JPS644330B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnetic powder suitable for high-density perpendicular magnetization recording. Magnetic recording generally relies on a method that uses magnetization in the in-plane longitudinal direction of the recording medium (shortest recording wavelength is about 1.2 μm). However, when attempting to achieve high recording density in this recording method using in-plane longitudinal magnetization, the demagnetizing field within the recording medium increases, making it difficult to achieve high density recording. In contrast to the above-mentioned recording methods, the perpendicular magnetization recording method reduces the demagnetizing field within the recording medium even if the recording density is increased, so it can be said to be essentially suitable for high-density recording. However, in this perpendicular magnetization method, it is necessary to have an axis of easy magnetization in a direction perpendicular to the recording medium surface, and a Co--Cr sputtered film has been developed as this type of recording medium. On the other hand, as the above-mentioned vertical medium, Japanese Patent Application Laid-Open No. 55-86103
A so-called coating type medium, in which magnetic powder and a binder are mixed and coated on a tape, as seen in the above publication, is also considered. Examples of the magnetic powder used in this case include hexagonal ferrite such as BaFe ₁₂ O ₁₉ . That is, since hexagonal ferrite has a flat plate shape and the axis of easy magnetization is perpendicular to the plane, it can be easily vertically aligned by magnetic field alignment treatment or mechanical treatment. However, the above-mentioned hexagonal ferrite has a high coercive force iHc and the head is saturated during recording, so some of the constituent atoms are It is necessary to reduce the coercive force to a value suitable for perpendicular magnetization recording by replacing it with a specific other atom. Furthermore, the crystal grain size of the hexagonal ferrite is selected to be in the range of 0.01 to 0.03 μm. The reason for this is that if it is less than 0.01 μm, it will not exhibit the ferromagnetism required for magnetic recording, and if it exceeds 0.3 μm, it will be difficult to advantageously perform perpendicular magnetization recording as high-density recording. In addition, as mentioned above, even if the magnetic powder has controlled coercive force and particle size,
If the magnetic powder does not have the property of being uniformly dispersed, a good recording medium cannot be obtained, so it is also necessary that the individual particles do not sinter and agglomerate, at least during the production of the magnetic powder. As shown in Japanese Patent Application Laid-open No. 56-67904, the present inventors have developed a method for producing hexagonal ferrite powder having the above characteristics by mixing a raw material for the desired ferrite with a glass-forming substance. After melting and pulverizing, the amorphous material obtained by melting and pulverizing the powder and rapidly cooling it is subjected to heat treatment to form fine ferrite particles suitable for the purpose. It has been found that it precipitates. Based on the above findings, the present invention aims to provide a method for easily producing fine powder of substituted hexagonal ferrite with good magnetic properties suitable for high-density magnetic recording with good mass productivity. To explain the present invention in detail below, the present invention includes a step of adding a glass-forming substance to a raw material mixture consisting of a basic component of hexagonal ferrite and a substitute component for reducing coercive force, mixing the mixture, cooling and pulverizing; A step of feeding the powder obtained by the pulverization into a high-temperature, high-speed plasma air stream to form a high-speed molten powder flow, and then rapidly cooling the molten particles to form an amorphous body; and heating the amorphous body. Treatment is performed to precipitate substitution type hexagonal ferrite in the form of fine particles in the amorphous body,
The method for producing magnetic powder for high-density magnetic recording is characterized by comprising a step of separating the fine particles, and is carried out, for example, as follows. First, a glass-forming substance such as boron oxide, silicon pentoxide phosphate, etc. is added to a mixture of the basic components of hexagonal ferrite and substitute components such as oxides, carbonates, and hydroxides for reducing the coercive force and melted. Then, it is cooled and pulverized into powder. The degree of refinement is sufficient as long as it can pass through the powder transport path of the plasma device shown in Figure 1, but the smaller the particles, the faster they will dissolve in the plasma, and economically, the smaller the particle size, the faster the particles will dissolve in the plasma. desirable. Thereafter, the prepared powder is fed from the powder feed path 2 into a high-temperature, high-speed plasma stream generated by a plasma device 1 whose main part is shown in FIG. 1 to form a molten powder stream 3. The molten powder (particles) in the molten powder stream 3 thus obtained is blown (injected) into a water tank 4, for example.
Rapidly cool to form an amorphous body. Next, the above amorphous body is subjected to heat treatment at about 600 to 900°C to precipitate fine particles of substituted hexagonal ferrite in the amorphous body, and then heated with dilute acetic acid, hydrochloric acid, hydrofluoric acid, etc. By etching and removing the glassy phase components by immersion in an aqueous solution, the particle size is 0.1~
Substituted hexagonal ferrite fine particles of about 0.3 μm can be easily obtained. In FIG. 1, 1a represents an anode, 1b represents a cathode, and 1c represents an argon-helium gas inflow path. Furthermore, in the method of the present invention, the particle size of the molten particles is controlled by the particle size of the powder particles to be subjected to plasma spraying. As mentioned above, it is possible to obtain a uniform amorphous state even by using a relatively simple cooling method such as thermal spraying into water, but it is also possible to obtain a uniform amorphous state using a relatively simple cooling method such as thermal spraying into water. Cooling means such as rapid cooling may also be used. Next, the present invention will be explained using specific examples. The magnetic powder to be produced consists of constituent ions.
We selected magnetoplumbite-type Ba ferrite, which aims to reduce the coercive force by replacing Fe ³⁺ with a combination of Co ²⁺ -Ti ⁴⁺ ions, and the amount of substitution is given by the molecular formula BaFe _12-2x Ti _x Co _x In O ₁₉ , x=0.8
And so. Also, as a glass forming substance, B ₂ O ₃ -
BaO glass was used. The mixing ratio of the ferrite raw material and the glass forming substance is B ₂ O ₃ …0.254 in molar ratio,
BaO…0.388, Fe ₂ O ₃ …0.274, TiO ₂ …0.042, CoO
...It was set to 0.042. First, the raw materials were thoroughly mixed in a mixer, melted in an electric furnace at 1400°C in an air atmosphere, and then poured into water to solidify. The solid was crushed and passed through a 270 mesh sieve to obtain a powder with a particle size of 50 μm or less. As shown in Figure 1, this powder is fed into a high-temperature, high-velocity plasma stream to create a high-velocity molten powder stream, which is sprayed into water to create a spherical shape with an average particle size of approximately 20 μm. A powder was obtained. That is, argon-helium gas is sent between the anode 1a and the cathode 1b,
Argon-helium is turned into plasma by arc discharge between the electrodes 1a and 1b, and a high-temperature, high-velocity plasma stream is ejected to form a so-called plasma jet.Then, the powder is fed from the powder feed path 2 along with argon gas into the plasma stream. The powder melted by the plasma gas was ejected as a molten powder stream 3, sprayed into a water tank 4, and rapidly cooled. The thermal spraying conditions of the present invention are a voltage of 40V and a current of 40V.
800A, and the distance from the molten powder spout to the water tank was 100 to 150 mm. According to the results of X-ray diffraction, the quenched powder obtained in the above manner was a completely uniform amorphous body. Next, this powder was heat-treated at 750°C for 4 hours in an air atmosphere, and then
After etching with a 20% acetic acid solution for 10 hours to remove the glass phase, X-ray diffraction was performed, and it was confirmed that it was a Ba ferrite single phase. In addition, the average particle diameter is as shown in the attached photo as Figure 2 (69000x magnification)
It was about 500 Å, which was extremely fine compared to conventional methods for producing hexagonal ferrite, and it had good plate-like properties and good dispersibility. In addition, since the raw material powder is melted in plasma in the present invention, the raw material powder is melted in an extremely short time and is superior in mass productivity compared to the conventional well-known manufacturing method of hexagonal ferrite. It became clear. The magnetic properties of the Ti--Co-substituted Ba ferrite magnetic powder obtained by the above-mentioned method of the present invention and, for example, the Tohoku University Scientific Measurement Research Institute Report Vol. 22, page 67 (1973
Table 1 shows a comparison of the magnetic properties of magnetic powders of single domain particles (average particle size approximately 0.1 μm) of the same composition obtained by a conventional solid-phase reaction such as that seen in 2010. Although the magnetic powder obtained by the present invention shows a slight decrease in σg due to fine particle size,
It can be seen that the magnetic properties are also comparable to magnetic powder obtained by conventional methods. It is clear that the σg of the present magnetic powder is larger than that of Ba ferrite of the same size (19 emu/g, Hc890 Oe), which was previously prototyped using the glass crystallization method. (IEEE Trans.Mag, MAG-7,
659 (1971)) [Table]

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram for explaining the embodiment of the method of the present invention, and Figure 2 is a substituted type obtained by the method of the present invention.
This is a transmission electron micrograph showing the state of Ba ferrite fine particles. 1...Plasma device, 1a...Anode, 1b...
Cathode, 2... Powder feed path, 3... Molten particle flow, 4
...Aquarium.

Claims (1)

[Scope of Claims] 1. A step of adding a glass-forming substance to a raw material mixture consisting of a basic component of hexagonal ferrite and a substituted component for reducing coercive force, mixing the mixture, cooling and pulverizing; a step of feeding the powder into a high-temperature, high-speed plasma air stream to form a high-speed molten powder flow, and then rapidly cooling the molten particles to form an amorphous body; and heating the amorphous body to form an amorphous body. Substituted hexagonal ferrite is precipitated in fine particles in the mass,
A method for producing magnetic powder for high-density magnetic recording, comprising the step of separating the fine particles.