JPS61152003A - Hexagonal system ferrite magnetic powder for magnetic recording - Google Patents

Abstract

PURPOSE:To reduce the temperature variation of coercive force by a method wherein a specific quantity of Fe<2+> is contained in the magnetic powder of substitution type hexagonal ferrite. CONSTITUTION:Fe<3+> is converted to Fe<2+> by performing an annealing in a reducing atmosphere on the hexagonal barium whereon a Co-Ti substitution is performed. Said reducing atmosphere is formed using hydrogen gas, forming gas containing H2 or carbon monoxide gas and the like. The desired temperature range of annealing is 350-500 deg.C or below. The annealing period is made longer at low temperature and it is made shorter at high temperature. The annealing is performed for 1hr at the temperature range of 350-500 deg.C or below. The barium ferrite formed as above contains Fe<2+> of 0.1-16wt%. The Hc of Ba ferrite at room temperature before annealing is 840Oe, and the Hc at 100 deg.C is 1,280Oe. The temperature characteristics of the coercive force of the magnetic powder can be improved effectively by the simple constitution as above- mentioned.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to magnetic powder suitable for high-density magnetic recording media using hexagonal ferrites 1 to 1 as magnetic materials, particularly magnetic recording with improved temperature characteristics of coercive force. The present invention relates to hexagonal ferrite powder for use.

[Technical background of the invention and its problems] Conventionally, magnetic recording has been carried out using magnetic powder made of acicular crystals such as γ-Fe2O3, cro2, CO coated-Fe203, etc.
One-dimensional recording is common in which magnetization is oriented in the track direction of a recording medium and residual magnetization in this direction is utilized.

However, this recording medium had the disadvantage that the higher the recording density, the greater the self-demagnetizing field within the medium, resulting in poor recording and reproducing characteristics, particularly in the short wavelength region.

In order to overcome this self-demagnetizing field and perform high-density recording, it is necessary to increase the coercive force of the medium and to make the magnetic layer thinner. However, at present, it is difficult to maintain the coercive force of the magnetic layer, and making the magnetic recording layer thinner leads to deterioration in the characteristics of reproduced signals.

For this reason, perpendicular magnetic recording, which uses residual magnetization in a direction perpendicular to the track surface of a magnetic recording medium, has been proposed for high-density recording. This perpendicular magnetic recording method is essentially suitable for high-density recording because the higher the recording density, the less the demagnetizing field in the recording medium. In this case, as a perpendicular recording medium, a co-Cr alloy film obtained by sputtering is known, and a coating method in which magnetic powder is dispersed in a binder is also being researched. In particular, the coating method using oxide magnetic powder has excellent corrosion resistance, abrasion resistance, surface properties, and high productivity, so it is thought that it will become the mainstream perpendicular recording method in the future.

In a magnetic recording medium consisting of a coated layer of magnetic powder, the axis of easy magnetization of the magnetic layer does not necessarily need to be oriented perpendicular to the substrate surface over the entire medium, but it is preferable that the orientation is as good as possible. . Hexagonal ferrites such as barium ferrite, strontium ferrite, calcium ferrite, lead ferrite, and composite ferrites in which these are mutually dissolved in solid solution are known as magnetic powders that are easily oriented vertically. These magnetic powders are hexagonal plate-shaped particles, and have an axis of easy magnetization in a direction perpendicular to the plate surface. For this reason, this magnetic powder is suitable for perpendicular magnetization recording because the plate surface easily becomes parallel to the substrate surface just by applying it, and the axis of easy magnetization can be easily oriented perpendicularly by magnetic field orientation treatment or mechanical orientation treatment. .

Since the coercive force Hc of this hexagonal ferrite is too large as it is, as is well known, part of the Fe is replaced with other elements such as AI, Ti, V, Or, and Mn.

Co, Ni, Cu, Zn, Ga, Nb, Ge.

By substituting with at least one of Sb, Ta, etc., the coercive force is lowered to 200 to 20,000 e, which is suitable for magnetic recording. By the way, it is said that the crystal grain size of this hexagonal ferrite is preferably in the range of o, oi to 0.3 μm. The reason for this is that if the thickness is less than 0.0 μm, it cannot exhibit the strong magnetism necessary for magnetic recording, and if it exceeds 0.3 μm, there will be little advantage in high-density recording.

However, the temperature increase of the coercive force of the hexagonal crystal ferrite 1- with the above characteristics was proposed by IE3MAG, which was announced as a part of the present invention.
-181122 (1982), it shows a tendency to increase as the temperature rises. He-90 at room temperature
008 becomes HC-14000e at 100℃
It ends up being more than that.

In magnetic recording, a magnetic medium is magnetized by a magnetic field generated by a magnetic head, that is, magnetic powder constituting the magnetic medium is magnetized to leave a record. The parameter that indicates whether or not a material is magnetized is coercive force. In hexagonal ferrite, for example, even if the magnetic field generated by the magnetic head is adjusted so that optimal recording remains on the magnetic medium at room temperature, if the temperature rises due to environmental changes, the coercive force changes and the magnetic head The disadvantage is that the generated magnetic field makes it impossible to perform optimal recording on the magnetic medium.

[Object of the Invention] The present invention was made in order to solve the problems in magnetic recording media using hexagonal ferrite, and in particular, to improve the temperature characteristics of coercive force.

[Summary of the Invention] The present invention is a substituted orthogonal ferrite in which temperature changes in coercive force can be reduced by containing 0.1 to 16% Fe2+ to magnetic powder. It is.

The present invention will be explained in more detail below. The substituted hexagonal ferrite used in the present invention is disclosed in, for example, JP-A-55-8610.
3. JP-A-56-67904, JP-A-56-16032
The one shown in the 8M publication can be used. co-T
By annealing hexagonal barium subjected to i-substitution in a reducing atmosphere, Fe2 can be converted to Fe2+. The reducing atmosphere is created using hydrogen gas, forming gas containing H2, -carbon oxide gas, or the like.

The annealing temperature is 300℃ or higher and 700℃ or lower, especially 350℃.
It is desirable that the temperature is higher than or equal to 500 °C and lower than 500 °C. The annealing time should be longer at low temperatures and shorter at high temperatures;
For temperatures below C, annealing may be performed for as long as one hour. In the barium ferrite thus produced, 0.05 WT% to 17% F e 3+ can be contained as F e 2 treasure. Room temperature Ha of Ba ferrite before annealing
was 8400e, and HC at 100°C was 12800e.

It was found that in Ba ferrite in which 3+ Fe was changed to 1.6% Fe2+, Hc=19500e at room temperature did not change at all with temperature up to 100°C. This will be explained in detail in Examples below.

[Embodiments of the invention] Chemical formula aao ” Fe Co T ! 0
3510.3 0.85 018 magnetic powder 1k with an average particle size of 0.08 μm
Prepared CI. This magnetic powder 100Q was separated and subjected to a predetermined temperature treatment in a tubular electric furnace that can be adjusted to a town atmosphere.

The treatment temperature varies from 270'C to 650C, and each treatment time is 1 hour. Table 1 shows the properties of the obtained magnetic powder. As Fe2+ increases, the temperature gradient of HC decreases.When Fe2+ is 1.6%, HC decreases from room temperature to 10%.
There is no change at all down to 0°C. As Fe2+ increases, this slope becomes negative, indicating that )(C decreases with increasing temperature.

Comparative Example H of magnetic powder with different HC value by changing CoTi substitution amount
The temperature change of C was measured. The results are shown in Table 2. H.C.
It can be seen that as the temperature gradient increases, the temperature gradient of HC decreases, but it is also found that it is larger than the temperature gradient values shown in the examples.

From the results shown in Examples and Comparative Examples, it was found that the temperature change of HC can be greatly improved by adding Fe@:Fe2+(,:) in Ba ferrite.

Table 1 l-1c (100) -Hc (20) 1-IC temperature gradient = □ (100-20)・Hc (20) )-1e(20), Hc (100): Temperature 20.
HC below T-margin table 2 at 100°C [Effects of the invention] As is clear from the above explanation, according to the present invention, the temperature characteristics of the coercive force of magnetic powder can be effectively improved with a simple configuration. I can do it.

Claims (1)

[Claims] A hexagonal ferrite magnetic powder for magnetic recording, characterized in that the hexagonal ferrite powder contains a substitution element for coercive force control, and contains 0.1 to 16 wt% of Fe^2^+.