JP2000260076A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent signal resolution and a high S/N ratio in a magneto-optical recording medium based on a CAD(Center Aperture Detection) system. SOLUTION: This magneto-optical recording medium is provided with a recording layer 1, a reproduction assisting layer 2, a cut layer 4 and a recording layer 3. The reproducing layer 1, the reproduction assisting layer 2 and the recording layer 3 are made of rare earth-transition metal magnetic layers at respective Curie temperatures of Tc1, Tc2 and Tc3, the easy magnetization axis of the recording layer 3 is set in a direction vertical to a film surface at a room temperature TRT, and the cut layer 4 is made of a non-magnetic layer. For the reproducing layer 1, its easy magnetization axis is set in a direction parallel to the film surface at the room temperature TRT and, at a reproducing temperature TI higher than this room temperature TRT, the easy magnetization axis is set in a direction vertical to the film surface. For the reproducing assisting layer 2, its easy magnetization axis is set in a direction parallel to the film surface from the room temperature TRT to Curie temperature Tc2. The relation of Curie temperatures among the magnetic layers is set at TC1> Tc2>TI, and at TC3>Tc2.

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 which can realize particularly stable reproduction of recorded information and high-density recording.

[0002]

2. Description of the Related Art In a magneto-optical recording medium, for example, a magneto-optical disk, a magnetic super-resolution disk can be mentioned as a technique capable of reproducing a high-density recording signal. Among them, a so-called CAD (Center Aperture) using an in-plane magnetized film as a reproducing layer.
For the recording medium of the (Detection) method, the same signal processing method as that of a normal recording medium can be applied with little distortion of the reproduction signal. No external magnetic field is required for super-resolution reproduction. For such reasons, attention has been paid.

[0003] The magneto-optical recording medium based on the CAD method is as follows.
As shown in FIG. 2 which is a schematic cross-sectional view of the basic structure, it has a reproducing layer 1, a reproducing auxiliary layer 2, a cutting layer 4, and a recording layer 3. The reproducing layer 1 and the auxiliary reproducing layer 2 are constituted by magnetic layers having in-plane anisotropy, the recording layer 3 is constituted by a magnetic layer having perpendicular anisotropy, and the cutting layer 4 is constituted by a non-magnetic layer. Consisting of In the recording layer 3, a magnetic domain is formed as schematically shown by a recording mark M recorded in response to a recording signal, that is, an arrow.

[0004] Reading and writing of the recording of this magneto-optical recording medium,
That is, reproduction is performed by irradiating the recording medium with the reproduction laser beam L, and in the heating section A generated by the irradiation of the laser beam, the magnetization of the reproduction auxiliary layer 2 is lost.
A reproducing window W, a so-called aperture, is formed here. Through this reproducing window W, the reproducing layer 1 is magnetically coupled to the recording layer 3, and the recording mark M is transferred to the reproducing layer 1. The recording signal is read out by causing rotation and detecting the Kerr rotation angle.

That is, in this system, the reproducing layer 1
Has an in-plane magnetic anisotropy, the presence or absence of a recording signal cannot be determined in a normal state, but the magnetization of the reproducing layer 1 exhibits perpendicular anisotropy due to a rise in temperature during irradiation with the reproducing laser beam. Since the recording mark M is transferred and becomes reproducible by receiving the magnetic coupling force from the recording layer 3, the size of the reproducing window W for realizing the visual field restriction largely depends on the reproducing power. On the other hand, in order to obtain a large reproduction light intensity, the reproduction power must be increased, and as a result, the signal resolution (MTF) and the S / N of the reproduction signal are incompatible.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording medium capable of obtaining excellent signal resolution and high S / N.

[0007]

SUMMARY OF THE INVENTION Magneto-optical recording according to the present invention
The medium has a reproduction layer, a reproduction auxiliary layer, a cutting layer, and a recording layer.
You. The playback layer, playback assistance layer, and recording layer
Temperature is Tc₁, Tc_Two, Tc_ThreeRare earth-transition metal magnetism
The recording layer is formed at room temperature T_RTThe axis of easy magnetization is
In the vertical direction, the cutting layer comprises a non-magnetic layer. The regeneration layer is
Room temperature T_RT, The axis of easy magnetization is parallel to the film surface, and room temperature T_RT
Higher regeneration temperature T₁And the axis of easy magnetization is perpendicular to the film surface.
Become. The regeneration assisting layer is at room temperature T_RTMore Curie temperature T
c_TwoThe axis of easy magnetization is set in the direction parallel to the film surface. Soshi
The relationship between the Curie temperatures of the respective magnetic layers is expressed by Tc₁> Tc_Two
> T₁And Tc _Three> Tc_TwoTo be selected.

In the recording layer, a recording mark, ie, a magnetic domain is formed in accordance with a recording signal. It has been found that when reproduction is performed on the magneto-optical recording medium having this configuration by the CAD method, an increase in the reproduction signal amplitude of the shortest recording mark, stable signal reproduction, and high-density recording / reproduction can be realized.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a magneto-optical recording medium according to the present invention will be described. FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of the magneto-optical recording medium according to the present invention, but the present invention is not limited to this example. In the magneto-optical recording medium shown in FIG. 1, for example, a transparent dielectric layer 12, a reproducing layer 1, a reproducing auxiliary layer 2, a cutting layer 4, a recording layer 3, A transparent dielectric layer 13 and a metal layer 14 are sequentially applied.

The transparent dielectric layer 12 is provided for obtaining a car enhancement effect, and has a refractive index different from that of the transparent substrate 11, for example, silicon nitride, silicon oxide, zinc sulfide, for example, having a thickness of 4 mm.
It is composed of a 0 nm Si ₃ N ₄ layer.

[0011] reproducing layer 1, rare earth - made the transition metal magnetic layer, the orientation axis of easy magnetization is parallel to the film surface direction at room temperature T _RT, the reproduction of the heating temperature _{T 1 (T 1> T RT} ), membranes It has the property of facing in the direction perpendicular to the surface. The reproducing layer 1 is made of, for example, Gd ₂₉ (Fe ₈₀ Co ₂₀ ) _{71 having a} thickness of 30 nm.

[0012] auxiliary reproduction layer 2, in the temperature range up to the Curie temperature Tc ₂ from room temperature T _RT, axis of easy magnetization, has a characteristic that faces the direction parallel to the layer surface. The auxiliary reproduction layer 2 has a thickness of, for example, 10 nm and is made of Gd ₁₂ Fe _{88 in} which transition metal is dominant.

The cutting layer 4 may be basically made of a non-magnetic material, for example, an Al layer having a thickness of 3 nm.

The recording layer 3 has such a composition that high-quality recording can be performed and that the leakage magnetic field from the recording mark increases at the reproduction temperature T ₁ . For example, with a film thickness of 60 nm,
Constituted by _{Tb 2 1 (Fe 80 Co 20} ) 79 of the compensation composition.

For the purpose of adjusting recording sensitivity and improving the quality of recording / reproducing signals, a transparent dielectric layer 13 made of, for example, Si ₃ N ₄ having a film thickness of 20 nm and a film having thermal conductivity, for example, A metal layer 14 of Al having a thickness of 30 nm is formed.

The recording of information on the magneto-optical recording medium can be performed by, for example, well-known magnetic field modulation. That is, the recording is performed by a recording head configured to move in a direction parallel to a radial direction of the disk with the magneto-optical recording medium according to the present invention described above, for example, a magneto-optical disk interposed therebetween. The recording head by this magnetic field modulation
Laser light is emitted from, for example, the substrate 11 side, and a magnetic field generator is provided substantially opposite to the laser light irradiation position. This magnetic field generator reverses the direction of application of the magnetic field in the direction perpendicular to the magneto-optical recording medium surface, that is, the disk surface, in accordance with the recorded information. Is formed.

The reproduction of the recording from the magneto-optical recording medium is performed as follows.
As described above, this is performed by irradiating the recording medium with the reproduction laser beam L as shown in FIG. in this case,
In the heating section A generated by this laser beam irradiation,
When the in-plane easy axis of magnetization of the reproducing layer 1 is oriented in the vertical direction as shown by, for example, a downward arrow in FIG. 2 and the magnetization of the reproducing auxiliary layer 2 disappears, the reproducing window W, so-called, An aperture is formed, and the reproducing layer 1 is magnetically coupled to the recording layer 3 through the reproducing window W, the recording mark M is transferred to the reproducing layer 1, and the transferred recording mark causes Kerr rotation of the reproducing laser beam. The recording signal is read by detecting the car rotation angle.

When the temperature of the heating section A returns to room temperature after the laser beam passes, the reproduction window W is closed because the magnetization state of the reproduction auxiliary layer 2 returns to the in-plane direction. Also in 1, the magnetization state returns to the in-plane direction, and the recording signal is covered. In this way, the recorded information is read out or reproduced sequentially as the laser light moves on the magneto-optical recording medium.

In the configuration of the present invention, this operation was performed smoothly. In order for this operation to be performed smoothly, each magnetic layer, that is, the reproduction layer 1, the reproduction auxiliary layer 2, and the recording layer 3
Is required to be controlled in advance, but the temperature characteristics of each layer having the above-described configuration, that is, the reproducing layer 1, the reproducing auxiliary layer 2, and the recording layer 3 are represented by curves 31, 32, and 33 in FIG. , Tc ₁ > Tc ₂ , and Tc ₃ > Tc ₂
The relationship holds.

In the above-described structure, the relationship between the ratio (atomic%) of the rare-earth metal RE to the transition metal TM in the reproducing layer 1 and the temperature at which the magnetization starts to be perpendicular to the reproducing layer 1 is as follows. In the case of Gd ₂₉ (Fe ₈₀ Co ₂₀ ) ₇₁ of _{No. 1,} it is the plot point P ₁ plotted in FIG.
Therefore, if the reproduction temperature T ₁ in the above-described configuration is selected to be a temperature at which the magnetization starts to be perpendicular to the reproduction layer 1, Tc ₂ > T ₁ from FIGS.

The plot points P ₂ and P ₂ in FIG.
₃ means Gd ₂₈ (Fe ₈₀ Co ₂₀ ) ₇₂ and Gd ₃₀ (Fe ₈₀ C
9 plots the temperature at which the respective magnetizations start to turn in the vertical direction for o ₂₀ ) ₇₀ . Thus, as is apparent, the reproducing layer 1 of the point P _3, Gd ₃₀ (Fe ₈₀
Co ₂₀ ) ₇₀ , T ₁ is about 500 K °
Therefore, Tc ₂ <T ₁ .

A magneto-optical recording medium (magneto-optical disk) according to the present invention in which the reproducing layer 1 is Gd ₂₉ (Fe ₈₀ Co ₂₀ ) _71.
When, the Tc ₂ <T ₁ described above Gd ₃₀ (Fe ₈₀ C
o ₂₀ ) The respective frequency characteristics of the case of ₇₀ were measured.

In this case, the recording was performed by magnetic field modulation recording using a floating magnetic head. This recording was performed by applying a magnetic field of about 300 [Oe] modulated according to the recording data, and performing pulsed light emission in which the laser beam was adjusted to be one pulse. In this case, the linear velocity of the disk was set to 5 m / sec, and the recording laser power was adjusted so that the signal became optimal. The wavelength of the laser light is 650 nm
, The objective lens aperture N. of the used optical system. A. Is 0.7
And Then, on a disc to be recorded on both lands and grooves having a track pitch of 0.45 μm,
Reproduction RF when recording / reproducing at 195 μm / bit
The (high frequency) signal was as shown in FIGS.

As is apparent from a comparison of these, FIG.
The magneto-optical disk according to the present invention has a large so-called eye.
An opening eye pattern can be obtained, and Tc shown in FIG._Two
<T ₁Gd becomes₃₀(Fe₈₀Co₂₀)₇₀Composed by
The eye is narrow, that is, the frequency characteristics are poor.
You. Specifically, the reproduction layer 1 is composed of Gd₂₉(Fe₈₀Co₂₀)
₇₁In the example of the present invention, the shortest recording mark (IT is 0.
195 μm). Against this
And the normal reproducing layer Gd₃₀(Fe₈₀Co₂₀)₇₀By
When this is achieved, the signal amplitude hardly increases,
Magneto-optical recording media with high frequency characteristics
You can see that it is doing.

As shown by point P ₂ in FIG. 4, Gd ₂₈ (Fe ₈₀ Co ₂₀ ) ₇₂ actually satisfies the above-mentioned CAD in spite of Tc ₂ <T _1. Not done.

Therefore, in the present invention, when the composition atomic ratio of the rare earth metal and the transition metal in the reproducing layer 1 is X%,
Select 8% <X% <30%.

As described above, the magneto-optical recording medium according to the present invention can increase the reproduction signal amplitude of the shortest mark signal in the reproduction of the CAD system, and can realize stable signal reproduction and, consequently, high-density recording and reproduction. It is.

[0028]

As described above, the magneto-optical recording medium according to the present invention has characteristics suitable for application to the CAD system reproduction, and the reproduction signal amplitude of the shortest mark signal is increased.
As a result, stable signal reproduction and high-density recording / reproduction can be realized, and the object of obtaining excellent signal resolution and high S / N described at the beginning can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of a magneto-optical recording medium according to the present invention.

FIG. 2 is an explanatory diagram of a basic configuration of a magneto-optical recording medium based on a CAD reproducing method and a reproducing operation thereof.

FIG. 3 is a temperature characteristic diagram of each magnetic layer of the magneto-optical recording medium according to the present invention.

FIG. 4 is a diagram plotting a relationship between a ratio of a rare earth to a transition metal in a reproducing layer and a temperature at which an easy axis of magnetization is oriented in a vertical direction.

FIG. 5 is a frequency characteristic diagram of an example of the magneto-optical recording medium according to the present invention.

FIG. 6 is a frequency characteristic diagram of a comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reproduction layer, 2 ... Reproduction auxiliary layer, 3 ... Recording layer, 4 ... Cutting layer, 11 ... Transparent substrate, 12 ...
Transparent dielectric layer, 13 ... Transparent dielectric layer, 14 ... Metal layer

Continued on the front page (72) Inventor Yasuhito Tanaka 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Yukatsu Nakaoki 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F term (reference) 5D075 EE03 FF04 FF12

Claims (2)

[Claims] The present invention has a reproducing layer, a reproducing auxiliary layer, a cutting layer, and a recording layer. The reproducing layer, the reproducing auxiliary layer, and the recording layer have a Curie temperature of Tc ₁ , Tc ₂ , and Tc ₃ , respectively, and are rare earth-transition metal. made of a magnetic layer, the recording layer, the magnetization easy axis at room temperature T _RT, in a direction perpendicular to the film surface, the cutting layer is made of non-magnetic layer, the reproducing layer, the magnetization easy axis film at room temperature T _RT in plane-parallel direction, and at room temperature T _RT higher regeneration temperature T _1, the axis of easy magnetization becomes perpendicular to the film surface direction, the auxiliary reproducing layer has a Curie temperature Tc above room T <sub>RT
2. A</sub> magneto-optical recording medium, wherein up to ₂ , the axis of easy magnetization is in the direction parallel to the film surface, and Tc ₁ > Tc ₂ > T ₁ and Tc ₃ > Tc ₂ . 2. The reproduction layer and the reproduction auxiliary layer are made of Gd as a rare earth metal and Fe or Fe as a transition metal.
And the composition atomic ratio of the rare earth metal and the transition metal in the reproducing layer is X
2. The magneto-optical recording medium according to claim 1, wherein 28% <X% <30%, where% is selected.