JPH0618073B2 - Magnetic powder for magnetic recording - Google Patents

Description

TECHNICAL FIELD The present invention relates to magnetic powder for magnetic recording, and more specifically to hexagonal ferrite magnetic powder composed of fine particles suitable for high density magnetic recording media. is there.

(Prior Art) In recent years, along with a demand for higher density in magnetic recording, a perpendicular magnetic recording method for recording a magnetic field in a thickness direction of a magnetic recording medium has been attracting attention. The magnetic material used in such a perpendicular magnetic recording system must have an easy axis of magnetization in a direction perpendicular to the surface of the recording medium.

A hexagonal ferrite having uniaxial magnetization anisotropy, for example, Ba ferrite (BaFe ₁₂ O ₁₉ ) is a hexagonal plate-like crystal and has an easy axis of magnetization in a direction perpendicular to the plate surface. This type of magnetic material satisfies the above requirements as a magnetic material for perpendicular magnetic recording. The magnetic material has an appropriate coercive force (Hc, usually about 300 to 20,000 e) and a saturation magnetization (σs) as large as possible, and the average particle diameter of the magnetic powder is 0.3 μm or less in view of the recording wavelength. It is necessary to be.

By the way, since Ba ferrite has a coercive force of 50000e or more and is too large as a magnetic material for magnetic recording as it is, a method of substituting a part of Fe with Co and Ti to reduce the coercive force is proposed. (For example, JP-A-55-86103, JP-A-59-175707, IEEE Trans. On Magn., MAG-18, 16
(1982) P. 1122).

(Problems to be Solved by the Invention) Incidentally, in the known magnetic powder in which a part of Fe is replaced by Co and Ti, even if the composition ratios of the constituent elements are almost the same, the manufacturing method and the manufacturing conditions of the magnetic powder , The coercive force and the saturation magnetization are completely different as shown in Table 1. This means that if only part of Fe is replaced with Co and Ti,
It shows that the control of the coercive force is still insufficient.

(Means for Solving the Problems) The inventors of the present invention have earnestly studied to develop a magnetic powder for perpendicular magnetic recording that does not have such a conventional defect, and as a result, in addition to the conventional Co and Ti, more specific It has been found that adding metal is effective, and has completed the present invention.

In other words, the general formula ^{_{Fe a Co b Ti c M I}} d M II e O f ( wherein ^{M I} by the present invention represents Ba, Sr, at least one metallic element selected from Ca and Pb, M ^II is La, T
Represents a combination of at least one metal element selected from h, Gd, Yb and U, a combination of Sm, La and U and a combination of Nd and La, wherein a, b, c, d, e and f Are the numbers of Fe, Co, Ti, M ^I , M ^II and O atoms, respectively, a is 8 to 11.8, b is 0.05 to 2.0, and c is 0.0.
5 to 2.0, d is 0.5 to 3.0, and e is 0.01 to 2.0,
f represents the number of oxygen atoms satisfying the valences of other elements. ) And having an average particle size of 0.01 to 0.3 μm, a magnetic powder for magnetic recording is provided.

In the present invention, the number of atoms a to e of each component element of the magnetic powder is
Must be within the above numerical range, and outside this range, it is difficult to obtain a magnetic powder having a coercive force and saturation magnetization suitable for magnetic powder for magnetic recording.

The ratio of each component of the magnetic powder is preferably 8 to 11.8 for a and 0 for b.
1 to 1.5, c is 0.1 to 1.5, d is 0.8 to 2.0, and e is 0.02 to 1.
It takes a value of 0, and f is the number of oxygen atoms satisfying the valences of other elements. The magnetic powder of the present invention may have particles in which the crystals of the magnetic powder particles obtained do not have a normal hexagonal plate shape depending on the production method or production conditions, but the number of atoms of the present invention is Within the range, the object of the present invention can be sufficiently achieved.

According to the magnetic powder of the present invention, the coercive force and the saturation magnetization that must be provided as the magnetic powder for magnetic recording are provided even when the manufacturing method and the manufacturing conditions are different. It is considered that this is because the magnetic powder according to the present invention has a completely different function from the conventional magnetic powder containing Co and Ti.

The magnetic powder according to the present invention may be obtained by various methods known in the art, for example, a glass crystallization method, a coprecipitation method, a flux method,
It can be produced by a hydrothermal synthesis method or the like. Examples of the raw material for each element used include oxides, ammonium salts, nitrates, carbonates, organic acid salts, salts such as halides, free acids, acid anhydrides, condensed acids and the like.

The magnetic powder according to the present invention is a plate-like particle having an easy axis of magnetization in the hexagonal C plane, and is suitable as a magnetic material for perpendicular magnetic recording.

Among the magnetic powders according to the present invention, particularly coercive force of 300 to 200
Those having 0 Oe and a saturation magnetization of 40 emu / g or more are preferred.

Hereinafter, the present invention will be described in more detail with reference to examples. The coercive force and saturation magnetization in the examples were obtained by filling the obtained magnetic powder into a glass test tube having an inner diameter of 5 mm and a length of 5 cm and using a direct current magnetization characteristic measuring machine to measure a maximum applied magnetic field of 3500.
Oe. The average particle size was calculated by calculating the maximum diameter of 400 particles from a photograph obtained with a transmission electron microscope and calculating the arithmetic mean. X-ray diffraction was carried out on the examples given here, and in each case, the crystal phase of the magnetic powder was a hexagonal ferrite having a magnetobrumbite structure.

Further, the empirical formula of the magnetic powder shown in the examples uses the atomic ratio of each metal at the time of preparing the raw materials. The display of oxygen in the magnetic powder component is omitted for simplification.

Example 1 BaCl ₂ .2H ₂ O 0.55 mol, TiCl ₄ 0.375 mol, CoCl ₂ .6H ₂ O 0.37
5 mol, 0.05 mol of La (NO ₃ ) ₃ and 5.1 mol of FeCl ₃ .6H ₂ O 10 mol
Was dissolved in this order in distilled water, and this was designated as solution A. NaOH
17.5 mol and Na ₂ CO ₃ 4.72 mol were dissolved in 15 room temperature distilled water, and this was designated as solution B. Solution B was gradually added to solution A heated to 50 ° C., and then stirred at 50 ° C. for 16 hours. The pH after stirring was 10.5. The coprecipitate thus obtained was separated, washed thoroughly with water, dried at 150 ° C., and fired at 900 ° C. for 2 hours in an electric furnace. The Ba ferrite thus obtained is Ba
_1.1 Fe _10.2 Co _0.9 Ti _0.9 La _0.1

This fine particle powder had a plate shape with an average particle size of 0.12 μm, a coercive force of 736 Oe, and a saturation magnetization of 57 emu / g.

Comparative Example 1 Ba-ferrite was manufactured by the same method as in Example 1 except that lanthanum nitrate was removed. The obtained Ba-ferrite is represented by Ba _1.1 Fe _10.5 Co _0.75 Ti _0.75 . This fine particle powder has a plate shape with an average particle size of 0.25 μm and has an Hc of 444O.
e and σs were 35 emu / g.

Other for changing the examples 2 to 8 M ^I component M ^II components and composition ratio to prepare a magnetic powder shown in Table 2 in the same manner as in Example 1. It should be noted that chloride was used as the raw material of the M ^I component, and nitrate (U is uranyl nitrate) was used as the raw material of the M ^II component.

Claims (3)

[Claims] 1. A magnetic powder for magnetic recording Fe _a Co _b Ti _c M ^I _d M ^II _e represented by the following general composition formula and having an average particle diameter of 0.01 to 0.3 μm. O _f (wherein ^{M I} represents Ba, Sr, at least one metallic element selected from Ca and Pb, M ^II is La, Th, Gd, at least one metallic element selected from Yb and U, Sm And La and U, and Nd and La, where a,
b, c, d, e and f are Fe, Co, Ti and M, respectively.
Is the number of atoms of ^I , M ^II and O, and a is 8 to 11.8, b
Is 0.05 to 2.0, c is 0.05 to 2.0, and d is 0.
5 to 3.0 and e have a value of 0.01 to 2.0, and f is the number of oxygen atoms satisfying the valences of other elements. ). 2. A is 8 to 11.8, b is 0.1 to 1.5,
c is 0.1 to 1.5, d is 0.8 to 2.0, and e is 0.
The magnetic powder for magnetic recording according to claim 1, wherein the magnetic powder has a value of 02 to 1.0, and f is the number of oxygen atoms satisfying the valences of other elements. 3. The magnetic powder for magnetic recording according to claim 1, which has a coercive force of 300 to 20,000 e and a saturation magnetization of 40 emu / g or more.