JPS6252744A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To improve recording efficiency without unnecessarily increasing the recording power of laser light in the stage of recording by the simple construction in which a metal or metalloid having relatively small heat conductivity is used as a reflection layer and which eliminates the need for a heat insulating layer. CONSTITUTION:This photomagnetic recording medium is made into the three- layered construction in which the reflection layer 12 and recording layer 11 are formed by vapor deposition or sputtering in this order on one surface of a transparent substrate and the laser light F is made to directly irradiated on the recording layer 11 positioned at opposite side of the transparent substrate 10. GdTbFe.TbFeCO, etc. which have vertical anistropy and are an amorphous magnetic material are used for the recording layer 11. The metal or metalloid having good reflectivity and relatively low heat conductivity is used for the reflection layer 12. Materials such as bismuth Bi, antimony Sb, tellurium Te, arsenic As and selenium Se are used for the metal or the metalloid.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is characterized in that information written at a single point is recorded,
The present invention relates to a magneto-optical recording medium in which information is reproduced by Kerr effect reading.

2. Description of the Related Art Magneto-optical recording media are generally formed by depositing a recording layer made of a rare earth iron-based thin film having perpendicular anisotropy on a transparent substrate. Information is recorded on this medium by applying a magnetic field to the medium and irradiating the medium with a laser beam, making the medium more than one point of Curie and reversing the applied magnetic field. Reproduction is performed by Kerr effect readout in which laser light reflected by a recording layer to which a magnetic field is applied is Kerr-rotated in a direction in which the polarization angle of the reflected light differs depending on the direction in which the magnetic field is applied.

If the amount of light incident on the body is expressed as , then there is a relationship of S / N c + r sin = D / R. Therefore, in order to increase the S/N ratio, it is sufficient to increase the reflectance R1 and the Kerr rotation angle θK. However, since the reflectance R is approximately determined by the material used for the recording layer, the effect cannot be enhanced. Therefore, conventional methods have been used to increase the Kerr rotation angle θ. this is,
This is a method in which a reflective layer is provided on the back surface of the recording layer facing the laser beam irradiation side, and the reflected light on the surface of the recording layer is superimposed on the reflected light that has passed through the recording layer and been reflected on the reflective layer. According to this, when the reflected light from the reflective layer passes through the recording layer, it is subjected to the Schifferraday effect, and the apparent Kerr rotation angle (magneto-optic rotation angle) of the reflected light from the medium is increased. This aims to substantially improve the S/N ratio.

Problems to be Solved by the Invention However, conventionally, in this type of medium, the reflective layer is made of aluminum AI, copper Ou, silver Ag, which have good reflectivity.
・Metals with relatively high thermal conductivity, such as gold and Au, were used. For this reason, when recording information on the recording layer, even if a laser beam is irradiated with a recording power that raises the temperature of the medium to more than the Curie point, the irradiated heat is diffused by the reflective layer and the problem does not reach the Curie point. Something happened. Therefore,
It was necessary to increase recording power. Therefore, in the past, a structure was adopted in which a heat insulating layer such as SIO or a dielectric film was provided between the reflective layer and the recording layer to prevent the irradiation heat of the laser beam of the recording power from diffusing.

However, if this heat insulating layer is made too thick, interference will occur between the light reflected on the surface of the recording layer and the light reflected on the reflective layer.

Therefore, the thermal insulation layer must have a uniform thickness without optical effects. If this is not done, there will be a problem that it will not be possible to read out light of different wavelengths, or that it will become partially unreadable. Therefore, in producing magneto-optical recording media, extremely precise film thickness control is required, particularly when forming a heat insulating layer by vapor deposition or sputtering, making production management of magneto-optical recording media troublesome.

Therefore, the present invention has been devised in view of the above points, and has a simple structure that does not require a heat insulating layer, increases the apparent Kerr rotation angle, and improves recording efficiency without increasing the recording power more than necessary. <The purpose is to improve the LSN ratio.

In order to achieve an objective that is more than a means to solve the problems, the present invention provides a transparent base station ■-
A reflective layer made of a metal or metalloid with relatively low thermal conductivity and a recording layer made of an amorphous magnetic material such as a rare earth iron thin film having perpendicular anisotropy are placed on the surface of the recording layer on the laser beam irradiation side. It has a three-layer structure.

Effects Since the magneto-optical recording medium of the present invention has a reflective layer made of a metal or semimetal with relatively low thermal conductivity, the diffusion of laser beam irradiation heat by the reflective layer during recording can be extremely reduced, and the heat insulating layer becomes unnecessary. Further, the apparent Kerr rotation angle can be increased by the interaction of the Kerr effect due to surface reflection of the recording layer and the Faraday effect of reflected light transmitted through the recording layer and reflected by the reflective layer.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 and 2 show a magneto-optical recording medium according to the present invention, in which 10 is a transparent substrate, * is a recording layer, 12 is a reflective layer, and F is a laser beam.

FIG. 1 shows a reflective layer 12 and a recording layer on one side of a transparent substrate 10.
are formed by vapor deposition or sputtering in this order, and is a magneto-optical recording medium with an eight-layer structure in which laser light F is directly irradiated onto the recording layer on the opposite side of the transparent substrates i&10.

FIG. 2 shows a recording layer and a reflective layer 12 on one side of a transparent substrate 10.
It is a magneto-optical recording medium with an eight-layer structure in which the recording layer is irradiated with laser light F from the transparent substrate 10 side.

The structure of the magneto-optical recording medium may be either shown in FIG. 1 or FIG. 2 described above.

It should be noted that the magneto-optical recording medium is formed into a disk shape, and a recording trunk is formed in the circumferential direction of the medium, and it goes without saying that recording and reproduction are performed by following the beam spot of the laser beam F to this recording trunk. .

The transparent substrate 10 may be made of glass, PC (polycarbonate)-PMMA (polymethyl methacrylate), etc.
) Easy to mold, ・) High light transmittance, 1) Excellent weather resistance, heat resistance, and chemical resistance, 1) High surface hardness,
(2) A material that satisfies conditions such as low optical anisotropy (low birefringence) is used.

As the recording layer, an amorphous magnetic material such as GdTbFe-TbFe0° having perpendicular anisotropy is used. The Curie point temperature and Kerr rotation angle of these rare earth iron-based materials having vertical anisotropy, such as GdFe-GdTbFe, are shown in the table below.

Next, as the reflective layer 12, a metal or metalloid having good reflectance and relatively low thermal conductivity is used. As this metal or metalloid, bismuth Bi-antimony S
Materials such as b@tellurium, Te, arsenic, As, selenium, and Se are used. The thermal conductivity of these materials is shown in the table below.

As shown in the above table, bismuth Bi, etc. used as the reflective layer of the magneto-optical recording medium of this example is different from Al-
Its thermal conductivity is extremely low compared to Ag-Au/Ou and the like. Thereby, the diffusion of heat irradiated with laser light onto the medium during recording can be extremely reduced. Therefore, there is no need to provide a heat insulating layer between the reflective layer and the recording layer.
One-point writing can be reliably performed without increasing the recording power of the laser beam irradiated onto the medium during recording more than necessary.

Furthermore, since the medium according to this embodiment does not require a heat insulating layer that may act as an interference layer, when producing the medium,
Film thickness management and control during layer formation, which requires extremely high precision, becomes unnecessary. Therefore, production management of media can be easily performed.

Furthermore, during playback, reflected light whose polarization plane angle is rotated due to the Kerr effect due to surface reflection of the recording layer, and reflected light that passes through the recording layer and is reflected to the reflective layer, and the polarization plane angle is changed due to the Faraday effect caused by passing through the recording layer. By combining with the rotated reflected light, the Kerr rotation angle of the reflected light from the medium increases in appearance. This allows the actual S of the medium during playback.
N ratio increases.

[Experiment example]

The light according to the present invention has the structure shown in FIG. 1 or 2, in which a recording layer (()dTbFe ) and a reflective layer (Te) are deposited on a transparent substrate (PMMA) 10 with a thickness of 1.2. A magnetic recording medium and a recording layer (Gd) on a transparent substrate (PMMA)
TbFe) was deposited on a medium with a wavelength of λ=78.
Recording/reproducing experiments were conducted using a magneto-optical head having 0 to 830 laser beams and an objective lens with a numerical aperture NA of 0.55. As a result, the S/N ratio of a medium with only a recording layer was about 40 dB, but when the medium structure according to the present invention was adopted, it improved by several dB.

As described in detail, the magneto-optical recording medium of the present invention uses a metal or metalloid with relatively low thermal conductivity as the reflective layer, and has a simple structure that does not require a heat insulating layer. It is possible to increase recording efficiency without increasing the recording power of laser light more than necessary during recording, and it also makes layer formation easier by making film thickness management and control that requires precision during media production rough and loose. be able to.

Furthermore, since the apparent Kerr rotation angle of the light reflected from the medium during reproduction can be increased, the S/N ratio can be practically increased, and a signal level with a high ON ratio can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one cross-sectional structure of a magneto-optical recording medium according to the present invention, and FIG. 2 is a cross-sectional view showing another cross-sectional structure of the medium. 10......Transparent substrate...
......Recording layer, 12......Reflection layer, F...
......Laser light. Patent applicant: NEC Home Electro Fig. 1

Claims (2)

[Claims] (1) On one surface of a transparent substrate, a reflective layer made of a metal or metalloid with relatively low thermal conductivity and a recording layer made of an amorphous magnetic material such as a rare earth iron thin film with perpendicular anisotropy are coated with a laser beam. A magneto-optical recording medium having a three-layer structure in which the recording layer is on the light irradiation side. (2) The magneto-optical recording medium according to claim (1), wherein the reflective layer is formed using any one of bismuth Bi, antimony Sb, tellurium Fe, arsenic As, selenium Se, etc.