JPH0582325A - Composite oxide magnetic powder and optomagnetic recording medium using the same - Google Patents

Abstract

PURPOSE:To provide composite oxide magnetic powder to be desirably used for an optical isolator, an optical circulator, an optical switch, an optical waveguide, an optical memory, etc., and an optomagnetic recording medium having high density recording, large S/N ratio and excellent productivity in which a magnetooptical effect is large and optical permeability is excellent and particularly influence of miniaturization to a surface layer is small. CONSTITUTION:Composite oxide magnetic powder represented by a general formula RaBibFecMdOe (where R is one or more types of rare earth elements selected from a group consisting of Y and lanthanum series elements, M is one or more elements selected from a group consisting of Al, Ga, Cr, Mn, Sc, In, Ru, Rh, Co, Fe(II), Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Pb, Mo, V, Nb and Ta) wherein the surfaces of rare earth element iron garnet fine particles having an average particle size of 30-1000Angstrom are covered with silica, and an optomagnetic recording medium comprising a magnetic layer made of the composite oxide magnetic powder and binder provided on a board.

Description

Detailed Description of the Invention

[0001]

The present invention has excellent magneto-optical characteristics,
The present invention relates to a composite oxide magnetic powder suitable for applications such as an optical isolator, an optical circulator, an optical switch, an optical waveguide, and an optical memory, and a magneto-optical recording medium using the same.

[0002]

2. Description of the Related Art Heretofore, as a magnetic material having an excellent magneto-optical effect, one made of an amorphous alloy of a rare earth metal and a transition metal has been known. However, the magnetic material made of such an amorphous alloy is susceptible to oxidative corrosion and has a drawback that the magneto-optical characteristics are deteriorated. Further, since the amorphous alloy has low light transmittance, the magneto-optical effect (Kerr effect) due to the reflection on the surface is used. However, the amorphous alloy generally has a small Kerr rotation angle, which causes a problem of low sensitivity. there were.

On the other hand, Japanese Patent Publication No. 56-15125 proposes a magneto-optical material using a garnet polycrystalline oxide thin film. A magnetic material using this oxide has excellent corrosion resistance and has an advantage of high sensitivity because reproduction is performed by utilizing the magneto-optical effect (Faraday effect) due to the transmitted light of the magnetic film. However, since it is polycrystalline, there is a drawback that noise increases due to light scattering at the grain boundaries, birefringence, and domain wall motion.

Further, when the above-mentioned magnetic thin film is formed on a substrate, there is a problem that only a substrate having heat resistance can be used because the production temperature is as high as 500 ° C. or higher.

On the other hand, Japanese Patent Application Laid-Open No. 62-119758 discloses a coating type magneto-optical recording material using yttrium iron garnet particles. In such a coating type medium, there is no adverse effect of the crystal grain boundary like the polycrystalline oxide thin film, but the garnet particles described in the publication are:
Since the particle diameter is as large as 1.5 μm and light is scattered when such particles are used, it is not suitable for the use of light of submicron wavelength.

Therefore, the present applicant has proposed rare earth iron garnet fine particles having an average particle diameter of 30 to 1000 Å as a magnetic powder suitable for the use of light of submicron wavelength without scattering of light. (JP-A-3-159
No. 915)

However, when the particle diameter is reduced to 1000 Å or less, the influence of the surface layer of the particles becomes large, and there is a problem that the original magnetic characteristics are not sufficiently exhibited as compared with the bulk material. Furthermore, when a thermal decomposition product such as a nitrate is used as a binder when it is used as a medium, there is a problem that the preparation process of the binder is complicated due to poor acid resistance.

[0008]

It is an object of the present invention to solve the above problems, excellent corrosion resistance, large magneto-optical effect, excellent light transmittance, and less influence of surface layer due to atomization, optical isolator, optical circulator, optical An object of the present invention is to provide a composite oxide magnetic powder suitable for applications such as switches, optical waveguides, and optical memories, and a method for producing the same.

Further, the present invention enables high density recording,
It is an object to provide a magneto-optical recording medium having a large S / N ratio and excellent productivity.

[0010]

[Means for solving problems]

The present invention have the general formula _{R a Bi b Fe c M d} O e ( wherein, R represents one or more rare earth elements selected from the group consisting of Y and lanthanides, M is Al, Ga, Cr, M
n, Sc, In, Ru, Rh, Co, Fe (II), Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, H
f, Sn, Pb, Mo, V, Nb, and Ta represent one or more elements selected from the group consisting of a + b + c + d = 7.0 to 8.0,
a + b = 2.0 to 3.5, c + d = 4.0 to 6.0, a
= 0.5-3.5, b = 0-2.5, c = 3.0-6.
0, d = 0 to 2.0, and e is the number of oxygen atoms satisfying the valences of other elements. ), And a rare earth iron garnet fine particle having an average particle diameter of 30 to 1000Å coated with silica on the surface thereof, to a composite oxide magnetic powder.

The present invention also relates to a magneto-optical recording medium characterized in that a magnetic layer comprising the above-mentioned composite oxide magnetic powder and a binder is provided on a substrate.

As the rare earth iron garnet fine particles in the present invention, garnet represented by R ₃ Fe ₅ O ₁₂ or the garnet in which a part of the rare earth element is replaced with Bi, and / or a part of Fe is M. The one replaced with is used.

R in the above general formula is Y, La, Ce, Pr, N
One or more rare earth elements selected from the group consisting of d, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Further, M is an element capable of substituting for iron, and Al, Ga, Cr, Mn, Sc, In, Ru, Rh, C
o, Fe (II), Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Pb, Mo, V,
Indicates one or more elements selected from the group consisting of Nb and Ta. Among M elements, trivalent elements Al, Ga, Cr, Mn, Sc, In, Ru, R
h and Co are independently divalent elements Co, Fe, Cu, Ni and Zn, or monovalent elements Li are tetravalent elements Si, Ge, Zr, Ti, Hf, Sn, Pb and Mo, or 3 in combination with pentavalent elements V, Nb and Ta
Substitution as an element equivalent to valence is preferable.

The proportions of the respective elements in the above general formula are a + b + c + d = 7.0 to 8.0 and a + b = 2.0.
.About.3.5, c + d = 4.0 to 6.0, a = 0.5 to 3.
5, b = 0 to 2.5, c = 3.0 to 6.0, d = 0
2.0, and e is the number of oxygen atoms satisfying the valences of other elements.

In the present invention, the Faraday rotation angle can be increased by substituting a part of the rare earth element of garnet with Bi of preferably 0.2 to 2.5.
Further, by substituting part of iron with M of preferably 0.3 to 2.0, the Curie temperature can be lowered and the saturation magnetization can be reduced. Further, in the present invention, a part of R of the rare earth iron garnet fine particles further comprises Pb, Ca, Mg
May be substituted with a divalent element such as
Charge compensation may be performed with a valent or pentavalent element.

The average particle diameter of the rare earth iron garnet fine particles in the present invention is 30 to 1000Å, preferably 100 to
It is 600Å. If the average particle size is smaller than 30Å, it becomes superparamagnetic due to thermal agitation. Also, 10
When it is larger than 00Å, light scattering occurs and noise is generated, which is not preferable. Further, the particle shape is preferably optically symmetrical, and preferably spherical, but may be polyhedral or amorphous.

The composite oxide magnetic powder of the present invention is obtained by coating the surface of the rare earth iron garnet fine particles with silica. The coating amount of silica may be such that the entire surface of the rare earth iron garnet fine particles is coated, but the thickness of the coating layer is usually 5 to 40Å, preferably 10 to 30Å. For example, for particles having an average particle size of 400 to 500Å, the range of 0.5 to 15 wt% in terms of SiO ₂ weight is preferable. When the coating amount of silica is less than the above range,
There is no effect of improving the magnetic properties, and when the amount is more than the above range, the magnetic properties are no longer improved, and on the contrary, the ratio of the rare earth iron garnet fine particles decreases, and the magnetic properties deteriorate.

In the present invention, the reason why the magnetic characteristics are improved by coating the surface of the fine particles of rare earth iron garnet with silica is that, as shown in FIG. 1, the surface layer of the fine solid particles has a non-magnetic region. Are present, which reduces the magnetic properties of the entire particle. On the other hand, in the composite oxide magnetic particles in which the surface of the fine particles of the present invention is coated with silica, it is considered that the non-magnetic region of the particle surface layer is reduced and therefore the magnetic properties are improved. Furthermore, since the surface of the fine particles of the composite oxide magnetic powder of the present invention is coated with silica, the acid resistance is also improved.

The method for producing the fine particles of the rare earth iron garnet is not particularly limited as long as the particles having the above-mentioned characteristics can be obtained, and the hydrothermal synthesis method, the coprecipitation method, the melting method, the alkoxide method, the vapor phase method and the like are produced. A method is used.

The method for producing rare earth iron garnet fine particles by the coprecipitation method will be described below. A precipitate is prepared by mixing a solution containing each element ion selected in a ratio that constitutes the rare earth iron garnet represented by the general formula with an alkali so that the alkali concentration after mixing is 0.1 to 8M. And rare earth iron garnet fine particles are obtained by calcining the precipitate at 600 to 900 ° C.

The solution containing each element ion can be obtained by dissolving a compound of each element, for example, a nitrate, a sulfate or a chloride in a solvent. As the solvent, it is sufficient that the compound of each element is dissolved, usually, water, alcohols,
Ethers and mixed solvents thereof are used.

The solution containing each of the elemental ions has a total ion concentration of 0.01-2.
It is desirable to prepare it so that it becomes 0M. If the total ion concentration is less than 0.01 M, the amount of garnet produced is small, and if it is more than 2.0 M, the particles become large and a heterogeneous phase is produced, which is not preferable.

The proportion of each element ion can be the proportion of each element constituting the rare earth iron garnet represented by the above general formula, but R and Bi are 10 mol% more than the necessary amount. It may be used in an excessive amount up to a certain degree.

As the alkali, sodium hydroxide, potassium hydroxide, aqueous ammonia, diethylamine, ethanolamine and the like are used. The amount of alkali used is such that the alkali concentration in the solution after mixing the alkali is 0.1 to 8
It should be chosen to be M, preferably 0.5-2M. If the amount of alkali is too small, the particles produced will become large and unreacted substances will remain. In addition, it is not economical to use too much alkali.

As a method of mixing the solution containing each element ion and the alkali, for example, there is a method of adding the solution containing each element ion to an aqueous solution of alkali, or a method of continuously mixing both. The precipitation may be performed at once or in multiple stages.

Next, the precipitate obtained is washed with water to remove free alkali components, filtered, dried and calcined to obtain rare earth iron garnet fine particles. Although the firing temperature varies depending on the composition of the rare earth iron garnet, it can usually be set in the range of 600 to 900 ° C. If the firing temperature is too low, crystallization will not be sufficient, and if the temperature is too high, particles will become large and sintering will occur, which is not preferable. A firing time of 10 minutes to 30 hours is suitable.
The firing atmosphere is not particularly limited, but an air atmosphere is generally convenient.

In the present invention, the composite oxide magnetic powder is obtained by coating the surface of the rare earth iron garnet fine particles with silica. The silica is coated by depositing, adsorbing or dipping the silicon compound on the fine particles of rare earth iron garnet, and then heat-treating the treated product at a temperature of 300 to 600 ° C. As the silicon compound, water glass, sodium metasilicate, silane coupling agent, silicone oil or the like is used. The heat treatment temperature is 300 to
It is in the range of 600 ° C. If the heat treatment temperature is lower than 300 ° C, the bond between SiO ₂ and the rare earth iron garnet particles will be weak,
Magnetic properties are not improved. On the other hand, if the temperature is higher than 600 ° C., diffusion of silicon occurs and the magnetic characteristics are deteriorated.

The composite oxide magnetic powder of the present invention is excellent in corrosion resistance, has a large magneto-optical effect, excellent light transmittance, and is less affected by the surface layer due to atomization, and is an optical isolator, an optical circulator, an optical switch, an optical switch. It is preferably used for applications such as waveguides and optical memories.

Further, in the present invention, a magneto-optical recording medium can be obtained by providing a magnetic layer comprising the above-mentioned composite oxide magnetic powder and a binder on the substrate.

As the binder, an amorphous inorganic oxide binder or an organic binder is used. As the inorganic binder, a nitrate aqueous solution according to the garnet composition,
A deflocculation product of a coprecipitated neutralized product conforming to the garnet composition, a metal alcoholate, a silanol compound and its derivative, an organic silicon compound, an amorphous inorganic oxide produced by heat-treating an acetylacetone metal salt, molten glass, etc. Is mentioned.

As the organic binder, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinylidene chloride copolymer, a cellulose derivative such as a nitrocellulose resin, an acrylic resin, a polyvinyl butyral resin, an epoxy resin, a polyurethane resin, or a phenoxy resin. Resin, polyester resin, phenol resin, polyamide resin, melamine resin and the like can be mentioned.

In particular, in order to reduce noise due to light scattering, it is desirable that the refractive index of the binder matches the refractive index of the rare earth iron garnet fine particles, and the deviation from the refractive index of the rare earth iron garnet fine particles is ± 20% or less. In particular, it is preferably ± 10% or less.

The thickness of the magnetic layer is 0.05 to 2.0 μm,
In particular, the range of 0.2 to 1.0 μm is preferable in terms of the stability of recorded bits.

The magnetic layer is prepared by dissolving or dispersing the composite oxide magnetic powder and the binder in water or an organic solvent to prepare a magnetic coating material, applying this on a substrate, and then curing the binder by heat treatment or the like. It is formed.

At this time, stress is applied to the composite oxide magnetic fine particles due to curing of the binder, so that the magnetization of the composite oxide magnetic fine particles can be aligned in the direction perpendicular to the substrate. In addition, orientation processing such as magnetic field orientation may be performed.

The substrate is not particularly limited, and a single crystal substrate, a polycrystal substrate, an amorphous substrate such as glass, an inorganic material substrate such as a composite substrate, an acrylic resin, a polycarbonate resin, a polyester resin, a polyamide resin, An organic material substrate such as a polyimide resin can be used.

A light reflection layer may be provided between the substrate and the magnetic layer or on the magnetic layer. As the light reflection layer, C
u, Cr, Al, Ag, Au, TiN, etc. are used. This light reflection layer is
It is formed on the substrate or on the magnetic layer by a coating method, a plating method, a vapor deposition method, or the like.

[0038]

The present invention will be described in more detail with reference to the following examples. Examples 1 to 3 and Comparative Example 1 1.93 mol of ammonia was dissolved in 80 ml of water, and separately, 0.020 mol of bismuth nitrate, 0.040 mol of dysprosium nitrate, and iron nitrate of 0.
096 mol and 0.004 mol of aluminum nitrate in 5N-nitric acid solution 2
It was dissolved in 20 ml. Then, the nitric acid solution was gradually added dropwise to the ammonia solution while stirring to neutralize the solution, thereby forming a precipitate. After washing the obtained precipitate with water, filtering and drying,
A mixture having a molar ratio of NaCl: LiCl = 3: 7 as a flux was mixed with the precipitate in an amount of 100 wt% and the mixture was calcined at 690 ° C.
The obtained fired product was washed with water to remove the flux, filtered and dried to obtain garnet fine particles. The obtained garnet fine particles had an average particle diameter of 450Å, and as a result of X-ray powder diffraction spectrum and composition analysis, Bi ₁ Dy ₂ Fe _4.8 Al _0.2 O
_{It was 12} , and it was a garnet single phase.

No. 4 water glass was added to the slurry in which the obtained garnet fine particles were dispersed by acidification with acetic acid, and then the slurry was neutralized with ammonia to adsorb silica on the surface of the garnet fine particles. Then, after filtration and drying,
Heat treatment was performed at 400 ° C. to obtain a composite oxide magnetic powder. Table 1 shows the results of measuring the saturation magnetization of the obtained composite oxide magnetic powder. It can be seen that the magnetic properties of the garnet particles are improved by coating with silica. Also,
The result of measuring the elution amount of the obtained composite oxide magnetic powder with respect to concentrated nitric acid is shown in FIG. 2 for the elution amount of Fe. It can be seen that the acid resistance of the garnet fine particles is improved by coating with silica.

Example 4 3.61 mol of ammonia was dissolved in 750 ml of water, and separately, 0.04 mol of bismuth nitrate, 0.08 mol of dysprosium nitrate and iron nitrate were dissolved.
0.18 mol and 0.02 mol of aluminum nitrate in 5N nitric acid solution
Dissolved in 400 ml. Then, the nitric acid solution was gradually added dropwise to the ammonia solution while stirring to neutralize the solution, thereby forming a precipitate. After the obtained precipitate was washed with water, filtered and dried, 25 wt% of a mixture having a molar ratio of KBr: KI = 1: 1 as a flux was mixed with the precipitate, and the mixture was calcined at 670 ° C. The obtained fired product was washed with water to remove the flux, filtered and dried to obtain garnet fine particles. The obtained garnet fine particles had an average particle diameter of 440Å, and as a result of X-ray powder diffraction spectrum and composition analysis, Bi ₁ Dy ₂ Fe _4.5 Al _0.5 O ₁₂
And was a garnet single phase.

The obtained garnet fine particles were dispersed in acetic acid and the slurry was mixed with No. 4 water glass in an amount of 6.82 wt% based on the weight of SiO ₂ with respect to the fine particles, and the slurry was neutralized with ammonia to give silica to garnet. The particles were adsorbed on the surface. Then, after filtration and drying, heat treatment was performed at 400 ° C. to obtain a composite oxide magnetic powder. The saturation magnetization of the obtained composite oxide magnetic powder was increased by 7% as compared with the garnet fine particles before being coated with silica.

Next, this composite oxide magnetic powder was mixed with bismuth nitrate, yttrium nitrate and ferric nitrate to Bi: Y: Fe.
It was added to an aqueous solution containing a molar ratio of 28:10:62 and sufficiently dispersed, and then coated on a glass substrate having a diameter of 3 inches and a thickness of 1 mm. Then, by thermally decomposing at 250 ° C., an amorphous BiYFe oxide film containing the composite oxide magnetic powder was formed. The thickness of the obtained film was 0.5 μm. A magneto-optical recording medium was obtained by forming a reflection film of aluminum on this coating film by a vapor deposition method.

633 in the direction perpendicular to the film surface of the obtained medium
The Faraday rotation angle with respect to nm light was measured by a polarization plane modulation method and found to be 1.0 deg. The S / N ratio of this medium was evaluated to be 50 dB.

Example 5 3.61 mol of ammonia was dissolved in 750 ml of water, and separately, 0.068 mol of bismuth nitrate, 0.052 mol of dysprosium nitrate and iron nitrate were dissolved.
0.160 mol and 0.040 mol of aluminum nitrate in 5N nitric acid solution
Dissolved in 400 ml. Then, the nitric acid solution was gradually added dropwise to the ammonia solution while stirring to neutralize the solution, thereby forming a precipitate. The obtained precipitate was washed with water, filtered and dried, and then a mixture having a molar ratio of KBr: KI = 1: 1 was mixed as a fluxing agent in an amount of 50 wt% with respect to the precipitate, and the mixture was calcined at 670 ° C. The obtained fired product was washed with water to remove the flux, filtered and dried to obtain garnet fine particles. The obtained garnet fine particles had an average particle size of 380Å, and as a result of X-ray powder diffraction spectrum and composition analysis, Bi _1.7 Dy _1.3 Fe ₄ Al ₁ O ₁₂
And was a garnet single phase.

To the slurry in which the obtained garnet fine particles were dispersed in acetic acid, 3.98 wt% of No. 4 water glass was mixed with the fine particles in terms of SiO ₂ weight, and the slurry was neutralized with ammonia to give silica garnet. The particles were adsorbed on the surface. Then, after filtration and drying, heat treatment was performed at 400 ° C. to obtain a composite oxide magnetic powder. The saturation magnetization of the obtained composite oxide magnetic powder was increased by 12% as compared with the garnet fine particles before being coated with silica.

Next, this composite oxide magnetic powder was mixed with bismuth nitrate, yttrium nitrate, and ferric nitrate into Bi: Y: Fe.
It was added to an aqueous solution containing a molar ratio of 28:10:62 and sufficiently dispersed, and then coated on a glass substrate having a diameter of 3 inches and a thickness of 1 mm. Then, by thermally decomposing at 250 ° C., an amorphous BiYFe oxide film containing the composite oxide magnetic powder was formed. The thickness of the obtained film was 0.5 μm. A magneto-optical recording medium was obtained by forming a reflection film of aluminum on this coating film by a vapor deposition method.

633 in the direction perpendicular to the film surface of the obtained medium
The Faraday rotation angle with respect to nm light was measured by a polarization plane modulation method and found to be 1.7 deg. The S / N ratio of this medium was evaluated to be 52 dB.

Example 6 3.34 mol of diethylamine was dissolved in 750 ml of water, and separately, 0.040 mol of bismuth nitrate, 0.080 mol of dysprosium nitrate, 0.188 mol of iron nitrate, 0.008 mol of cobalt nitrate and 0.004 mol of vanadium sulfate oxide were added to 400 ml of 5N-nitric acid solution. Dissolved. Then, while the diethylamine solution was stirred, a nitric acid solution was gradually added dropwise for neutralization to form a precipitate. The precipitate obtained was washed with water, filtered and dried, and then used as a fluxing agent in KBr: KI.
= 1: 1 molar ratio of the mixture to the precipitate 25 wt%,
The mixture was calcined at 700 ° C. The obtained fired product was washed with water to remove the flux, filtered and dried to obtain garnet fine particles. The obtained garnet fine particles have an average particle diameter of 430.
Further, as a result of X-ray powder diffraction spectrum and composition analysis, it was Bi ₁ Dy ₂ Fe _4.7 Co _0.2 V _0.1 O ₁₂ , and it was a garnet single phase.

The resulting garnet fine particles were dispersed in acetic acid and the slurry was mixed with No. 4 water glass in an amount of 5.28 wt% based on the weight of SiO ₂ of the fine particles. The slurry was neutralized with ammonia to give silica garnet. The particles were adsorbed on the surface. Then, after filtration and drying, heat treatment was performed at 400 ° C. to obtain a composite oxide magnetic powder. The saturation magnetization of the obtained composite oxide magnetic powder was increased by 10% as compared with the garnet fine particles before being coated with silica.

Next, this composite oxide magnetic powder was mixed with bismuth nitrate, yttrium nitrate, and ferric nitrate into Bi: Y: Fe.
It was added to an aqueous solution containing a molar ratio of 28:10:62 and sufficiently dispersed, and then coated on a glass substrate having a diameter of 3 inches and a thickness of 1 mm. Then, by thermally decomposing at 250 ° C., an amorphous BiYFe oxide film containing the composite oxide magnetic powder was formed. The thickness of the obtained film was 0.5 μm. A magneto-optical recording medium was obtained by forming a reflection film of aluminum on this coating film by a vapor deposition method.

633 in the direction perpendicular to the film surface of the obtained medium
The Faraday rotation angle with respect to the light of nm was 1.1 deg when measured by the polarization plane modulation method. The S / N ratio of this medium was evaluated to be 55 dB.

Comparative Example 2 The silica-free garnet fine particle powder obtained in Comparative Example 1 contained bismuth nitrate, yttrium nitrate and ferric nitrate in a molar ratio of Bi: Y: Fe = 28: 10: 62. It was added to an aqueous solution and sufficiently dispersed, and then coated on a glass substrate having a diameter of 3 inches and a thickness of 1 mm. Then 2
An amorphous BiYFe oxide film containing garnet fine particle powder was formed by thermal decomposition at 50 ° C. The thickness of the obtained film was 0.5 μm. A magneto-optical recording medium was obtained by forming a reflection film of aluminum on this coating film by a vapor deposition method.

633 in the direction perpendicular to the film surface of the obtained medium
The Faraday rotation angle with respect to nm light was measured by a polarization plane modulation method, and was found to be 0.9 deg. The S / N ratio of this medium was evaluated to be 45 dB.

[0054]

The composite oxide magnetic powder of the present invention is excellent in corrosion resistance, has a large magneto-optical effect, and is excellent in light transmittance, and is suitable for applications such as optical isolators, optical circulators, optical switches, optical waveguides, and optical memories. Used for. In particular, the influence of the surface layer due to atomization is small, and the magnetic properties such as saturation magnetization and Faraday rotation angle are improved. Furthermore, it has excellent acid resistance. Further, the magneto-optical recording medium using the composite oxide magnetic powder of the present invention is excellent in corrosion resistance, has a large magneto-optical effect, has a large S / N ratio, and is suitable for high-density magneto-optical recording. Furthermore, it can be manufactured by a coating method,
The productivity is also good.

[Brief description of drawings]

FIG. 1 is a schematic view showing a state of a surface layer of garnet fine particles with and without a silica coating layer.

FIG. 2 is a diagram showing the relationship between the thickness of the silica coating layer and the elution amount of Fe with respect to concentrated nitric acid in the composite oxide magnetic powder of the present invention.

[Table 1]

Claims (3)

[Claims] 1. A compound represented by the general formula R _a Bi _b Fe _c M _d O _e (wherein R represents one or more rare earth elements selected from the group consisting of Y and lanthanum series elements, and M represents Al, Ga, Cr, M).
n, Sc, In, Ru, Rh, Co, Fe (II), Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, H
f, Sn, Pb, Mo, V, Nb, and Ta represent one or more elements selected from the group consisting of a + b + c + d = 7.0 to 8.0,
a + b = 2.0 to 3.5, c + d = 4.0 to 6.0, a
= 0.5-3.5, b = 0-2.5, c = 3.0-6.
0, d = 0 to 2.0, and e is the number of oxygen atoms satisfying the valences of other elements. ) And having a mean particle size of 30 to 1000Å, rare earth iron garnet fine particles coated with silica on the surface thereof, a composite oxide magnetic powder. 2. The rare earth iron garnet fine particles according to claim 1, after depositing, adsorbing or immersing a silicon compound, the treated product is heat-treated at a temperature of 300 to 600 ° C. Method for producing composite oxide magnetic powder. 3. A magneto-optical recording medium comprising a magnetic layer comprising the composite oxide magnetic powder according to claim 1 and a binder provided on a substrate.