JPH0753580B2 - 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.

Hexagonal ferrite with uniaxial magnetization anisotropy, for example
Ba ferrite (BaFe ₁₂ O ₁₉ ) is a hexagonal plate-shaped crystal that has an easy axis of magnetization in the direction perpendicular to the plate surface and satisfies the above requirements as a coating film type magnetic material for perpendicular magnetic recording. To do. The magnetic material should have an appropriate coercive force (Hc, usually about 300 to 2000 Oe) and a saturation magnetization as large as possible (σs, at least 40 emu / g or more), and the average particle diameter of the magnetic powder should be the recording wavelength. It is necessary to be 0.3 μm or less from the above relationship and 0.01 μm or more from the superparamagnetic relationship. In this range, it is preferable that the average particle size is small in view of noise.

By the way, Ba ferrite has a coercive force of 5000 Oe or more,
Since it 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 lower the coercive force has been proposed (for example, JP-A-55-86103, JP-A-55-86103). Sho 59-175707, IEEE Trans.on Magn., MA
G-18, 16 (1982) P.1122 etc.).

(Problems to be Solved by the Invention) The coercive force required as a magnetic material for magnetic recording is usually about 300 to 2000 Oe, but the required coercive force depends on the use of the magnetic material for magnetic recording. Since the values of magnetic force are different, it is necessary to have a constant value of coercive force according to each application. Therefore, it is not enough to simply reduce the coercive force, and it must be controlled to a constant coercive force according to the application.

In the known magnetic powder in which a part of Fe is replaced with Co and Ti, the coercive force and the saturation magnetization are quite different, as shown in Table 1, even if the composition ratios of the constituent elements are almost the same. This suggests that the control of the coercive force is insufficient when a part of Fe is replaced with Co and Ti.

For the purpose of recognizing this, the present inventor has co-precipitation method and co-precipitation method in which flux is mixed in the co-precipitate obtained in the middle step of the co-precipitation method, and the mixture is baked at a high temperature, and then the flux is washed and removed. Method was used to produce hexagonal ferrite magnetic powder for magnetic recording in which part of Fe was replaced with Co and Ti, and this was repeated many times under the same operating conditions, and the coercive force of the obtained magnetic powder was constant. Tried whether the value of is controlled.

As a result, even when manufactured under the same operating conditions, the coercive force, the saturation magnetization, the particle size, etc. of the obtained hexagonal ferrite were different for each production lot, and the variation in the coercive force was particularly remarkable. .

This means that in the case of hexagonal ferrite in which a part of Fe is replaced by Co and Ti, there is a slight non-uniformity of conditions that cannot be controlled by normal operation during the manufacturing process, and it is mixed during manufacturing. It is considered that the coercive force and the saturation magnetization are sensitively affected by minute impurities and the like.

From this, it was found that the coercive force could not be controlled by the ordinary coprecipitation method or the coprecipitation-Flack method when a part of Fe was replaced by Co and Ti.

(Means for Solving Problems) The inventors of the present invention have earnestly studied to develop a magnetic powder suitable for perpendicular magnetic recording which does not have such a conventional defect, and as a result, it is represented by the following general composition formula. They found that the magnetic powder for magnetic recording is effective, and completed the present invention.

That is, according to the present invention, the general composition formula Fe _a Co _b Ti _c M ^I _d M ^II _e M ^III _f O _g (where M ^I represents at least one metal element selected from Ba, Sr, Ca and Pb, M ^II represents Mo and / or W, M ^III represents at least one element selected from Si, Ge, Sn, Sb, Ni, Cu and V [provided that M ^II is W or M ^III
There combinations combination of the Sn, M ^II is W, M ^III is Sb combinations and M ^II is W, M ^III is Sn and Sb except], a,
b, c, d, e, f, and g are the numbers of Fe, Co, Ti, M ^I , M ^II , M ^III, and O atoms, respectively, a is 8 to 11.8, and b and c are 0.05 to 2.
0 and d have values of 0.5 to 3.0, e and f have values of 0.001 to 3.0, and g 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 of each component element of the magnetic powder is a to g
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 preferred magnetic powder is 8 to 11.8 for a, 0.1 to 1.5 for b and c, 0.8 to 0.2 for d, and 0.005 to 2.0 for e and f.
And g is the number of oxygen atoms satisfying the valences of other elements. The magnetic powder of the present invention, depending on the production method or production conditions, may be a mixture of particles in which the crystals of the obtained magnetic fine particles do not have a normal hexagonal plate shape, but the number of atoms of the present invention is Within the range, the object of the present invention can be sufficiently achieved.

In the magnetic powder of the present invention, there is almost no variation in the characteristics of the magnetic powder between lots when the manufacturing operation conditions are the same, and the magnetic powder has a coercive force that must be provided as magnetic powder for magnetic recording. Needless to say, it is characterized by further having excellent saturation magnetization and having a small average particle size. This means that the magnetic powder according to the present invention is
It is considered that this is because it has a completely different function from the magnetic powder containing Ti 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. In particular, it is suitable for a coprecipitation method and a coprecipitation-flux method in which a water-soluble flux is mixed with a coprecipitate obtained in the middle of the coprecipitation method, the mixture is baked at a high temperature, and then the flux is washed and removed.

The production of the magnetic powder of the present invention will be described below by taking the coprecipitation method and the coprecipitation flux method as an example.

That is, as the raw material compound of each metal element constituting the magnetic powder according to the present invention, oxides, oxyhydroxides, hydroxides, ammonium salts, nitrates, sulfates, carbonates, organic acid salts, halides, alkalis Examples thereof include salts such as metal salts, free acids, acid anhydrides and condensed acids. Water-soluble compounds are particularly preferable. The raw material compounds of the respective metal elements are preferably mixed and dissolved in water so as to form an aqueous solution.
When it is more convenient to mix and dissolve in an alkaline aqueous solution, it is mixed and dissolved in an alkaline aqueous solution described later.

On the other hand, the alkali component used in the alkaline aqueous solution may be any water-soluble one, and examples thereof include alkali metal hydroxides and carbonates, ammonia, and ammonium carbonate.
For example, NaOH, Na ₂ CO ₃ , NaHCO ₃ , KOH, K ₂ CO ₃ , NH ₄ OH, (NH ₄ ) ₂ C
O _{3 and the} like are used, and in particular, a combination of hydroxide and carbonate is prized.

Then, the metal ion aqueous solution and the alkaline aqueous solution are mixed to form a coprecipitate. The coprecipitate thus obtained is thoroughly washed with water and then separated. The cake-like or slurry-like coprecipitate thus obtained is, in the case of the coprecipitation method,
This is dried and then baked at 600 to 1100 ° C for 10 minutes to 30 hours at high temperature to obtain the corresponding hexagonal ferrite magnetic powder. When the coprecipitation-flux method is used, a water-soluble flux (for example, an alkali metal halide such as sodium chloride or potassium chloride, an alkaline earth metal halide such as barium chloride or strontium chloride, or a sulfuric acid) is added to the coprecipitate. Sodium, potassium sulphate, sodium nitrate, potassium nitrate, and mixtures thereof) in an appropriate amount, and dry it.
After baking at a high temperature of 0 to 1100 ° C. for 10 minutes to 30 hours, the water-soluble flux is washed with water or an acid aqueous solution, washed with water if necessary, and then dried to obtain the corresponding hexagonal ferrite magnetic powder.

As described above, the specific production examples of the magnetic powder of the present invention have been described by taking the coprecipitation method and the coprecipitation flux method as an example. Of course, if the produced magnetic powder is the magnetic powder represented by the general composition formula of the present invention, Needless to say, it may be manufactured by any method.

(Effects of the Invention) The magnetic powder according to the present invention is a plate-like particle having an easy axis of magnetization on the hexagonal C-plane, and when manufactured under the same operating conditions, the variation between lots is very small. However, it is suitable as a magnetic material for magnetic recording because it has a larger saturation magnetization and a smaller average particle diameter than the known magnetic powder in which a part of Fe is replaced with Co and Ti.

(Example) Hereinafter, the present invention will be described more specifically with reference to Examples. The coercive force and the saturation magnetization in the examples were measured with a maximum applied magnetic field of 10 KOe using a VSM (oscillating magnetometer).

The average particle size is 40 from the photograph obtained with a transmission electron microscope.
The maximum diameter of 0 particles was measured and calculated by the arithmetic mean.

Further, the composition formula of the magnetic powder shown in the examples uses the atomic ratio of each element 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.
375 moles and FeCl ₃ .6H ₂ O 5.25 moles were dissolved in 10 distilled water in this order to obtain a solution A. NaOH 17.5 mol, Na ₂ C
O ₃ 4.72 mol, Na ₂ SiO ₃ .9H ₂ O 0.2 mol, and (NH ₄ ) ₁₀ W ₁₂
The O ₄₁ · 5H ₂ O0.00833 mol was dissolved in room temperature distilled water 15,
This was designated as solution B. Solution A heated to 50 ° C. was gradually added to solution B and then stirred at 50 ° C. for 16 hours. The pH after stirring was 10.1. The coprecipitate thus obtained is separated and washed with water 15
It was dried at 0 ° C and calcined at 880 ° C for 1.5 hours in an electric furnace. The Ba-ferrite thus obtained is Ba _1.1 Fe _10.5 Co _0.75 Ti.
_0.75 W _0.2 Si _0.4 .

The same operation was repeated 5 times to examine the variations in the average particle size, coercive force, and saturation magnetization of the magnetic powder for each lot. The results are shown in Table 2. From Table 2, the magnetic powder according to the present invention not only has very small variation between lots,
It can be seen that, as compared with Comparative Example 1, the average particle size is small and the saturation magnetization is large.

Comparative Example 1 Ba-ferrite was produced in the same manner as in Example 1 except that sodium metasilicate and ammonium tungstate were removed. The obtained Ba-ferrite is Ba _1.1 Fe.
_10.5 Co _0.75 Ti _0.75 .

The same operation was repeated 5 times to examine the variations in the average particle size, coercive force, and saturation magnetization of the magnetic powder for each lot.
The results are shown in Table 3.

The magnetic powders known from Table 3 have a very large lot-to-lot variability, and in the normal operation as in the present invention of Example 1,
It can be seen that the coercive force cannot be controlled.

Example 2 The coprecipitate obtained in Example 1 was separated and washed with water, and 400 g of NaCl was added as a lux to the cakey coprecipitate slurry, which was thoroughly mixed and the water was evaporated to dryness. To
It was baked in an electric furnace at 870 ° C for 1.5 hours. The calcined product was washed with water until the soluble matter disappeared, and then dried and dried to obtain Ba-ferrite having the same composition formula as in Example 1.

The same operation was repeated 5 times from the step of producing the coprecipitate cake, and the variations in the average particle size, coercive force, and saturation magnetization of the magnetic powder for each lot were examined. The results are shown in Table 4.

It can be seen from Table 4 that the magnetic powder according to the present invention can be obtained as a uniform magnetic powder with less variation among lots.

Comparative Example 2 Using the coprecipitate obtained in Lot No. C1-1 of Comparative Example 1, the same operation as in Example 2 was repeated 5 times, and the average particle size of the magnetic powder, the coercive force of each lot, And the variation of saturation magnetization was investigated. The results are shown in Table 5. In this comparative example, although the same coprecipitate was used in all the lots, the magnetic powder having a known composition had a very large variation among lots, and thus, the magnetic powder having the same composition as in Example 2 of the present invention was used. However, it was impossible to control the coercive force.

Example 3 In the same manner as in Example 1 except that the amount of NaOH was 10.0 mol,
Solution A and solution B were prepared.

Solution A and solution B heated to 50 ° C. were mixed, placed in an evaporation dish, and water was evaporated with sufficient stirring until the water content became 50%. This is further dried in a dryer and then 870
Baking was performed in an electric furnace at ℃ for 1.5 hours. The calcined product was washed with water until the soluble matter was removed, and then dried and dried to obtain Ba-ferrite having the same composition formula as in Example 1.

The fine particle powder thus obtained was plate-shaped with an average particle size of 0.09 μm, the coercive force was 610 Oe, and the saturation magnetization was 55 meu / g.

Further, the same operation was repeated 5 times, and the experiment showed that the average particle size of the magnetic powder and the saturation magnetization were the same as the above for each lot, and the coercive force variation was ± 1.5%.
It was very small within.

Examples 4 to 22 Magnetic powders shown in Table 6 were prepared in the same manner as in Example 2 except that the composition ratios of the M ^I component, the M ^II component, the M ^III component and each metal component were changed. The raw material for the M ^I component is chloride, and the raw material for the M ^II component is ammonium salt.
^As the raw material for the ^III component, Si was sodium metasilicate or water glass, Ge, Sn, and Sb were chlorides, Ni was nitrate, Cu was chloride or hydroxide, and V was ammonium salt. The raw material compounds of Si, Mo, V, and W were dissolved in the alkaline aqueous solution.

Further, with respect to each of the magnetic powders shown in Table 6, the experiment was repeated 5 times by the same operation, and the variations in the average particle size, the coercive force, and the saturation magnetization of the magnetic powders from lot to lot were also investigated. The variation between lots was in the same range as in Example 2, and was extremely small.

Claims (1)

[Claims] 1. A magnetic powder for magnetic recording Fe _a Co _b Ti _c M ^I _d M ^II _e M ^III _f represented by the following general composition formula and having an average particle diameter of 0.01 to 0.3 μm. O _g (wherein M ^I represents at least one metal element selected from Ba, Sr, Ca and Pb, M ^II represents Mo and / or W, M ^III represents Si, Ge, Sn, Sb, Ni , Cu and V, at least one element being selected, provided that M ^II is W, M ^III is Sn, M ^II is W, M ^III is Sb, and M ^II is W, M ^III. Except for a combination of Sn and Sb], a, b, c, d, e, f, and g are Fe,
It is the number of atoms of Co, Ti, M ^I , M ^II , M ^III and O, and a is 8
.About.11.8, b and c are 0.05 to 2.0, d is 0.5 to 3.0, and e and f are 0.001 to 3.0, and g is the number of oxygen atoms satisfying the valences of other elements. ).