JPH0677031A - Manufacture of composite ferrite magnetic powder - Google Patents

Abstract

PURPOSE:To obtain a composite ferrite magnetic powder having excellent orientation, high saturation magnetization as well as minor temperature fluctuation in coercive force and low electric resistance of the powder by forming a specific spinel ferrite layer on the surface of specific ferrite powder. CONSTITUTION:The hexagonal system ferrite powder displaying hexagonal platy shape in the crystalline structure having the whole broad peak excluding those on 110 and 220 surface in X-ray diffraction spectrum usin Kalpha rays of Cu are heat-treated. Next, a spinel ferrite layer represented by a general formula of a (M 'O) Fe2O3 (where M' represents exceeding one kind of metallic elements selected out of Co, Ni, Zn, Cu, Mg, Mn and Fe(II) while O<a<=1) is formed on the surface of the ferrite powder. Through these procedures, the title compound ferrite powder having excellent orientation, high saturation magnetization as well as minor temperature fluctuation in coercive force and low electric resistance of the powder can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a new composite ferrite magnetic powder. More specifically, the present invention has a coercive force of 200 to 2000 Oe, which is suitable for use in a magnetic recording medium for high density recording, has improved saturation magnetization as compared with the conventional one, and has a coercive force The present invention relates to a method for producing a composite ferrite magnetic powder having a small temperature change and a low electric resistance of the powder. recent years,
Along with the demand for higher density magnetic recording, a perpendicular magnetic recording system using magnetoplumbite type ferrite magnetic powder as a magnetic recording medium is under development.
Applications such as 8 mm tape and high-definition tape are considered. As magnetoplumbite-type ferrite magnetic powder used in the perpendicular magnetic recording method, one having an appropriate coercive force (200 to 2000 Oe), high saturation magnetization, small temperature change of coercive force, and good orientation Is desired.

[0002]

2. Description of the Related Art Conventionally, various methods such as a coprecipitation method, a glass crystallization method, and a hydrothermal synthesis method are known as methods for producing magnetoplumbite type ferrite magnetic powder. About the chemical method, Japanese Patent Publication Sho 60-155
Japanese Patent Laid-Open No. 59-175, which is disclosed in JP-A-75-175
It is proposed in Japanese Patent No. 707, Japanese Patent Publication No. 60-12973, Japanese Patent Publication No. 60-15576, Japanese Patent Laid-Open No. 60-137002, and the like. However, the magnetoplumbite ferrite magnetic powder obtained by any of the above methods has a saturation magnetization of 6
There were drawbacks such as a low value of 0 emu / g or less and a large change in coercive force with temperature.

On the other hand, the magnetoplumbite type ferrite magnetic powder has a higher electric resistance than the conventional Co-γ-Fe ₂ O ₃ , so that a large amount of a conductive substance is added when it is used as a coating medium. Therefore, there is a problem that the electromagnetic conversion characteristics are deteriorated. As a method for solving these problems, Japanese Patent Laid-Open Nos. 62-139122 and 62-13
No. 9124, No. 62-265122, No. 63-144118, and No. 63-144119, it is proposed to coat the surface of ferrite magnetic powder with spinel ferrite. The ferrite magnetic powder obtained by this, although the various characteristics are actually improved, in order to coat a large amount of spinel type ferrite on the surface of the ferrite magnetic powder,
There is a problem that the orientation of the particles becomes poor, the squareness ratio becomes small when formed into a coating film, and the easy axis of magnetization deviates from the C axis.

[0004]

The object of the present invention is to solve the above problems,
To provide a method for producing a composite ferrite magnetic powder which is fine particles and has a coercive force of 200 to 2000 Oe, a high saturation magnetization, a small change in coercive force with temperature, a low electric resistance of the powder, and an excellent orientation. is there.

[0005]

The present invention relates to Cu Kα
In the X-ray diffraction spectrum using X-rays, hexagonal ferrite particles having a hexagonal plate shape and having a crystal structure in which all peaks except the (110) plane and (220) plane are broad are suspended in water. Turbid, to which the dispersant and C
An aqueous solution containing one or more metal ions selected from o, Ni, Zn, Mg, Mn and Cu and an aqueous solution containing Fe ²⁺ and an alkaline aqueous solution are added, and the resulting mixed suspension is added in an amount of 50 to 2 in a non-oxidizing atmosphere.
After heat treatment at 00 ° C., washing, filtration, and then heat treatment at 100 to 500 ° C. in a non-oxidizing atmosphere, the surface of the ferrite particles is characterized by the general formula a (M′O)
・ Fe ₂ O ₃ (However, M'is Co, Ni, Zn, Cu, Mg, Mn and Fe (II)
One or more metal elements selected from the following, and 0 <a ≦ 1. ) Relates to a method for producing a composite ferrite magnetic powder having a spinel ferrite layer formed therein.

In the composite ferrite magnetic powder of the present invention,
As shown in Fig. 1, the ferrite particles that serve as nuclei are Cu K
Crystal structure in which only two peaks of (110) plane (2Θ = 30.3 °) and (220) plane (2Θ = 62.9 °) are sharp and all other peaks are broad in X-ray diffraction spectrum using α rays Have. As shown in FIG. 2, these peak positions substantially coincide with the peak positions of the X-ray diffraction spectrum of the conventionally known magnetoplumbite ferrite. In the present invention, by changing the crystal structure as described above, the saturation magnetization is improved and the ferrite magnetic powder having a small change in coercive force with temperature is obtained as compared with the conventional magnetoplumbite type ferrite. Also, in order to increase the density of magnetic recording, the particle size is 50n.
It is preferably m or less.

Such ferrite particles are manufactured by the following method. A solution containing A, Fe and M forming the ferrite particles and an alkali hydroxide are mixed so that the concentration of the alkali hydroxide in the solution after mixing is 3 M or more to form a precipitate, and the precipitate is formed. 120 to 3 containing slurry
After hydrothermal treatment at 00 ° C., the slurry containing the precipitate was washed and then treated with an acid to obtain a precipitate having a temperature of 700-700.
By firing at 950 ° C., the ferrite magnetic powder can be obtained.

A is one or more elements selected from Ba, Sr, Ca and Pb. As the compound of A, nitrate, chloride, hydroxide and the like are used. The amount of A used is preferably such that the concentration of A is in the range of 0.03 to 0.50 M in order to obtain particles with good crystallinity. As the Fe compound, nitrates, chlorides and the like are used. The amount of Fe used is preferably 8 to 12 gram atoms per 1 gram atom of A. If the amount of Fe is too small, the amount of ferrite magnetic powder produced is small,
Crystallinity also deteriorates. Further, if the amount of Fe is too large, hematite is by-produced, and the ferrite magnetic powder particles become large, resulting in poor magnetic properties. M is Co, Ni, Zn, Cu, Mg, Mn,
It is one or more elements selected from Fe (II), Bi, Si, Ti, Zr, Sn, Ta, Nb, Mo, V and W. As the compound of M, chloride, nitrate, ammonium salt and the like are used. As the alkali hydroxide, sodium hydroxide, potassium hydroxide or the like is used. The amount of alkali hydroxide used is required to be such that the alkali hydroxide concentration in the solution after mixing the alkali hydroxide is 3 M or more, and preferably in the range of 4 to 8 M.
If the amount of alkali hydroxide is too small, the particles become large, the particle size distribution becomes broad, and hematite is formed. Also, it is not economical to increase the amount of alkali hydroxide excessively.

The method of mixing the solution containing A, Fe and M with the alkali hydroxide is not particularly limited,
For example, there is a method of adding an aqueous solution of alkali hydroxide to a solution containing A, Fe and M. Then, the slurry containing the obtained precipitate is subjected to a hydrothermal treatment to generate and precipitate fine crystals. The temperature of hydrothermal treatment is 120 to 300 ° C. If the temperature is too low, the formation of crystals will not be sufficient, and if the temperature is too high, the particle size of the ferrite powder finally obtained will be large, such being undesirable. Hydrothermal treatment time is normal,
It takes about 0.5 to 20 hours, and an autoclave is usually used for hydrothermal treatment. In the present invention, before the hydrothermal treatment, the precipitate-containing slurry is treated at a temperature of 50 ° C. or lower at 0.5
After aging for ~ 48 hours, a solution containing Bi may be added.
The amount of Bi added is 1 to 5 mol%, preferably 2 to 4 mol%, based on the total amount of Fe and M. By adding Bi, the particle size of the ferrite magnetic powder can be 50 nm or less and the plate ratio can be 5 or less.

Next, the precipitate of fine crystals produced by the hydrothermal treatment is washed with water to remove free alkali,
The slurry containing the precipitate is acid-treated. For acid treatment, nitric acid,
An inorganic acid such as hydrochloric acid or an organic acid such as acetic acid or propionic acid can be used. Due to the acid treatment, the component A mainly in the fine particles is partially eluted. The ratio can be controlled by the conditions such as the addition amount of acid in the acid treatment, temperature and time. Next, the obtained precipitate is washed with water and then baked to obtain a ferrite magnetic powder.

In the firing, it is preferable to mix a flux with the precipitate obtained in advance. As the flux, at least one of sodium chloride, barium chloride, potassium chloride, strontium chloride and sodium fluoride is used. The amount of the flux used is preferably 10 to 180% by weight, more preferably 30 to 120% by weight, based on the precipitate (dry matter basis). If the amount of flux is too small, particle sintering will occur,
Also, if too much, there is no advantage in doing so and it is not economical. The method of mixing the precipitate and the flux is not particularly limited, and for example, the flux may be added to the slurry of the precipitate and wet-mixed, and then the slurry may be dried, or after drying the precipitate,
A flux may be added and dry mixing may be performed. The firing temperature is 700 ~
The temperature is 950 ° C, preferably 800 to 930 ° C. If the temperature is too low, crystallization does not proceed and the saturation magnetization becomes low. On the other hand, if the temperature is too high, particles become large and sintering occurs, which is not preferable. A firing time of about 10 minutes to 30 hours is suitable.

The composite ferrite magnetic powder of the present invention comprises
General formula a (M'O) ・ Fe on the surface of the elite particles₂O₃(However
M'is one selected from Co, Ni, Zn, Cu, Mg, Mn and Fe (II).
It is a metal element of at least one kind, and 0 <a ≦ 1. )
A spinel ferrite layer is formed. Of the present invention
The composite ferrite magnetic powder suspends the ferrite particles in water.
Turbidize it with a dispersant and Co, Ni, Zn, Mg, Mn and Cu
One or more selected metal ions and Fe ²⁺Water containing
Solution and alkaline aqueous solution are added, and the resulting mixed suspension is
After heat treatment at 50 to 200 ° C in an oxidizing atmosphere, wash
Clean, filter, then 100-50 in non-oxidizing atmosphere
Obtained by heat treatment at 0 ° C.

To form the spinel ferrite layer, first, ferrite particles are sufficiently dispersed in water to prepare a suspension solution, to which a dispersant is added in a non-oxidizing atmosphere. An aqueous solution is added and then an alkaline aqueous solution is added to deposit the hydroxide on the surface of the fine particles. Alternatively, the order of adding the metal ion aqueous solution and the alkaline aqueous solution may be reversed. The molar ratio of one or more metal ions selected from Co, Ni, Zn, Mg, Mn and Cu to Fe ²⁺ is preferably 1: 2 to 20, and particularly preferably 1: 3 to 12.

As the dispersant, phosphorus compounds such as sodium metaphosphate and phosphoric acid ester are used. The amount of the dispersant added is 0.1 to the total amount of the metal ions and Fe ^2+.
5 mol% is preferable. The addition of the dispersant improves the orientation of the obtained composite ferrite magnetic powder. Then, the obtained mixed suspension is subjected to 50 to 2 in a non-oxidizing atmosphere.
Heat treatment at 00 ° C. The heat treatment forms a spinel ferrite layer on the surface of the fine particles. Heat treatment is 50
˜200 ° C., but especially at a low temperature of 50 to 120 ° C., the orientation of the obtained particles in the coating film is improved and the squareness ratio is improved. If the heat treatment is insufficient, the amount of spinel ferrite produced will be small, and if it is excessively performed, the characteristics will not be improved. The proportion of the spinel ferrite layer is 5 to 30% by weight, preferably 10 to 20% by weight, based on the ferrite particles. If it is less than this range, the saturation magnetization is high, the change in coercive force with temperature is small, and the electric resistance of the powder cannot be obtained, and if it is more than this range, the orientation of the particles deteriorates, Perpendicular magnetic anisotropy deteriorates.

Further, in the present invention, the spinel ferrite layer may partially contain an oxide of a metal element constituting the spinel ferrite. Then, the obtained powder is heated to 100 to 500 ° C., preferably 1 in a non-oxidizing atmosphere.
Heat treatment is performed at 50 to 400 ° C. The non-oxidizing atmosphere is preferably an inert gas such as nitrogen or helium, or in vacuum. In the present invention, by using the ferrite particles, a spinel ferrite layer is formed on the surface of the ferrite particles with a three-dimensional regularity. As a result, a composite ferrite magnetic powder having a high saturation magnetization, a small change in coercive force with temperature, a small electric resistance, and an excellent orientation can be obtained. Furthermore, by subjecting this magnetic powder to a heat treatment in a non-oxidizing atmosphere, In addition, it is possible to prevent deterioration of various improved characteristics over time.

A magnetic recording medium can be obtained by applying the composite ferrite magnetic powder obtained by the present invention together with a binder resin onto the surface of a support. As the binder resin, for example, vinyl chloride-vinyl acetate copolymer, cellulose derivative, polyurethane resin, epoxy resin or the like is used. Further, as the support, for example, a polyethylene terephthalate film, a polyamide resin film, a polyimide resin film or the like is used. Also,
Further, a dispersant, a lubricant, a curing agent, an abrasive and the like can be added. Examples of the dispersant include lecithin, examples of lubricants include higher fatty acids and fatty acid esters, examples of curing agents include bifunctional or higher functional isocyanate compounds, and examples of abrasives include Cr ₂ O ₃ and Al ₂ O. ₃ , α-Fe ₂ O ₃
Etc. are used. As a method of manufacturing a magnetic recording medium,
A usual method, for example, a method in which magnetic powder, a binder resin, and an additive are kneaded together with a solvent to produce a magnetic coating material, the magnetic coating material is applied to a support, and then an orientation treatment, a drying treatment, and the like are applied.

[0017]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. Example 1 Ferric nitrate 3.251 mol, cobalt nitrate 0.184 mol, titanium tetrachloride 0.061 mol and zinc nitrate 0.184 mol, deionized water 1800
Then, 0.460 mol of barium hydroxide and 37 mol of caustic soda were dissolved in 2000 ml of deionized water, and both solutions were mixed to form a precipitate. Next, the slurry containing the formed precipitate was aged at 20 ° C. for 6 hours, and then bismuth nitrate was adjusted to 0.
A solution of 092 mol dissolved in 50 ml of 2N-HNO ₃ solution was added.
The slurry containing the obtained precipitate was placed in an autoclave,
Hydrothermal treatment was performed at 140 ° C. for 6 hours. Then, the obtained precipitate was thoroughly washed with water, 100 ml of acetic acid was added to make a 0.2N solution, and the mixture was treated at 80 ° C for 2 hours. The precipitate obtained was washed thoroughly with water, filtered and dried. NaCl and BaCl were used as fluxing agents.
The weight ratio of ₂ · 2H ₂ O is 1: 100 relative to the mixture the precipitate of 1
% By weight was added and mixed. This mixture is placed under a nitrogen atmosphere for 8
It was baked at 60 ° C. for 2 hours. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder.

The X-ray diffraction spectrum of the obtained ferrite magnetic powder is 2Θ = 30.3 ° and 2Θ = 6 as shown in FIG.
Only two peaks at 2.9 ° were sharp and all other peaks were broad. The characteristics of this ferrite magnetic powder are as follows: particle size 0.042 μm Plate ratio 3.5 Coercive force 460 Oe Saturation magnetization 64.4 emu / g Temperature change of coercive force 0.2 Oe / ° C Electric resistance of powder compact 1.2 × 10 ⁷ Ω ・It was cm.

100 g of this ferrite magnetic powder was suspended in 1000 ml of water, and 0.00378 mol of sodium metaphosphate was added. Separately, 200 ml of water was added with 0.027 mol of cobalt chloride and ferrous chloride.
After adding a solution in which 0.162 mol was dissolved and thoroughly mixing,
Add a solution of 1.7 mol of caustic soda in 300 ml of water,
It was aged in a nitrogen atmosphere at 20 ° C. to form a spinel ferrite layer of 15% by weight on the surface of the ferrite fine particles. Then
After washing and filtering the obtained slurry, the powder was heat-treated at 400 ° C. for 1 hour in a nitrogen atmosphere. The characteristics of the obtained composite ferrite magnetic powder were coercive force 660 Oe, saturation magnetization 68.8 emu / g, temperature change of coercive force -0.6 Oe / ° C, and electric resistance of the powder compact was 3.2 × 10 ⁴ Ω · cm.

Further, a magnetic coating material having the following composition was prepared using this composite ferrite magnetic powder. Magnetic powder 100 parts by weight PVC-vinyl acetate copolymer 10 parts by weight Polyurethane resin 10 parts by weight Lecithin 2 parts by weight Stearic acid 2 parts by weight Methyl ethyl ketone 70 parts by weight Methyl isobutyl ketone 70 parts by weight Cyclohexanone 70 parts by weight When the squareness ratio of the coating film medium obtained by coating on the surface of a terephthalate film was measured, it was 0.60.

Example 2 3.251 mol of ferric nitrate, 0.368 mol of cobalt nitrate and 0.061 mol of titanium chloride were dissolved in 1800 ml of deionized water, and separately, 0.460 mol of barium hydroxide and 37 mol of caustic soda were dissolved in 2000 ml of deionized water. The two solutions were mixed to form a precipitate. Next, the slurry containing the formed precipitate was aged at 20 ° C. for 6 hours, and then a solution prepared by dissolving 0.092 mol of bismuth nitrate in 50 ml of 2N-HNO ₃ solution was added. The slurry containing the obtained precipitate was placed in an autoclave and hydrothermally treated at 140 ° C. for 6 hours. Then, the obtained precipitate was thoroughly washed with water, nitric acid was added to make a 0.1 N solution, and the mixture was treated at 70 ° C. for 3 hours. The precipitate obtained was washed thoroughly with water, filtered and dried, and the weight ratio of NaCl to BaCl ₂ .2H ₂ O as a flux was 1: 1.
100% by weight of the mixture of 1 was added and mixed. The mixture was calcined under a nitrogen atmosphere at 870 ° C. for 2 hours. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder.

In the X-ray diffraction spectrum of the obtained ferrite magnetic powder, only two peaks at 2Θ = 30.3 ° and 2Θ = 62.9 ° were sharp, and all other peaks were broad.
The characteristics of this ferrite magnetic powder are as follows: particle size 0.040 μm Plate ratio 3.7 Coercive force 450 Oe Saturation magnetization 62.6 emu / g Coercive force temperature change 0.3 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm. Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1. The characteristics of the obtained composite ferrite magnetic powder were coercive force 670 Oe, saturation magnetization 67.8 emu / g, coercive force temperature change -0.6 Oe / ° C, and electric resistance of the powder compact was 3.1 × 10 ⁴ Ω · cm. Also, using this composite ferrite magnetic powder,
A coating medium was prepared in the same manner as in Example 1. The squareness ratio of this medium was measured and found to be 0.59.

Example 3 Ferrite magnetic powder was obtained in the same manner as in Example 1 except that bismuth nitrate was not added. The X-ray diffraction spectrum of the obtained ferrite magnetic powder is 2θ.
= Only two peaks at 30.3 ° and 2Θ = 62.9 ° are sharp,
All other peaks were broad. The characteristics of this ferrite magnetic powder are as follows: particle size 0.062 μm Plate-like ratio 7.5 Coercive force 450 Oe Saturation magnetization 64.2 emu / g Temperature change of coercive force 0.2 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm.

Example 1 using this ferrite magnetic powder
In the same manner as above, a spinel ferrite layer was formed on the surface of the ferrite fine particles. The properties of the obtained composite ferrite magnetic powder were coercive force 670 Oe, saturation magnetization 68.1 emu / g, coercive force temperature change -0.6 Oe / ° C, and electric resistance of the powder compact was 3.1 × 10 ⁴ Ω · cm. Also, using this composite ferrite magnetic powder,
A coating medium was prepared in the same manner as in Example 1. The squareness ratio of this medium was measured and found to be 0.70.

Example 4 A ferrite magnetic powder was obtained in the same manner as in Example 2 except that bismuth nitrate was not added. The X-ray diffraction spectrum of the obtained ferrite magnetic powder is 2θ.
= Only two peaks at 30.3 ° and 2Θ = 62.9 ° are sharp,
All other peaks were broad. The characteristics of this ferrite magnetic powder are as follows: particle size 0.070 μm Plate ratio 6.7 Coercive force 440 Oe Saturation magnetization 62.2 emu / g Coercive force temperature change 0.3 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm.

Using this ferrite magnetic powder, Example 1
In the same manner as above, a spinel ferrite layer was formed on the surface of the ferrite fine particles. The characteristics of the obtained composite ferrite magnetic powder were a coercive force of 670 Oe, a saturation magnetization of 67.6 emu / g, and a change of coercive force with temperature of -0.6 Oe / ° C. The electric resistance of the powder compact was 3.9 × 10 ⁴ Ω · cm. Also, using this composite ferrite magnetic powder,
A coating medium was prepared in the same manner as in Example 1. The squareness ratio of this medium was measured and found to be 0.69.

Comparative Example 1 Ferrite magnetic powder was obtained in the same manner as in Example 3, except that the acid treatment was not performed. The X-ray diffraction spectrum of the obtained ferrite magnetic powder is shown in FIG. The characteristics of this ferrite magnetic powder are as follows: particle size 0.061 μm Plate-like ratio 7.7 Coercive force 460 Oe Saturation magnetization 58.2 emu / g Coercive force temperature change 2.9 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm.

Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1 except that no dispersant was added. The characteristics of the obtained composite ferrite magnetic powder were a coercive force of 570 Oe, a saturation magnetization of 60.1 emu / g, and a change of coercive force with temperature of 1.6 Oe / ° C. The electric resistance of the powder compact was 6.1 × 10 ⁶ Ω · cm. Also, using this composite ferrite magnetic powder,
A coating medium was prepared in the same manner as in Example 1. The squareness ratio of this medium was measured and found to be 0.62.

Comparative Example 2 A ferrite magnetic powder was obtained in the same manner as in Example 4, except that the acid treatment was not carried out. The characteristics of the obtained ferrite magnetic powder are as follows: particle size 0.072 μm Plate-like ratio 6.5 Coercive force 410 Oe Saturation magnetization 56.1 emu / g Temperature change of coercive force 3.2 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm.

Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1 except that no dispersant was added. The characteristics of the obtained composite ferrite magnetic powder were coercive force 530 Oe, saturation magnetization 58.1 emu / g, coercive force temperature change 1.6 Oe / ° C, and the electric resistance of the powder compact was 5.8 × 10 ⁶ Ω · cm. Also, using this composite ferrite magnetic powder,
A coating medium was prepared in the same manner as in Example 1. The squareness ratio of this medium was measured and found to be 0.61.

Comparative Example 3 A spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1 except that the ferrite magnetic powder obtained in Example 1 was used and no dispersant was added. Using this composite ferrite magnetic powder, a coating medium was prepared in the same manner as in Example 1. The squareness ratio of this medium was measured and found to be 0.52.

[0032]

EFFECT OF THE INVENTION The composite ferrite magnetic powder obtained by the present invention has dramatically improved saturation magnetization as compared with the conventional one, and further has a small change in coercive force with temperature and a small electric resistance of the powder. It has excellent dispersibility and is suitable for use as a magnetic recording material for high density recording.

[Brief description of drawings]

FIG. 1 is a diagram showing an X-ray diffraction spectrum of a ferrite magnetic powder obtained in Example 1 of the present invention.

FIG. 2 is a diagram showing an X-ray diffraction spectrum of the ferrite magnetic powder obtained in Comparative Example 1 of the present invention.

Claims (2)

[Claims] 1. A hexagonal plate having a hexagonal plate-like structure having a crystal structure in which all peaks except broad peaks of (110) plane and (220) plane in an X-ray diffraction spectrum using Kα ray of Cu are broad. Crystalline ferrite particles are suspended in water, to which a dispersant and an aqueous solution containing at least one metal ion selected from Co, Ni, Zn, Mg, Mn, and Cu and Fe ²⁺ and an alkaline aqueous solution are added. The obtained mixed suspension is heat-treated at 50 to 200 ° C. in a non-oxidizing atmosphere and then washed,
Filter, then 100-500 ° C in non-oxidizing atmosphere
The surface of the ferrite particles is characterized by being heat-treated with the general formula a (M'O) .Fe ₂ O ₃ (where M'is Co, Ni, Z
One or more metal elements selected from n, Cu, Mg, Mn and Fe (II), and 0 <a ≦ 1. The manufacturing method of the composite ferrite magnetic powder in which the spinel ferrite layer represented by this is formed. 2. The method for producing a composite ferrite magnetic powder according to claim 1, wherein the ferrite particles have a particle diameter of 50 nm or less and a plate ratio of 5 or less.