KR20160014412A - Composite magnetic particle for wireless power charge and method of preparing the same - Google Patents

Abstract

The present invention relates to composite magnetic particles to charge wirelessly and a producing method thereof and, more specifically, relates to production of composite magnetic particles capable of implementing a high-efficiency wireless charging technique through improved magnetic permeability and a saturation magnetization value by comprising a metal core and a Ni-Zn based ferrite shell enclosing the core.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite magnetic particle for wireless charging,

Field of the Invention [0002] The present invention relates to a composite magnetic particle for wireless charging and a manufacturing method thereof.

A technology for converting electrical energy into an electromagnetic wave capable of being transmitted wirelessly is referred to as wireless charging or wireless power transmission (WPC). According to the implementation method, the electromagnetic induction method and the magnetic resonance method are categorized. Among them, the electromagnetic induction method is commercialized and standardization has already been made.

In the electromagnetic induction system, a magnetic field is induced by flowing a current to a power transmission coil, and a magnetic field which changes with time induces a current to a power receiving coil, thereby operating the principle of supplying electric charge to the battery connected thereto. The power transmission efficiency is as high as 90% or more and there is no harm to the human body, and it is possible to apply to a wide range of applications such as a device requiring a small electric power such as a smart phone and a device requiring a large electric power such as an electric car.

Electromagnetic waves radiated in free space are propagated in air and when they meet with other medium, part of the incident surface is reflected, disappears in the medium, and permeates out of the medium depending on the properties of the medium such as permeability, permittivity, electrical conductivity and electrical resistance . The electromagnetic wave energy entering from the incidence plane is converted into heat energy according to the loss characteristic of the medium and is absorbed or propagated along the medium shape or transmitted to the other side of the medium.

The magnetic material used for wireless charging should react easily to the magnetization direction of the material according to the phase change of the external alternating magnetic field, and it is necessary to attract magnetic field distributed in the space to the inside of the material, Thereby forming a circuit. In this case, the magnetic permeability of the magnetic material is an index indicating the degree of raising the magnetic flux, and a magnetic material having a high magnetic permeability is required in order to minimize the leakage magnetic field.

Soft magnetic ferrite is mainly used as a magnetic material used for wireless charging using a magnetic field. Generally, ferrites having soft magnetic properties can be divided into two types of Mn-Zn ferrite and Ni-Zn ferrite. Both have a cubic-shaped spinel lattice structure. As the spinel ferrite, Mn-Zn type, Ni-Zn type, Ni-Mn type, and so on, are in accordance with Snoek's limit rule. The limit rule of Snoek means that the product of the magnetic permeability and the frequency of the magnetic material has a certain limit value, so the resonance frequency becomes lower when the permeability increases. The commercially available Mn-Zn ferrite has a permeability of about 1,400 to 10,000 and is used in a frequency band of about 1 kHz to 1 MHz, and the Ni-Zn ferrite has a permeability of about 30 to 2,000 and is used in a frequency band of about 1 MHz to 300 MHz.

In the material for wireless charging, a material which strongly generates an AC magnetic field in a specific current range is selected as a transmission part, and a magnetic field which is transmitted through a battery case made of a metal material is blocked, Is selected. In general, a Mn-Zn magnetic material having a thickness of 1 mm and a permeability of about 2400 is used for the transmission part, and a metal material having a thickness of 0.2 to 0.4 mm, a permeability of 40 to 200, and a saturation magnetization of about 6,000 G is used.

In the case of magnetic materials for wireless charging, if the magnetic loss can not be kept low, the AC magnetic field will be lost as thermal energy due to electromagnetic interference and eddy current in the magnetic material, and heat will be generated. It can be compared by measuring the core loss, and the core loss is expressed as the sum of hysteresis loss, eddy current loss, and residual loss.

Korean Patent Laid-Open Publication No. 2009-0057752 discloses a method for improving the insulation characteristic by introducing an oxide layer into the soft magnetic powder as a method for preventing the generation of eddy current in the soft ferrite.

In addition, the magnetic material generally uses an organic solvent in the post-treatment process during the manufacturing process. In this case, it is required that the magnetic material has excellent oxidation stability in order to perform the process stably without reacting with the organic solvent. Oxidation stability of magnetic materials is important not only in terms of stability at the time of production but also in improving the storage stability of the produced magnetic material and reducing the risk of subsequent fire.

Korean Patent Publication No. 10-2009-0057752

The present invention aims to provide composite magnetic particles having an improved permeability and a saturation magnetization.

An object of the present invention is to provide composite magnetic particles excellent in oxidation stability.

It is another object of the present invention to provide a method for producing the composite magnetic particles.

1. A composite magnetic particle of a core-shell structure, comprising a metal core and a Ni-Zn ferrite shell surrounding the core.

2. The composite magnetic particle of core-shell structure according to item 1, wherein the core is at least one selected from among alloy particles including alpha-iron particles and alpha-iron.

3. The composite magnetic particle of the core-shell structure according to item 1, wherein the core has an average major axis length of 50 to 500 nm.

4. The core-shell structure composite magnetic particles according to item 1, wherein the core has an insulating layer formed on its surface.

5. The composite magnetic particle of the core-shell structure according to item 4, wherein the insulating layer is an oxide layer of a metal constituting the core.

6. The composite magnetic particle of the core-shell structure according to item 4, wherein the insulating layer is formed to a thickness of 2 to 20 nm.

7. The core-shell structure composite magnetic particles according to item 1, wherein the shell is a Ni-Zn ferrite having a Ni / Zn molar ratio of 0.3 to 0.9.

8. The core-shell structure composite magnetic particles according to item 1, wherein the shell is a Ni-Zn ferrite having a Ni / Zn molar ratio of 0.4 to 0.7.

9. The composite magnetic particle of the core-shell structure according to item 1, wherein the thickness of the shell is 10 to 100 nm.

10. The composite magnetic particle of core-shell structure according to item 1, wherein the composite magnetic particles are comprised of 30 to 70% by volume of the core and 70 to 30% by volume of the shell.

11. reducing the metal oxide to form a metal core; And

And a step of epitaxially growing a Ni-Zn ferrite on the surface of the metal core to form a shell.

12. The method of claim 11, further comprising the step of forming an insulating layer on the surface of the metal core prior to the step of forming the shell.

13. The method for producing a composite magnetic particle of a core-shell structure according to item 12, wherein the formation of the insulating layer oxidizes the surface of the metal core.

The composite magnetic material of the present invention has a high magnetic permeability and a high saturation magnetization value. Thus, the energy charging efficiency can be increased when used as the material of the wireless charging device.

The composite magnetic material of the present invention also has excellent oxidation stability. This facilitates the production, handling and storage of the composite magnetic material and reduces the deterioration of the properties.

1 is a cross-sectional view of a composite magnetic particle of a core-shell structure according to an embodiment of the present invention.
2 is a cross-sectional view of a composite magnetic particle of a core-shell structure according to an embodiment of the present invention.
FIG. 3 is a view showing a composite magnetic particle having a core-shell structure according to the present invention through a transmission electron microscope (TEM).

The present invention relates to a composite magnetic particle capable of realizing a high efficiency wireless charging technique with a remarkably improved magnetic permeability and saturation magnetization value by including a metal core and a Ni-Zn ferrite shell surrounding the core.

Hereinafter, the present invention will be described in more detail.

The composite magnetic particles of the present invention include a metal core and a Ni-Zn ferrite shell surrounding the core. 1 shows a cross section of a composite magnetic particle according to one embodiment of the present invention.

The metal core of the composite magnetic particles of the present invention causes the composite magnetic particles of the present invention to exhibit high permeability and high resistance characteristics.

As the core, a metal known in the art can be used. For example, an alloy containing alpha-iron (alpha-Fe) or alpha-iron (alpha -Fe) may be used. When these metals are used, it is preferable that a magnetic material having a high magnetic permeability and low performance deterioration due to eddy current loss can be produced.

The particle size of the core is not particularly limited and may be selected in consideration of the range of powders commonly used in the art. For example, the average major axis length of the core particles may be between 50 and 500 nm. The metal magnetic particles can avoid the problem of the loss of magnetic property (superparamagnetism) due to non-pulverization when the average major axis length is in the above range. Preferably, the average major axis length of the core particles may be between 50 and 300 nm. When the shape magnetic anisotropy is required, the axial ratio (major axis / minor axis) is also an important factor, so that the axial ratio is preferably 2 or more.

The core may be contained in an amount of 30 to 70% by volume in the composite magnetic particles of the present invention. When the core is contained in less than 30% by volume in the composite magnetic particles, the permeability and saturation magnetization of the composite magnetic particles are lowered. When the core is contained in an amount exceeding 70% by volume, the stability of the composite magnetic particles may be deteriorated.

In another embodiment of the present invention, the core may have an insulating layer formed on its surface.

Figure 2 shows a cross-section of a composite magnetic particle according to one such embodiment of the present invention.

The insulating layer serves to provide a bonding force so that the shell can be stably fixed to the ferrite core and to suppress eddy current flow caused by electromagnetic wave contact with the compound magnetic material provided by the present invention, thereby reducing eddy current loss.

The insulating layer may be a layer formed of an insulating material known in the art. For example, an oxide layer. It may preferably be an oxide layer of the metal core in that the insulating layer can be more easily formed and the process yield can be improved.

The thickness of the insulating layer is not particularly limited, and may be, for example, 2 to 20 nm in thickness. If the thickness of the insulating layer is less than 2 nm, the bonding strength with the shell layer may be deteriorated and the oxidation stability of the powder may be deteriorated. If the thickness exceeds 20 nm, the magnetic properties may be reduced. Preferably, the insulating layer has a thickness of 5 to 20 nm.

Among the composite magnetic particles of the present invention, the shell allows the composite magnetic particles of the present invention to exhibit high frequency, low loss and high permeability characteristics, and can also improve oxidation stability.

As the shell, soft Ni-Zn ferrite having high permeability and low loss can be used. As a specific example, a ferrite having a Ni / Zn molar ratio of 0.3 to 0.9 may be used. If the molar ratio of Ni / Zn in the ferrite is less than 0.3, there is a problem that the magnetic property is not exhibited. If the ratio is more than 0.9, there is a problem that the permeability is rapidly lowered. More preferably, a Ni-Zn ferrite having a Ni / Zn molar ratio of 0.4 to 0.7 is used

Further, the Ni-Zn ferrite may further include another metal component, and may further include, for example, copper, cobalt, and the like. The shell is formed on the surface of the core and may be formed to have an appropriate thickness depending on the size of the core. For example, a thickness of 10 to 100 nm. When the thickness of the shell is less than 10 nm, the high-frequency characteristics of the magnetic particles can not be realized properly, and when the thickness exceeds 100 nm, the magnetic permeability characteristics of the magnetic particles may be deteriorated.

The ratio of the shell to the entire composite magnetic particles of the present invention is not particularly limited and may be, for example, 30 to 70% by volume in the composite magnetic particles. If the shell is contained in an amount of less than 30% by volume in the composite magnetic particles, the high-frequency characteristics of the magnetic particles can not be realized properly. If the shell is contained in excess of 70% by mole, the magnetic permeability characteristics of the composite magnetic particles may deteriorate. In the present invention, the volume of the core, the volume of the insulating layer, and the volume of the shell layer were calculated by considering the crystallite as spherical.

The present invention also provides a method of producing the composite magnetic particles of the core-shell structure.

According to an embodiment of the present invention, first, the metal oxide is reduced to form a metal core.

The metal oxide may be selected from metal oxides known in the art. For example, hematite, magnetite, goethite and the like can be used. Among them, the magnetite may be, for example, produced by oxidizing an aqueous solution of ferrous iron under aeration conditions at a temperature of 70 to 90 ° C and a pH of 7 to 8, but is not limited thereto.

The metal core may be formed by reducing the metal oxide by methods known in the art. As the reduction method, a method selected from dry reduction or wet reduction can be used, and it is preferable to use the dry reduction method in view of reducing the reaction time and improving the reduction reproducibility. The wet reduction is generally carried out in an aqueous solution containing an amine group, an aldehyde group and the like. In the case of pure iron, since the reduction potential is high and reoxidation easily occurs, it is very difficult to carry out the desired reduction reaction stably by wet reduction. The metal core can be formed by, for example, reducing the metal oxide through a method using an air fluidized bed under a hydrogen atmosphere, but is not limited thereto.

The metal core may have a major axis length within the aforementioned range. Thereafter, an insulating layer is formed on the metal core, and then a Ni-Zn ferrite shell is formed.

The method for forming the shell is not particularly limited, and for example, it is possible to form the core surface by epitaxial growth of Ni-Zn ferrite. More specifically, it can be performed by forming an interface having a spinel structure in the core and growing a Ni-Zn ferrite having the same crystal structure. The epitaxial growth of the Ni-Zn ferrite may be performed by adding water to the core dispersion in advance and dropping the Ni-Zn ferrite solution or by dropping water into the solution containing the core and the Ni-Zn ferrite . In the examples of the present invention, water was previously added to the core dispersion and then a Ni-Zn ferrite solution was dropped.

The shell may be formed to satisfy the thickness within the above-mentioned range and the ratio to the core. The thickness of the formed shell can be controlled by controlling the reaction time for growing the Ni-Zn ferrite on the core surface.

The core may further include an insulating layer on its surface, in which case it may further comprise forming an insulating layer on the surface of the core prior to forming the shell on the core.

The insulating layer may be formed by a known method as an insulating material known in the art, but it is preferably formed by oxidizing the surface of the core in order to easily form the insulating layer without any additional material or additional process, .

The method of oxidizing the core surface is not particularly limited and can be carried out by a known method, for example, by slowly oxidizing the core surface under an oxygen partial pressure of 10 to 100 mmHg.

The insulating layer may be formed to a thickness within the above-mentioned range, and the thickness thereof may be adjusted by adjusting the reaction time.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to be illustrative of the invention and are not intended to limit the scope of the claims. It will be apparent to those skilled in the art that such variations and modifications are within the scope of the appended claims.

Example

[Example 1]

3000 cc of distilled water was added to the reactor capable of controlling the temperature of 5000 cc, and then nitrogen gas was vented to remove dissolved oxygen. While the temperature of the reactor was maintained at 45 ° C, the solution was quantitatively determined to have a concentration of 0.15 mol of ferrous sulfate (a special reagent), and the solution was added at once to a concentration of caustic soda (sodium hydroxide) of 0.75 mol, . Ferrous hydroxide was aged for 30 minutes, air was blown at a flow rate of 30 cc / min, and oxidation was continued for 120 minutes to grow oxyhydroxide. The end point of the reaction was confirmed by potassium cyanide titration.

After the oxidation was completed, a small amount of a water glass solution was added to obtain a powder of oxyhydroxide particles having silicon adhered on the surface of oxyhydroxide. The powder was filtered and then dried at 130 ° C for 24 hours to obtain a solid. 100 g of this solid was placed in an alumina vessel and calcined at 750 캜 in the atmosphere to obtain iron oxide containing hematite as a main component.

The obtained iron oxide mainly composed of hematite was placed in a reducing device composed of a quartz tube, and the powder was flowed at a flow rate of 4 L / min of hydrogen gas at the lower part, followed by reduction treatment at 400 ° C. for 60 minutes. The end point of the reduction reaction was determined by observing the condensation phenomenon or measuring the amount of water vapor in the exhaust gas.

3000 cc of distilled water was added to the reactor capable of controlling the temperature of 5000 cc, and then nitrogen gas was vented to remove dissolved oxygen. The metal magnetic powder thus prepared was put in, and the temperature was raised to 80 캜 while nitrogen gas was passed. At this time, the pH of the reactor was maintained at 11.0.

A solution of 0.25 mol, 0.10 mol and 0.15 mol of each of iron chloride, nickel chloride and zinc chloride was prepared and fed through a metering pump at 10 cc / min. To maintain the pH at 11.0, Ni-Zn ferrite was epitaxially grown for 120 minutes while caustic soda (sodium hydroxide) solution was added.

After completion of the reaction, the slurry was filtered, and then dried at 130 ° C. for 24 hours to obtain a solid powder of core-shell structure composite magnetic particles.

[Example 2]

3000 cc of distilled water was added to the reactor capable of controlling the temperature of 5000 cc, and then nitrogen gas was vented to remove dissolved oxygen. While the temperature of the reactor was maintained at 45 ° C, the solution was quantitatively determined to have a concentration of 0.15 mol of ferrous sulfate (a special reagent), and the solution was added at once to a concentration of caustic soda (sodium hydroxide) of 0.75 mol, . Ferrous hydroxide was aged for 30 minutes, air was blown at a flow rate of 30 cc / min, and oxidation was continued for 120 minutes to grow oxyhydroxide. The end point of the reaction was confirmed by potassium cyanide titration.

After the oxidation was completed, a small amount of a water glass solution was added to obtain a powder of oxyhydroxide particles having silicon adhered on the surface of oxyhydroxide. The powder was filtered and then dried at 130 ° C for 24 hours to obtain a solid. 100 g of this solid was placed in an alumina vessel and calcined at 750 캜 in the atmosphere to obtain iron oxide containing hematite as a main component.

The obtained iron oxide mainly composed of hematite was placed in a reducing device composed of a quartz tube, and the powder was flowed at a flow rate of 4 L / min of hydrogen gas at the lower part, followed by reduction treatment at 400 ° C. for 60 minutes. The end point of the reduction reaction was determined by observing the condensation phenomenon or measuring the amount of water vapor in the exhaust gas.

The pure iron powder was immersed in a container solvent in which dissolved oxygen was removed to draw it into the atmosphere. A small amount of ammonia water was added to the organic solvent while air was blown into the solution to form an insulating layer on the surface. The organic solvent slurry of the metal magnetic particles was precipitated using a centrifugal separator, and the supernatant liquid was removed to obtain a powder of metal magnetic particles having an insulating layer formed thereon.

3000 cc of distilled water was added to the reactor capable of controlling the temperature of 5000 cc, and then nitrogen gas was vented to remove dissolved oxygen. The metal magnetic powder with the insulating layer formed thereon was introduced, and the temperature was raised to 80 캜 while nitrogen gas was passed. At this time, the pH of the reactor was maintained at 11.0.

A solution of 0.25 mol, 0.10 mol and 0.15 mol of each of iron chloride, nickel chloride and zinc chloride was prepared and fed through a metering pump at 10 cc / min. To maintain the pH at 11.0, Ni-Zn ferrite was epitaxially grown for 120 minutes while caustic soda (sodium hydroxide) solution was added.

After completion of the reaction, the slurry was filtered, and then dried at 130 ° C. for 24 hours to obtain a solid powder of core-shell structure composite magnetic particles.

[Examples 3 to 11]

Except that a core, an insulating layer and a shell were formed and ferrite was used as shown in Table 1 below. The major axis length of the formed core was controlled by varying the air inflow rate or reaction temperature during the production of oxy iron hydroxide. The length of the major axis of the formed core was measured using a transmission electron microscope (TEM). The thickness of the insulating layer to be formed was controlled by changing the insulating layer forming time and the reactive oxygen partial pressure, and the thickness of the insulating layer formed was measured using a transmission electron microscope (TEM). The thickness of the formed ferrite shell was controlled by changing the reaction time for epitaxial growth. The thickness of the formed ferrite shell was measured by measuring the major axis length of the core before forming the shell and measuring the major axis length of the magnetic particles of the finally obtained core-shell structure.

[Comparative Example 1]

3000 cc of distilled water was added to the reactor capable of controlling the temperature of 5000 cc, and then nitrogen gas was vented to remove dissolved oxygen. And the temperature was raised to 80 캜 while nitrogen gas was passed therethrough. At this time, the pH of the reactor was maintained at 11.0.

A solution of 0.25 mol, 0.10 mol and 0.15 mol of each of iron chloride, nickel chloride and zinc chloride was prepared and fed through a metering pump at 10 cc / min. The mixed solution was coprecipitated while caustic soda (sodium hydroxide) solution was added to maintain the pH at 11.0. The coprecipitated metal hydroxide slurry was filtered, washed, dried at 130 ° C. for 24 hours, and pulverized in an agate mortar for 1 hour to prepare a powder of spherical Ni-Zn ferrite particles having a particle size of 200 nm.

[Comparative Example 2]

Except that Mn-Zn ferrite was used instead of Ni-Zn ferrite. 0.25 mol, 0.10 mol, and 0.15 mol of each solution of iron chloride, manganese chloride and zinc chloride were used.

[Comparative Example 3]

Except that the Ni-Zn ferrite was not epitaxially grown.

Particle size
ferrite Core-shell structure
Long axis (nm) Metal core long axis (nm) Insulation layer thickness (nm) Shell Thickness (nm) Core / shell volume ratio Kinds
(AB system) A / B mole ratio Example 1 200 - 30 65.8 / 34.2 230 Ni-Zn 0.67 Example 2 200 10 30 63.7 / 36.3 240 Ni-Zn 0.67 Example 3 170 10 30 58.9 / 41.1 210 Ni-Zn 0.67 Example 4 190 10 30 62.2 / 37.8 230 Ni-Zn 0.67 Example 5 210 10 35 61.0 / 39.0 255 Ni-Zn 0.67 Example 6 200 10 30 63.7 / 36.3 240 Ni-Zn 0.6 Example 7 450 20 80 59.3 / 40.7 550 Ni-Zn 0.6 Example 8 80 10 15 54.4 / 45.6 105 Ni-Zn 0.6 Example 9 200 10 30 63.7 / 36.3 240 Ni-Zn 0.4 Example 10 200 10 30 63.7 / 36.3 240 Ni-Zn 0.8 Example 11 200 5 90 31.9 / 68.1 295 Ni-Zn 0.6 Comparative Example 1 Ni-Zn ferrite single particles 200 Ni-Zn 0.67 Comparative Example 2 Mn-Zn ferrite single particles 200 Mn-Zn 0.67 Comparative Example 3 200 10 - 210 - -

[Test Example]

The magnetic properties and stability of the core-shell magnetic particles prepared in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 2 below.

(1) Measurement of permeability

Magnetic composites were prepared by mixing magnetic particles and PVA resin in a toroidal shape by uniaxial pressing and sintering. The real part and the imaginary part permeability were measured by using an impedance analyzer (Impedence Analyzer E4991A, Agilent).

 (2) Saturation magnetization  Measure

The saturation magnetization value of the magnetic particles was determined by measuring a magnetic hysteresis curve using a vibrating sample magnetometer (Model 7407, Lakeshore).

 (3) Measurement of oxidation stability

The oxidative stability of the magnetic particles was evaluated under a 60 ° C 80% constant temperature and humidity environment. The saturation magnetization value was measured after the magnetic powder was exposed for 48 hours under the constant temperature and humidity environment and compared with the saturation magnetization value of the compound magnetic powder not exposed under the environment, The stability was measured.

[Equation 1]

Oxidation stability (%) = [saturation magnetization value after 48 hours exposure of magnetic particles under constant temperature and humidity environment / saturation magnetization value of magnetic particles not exposed under constant temperature and humidity environment]

Investment ratio Saturation magnetization (emu / g) Oxidation stability (%) Example 1 1900 120 70 Example 2 2300 110 85 Example 3 2500 110 85 Example 4 2400 125 80 Example 5 2200 100 95 Example 6 2200 120 85 Example 7 1600 130 95 Example 8 1900 105 80 Example 9 1300 120 85 Example 10 1400 120 85 Example 11 1800 125 75 Comparative Example 1 1300 65 100 Comparative Example 2 1600 75 80 Comparative Example 3 1800 90 75

Referring to Table 2, it can be seen that Examples 1 to 11 corresponding to the magnetic particles of the present invention exhibit excellent magnetic permeability and saturation magnetization.

In Examples 1 to 8 and Example 11, permeability and saturation magnetization were further improved when the molar ratio of Ni-Zn ferrite was in the range of 0.4 to 0.7.

In Comparative Examples 1 and 2, it can be seen that the permeability and the saturation magnetization are significantly lowered when the metal core component is not included.

Comparing Example 2 and Comparative Example 3, permeability, saturation magnetization, and oxidation stability were all improved when a shell layer was formed.

Examples 2 to 11 show excellent oxidation stability when both the insulating layer and the shell layer are included.

Claims (13)

A composite magnetic particle having a core-shell structure including a metal core and a Ni-Zn ferrite shell surrounding the core
The composite magnetic particle of claim 1, wherein the core is at least one selected from among alloy particles including alpha-iron particles and alpha-iron.
The composite magnetic particle of claim 1, wherein the core has an average major axis length of 50 to 500 nm.
The composite magnetic particle of claim 1, wherein the core has an insulating layer formed on its surface.
5. The composite magnetic particle according to claim 4, wherein the insulating layer is an oxide layer of a metal constituting the core.
5. The composite magnetic particle according to claim 4, wherein the insulating layer is formed to a thickness of 2 to 20 nm.
The composite magnetic particle of claim 1, wherein the shell is a Ni-Zn ferrite having a Ni / Zn molar ratio of 0.3 to 0.9.
The composite magnetic particle of claim 1, wherein the shell is a Ni-Zn ferrite having a Ni / Zn molar ratio of 0.4 to 0.7.
The composite magnetic particle of claim 1, wherein the thickness of the shell is 10 to 100 nm.
The composite magnetic particle of claim 1, wherein the core-shell structure comprises 30 to 70% by volume of the core and 70 to 30% by volume of the shell.
Reducing the metal oxide to form a metal core; And
And a step of epitaxially growing a Ni-Zn ferrite on the surface of the metal core to form a shell.
12. The method of claim 11, further comprising forming an insulating layer on the surface of the metal core prior to forming the shell.
13. The method of claim 12, wherein the formation of the insulating layer comprises oxidizing the surface of the metal core.

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