JPH06131733A - Signal recording and reproducing method for magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To make optical modulation overwriting possible and to obtain an ultra- resolution effect by impressing a magnetic field to an auxiliary recording layer and a magneto-optical recording layer to direct the sub-lattice magnetizations of these layers to the same direction at the time of reproducing and executing reproducing by irradiation of the recording layer and the auxiliary recording layer with reproducing light of the intensity at which these layers attain the specific ultimate temps. CONSTITUTION:The recording layer is formed by using TbFe, etc., having a relatively low Curie temp. and large coercive force. The auxiliary recording layer is formed by using TbFeCo, etc., having the relatively high Curie temp. and the coercive force larger than the coercive force of the recording layer. The stabilizing magnetic field is impressed to the auxiliary recording layer and the recording layer to direct the sub-lattice magnetizations of these layers to the same direction at the time of reproducing. The reproducing is executed by irradiating these layers in this state with the reproducing light of the intensity at which the max. ultimate temp. of the recording layer exceeds its Curie temp. and that the max. ultimate temp. of the auxiliary recording layer is below its Curie temp. As a result, the optical modulation overwriting is made possible and the ultra-resolution effect is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing method for a magneto-optical recording medium.

[0002]

2. Description of the Related Art Magneto-optical recording media have been put to practical use as high-density, low-cost rewritable information recording media. In particular, a medium using a recording layer of an amorphous alloy of rare earth and a transition metal shows extremely excellent characteristics. The remaining major drawback of the magneto-optical recording medium is that overwrite cannot be performed. That is, since the conventional magneto-optical recording medium needs an erasing process before recording, one rotation requires two rotations to reduce the data transfer rate.

In recent years, several methods have been proposed as a method for performing this overwriting in a magneto-optical recording medium. Among them, a particularly promising method is a light modulation overwrite method using a multilayer film. This method is discussed in Proceedings of the 34th Joint Lecture on Applied Physics 28PZL-3 (1987), which is a perpendicular magnetization layer (magneto-optical recording layer) having a low Curie temperature and a high coercive force and the recording. It is composed of a perpendicular magnetization layer (recording auxiliary layer) having a high Curie temperature and a low coercive force relatively to the layer. The overwriting means first applies an initializing magnetic field (Hini) of a magnitude sufficient to align the magnetization directions of the recording auxiliary layer and does not affect the magneto-optical recording layer, and then applies a bias magnetic field (Hb). On the other hand, a binary modulated light beam of high power (PH) and low power (PL) is emitted. When the PL irradiation is performed, the recording auxiliary layer is not inverted, and the magneto-optical recording layer is oriented in a direction to be stabilized by exchange coupling with the recording auxiliary layer. When the PH irradiation is performed, the recording auxiliary layer is inverted by the bias magnetic field (Hb). Accordingly, the magneto-optical recording layer faces in the opposite direction to the case of PL, and the binary modulation enables overwriting.

In addition to such a medium having two magnetic layers, a layer which plays a role of initialization is provided next to the recording auxiliary layer,
A three-layer or four-layer structure without the initializing magnet has also been proposed. In any of the above methods, it is known that the exchange coupling force between the magneto-optical recording layer and the recording auxiliary layer greatly affects the characteristics. To control this exchange coupling force, the perpendicular magnetic field of GdFeCo or the like is used. An intermediate layer made of a material having small anisotropy is also provided.

On the other hand, in recent years, a method for obtaining a so-called super-resolution effect has been developed in which an exchange coupling multilayer film is used to reproduce a recording smaller than the diffraction limit of reproduction light. As the medium, a medium in which three layers of a reproducing layer having a low coercive force and a high Curie temperature, a control layer having a low Curie temperature, and a recording layer having a high coercive force and a high Curie temperature are exchange-coupled is used. When heated by reproducing light while applying a reproducing magnetic field, at the high temperature part of the medium,
Exchange coupling breaks. Therefore, the reproducing layer faces the direction of the reproducing magnetic field and the recorded bits are erased. Therefore, only the low temperature portion is reproduced, and the reproduction range is narrowed as a result, so that the same effect as when the reproduction light is narrowed down can be obtained, and high density recording bits can be reproduced. The erased recording bit is restored by being transferred from the recording layer when the medium temperature becomes low and the exchange coupling is restored.

[0006]

As described above, the light modulation overwrite and the super-resolution technique have very excellent characteristics. However, there has not been a method that has both of them at the same time, that is, a method capable of performing light modulation overwriting and obtaining a super-resolution effect has not existed so far. A magnetic field modulation method has been proposed as an overwrite method for a medium that obtains a super-resolution effect.
It had the drawbacks that it could not be used for the medium in which two sheets were pasted together, and it was weak against dust.

[0007]

Means for Solving the Problems As a result of studies made by the present inventors to solve the above-mentioned problems, it has been found that a super-resolution effect can be obtained at the same time by devising a reproducing method of an optical modulation overwrite medium. I found it. The gist of the present invention is that a magneto-optical recording layer having a Curie temperature TC1 and a coercive force HC1 at room temperature and a recording auxiliary layer having a Curie temperature TC2 and a coercive force HC2 at room temperature are formed in this order on a substrate. Is
The above-mentioned TC1, TC2, HC1, HC2 satisfy TC1 <TC2, HC1> HC2, and the recording light is modulated into a high power and a low power by at least the step of aligning the magnetization of the recording auxiliary layer in one direction and recording. A signal recording / reproducing method for a magneto-optical recording medium, which is characterized in that a signal is reproduced by the following method in a magneto-optical recording medium capable of performing overwriting through the step of performing (a) recording assistance during writing. By applying a magnetic field in a direction opposite to the magnetization direction in which the layers are aligned, the sub-lattice magnetization of the recording auxiliary layer is oriented in the same direction as the sub-lattice magnetization of the recording layer. Ultimate temperature TMmax is T
Mmax> TC1, and the maximum reaching temperature TAmax of the recording auxiliary layer is TAmax <TC2.

Here, HC1 and HC2 all represent coercive force in the case of a single layer without exchange coupling. Hereinafter, the present invention will be described in detail. Examples of the substrate of the medium used in the present invention include transparent substrates such as glass and plastics such as acrylic resin and polycarbonate resin. The substrate generally has a thickness of about 1.2 mm.

In the present invention, a magneto-optical recording layer and a recording auxiliary layer are provided on the substrate. As the magneto-optical recording layer, one having a relatively low Curie temperature TC1 and a large coercive force HC1 is used. For example, TbFe, TbFeCo, DyFe, DyF
Examples thereof include eCo and TbDyFeCo. TC1 is preferably 120 ° C or higher and 200 ° C or lower, and H
C1 is preferably 10 kOe or more. Film thickness is 3
About 0 to 100 nm is preferable.

As the auxiliary recording layer, one having a relatively high Curie temperature TC2 and a coercive force HC2 smaller than HC1 is used. For example, TbFeCo, DyFeCo, DyCo, T
bDyFeCo, TbCo, GdDyFe, GdDyF
Examples thereof include eCo, GdTbFe, GdTbFeCo and the like. It is preferable that TC2 is not less than 180 ° C. and not more than 250 ° C., but naturally it must be larger than TC1.

A smaller value of HC2 is preferable for reducing the initializing magnetic field (Hini), but the auxiliary recording layer is subjected to an effective bias magnetic field due to exchange coupling with the magneto-optical recording layer, so it was initialized. In order for the state to exist stably, a certain amount of HC2 is required. It is generally preferable that HC2 is about 1 kOe or more and 4 kOe or less. The film thickness of the recording auxiliary layer is 50 nm or more and 150 nm
The following are preferred.

An intermediate layer for reducing the exchange coupling force may be inserted between the magneto-optical recording layer and the recording auxiliary layer. As the intermediate layer, one that reduces the exchange coupling force to about 1/3 to 2/3 is preferably used, and specifically, GdFeCo or the like having small perpendicular magnetic anisotropy is provided with a thickness of about 1 nm to 20 nm. Is preferred. As the intermediate layer, it is also possible to use a layer obtained by oxidizing or nitriding the magneto-optical recording layer or the recording auxiliary layer.

In order to manufacture a medium that does not use an initializing magnetic field, a control layer and an initializing layer are provided after the recording auxiliary layer.
The control layer preferably has a Curie temperature equal to or lower than the Curie temperature of the magneto-optical recording layer. As the control layer, one having a Curie temperature of about 100 to 150 ° C. is usually used. The initialization layer is preferably one having a higher Curie temperature than either the magneto-optical recording layer or the recording auxiliary layer. As the initialization layer, one having a Curie temperature of 300 ° C. or higher is usually used. The thickness of the control layer is preferably 5 to 30 nm, and the thickness of the initial layer is preferably 10 to 50 nm.

Since the alloy of rare earth and transition metal used in the magnetic layer is very easily oxidized, it is a preferred embodiment of the present invention to provide protective films on both sides of the magnetic layer. As the protective layer, SiN, AlN, TaO, TiO, ZnS or the like is preferably used. The thickness of the protective layer is 50 to 200 nm
A degree is preferable. The protective layer between the substrate and the magnetic layer also serves as an interference layer that lowers the reflectance due to the interference effect. As a method of forming each layer on the substrate, sputtering, electron beam vapor deposition, CVD method or the like is used, and the use of the sputtering method is particularly preferable because a high-quality film having high anisotropy can be obtained.

When overwriting with the above medium,
As described in the related art, it is necessary to initialize the recording auxiliary layer in the same direction. At this time, if the sub-lattice magnetization direction is different from that of the magneto-optical recording layer in which recording is performed, a domain wall is generated between the two. In the present invention, a stabilizing magnetic field is applied during reproduction. The direction of the stabilizing magnetic field is opposite to that of the initialization of the recording auxiliary layer. That is, since it is a direction to extinguish the domain wall, the domain wall disappears in a small magnetic field of 1 kOe or less, and the sublattice magnetizations of the two layers face the same direction. Therefore,
As a result, the recording bit is transferred to the recording auxiliary layer. The stabilizing magnetic field applying means may be the same as the recording magnetic field applying means, or may be provided separately.

In this state, further, the maximum reaching temperature TMmax of the magneto-optical recording layer is TMmax> TC1 and the maximum reaching temperature TAmax of the recording auxiliary layer is TAmax <TC2. Perform. The maximum reached temperature TMmax of the magneto-optical recording layer and the maximum reached temperature TAmax of the recording auxiliary layer occur between the recording layer and the recording auxiliary layer due to the influence of the thickness of each layer when reproducing light is applied from the recording layer side. Take advantage of the temperature difference. Usually, a temperature difference of about 10 to 20 ° C. occurs between the recording layer and the recording auxiliary layer.

In this way, the bits disappear and the magneto-optical signal disappears in the high temperature portion of the magneto-optical recording layer. Since the reproduction signal is obtained only from the low temperature part, it is substantially the same as the spot diameter of the reproduction light being reduced, and high resolution can be obtained. When the temperature of the medium is cooled and the magnetization of the magneto-optical recording layer is recovered, the recording bit is transferred to the magneto-optical recording layer by the exchange coupling force with the recording auxiliary layer.

That is, according to the present invention, each time reproduction is performed, recording is transferred twice, that is, magneto-optical recording layer → recording auxiliary layer → magneto-optical recording layer. As shown in the technique of light modulation overwrite, such transfer coupling by transfer coupling is a highly reliable process and sufficiently endures repeated reproduction. When moving from reproduction to recording, normal optical modulation overwrite can be performed by lowering the reproduction power to cut the stabilizing magnetic field and then applying the recording magnetic field.

In this case, the masked portion of the high temperature portion is
Since there is no signal, the super-resolution effect is smaller than in the prior art in which the magnetization is aligned in one direction by the reproducing magnetic field. However, the method of the present invention can be realized by at least two magnetic layers, and has great significance in terms of process simplification and cost reduction. Moreover, there is also a big merit that it can be over-lit. .

[0020]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist. Example 1 Si is sputtered on a polycarbonate substrate.
An 80 nm thick protective layer of N, Tb21 (Fe93Co
7) Thickness 35 consisting of 79 (values are component ratios, the same applies below)
a magneto-optical recording layer having a thickness of 10 nm, an intermediate layer having a thickness of 10 nm made of Gd28 (Fe93Co7), and a recording auxiliary layer having a thickness of 80 nm made of Dy28 (Fe60Co40). The coercive force of the magneto-optical recording layer is 12 kOe and the Curie temperature is 180 ° C. The coercive force of the recording auxiliary layer was 1.8 kOe and the Curie temperature was 280 ° C. Finally, a Si3N4 protective layer was formed to a thickness of 80 nm.

The disk thus obtained had an initializing magnetic field of 3 kO when rotated at a linear velocity of 11.3 m / s.
e, recording magnetic field 300 (Oe), PH = 9 mW, PL = 4 m
Overwriting was possible with W. Disk speed 1
After rotating at 1.3 m / s for recording, 800 (O
FIG. 1 shows the results of measuring the bit length dependence of the reproduced signal when the reproducing power Pr is 2.8 mW as an example and 1 mW as a comparative example with the stabilizing magnetic field of e) applied. Shown in. When Pr is 2.8 mW, the characteristics are improved in a short bit length as compared with the case where Pr is 1 mW, and it can be seen that the super-resolution effect is obtained.

When no stabilizing magnetic field is applied, P
There was no difference when r was 1 mW, but Pr was 2.8.
In mW, the recording disappeared and the reproduction could not be performed. Example 2 Up to the recording auxiliary layer was manufactured in the same manner as in Example 1. afterwards,
A 20 nm-thick control layer made of Tb18 (Fe97Co3) 82 and a 30 nm-thick initialization layer made of Tb23Co77 were formed. The coercive force of the control layer was 6 kOe and the Curie temperature was 140 ° C., and the coercive force of the initialization layer was 22 kOe and the Curie temperature was 400 ° C. or higher. A protective layer of Si3N4 having a thickness of 80 nm was formed on the initializing layer as in Example 1.

The disk thus obtained has a recording magnetic field of 300 (O) when rotated at a linear velocity of 5.7 m / s.
e), PH = 9 mW, PL = 3.5 mW, overwriting was possible. No initialization magnetic field was needed. After rotating the disc at a linear velocity of 5.7 m / s for recording, 800
With the stabilizing magnetic field of (Oe) applied, the bit length dependence of the reproduced signal was measured when the reproducing power Pr was 2.8 mW as an example and when it was 1 mW as a comparative example. A result similar to that of 1 was obtained, and when Pr was 2.8 mW, an improvement in CNR of about 10 dB was observed at a bit length of 0.5 μm compared with the case where Pr was 1 mW, and a super-resolution effect was obtained. I found out that In addition,
When the stabilizing magnetic field was not applied, there was no difference when Pr was 1 mW, but when Pr was 2.8 mW, recording disappeared and reproduction could not be performed.

[0024]

When the reproducing method of the magneto-optical recording medium according to the present invention is used, the optical modulation overwriting is possible and the super-resolution effect can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing a super-resolution effect in Example 1.

[Explanation of symbols]

 1: Graph when Pr is 2.8 mW (present invention) 2: Graph when Pr is 1 mW

Claims (3)

[Claims] 1. A magneto-optical recording layer having a Curie temperature TC1 and a coercive force HC1 at room temperature, and a recording auxiliary layer having a Curie temperature TC2 and a coercive force HC2 at room temperature are formed in this order on a substrate. , TC1, TC2, HC1, and HC2 satisfy TC1 <TC2 and HC1> HC2, and at least the step of aligning the magnetization of the recording auxiliary layer in one direction and recording by modulating recording light to high power and low power are performed. A signal recording / reproducing method for a magneto-optical recording medium, which is characterized in that a signal is reproduced by the following method in a magneto-optical recording medium capable of performing overwriting through the steps. By applying a magnetic field in a direction opposite to the aligned magnetization direction, the sub-lattice magnetization of the recording auxiliary layer is oriented in the same direction as the sub-lattice magnetization of the recording layer. Ultimate temperature TMmax
, TMmax> TC1 and the maximum attainable temperature TAmax of the recording auxiliary layer is TAmax <TC2. 2. A medium having an intermediate layer provided between a magneto-optical recording layer and a recording auxiliary layer and having a perpendicular magnetic anisotropy lower than that of either layer is used. Signal recording / reproducing method for magneto-optical recording medium. 3. A control layer having a Curie temperature equal to or lower than the Curie temperature of the magneto-optical recording layer on the side of the recording auxiliary layer opposite to the side facing the magneto-optical recording layer, the recording auxiliary layer and the magneto-optical recording. 2. The signal recording / reproducing method for a magneto-optical recording medium according to claim 1, wherein a medium provided with an initialization layer having a Curie temperature higher than either of the layers is used.