JP3251753B2 - Method for producing Ba ferrite magnetic powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hexagonal ferrite fine particles applicable to high-density magnetic recording, high-performance permanent magnets, and magnetic fibers. It is suitable.

[0002]

2. Description of the Related Art Hexagonal ferrite magnetic powder is used as a material for high-density magnetic recording, high-performance permanent magnets, and magnetic fibers. In particular, in recent years, in the field of magnetic recording, a perpendicularly oriented medium coated with fine magnetic powder of hexagonal ferrite represented by Ba ferrite has attracted attention. This hexagonal ferrite is a plate-like crystal and has an easy axis of magnetization in the direction perpendicular to the plate surface, so that it is possible to produce a perpendicularly-oriented medium. Compared with the conventional medium, there is a feature that a higher output can be obtained in a short wavelength region. As a method of producing such magnetic powder for high-density magnetic recording, a glass crystallization method, a hydrothermal synthesis method, a coprecipitation flux method, and the like are well known. The method is particularly preferred.

In the glass crystallization process, first, a glass forming substance and a hexagonal ferrite component are mixed, then melted at a high temperature, and the melt is rapidly cooled to produce an amorphous body. Then, the amorphous body is heat-treated at a temperature equal to or higher than the glass transition point to crystallize hexagonal ferrite fine particles in the amorphous body. And finally, by selectively removing glass components other than hexagonal ferrite with a thin solution such as acetic acid or hydrochloric acid,
Only hexagonal ferrite fine particles were extracted.

[0004]

By the way, in recent coating-type media, in order to improve short wavelength characteristics and achieve high-density recording, there is a general tendency to form fine particles. Recently, it is becoming clear that it is important that the SFDr of the magnetic powder is small in order to improve the recording density. Where S
The FDr is a value obtained by dividing a half-value width in a differential curve of a remanence magnetization curve by a remanent coercive force Hr, and an SFD (swithcing field) which has been often used conventionally.
distribution) rather than the actual recording / reproducing process, and physically interpreted as corresponding to the irreversible magnetization reversal distribution of the particle aggregate.

However, the conventional glass crystallization method has the disadvantage that the saturation magnetization of the magnetic powder generally becomes smaller as the particle size becomes smaller and the squareness ratio becomes much smaller than the theoretical value of 0.5. Further, there is a problem that the value of SHDr, which is an important parameter relating to the high-density recording characteristics, increases with finer particles. For this reason, despite the indispensable conditions for improving the recording density, the improvement in the short-wavelength characteristics due to the atomization is not as great as expected because the factors that improve the output characteristics of the medium and the factors that deteriorate the media are opposed. It was actual. The present invention has been made in view of this point, and it is an object of the present invention to provide a hexagonal ferrite magnetic powder which has sufficient saturation magnetization and squareness ratio and has a small SHDr while being fine particles in a glass crystallization method. With the goal.

[0006]

In this glass crystallization method, in order to obtain desired hexagonal ferrite fine particles, precise control of various production conditions such as melting, quenching, and crystallization steps of raw materials is required. It is. The present inventors have conducted intensive studies to obtain hexagonal ferrite magnetic powder having such fine particles and good characteristics, and as a result, the magnetic properties of the glass obtained in the melting and quenching process are particularly important. By controlling the value within a predetermined range, it has been found that a magnetic powder satisfying the above characteristics can be obtained, and the present invention has been achieved.

That is, according to the present invention, a raw material mixture of a glass-forming substance and a hexagonal ferrite component is melted, and the melt is quenched to form an amorphous body. A heat treatment at a temperature to crystallize the hexagonal ferrite fine particles therein, and then removing components other than the hexagonal ferrite fine particles, wherein the glass crystallization method comprises the steps of: Is controlled in the range of 0.1 emu / g to 2 emu / g. The saturation magnetization is a VSM value at a magnetic field of 10 kOe. When the saturation magnetization of the amorphous body is 0.1 emu / g or less, the obtained magnetic powder is more difficult to make finer than the present invention, and at the same time, in particular, the squareness ratio and the value of the saturation magnetization are generally low. It tends to be small. Fine particles can be formed by adjusting the crystallization temperature, but the magnetic properties are further deteriorated.

On the other hand, when the value of magnetization of the amorphous material is larger than 2 emu / g, it is not as easy to form fine particles as in the present invention, and particularly, the SFDr value tends to increase. Also in this case, when the fine particles are realized by adjusting the crystallization temperature, the magnetic characteristics are further deteriorated. It is not always clear why good magnetic powder is obtained by controlling the magnetization of the amorphous body to the above range, but in the region where the magnetization is smaller than 0.1 emu / g, each element is probably an ion. When it is not completely activated in the glass and exceeds 2 emu / g, a micro-ordered state is generated in the disordered state of the glass, which inhibits the formation of uniform crystal nuclei. Conceivable. In order to realize the present invention, a glass composition,
The optimal combination of the melting and quenching steps is important, and the optimal conditions for each step are not uniquely determined. In the present invention, by monitoring the magnetism of the produced glass and controlling it in the above range, a fine particle magnetic powder having excellent magnetic properties can be obtained.

In the present invention, the magnetic powder includes M-type BaFe12019 and W-type BaMe ₂ Fe16027.
(Note that Me represents a metal element.) Or hexagonal ferrite in which some of those atoms are substituted by another element, or composite powder of M and W, or composite hexagonal ferrite of M and spinel The basic components constituting the hexagonal ferrite are BaO, SrO, CaO, and PbO.
And at least one selected from the group consisting of Fe ₂ O ₃ and Co, Ni, Cu, Zn, Ti, Mg, Nb, and Sb as components for controlling coercive force or saturation magnetization.
At least one selected from n, Zr, V, Cr, Mo, Al, Ge, and W is given.

Of the hexagonal ferrites, A
On (Fe12-x-yM1xM2yO19-a)
(Where A is at least one element selected from Ba, Sr, and Ca, M1 is at least one element selected from divalent, M2 is at least one element selected from 4-6, and a is [x + ( 3-m) y] / 2 (where m is the average valence of M2), n is a number from 0.8 to 3, x or y is at least 0, and x and y are 3 and 2 respectively. The following numbers are preferred. And especially M1
It is effective to use at least one element selected from Co, Zn, and Ni.

The use of the magnetic powder in the present invention is broad as described above. Particularly, when the magnetic powder is used for a magnetic recording medium, it is required to be magnetically stable. If the coercive force is about 30 nm and the coercive force is too high, the head magnetic field is saturated during recording, and if the coercive force is too low it becomes impossible to hold the recording signal.

[0012]

【Example】

(Example 1 and Comparative Example 1) B ₂ O ₃ =
31.35 mol%, BaO = 28.68 mol%, Li ₂
O = 4 mol%, Na ₂ O = 4 mol%, Fe ₂ O ₃ = 2
7.33 mol%, CoO = 2.21 mol%, ZnO =
500 g of a powder raw material having a composition of 1.5 mol% and Nb ₂ O ₅ = 0.93 mol% was selected, dry-mixed, and then placed in a platinum crucible having a nozzle at the tip, 1,050.
C to 1600C (Example 1-1; 1,150C, Example 1-2; 1,250C, Example 1-3; 1,450C,
Comparative Example 1-1; 1,050 ° C, Comparative Example 1-2; 1,60
(0 ° C.) for 20 minutes. The melt was flowed at a flow rate of 5 g / sec at 500 rpm, a nip pressure of 5 ton, and a diameter of 20 c.
Rolled and quenched with a twin roll of bearing steel having a length of 30 cm and a length of 30 cm to produce glass flakes. Next, the glass flakes were subjected to a heat treatment at 730 ° C. × 4H to generate Ba ferrite. This is then washed with an acid to obtain Ba.
Ba ferrite fine particles were obtained by selectively removing components other than ferrite and washing and drying with water.

Example 2 and Comparative Example 2 In Example 1, the melting temperature was set to 1,250 ° C., and the amount of the melt flowing out was 2 to 20 g / sec (Example 2-1; 2 g / sec, Example 2-2; 5 g / sec, Example 2-3; 20 g / sec, Comparative Example 2
-1; 0.5 g / sec, Comparative Example 2-2; 50 g / sec) to produce glass flakes and magnetic powder under the same conditions as in Example 1.

Table 1 shows the properties of the glass flakes and magnetic powder obtained in Example 1 and Comparative Example 1, and Table 2 shows the properties of the glass flakes and magnetic powder obtained in Example 2 and Comparative Example 2. .

As is evident from the above results, the magnetic powder according to the present invention can be easily formed into fine particles, has a high saturation magnetization, a high squareness ratio, and a very small SFDr.
Therefore, it is suitable as a magnetic powder for high-density magnetic recording. In addition, it was confirmed that the magnetic powder obtained according to the present invention was excellent in medium characteristics particularly at short wavelengths due to such characteristics. The effect of the present invention is basically recognized even if the glass composition and the ferrite composition change.

[0016]

[Table 1]

[0017]

[Table 2]

FIG. 1 is a graph showing the relationship between the melting temperature and the magnetic characteristics of the flake and magnetic powder and SFDr based on the data shown in Tables 1 and 2 above. Magnetic Properties and SFD
FIG. 2 shows a graph of the relationship with r. In the figure, “white circle” and “black circle” indicate melting conditions of 1,15.
Example 1 at 0, 1, 250 and 1,450 ° C.
A few data and 1,050 ° C outside the lower range,
The data of Comparative Examples 1 and 2 at 1600 ° C. outside the upper range are shown respectively. The "white triangle" mark and the "black triangle" mark indicate the data of Examples 1, 2, and 3 when the glass outflow rate was 2, 5, and 20 g / sec, and the values of 0.
Data of Comparative Examples 1 and 2 at 5, 50 g / sec are shown, respectively.

Based on the data shown in Tables 1 and 2, the correlation between the smaller SFDr and the larger squareness ratio is better for the embodiment of the present invention and the comparative example. Is shown in FIG. As is apparent from FIG. 3, the SFDr value and the squareness value of the Ba ferrite magnetic powder obtained by the manufacturing method shown in the example of the present invention converge in a desirable direction, and those of the comparative example in which the Ba ferrite magnetic powder is widely spread. In contrast.

[0020]

As is evident from the above results, the magnetic powder according to the present invention can be easily made into fine particles, and has a large saturation magnetization, a large squareness ratio and a very small SFDr.
Therefore, it is suitable as a magnetic powder for high-density magnetic recording. Further, the magnetic powder obtained by the present invention due to such characteristics is excellent in medium characteristics especially at a short wavelength.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between SFDr and saturation magnetization with respect to melting temperature in Examples and Comparative Examples of the present invention.

FIG. 2 is a graph showing the relationship between the SFDr and the saturation magnetization with respect to the outflow amount of glass in Examples and Comparative Examples of the present invention.

FIG. 3 is a graph showing compatibility between SFDr and squareness ratio in an example of the present invention and a comparative example.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Etsuji Ogawa 1 Toshiba-cho, Komukai, Koyuki-ku, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Hajime Takeuchi Hajime Takeuchi Toshiba-cho, Koyuki-ku, Kawasaki-shi, Kanagawa No. 1 Toshiba Corporation Research and Development Center (56) References JP-A-4-284604 (JP, A) JP-A-64-42104 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H01F 1/10-1/11 C01G 49/00

Claims (4)

(57) [Claims] 1. A raw material mixture of a glass-forming substance and a hexagonal ferrite component is melted, and the melt is quenched to produce an amorphous body. By heat treatment, after crystallizing the hexagonal ferrite fine particles therein, in a method for producing a magnetic powder including a step of removing components other than the hexagonal ferrite fine particles, the magnetization of the amorphous body 0.1 emu / g-2 emu /
g. A method for producing magnetic powder of hexagonal ferrite fine particles, wherein the magnetic powder is controlled in the range of g. 2. The method according to claim 1, wherein the hexagonal ferrite is AO.n (F
e12-xyM1x2yO19-a), where A is B
at least one element selected from the group consisting of a, Sr, and Ca; M1 is at least one element selected from a divalent group; M2 is at least one element selected from a tetravalent to hexavalent group; (3-m) y] / 2 (m is M2
N is a number from 0.8 to 3,
2. The method according to claim 1, wherein x and y each include a component represented by 0 or more and a number of 3 or less. 3. The temperature at which the raw material mixture is melted is 1,1.
The method according to claim 1, wherein the temperature is 50 to 1,450 ° C. 4. 4. The method according to claim 1, wherein the melt is cooled at a flow rate of 2 to 20 g / sec.