JPH0669018A - Manufacture of compound ferrite magnetic powder - Google Patents

Abstract

PURPOSE:To use the compound ferrite magnetic particles as a pertinent magnetic recording material for high density recording wherein the saturation magnetization is rapidly enhanced compared with conventional one having small temperature fluctuation in coercive force, lower electric resistance as well as the particle diameter and platy structure ratio exceeding specific value. CONSTITUTION:The ferrite fine particles represented by a general formula of AO.n (Fe12-x-ySbxMyO18-z) are suspended in water whereto water solution and alkali water solution containing a dispersing agent and exceeding one kind of metallic ions and Fe<2+> selected from Co, Ni, Zn, Mg, Mn and Cu are added and then the resultant mixed suspension is heat-treated at 50-200 deg.C in non-oxidative atmosphere and then washed and filtered to be heat-treated again at 100-500 deg.C in the non-oxidative atmosphere.

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 temperature of The change is small, the electric resistance of the powder is small, and the particle size is 50.
The present invention relates to a method for producing a composite ferrite magnetic powder having a thickness of not more than nm and a plate ratio of 5 or more. In recent years, along with the demand for high density of magnetic recording, the development of a perpendicular magnetic recording system using magnetoplumbite type ferrite magnetic powder as a magnetic recording medium has been promoted, and the applications such as DAT tape, 8 mm tape and HDTV tape have been developed. It is considered.
The magnetoplumbite ferrite magnetic powder used in the perpendicular magnetic recording system is a fine particle with an appropriate coercive force (200 to 2000 Oe), a high saturation magnetization, a small coercive force temperature change, and an electric resistance. It is desired to be small and have good orientation.

[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. In particular, the particle size required for high density
It was difficult to obtain fine particles having a uniform particle shape of 50 nm or less and excellent magnetic properties.

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,
The coercive force is 200 to 2000 Oe, the saturation magnetization is high,
The change in coercive force with temperature is small, the electric resistance of the powder is small,
Another object of the present invention is to provide a method for producing a composite ferrite magnetic powder having a particle size of 50 nm or less and a plate ratio of 5 or more and excellent orientation.

[0005]

[Means for solving problems]

The present invention has the general formula _{AO · n (Fe 12-xy} Sb x M y O 18-z) ( however, A is indicated Ba, Sr, one or more elements selected from Ca and Pb, M is, Co , Ni, Zn, Cu, Mg, Mn, Fe (II), Si,
Indicates one or more elements selected from Ti, Zr, Sn, Ta, Nb, Mo, V and W, n = 1.2 to 3.0, x = 0.01 to 0.6, y = 0.1 to 4.
It is a numerical value of 0 and 0 <z <2. ) Ferrite fine particles represented by) are suspended in water, and a dispersant and Co, Ni, Zn, M
Fe ²⁺ and one or more metal ions selected from g, Mn and Cu
Aqueous solution containing and an aqueous alkali solution are added, and the resulting mixed suspension is heat-treated at 50 to 200 ° C. in a non-oxidizing atmosphere, washed, filtered, and then 100 to 500 in a non-oxidizing atmosphere. The ferrite fine particles represented by the above general formula characterized by heat treatment at
(M′O) · Fe ₂ O ₃ (where M ′ is one or more metal elements selected from Co, Ni, Zn, Cu, Mg, Mn and Fe (II), 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,
The ferrite fine particles that form the core are of the general formula AO ・ n (Fe
Represented by _{12-xy Sb x M y O} 18-z). In the general formula, A represents one or more elements selected from Ba, Sr, Ca and Pb, and M represents Co, Ni, Zn, Cu, Mg, Mn, Fe (II), Si, Ti, Zr, Sn, T
indicating one or more elements selected from a, Nb, Mo, V and W,
n = 1.2-3.0, preferably 1.4-2.5, x = 0.01-
The value is 0.6, preferably 0.1 to 0.4, and y = 0.1 to 4.0. Further, z is z when the average valence of M is m.
= (3-m) y / 2, a numerical value represented by 0 <z <
2, preferably 0.2 <z <1.5.

In the present invention, a part of Fe is replaced by M as shown in the above general formula, and n is set in the range of 1.2 to 3.0, so that it is saturated as compared with the conventional magnetoplumbite type ferrite. Magnetization is improved, and ferrite magnetic powder having a small change in coercive force with temperature can be obtained. Further, by substituting a part of Fe with Sb, the particle size of the ferrite magnetic powder can be 50 nm or less and the plate ratio can be 5 or more.

Such ferrite fine particles are manufactured by the following method. A constituting the ferrite fine particles,
A solution containing Fe, Sb and M 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 slurry containing the precipitate is mixed with 1
After hydrothermal treatment at 20 to 300 ° C., the slurry containing the precipitate is washed, and then the slurry contains one or more metal ions selected from Co, Ni, Zn, Mg, Mn and Cu and Fe ²⁺ . Aqueous solution and alkaline aqueous solution were added, and the obtained mixed suspension was heat treated at 50 to 200 ° C.
By firing at 00 to 950 ° C, the ferrite fine particles can be obtained.

As the compound of A, nitrates, chlorides, hydroxides and the like are used. The concentration of A is 0.03.
It is desirable to adjust the content to be in the range of 0.50 M in order to obtain particles with good crystallinity. As the compound of Fe, nitrate,
Chloride or the like is 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 will be small and the crystallinity will deteriorate. 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. A chloride or the like is used as the compound of Sb. As the compound of M, chloride, nitrate, ammonium salt and the like are used.

As the alkali hydroxide, sodium hydroxide, potassium hydroxide and the like are used. The amount of alkali hydroxide to be used is such that the alkali hydroxide concentration in the solution after mixing the alkali hydroxide is 3 M or more, and it is 4 to 8
The range of M is preferred. 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. Regarding the method of mixing the solution containing A, Fe, Sb and M and the alkali hydroxide,
Although not particularly limited, there is a method of adding an aqueous solution of alkali hydroxide to a solution containing A, Fe, Sb and M, for example.

Next, the slurry containing the obtained precipitate is subjected to a hydrothermal treatment to produce fine crystals and precipitate.
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. The hydrothermal treatment time is usually about 0.5 to 20 hours, and an autoclave is usually adopted for the hydrothermal treatment. Next, the precipitate of fine crystals produced by the hydrothermal treatment is washed with water to remove free alkali components, and then the slurry contains one or more metal ions selected from Co, Ni, Zn, Mg, Mn and Cu. And an aqueous solution containing Fe ²⁺ and an alkaline solution are added, and the obtained mixed suspension is heat-treated at 50 to 200 ° C. As the compounds of Co, Ni, Zn, Mg, Mn and Cu, those soluble in water such as their nitrates, chlorides and sulfates are used, and as the compounds of Fe, ferrous sulfate and ferric chloride are used. Iron iron is commonly used.

Then, the obtained precipitate is washed with water and then fired to obtain fine ferrite particles. In the calcination, it is preferable to mix a flux with the precipitate obtained in advance. As the flux, sodium chloride, barium chloride,
At least one of 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 the flux is too small, the particles will sinter, and if the amount is too large, there will be no advantage due to the increased amount and it will not be 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 the precipitate may be dried and then the flux is added. You may dry-mix. The firing temperature is 700 to 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 has the general formula a (M'O) .Fe ₂ O ₃ (where M'is Co, Ni, Zn, Cu, Mg, Mn and Fe on the surface of the ferrite fine particles. A spinel ferrite layer represented by 0 <a ≦ 1 which is one or more metal elements selected from (II) is formed. The composite ferrite magnetic powder of the present invention, the ferrite fine particles are suspended in water, a dispersant, Co, Ni, Zn, Mg, Mn and one or more metal ions selected from Cu and Fe ²⁺ . After adding the aqueous solution and the alkaline aqueous solution to the mixture and heating the resulting mixed suspension at 50 to 200 ° C. in a non-oxidizing atmosphere,
Wash, filter, then 100-5 in non-oxidizing atmosphere
It is obtained by heat treatment at 00 ° C.

To form the spinel ferrite layer, first, fine ferrite particles are sufficiently dispersed in water to prepare a suspension solution, and a dispersant is added to the suspension solution 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 preferably 0.1 to 5 mol% with respect to the total amount of the metal ions and Fe ²⁺ .
The addition of the dispersant improves the orientation of the obtained composite ferrite magnetic powder.

Next, the obtained mixed suspension is heat-treated at 50 to 200 ° C. in a non-oxidizing atmosphere. The heat treatment forms a spinel ferrite layer on the surface of the fine particles.
The heat treatment is performed at 50 to 200 ° C., especially 50 to 1
By carrying out at a low temperature of 20 ° 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 fine 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 fine particles represented by the above general formula, a spinel ferrite layer is formed on the surface of the ferrite fine particles with 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 coating the composite type ferrite magnetic powder obtained by the present invention together with a binder resin on 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 or the like is used. As a method for producing a magnetic recording medium, a usual method is used, for example, magnetic powder, binder resin, and additives are kneaded together with a solvent to produce a magnetic coating material, and the magnetic coating material is applied to a support, followed by orientation treatment and drying. Examples of the method include treatment.

[0018]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. Example 1 Ferric chloride 2.519 mol, antimony trichloride 0.061 mol, cobalt chloride 0.061 mol, nickel chloride 0.061 mol, titanium tetrachloride 0.123 mol and zinc chloride 0.123 mol, deionized water 1800 ml
Then, 0.368 mol of barium hydroxide and 36 mol of caustic soda were separately dissolved in 2000 ml of deionized water, and both solutions were mixed to form a precipitate. The slurry containing the obtained precipitate was placed in an autoclave and hydrothermally treated at 140 ° C. for 6 hours. Then, the resulting precipitate was thoroughly washed with water, and the slurry was added to 200 ml of water with 0.061 mol of cobalt chloride and 0.1 ml of zinc chloride.
After adding a solution in which 22 mol and 0.549 mol of ferrous chloride were dissolved and thoroughly mixed, a solution in which 1.7 mol of caustic soda was dissolved in 300 ml of water was added, and the mixture was aged at 80 ° C. Next, the resulting precipitate was thoroughly washed with water, filtered and dried, and a mixture of NaCl and BaCl ₂ .2H ₂ O in a weight ratio of 1: 1 was added to the precipitate as 100% by weight. % Was added and mixed. The mixture was calcined under a nitrogen atmosphere at 860 ° C for 2 hours. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder.

The composition of the obtained ferrite magnetic powder was BaO.1.6 (Fe _10.0 Sb _0.2 Co _0.4 Ni _0.2 Zn _0.8 Ti _0.4 O _17.5 ) as a result of composition analysis. The characteristics of this ferrite magnetic powder were a particle size of 0.046 μm, a plate ratio of 6.8, a coercive force of 540 Oe, a saturation magnetization of 64.4 emu / g, and a change of coercive force with temperature of 0.2 Oe / ° C. The electric resistance of the powder compact was 1.2 × 10 ⁷ Ω · 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 a coercive force of 760 Oe, a saturation magnetization of 68.4 emu / g, and a change of coercive force with temperature of -0.7 Oe / ° C. The electric resistance of the powder compact was 3.4 × 10 ⁴ Ωcm.

A magnetic coating material having the following composition was prepared using the 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 0.70.

Example 2 Ferric chloride 2.639 mol, antimony trichloride 0.061 mol, cobalt chloride 0.061 mol, nickel chloride 0.061 mol, titanium tetrachloride 0.061 mol and zinc chloride 0.061 mol, deionized water 1800 ml
Then, 0.368 mol of barium hydroxide and 36 mol of caustic soda were separately dissolved in 2000 ml of deionized water, and both solutions were mixed to form a precipitate. 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, and then the slurry was added to 200 ml of water, 0.061 mol of cobalt chloride and zinc chloride.
A solution prepared by dissolving 0.123 mol and 0.552 mol of ferrous chloride was added and mixed thoroughly, and then a solution prepared by dissolving 1.7 mol of caustic soda in 300 ml of water was added and aged at 80 ° C. Next, the resulting precipitate was thoroughly washed with water, filtered and dried, and a mixture of NaCl and BaCl ₂ .2H ₂ O in a weight ratio of 1: 1 was added to the precipitate as 100% by weight. % 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.

The composition of the obtained ferrite magnetic powder was BaO.2.0 (Fe _10.4 Sb _0.2 Co _0.4 Ni _0.2 Zn _0.6 Ti _0.2 O _17.5 ). The characteristics of this ferrite magnetic powder are as follows: particle size 0.045 μm Plate ratio 6.9 Coercive force 530 Oe Saturation magnetization 63.3 emu / g Coercive force temperature change 0.3 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 characteristics of the obtained composite ferrite magnetic powder were coercive force 770 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 0.69.

Comparative Example 1 Ferric nitrate 3.129 mol, cobalt nitrate 0.123 mol, nickel nitrate 0.061 mol, titanium tetrachloride 0.123 mol and zinc nitrate 0.24
Dissolve 5 mol in 1800 ml of deionized water and separately add 0.460 mol of barium hydroxide and 37 mol of caustic soda to 2000 m of deionized water.
It was dissolved in 1 and both solutions were mixed to form a precipitate. The slurry containing the obtained precipitate was placed in an autoclave and
Hydrothermal treatment was performed at 0 ° C. for 6 hours. Next, the precipitate obtained is thoroughly washed with water, then filtered and dried.
A mixture of NaCl and BaCl ₂ .2H ₂ O at a weight ratio of 1: 1 was added and mixed at 100% by weight with respect to the precipitate. The mixture was calcined under a nitrogen atmosphere at 860 ° C for 2 hours. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder.

As a result of compositional analysis, the obtained ferrite magnetic powder was BaO · 0.99 (Fe _10.2 Co _0.4 Ni _0.2 Zn _0.8 Ti _0.4 O _17.5 ). The characteristics of this ferrite magnetic powder are as follows: particle size 0.061 μm Plate ratio 7.7 Coercive force 560 Oe Saturation magnetization 60.2 emu / g Coercive force temperature change 2.3 Oe / ° C Electric resistance of powder compact 1.8 × 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 properties of the obtained composite ferrite magnetic powder were a coercive force of 650 Oe, a saturation magnetization of 62.3 emu / g, and a change of coercive force with temperature of 1.6 Oe / ° C. The electric resistance of the powder compact was 5.6 × 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 Ferric nitrate 3.252 mol, cobalt nitrate 0.123 mol, nickel nitrate 0.061 mol, titanium tetrachloride 0.061 mol and zinc nitrate 0.18
Dissolve 4 mol in 1800 ml deionized water, separately, 0.460 mol barium hydroxide and 37 mol caustic soda, deionized water 200
It was dissolved in 0 ml and both solutions were mixed to form a precipitate.
The slurry containing the obtained precipitate was placed in an autoclave,
Hydrothermal treatment was performed at 140 ° C. for 6 hours. Next, the resulting precipitate was thoroughly washed with water, filtered and dried, and a mixture of NaCl and BaCl ₂ .2H ₂ O in a weight ratio of 1: 1 was added to the precipitate as 100% by weight. % 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.

The composition of the obtained ferrite magnetic powder was BaO.1.0 (Fe _10.6 Co _0.4 Ni _0.2 Zn _0.6 Ti _0.2 O _17.5 ) as a result of composition analysis. The characteristics of the obtained ferrite magnetic powder are as follows: particle size 0.066 μm Plate ratio 7.8 Coercive force 540 Oe Saturation magnetization 60.1 emu / g Temperature change of coercive force 2.4 Oe / ° C Electric resistance of powder compact 1.9 × 10 ⁷ It was Ω · 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 properties of the obtained composite ferrite magnetic powder were coercive force 660 Oe, saturation magnetization 61.8 emu / g, coercive force temperature change 1.7 Oe / ° C, and the electric resistance of the powder compact was 6.9 × 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.

[0031]

EFFECTS OF THE INVENTION The composite ferrite magnetic powder obtained by the present invention has a dramatically improved saturation magnetization, a small change in coercive force with temperature, a small electric resistance of the powder, and Since the particle size is 50 nm or less and the plate ratio is 5 or more, it is suitably used as a magnetic recording material for high density recording.

Claims (2)

[Claims] 1. The general formula AO.n (Fe _12-xy Sb _x M
_y O _18-z ) (where A is one or more elements selected from Ba, Sr, Ca and Pb, and M is Co, Ni, Zn, Cu, Mg, Mn, Fe (II), Si ,
Indicates one or more elements selected from Ti, Zr, Sn, Ta, Nb, Mo, V and W, n = 1.2 to 3.0, x = 0.01 to 0.6, y = 0.1 to 4.
It is a numerical value of 0 and 0 <z <2. ) Ferrite fine particles represented by) are suspended in water, and a dispersant and Co, Ni, Zn, M
Fe ²⁺ and one or more metal ions selected from g, Mn and Cu
Aqueous solution containing and an alkaline aqueous solution are added, and the obtained mixed suspension is heat-treated at 50 to 200 ° C. in a non-oxidizing atmosphere, washed, filtered, and then 100 to 500 in a non-oxidizing atmosphere. The ferrite fine particles represented by the above general formula characterized by heat treatment at
(M′O) · Fe ₂ O ₃ (where M ′ is one or more metal elements selected from Co, Ni, Zn, 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 particle size of the ferrite magnetic powder is 50 nm or less and the plate ratio is 5 or more.