JPH0616449B2 - Manufacturing method of hexagonal ferrite for magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hexagonal ferrite for magnetic recording media, and more particularly to a method for producing hexagonal ferrite suitable for perpendicular magnetic recording. BACKGROUND OF THE INVENTION Magnetic recording As for using, audio, video,
There are office automation equipment, etc., and these industries are one of the industries that continue to grow.

As a recording medium used for such magnetic recording,
Metal oxides are generally used, and among them, needle-shaped ferrite (γ-Fe ₂ O ₃ ) is widely used.
This acicular ferrite powder easily aggregates, and its shape is disadvantageous for use as a perpendicular magnetic recording medium. However, in recent years, along with the downsizing of the magnetic recording equipment, it has been required to improve the recording density of the recording medium. To meet this demand, it is advantageous to use a magnetic recording medium capable of perpendicular magnetic recording. Is.

As a recording medium of the perpendicular magnetic recording system, hexagonal ferrite is preferable (Japanese Patent Laid-Open No. 56-67904), but the problem is that hexagonal ferrite has a saturation magnetization value of about 60 em for use as a recording medium.
It is as low as u / g.

The saturation magnetization of hexagonal ferrite is brought about by the Fe atoms in the hexagonal ferrite, but 4 of the 12 Fe atoms contained in one molecule have spin directions that are the same as those of the other 8 Fe atoms. It has been low so far because it is oriented in the direction of canceling the magnetization. That is, the strength of magnetization depends on the Fe atom,
This is because only 4-4 = 4-4 contributed.

Japanese Examined Patent Publication No. 48-22265 discloses a method for producing the above hexagonal ferrite.

[Object of the Invention]

The present invention is to provide a method for producing a hexagonal ferrite for a magnetic recording medium having an improved saturation magnetization value.

[Outline of Invention]

The reason why the saturation magnetization value of hexagonal ferrite is not strong is as described above.

Therefore, since the present inventors have found that two of the four Fe atoms exist at positions (four-coordinates) different from each other in terms of crystallography, these two are managed to be replaced with a nonmagnetic atom or a weak magnetic atom. We thought that hexagonal ferrite with relatively high saturation magnetization could be obtained if possible.

The present inventors have made various studies to replace tetracoordinated Fe in hexagonal ferrite with non-magnetic or weakly magnetic atoms, and as a result, succeeded in producing the intended hexagonal ferrite.

The present invention relates to a method for producing a hexagonal ferrite for a magnetic recording medium, which comprises substituting 2 or less of Fe atoms in a general formula, MFe ₁₂ O ₁₉ hexagonal ferrite, with one or more atoms of Al, Cd and Zn. M oxide powder, Fe oxide powder and A
A mixed powder containing one or more powders of 1, Cd and Zn is melted, and the melt is cooled and poured into the circumferential surface of a rotating rotating roll to be vitrified, which is rapidly cooled and solidified, and then the solidified solidified product. Is heat-treated at 600 to 750 ° C. to precipitate the hexagonal ferrite of the above general formula, and then the glass component is dissolved and removed from the solidified material by a chemical, which is a method for producing a hexagonal ferrite for a magnetic recording medium.

[M is a metal selected from Ba, Sr and Pb]

The substitution degree of Al, Cd, and Zn of the ferrite (MFe ₁₂ O ₁₉ ) may be within a range satisfying (Alwt% / 9) + (Cdwt% / 30) + (Znwt% / 20) ≦ 1. If it exceeds this range, the saturation magnetization value decreases.

The method for producing the ferrite of the present invention comprises adding a glass-forming substance to the basic component of the ferrite and adding Al, Cd,
Zn is added. For example, BeO, Fe ₂ O ₃ , B ₂ O ₅
A mixture of one or more of Al, Cd, and Zn is melted to form glass, and the molten glass is rapidly cooled to form amorphous glass. By reheating this amorphous glass, fine hexagonal ferrite with a grain size of about 0.1 μm precipitates in the glass. The hexagonal ferrite of the present invention can be obtained by dissolving and removing the glass component with an acid. However, it is important that the reheating temperature of the amorphous glass is 600 ° C. or higher and 750 ° C. or lower. If the temperature exceeds 750 ° C., the effect of improving the saturation magnetization value may decrease, probably because the Fe atoms in the hexagonal ferrite do not sufficiently substitute with the above-mentioned elements. If the temperature is lower than 600 ° C, precipitation of hexagonal ferrite is insufficient and a sufficient amount of hexagonal ferrite cannot be obtained.

As the ferrite, needle-shaped ferrite (Fe
₂ O ₃ ) or ordinary hexagonal ferrite (MFe
₁₂ O ₁₉ ), or a mixture of both may be used.

Example of Invention

Example 1 53 wt% of BaO powder, 26% of Fe ₂ O ₃ powder, 5 wt% of Al powder and 16 wt% of B ₂ O ₃ powder were well mixed and then heated to 1400 ° C. in a platinum crucible and melted.

This molten glass was rapidly cooled using an apparatus as shown in FIG. 1 to obtain amorphous glass.

The glass 2 melted in the crucible 1 is dropped on the cooling roll 4. The cooling roll 4 is guided by a guide roller 6, and is in contact with a cooling belt 5 that moves along the cooling roll 4 at the surface peripheral speed and the peripheral speed of the cooling roll 4. The molten glass 2 is dropped between the cooling roll 1 and the cooling belt 5 and sequentially cooled. A belt cooling device 7 is provided to help the cooling belt 5 sandwich the molten glass 2 with the cooling roll 1 to cool it. Further, the cooling roll 1 is also provided with a roll cooling device 8 in order to control the cooling rate.

The cooled solid glass 3 is scraped off by the peeling device 9. Since the solid glass 3 is rapidly cooled, it becomes an amorphous glass.

By reheating the obtained amorphous glass, hexagonal ferrite is crystallized, and at the same time, tetracoordinate Fe ions in the hexagonal ferrite are replaced, but the heating temperature at that time is changed. In order to see the effect, the temperature was changed and the treatment was performed, and the effect on the saturation magnetization value was investigated.

After heating for 30 hours in the atmosphere with respect to each of which the temperature was changed between 500 ° C. and 900 ° C., the glass component was dissolved by boiling in an acetic acid aqueous solution for 2 hours, and the glass component of the present invention having a particle size of about 0.1 μm Hexagonal ferrite powder was prepared.

The above ferrite powder was enclosed in a quartz tube having an inner diameter of 5 mm × 90 mm and magnetized in a magnetic field of 10 o'clock, and the saturation magnetization value was measured to examine the influence of the heat treatment temperature. Results are shown in FIG.

As is clear from FIG. 2, the magnetization intensity rapidly increases at a heating temperature of 750 ° C. or lower. That is, in other words, it shows that the substitution of Fe atoms in the hexagonal ferrite proceeds at 750 ° C. or lower.

Those heated at a reheating temperature of less than 600 ° C. or higher than 850 ° C. had poor crystallization of hexagonal ferrite and the amount of ferrite recovered by glass dissolution with acetic acid was small. In consideration of practicality, the reheating temperature is preferably in the range of 600 ° C to 750 ° C.

Example 2 53% by weight of BaO powder, 18% by weight of Fe ₂ O ₃ powder,
After thoroughly mixing 16 wt% of B ₂ O ₃ powder, 2 wt% of Al powder and 11 wt% of Cd powder, 1400 in a platinum crucible.
It was heated to ℃ and melted. In the same manner as in Example 1, a hexagonal ferrite of the present invention was obtained. The magnetization characteristics of the ferrite powder were similar to those shown in FIG.

Example 3 53% by weight of BaO powder, 20% by weight of Fe ₂ O ₃ powder,
After thoroughly mixing 16 wt% of B ₂ O ₃ powder, 1 wt% of Al powder, 3 wt% of Cd powder and 7 wt% of Zn powder, the mixture was heated to 1400 ° C. in a platinum crucible and melted. In the same manner as in Example 1, a hexagonal ferrite of the present invention was obtained. The magnetization characteristics of the ferrite powder were similar to those shown in FIG.

Example 4 53 wt% BaO powder, 16 wt% Fe ₂ O ₃ powder,
18 wt% B ₂ O ₃ powder, 6 wt% Zn powder and Cd
After mixing 9 wt% of powder well, 140 in a platinum crucible
It was heated to 0 ° C. and melted. In the same manner as in Example 1, a hexagonal ferrite of the present invention was obtained. The magnetization characteristics of the ferrite powder were similar to those shown in FIG.

Example 5 44 wt% BaO powder, 15 wt% Fe ₂ O ₃ powder,
20 wt% BaFe ₁₂ O ₁₉ powder, 16 wt B ₂ O ₃ powder
%, Al powder 5 wt% were mixed well, and then heated to 1400 ° C. in a platinum crucible and melted. In the same manner as in Example 1, a hexagonal ferrite of the present invention was obtained. The magnetization characteristics of the ferrite powder were similar to those shown in FIG.

〔The invention's effect〕

The hexagonal ferrite obtained in the present invention had a magnetization intensity of about 50% up as compared with the conventional one. Using this, a magnetic recording medium was created. As a result, the reproduction output was about 50% higher than that of the conventional hexagonal ferrite, and the recording was clear.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for producing hexagonal ferrite according to the present invention, and FIG. 2 is a curve diagram showing a relationship between a heat treatment temperature and a saturation magnetization value during production of hexagonal ferrite. 2 ... Molten glass, 3 ... Solidified glass, 4 ... Cooling roll, 5 ... Cooling belt, 7, 8 ... Cooling device, 10 ...
Roll cleaning roller.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Ogawa 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture, Hitachi Research Institute, Ltd. (72) Tetsuro Uchida 4026 Kuji Town, Hitachi City, Ibaraki Prefecture, Hitachi Corporation Inside Hitachi Research Laboratory (56) Reference JP-A-56-60001 (JP, A) JP-A-56-118305 (JP, A) JP-A-58-2225 (JP, A) JP-A-59-106107 (JP, A) JP 60-229307 (JP, A) JP 60-81028 (JP, A) JP 61-24207 (JP, A) JP 60-127242 (JP, A) JP 60 -161602 (JP, A)

Claims (1)

[Claims] 1. A method for producing a hexagonal ferrite for a magnetic recording medium, wherein 2 atoms or less of Fe atoms in the general formula, MFe ₁₂ O ₁₉ hexagonal ferrite are substituted with one or more atoms of Al, Cd and Zn, The M oxide powder, the Fe oxide powder, and
A mixed powder containing one or more powders of Al, Cd, and Zn is melted, and the melt is cooled and poured into the circumferential surface of a rotating rotating roll to be vitrified, which is rapidly cooled and solidified, and then the solidified solidified product. Is heat-treated at 600 to 750 ° C. to precipitate the hexagonal ferrite of the above general formula, and then the glass component is dissolved and removed from the solidified material by a chemical, and a method for producing a hexagonal ferrite for a magnetic recording medium. [M is a metal selected from Ba, Sr and Pb]