JP2021011625A - Magnetic powder, composite magnetic substance and magnetic component - Google Patents

Abstract

To provide a magnetic powder or the like simultaneously realizing high magnetic permeability and low magnetic loss in a high frequency region of 5GHz or higher.SOLUTION: A magnetic powder includes magnetic particles, each having Fe and Co as main components. A magnetic particle includes an oxide of one or more kinds of elements selected from Mg, Al, Si, Ca, and Y. In the magnetic particles, an average atomic ratio of Fe is X1, an average atomic ratio of Co is X2, and X1/X2=α, in which an average value of the α is 1.0 to 4.0, inclusive, and a CV value of the α is 0.30 or less. An average major axis diameter of the magnetic particles is 100 nm or less. An average axial ratio of the magnetic particles is 6.0 to 10.0, inclusive. Coercive force of the magnetic powder is 2500Oe or more, saturation magnetization of the magnetic powder is 100 Am2/kg or more, and a volume resistivity of a compact obtained by compressing and molding the magnetic powder is 1.0×104 Ω cm or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to magnetic powders, composite magnetic materials and magnetic components.

In Patent Document 1, the shape, coercive force and saturation magnetization of the metal powder are set within a specific range, and the insulating property of the metal powder is further enhanced to obtain high magnetic permeability and low magnetic loss in the frequency band of 1 GHz or more and 5 GHz or less. Compatible magnetic powders and the like are described.

International Publication No. 2013/168411

At present, it is required to provide a magnetic powder having a higher magnetic permeability and a lower magnetic loss in a high frequency region of 5 GHz or more.

An object of the present invention is to provide a magnetic powder or the like that has both high magnetic permeability and low magnetic loss in a high frequency region of 5 GHz or higher.

In order to achieve the above object, the magnetic powder of the present invention is used.
It is a magnetic powder composed of magnetic particles containing Fe and Co as main components.
The magnetic particles contain oxides of one or more elements selected from Mg, Al, Si, Ca, and Y.
The average atomic ratio of Fe in the magnetic particles is X1, the average atomic ratio of Co is X2, X1 / X2 = α, the average value of α is 1.0 or more and 4.0 or less, and the CV value of α is 0. .30 or less,
The average major axis diameter of the magnetic particles is 100 nm or less, and the average axial ratio of the magnetic particles is 6.0 or more and 10.0 or less.
The coercive force of the magnetic powder is 2500 Oe or more, the saturation magnetization of the magnetic powder is 100 Am ² / kg or more, and the volume resistivity of the molded product formed by pressurizing the magnetic powder is 1.0 × 10 ⁴ Ω. -It is characterized by being cm or more.

In order to achieve the above object, the composite magnetic material of the present invention is used.
A composite magnetic material containing the above magnetic powder and resin,
The volume ratio of the magnetic particles in the composite magnetic material is 5.0% by volume or more and 50% by volume or less.
Wherein the volume resistivity of the composite magnetic body is 1.0 × 10 ⁶ Ω · cm or more.

The magnetic powder and composite magnetic material of the present invention have the above-mentioned characteristics, and thus become a magnetic powder and composite magnetic material having both high magnetic permeability and low magnetic loss in a high frequency region of 5 GHz or higher.

In the composite magnetic material of the present invention, the real part of the complex relative magnetic permeability at a frequency of 5 GHz is μ'r, the imaginary part of the complex relative magnetic permeability is μ "r, and tan δ = μ" r / μ'r. May be greater than 1.3, tan δ may be less than 0.05, and the resonance frequency may be 10 GHz or higher. Note that tan δ is a magnetic loss.

The magnetic component of the present invention uses the above magnetic powder or the above composite magnetic material.

It is a figure which shows the major axis length and minor axis length in a magnetic particle.

Hereinafter, the present invention will be described based on the embodiments shown in the drawings.

The magnetic powder of this embodiment is a magnetic powder composed of magnetic particles containing Fe and Co as main components. The magnetic particles contain oxides of one or more elements selected from Mg, Al, Si, Ca, and Y. The term "Fe and Co as main components" refers to a case where the total content of Fe and Co with respect to the entire magnetic particles is 50 at% or more.

The magnetic particles contain oxides of one or more elements (non-magnetic metal elements) selected from Mg, Al, Si, Ca, and Y. When the magnetic particles contain one or more oxides selected from Mg, Al, Si, Ca and Y, the resistance between the magnetic particles increases. Further, the crystal growth of the magnetic particles is suppressed, and the magnetic particles are less likely to be sintered. As a result, in the process of manufacturing the magnetic particles described later, it becomes easy to obtain the particle shape of the magnetic particles without changing the particle shape of the goethite particles. Then, it becomes easy to improve each parameter regarding the particle shape of the magnetic particles. The above effect is particularly significant when the structure is such that one or more oxides selected from Mg, Al, Si, Ca and Y cover the periphery of the portion composed of Fe and Co.

The smaller the content of one or more oxides selected from Mg, Al, Si, Ca and Y in the magnetic particles, the more easily the particle shape changes in the process of producing the magnetic particles from the goethite particles. As a result, the composition variation among the magnetic particles also increases. Further, the resistance between the magnetic particles becomes small, and the volume resistivity of the magnetic material containing the magnetic powder tends to decrease. On the other hand, the larger the content of one or more oxides selected from Mg, Al, Si, Ca and Y, the more difficult it is to increase the saturation magnetization. Further, it becomes difficult to increase the average axial ratio of the magnetic particles. It is preferable to contain an oxide of Al.

Further, a part of Fe contained in the magnetic particles may be oxidized. Since a part of Fe is oxidized, the volume resistivity becomes large. Further, the structure may be such that the oxide of Fe covers the periphery of the portion composed of Fe and Co.

Then, the average atomic ratio of Fe in the magnetic particles is X1, the average atomic ratio of Co is X2, X1 / X2 = α, the average value of α is 1.0 or more and 4.0 or less, and the CV value of α is It is 0.30 or less.

X1 / X2 is a value obtained by dividing the Fe content ratio by the Co content ratio in the magnetic particles. The average value of α is the average value of α in each magnetic particle. The average value of α is substantially the same as the value obtained by dividing the Fe content of the entire magnetic powder by the Co content on the basis of the number of atoms. The CV value of α is a parameter representing the variation of α in each magnetic particle, that is, the variation of the composition between the magnetic particles. The smaller the CV value of α, the smaller the variation in α, and the smaller the variation in composition between the magnetic particles.

The magnetic powder according to this embodiment has good magnetic characteristics (high saturation magnetization and high coercive force) when the average value of α is 1.0 or more and 4.0 or less. When the average value of α is too small (when Co is too large), it becomes difficult to increase the average axial ratio described later, the saturation magnetization tends to decrease, and μ'r tends to decrease. When the average value of α is too large (when Co is too small), the volume resistivity of the magnetic powder tends to decrease and μ'r tends to decrease.

The magnetic powder according to this embodiment has good magnetic characteristics by setting the CV value of α to 0.30 or less, and has a high μ'r and a low tan δ especially in a high frequency region of 5 GHz or more. It becomes a powder. The same effect can be obtained with a composite magnetic material or a magnetic component containing the magnetic powder. If the CV value of α is too large, the μ ″ r-half width, which will be described later, tends to be large, and tan δ tends to be large.

The measuring method of X1 and X2 is not particularly limited. For example, it can be calculated by performing point analysis on 5 points or more, preferably 10 points or more in the magnetic particles using STEM-EDX or the like, measuring the atomic ratio of Fe and the atomic ratio of Co at each point, and averaging them. .. There is no particular limitation on the observation magnification of STEM. For example, it may be about 20000 to 40,000 times. If the observation magnification of STEM is too high or too low, it becomes difficult to properly measure X1 and X2. Further, the spot diameter of the electron beam (hereinafter, simply referred to as the beam diameter) on the measurement sample surface of the point analysis is appropriately set according to the observation magnification of STEM. For example, it may be about 0.2 to 1.0 nm. Further, in order to make the beam diameter within the above range, for example, STEM having a field emission type electron gun may be used.

There is no particular limitation on the method of calculating the average value of α and the CV value of α. For example, the average value of α can be calculated by calculating α for 10 or more, preferably 30 or more magnetic particles contained in the magnetic powder and averaging them. Further, the CV value of α can be calculated by calculating the standard deviation of α and dividing the standard deviation of α by the average value of α.

The magnetic particles contained in the magnetic powder according to the present embodiment have an average major axis diameter of 100 nm or less and an average axial ratio of 6.0 or more and 10.0 or less. When the average major axis length and the average axis ratio of the magnetic particles are within the above ranges, the magnetic powder has good magnetic characteristics, has a high μ'r and a low tan δ, especially in a high frequency region of 5 GHz or more. Become.

If the average major axis length is too large, tan δ tends to be large. There is no particular lower limit to the average major axis length. For example, it is 5 nm or more. Further, when the average axial ratio is too small, the coercive force tends to decrease, and tan δ tends to increase as the resonance frequency decreases. On the other hand, if the average axial ratio is too large, the shape magnetic anisotropy becomes too large, and μ'r decreases.

There is no particular limitation on the method of calculating the major axis length and the minor axis length of the magnetic particles. For example, the method shown below is used.

First, using SEM, TEM, or the like, a magnetic particle 1 whose major axis length and minor axis length are measured is photographed as a two-dimensional image. As shown in FIG. 1, an ellipse 1a circumscribing the magnetic particle 1 is drawn on the captured two-dimensional image, and the length of the major axis L1 of the ellipse 1a is defined as the major axis length and the length of the minor axis L2 is defined as the minor axis length. To do.

Then, the major axis length and the minor axis length are measured for 150 or more, preferably 200 or more magnetic particles, and averaged to calculate the average major axis length and the average minor axis length. Further, (average major axis length) / (average minor axis length) is taken as the average axial ratio.

Further, the magnetic powder according to the present embodiment has a coercive force of 2500 Oe or more and a saturation magnetization of 100 Am ² / kg or more. By using a magnetic powder having a coercive force of 2500 Oe or more, the resonance frequency can be shifted to the high frequency side, and the tan δ of the composite magnetic material and the magnetic component can be reduced particularly in the high frequency region of 5 GHz or more. Further, by using a magnetic powder having a saturation magnetization of 100 Am ² / kg or more, it is possible to shift the resonance frequency to the high frequency side while maintaining a high μ'r, and tan δ particularly in the high frequency region of 5 GHz or more. Can be made smaller.

There is no upper limit to the coercive force, but it is, for example, 3500 Oe or less. The higher the coercive force, the higher the resonance frequency, the lower the tan δ, and the lower the μ'r. There is no upper limit to the saturation magnetization, but it is, for example, 200 Am ² / kg or less. The higher the saturation magnetization, the higher the resonance frequency, the lower the tan δ, and the higher the μ'r. On the other hand, when the saturation magnetization is increased by reducing the amount of oxide of the non-magnetic metal element, the volume resistivity is decreased and tan δ is increased.

The resonance frequency is the frequency at which μ ″ r is the highest. Generally, in a magnetic powder, μ ′ r and tan δ increase as the frequency increases, and natural resonance occurs in a specific frequency band. At frequencies above the resonance frequency, μ'r becomes significantly smaller. Therefore, it is necessary to use magnetic powder at frequencies below the resonance frequency. Here, in order to increase the resonance frequency, saturation magnetization and magnetic heterogeneity are required. It is necessary to improve the sex.

Known magnetic anisotropy includes crystal magnetic anisotropy and shape magnetic anisotropy, but in an aggregate of magnetic particles such as magnetic powder, magnetic anisotropy depends on the composition of the magnetic particles. Changes. In the aggregate of magnetic particles, the composition of each magnetic particle is not always constant and varies. Therefore, each magnetic particle has a variety of magnetic anisotropy.

Natural resonance in each magnetic particle occurs at a frequency corresponding to the magnetic anisotropy of each magnetic particle. As described above, in the aggregate of magnetic particles, each magnetic particle has different magnetic anisotropy and exhibits a resonance frequency corresponding to the magnetic anisotropy. Therefore, the entire aggregate of magnetic particles has a peak width corresponding to the variation in the composition between the magnetic particles due to the superposition of the natural resonances of the individual magnetic particles. Therefore, even when the magnetic material is used at a frequency considerably lower than the resonance frequency, the influence of natural resonance occurs, and μ'r becomes large and tan δ becomes large.

That is, by reducing the variation in the composition of the individual magnetic particles contained in the magnetic powder, the width of the peak of μ ″ r caused by the natural resonance of the entire magnetic powder, that is, the μ ″ r-full width at half maximum (μ ″ r is the maximum. The width of the frequency band, which is 1/2 or more of the value) can be reduced. In other words, the peak becomes sharper, and the influence of natural resonance can be reduced when the magnetic powder is used in the frequency band smaller than the resonance frequency. , Tan δ can be made smaller. From the above, the magnetic powder having a higher resonance frequency and a smaller μ ″ r-half width is more suitable for use in a higher frequency band.

Further, the magnetic powder according to the present embodiment has high insulation between magnetic particles. Specifically, it is the volume resistivity of the molded body formed by pressurizing at a pressure 64MPa is 1.0 × 10 ⁴ Ω · cm or more. By using magnetic particles having high insulating properties, the tan δ of the magnetic particles themselves, the tan δ of the composite magnetic material, and the tan δ of the magnetic component can be reduced.

Further, even if the magnetic powder contains other elements such as V, Cr, Mn, Cu, Zn, Ni, Sr, Ba, lanthanoid, Ti, Zr, Hf, Nb, Ta, Zn, Ga and the like. Good. The content of other elements is not particularly limited, but may be 20% by mass or less in total with respect to the entire magnetic powder.

Next, the composite magnetic material according to this embodiment will be described.

The composite magnetic material according to the present embodiment includes the above-mentioned magnetic powder and resin. The type of resin is not particularly limited, and any resin having insulating properties may be used. For example, silicone resin, phenol resin, acrylic resin, epoxy resin and the like can be mentioned. Further, two or more kinds of resins may be combined.

The volume ratio of the magnetic particles in the composite magnetic material according to the present embodiment is 5.0% by volume or more and 50% by volume or less. The presence of magnetic particles having a large average axial ratio in the resin at a volume ratio within the above range facilitates the formation of a magnetic network. Then, in the high frequency region of 5 GHz or more, it becomes easy to achieve both high μ'r and low tan δ.

Furthermore, μ'r at a frequency of 5 GHz may be greater than 1.3, μ ″ r at a frequency of 5 GHz may be less than 0.05, and the resonance frequency may be 10 GHz or higher.

Moreover, the composite magnetic body according to the present embodiment is a volume resistivity of 1.0 × 10 ⁶ Ω · cm or more. That is, the composite magnetic material according to the present embodiment has high insulation between magnetic powders and resin. Due to the high insulating property of the composite magnetic material, the tan δ of the composite magnetic material and the tan δ of the magnetic component containing the composite magnetic material can be reduced.

Here, there is no particular limitation on the method of calculating the volume ratio of the magnetic particles. For example, the method shown below can be mentioned.

First, the cross section obtained by cutting the composite magnetic material is polished to prepare an observation surface. Next, the observation surface is observed using an electron microscope (SEM). Calculate the area ratio of the magnetic particles to the area of the entire observation surface. Then, in the present embodiment, it is considered that the area ratio and the volume ratio are equal.

An example of a method for calculating the volume ratio of magnetic particles to the total area of the observation surface will be described.

Noise is removed and binarized with respect to the SEM image obtained by using an electron microscope. Then, assuming that the white portion of the binarized image is a magnetic particle, the area ratio of the white portion to the area of the entire observation surface is calculated. The area ratio is the area ratio of the magnetic particles to the area of the entire observation surface.

Further, in calculating the volume ratio of the magnetic particles, the observation surface has a size including a total of 500 or more, preferably 1000 or more magnetic particles. The number of observation surfaces may be a plurality, and the size may include a total of 5000 or more.

Further, the type of magnetic component according to the present embodiment is not particularly limited. It may contain the above magnetic powder or composite magnetic material.

The magnetic powder and the like according to the present embodiment are particularly used for magnetic components used in electronic devices for 5th generation mobile communication, which are expected to have a frequency band exceeding 5 GHz, such as inductors, EMI filters for high frequency noise countermeasures, and antennas. It is preferably used. Further, providing a magnetic powder or the like having both high magnetic permeability and low loss also contributes to miniaturization of magnetic parts.

Hereinafter, the method for producing the magnetic powder and the composite magnetic material according to the present embodiment will be described, but the method for producing the magnetic powder and the composite magnetic material according to the present embodiment is not limited to the following methods.

The method for producing magnetic powder according to the present embodiment includes a step of producing goethite seed crystal particles by a seed crystal formation reaction, a step of growing a goethite layer on the surface of the goethite seed crystal particles by a growth reaction, and a step of producing goethite particles. It includes a step of heating and dehydrating the particles to prepare goethite particles, and a step of heat-treating the goethite particles and then heating and reducing them in a reducing gas atmosphere to prepare magnetic powder.

In order to obtain the magnetic particles according to the present embodiment, it is important to use goethite particles having a uniform particle size and composition, no dendritic particles mixed in, and an appropriate shape and axial ratio. is there. In addition, it is important to prepare a magnetic powder while maintaining the particle shape and uniform particle size of goethite particles. Preferably, the shape, axial ratio, etc. of the magnetic particles are substantially the same as the shape, axial ratio, etc. of the goethite particles described above.

First, goethite seed crystal particles are produced by a seed crystal formation reaction. There is no particular limitation on the method for producing goethite seed crystal particles. For example, first, a suspension containing a ferrous-containing precipitate obtained by reacting an alkaline aqueous solution with a ferrous salt aqueous solution is prepared. Then, after the suspension is aged in a non-oxidizing atmosphere, goethite seed crystal particles are produced by aerating the suspension with an oxygen-containing gas.

There is no particular limitation on the type of alkaline aqueous solution. For example, a mixed alkaline aqueous solution of an aqueous ammonium hydrogen carbonate solution and an aqueous ammonia solution, a mixed alkaline aqueous solution of a sodium carbonate aqueous solution and sodium hydroxide, and the like can be mentioned. There is no particular limitation on the type of ferrous salt aqueous solution. For example, an aqueous solution containing Fe ²⁺ such as an aqueous solution of ferrous sulfate and an aqueous solution of ferrous chloride can be mentioned.

There are no particular restrictions on the type of non-oxidizing atmosphere. For example, a nitrogen gas atmosphere, a hydrogen gas atmosphere, and the like can be mentioned. There are no particular restrictions on the aging conditions. For example, it may be 40 to 80 ° C. for 30 to 300 minutes. There are no particular restrictions on the flow rate of the oxygen-containing gas or the ventilation time.

The cobalt compound is then added and aged to complete the reaction. The type of cobalt compound is not particularly limited. For example, an aqueous solution containing Co ²⁺ such as an aqueous solution of cobalt sulfate can be mentioned. Then, air may be aerated to oxidize a part of Fe ²⁺ contained in the goethite seed crystal particles.

Next, a goethite layer is grown on the surface of the goethite seed crystal particles by a growth reaction to prepare goethite particles. There is no particular limitation on the method of growing the goethite layer. For example, an aqueous solution of a compound containing one or more elements selected from Mg, Al, Si, Ca and Y is newly added and mixed in a suspension containing gateite seed crystal particles. Then, the oxygen-containing gas is aerated to grow a goethite layer on the particle surface of the spindle-shaped goethite seed crystal particles to generate spindle-shaped goethite particles. The result is goethite particles containing one or more oxides selected from Mg, Al, Si, Ca and Y in the goethite layer.

The average thickness of the goethite layer is not particularly limited. In particular, the average value of α and the CV value of α may be appropriately controlled so as to be within a specific range.

The type of the alkaline aqueous solution and the type of the ferrous salt aqueous solution are not particularly limited, and for example, the same type of alkaline aqueous solution and ferrous salt aqueous solution as in the preparation of the gateite seed crystal particles may be used. Further, the type of the compound containing one or more elements selected from Mg, Al, Si, Ca and Y is not particularly limited. For example, sulfates of one or more elements selected from Mg, Al, Si, Ca and Y can be mentioned.

Then, a goethite particle-containing slurry is obtained by the above reaction. The pH of the goethite particle-containing slurry at this point may be 8 to 11.

Further, in a preferred embodiment, the shape of the goethite particles at this point is generally the shape of the finally obtained magnetic particles. The average major axis diameter and the average axis ratio at this point can be controlled mainly by changing the amount of Co and changing the timing of adding the non-magnetic metal. Specifically, when the solid solution amount of Co is increased, goethite particles having a short average major axis diameter can be obtained, and goethite particles having an appropriately large average axis ratio can be obtained. Further, the average axial ratio can be controlled mainly by changing the addition timing of the non-magnetic metal. Among the non-magnetic metals, Al has a crystal growth control effect, and it is known that the average axial ratio changes greatly depending on the timing of addition. Specifically, adding an Al compound during the formation of goethite particles causes a decrease in the average axial ratio. In particular, when the formation reaction of goethite particles is carried out in the state where the divalent Co ion (Co ²⁺ ) and the Al compound are present at the same time, the average axial ratio of the obtained goethite particles is lowered. In order to obtain goethite particles having a large average axis ratio, it is preferable to separate the goethite particle formation reaction into a seed crystal formation reaction and a growth reaction as described above. Then, Co ^2+, which has the effect of preferably increasing the average axial ratio, is added at the time of the seed crystal formation reaction and dissolved. In this way, when the non-magnetic metal is added (during the growth reaction), Co ²⁺ is substantially absent, thereby inhibiting the decrease in the average axial ratio due to the addition of the non-magnetic metal and increasing the average axial ratio. Getite particles are obtained. The average value of α can be controlled mainly by changing the addition ratio of Fe ²⁺ and Co ²⁺ . The CV value of α can be controlled mainly by changing the uniformity of the system during the formation of goethite particles. Specifically, the more uniformly Fe ²⁺ and Co ²⁺ are present in the system, the smaller the CV value of α tends to be.

Next, the obtained goethite particle-containing slurry is filtered off to obtain goethite particles. There is no particular limitation on the method of filtering. For example, a press filter may be used. Further, the goethite particles filtered out may be washed with an alkaline aqueous solution, for example, aqueous ammonia. Then, it is further washed with ion-exchanged water to obtain a press cake of goethite particles.

Next, the above press cake of goethite particles is granulated to obtain a granulated product. The granulation method is arbitrary. For example, there is a method of extrusion molding with a molding plate having a hole diameter of 1 to 10 mm using an extrusion molding machine. The granules are then heated and dried. For example, it may be heated and dried in a non-reducing atmosphere (for example, in a nitrogen gas atmosphere) at 50 to 150 ° C. for 1 to 10 hours. The dried granules are further heated and dehydrated. For example, it may be dehydrated by heating in an oxygen-containing atmosphere (for example, in air) at 100 to 500 ° C. for 1 to 10 hours. Further, it can be dehydrated by heating at 300 to 700 ° C. for 1 to 10 hours in an oxygen-containing atmosphere to obtain a granulated product of hematite particles.

Next, the granulated product of hematite particles is heat-reduced in a reducing atmosphere (for example, in a hydrogen gas atmosphere) at 350 to 700 ° C. for 1 to 10 hours to obtain a magnetic powder. If the temperature of heat reduction is too low, the progress of the reduction reaction is too slow and the heat reduction takes a long time. Further, the growth of the crystal contained in the magnetic particles becomes insufficient, and it becomes difficult to keep the saturation magnetization and the coercive force within a predetermined range. If the heat reduction temperature is too high, the reduction reaction will proceed too rapidly, causing deformation and sintering of the particles. As a result, it becomes difficult to keep the average major axis length, the average axis ratio, and / or the CV value of α within a predetermined range.

The magnetic powder after heat reduction is taken out into the air by a well-known method. As a well-known method, for example, there is a method of immersing a magnetic powder in an organic solvent and removing the organic solvent in air. Further, a method in which the atmosphere in which the reduced magnetic powder is present is once changed from the reducing atmosphere to an inert gas atmosphere, and then the oxygen content in the inert gas atmosphere is gradually increased to finally change the atmosphere to air. There is. Further, there is a method in which the magnetic powder is gradually oxidized using a gas in which oxygen and water vapor are mixed and then taken out into the air. Further, a metal oxide film may be formed on the surface of the magnetic particles by taking out the magnetic powder into the air.

The step of heating and dehydrating the goethite particles to produce hematite particles may be omitted, or the goethite particles may be heated and reduced to produce magnetic powder. When the goethite particles are heat-reduced, the heat treatment may be performed in a non-reducing atmosphere before the heat reduction. The heat treatment makes it easier to maintain the shape of the particles. Examples of the non-reducing atmosphere include air, oxygen gas, nitrogen gas and the like. The temperature of the heat treatment is not particularly limited, but may be appropriately selected depending on the type and content of one or more elements selected from Mg, Al, Si, Ca and Y from 400 ° C. to 750 ° C. The time of the heat treatment is not particularly limited and may be 1 to 10 hours. If the temperature of the heat treatment is too low, the time required for the heat treatment becomes long. If the heat treatment temperature is too high, it will cause deformation and sintering of goethite particles. As a result, it becomes difficult to keep the average major axis length, the average axis ratio, and / or the CV value of α within a predetermined range.

Then, the composite magnetic material can be obtained by mixing the magnetic powder obtained by the above method and the resin and drying them. As the resin, an insulating resin is used. By mixing the magnetic powder and the resin, the insulating property between the magnetic particles can be enhanced. As a result, the magnetic loss associated with the generation of eddy current can be reduced.

The device used for mixing the magnetic powder and the resin is not particularly limited. For example, a stirrer / mixer such as a pressurized kneader or a ball mill may be used. Further, the mixing conditions are not particularly limited. For example, it may be 20 to 60 minutes at room temperature. By setting the mixing condition within the above range, the magnetic particles are efficiently coated with the resin.

From the viewpoint of enhancing the dispersibility between the magnetic particles and the resin, the above mixing may be carried out in the presence of an organic solvent. In other words, the magnetic powder, the resin, and the organic solvent may be mixed. When mixing is carried out in the presence of an organic solvent, the mixture obtained by mixing at room temperature for 20 to 60 minutes is dried at about 50 to 100 ° C. for 10 minutes to 10 hours to volatilize the organic solvent to prepare the organic solvent. It may be removed. By mixing under the above conditions, the magnetic particles are more efficiently coated with the resin.

The type of organic solvent is not particularly limited. Examples thereof include oils such as mineral oils, synthetic oils and vegetable oils, and organic solvents such as acetone and alcohol.

Further, a mixture of the magnetic powder and the resin is molded to obtain a composite magnetic material. There is no particular limitation on the molding method. For example, the mold of the press machine may be filled with the mixture and compression molded. The conditions for compression molding are not particularly limited, and the bulk density of the mixture, the viscosity of the mixture, the shape of the target composite magnetic material, the dimensions of the target composite magnetic material, the density of the target composite magnetic material, etc. It may be decided as appropriate according to the situation. The molding pressure may be, for example, about 0.5 to 10 ton · f / cm ² or about 1.0 to 6.0 ton · f / cm ² . Further, the holding time at the maximum pressure may be about 0.1 seconds to 1 minute.

Next, the present invention will be described in more detail based on specific examples, but the present invention is not limited to the following examples.

First, the method for producing the magnetic powder and the composite magnetic material in Example 1 of Table 1 below will be described.

(Goethite seed crystal particles)
30 L of a mixed alkaline aqueous solution containing 20 mol of ammonium hydrogen carbonate and 60 mol of aqueous ammonia was prepared. Next, 30 L of the mixed alkaline aqueous solution was put into a reaction tower equipped with a stirrer equipped with a bubble dispersion blade. The stirrer was rotated at a speed of 400 rpm, and the temperature of the mixed alkaline aqueous solution was adjusted to 50 ° C. while aerating nitrogen gas at a flow rate of 60 L / min.

Next, 16 L of a ferrous sulfate aqueous solution containing 1.25 mol / L of Fe in terms of Fe ²⁺ was put into the reaction tower while agitating nitrogen gas at a flow rate of 60 L / min and aged for 30 minutes. Next, 4 L of a cobalt sulfate aqueous solution containing Co ^{2+ in} terms of Co ²⁺ was added and aged for another 3 hours to complete the reaction. Then, air was aerated at a flow rate of 2 L per minute to oxidize a part of Fe ²⁺ contained in the goethite seed crystal particles to prepare a suspension containing the goethite seed crystal particles.

(Goethite particles)
Next, 1 L of an aluminum sulfate aqueous solution containing 1.6 mol / L of Al in terms of Al ³⁺ was newly added into the suspension containing the gateite seed crystal particles and aged for 30 minutes, and the particles were aged on the surface of the gateite seed crystal particles. A gateite layer containing an oxide of Al was grown to generate spindle-shaped gateite particles. Then, a goethite particle-containing slurry was obtained. The pH of the goethite particle-containing slurry at this time was 8.4.

Next, the obtained goethite particle-containing slurry was filtered off to obtain goethite particles. A press filter was used for filtering. Further, the goethite particles filtered out were washed with aqueous ammonia adjusted to pH = 10.5 with ammonia. Then, it was further washed with ion-exchanged water to obtain a press cake of goethite particles.

(Hematite particles)
The press cake of goethite particles obtained in the above step was extruded and molded on a molding plate having a pore size of 3 mm using an extrusion molding machine to obtain a granulated product. The granules were then heated at 120 ° C. for 3 hours and dried. The dried granules were further heated in air at 300 ° C. and dehydrated for 3 hours. Further, it was heated in air at 600 ° C. and dehydrated for 3 hours to obtain a granulated product of hematite particles.

(Magnetic powder)
A magnetic powder was obtained by heating and reducing the granulated product of hematite particles at 500 ° C. for 5 hours in a hydrogen gas atmosphere. The magnetic powder after heat reduction was further subjected to surface oxidation treatment by slow oxidation and taken out into the air.

(Composite magnetic material)
Then, the above magnetic powder, resin and organic solvent were mixed. An epoxy resin was used as the resin. Acetone was used as the organic solvent. The amount of the resin was set so that the volume ratio of the magnetic particles in the finally obtained composite magnetic material became 20 vol%.

The above mixing was carried out at room temperature for 60 minutes using a ball mill. Then, the obtained mixture was dried at 80 ° C. for 3 hours to remove the organic solvent.

Next, a mixture from which the organic solvent had been removed was molded to obtain a molded product. Molding was carried out by filling a mold of a press machine with a mixture from which an organic solvent had been removed and pressurizing the mixture. The pressure at the time of pressurization was set to ² ton f / cm ² , and the holding time at ² ton f / cm ² was set to 10 seconds.

The obtained molded product was thermoset at 180 ° C. for 3 hours to obtain a composite magnetic material. Further, by cutting out the composite magnetic material, a magnetic core for measuring magnetic characteristics was obtained. A rectangular parallelepiped-shaped magnetic core of 1 mm × 1 mm × 100 mm and a toroidal-shaped magnetic core having an outer diameter of 7 mm, an inner diameter of 3 mm, and a thickness of 1 mm were obtained.

Regarding the other examples and comparative examples in Table 1, the average axial ratio, saturation magnetization, coercive force, average major axis diameter, mean value of α, and CV value of α can be changed by appropriately changing the above experimental conditions. , The volume ratio of the magnetic particles and the volume resistance were appropriately changed. The average major axis diameter and the average axis ratio change mainly by changing the amount of Co and the timing of adding the non-magnetic metal. Saturation magnetization changes mainly by changing the contents of Fe, Co and non-magnetic metal. The coercive force changes mainly by changing the average axis ratio and the average major axis diameter. The average value of α changes mainly by changing the amount of ferrous sulfate aqueous solution used and / or the amount of cobalt sulfate aqueous solution used. The CV value of α changes mainly by changing the homogeneity of each ion in the reaction system. The volume ratio of the magnetic particles changes mainly by changing the mixing ratio of the magnetic powder and the resin. The volume resistivity changes mainly by changing the content of the non-magnetic metal. Comparative Example 11 in Table 1 is a comparative example in which an aqueous aluminum sulfate solution was not used.

(Shape of magnetic particles)
The shape of each magnetic particle in the magnetic powder was observed using a transmission electron microscope (JEM-2100FCS manufactured by JEOL Ltd.). Specifically, a plurality of images in which the observation magnification was appropriately set were taken, and 200 or more magnetic particles monodispersed from the plurality of images were randomly selected. Then, the major axis length and the minor axis length of the selected individual magnetic particles were measured, and the average major axis length and the average minor axis length were calculated. Then, the average axis ratio was calculated by dividing the average major axis length by the average minor axis length.

(Α in one magnetic particle)
Point analysis was performed at 10 points on one magnetic particle using STEM-EDX. The observation magnification of STEM was 32000 times, and the beam diameter was 0.5 nm. X1 was calculated by averaging the atomic concentrations of Fe at 10 locations, and X2 was calculated by averaging the atomic concentrations of Co at 10 locations. Then, α in one magnetic particle was calculated from X1 and X2 of one magnetic particle.

(Mean value of α and CV value of α)
Thirty or more magnetic particles contained in the magnetic powder were randomly selected, and α in each magnetic particle was calculated. Then, the average value of α and the standard deviation of α were calculated from α in each magnetic particle. Further, the CV value of α was calculated by dividing the standard deviation of α by the average value of α.

(Magnetic characteristics)
The saturation magnetization and coercive force of the magnetic powder were measured with an external magnetic field of 795.8 kA / m (10 kOe) using a vibrating sample magnetometer (VSM-3S-15 manufactured by Toei Kogyo Co., Ltd.).

μ'r and tan δ were measured by a perturbation method using a network analyzer (N5222A manufactured by Agilent Technologies Co., Ltd.) and a cavity resonator (manufactured by Kanto Electronics Applied Development Co., Ltd.) on the above-mentioned rectangular parallelepiped magnetic core. In this example, μ'r was good at 1.30 or more, and tan δ was good at 0.050 or less.

The resonance frequency and μ ″ r-full width at half maximum were measured by the following method. First, the above toroidal-shaped magnetic core was measured by a coaxial S-parameter method using a network analyzer (N5222A manufactured by Azilent Technology Co., Ltd.). The μ ″ r was measured by changing the frequency from 100 MHz to 18 GHz. Then, the frequency at which μ ″ r is maximized is the resonance frequency, the frequency included in the band below the resonance frequency among the frequencies at which μ ″ r is 1/2 of the maximum value is fr1, and (resonance frequency −fr1) is 2. The value obtained by multiplying was defined as the μ ″ r-half width. In Comparative Example 7, it was confirmed that the resonance frequency exceeded 18 GHz. In this example, the resonance frequency was preferably 10 GHz or higher, and μ ″ r. -The half-value width was set to be good at 9.0 GHz or less, and further improved at 7.0 GHz or less.

(Volume resistivity)
The volume resistivity of the molded product obtained by pressurizing the magnetic powder at 64 MPa and the volume resistivity of the composite magnetic material were measured using a high-performance high resistivity meter Hiresta manufactured by Mitsubishi Chemical Corporation Analytech Co., Ltd.

(Volume ratio of magnetic particles)
First, the cross section obtained by cutting the composite magnetic material was polished to prepare an observation surface. Next, the observation surface was observed using an electron microscope (SEM). The area ratio of the magnetic particles to the area of the entire observation surface was calculated. Then, in the present embodiment, the area ratio and the volume ratio are considered to be equal.

From Table 1, the magnetic cores of the examples within the scope of the present invention were all good in resonance frequency, μ "r-full width at half maximum, μ'r and tan δ.

On the other hand, the magnetic core of the comparative example, which is outside the scope of the present invention, is inferior in any one or more of the resonance frequency, μ "r-full width at half maximum, μ'r and tan δ.

1 ... Magnetic particles 1a ... Ellipse (circumscribing magnetic particles)

Claims (5)

It is a magnetic powder composed of magnetic particles containing Fe and Co as main components.
The magnetic particles contain oxides of one or more elements selected from Mg, Al, Si, Ca, and Y.
The average atomic ratio of Fe in the magnetic particles is X1, the average atomic ratio of Co is X2, X1 / X2 = α, the average value of α is 1.0 or more and 4.0 or less, and the CV value of α is 0. .30 or less,
The average major axis diameter of the magnetic particles is 100 nm or less, and the average axial ratio of the magnetic particles is 6.0 or more and 10.0 or less.
The coercive force of the magnetic powder is 2500 Oe or more, the saturation magnetization of the magnetic powder is 100 Am ² / kg or more, and the volume resistivity of the molded product formed by pressurizing the magnetic powder is 1.0 × 10 ⁴ Ω. -A magnetic powder characterized by being cm or more. A composite magnetic material containing the magnetic powder according to claim 1 and a resin.
The volume ratio of the magnetic particles in the composite magnetic material is 5.0% by volume or more and 50% by volume or less.
Composite magnetic body characterized by a volume resistivity of the composite magnetic body is 1.0 × 10 ⁶ Ω · cm or more. Assuming that the real part of the complex relative permeability at a frequency of 5 GHz is μ'r, the imaginary part of the complex magnetic permeability is μ'r, and tan δ = μ ″ r / μ ′ r, μ ′ r is larger than 1.3 and tan δ. The composite magnetic material according to claim 2, wherein is less than 0.05 and the resonance frequency is 10 GHz or more. A magnetic component using the magnetic powder according to claim 1. A magnetic component using the composite magnetic material according to claim 2 or 3.

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