formed by plating. Fine particles. 5. The magnetic multilayer fine particles according to claim 1, wherein at least one of the coating layers is a ferrite plating layer. 6. A magnetic multilayer fine particle dispersion medium in which the magnetic multilayer fine particles according to claim 1 are dispersed in a binder and molded. 7. A radio wave absorber in which the magnetic multilayer fine particles according to claim 1 are dispersed in a binder and molded. 8. A magneto-optical effect material comprising the magnetic multilayer fine particles according to claim 1 dispersed and molded in a binder. 9. Production of magnetic multi-layer fine particles for producing magnetic multi-layer fine particles by coating a magnetic layer on the surface of fine particles functional with respect to an electromagnetic field by at least one of ferrite plating and electroless plating. Method.