JPH0232690B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a photothermal magnetic recording medium used for magneto-optical memory, magnetic recording, display elements, etc., and in particular, magnetic thin film recording that can be read using magneto-optic effects such as magnetic force effect or Faraday effect. It's about the medium. Conventionally, MnBi,
Polycrystalline thin films such as MnCuBi, Gdco, GdFe,
Amorphous thin films such as TbFe, DyFe, GdTbFe, and TbDyFe, and single crystal thin films such as GdIG are known. Among these thin films, we are focusing on the film-forming efficiency for producing large-area thin films at temperatures near room temperature, the writing efficiency for writing signals with small photothermal energy, and the reading efficiency for reading written signals with a good S/N ratio. In view of this, recently, the amorphous thin film is considered to be excellent as a photothermal magnetic recording medium. However, various drawbacks have been pointed out even in these amorphous thin films. For example, GdFe has a small coercive force, making recorded information unstable.
Furthermore, GdFe and Gdco perform writing using magnetic compensation points, and the film composition must be strictly controlled during film formation in order to make the writing efficiency uniform. TbFe, DyFe, and TbDyFe write at the Curie point, so the film composition does not need to be controlled so strictly, but because the Curie point is low at 100°C or less, it is not possible to use high-power light when reading out signals. There are some difficulties. If the Curie temperature is low, the writing efficiency will improve, but the written signal will be disturbed by the ambient temperature or read light. Therefore, considering the usage conditions, the magnetic transformation temperature is 100℃.
The above is desirable. Readout S/N by reflected light
If the reflectance is R and the Kerr rotation angle is θ _K , then R・
Proportional to _θK . Therefore, in order to read out data with a good S/N ratio, it is sufficient to increase the Kerr rotation angle. In Table 1,
The Kerr rotation angle of the amorphous magnetic film is shown.

【table】

[Table] Among these, GdTbFe has the largest Kerr rotation angle. However, even this value is not sufficient, and research is underway to further increase the Kerr rotation angle. SUMMARY OF THE INVENTION An object of the present invention is to provide a photothermal magnetic recording medium that has excellent thermal stability and has a sufficiently large Kerr rotation angle and can be read with a good signal-to-noise ratio. That is, in a photothermal magnetic recording medium, the medium is
The above objective is achieved by constructing the magnet from a quaternary amorphous magnetic alloy of Gd-Tb-Fe-Co. Further, in the photothermal magnetic recording medium according to the present invention, Fe is used as a composition to have sufficient magnetic anisotropy to orient the axis of easy magnetization in a direction perpendicular to the film surface.
The combined atomic ratio of and Co is 50atom% to 90atom%
It is desirable to exist within the range of . Particularly preferred is 70 atom% to 85 atom%. Furthermore, in the photothermal magnetic recording medium according to the present invention, in order for the Kerr rotation angle to be sufficiently large compared to the value of conventional constituent elements, the combined atomic ratio of Fe and Co must be 100.
%, it is desirable that Co exists in an atomic ratio of 0.5 atom% or more to Fe. Hereinafter, the photothermal magnetic recording medium of the present invention will be explained in detail. In the photothermal magnetic recording medium according to the present invention,
By forming an amorphous magnetic medium using a combination of Gd-Tb-Fe-Co, a recording medium with excellent magneto-optic constant values was obtained. As is clear from the examples described later, this result is 0.27 for GdTbFe, which is the largest known Kerr rotation angle.
It has a value that far exceeds the average. In addition, the Gd-Tb-Fe-Co amorphous 4 of the present invention
The original alloy photothermal magnetic recording medium must have a sufficient easy axis of magnetization so that the easy axis of magnetization is oriented in a direction perpendicular to the film surface. To achieve this, it is first necessary to compose the thin film with an amorphous material, which requires the following steps:
This is achieved by forming a thin film using a sputtering method, a vacuum evaporation method, or the like. The composition to have sufficient magnetic anisotropy and sufficient Kerr rotation angle is the composition of Gd, Tb, Fe, and Co (Gd _1-Z Tb _Z ) _1-Y (Fe _1-X Cox) Let y be X,
It is desirable that Y and Z satisfy 0.005≦X≦1, 0.5≦Y≦0.9, and 0<Z<1. Hereinafter, the present invention will be explained in detail with reference to Examples. Example 1 In a high-frequency sputtering device, a 3-inch square white glass plate was used as a substrate, and a 5-mm square piece of Gd, Tb, and Co uniformly arranged on a 4-inch Fe surface was used as a target. 1.5×10 ^-5 Pa inside the chamber
After evacuating to below, add Ar gas 4×
Ar pressure was introduced to 10 ^-1 Pa, and the Ar pressure was brought to 3 Pa by operating the main valve of the vacuum exhaust system. The film was formed using a sputtering power of 200W from a high frequency power source.
The film thus formed with a thickness of 1500 Å had an axis of easy magnetization in the direction perpendicular to the film surface, and was amorphous based on X-rays. Also, as a result of compositional analysis, this magnetic film is
(Gd _0.5 Tb _0.5 ) _0.21 (Fe _0.95 Co _0.05 ) _0.79 , and the Kerr rotation angle was 0.37 degrees when measured using a He--Ne laser with an oscillation wavelength of 633 nm. This is approximately from the Kerr rotation angle value of (Gd _0.5 Tb _0.5 ) _0.21 Fe _0.79 , which was created in the same way.
It was 30% larger. The compositions and Kerr rotation angles of Examples 2 to 5, which were prepared in the same manner as in the first example except for changing the amount of Co on the Fe target in the first example, were as follows. Ta.

[Table] Figure 1 shows how the Kerr rotation angle changes in response to changes in the amount of Co. The vertical axis shows the Kerr rotation angle, and the horizontal axis shows the amount of Co. like this
By changing the amount of Co relative to Fe,
Magnetic films having Kerr rotation angles of various different values were obtained, and their Kerr rotation angles were significantly larger than those of magnetic films of conventional construction. Gd on the Fe target in the first example,
The compositions and Kerr rotation angles of Examples 6 to 12, which were prepared in the same manner as in the first example except for changing the amounts of Tb and Co, were as follows.

[Table] The Kerr rotation angles in the sixth to twelfth embodiments were also sufficiently large compared to the Kerr rotation angles in the previous configurations. As described above, in the photothermal magnetic recording medium according to the present invention, by forming it as a quaternary amorphous magnetic film made of Gd-Tb-Fe-Co, a large magneto-optical constant that could not be obtained conventionally can be obtained. It can be said to be an excellent photothermal magnetic recording medium that can be read with a good S/N ratio and is easy to form.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of Co and the Kerr rotation angle in one composition of a photothermal magnetic recording medium according to the present invention.

Claims (1)

[Claims] 1. A photothermal magnetic recording medium having a recording layer made of a magnetic alloy thin film having an axis of easy magnetization perpendicular to the film surface, wherein the magnetic alloy has the following composition: (Gd _1-X Tb _X ) _{1 -Y} (Fe _1-Z Co _Z ) _Y , where 0<X<1 0.5≦Y≦0.9 0.005≦Z<1.