JPS5814507A - Manufacture of magnetic powder for magnetic recording media - Google Patents

Abstract

PURPOSE:To obtain high preservability of manget, by forming an alpha-Fe2O3-structured layer on the surface of a needle gamma-Fe2O3-structured layer. CONSTITUTION:gamma-Fe2O3 is obtained by oxidizing needle Fe2O3 in the air. A structural defect within the gamma-Fe2O3 powder decreases preservability. When the needle gamma-Fe2O3 powder of low preservability is annealed under neutral atmosphere at 200-450 deg.C, an alpha-Fe2O3-structured layer is united on the surface of gamma- Fe2O3-structured layer. This enables the high preservability.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to Fi magnetic powder 6 [magnetic powder for recording and its manufacturing method].

Until now, 1-Fe, Os has been used as magnetic powder for magnetic recording.

Acicular magnetic powders such as Oo-adhesive-FelOs CrO2 are mainly put into practical use. In magnetic recording, there is a demand for higher recording density, and in response to this demand, the coercive force of magnetic powder has been praised and attempts have been made to improve this. That is, acicular r -Fe1O,
In the particles, the manufacturing process is a-FeOOHt-reduction to produce Fe3O4, which is further oxidized to 1-FeTO
High coercive force has been achieved by strictly controlling the process. However, this method has drawbacks such as strict process management and large variations in lofts during production. Furthermore, r −Fe
10g K Co ions were deposited and fcCo-deposited r
- Fe1O1 is available, but it has drawbacks such as high manufacturing costs because it requires the use of expensive Co1 and methods such as autoclaving to deposit Co ions. I did it. The present invention provides a low manufacturing cost method that does not have these disadvantages, that is, N, gas,
Low coercive force Or-F in neutral atmosphere gas such as Ar gas
By annealing the e103 powder, r-Fe1O, high coercive r-Fe with α-Fe*Osk generated on the surface,
O.

'fr.

That is, the present invention relates to a magnetic powder for magnetic recording media consisting of acicular r -Fe1O, a structural layer, and an α-FelO1 structural layer formed on the surface thereof, and furthermore, the acicular r -Fe1on lf& is 200-4 depending on the atmosphere
The present invention relates to a method for producing magnetic powder for magnetic recording media, which is characterized by annealing at 50°C.

The present invention will be explained in detail below.

Acicular Fe50. By oxidizing in air, r-F
20g of e was obtained. At this point, the coercive force becomes low (due to defects on the S inverse in the r-Ii'e 10g powder). This low coercive force acicular γ-Fe, O, powder is mixed with N, gas, and Ar gas.
By annealing in an alternative non-oxidizing and non-reducing gas, that is, a gas that generates a neutral atmosphere, γ
-The coercive force of Fe20g increases. Annealing temperature t12
Below 00℃, the coercive force does not increase and there is no effect;
If the temperature exceeds 50"0, the saturation magnetization decreases, so it is not desirable for magnetic recording.
T-X-ray analysis of magnetic powder annealed with r Fez
In addition to O1ll construction, a-Fe warehouse 0. It turns out that a structure exists. r -Fe1 after 7 anneals at 450°C or higher
In the xl analysis of Os, the diffraction peak from a-Fe, O, @ structure becomes very large, and it is assumed that a large amount of non-magnetic α-Fe2O3 is generated by annealing at high temperature and the saturation magnetization decreases. Conceivable. where r −Veto
α-F e in ginseng powder! Considering the reason why the pm layer is formed, two things can be considered when a diffraction peak from the y -Fe1O@ structure and a diffraction peak from the α-Veto@ structure are present in X-ray diffraction. That is, the a-Fe20B structure layer described in the present invention is r -Fe, 0g
Among the zero magnetic characteristics, saturation magnetization is formed on the powder surface, and when α-Fe@OH structure powder and y -Fe1on structure powder coexist. Since it is shown as a sum with the Peso1 structural part, it is impossible to distinguish between the two cases. However, the coercive force of non-magnetic α-Fe is 0. is zero in the case of r-Fel
Obtained only from the O1 structure. When α-FelOB structured powder and r-FetOmlJt structured powder are co-milled, there is no change in coercive force even after annealing because it is obtained only from r-Fe, O, structured powder. However, r
It is considered that the -Fe, O, structure and the α-Fe10g structure are integrated. The powder without annealing has a yellow color, but the one that has been annealed has a brown color, and even after annealing at a high temperature, the retention force does not become zero and there is still r -F6,0. Structure exists. The reason for this increase in the holding force of the integrated powder is thought to be that the α-Fez0g structure layer on the surface of the γ-Fe203 powder increases the holding force by the same effect as, for example, the deposited 00 layer. The details will have to wait for academic consideration.

Annealing of the powder can be carried out, for example, in an electric furnace. In this case, the powder is usually packed in a large-sized pod containing AJ*Oa or the like as a main component. When annealing the powder by controlling the atmosphere, the above method requires the atmospheric gas to penetrate between the powders at the bottom of the pod, making it difficult to anneal uniformly. For this reason, good effects can be obtained by making the powder filling layer thinner. 1.
However, in order to obtain an even better effect, it is preferable to bring the powder into contact with an atmospheric gas, that is, to fluidize the powder as if it were a liquid. There are two methods of fluidization that can be applied, including mechanical stirring, fluidization by sucking gas into the powder, and full application of ultrasonic vibration.

Examples will be described below.

Example The r-FetOl used in this example was manufactured by Pfier, USA.
It was made by a company and had a saturation magnetization of 7B, 1 emu/p, and a coercive force output C=375θe. The electric furnace used for annealing was a fluidized heating furnace manufactured by Toshi Engineering Co., Ltd. This is a metal cylinder with a gas inlet at the bottom, and a filter at the top, which prevents the powder from coming out of the cylinder. Furthermore, the upper end of this metal cylindrical part that extends outside the electric furnace is connected to a thin pipe, so that at the same time as the inflowing gas exits, external gas will not flow in and disturb the atmosphere during annealing. .

30g of the above y-Pe5os powder was put into this metal tube, and N was applied from the gas inlet. The gas tube flows at a rate of 2 CC/min. After the interior of the metal cylinder is sufficiently replaced with gas, the metal cylinder is placed in an electric furnace that is heated to a predetermined temperature. The thermocouple placed inside the metal cylinder was left at '41 for 30 minutes until it reached a predetermined temperature. (Extraction) Leave the removed metal cylinder at room temperature until it cools down sufficiently.

This is t, when the powder is taken out from the metal cylinder still at high temperature, %
'>'<To prevent the powder from deteriorating due to the atmosphere 6. . The saturation magnetism (; (Ms) and coercive force iHc of r -Fe2O3 thus treated are shown in the table and figure.

The results of this table show that MS decreases rapidly at temperatures above 450°C. It is also clear that iHc K has no effect at temperatures below 200°C. In this way, 1-Fe, Os is combined with N, gas forming a neutral atmosphere, and at 200°C to 450°C.
It can be seen that iHc can be increased by Neiling.

[Brief explanation of the drawing]

Figures 1 and s2 are diagrams showing the relationship between the annealing temperature and magnetic properties of magnetic powder.

Claims (1)

[Claims] (1) Magnetic powder for magnetic recording media consisting of an acicular r-Fe10B structural layer and an α-re, O, structural layer formed on its surface. (2) Acicular r-1'e101 powder was heated in a neutral atmosphere for 2
A method for producing magnetic powder for magnetic recording media, the method comprising annealing at 00 to 450°C.