JPS6194303A - Manufacture of hexagonal system ferrite particle powder - Google Patents

Abstract

PURPOSE:To obtain a greater aspect ratio ferrite particle by heat-treating amorphous material wherein raw material mixture containing the basic element of hexagonal system ferrite, B2O3 and CuO is melted and rapidly cooled. CONSTITUTION:The basis elements of hexagonal system ferrite B2O3 and CuO are added with B2O3, a glass forming material and Cu, the glass softening point is lowered and are enabled sufficient diffusion at a low temperature. This enables to make the hexagonal system ferrite of a sufficient grain diameter by heat treatment of 800 deg.C or lower temperature and an aspect ratio is made greater. That is, a mixture of 24% B2O3, 31% Fe2O3, 32% BaO, 5% CoO, 5% TiO2 and 3% CuO in each atom% is heated at 1,300 deg.C to be melted and is made amorphous by rapid cooling. Then, heat-treated for 4hr at 750 deg.C and glass is removed with 20% acetic acid heated at 80 deg.C. Then, washed with water and the powder which is excellent in saturated magnetization and coercive force and has an aspect ratio 7 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing hexagonal ferrite particle powder used as magnetic powder in a coated perpendicular magnetic recording medium.

[Conventional technology]

Conventionally, magnetic recording and reproducing methods for magnetic recording media such as magnetic tapes include γ-F eaoi and cobalt-coated γ.
-F ez03. So-called longitudinal recording is common, in which magnetic powder made of acicular crystals such as CrOl is oriented in the longitudinal direction of a recording medium, and the residual magnetization in the longitudinal direction of these magnetic powders is utilized.

However, this type of magnetic recording medium has the property that the demagnetizing field within the magnetic recording medium increases as the recording density increases, and for example, short wavelength recording is performed in response to the aforementioned higher density. If this is attempted, self-demagnetization loss and recording demagnetization loss will increase, resulting in poor recording and reproducing characteristics. If the recording layer of the magnetic recording medium is made thinner or the coercive force is increased in an attempt to suppress the demagnetization loss, problems such as a decrease in the output of the reproduced signal or saturation of the recording head, making it impossible to perform sufficient recording, may occur. There is a limit to the increase in density achieved by the above-mentioned longitudinal recording.

Therefore, conventionally, a perpendicular magnetic recording method has been proposed that uses residual magnetization in a direction perpendicular to the surface of a magnetic recording medium. This perpendicular magnetic recording system is known to reduce the demagnetizing field in the recording medium as the recording density increases, and is suitable for high-density recording.

In the magnetic recording medium used in this perpendicular magnetic recording method, it is necessary to have an axis of easy magnetization in a direction perpendicular to the magnetic layer surface, so it is difficult to use conventional acicular magnetic powder. C.

A magnetic recording medium such as a so-called vapor-deposited tape has been proposed in which a magnetic recording layer is formed by directly depositing -Cr alloy or the like on a base film by vacuum deposition or sputtering. However, this type of magnetic recording medium has problems in terms of running durability and production efficiency, and for this reason, recording media for perpendicular magnetic recording that can be manufactured by a coating method are being considered. . As the magnetic powder of this coating type perpendicular magnetic recording medium, hexagonal ferrite particle powder such as BaFe□04 is used, for example. The reason for using this hexagonal ferrite particle powder is that this ferrite has a flat plate shape, and after coating, the plate surface of the hexagonal ferrite particle tends to be parallel to the recording medium surface, and the axis of easy magnetization is on the plate surface. This is because vertical alignment can be easily performed by magnetic field alignment treatment or mechanical alignment treatment because it is perpendicular to .

In this way, by manufacturing perpendicular magnetic recording media using the above-mentioned hexagonal ferrite fine powder using a coating method, it is possible to produce recording media with excellent running durability and support for perpendicular magnetic recording with high production efficiency. It becomes possible to manufacture with

By the way, one of the methods for manufacturing the above-mentioned hexagonal ferrite particles is to mix and melt the hexagonal thread ferrite basic component and the glass forming substance, make it amorphous, and then heat treat it to form hexagonal crystals in the glass matrix. A so-called glass crystallization method for precipitating ferrite-based fine particles is known.

In the production of hexagonal ferrite by such a glass crystallization method, usually B, 03. B a O, F e, 03
The main component is Co and Ti for coercive force Hc low range.
is added. A glass body with this composition has a softening point of 900°C or higher, and sufficient diffusion does not occur below 800°C. It is necessary to perform heat treatment above ℃.

On the other hand, the plate ratio (ratio of grain size to thickness) of hexagonal ferrite
Low-temperature heat treatment is better, and heat treatment at 800° C. or lower is desirable from the viewpoint of the plate ratio.

Therefore, in the glass amorphization method, Fe.

When the 03-B a O-B103 type component is used as a raw material, it is difficult to produce hexagonal ferrite particles with a particle size of about 0.1 μm and a large plate-like ratio.

[Problem that the invention seeks to solve]

As described above, when B, O, and the like are used as glass-forming substances in the glass crystallization method, a major drawback is a decrease in the plate-like ratio due to the high glass softening point.

Therefore, the present invention has been proposed to eliminate such drawbacks, and is
B. It is possible to lower the glass softening point of the 03-based glass composition, thereby precipitating hexagonal ferrite particles with a sufficient particle size at low temperatures, and producing hexagonal ferrite particles with a high platelet ratio. An object of the present invention is to provide a method for producing hexagonal ferrite particles.

[Means for solving problems]

As a result of intensive research to achieve the above-mentioned object, the present inventors have developed Fe, 03-B a O-B20. The present invention was completed by discovering that the addition of Cu is effective in lowering the glass softening point of the hexagonal ferrite composition, and by adding a raw material mixture containing the basic components of hexagonal ferrite, BiO, and CuO. It is characterized in that after it is melted and rapidly cooled to become an amorphous body, this amorphous body is subjected to a heat treatment.

[Effect]

In this way, in the glass crystallization method, by further adding CuO to the basic component of hexagonal ferrite (F e203. Ba O) and the glass forming substance (B203), the glass softening point is lowered and the glass softening point is lowered. Sufficient diffusion will occur. As a result, hexagonal ferrite particles having a sufficient particle size are generated by heat treatment at 800° C. or lower, and the plate-like ratio of the obtained hexagonal ferrite particles increases.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described.

In the present invention, first, the general formula MO-n(Fe) is used.

03) (In the formula, M represents at least one of Ba, Sr, and Ca, and n = 5 to 6.) Each element constituting the hexagonal ferrite is adjusted to satisfy the above general formula. The basic components of hexagonal ferrite are contained in a proportion of 0.5%, B, which is a glass-forming substance, and 0.0%. A raw material mixture containing CuO as an additive is prepared, mixed well, and then melted in, for example, a platinum crucible.

Here, the addition of CuO is important, as it can lower the heat treatment temperature, which will be described later.

The amount of CuO added is B, which is a glass forming substance.
, 03 is preferably 10 to 20 atom %. If the amount added is less than 10 atom %, a sufficient effect cannot be expected; on the contrary, if it exceeds 20 atom %, hexagonal ferrite particles are obtained. There is a risk that the magnetic properties of

This melt is then rapidly cooled to form an amorphous material. This amorphization can be achieved by any conventional method, such as a twin-roll method or a single-roll method.

Although the resulting amorphous body contains the elements constituting hexagonal ferrite, it has not yet crystallized. Therefore, crystallization is promoted by further heat-treating the amorphous material obtained by the rapid cooling. At this time, since CuO is added to the raw material mixture, the glass softening point of the amorphous body is lowered to 800
Heat treatment at temperatures below °C causes sufficient diffusion, and hexagonal ferrite particles with a sufficient particle size are precipitated.

Subsequently, the amorphous body, in which crystallization is performed by this heat treatment and hexagonal ferrite particles are precipitated, is treated with dilute acid to melt and remove the glass component and separate the hexagonal ferrite particle powder. The dilute acids used in the above dilute acid treatment include dilute acetic acid,
Examples include organic acids or inorganic acids such as dilute hydrochloric acid and dilute nitric acid.

Finally, the separated crystals are washed with water and dried to obtain hexagonal ferrite particles.

The present invention will be explained below with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

Example.

-B20324 atomic%, Fezo331 atomic%, B
a032 atomic%, CoO3 atomic%, Ti025 atomic%,
A raw material mixture containing 3 atomic % of CuO was prepared, mixed well, and then heated and melted at 1300° C. in a platinum nozzle.

Next, this melt was spouted from the tip of a nozzle using Ar gas and rapidly cooled by a twin roll method to obtain an amorphous material.

Further, the above amorphous body was heat-treated at 750°C for 4 hours, and the glass content was removed with 20% acetic acid heated to 80°C.

Finally, it was washed with water to obtain hexagonal ferrite particle powder.

The saturation magnetization amount of the obtained hexagonal ferrite particle powder is 7F
3 is 57. 5emu/g, coercive force Hc is 12900e
.

σr/σs is 0.47. Particle size is 0.12μ, plate ratio is 7
Met.

Comparative Example I.

B, 0325 atomic%, Fe, 0332 atomic%, B
A raw material mixture containing 33 at. % of aO, 5 at. % of Co, and 15 at.

Next, this melt was spouted from the tip of a nozzle using Ar gas and rapidly cooled by a twin roll method to obtain an amorphous material.

Further, the amorphous body was heat treated at 900°C for 4 hours, and the glass content was removed with 20% acetic acid heated to 80°C.

Finally, it was washed with water to obtain hexagonal ferrite particle powder.

Saturation magnetization amount σs of the obtained hexagonal ferrite particle powder
is 57. lemu/g + coercive force He is 13600e
.

σr/σS is 0.44. Particle size is 0.08μ, plate ratio is 3
．． It was 5.

Comparative Example 2 In Comparative Example 1, the heat treatment temperature was 800°C,
Hexagonal ferrite particles were produced in the same manner as in Comparative Example I except for the following.

Saturation magnetization amount σs of the obtained hexagonal ferrite particle powder
is 56, 5emu/g, coercive force Hc is 13100e
.

σr/σs is 0.43. Particle size is O, O4#, plate ratio is 2
．． It was 5.

From these Examples and Comparative Examples, it can be seen that by adding CuO, hexagonal ferrite particles with a sufficient particle size are precipitated by low-temperature heat treatment, and the plate-like ratio is also extremely excellent.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
FezOB B a C in O-B103 raw material components
Since uO is added, the glass softening point is lowered, and it becomes possible to precipitate hexagonal ferrite particles with a sufficient particle size by low-temperature heat treatment. Therefore, it is possible to produce hexagonal ferrite particles having a large plate-like ratio.

Claims (1)

[Claims] Basic components of hexagonal ferrite, B_2O_3 and Cu
A method for producing hexagonal ferrite particles, which comprises melting a raw material mixture containing O, rapidly cooling the mixture to form an amorphous body, and then subjecting the amorphous body to a heat treatment.