JPS6092403A - Iron oxide magnetic powder - Google Patents

Abstract

PURPOSE:To provide titled magnetic powder having a good magnetic characteristic and excellent thermal stability by forming magnetoplumbite type ferrite layer on the particle surface of iron oxide magnetic powder formed a solid solution of needlelike cobalt on the surface having triaxial anisotropy. CONSTITUTION:Salt of Ba, Sr, Pb, Ca, etc. and ferric salt are added and dissolved into an aq. dispersion of iron oxide magnetic powder formed a solid solution of needlelike cobalt on the surface to effect reaction and further the suspension is heated to grow the resulted product of reaction by which a magnetoplumbite type ferrite layer consisting of BaO.6Fe2O3, SrO.6Fe2O3, PbO.6Fe2O3, CaO. 6Fe2O3 or the like is formed on the particle surface of said magnetic powder preferably at about 3-15wt% by the weight of the iron oxide magnetic powder formed a solid solution of cobalt. Then the magnetoplumbite type ferrite of which the coercive force is increased with an increase in temp. improves the temp. dependency of the iron oxide magnetic powder solutionzied with cobalt by which the magnetic powder having excellent thermal stability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to iron oxide magnetic powder having triaxial anisotropy suitable for use in magnetic recording media. An object of the present invention is to provide iron oxide magnetic powder having triaxial anisotropy.

In general, cobalt-containing iron oxide magnetic powder has a higher coercive force than iron oxide magnetic powder, which is commonly used as a recording element in conventional magnetic recording media, so it is useful as a recording element in high-performance magnetic recording media. In particular, cobalt-solid-solute iron oxide magnetic powder, in which cobalt is uniformly dissolved inside particles of iron oxide magnetic powder, has triaxial magnetic anisotropy, and magnetic recording obtained using it has triaxial magnetic anisotropy. Since the medium exhibits large magnetization in all directions, it is extremely useful for high-density recording magnetic recording media that utilize perpendicular magnetization components.

However, although this type of cobalt solid-solute iron oxide magnetic powder has characteristics that are suitable for high-density recording using a perpendicular magnetization component, its coercive force has a strong temperature dependence (it is difficult to maintain a high coercive force at low temperatures). Even if it has, the problem is that the coercive force decreases as the temperature rises, resulting in poor thermal stability.

In view of the current situation, the inventor conducted various machining tests and found that when a magnetic brambite-type ferrite layer is deposited on the particle surface of acicular cobalt solid-solubilized iron oxide magnetic powder having three-ring anisotropy, Since the magneto-7 top plan height type ferrite formed on the particle surface has a temperature dependence opposite to that of the cobalt solid solution iron oxide magnetic powder, in which the coercive force increases as the temperature increases, the coercive force of both of them is temperature dependent. It was discovered that the temperature dependence of the coercive force of the cobalt-solid-solubilized iron oxide magnetic powder was improved through the mutual interaction of the two, and that thermal demagnetization was reduced and the thermal stability was improved, leading to the creation of this invention. Ta.

In this invention, the magnetic brambite-type ferrite formed on the particle surface of the cobalt solid solution iron oxide magnetic powder has a magnetic brambite-type crystal structure,
The temperature dependence of coercive force is opposite to that of cobalt solid solution iron oxide magnetic powder, and the coercive force increases as the temperature increases. Therefore, when magnetic blanbite-type ferrite N, which has such temperature dependence of coercive force, is formed on the particle surface of cobalt solid-solute iron oxide magnetic powder, the cobal (solid-solute iron oxide magnetic powder) becomes smaller as the temperature increases. The temperature dependence of coercive force is
By magnet brambite type ferrite? lli
This reduces heating demagnetization and improves the thermal stability of coercive force. Such magnet plan high 1-type ferrite is Ba0.6Fe203. , Sr0・6F
e203, PbO・6Fe203, Ca0・6Fe2
Barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, etc. represented by chemical formulas such as 03 are preferably used. The formation of these magnet branbite-type ferrite layers on the particle surfaces of cobalt solid-solubilized iron oxide magnetic powder is achieved by adding salts such as barium, strontium, lead, calcium, etc. to an aqueous dispersion of cobalt solid-solubilized iron oxide magnetic powder. This is done by adding and dissolving ferrous salts, causing a reaction, and further heating to grow the reaction product.Since barium ions, strontium ions, lead ions, calcium ions, etc. are large, cobalt solid solution iron oxide magnetism occurs. It is not diffused into the inside of the powder particles, but is deposited on the particle surfaces to form a magnetic brambite-type ferrite layer. The content of magnet branbite type ferrite in the iron oxide magnetic powder in which a magnet branbite type ferrite layer is formed on the particle surface of the cobalt solid solution iron oxide magnetic powder is as follows: If it is less than 3% by weight, the temperature dependence of the coercive force of the cobalt solid solution iron oxide magnetic powder will not be sufficiently improved.
The temperature dependence of the coercive force of the cobalt solid-soluble iron oxide magnetic powder is improved as the amount increases, but when the amount exceeds 15% by weight,
The contribution of the triaxial anisotropy of the magneto-sotoplanheit type ferrite powder (cobalt solid-solute iron oxide magnetism due to its -axis anisotropy) becomes smaller, and the magnetization using the perpendicular magnetization component is Since it becomes unsuitable for use in density recording magnetic recording media, it is preferably within the range of 3 to 15% by weight based on the cobalt solid solution iron oxide magnetic powder, and the contribution ratio to the cobalt coercive force is less than that of the cobalt solid solution iron oxide magnetic powder. It is preferable that the ratio is in the range of 5:5 to 9:1 for magnet branby type I fuconilite.

In addition, the cobalt solid-dissolved iron oxide magnetic powder is preferably acicular and has triaxial anisotropy, with cobalt uniformly dissolved inside the particles, and the content ratio of cobalt is determined so that the coercive force is determined by the magnetic recording medium. In order to make the content suitable for use, it is preferable to contain it within a range of 5 to 25% by weight based on iron.

The iron oxide magnetic powder, which is formed by providing a magnetic brambite ferrite layer on the particle surface of the cobalt solid-solubilized iron oxide magnetic powder, has improved temperature dependence, less thermal demagnetization, and good thermal stability. Therefore, if this type of iron oxide magnetic powder is used, a magnetic recording medium with good thermal stability and suitable for high-density recording using a perpendicular magnetization component can be obtained.

Next, embodiments of the invention will be described.

Example 1 Acicular γ- with a major axis diameter of 0.3μ and an axial ratio (major axis diameter/minor axis diameter) of 8
After dispersing 1700 g of Fe203 powder in 12N (7) water, 240 g of ferrous sulfate) and 480 g of ferrous sulfate were added to this.
Add and dissolve 1,650 g of caustic soda, then add 61 aqueous solution of caustic soda containing 1,650 g of caustic soda and stir.
The reaction was carried out at 5°C for 8 hours. After the reaction is complete, wash with water, dehydrate,
After drying, it was heat-treated in air at 450° C. for 3 hours to obtain cobalt solid-dissolved iron oxide magnetic powder. This cobalt solid solution iron oxide magnetic powder had a coercive force of 650 oersted, a saturation magnetization of 73.2 emu 7 g, and a square shape of 0.69. Next, this cobalt solid F6 iron magnetic powder 1000
g is dispersed in 77I of water, and 38 g of barium chloride is added to this.
and 507 g of ferric chloride were added and melted, and an aqueous solution 31 of caustic soda containing 800 g of caustic soda was added and reacted at 90°C for 3 hours with ffi ('I'). After the reaction, washing with water, dehydration, 70 in the air after drying
Heat treatment was performed at 0°C for 3 hours to obtain Kobal I solid solution iron oxide magnetic powder with barium ferrite C adhered to the particle surface. The thus obtained iron oxide magnetic powder had a coercive force of 880 oersteds at a temperature of 20°C, a saturation magnetization of 68.2 emu/g, and a square shape of 0.71.

Example 2 In Example 1, barium chloride was added from 38 g to 67 g to an aqueous dispersion in which cobalt solid-dissolved iron oxide magnetic powder was dispersed.
A barium ferrite layer was formed on the particle surface in the same manner as in Example 1, except that the amount of ferric chloride was changed from 507 g to 890 g, and the amount of caustic soda was changed from 800 g to 850 g. . :1 Pal I solid solution iron oxide magnetic powder was obtained. The coercive force of this iron oxide magnetic powder at a temperature of 20° C. is 1120 oersted, and the saturation magnetization is (i6.4 emu 7 g, square shape is 0.72).

Comparative Example 1 Acicular r- with a major axis diameter of 0.3μ and an axial ratio (major axis diameter/minor axis diameter) of 8
After dispersing 1200g of Fe203 powder in 9β water,
To this, 314 g of cobal sulfate) and 622 g of ferrous sulfate were added and dissolved, and then an aqueous solution of caustic soda 51 in which 1390 g of caustic soda was dissolved was added and heated to 45°C without stirring.
The reaction was carried out for 8 hours. After the reaction was completed, the product was washed with water, dehydrated, dried, and then heat-treated in air at 450° C. for 3 hours to obtain cobalt solid-dissolved iron oxide magnetic powder. This cobalt solid solution iron oxide magnetic powder has a coercive force of 890 oersteds at a temperature of 20°C, a saturation magnetization of 73.4 emu 7g, and a square shape of 0.7
It was 1.

The temperature dependence of coercive force and heating demagnetization were investigated for the iron oxide magnetic powders obtained in each Example and Comparative Example. The temperature dependence of the coercive force is the coercive force (llc2(+
) and the coercive force (llc6(1)) at 60°C, and the rate of change (IIC2°-11c6°/l1c2°)
Tangled. In addition, thermal demagnetization was performed by saturated magnetizing iron oxide magnetic powder filled in a cylindrical container in a magnetic field of 10 KOe and measuring the saturation residual magnetization σsr, and then storing this sample at 60°C for 2 hours. , measure the residual magnetization amount σr again at room temperature, and calculate the reduction rate of the residual magnetization amount (σS ``−σr/
σsr).

The table below shows the results.

As is clear from the above table, the iron oxide magnetic powder obtained in Examples 1 and 2 has a higher temperature dependence of coercive force than the cobalt-containing iron oxide magnetic powder obtained in Comparative Example 1. is small and the heating M(II) is small, which indicates that the iron oxide magnetic powder obtained by the present invention suffers little heating demagnetization and has excellent thermal stability.

Patent applicant: Hitachi Maxell, Ltd. ,・Goni i'

Claims (1)

[Claims] 1. Iron oxide magnetic powder formed by forming a magnet brambite type ferrite layer on the particle surface of acicular cobalt solid solution iron oxide magnetic powder having triaxial anisotropy.