JPH05210880A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium having high reflectivity, low thermal conductivity of a reflecting film, high sensitivity, and high CN ratio for reproducing by using a Cu alloy containing at least one kind of rare earth metal as a reflecting film. CONSTITUTION:This recording medium has a four-layer structure comprising a first dielectric film, recording film, second dielectric film, and reflecting film on a transparent substrate. The reflecting film consists of a Cu alloy containing at least one kind of rare earth metal. The rare earth element is yttrium or tantalum, and its amt. is 0.05-6 atomic %. Thereby, the obtd. reflecting film has higher reflectivity and lower thermal conductivity than a conventional Al alloy film Thus, the obtd. magneto-optical recording medium has high sensitivity and high CN ratio for reproducing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium, and more particularly to a magneto-optical recording medium having a reflective film having a high reflectance and a low thermal conductivity.

[0002]

2. Description of the Related Art In recent years, with the progress of information-oriented society, high-density and large-capacity recording media are required. Among them, magneto-optical disks are capable of rewriting information and
Since the medium can be exchanged, attention and research and development are continuing. Currently used recording media include a rare earth-transition metal film such as TbFeCo used as a recording film, which has a small Kerr rotation angle, but has a C / N ratio during reproduction. Since it is proportional to the product of the rotation angle and the square root of reflectance, the CN ratio is disadvantageously small. Therefore, for this purpose, a film structure having an interference film or a film structure having a reflection film is widely used for the purpose of increasing the Kerr rotation angle.
The most commonly used film structure is a four-layer film structure in which a first dielectric film, a recording film, a second dielectric film and a reflective film are formed in this order on a transparent substrate as shown in FIG. is there.

In the film structure having such a reflective film, the property of the reflective film is closely related to the performance of the magneto-optical recording medium. In the structure in which the second dielectric film is absent in FIG. 4, light incident on the magneto-optical recording medium from the drive head is transmitted through the recording film, reflected by the reflective film, and transmitted through the recording film again. The optical rotation angle is increased by utilizing the Faraday rotation when transmitting through the recording film. In addition, in the structure having the second dielectric film, in addition to the structure lacking this film, the multiple reflection at the second dielectric film between the recording film and the reflective film is utilized. The optical rotation angle at the time of reading is further increased, and the CN ratio at the time of reading is increased. Therefore, the larger the reflectance of the reflective film, the better. Further, in the magneto-optical recording medium, the incident light is absorbed by the recording film and the temperature rises to raise the temperature to near the Curie temperature or the compensation temperature for recording. Therefore, it is possible to record with a smaller power when the recording film is more likely to accumulate heat. Therefore, in order to reduce the heat radiation amount, it is preferable that the thermal conductivity of the reflective film is small.

[0004]

Although Al is conventionally used as the reflective film, pure Al has a reflectance of about 800 nm at the wavelength of the semiconductor laser used in the magneto-optical disk of 800 nm. Although it is as large as 86%,
Since both this and thermal conductivity have a large value of 150 W / mK, the recording sensitivity is not sufficient, and the rotational speed of the drive is increased and the linear velocity is increased in order to increase the transfer speed. As a result, the laser irradiation amount per unit area of the magneto-optical recording medium becomes small, and there is a disadvantage that sufficient recording sensitivity cannot be obtained. Therefore, a reflective film using Pd or Pt having a small thermal conductivity has been proposed for this (see JP-A-1-264649), but such a metal has a low reflectance of 60 to 70%, The use of Al-rare earth alloys with high reflectance and low thermal conductivity has also been proposed because of the disadvantage that the CN ratio at the time of reading is reduced (JP-A-3-
However, a better reflection film is desired.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a magneto-optical recording medium which has solved such disadvantages, and it is a magneto-optical recording medium having at least a recording film and a reflective film on a substrate, The film is a Cu alloy containing at least one kind of rare earth element.

That is, the inventors of the present invention have conducted various studies to develop a reflective film having a high reflectance and a low thermal conductivity. As a result, if it is made of a Cu alloy containing at least one rare earth element, a high reflectance is obtained. It is possible to obtain a reflective film having a small thermal conductivity while maintaining the rate, and therefore, it is possible to obtain a magneto-optical recording medium having a high recording sensitivity or capable of adjusting the recording sensitivity. The present invention has been completed by finding and advancing research on the amount of rare earth elements used in this Cu alloy. This will be described in more detail below.

[0007]

The present invention relates to a magneto-optical recording medium,
In a magneto-optical recording medium having at least a recording film and a reflective film on a substrate, this is characterized in that the reflective film is a Cu alloy containing at least one kind of rare earth element. Since the reflection film formed by this has a higher reflectance and a lower thermal conductivity than the Al-rare earth alloy, a magneto-optical recording medium using this as a reflection film has a high sensitivity and a large CN ratio at the time of reading. The advantage is that

The magneto-optical recording medium of the present invention has at least a recording film and a reflective film on a substrate, which is a known first dielectric film and recording film on the transparent substrate shown in FIG. ,
A four-layer structure is formed by depositing a second dielectric film and a reflective film in this order. This is a film structure without the first dielectric film, a film structure without the second dielectric film, Further, the recording film is not only a rare earth transition metal alloy single layer film but also an exchange coupling multilayer film, Fe-Co.
It may be a thin film multilayer film such as.

However, the reflective film in the magneto-optical recording medium of the present invention is made of a Cu alloy containing at least one rare earth element. The rare earth elements contained in this Cu alloy are Y or tantanoid elements, but if the content is less than 0.05 atomic%, the thermal conductivity of electrons is 100 W / mK.
Since the reflectance becomes 86% or less when it is larger than 6 atom%, it is preferable to set it in the range of 0.05 to 6 atom%. A magneto-optical recording medium having high sensitivity and a large CN ratio at the time of reading can be obtained.

Regarding the reflective film in the magneto-optical recording medium of the present invention, the thermal conductivity is reduced by increasing the amount of rare earth added in the outer peripheral portion where the linear velocity becomes high and the recording sensitivity deteriorates, compared with the inner peripheral portion. Alternatively, the concentration distribution of the additive may be provided from the inner circumference to the outer circumference, and further, the reflection film may have a film thickness gradient so that the outer circumference is thinner than the inner circumference.

[0011]

EXAMPLES Next, examples of the present invention will be given. Example 6 kinds of Cu alloys were prepared by adding 0.05-15 atom% of yttrium (Y) to copper (Cu), and the reflectance of this Cu alloy was measured at a wavelength of 780 nm. The results shown in FIG. 1 were obtained. The value of the thermal conductivity of this Cu alloy was obtained by measuring the sheet resistance at room temperature and obtaining it according to Widemann-Frantz's law, and the result as shown in FIG. 2 was obtained. This Cu-Y
When the reflectance and the thermal conductivity of the alloy are compared with those of the Al-Y alloy, they are as shown in FIG. 3. Therefore, in addition to FIG. 1 and FIG. The one with atomic% added has a higher reflectance than the Al alloy,
It was confirmed that the thermal conductivity was low. In addition, when the reflectance and the thermal conductivity of electrons of this Cu-Y alloy are compared with those of the Al-Y alloy, they are as shown in FIG. 3, and thus this Cu-Y alloy is superior to the Al-Y alloy. It was confirmed that the reflectance was high and the thermal conductivity was low.

[0012]

The present invention relates to a magneto-optical recording medium, and in the magneto-optical recording medium having at least a recording film and a reflective film on a substrate as described above, the reflective film is at least one of rare earth elements. It is characterized by comprising a Cu alloy containing the above. According to this, a Cu alloy of this kind has a higher reflectance and a lower thermal conductivity than an Al alloy. Therefore, this magneto-optical recording medium has the advantages of high sensitivity and a large CN ratio at the time of reading.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of Y added and the reflectance of a Cu—Y alloy used as a reflective film in the magneto-optical recording medium of the present invention.

FIG. 2 is a graph showing the relationship between the amount of Y added and the thermal conductivity of a Cu—Y alloy used as a reflective film in the magneto-optical recording medium of the present invention.

FIG. 3 Cu—Y alloy used in the present invention and known Al
3 is a graph showing a relationship between reflectance with respect to a Y alloy and thermal conductivity.

FIG. 4 is a diagram showing a configuration of a magneto-optical recording medium having a known four-layer film structure.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Tawara Shin-Etsu Chemical Co., Ltd. Corporate Research Center, 3-2-1 Sakado, Takatsu-ku, Kawasaki City, Kanagawa Prefecture

Claims (2)

[Claims] 1. A magneto-optical recording medium having at least a recording film and a reflective film on a substrate, wherein the reflective film is a Cu alloy containing at least one or more rare earth elements. 2. The amount of rare earth in the Cu alloy is 0.05 atomic%.
The magneto-optical recording medium according to claim 1, wherein the content is 6 atomic% or less.