JPH0712933B2 - 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 must 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 is 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 diameter 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 is required depending 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 the coercive force must be controlled to a constant value 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 confirming this, the present inventor has studied the coprecipitation method and the coprecipitation-flux method (mixing the flux with the coprecipitate obtained in the intermediate step of the coprecipitation method to perform high temperature firing, and then washing the flux with water. A hexagonal ferrite magnetic powder for magnetic recording in which a part of Fe was replaced by Co and Ti was produced by the removal method, and this was repeated many times under the same operating conditions. I tried to see if it was controlled to a constant value.

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

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

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

(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, a magnetic recording medium represented by the following general composition formula The inventors have found that magnetic powder is effective and have 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 Si and / or Sn, M ^III represents at least one element selected from Ni, Cu, V, Nb, Ta and Zr, and a, b, c, d, e, f and g are The numbers of atoms of Fe, Co, Ti, M ^I , M ^II , M ^III and o, respectively,
8 to 11.8, b and c 0.05 to 2.0, d 0.5 to 3.0 and e and f 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 magnetic powder is preferably 8 to 11.8 for a, 0.1 to 1.5 for b and c, 0.8 to 2.0 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.

In the magnetic powder of the present invention, depending on the production method or production conditions, there may be mixed particles in which the crystals of the obtained magnetic powder particles do not have a normal hexagonal plate shape, but the number of atoms is the present invention. Within the range, the object of the present invention can be sufficiently achieved.

According to 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 having a further excellent saturation magnetization and having a small average particle size. This is considered to be 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. 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 a step 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 a 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, alkali halides 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
CO _{3 and the} like are used, and the combination of hydroxide and carbonate is especially 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,
After drying, it is baked at 600 to 1100 ° C for 10 minutes to 30 hours at high temperature to obtain the corresponding hexagonal ferrite magnetic powder. In the case of the coprecipitation-flux method, the coprecipitate contains 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). Sodium, potassium sulfate, sodium nitrate, potassium nitrate,
And a mixture of these, etc.) is added and dried,
After firing at 600 to 1100 ° C for 10 minutes to 30 hours at high temperature, the water-soluble flux is washed with water or an acid aqueous solution, washed with water if necessary, and dried to obtain the corresponding hexagonal ferrite magnetic powder.

Although the specific examples of the production of the magnetic powder of the present invention have been described above by taking the coprecipitation method and the coprecipitation flux method as an example, it goes without saying that the produced magnetic powder may be the magnetic powder represented by the general composition formula of the present invention. However, it may be manufactured by any method.

(Effect of the invention) 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 when manufactured under the same operating conditions, not only there is very little variation among lots, It is suitable as a magnetic material for magnetic recording because it has a saturation magnetization larger than that of a known magnetic powder obtained by substituting a part of Fe with Co and Ti and has a smaller average particle size.

(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 (vibrating magnetometer). The average particle diameter was calculated by calculating the maximum diameter of 400 particles from a photograph obtained with a transmission electron microscope and calculating 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 mol, CuCl ₂ .2H ₂ O 0.1 mol, and FeCl ₃ .6H ₂ O 5.25 mol were dissolved in this order in 10 l of distilled water to obtain a solution A.

NaOH 17.5 mol, Na ₂ CO ₃ 4.72 mol, and Na ₂ SiO ₃ · 9H ₂ O0.2
The mol was dissolved in 15 l of room temperature distilled water, and this was designated as solution B. After slowly adding Solution B to Solution A heated to 50 ℃, at 50 ℃
It was stirred for 16 hours. The pH after stirring was 10.25. The coprecipitate thus obtained was separated, washed with water, dried at 150 ° C., and fired at 880 ° C. for 1.5 hours in an electric furnace. The Ba-ferrite thus obtained is represented by Ba _1.1 Fe _10.5 Co _0.75 Ti _0.75 Si _0.4 Cu _0.2 .

The same operation was repeated 5 times, 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 2.

It can be seen from Table 2 that the magnetic powder according to the present invention has not only a very small variation among lots but also a smaller average particle size and a larger saturation magnetization as compared with Comparative Example 1.

Comparative Example 1 Ba-ferrite was produced in the same manner as in Example 1 except that sodium metasilicate and cupric chloride were omitted.
The obtained Ba-ferrite is represented by 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.

It can be seen from Table 3 that the known magnetic powder has a very large lot-to-lot variation, and the coercive force cannot be controlled by the normal operation of the present invention of Example 1.

Example 2 The coprecipitate obtained in Example 1 was separated and washed with water to obtain a cake-like coprecipitate slurry, and 400 g of NaCl was used as a flux.
Was added and mixed well, and then the water content was evaporated to dryness, and this 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 and The variation of saturation magnetization was investigated. The results are shown in Table 5. Even though the same coprecipitate was used in all the lots in this comparative example, the magnetic powder having a known composition had a very large variation among lots, and thus the magnetic powder having the same composition as that of Example 2 of the present invention was used. In operation, the coercive force could not be controlled.

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

Liquids A and 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%. After further drying this in a dryer, 870
It was baked in an electric furnace at 1.5 ° C for 1.5 hours. The calcined product is washed with water until the soluble product is removed, dried and dried, and the compositional formula similar to that of Example 1 is shown. Ba-ferrite was obtained.

The fine particle powder thus obtained was plate-shaped with an average particle size of 0.08 μm, the coercive force was 847 Oe, and the saturation magnetization was 53 emu / g.

In addition, when the same operation was repeated 5 times and an experiment was conducted,
The average particle size and saturation magnetization of the magnetic powder for each lot are the same as above, and the variation of coercive force is ± 1.5.
It was very small, within%.

Examples 4 to 23 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 Si for sodium metasilicate, Sn.
Is a chloride, V is an ammonium salt, Nb and Ta are oxides, Ni and Zr are nitrates as raw materials for the M ^III component,
For Cu, chloride or hydroxide was used. The raw material compounds of Si and V were dissolved in an 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 (where M ^I represents at least one metal element selected from Ba, Sr, Ca and Pb, M ^II represents Si and / or Sn, and M ^III represents Ni, Cu, V, Nb, Ta And at least one element selected from Zr, where 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, 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. ).