JPH0633116A - Ferromagnetic metallic powder for magnetic recording medium and production thereof - Google Patents

Abstract

PURPOSE:To obtain the ferromagnetic metallic powder for magnetic recording media having excellent magnetic characteristics and excellent weatherability and the ferromagnetic metallic powder the production cost of which is low through a relatively simple process. CONSTITUTION:A Co<2+> salt and an Fe<3+> salt are brought into reaction in a basic. aq. soln. of >=7pH to form the hydroxide of the Co<2+> and the hydroxide of the Fe<3+>. An org. matter crystallization suppressing agent is then added to these hydroxides and thereafter, the hydroxides are heated and held at >=40 deg.C to effect a reaction. The Co<2+> salt and the Fe<2+> salt are otherwise brought into reaction in the basic aq. soln. of >=7pH to form the hydroxide of the Co<2+> and the hydroxide of the Fe<2+>. The org. matter crystallization suppressing agent is then added to these hydroxides. While the hydroxides are heated and held at >=40 deg.C, an oxidation reaction is effected in an oxidative atmosphere to form cobalt ferrite. The ferromagnetic metallic powder for magnetic recording media is obtd. by the method of subjecting this cobalt ferrite to filtering, washing and drying, then subjecting the cobalt ferrite to a reduction in a reducing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferromagnetic powder for a magnetic recording medium, and more particularly to a method for producing needle-shaped ferromagnetic powder having high magnetic properties and excellent stability. .

[0002]

2. Description of the Related Art Magnetic recording has made remarkable progress due to its features such as reusable use of media and ease of computerization of information among various recording systems. High density recording is constantly required for magnetic recording media such as magnetic tapes, magnetic disks and magnetic drums used therein.

A magnetic recording medium has a structure in which a magnetic layer is provided on a tape-shaped or disk-shaped non-magnetic support, and in order to meet the demand for high density recording, a ferromagnetic material having excellent electromagnetic conversion characteristics is used. A so-called metal thin film type magnetic recording medium using a metal thin film as a magnetic layer has been proposed. However, the magnetic recording medium using the metal thin film as a magnetic layer has problems that the manufacturing cost is high and practical properties such as weather resistance and durability are poor.

On the other hand, a so-called coating type magnetic recording medium mainly composed of a ferromagnetic powder and a binder resin has excellent practical characteristics and has been used as a magnetic recording medium for a long time, and its improvement has been made. Then, the improvement of the characteristics of the ferromagnetic powder used therein has greatly contributed to the improvement of the recording density. As the ferromagnetic powder used in the coating type magnetic recording medium, iron oxide powder, cobalt modified iron oxide powder, CrO ₂ powder, metallic magnetic powder, and plate-shaped hexagonal ferrite powder typified by barium ferrite are known. ing. Among them, the magnetic metal powder is most excellent for the magnetic recording medium requiring high recording density, and is used for the magnetic recording medium for 8 mm video. The shape of the particles is usually from the viewpoint of maintaining high coercive force. It is needle-shaped. In recent years, in order to meet the demand for higher magnetic recording density, higher performance has been pursued.

Ferromagnetic metal powders are usually manufactured by using goethite as a starting material and performing dehydration and hydrogen reduction by a high temperature gas phase reaction. Then, in order to secure the stability in the air, it is necessary to form an oxide layer on the particle surface of the powder, and the saturation magnetic flux density becomes much lower than the bulk value.

Fe—Co to improve the saturation magnetic flux density
The alloy of Fe-Co is C
It is known that the saturation magnetic flux density is maximized when o is about 30%. However, if 30% of Co / Fe was added as a Co compound during the goethite formation reaction, a mixed phase of Co-modified acicular goethite and granular cobalt ferrite was obtained, and a magnetic material with a particularly high saturation magnetic flux density could not be obtained. . There is also a method of adsorbing a Co compound on goethite, but when trying to adsorb 30% of Co / Fe, amorphous particles of a Co compound different from the Co adsorbed goethite particles are generated. As described above, there have been various problems in improving the saturation magnetic flux density by Fe—Co alloying, and it has not been sufficiently made.

On the other hand, as disclosed in Japanese Patent Publication No. 43-20117, cobalt ferrite (CoFe2
It has been proposed to dry-reduce O4) to obtain a ferromagnetic metal powder having a high Co content. However, the particle shape of the cobalt ferrite powder is cubic, and a needle-like shape having a high coercive force due to shape anisotropy cannot be obtained.
Only a coercive force of less than 000 Oersted was obtained.

Further, in the case of the above-described method for producing a ferromagnetic metal powder using goethite as a starting material, it is possible to obtain a ferromagnetic metal powder in which the acicular shape of the goethite particles is maintained. There was dehydration and deoxidation, and the particles had many voids and branches, and the shape was a mere form. The particles were easily broken, and the particle size distribution and coercive force distribution were wide, and the coercive force that could be obtained was also limited.

In Japanese Patent Publication No. 60-42174, a specific organic substance is added as a crystallization controlling agent to a suspension of ferric hydroxide, and it has excellent acicularity without pores. A method of making ferric oxide is disclosed. It is also described that a metallic magnetic powder can be obtained by causing a reducing agent such as hydrogen gas to act on the ferric oxide. Furthermore, JP-A-51-
Japanese Patent No. 25454 and Japanese Patent Application Laid-Open No. 53-123898 disclose a method of obtaining a ferromagnetic metal powder having an excellent acicular ratio by reducing acicular iron oxide containing various chelate compounds.

Ferromagnetic metal powder has excellent magnetic properties as a ferromagnetic powder for a coating type magnetic recording medium, but it is less susceptible to chemical changes, especially under high temperature and high humidity environmental conditions. There was a problem of weather resistance that deteriorated.

There is still no effective method for the problem of weather resistance, and the above-mentioned JP-B-60-42174, JP-A-51-25454 and JP-A-53-1.
Even the method disclosed in Japanese Patent No. 23898 could not be dealt with.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is a ferromagnetic metal powder for a magnetic recording medium having excellent magnetic characteristics and weather resistance, and its production. Its main purpose is to provide a method.

Another object of the present invention is to provide a method for producing a ferromagnetic metal powder which has a relatively simple process and is inexpensive to produce.

[0014]

In order to achieve the above-mentioned object of the present invention, when spinel ferrite is produced by a liquid phase reaction, the inventor usually turns it into granular particles and does not have a needle-like shape. The present invention was found to be acicular particles when used as a crystallization inhibitor, and as a result of further studies, the present invention was focused on cobalt ferrite.

The above object of the present invention is to provide Co²⁺Salt and Fe³⁺salt
React with Co in a basic aqueous solution of pH 7 or above²⁺of
Hydroxide and Fe³⁺To produce the hydroxide of
After adding the crystallization inhibitor, raise the temperature and keep at 40 ° C or higher
And react to produce cobalt ferrite.
Filter and wash water and dry ruthoferrite before returning.
Of ferromagnetic metal powder for magnetic recording that reduces in an original atmosphere
Manufacturing method or Co ²⁺Salt and Fe²⁺PH of 7 or more with salt
Co in a basic aqueous solution²⁺Hydroxide and Fe²⁺
To produce hydroxide, then add organic crystallization inhibitor
Then, the temperature is raised and the temperature is maintained at 40 ° C. or higher while the atmosphere is oxidizing.
Cobalt ferrite is produced by oxidizing in the air.
Then, the cobalt ferrite is filtered, washed with water and dried.
And then reduce in a reducing gas atmosphere to produce ferromagnetic powder.
For producing ferromagnetic powder for magnetic recording medium and ferromagnetism
The metal content is 90% by weight or more, the Co content is 20 to
35 atomic%, the acicular ratio is 1.5: 1 to 10: 1,
Ignition temperature in air is over 200 ℃ and saturation magnetization
Of 150 emu / g or more for ferromagnetic metal powders for magnetic recording media
Can be achieved by the end.

That is, according to the present invention, Co ²⁺ hydroxide and Fe
Needle-shaped cobalt ferrite by heating reaction or oxidation reaction of ³⁺ hydroxide or Co ²⁺ hydroxide and Fe ²⁺ hydroxide with addition of organic crystallization inhibitor And reducing the cobalt ferrite to obtain a high Co content of 20 to 35 atomic%,
A ferromagnetic metal powder for magnetic recording media having an acicular ratio of 1.5: 1 to 10: 1, an ignition temperature in air of 200 ° C. or higher, excellent weather resistance, and a saturation magnetization of 150 emu / g or higher. To get it.

According to the method of the present invention, the organic crystallization inhibitor is coordinately bonded to the particle surface of cobalt ferrite to suppress the direction of particle growth and to obtain the final particle morphology. It is presumed that it will be controlled in a similar manner. As a result, the coercive force of the obtained ferromagnetic metal powder can be increased.

Further, since the Fe-Co composition is in a state close to the content corresponding to the maximum peak value of the Slater-Pauling curve, the saturation magnetization can be made as large as 150 emu / g. And, as a particularly excellent advantage, the weather resistance, which is a big drawback of the conventional ferromagnetic metal powder, is remarkably improved. Furthermore, the ferromagnetic metal powder of the present invention is characterized in that a dense ferromagnetic metal powder having a structure with few pores and branches can be obtained, which is one of the factors of the various excellent properties described above. Can also be considered.

The method for producing the ferromagnetic metal powder of the present invention is C
pH of o ²⁺ salt and Fe ³⁺ salt or Co ²⁺ salt and Fe ²⁺ salt
Co ²⁺ hydroxide and Fe ³⁺ hydroxide obtained by reacting in a basic aqueous solution of 7 or more or Co ²⁺ hydroxide and Fe ²⁺ hydroxide are relatively mild. Since it is a method of reacting under conditions to obtain cobalt ferrite, it has a manufacturing and economic advantage that it can be manufactured under conditions that are relatively simple and the manufacturing cost is low.

Various organic compounds can be used as the organic crystallization inhibitor in the present invention.
-42174 is an organic compound selected from organic phosphonic acids, hydroxycarboxylic acids, and salts and esters thereof. Specifically, the organic phosphonic acids include aminotri (methylenephosphonic acid) and 1-hydroxy. Ethylidene-1,1-diphosphonic acid, ethylenediaminetetra (methylenesulfonic acid), hydroxymethylenediphosphonic acid, methylenediphosphonic acid, ethylene-1
-2 diphosphonic acid and the like, and as the hydroxycarboxylic acid, mainly aliphatic hydroxycarboxylic acid such as citric acid, tartaric acid, dihydroxyglutanic acid, glycolic acid, salicylic acid is used, and among them, citric acid and ethylenediaminetetramethylenesulfonic acid are used. preferable.

The addition amount of the organic crystallization inhibitor in the present invention to the Co ²⁺ hydroxide and the Fe ³⁺ hydroxide or the Co ²⁺ hydroxide and the Fe ²⁺ hydroxide is the total. The sum of metals (Fe and Co and other added metals) is 1 × 10 ^{−6 to} 3 mol, preferably 1 × 10 ⁻³ , per mol of the metal.
Is 0.5 mol. For example, 1 mol of ferric sulfate and 1 mol of cobalt sulfate are dissolved in 5 liters of water, and 3N NaOH is added to adjust the pH to 7 or more. Next, 0.3 mol of citric acid as an organic crystallization inhibitor (total metal 1
A solution of 1 mol of water (0.1 mol per mol) is brought to a predetermined reaction temperature.

If the addition amount of the organic crystallization inhibitor is small, it becomes difficult to obtain needle-shaped ferromagnetic metal powder, and even if it is obtained, it becomes mixed with granular particles, and if it is too large, crystallization occurs. It is not desirable because it will not progress.

The cobalt ferrite is produced by adding a predetermined amount of the organic crystallization inhibitor to the hydroxide suspension, and then adding the liquid at 40 ° C. or higher, preferably 60 to 100.
A temperature of 0 ° C. is usually maintained for 1 to 20 hours. Further, in order to increase the reaction rate, the reaction may be carried out at 100 ° C. or higher in an autoclave.

When the temperature at which cobalt ferrite is formed is less than 40 ° C., crystallization does not proceed sufficiently, which is not desirable.

The ferromagnetic metal powder for magnetic recording media of the present invention
Co as a raw material to be manufactured²⁺Salt, Fe ³⁺Salt and Fe²⁺salt
Has traditionally been used in the manufacture of ferromagnetic materials for magnetic recording media.
It is possible to use various substances such as salt.
Ferrous oxide, ferric chloride, ferrous sulfate, ferric sulfate, nitric acid
Ferrous iron, ferric nitrate, cobalt chloride, cobalt sulfate, glass
Examples thereof include chlorides such as cobalt acid, sulfates, and nitrates.

Co ²⁺ salt and Fe ³⁺ salt or Co ²⁺ salt and F
The e ²⁺ salt ratio of Co ²⁺ and Fe ³⁺ or Co ²⁺ and Fe ²⁺ 1: Although 2 moles is the composition of ordinary cobalt ferrite, the Co content of the adjustment is Co ²⁺ salt one It is also possible to use an Fe ²⁺ salt instead of the part. Therefore, the ratio is the molar ratio C
o ²⁺ / (Co ²⁺ + Fe ²⁺ + Fe ³⁺ ), 0.20 to 0.
The pH of the basic aqueous solution is usually adjusted to 7 or higher, preferably 12 or higher so as to be in the range of 35. As the alkali in that case, for example, an alkali metal such as sodium hydroxide, calcium hydroxide or potassium hydroxide, a hydroxide of alkaline earth and ammonia can be used.

Then, for example, an aqueous solution of sodium hydroxide is added to an aqueous solution of cobalt sulfate and ferric sulfate, or an aqueous solution of potassium hydroxide is added to an aqueous solution of cobalt chloride and ferrous chloride to produce Co ^{2 +} Hydroxide and Fe ³⁺
And hydroxides of Co ²⁺ and Fe ²⁺ .

Next, the obtained suspension of hydroxide is reacted under the above-mentioned conditions to form acicular cobalt ferrite. When Fe ²⁺ salt is used as a starting material, air may be aerated as an oxidant in the suspension, or sodium nitrate or the like may be added. The concentration of the hydroxide, which is a reaction product in the reaction solution at that time, is within a stirrable range and affects the particle size of the cobalt ferrite produced, and is experimentally determined, so it cannot be unconditionally determined. Usually, the sum of all metals can be selected from 0.01 mol to 1.0 mol per liter.

The slurry of cobalt ferrite obtained as described above is washed with water, subjected to a sintering preventing treatment, further washed with water, filtered and dried.

The sintering prevention treatment at that time is carried out by adding, for example, water glass, aluminum sulfate or water glass and aluminum sulfate to a slurry of cobalt ferrite to adjust the pH.
Should be 8 or more.

There are no particular restrictions on the process conditions of washing and filtration, and conventionally known methods can be employed.

The cobalt ferrite powder obtained by drying was placed in a furnace, heat-treated at 300 to 700 ° C. in an air or nitrogen atmosphere, and then at 350 to 500 ° C., a reducing gas mainly containing hydrogen gas was passed through the furnace. It is reduced to produce metal powder.

Next, a gas having an adjusted oxygen concentration was passed through to gradually oxidize the surface of the particles (gradual oxidation in the gas phase) or suspend a metal powder in an organic solvent to contain oxygen in the suspension. After passing through an oxidizing gas to gradually oxidize (gradually oxidize in the liquid phase), it is dried to obtain the ferromagnetic metal powder for a magnetic recording medium of the present invention.

As a gradual oxidation method, a method in which cobalt ferrite is reduced and then taken out in water is also possible.

The ferromagnetic metal powder obtained by the above manufacturing method has a ferromagnetic metal content of 90% by weight or more, a large Co content of 20 to 35 atomic%, and an acicular ratio. 1.5: 1 to 10: 1 and a coercive force of 100
Magnetic properties of 0 oersted and saturation magnetization of 150 emu / g or more are superior to those of conventional ferromagnetic metal powders using, for example, goethite as a starting material. And, as a further unique feature, the ignition temperature in air is 200 ° C.
It is extremely high as described above, that is, the oxidation stability is very good, so that the weather resistance, which has been a problem of the ferromagnetic metal powder for magnetic recording media, can be remarkably improved.

In the present invention, the ignition temperature in the air is 500 ° C. at a temperature rising rate of 200 mg of the sample at 5 ° C./min in an air atmosphere of normal pressure using a differential thermal balance manufactured by Vacuum Riko Co., Ltd. This is the rapid exothermic temperature of the sample that is measured by raising the temperature up to and is read from the exothermic / endothermic curve.

The ferromagnetic metal powder for magnetic recording media of the present invention has a content of the ferromagnetic metal mainly composed of Co and Fe of 90.
%, More preferably 90 to 98% by weight. When the content of the ferromagnetic metal is less than 90% by weight, the saturation magnetic flux density becomes small, which is not desirable. In order to set the content of the ferromagnetic metal in the above range, in the above-mentioned manufacturing method,
It is important to adjust the amount of sintering inhibitor.

The content of Co in the ferromagnetic metal powder of the present invention is 20 to 35 atom%, preferably 25 to 33 atom%. The Co content is based on the starting Co ions and F
The ratio of e-ions may be adjusted. Co content is 20
If it is less than atomic%, the saturation magnetic flux density will not be sufficient, and if it exceeds 35 atomic%, cobalt ferrite particles and cobalt compound will be mixed during the liquid phase reaction, which is not preferable.

The acicular ratio of the particles of the ferromagnetic metal powder in the present invention is 1.5: 1 to 10: 1, preferably 2: 1 to.
When the acicular ratio is 8: 1 and the acicular ratio is less than 1.5: 1, the coercive force is not sufficiently large, and when it exceeds 10: 1, the magnetic recording medium is manufactured. Dispersion becomes difficult, which is not preferable.

In order to make the acicular ratio within the above range, it is effective to adjust the amount of the organic crystallization inhibitor, and increasing the amount of the organic crystallization inhibitor can increase the acicular ratio. it can.

The magnetic properties of the ferromagnetic metal powder for magnetic recording media of the present invention are such that the saturation magnetization is 150 emu / g or more, preferably 150 to 180 emu / g. In order to set the saturation magnetization to 150 emu / g or more, it is essential that the gradual oxidation treatment of the ferromagnetic metal powder after reduction does not occur among particles, and while stirring the ferromagnetic metal powder, The treatment may be performed for a long time (for example, 5 hours) in an atmosphere of low oxygen concentration (for example, 0.1% by weight).

Further, although the metal powder is used, the factor that causes the characteristic of the ferromagnetic metal powder for magnetic recording media of the present invention that the ignition temperature in air is as high as 200 ° C. or higher is still unknown. However, because the crystallographic structure of the particle surface of the ferromagnetic metal powder is dense and has few defects, there are few active sites that are the origin of oxidation, or the amount of Co atoms is large. It is estimated that there is not.

The ferromagnetic metal powder for magnetic recording media of the present invention is characterized by a relatively small particle size. That is, the major axis is 0.02 to 0.3 μm, the acicular ratio is about 1.5 to 10 and the specific surface area is 10 m ² / g.
To 200 m ² / g.

In carrying out the present invention, a small amount of another element may be added in order to control the particle size, shape and magnetic properties. As other elements, specifically Z
It is also possible to use n, Ni, Cr, Mn, Al, Si, P, Ti, and rare earth elements together. In addition, it is possible to add a nuclide of spinel ferrite in advance during the reaction. A coating solution obtained by kneading and dispersing the ferromagnetic metal powder for a magnetic recording medium of the present invention in a binder resin together with various additives such as a dispersion solvent, a lubricant and an abrasive has a predetermined thickness on a non-magnetic support. A magnetic recording medium can be obtained by applying the coating solution. There are no particular restrictions on the material and manufacturing process therefor, and various known techniques can be employed. For example, various materials and methods described in JP-A-4-29301 are used. Above all, it is particularly effective to select a polar group-containing vinyl chloride resin and a polar group-containing polyurethane resin as the binder resin in order to obtain a magnetic recording medium for high density recording.

[0045]

【Example】

Example 1 84.3 g of cobalt sulfate heptahydrate and ferric sulfate heptahydrate 15
An aqueous solution prepared by dissolving 8 g in 1000 ml (ml) of distilled water and 126 g of caustic soda in 2000 ml of distilled water
Was added to the alkali solution dissolved in the above solution with stirring. Next, a solution prepared by dissolving 1.7 g of citric acid in 200 ml of distilled water was added, and the reaction solution was heated to 100 ° C. After 10 hours, the temperature was returned to room temperature, the reaction mother liquor was suction-filtered, solid-liquid separated, and then washed with distilled water. The cake was taken out, 2000 ml of distilled water was added, and the mixture was stirred again to form a slurry. 5 for Si / (Co + Fe)
Water glass was added so that the amount became 100% and the treatment was performed for 2 hours. After solid-liquid separation, it was washed with water and dried to obtain a black powder. This powder was put into a firing furnace and heated at 500 ° C. for 2 hours while passing nitrogen gas. Then, the temperature was raised to 400 ° C., hydrogen gas was bubbled for 4 hours, and then the temperature was returned to room temperature. A mixed gas with nitrogen adjusted to an oxygen concentration of 0.1% was passed for 5 hours to gradually oxidize, and then taken out into the atmosphere. When this powder was observed with a transmission electron microscope (TEM), the particle shape was 0.05 μm in the major axis and the acicular ratio was 2.
The magnetic characteristics were measured by a vibrating sample magnetometer (VSM) and applied magnetic field of
Hc1 when measured with kOe (Kilo-Oersted)
The values were 050 Oe and σs 171 emu / g. The ignition point was not recognized up to 500 ° C.

Example 2. The reaction was carried out under the same conditions as in Example 1 except that methylenephosphonic acid was changed to 4.5 g instead of citric acid. The particle shape of the obtained alloy has a long axis of 0.
08 μm, needle ratio 6, Hc1542Oe, σs165e
It was mu / g. Further, the ignition point was not recognized up to 500 ° C.

Example 3 In place of 84.3 g of cobalt sulfate heptahydrate of Example 1, 50.6 g of cobalt sulfate heptahydrate and ferrous sulfate heptahydrate 33.
A ferromagnetic metal powder was produced under the same conditions as in Example 1 except that the number was 4. The obtained ferromagnetic metal powder has an Hc of 10
It was 50 Oe and σs was 171 emu / g. And
The ignition point was not recognized up to 500 ° C.

Example 4. Cobalt sulfate heptahydrate 84.3 g
And 167 g of ferric sulfate heptahydrate dissolved in 1000 ml of distilled water, 72 g of caustic soda was added to 2000 ml of distilled water.
Nitrogen was bubbled through the alkaline solution dissolved in ml, and the solution was added while stirring. Next, 1.7 g of citric acid dissolved in 200 ml of distilled water was added, and the reaction solution was heated to 100 ° C.
Then, the atmosphere was replaced with nitrogen and air was aerated at 1 liter per minute. 10
After a lapse of time, the temperature was returned to room temperature, the reaction mother liquor was suction-filtered, solid-liquid separated, and washed with distilled water. The cake thus obtained was taken out, 2000 ml of distilled water was added, and the mixture was stirred again to obtain a slurry. Water glass was added so that Si / (Co + Fe) would be 5%, and the mixture was treated for 2 hours. After solid-liquid separation, it was washed with water and dried to obtain a black powder. This powder was put into a firing furnace and heated at 500 ° C. for 2 hours while passing nitrogen gas. Then 400
C., hydrogen gas was bubbled for 4 hours, and then the temperature was returned to room temperature. A mixed gas with nitrogen adjusted to an oxygen concentration of 0.1% was passed for 5 hours to gradually oxidize, and then taken out into the air to obtain a sample of ferromagnetic metal powder. This sample powder was used as a transmission electron microscope (TE
As a result of observation under M), the particle shape was 0.13 μm in the major axis and the acicular ratio was 3. Magnetic characteristics are vibration sample type magnetometer (VSM)
Hc1460O measured at 10 KOe applied magnetic field
e, σs 183 emu / g. The ignition point is 274
It was ℃.

Comparative Example 1. A ferromagnetic metal powder was prepared under the same conditions as in Example 1 except that the crystallization inhibitor was not added, and as a result, the particle shape was granular particles having a diameter of 0.04 μm (the acicular ratio was approximately 1), and Hc580Oe , Σs174 emu /
It was g. Further, the ignition point was not recognized up to 500 ° C.

Comparative Example 2. Example 1 except that goethite having a long axis of 0.2 μm and an acicular ratio of 8 was used instead of cobalt ferrite. Hydrogen reduction under the same conditions as above, the particle shape is almost the same as before reduction, Hc1360, σs114e
A ferromagnetic metal powder having a mu / g was obtained. And the ignition point was 125 degreeC.

[0051]

EFFECT OF THE INVENTION By reacting a Co ²⁺ salt with an Fe ³⁺ salt, Co
By producing a hydroxide of ^{2+ and} a hydroxide of Fe ³⁺ , then adding an organic crystallization inhibitor, and reducing the cobalt ferrite produced by heating in a reducing atmosphere, It is possible to obtain a needle-like ferromagnetic metal powder for a magnetic recording medium, which has excellent magnetic properties such as coercive force and saturation magnetization, and in particular, has an extremely high oxidation stability with an ignition temperature of 200 ° C. or higher.

Claims (4)

[Claims] 1. A Co ²⁺ salt and an Fe ³⁺ salt are reacted in a basic aqueous solution having a pH of 7 or more to produce a Co ²⁺ hydroxide and an Fe ³⁺ hydroxide, and then crystallization of an organic substance. After adding the inhibitor, the temperature is raised and the temperature is kept at 40 ° C. or higher to cause a reaction to generate cobalt ferrite, and the cobalt ferrite is filtered, washed with water and dried, and then reduced in a reducing atmosphere. Manufacturing method of ferromagnetic metal powder for magnetic recording medium. 2. A Co ²⁺ salt and an Fe ²⁺ salt are reacted in a basic aqueous solution having a pH of 7 or more to form a Co ²⁺ hydroxide and an Fe ²⁺ hydroxide, and then organic substance crystallization is performed. After adding the inhibitor, the temperature is raised and the temperature is maintained at 40 ° C. or higher to cause an oxidation reaction in an oxidizing atmosphere to generate cobalt ferrite,
A method for producing a ferromagnetic powder for a magnetic recording medium, wherein the cobalt ferrite is filtered, washed with water and dried, and then reduced in a reducing gas atmosphere to obtain a ferromagnetic powder. 3. The organic compound crystallization inhibitor is an organic compound selected from organic phosphonic acids, hydroxycarboxylic acids, salts and esters thereof.
7. A method for producing a ferromagnetic powder for a magnetic recording medium according to. 4. A ferromagnetic metal content of 90% by weight or more,
Co content is 20 to 35 atomic%, and needle ratio is 1.5: 1.
10 to 10 and an ignition temperature in air of 200
A ferromagnetic metal powder for a magnetic recording medium, which has a saturation magnetization of 150 emu / g or more at a temperature of ℃ or more.