JPS63185003A - Magnetic powder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To enable the fine adjustment of appropriate coercive force and easy controlling by adding at least one element selected from a group of Al, Cr, Si and Mg at the time of substituting component elements to reduce the coercive force of hexagonal system ferrite. CONSTITUTION:The essential components of hexagonal system ferrite wherein the mean particle size is 0.01-0.3 mum and the coercive force is 200-2000 Oe contain at least one element selected from a group of iron, oxygen, Ba, Sr and Ca, at least one element selected from a group of Ti, Co, Zn, Zr and Ge and at least one element selected from a group of Al, Cr, Si and Mg. If the mean particle size of this magnetic powder is less than 0.01 mum, ferromagnetism is lost and if exceeds 0.3 mum, a multimagnetic domain structure is formed and this is not desirable. If the coercive force is less than 200 Oe, the maintaining of a recording signal is made difficult and if exceeds 2000 Oe, a head magnetic field is saturated and recording becomes difficult.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Application of M Tojo) The present invention relates to a magnetic powder for magnetic recording media that is controlled to a fine positive coercive force and at the same time maintains high saturation magnetization.

(Prior Art) Conventionally, magnetic recording media used for video recording, digital recording, etc. are made by coating acicular magnetic powder such as γ-k ez o31 Cr O□ on the surface of a base film together with an organic binder. It has been subjected to orientation treatment.

In order to obtain a sufficient S/N ratio in this magnetic recording medium, it is necessary to make the particle size of the magnetic powder applied to the base film sufficiently small. For example, in the case of current video recording, acicular magnetic powder having a length of about 0.3 μm is used, but it is desired to further improve the recording density.

Recently, it has become possible to use hexagonal ferrite with an average grain size of 0.3 μm or less. This hexagonal ferrite usually has too high a coercive force on its own to allow magnetic recording, so the -S constituent atoms are replaced with specific other atoms to reduce the coercive force. However, if you perform a replacement operation like the one above,
The obtained macrogonal ferrite has a lower saturation magnetization than before the substitution, and at the same time, a small change in the amount of substitution causes a large fluctuation in coercive force, which is difficult to control, which is an inconvenient situation. Therefore, there is a strong desire for a macrogonal ferrite whose coercive force can be easily controlled to an appropriate value and whose saturation magnetization is easy.

(Problems to be Solved by the Invention) As described above, when the constituent atoms of macrogonal ferrite are replaced in order to reduce the coercive force, the saturation magnetization decreases and the &M of The problem is that it is difficult to control the coercive force to an appropriate level because the coercive force fluctuates significantly.

The present invention was made to solve the above problems,
It is an object of the present invention to provide magnetic powder for magnetic recording media that can finely adjust and easily control appropriate coercive force and at the same time has high saturation magnetization.

[Structure of the Invention] (Means for Solving the Problems) As a result of various experimental studies to achieve the above object, the present inventor has developed the following methods to reduce the coercive force of macrogonal ferrite:
When replacing its constituent atoms, 11 u pCr , 8i
It has been found that by adding at least one element selected from the group consisting of Mg and Mg, the reduction in coercive force is not rapid and can be finely adjusted, and the saturation magnetization hardly decreases. That is, the magnetic powder for magnetic recording media of the present invention has an average particle size of 0.01 to 0.3 μm and a coercive force of 200 to 20 μm.
It is made of 00 Oe hexagonal ferrite, and the essential components of this hexagonal ferrite are iron, oxygen, and Ba.

at least one polar element distant from the group of Br and Ca;
at least one element selected from the group of Ti, Co, Zn, Zr, and Ge, and A4. Cr, Si.

It contains at least one element selected from the MgI) group. This magnetic powder has an average particle size of 0.01
It consists of hexagonal ferrite with a diameter of ~0.3 μm, but if the average grain size is less than 0.01 μm, ferromagnetism is lost;
If it exceeds μm, a multi-domain structure is not desirable.

(Function) As the magnetic powder of the present invention, hexagonal ferrite of each pole can be applied, but mag-dobrambite type is particularly preferable in that it is easy to crystallize. Therefore, the following explanation will be based on the magnetoplumpite type hexagonal heptagonal crystal system.

Magnetoplumpite type hexagonal 7-elite is human 0-6
Fe20. That is, it is expressed as A-re1□-xMxO□. In the formula, it is at least one element selected from the details of AViBa, Br, and Ca, and M is an element that replaces a part of iron in the above constituent elements in order to reduce the coercive force of the 7-elite. At least one element encountered is from the group Ti, Co, Zn, ZrGe. Preferably Ti
It is preferable to replace one element of iron with two elements: and Co. X is the amount of substitution between the substituent element and iron.

When reducing the coercive force mentioned above, iron is replaced with ffl element λ so that the coercive force of the ferrite becomes 200 to 2000 Oe.
I play ffi chivalry in 1. The reason why the coercive force is limited to the above range is that if the coercive force is less than 200 Oe, it will be difficult to maintain recording <a, and if it exceeds 2000 Oe, the head magnetic field will become saturated and recording will become difficult. It is.

As the coercive force is reduced, the saturation magnetization is also reduced. In particular, when a part of re is replaced with Ti and Co, the coercive force is reduced by a large amount, and even if a small amount of ft is replaced, the coercive force is greatly reduced, making minute control difficult. Therefore, the present invention provides a method for performing this replacement operation when the person 4. Cr.

By adding at least one element selected from the group of s+ and Mg to the substituent element, it is possible to suppress the sudden decrease in coercive force and finely adjust YN, and also to reduce the saturation magnetization. This is the product of boring magnetic powder.

The method for producing magnetic powder of the present invention includes, for example, mixing and melting the basic components of hexagonal ferrite and a glass-forming substance, followed by rapid cooling to produce an amorphous body, and then heat-treating this amorphous body. A glass crystallization method or the like is applied, in which the desired ferrite crystal powder is precipitated using an acid bath, and then the glass-forming substance is removed using an acid bath.

(Example) Barium ferrite was selected as the desired magnetic crystal, and part of the Fe"+ ions in the barium ferrite was replaced with CO2+ -TB4+ ions to control the coercive force, resulting in B a Fe 1 o, 4 COo,s Ots
BaC03t H3BO3+ Fe203m #
TsO2*CoO was weighed. This basic mixture contains people J20. Add a predetermined amount of
The amorphous material obtained by heating and melting by heating at 780°C for 4 hours by pouring this melt onto a twin roll and rapidly cooling it was heated at 780°C for 4 hours to crystallize the ferrite particles, which was washed with a 220ml 1t% vinegar solution. After washing with water and drying, the required magnetic powder was obtained. The magnetic properties of this magnetic powder are shown in Table 1.

Examples 1 to 3 have the same basic mixture composition, and Examples 1 and 2 have A420. .

The content of Cr2O3 is different, and Example 3 has AJ20. I
It does not contain 20 g of Cr component. In the comparative example, the content M of TiO□ and CoO components in the basic mixture composition
1 by 0.2% by weight.

Table 1 As is clear from Table 1, the basic mixture composition has 40. By adding 0.5 m and 11% of each of Cr2O and Cr2O, the coercive force is reduced by 200C, and the amount of addition and the reduction width of the coercive force are in a proportional relationship. Also, the saturation magnetization is Q, 3 e
mu/g only decreases.

As shown in the comparative example, in the basic mixture composition T
When t 02 and Or, 03 are each increased by 0.2% by weight, the coercive force is significantly reduced to 225 Oe, and the saturation magnetization is also reduced by Q, 7 emu/g.

As mentioned above, the amount of substitution of T i Ox and CoO increases the coercive force by 112% only by increasing o by 1%.
06 will also be significantly reduced. Therefore, the coercive force is 1006
For variation, TiO□ and Co.

This results in a weight change of 0.01 weight for each, but it is difficult to finely control the amount of substitution. On the other hand, A4
0. Even if the amount of addition of 20 g of Cr and Cr is increased by 1%, the coercive force will only be reduced by 400C, and in order to change the coercive force by 1006%, each must be changed by 0.25%. It can be controlled very easily. Furthermore, the decrease in saturation magnetization is minimal.

By the way, people! 20. and Cr, 0. If the amount of each added exceeds 1% by weight, the melting properties of the mixture will deteriorate, it will take time for the raw material particles to completely decompose, and the saturation magnetization will be 0.
5 emu/g, and favorable results cannot be obtained.

〔Effect of the invention〕

As described above, the present invention has an average particle size of 0.01 to 0.3 μm.
, is made of hexagonal ferrite with a coercive force of 200 to 2000 Oe, and A4. Cr
, 8i, Mg, and contains at least one polar element selected from the group of Mg.
By adding a small amount of O3, the range of coercive force IQOe can be easily controlled, and the saturation magnetization can be maintained at a high level with almost no decrease.

Claims (2)

[Claims] (1) Average particle size 0.01~0.3μm, coercive force 200~
It is made of 2000 Oe hexagonal ferrite, and the essential components of this hexagonal ferrite are iron, oxygen, and Ba.
, Br, and Ca; at least one element selected from the group of Ti, Co, Zn, Zr, and Ge; and at least one element selected from the group of Al, Cr, Si, and Mg. 1. A magnetic powder for a magnetic recording medium, characterized in that it contains at least one element. (2) The magnetic powder for a magnetic recording medium according to claim 1, wherein the hexagonal ferrite is a magnetoplumpite ferrite.