JPH0363801B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for multipolar magnetizing a magnetic recording medium. [Prior art and its problems] In recent years, hard magnetic materials containing rare earth elements have been discovered, and because they have high coercive force and high energy product, they can be applied to magnetic encoders and pulse motors to improve performance by making them thicker. Research is being conducted to Hard magnetic films for such applications are used with multipole magnetization, and the pole width is becoming smaller as performance improves. However, this material has such a large coercive force that the commonly used multi-pole magnetization method limits the pole width to about 3 mm. One possible solution to this problem is local demagnetization using a laser. This laser method involves preheating a magnetic recording medium (hard magnetic film) containing rare earth elements formed on a substrate to a temperature of 0.1 to 0.95 times the Curie temperature Tc, magnetizing it, and then magnetizing that part again. Multi-pole magnetization is performed by this method. However, since magnetic materials containing rare earth elements are highly susceptible to oxidation, when they are heated, their properties deteriorate due to oxidation. Therefore, since the process cannot be carried out in air, a high vacuum device or a hydrogen atmosphere device is required, resulting in a large-scale device. To overcome this drawback, copper plating is applied as an oxidation-preventing film, but when this film is attached, the heat of the laser is absorbed by the protective film, so demagnetization cannot be performed effectively. [Object of the Invention] The present invention was invented to solve these problems, and it is an object of the present invention to provide a method for efficiently performing multi-pole magnetization. [Structure of the Invention] The present invention performs multipolar magnetization by combining magnetization and local demagnetization using a laser under specific conditions, and will be described below based on experimental examples. First, we used the sputtering method to deposit an SmCo ₅ film on a copper plate.
After 10μm of adhesion, a protective film of Cu or ZnSe, LaF ₃ , ZnS, MgF ₂ , LiF, BaF ₂ ,
Apply CaF ₂ to a thickness of 3 μm using a sputtering method. For these eight types of samples, in the thickness direction of the film
After applying an external magnetic field of 25KOe and magnetizing it in one direction,
Set it in the equipment shown in the drawing. The sample 1 is set on an X-Y automatic table 2 equipped with a heating plate 6, and is movable in the X-Y direction. Above sample 1 is optical system unit 3.
The diameter of the laser beam from the laser oscillator main body 4 can be adjusted by the lens 5. The experiment used a single-mode CO ₂ (carbon dioxide) gas laser and YAG (yttrium-aluminum).
Garnet) solid-state laser was used, the beam diameter was adjusted to 40 μm for the former and 5 μm for the latter, the power was 20 W,
After conducting the test under the conditions of a sample moving speed of 3 mm/s and a sample preheating temperature of 300°C, magnetic domains were observed by the Bitter method using a magnetic fluid. The thermally demagnetized part is magnetized in the opposite direction to the initial magnetization direction by the magnetic field of the part that was not demagnetized, so to check whether the thermal demagnetization is complete, you can check the width of the part that is magnetized in the opposite direction. . Uses CO ₂ laser, beam diameter 40μ
Table 1 shows the results when m is used.

[Table] Table 2 also shows the results using a YAG laser with a beam diameter of 5 μm.

【table】

〔Effect of the invention〕

As described above, according to the present invention, thermal demagnetization can be carried out efficiently and in air, so that multipolar magnetization of a magnetic recording medium containing a rare earth element becomes possible.

[Brief explanation of drawings]

The drawing is a schematic diagram showing the configuration of a laser thermal demagnetizer used in experiments of the present invention. 1: sample, 2: X-Y automatic table, 3: optical system unit, 4: laser oscillator body, 5: lens, 6: heating plate.

Claims (1)

[Claims] 1. After coating a magnetic recording medium containing a rare earth element formed on a substrate with a material having a low laser absorption rate, and heating the magnetic recording medium to a temperature of 0.1 to 0.95 times the Curie point temperature Tc. 1. A multi-pole magnetization method, which comprises magnetizing, then demagnetizing a part or plurality of the magnetized parts using a laser to a temperature above Tc, and then magnetizing the demagnetized parts again. 2 The laser device is a YAG laser, and the materials with low laser absorption are ZnSe, LaF ₃ , ZnS, MgF ₂ ,
2. The multipolar magnetization method according to claim 1, wherein at least one substance selected from the group consisting of LiF, BaF ₂ and CaF ₂ is used. 3. The multi-electrode assembly according to claim 2, wherein the laser device is a CO ₂ laser, and the material with low laser absorption is at least one substance selected from the group of ZnSe, ZnS, BaF ₂ and CaF ₂ . magnetic method.