JPH0712934B2 - 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 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) Incidentally, the coercive force required as a magnetic material for magnetic recording is usually about 300 to 2000 Oe, but the coercive force required depending on the use of the magnetic material for magnetic recording used. Since the value of is different, it is necessary to have a constant value of coercive force according to each application. Therefore, simply reducing the coercive force is not sufficient and 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 confirming this, the present inventor 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 baked at 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 by Co and Ti, and this was repeated many times under the same operating conditions. Tried whether the value is controlled.

As a result, even when manufactured under the same operating conditions, the coercive force, the saturation magnetization, the grain size, etc. of the obtained hexagonal ferrite varied depending on the production lot, and the coercive force was particularly uneven.

This means that in the case of a 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, It is considered that the coercive force and the saturation magnetization are sensitively affected by minute impurities mixed in.

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 at least one element selected from Cr, In, Tl and S, and M ^III represents Si, Ge,
Sn, Sb, Mo, W, V, Ni, Cu, Zr, P, Te, Bi, Cd, and at least one element selected from Ag, 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, a is 8 to 11.8, b and c is 0.05 to 2.0, and d is 0.5 to
3.0 and 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 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. As a matter of course, it has a feature that it has excellent saturation magnetization and has 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.

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.

Further, the sulfur source material may be any compound containing sulfur. 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,
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. In the case of the coprecipitation-flux method, a water-soluble flux (for example, an alkali metal halide salt such as sodium chloride or potassium chloride or an alkaline earth metal halide salt such as barium chloride or strontium chloride) is added to the coprecipitate washed with water. , Sodium sulphate, potassium sulphate, sodium nitrate, potassium nitrate, and mixtures thereof) or by evaporating the water from a mixture of an aqueous metal ion solution and an alkaline solution to dry it, and then drying it at 600-1100. 10 minutes to 3 at ℃
After firing at high temperature for 0 hours, the water-soluble flux is washed with water or an aqueous acid solution, and if necessary, further washed with water and dried to obtain the corresponding hexagonal ferrite magnetic powder.

Above, specific examples of the actual situation have been shown by taking the coprecipitation method and the coprecipitation flux method as examples, but of course, if the produced magnetic powder is the magnetic powder represented by the general composition formula according to the present invention, any method can be used. It may be manufactured.

(Effect 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, not only there is very little variation among lots, but also , Fe has a saturation magnetization larger than that of a known magnetic powder in which Co and Ti are partially substituted, and a powder having a small average particle size can be obtained, which is suitable as a magnetic material for magnetic recording.

Hereinafter, the present invention will be described in more detail with reference to examples. The coercive force and saturation magnetization in the examples were measured using VSM at a maximum applied magnetic field of 10 KOe and a measurement temperature of 28 ° C. 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, Cr (NO 3) 3 ·} 9H 2 O0.05 mol and FeCl ₃ · 6H ₂ O5.25
Mol was dissolved in 10 liters of distilled water in this order, and this was designated as solution A. NaOH17.5 mol, Na ₂ CO ₃ 4.72 mol of Na ₂ Sio ₃ · 9H ₂ O
0.2 mol was dissolved in 15 l of distilled water at room temperature, 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 10.2. The coprecipitate thus obtained was separated, washed with water and dried at 150 ° C.
It was baked in an electric furnace at 1.5 ° C for 1.5 hours. Ba− thus obtained
Ferrite is represented by Ba _1-1 Fe _10.5 Co _0.75 Ti _0.75 Cr _0.1 Si _0.4 .

The same operation is repeated 5 times, and the variations in the average particle size, coercive force, and saturation magnetization of the magnetic powder for each lot are examined. The results are shown in Table 2. From Table 2, the magnetic powder according to the present invention is
It can be seen that not only the variation between lots is very small, but also the average particle size is smaller and the saturation magnetization is larger than in Comparative Example 1.

Comparative Example 1 Ba-ferrite was produced in the same manner as in Example 1 except that sodium metasilicate and chromium nitrate were removed.
The resulting Ba- ferrite 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.

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 2 400 g of NaCl was added as a flux to the cake-shaped resonator slurry obtained by separating the coprecipitate obtained in Example 1 and washing with water, mixing it well, and evaporating the water to dryness.
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 was removed, 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 A was prepared in the same manner as in Example 1 except that the amount of NaOH was 11.0 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 with a dryer,
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 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 0.083 μm, the coercive force was 607 Oe, and the saturation magnetization was 56.5 emu / g.

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

Examples 4 to 27, except that the M ^I component, the M ^II component, the M ^III component and the composition ratio were changed,
Magnetic powders shown in Table 6 were prepared in the same manner as in Example 2. In addition, chloride is used as the raw material of the M ^I component, Na ₂ SO ₄ is used as the raw material of the M ^II component, and nitrate is used as the others, and Si is sodium metasilicate or water glass as the raw material of the M ^III component. , Sn and Sb are chlorides, Ni, Zr, Te, Bi, Cd, and Ag.
Is a nitrate, Cu is a chloride or hydroxide, and Mo, W, P, and V are ammonium salts. The raw material compounds of S, Si, Mo, V, P and W were dissolved in the alkaline aqueous solution.

Further, with respect to each of the magnetic powders shown in Table 6, repeated experiments were conducted five times by the same operation, and variations in the average particle size, coercive force, and saturation magnetization of the magnetic powders for each 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 at least one element selected from Cr, In, Tl and S, M ^III Is Si, Ge,
Sn, Sb, Mo, W, V, Ni, Cu, Zr, P, Te, Bi, Cd, and at least one element selected from Ag, 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, a is 8 to 11.8, b and c is 0.05 to 2.0, and d is 0.5 to
3.0 and e and f have values of 0.001 to 3.0, and g is the number of oxygen atoms satisfying the valences of other elements. ).