JPH0677341B2 - Magneto-optical memory medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a medium for a magneto-optical memory having improved information recording characteristics, corrosion resistance, and exchange coupling between magnetic films.

[Conventional technology]

A magneto-optical memory using a rare earth-iron group amorphous alloy thin film,
The read characteristics are not sufficient, and various proposals have been made for improving the read characteristics. One of them is an exchange-coupling double-layer film composed of a film having a good recording property and a film having a good reading property (for example, JP-A-57-78652). In the conventional exchange-coupling bilayer film, Tb-Fe and Dy-Fe were used for the recording layer, and Gd-Fe, Gd-Fe-Co, etc. were used for the reading layer.

[Problems to be solved by the invention]

Since information is recorded in the magneto-optical memory by utilizing the thermal action of laser light, the lower the Curie temperature of the magnetic film, the higher the recording sensitivity. Since the Curie temperature of the recording layer determines the recording sensitivity in the exchange-coupled two-layer magnetic film,
Lowering the Curie temperature of the recording layer increases the recording sensitivity.
However, considering the stability of recorded information and the temperature inside the magneto-optical memory drive device (> 50 ° C), the Curie temperature of the recording layer is preferably about 100 ° C. From this point of view, the Curie temperature of Tb-Fe, which was conventionally used as the recording layer, is slightly high at about 130 ° C, and that of Dy-Fe is slightly low at about 70 ° C, which means that the Curie temperature is practically optimal. I can't say.

Further, the corrosion resistance of the magnetic film is a very important issue for practical use of the magneto-optical memory. It has been known that in a rare earth-iron group amorphous alloy thin film, the corrosion resistance is improved as the iron group element is contained in a larger amount. In the exchange-coupling double-layer magnetic film, Gd-Fe-Co can be used for the readout layer, and the Co concentration can be increased to improve the readout characteristics and corrosion resistance. However, Tb-Fe and Dy-Fe are used for the recording layer,
Even if a small amount of Co is added to this, the Curie temperature rises considerably and the recording sensitivity deteriorates.

The present invention has been made to improve the above-mentioned conventional drawbacks, and its purpose is to use R-Fe-Co (R = T as a recording layer.
b, Dy), Gd-Fe-Co is used for the reading layer, and the recording layer is sandwiched between the reading layers to provide a medium for a magneto-optical memory having improved recording characteristics, corrosion resistance, and exchange coupling.

[Means for solving problems]

The present invention, which can achieve the above object, has a recording layer having a high coercive force and a low Curie temperature at room temperature, and a magnetic film having a three-layer structure in which exchange coupling is sandwiched between read layers having a low coercive force and a high Curie temperature. A medium for a magneto-optical memory, wherein the recording layer is R-Fe-Co and the read layer is Gd-Fe-CoM (where R is Tb and It is one or two elements selected from Dy.).

The difference between the conventional example and the magneto-optical memory medium of the present invention will be described in detail below.

First, the difference in Curie points of the recording layers of both media will be described. As a recording layer of a conventional medium, Tb-Fe, Dy-Fe, etc. were used, but as described above, Tb-Fe has a slightly high Curie temperature of about 130 ° C and Dy-Fe of about 70 ° C. Somewhat low. Therefore, ((Tb _1-X Dy _X ) − (Fe _1-Y Co _Y ) (0 ≦ x ≦
When various magnetic films represented by 1,0 ≦ y ≦ 0.3) were prepared, Tc = 130 (1-x) between the Curie temperature Tc and the atomic ratio x of Dy and the atomic ratio y of Co. ) + 70x + 600y (℃) was obtained. Therefore, x = 0.8, y = 0.0
When it is 3, the Curie temperature is about 100 ° C., which is lower than the Curie temperature of Tb-Fe, and a magnetic film having better temperature stability than Dy-Fe can be obtained. Based on this finding, the magnetic film containing R, Fe and Co was used as the recording layer of the magneto-optical memory medium of the present invention. The optimum value of the Curie temperature depends on the power of the laser used, the configuration of the optical system, the configuration of the medium, the rotational speed of the disc, the diameter of the disc, etc.
Although there may be some deviation from 100 ° C. such as 0 ° C., in that case as well, the values of x and y may be appropriately selected so as to obtain the Curie point. Further, the Curie point of the recording layer of the medium for magneto-optical memory of the present invention can be set to a value similar to the Curie point of the recording layer of the conventional medium. However, in general, if the recording sensitivity of the medium is high, the power of the laser used will be small and the optical system will be simple, so the cost will be low, and recording will be stable even against fluctuations in the recording power due to disturbance. Reliability increases. Therefore, it is desirable to lower the Curie point so that the recording sensitivity is as high as possible, but considering the stability against temperature, the Curie temperature should be higher, so the Curie point to be set is 90.
~ 120 ° C is preferred.

Next, the difference in corrosion resistance between the recording layers of the conventional example and the magneto-optical memory medium of the present invention will be described. During the corrosion process of a magnetic film composed of a rare earth-iron group amorphous alloy thin film, free oxygen existing in the film is mainly combined with a rare earth element to be oxidized, or oxygen and water are not absorbed through the interface between the magnetic film and the protective film. Regarding the former of these, which may be diffused and oxidized in the film,
It can be significantly improved by reducing the oxygen concentration in the target in sputtering or the evaporation source in vapor deposition, reducing the residual gas pressure in the vacuum device, and reducing the impurities in Ar gas. On the other hand, with regard to the latter, it is desired to improve the corrosion resistance of the magnetic film itself, though it can be considerably suppressed by a dense protective film containing no oxygen. In particular, when plastic is used for the substrate, the substrate has some degree of water absorption, and it is particularly desired to improve the corrosion resistance of the magnetic film as well as the protective film.
In the exchange-coupling two-layer magnetic film, the Curie point may be high in the readout layer, so that Gd-Fe-Co can be used, and the concentration of Co can be increased to improve the corrosion resistance. However, when Co is added to Tb-Fe of the recording layer of the conventional medium, the Curie temperature rises considerably even in a small amount, and the recording sensitivity is deteriorated.

In the present invention, a recording layer of R-Fe-Co whose corrosion resistance is slightly improved by adding a small amount of Co to Tb-Dy-Fe or Dy-Fe is used.
Further, by sandwiching the read layer having good corrosion resistance with Gd-Fe-Co, the corrosion from the interface between the magnetic layer and the protective layer is improved.

Further, in the exchange-coupling two-layer magnetic film, the size of the exchange coupling between the magnetic films greatly influences the characteristics of the medium, but the size of the exchange coupling considerably varies depending on the ultimate vacuum pressure at the time of fabrication. This is the effect of the residual gas adsorbed on the interface between the production of one magnetic film and the production of the next magnetic film, and this effect is considerably improved by improving the corrosion resistance. Therefore, the medium for a magneto-optical memory of the present invention using the recording layer with improved corrosion resistance is effective not only for improving the aging of the medium but also for improving the exchange coupling.

The magneto-optical memory medium of the present invention is characterized in that the magnetic film is configured as described above. In addition to the magnetic film, the reflective layer for effectively utilizing light and the magnetic film are protected to further provide a protective function. Various auxiliary layers, such as a protective layer for enhancing, may be optionally provided as desired.

〔Example〕

Example 1 A conventional example and the present invention
A 0 mmφ disk-shaped medium for magneto-optical memory was prepared, and recording sensitivity experiment was conducted. In the conventional example, the magnetic layer is a read layer: Gd-Fe-Co (Gd: Fe: Co = 18: 62: 20, film thickness 500Å) and a recording layer: Tb-Fe (Tb: Fe = 22: 78, film thickness 500Å). ), The magnetic film of the present invention is a Gd-Fe-Co (Gd: F
e: Co = 18: 62: 20, thickness 300 Å) readout layer, Dy- (F
e _1-Y Co _Y ) (y = 0.05, film thickness 400Å) was used as a three-layer film. Polycarbonate was used for the substrate.

At a rotation speed of 1800 rpm, a laser power of 4.9 mW and a bias magnetic field of 200 Oe were required for recording the medium of the conventional example, but the present invention has a laser power of 4.2 mW and a bias magnetic field of 200 Oe.
Recording was possible with e and the recording characteristics were improved.

In addition, in the corrosion resistance test using 1N NaCl aqueous solution,
In the conventional example, after soaking for 15 minutes, a considerable number of pinholes were visually observed, but in the case of the present invention, no pinholes were visually observed.

The exchange coupling measurement was not obtained as a value because it contained a considerable error, but the method of the present invention tended to be improved by about 1.5 times as compared with the conventional example.

Example 2 A medium for disk-shaped magneto-optical memory having a diameter of 130 mm according to the present invention was manufactured by using a normal sputtering method, and an experiment of recording sensitivity was conducted. The magnetic film is Gd-Fe-Co (Gd: Fe: Co = 18: 62:
(Tb _1-X Dy _X ) − (Fe _1-Y Co
The recording layer of _Y ) (X = 0.8, y = 0.03, film thickness 400Å) was formed as a three-layer film.

At 1800 rpm, laser power 4.3 mW, bias magnetic field
Recording was possible at 200 Oe, and the recording characteristics were improved.

In addition, in the corrosion resistance test using 1N NaCl aqueous solution,
No pinholes were visually observed.

〔The invention's effect〕

As described above, R-Fe-Co (R = Tb and / or Dy) is used for the recording layer, and Gd-Fe-Co is used for the reading layer.
The magneto-optical memory medium of the present invention having the recording layer sandwiched by the read layer has improved recording characteristics, corrosion resistance, and exchange coupling.

Claims (1)

[Claims] 1. A magneto-optical device comprising a recording layer having a high coercive force and a low Curie temperature at room temperature and a magnetic film having a three-layer structure in which exchange coupling is sandwiched between read layers having a low coercive force and a high Curie temperature. A memory medium, wherein the recording layer is R-Fe-Co and the read layer is Gd-Fe-
Medium for magneto-optical memory characterized by being Co (wherein R is one or two elements selected from Tb and Dy)