JPH08124230A - Magnetooptical recording medium and information reproduction method employing it - Google Patents

Abstract

PURPOSE: To enhance the line density of medium by magnetizing a reproduction layer in the direction for stabilizing the information stored in a memory layer when the temperature is lower than a compensation temperature but in one direction through magnetostatic coupling with the memory layer when the temperature is higher than the compensation temperature. CONSTITUTION: In the high temperature region 5 in a light spot 2, a reproduction layer 11 is constantly magnetized in the erasing direction and functions as a rear mask 5. Consequently, the spot 2 is restricted apparently to a region except the high temperature region 5, and other regions serve as an aperture region 3 and thereby a recording domain can be detected at a period shorter than the detection limit. Since a mask can be formed by varying the influence of effective field in the medium, principally the field Hst of magnetostatic coupling force from the memory layer 13, no external field is required. Since the field Hst is proportional to the saturation magnetization Ms2 of the memory layer 13, the saturation magnetization Ms2 is set high enough to sustain stability of recorded information but low enough to cause no reversal of erasure magnetization. This structure realizes high line density.

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 in which information is recorded and reproduced by a laser beam, and more particularly to a magneto-optical recording medium capable of high density and a magneto-optical reproducing method for the medium. It is a thing.

[0002]

2. Description of the Related Art As a rewritable high density recording system,
Using the thermal energy of a semiconductor laser to write magnetic domains in a magnetic thin film to record information, using the magneto-optical effect,
Attention has been paid to a magneto-optical recording medium for reading this information.

Further, in recent years, there is an increasing demand for increasing the recording density of this magneto-optical recording medium to obtain a recording medium having a larger capacity. The linear recording density of an optical disc such as a magneto-optical recording medium largely depends on the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens. That is, since the diameter of the beam waist is determined when the wavelength of the reproduction light and the numerical aperture of the objective lens are determined, the minimum mark length of about λ / 2NA is the limit of reproduction. On the other hand, the track density is limited mainly by crosstalk between adjacent tracks and depends on the spot diameter of the reproducing beam as well as the shortest mark length.

Therefore, in order to realize high density in the conventional optical disk, it is necessary to shorten the laser wavelength of the reproducing optical system or increase the numerical aperture NA of the objective lens.
However, it is not easy to shorten the laser wavelength due to problems such as element efficiency and heat generation. Also, increasing the numerical aperture of the objective lens not only makes it difficult to process the lens, but also increases the distance between the lens and the disc. Mechanical problems such as collision with the disk due to being too close to each other occur. Therefore, a technique for improving the recording density by devising the configuration of the recording medium and the reading method has been developed.

For example, in the magneto-optical reproducing method disclosed in Japanese Patent Laid-Open No. 3-93056, a medium structure as shown in FIG. 6 has been proposed. FIG. 6A shows a sectional view of an optical disc which is an example of the super-resolution technique. The substrate 20 is usually a transparent material such as glass or polycarbonate, and the interference layer 34, the reproducing layer 31, the intermediate layer 32, the memory layer 32, and the protective layer 35 are laminated on the substrate 20 in this order. The interference layer 34 enhances the Kerr effect, and the protective layer 35 is used to protect the magnetic layer. The arrow in the magnetic layer indicates the direction of magnetization or atomic magnetic moment in the film. When the medium composed of the reproducing layer, the intermediate layer, and the memory layer is irradiated with a light spot, the magnetic coupling between the reproducing layer and the memory layer in the high temperature portion of the temperature distribution of the medium generated at that time is controlled by the intermediate layer having a low Curie temperature. By cutting and aligning the magnetization of the reproducing layer in the portion where the magnetic coupling is broken by an external magnetic field in one direction, and partially masking the magnetic domain information of the memory layer in the light spot, We are trying to improve linear recording density by making it possible to reproduce periodic signals.

Further, in the super-resolution reproducing method disclosed in JP-A-3-93058 and JP-A-4-255946, a reproducing layer 31, an intermediate layer 32 and a memory layer 33 are formed as shown in FIG. Use medium. Prior to information reproduction, the initialization magnetic field 21 aligns the magnetization direction of the reproduction layer 31 in one direction to mask the magnetic domain information of the memory layer 33 and then irradiates the light spot 2 with the temperature distribution of the medium generated at that time. In the low temperature region, the reproduction layer 31 is maintained in the initialized state (the front mask 4 is formed), and in the high temperature region of the Curie temperature Tc2 or higher of the intermediate layer 32, the reproduction layer 31 is forcibly oriented in the direction of the reproduction magnetic field 22. (The rear mask 5 is formed.) The magnetic domain information of the memory layer 33 is transferred only in the medium temperature region to reduce the effective size of the reproduction spot, thereby reproducing the recording mark 1 below the light diffraction limit. It is possible and the linear density is improved.

In these known super-resolution systems, since the front mask 4 extends in the direction of the adjacent track in the low temperature region, an attempt is made to improve not only the linear recording density but also the track density.

[0008]

However, in the method disclosed in Japanese Unexamined Patent Publication No. 3-93056, although the resolution can be increased without degrading the signal quality, it is necessary to apply the reproducing magnetic field. According to the methods disclosed in Japanese Patent Laid-Open No. 93058 and Japanese Patent Laid-Open No. 4-255946, the magnetization of the reproducing layer 31 must be aligned in one direction prior to information reproduction, and the initialization magnet 21 for that purpose is added to the conventional device. Will be required. As described above, in the conventional super-resolution reproduction method, the resolution cannot be sufficiently increased,
There are problems that the magneto-optical recording / reproducing apparatus becomes complicated, the cost becomes high, and the miniaturization is difficult.

[0009]

In order to solve such problems, the present invention has a simple structure which does not require an initializing magnetic field and a reproducing magnetic field at the time of reproducing, and has a structure which is below the diffraction limit of light. An object of the present invention is to provide a magneto-optical recording medium capable of reproducing a recording mark with high signal quality and an optical information reproducing method using the medium.

The object is to provide a memory layer for storing information, a high Curie temperature and a low coercive force with respect to the memory layer, and a reproducing layer having a compensation temperature between room temperature and the Curie temperature of the memory layer. At least, the magnetization of the reproducing layer includes a region that is stably oriented with respect to the information stored in the memory layer in a temperature region below the compensation temperature thereof, and a temperature region above the compensation temperature thereof. Is achieved by a magneto-optical recording medium magnetized in one direction by magnetostatic coupling.

At least a memory layer for storing information, a high Curie temperature and a low coercive force with respect to the memory layer, and a reproducing layer having a compensation temperature between room temperature and the Curie temperature of the memory layer are provided. The magnetization of the reproducing layer includes a region which is oriented in a stable direction with respect to the information stored in the memory layer in a temperature region below its compensation temperature, and magnetostatic in a temperature region above its compensation temperature. In an information reproducing method of irradiating a magneto-optical recording medium magnetized in one direction by coupling with a light spot from the reproducing layer side, transferring the information accumulated in the memory layer to the reproducing layer to reproduce the information, The temperature of the reproducing layer in the irradiated light spot is raised to a temperature exceeding the compensation temperature of the reproducing layer, so that the magnetization of the reproducing layer in the high temperature portion is magnetized in one direction. In another area within the light spot, the information stored in the memory layer is transferred to the reproduction layer, and the information is reproduced by detecting the magneto-optical effect of the reflected light of the light spot. To be achieved.

[0012]

According to such a constitution of the present invention, since the portion of the reproducing layer corresponding to the high temperature region in the light spot at the time of reproduction reaches the temperature exceeding the compensation temperature, the net magnetization of the reproducing layer in the high temperature region is The direction becomes an anti-static coupling state, and as a result, the reproducing layer is affected by the static magnetic field of the memory layer, and the magnetic domain of the reproducing layer located in the high temperature region contracts, that is, the magnetization of the reproducing layer is in one direction. Since they are aligned, the recorded information in the memory layer is masked. In the areas other than the high temperature area in the light spot, the magnetization information of the memory layer is transferred to the reproducing layer by the magnetostatic coupling force or the exchange coupling force, so that the Kerr effect of the reflected light of the light spot from the medium Since the change is affected by the magnetization of the reproducing layer corresponding to a region other than the high temperature region in the light spot, if a change in the polar Kerr effect of the reflected light of the light spot is detected, it is recorded at a period below the light diffraction limit. It is possible to reproduce the recorded information and improve the linear density of the medium.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The magneto-optical recording medium of the present invention and the information reproducing method using the medium will be described below in detail with reference to the drawings.

The magneto-optical recording medium of the present invention comprises at least two magnetic layers, a reproducing layer and a memory layer, which is a perpendicular magnetization film, laminated on the transparent substrate side from the substrate side (FIG. 1).
(A)).

The reproducing layer is a layer for reproducing the magnetization information held in the memory layer, and is located closer to the incidence of light than the memory layer. The Curie temperature is set so that the Kerr rotation angle does not deteriorate during reproduction. Make it higher. Further, the coercive force of the reproducing layer needs to be smaller than the coercive force of the memory layer. It is also necessary that there is a compensation temperature between room temperature and the Curie temperature of the memory layer. This is because in this medium, the super-resolution reproduction is performed by forming the rear mask by setting the high temperature region in the light spot to a temperature region exceeding the compensation temperature of the reproduction layer during reproduction. Therefore, when the Curie temperature of the memory layer is the same as the compensation temperature of the reproducing layer or lower than the compensation temperature of the reproducing layer, the magnetization information of the memory layer is destroyed during reproducing, and the effect of the present invention is achieved. Can not do it. The Curie temperature of the memory layer is preferably 10 ° C. or higher, more preferably 20 ° C. or higher than the compensation temperature of the reproducing layer. However, if it is set too high, recording with a laser beam will not be easily performed, so it is desirable that the value be 28
It is preferably 0 ° C or lower, more preferably 240 ° C or lower. In other words, the compensation temperature of the reproducing layer is preferably 270 ° C.
The temperature is more preferably 230 ° C. or lower.

Further, the reproducing layer has a magnetization form which is a perpendicular magnetization film at room temperature and between room temperature and Curie temperature, or an in-plane magnetization film at room temperature and perpendicular magnetization between room temperature and compensation temperature. It is either a film or a film. Specific materials include, for example, rare earth-iron group amorphous alloys such as GdFeCo, GdTbFeCo, and GdDyFeC.
A material mainly containing GdFeCo such as o and NdGdFeCo is desirable because it has a high Curie temperature and a low coercive force, and the recording magnetic domain easily contracts in the high temperature region which is the main point of the medium.

When GdFeCo is used in the reproducing layer, the compensation temperature strongly depends on the composition of the rare earth element (Gd), so when the magnetic layer mainly containing GdFeCo is used in the reproducing layer, the amount of Gd is preferably set. It is desirable to set to 24 to 35 at%.

The memory layer is a layer for storing recorded information and is required to be able to stably hold magnetic domains. As a recording material, a material having a large perpendicular magnetic anisotropy and capable of stably holding a magnetized state, for example, TbFeCo, DyFeCo, Tb
A rare earth-iron group amorphous alloy such as DyFeCo is preferable.

Further, it is necessary that the memory layer has no compensation temperature at least above the temperature at which the reproducing layer is magnetostatically coupled with the memory layer. In the present invention, this is because the high temperature region in the light spot during reproduction is set to a temperature region that exceeds the compensation temperature of the reproduction layer, and the net magnetization of the reproduction layer is reversed in the direction opposite to that of the reproduction layer in the aperture region. This is because the rear mask is formed with the memory layer in a demagnetization coupled state, and the memory layer needs to store the same magnetization state in the transfer region and the rear mask region.

For example, when the ferrimagnetic rare earth-iron group element amorphous alloy thin film is used for the reproducing layer and the memory layer, the reproducing layer has a rare earth element sublattice magnetization dominant and the memory layer has the iron group element sublayer at room temperature. The lattice magnetization is dominant, or the rare earth element sub-lattice magnetization is dominant in both the reproducing layer and the memory layer. The ferrimagnetic rare earth-iron group element amorphous alloy thin film is suitable for the magnetic layer of the medium of the present invention because it easily realizes the above structure.

The above-mentioned reproducing layer and memory layer are at least
In the high temperature region within the light spot, the exchange coupling force must be blocked and the magnetostatic coupling force must work. In this case, the exchange coupling force acts between the reproducing layer and the memory layer at room temperature, and the exchange coupling force is interrupted in the high temperature region to cause magnetostatic coupling. The exchange coupling force is interrupted from the room temperature to the high temperature region. It is considered that the magnetostatic coupling force works. In order to realize the former form, a ferrimagnetic rare earth-iron group element amorphous alloy composed of a perpendicularly magnetized film having a Curie temperature in the temperature range of the high temperature region of the light spot between the reproducing layer and the memory layer is used. An intermediate layer may be provided. In this structure, the exchange coupling force acts between the reproducing layer and the memory layer via the intermediate layer at room temperature, and in the high temperature region, the intermediate layer reaches the Curie temperature and the magnetization disappears, so that the exchange coupling force between the reproducing layer and the memory layer. Is cut off and only the magnetostatic coupling force works. Further, in order to realize the latter mode, it is necessary that the reproducing layer has a rare earth element sublattice magnetization dominant and the memory layer has an iron group element sublattice magnetization dominant at room temperature. Further, in order to block the exchange coupling force acting between the reproducing layer and the memory layer from room temperature to a high temperature region, the interface between the reproducing layer and the memory layer is formed by plasma treatment after the reproducing layer is formed. It is effective to provide an intermediate layer between the reproducing layer and the memory layer in order to prevent the exchange coupling force from acting on or to block the exchange coupling (FIG. 1 (b)). The material of the intermediate layer is preferably a non-metal layer such as a dielectric, a non-magnetic metal layer, or a magnetic layer made of an in-plane magnetized film. By providing such an intermediate layer, the exchange force can be blocked more reliably as compared with the above-mentioned method by the plasma treatment.

The reproducing layer and the memory layer are made of Al, T
Elements such as i, Pt, Nb, and Cr may be added to improve the corrosion resistance. In addition to the above playback layer and memory layer,
SiNx, AlO to enhance the interference effect and protection performance
A dielectric such as x, TaOx, or SiOx may be provided. Also, to improve thermal conductivity, Al, AlTa, AlT
A layer having good thermal conductivity such as i, AlCr, or Cu may be provided. In addition, an initialization layer in which magnetization is aligned in one direction for performing light modulation overwrite, and an auxiliary layer for assisting recording and reproducing for adjusting exchange coupling force or magnetostatic coupling force may be provided. Further, a protective coat made of the dielectric layer or polymer resin may be provided as a protective film.

Next, the recording / reproducing process of the present invention will be described.

First, a recording magnetic domain is formed in the memory layer of the magneto-optical recording medium of the present invention according to a data signal. As the recording method, as the first recording method, after erasing once, the laser power is modulated while applying a magnetic field in the recording direction. As a second recording method, the laser power is modulated while applying an external magnetic field to overwrite the new data on the old data. For these optical modulation recordings,
If the intensity of the laser beam is determined in consideration of the linear velocity of the recording medium so that only the predetermined area in the light spot is near the Curie temperature of the memory layer, a recording magnetic domain smaller than the diameter of the light spot can be formed. , A signal with a period less than the diffraction limit of light can be recorded. Alternatively, as a third recording method, overwrite recording is performed by modulating an external magnetic field while irradiating a laser beam having a power such that the memory layer has a Curie temperature or higher. In this case, if the modulation speed is increased according to the linear velocity, a recording magnetic domain smaller than the diameter of the light spot can be formed.
It is possible to record a signal having a period less than the diffraction limit of light.

Further, as is clear from the mechanism described later, in order for the super-resolution of the present invention to function stably, it is necessary that the magnetization around the recording mark is oriented in the opposite direction to the mark. is there. In the most general first recording method, first, the laser power is kept constant at a high power while a constant magnetic field is applied, the magnetization of the track to be recorded is initialized (erasing operation), and then the direction of the magnetic field is changed. In the inverted state, the laser power is intensity-modulated to form a desired recording mark. At that time, if there is a random magnetized portion around the recording mark, noise may occur during reproduction.In order to improve the quality of the reproduced signal, it is generally necessary to erase in a wider width than the recording mark. Has been done. Therefore, since the magnetization around the recorded magnetic domain always faces the opposite direction to the magnetic domain, the super-resolution of the present invention operates stably in this recording method.

The second recording method is disclosed in Japanese Patent Laid-Open No. 62-
A medium having a structure as described in 175948 (this medium has a memory layer for holding recording information and a writing layer in which magnetization is oriented in one direction prior to recording), Although an erasing operation prior to recording is not required, when recording is performed on this medium, the laser intensities are Ph, Pl (Ph> Pl) depending on the recorded information while applying a constant magnetic field in the opposite direction to the writing layer. ) Between. When the medium is heated to a temperature Th corresponding to Ph, Th is set to be substantially equal to Tc of the writing layer, so that the magnetizations of the memory layer and the writing layer form magnetic domains in the direction of the external magnetic field, and the medium is Pl. If the temperature is raised up to a considerable temperature Tl, the direction of magnetization becomes the same as that of the writing layer. This process occurs independently of prerecorded magnetic domains. Here, considering the time when the medium is irradiated with the laser of Ph, the temperature of the portion forming the recording magnetic domain rises to Th,
Since the temperature distribution at this time has a two-dimensionally widened shape, even if the laser is raised to Ph, there is always a portion around the magnetic domain where the temperature rises only to Tl. Therefore, there is a portion having the opposite magnetization around the recording magnetic domain. That is, even with this recording method, the super-resolution of the present invention operates stably.

In the third recording method, a modulation magnetic field according to information is applied to the medium while irradiating the laser with high power DC, but the history of previously recorded magnetic domains is not left. In order to record new information, the width forming the magnetic domains must be constant. Therefore,
In this case, if no measures are taken, a region in which the magnetization direction is random exists around the recording magnetic domain, and the super-resolution of the present invention does not operate stably. Therefore, when performing magnetic field modulation recording, the initialization operation should be performed with a power higher than the normal recording power before shipping the medium or prior to the first recording, or for both the land and the groove. It is necessary to completely initialize the magnetization in advance.

Next, the reproducing method of the present invention will be described.

In the present invention, magnetic super-resolution is realized by apparently optically masking a part of the area within the light spot without applying an external magnetic field. 3 (a) (b)
(C) is a diagram showing a process in which a recording magnetic domain (hereinafter, simply referred to as a recording magnetic domain) of the reproducing layer transferred from the memory layer contracts in a high temperature region when the light spot moves. For the sake of simplicity, FIG. 3 shows the contraction process of one recording magnetic domain. Further, in FIG. 3, it is assumed that the magnetic material is a rare earth iron group ferrimagnetic material, the white arrow 30 indicates the entire magnetization, the black arrow 31 indicates the iron group sublattice magnetization, and the reproducing layer 11 is the RE-rich magnetic layer. As the memory layer 13, the TM-rich magnetic layer is described as an example. It should be noted that FIG. 2 shows the entire image at the time of reproduction with the temperature distribution added. Also in FIG. 2, white arrows indicate the entire magnetization, and black arrows indicate the iron group sublattice magnetization. Note that the description here will be given using a medium in which the exchange coupling force between the reproducing layer and the memory layer is cut off from room temperature to the high temperature region in the light spot, and the magnetostatic coupling force acts.

Since the temperature distribution of the medium has a limited thermal conductivity, it shifts from the center of the light spot in the direction opposite to the movement of the light spot. As shown in FIG. 3A, the recording magnetic domain 1 does not reach the high temperature region 5 just before the light spot 2 reaches the recording magnetic domain 1. In addition to the magnetic field Hst due to the magnetostatic coupling force from the memory layer 13, the effective magnetic field Hwb due to the Bloch domain wall energy and the static magnetic field Hleak from other regions of the reproducing layer are applied to the recording magnetic domain 1.
Hst works so as to stably hold the recording magnetic domain 1 of the reproducing layer, while Hwb works in the direction of contracting the recording magnetic domain.
Therefore, in order for the reproducing layer 11 to stably transfer the magnetization of the memory layer 13, the condition of (Equation 1) is required before the recording magnetic domain 1 reaches the high temperature region 5. (Equation 1) | Hwb ± Hleak | <Hc1 + Hst (T
<Th-mask) Hwb represents the Bloch domain wall energy of the reproducing layer 11 by σw
b, the radius of the recording magnetic domain 1 of the reproducing layer 11 is represented by (Equation 2), and the recording magnetic domain 1 acts in a direction of contracting (FIG. 4). (Equation 2) Hwb = σwb / 2Ms1r

Now, when the light spot further moves and the recording magnetic domain 1 enters a high temperature region in which the temperature exceeds the compensation temperature of the reproducing layer, the net magnetization of the reproducing layer is reversed.
For this reason, the recording magnetic domain receives an antiparallel static magnetic force from the memory layer. Therefore, Hst works to invert the recording magnetic domain like Hwb. FIG. 4 shows the magnetic field applied to the magnetic domain immediately before contraction. (Actually, the domain wall moves from the high temperature side and contracts the magnetic domain as shown in FIG. 4.) Therefore, the following (Equation 3) is established, and the Bloch domain wall 8 of the recording magnetic domain 1 moves in the direction in which the magnetic domain contracts. To do. (Equation 3) Hwb + Hst ± Hleak> Hc1 (T> T
h-mask)

Thus, as shown in FIG. 3B, the recording magnetic domain 1 contracts and inverts when it enters the high temperature region 5, and finally, as shown in FIG. 3C, all the magnetizations are in the erasing direction. Orient. The Th-mask shown in Equations 2 and 3 and FIG.
It is the same temperature as the compensation temperature of the reproducing layer.

Further, the static magnetic field H from the above-mentioned memory layer 13
st also acts on the magnetization in the erasing direction. However, when the magnetization in the erasing direction is reversed by Hst, the domain wall is formed over a wide range of the high temperature region 5, so that the domain wall energy greatly increases. Therefore, the magnetization in the same erasing direction is maintained without reversing the magnetization. Therefore, in the high temperature region 5, a region in which the magnetization is oriented in the erasing direction is always generated, and this is the rear mask 5
Becomes The effective magnetic field Hwb ′ of the Bloch domain wall energy when the erase magnetization is reversed is represented by (Equation 7) where R is the reversal domain radius. (Equation 4) Hwb ′ = σwb / 2Ms1R Therefore, the condition that the erase magnetization is not inverted by Hst is (Equation 11). (Equation 5) Hwb '> Hst

That is, as shown in FIG. 2, in the high temperature region 5 in the light spot 2, since the reproducing layer 11 is always a perpendicular magnetization film oriented in the erasing direction, it functions as an optical mask (rear mask 5). To do. Therefore, as shown in FIG. 2, the light spot 2 is apparently narrowed down to a narrow region excluding the high temperature region 5, and in the other regions, it becomes the aperture region 3 and the recording magnetic domain of the period below the detection limit ( The recording mark) can be detected.

A conventional super-resolution method is disclosed in Japanese Patent Laid-Open No. 4-25 / 1992.
As described in 5947, a mask is formed by using the external magnetic field Hr according to the relationship of (Equation 6). (Equation 6) Hr> Hc1 + Hwi In the present invention, the external magnetic field is not necessary because the mask is formed by changing the effect of the effective magnetic field inside the medium, mainly Hst instead of the external magnetic field Hr.

The value of Hst can be roughly calculated by using the radius of the recording magnetic domain 1, the distance from the magnetic domain of the memory layer 13, and the magnetization Ms2 of the memory layer assuming a cylindrical magnetic domain (Nagoya University). Doctoral dissertation, March 1985, "Research on the magnetism and magneto-optical effect of rare earth-iron group amorphous alloy thin films and their composite films", Tadashi Kobayashi, p. H
st is proportional to the saturation magnetization Ms2 of the memory layer (Equation 7). (Equation 7) Hst∽Ms2

Therefore, it is desirable that Ms2 be large enough to maintain the stability of the recorded information and small enough not to reverse the erase magnetization.

In the above description, the case where the light spot region other than the high temperature region is the aperture region is shown. However, in addition to the above conditions, the reproducing layer is an in-plane magnetized film at room temperature and is compensated for at room temperature. By using a film that forms a perpendicular magnetization film with respect to the temperature, not only the high temperature region in the light spot but also the low temperature region can be masked.

That is, in the low temperature region near room temperature, the magnetization information of the memory layer is masked by the in-plane magnetized film reproducing layer, and the magnetization information of the memory layer is magnetostatically coupled in the medium temperature region where the reproducing layer is the perpendicular magnetized film. Then, the magnetization information of the memory layer is masked by the above-mentioned mechanism in the high temperature region. Such a double mask type super-resolution can increase not only the linear density but also the track density.

Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the present invention is not limited to the following experimental examples as long as the gist thereof is not exceeded.

First, a magneto-optical recording medium in which the reproducing layer was a perpendicularly magnetized film at room temperature and between the room temperature and the Curie temperature was prepared and evaluated, and shown in Experimental Examples 1 and 2 below.

(Experimental Example 1) Each target of Si, Gd, Tb, Fe and Co was attached to a DC magnetron sputtering apparatus, and a glass substrate having a diameter of 130 mm and a polycarbonate substrate with a pre-groove were placed at a distance of 150 mm from the target. After fixing to the substrate holder installed at the position, the interior of the chamber was evacuated by a cryopump until a high vacuum of 1 × 10 −5 Pa or less was obtained. After evacuation, Ar gas was introduced into the chamber until the pressure reached 0.4 Pa, and then the SiN interference layer was set to 90 nm and Gd.
The FeCo reproducing layer is 40 nm, the SiN intermediate layer is 10 nm,
TbFeCo memory layer 35nm, SiN protective layer 70
In order to obtain a magneto-optical recording medium of the present invention having the structure shown in FIG. At the time of forming each SiN dielectric layer, N ₂ gas was introduced in addition to Ar gas, and reactive sputtering was performed so that the refractive index was 2.1 while adjusting the mixing ratio.

The composition of the GdFeCo reproducing layer is Gd ₂₄ (F
e ₆₈ Co ₃₂ ) ₇₆ at room temperature with RE rich and Ms of 120
emu / cc, compensation temperature is 200 ° C, Curie temperature is 3
It was at least 00 ° C. This reproducing layer was a perpendicular magnetic film at room temperature.

The composition of the TbFeCo memory layer is Tb.
₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀ was TM rich at room temperature, Ms was −230 emu / cc, and Curie temperature was 250 ° C. This medium was used for evaluation as follows.

First, 0.78 μm was added to this magneto-optical recording medium.
After recording the magnetic domain with the mark length of, the magnetic domain was observed with a polarization microscope while irradiating light with a semiconductor laser of 780 nm. It was confirmed that when the laser power was increased, the recording magnetic domain transferred in the central portion (high temperature region) of the light spot contracted and the magnetization was oriented in the erasing direction at a certain laser power. Next, the recording / reproducing characteristics were measured using this magneto-optical recording medium. The measurement is based on the N.V. of the objective lens. A. Is 0.55, the laser wavelength is 780 nm, the recording power is 7 to 13 mW, and the reproducing power is 3.0 to
The C / N ratio was set to be the highest within the range of 4.0 mW. The linear velocity was 9 m / s. First, after erasing the entire surface of the medium, 5.8, 11.3, 15 MH was recorded on the recording layer.
z carrier signal (mark length 0.78 μm,
(Corresponding to 0.40 μm and 0.30 μm)
The dependence of the C / N ratio on the mark length was investigated.

Next, crosstalk with adjacent tracks (hereinafter referred to as crosstalk) was measured. This is the same as recording a signal with a mark length of 0.78 μm on the land part and measuring a carrier signal (this is C1) by the above-mentioned method, and then tracking the adjacent groove part which has been erased. The signals (designated as C2) were measured and expressed as their ratio (C2 / C1). That is, since the experiment is performed assuming that the data is recorded on both the land and the groove, the effective track pitch is 0.8 μm. Both C / N and crosstalk were measured without applying an initializing magnetic field and a reproducing magnetic field.

The results are shown in Table 1. It can be seen that although the crosstalk was not improved, a high C / N was obtained at a short mark length.

(Experimental Example 2) Also, after omitting the intermediate layer and flowing a small amount of oxygen gas after forming the reproducing layer, the substrate was plasma-treated (the substrate was reverse-sputtered with RF of 300 W), and then the memory was formed. A magneto-optical recording medium similar to that of Experimental Example 1 was prepared except that the layers were formed. Even in this medium, the exchange coupling between the reproducing layer and the memory layer was blocked, and the super-resolution effect could be obtained without using the reproducing magnetic field. The same evaluation as in Experimental Example 1 was performed on this magneto-optical recording medium. The results are shown in Table 1. Crosstalk was not improved, but C / N
It is understood that a high value is obtained at a short mark length.

(Experimental Example 3) As in Experimental Example 1, S was formed on the substrate.
90 nm iN interference layer and 40 n GdFeCo reproducing layer
m, the SiN intermediate layer was 10 nm, the TbFeCo memory layer was 35 nm, and the SiN protective layer was 70 nm in that order to obtain the magneto-optical recording medium of the present invention having the structure shown in FIG. Each Si
At the time of forming the N dielectric layer, N ₂ gas was introduced in addition to Ar gas, and the film was formed by reactive sputtering so that the refractive index was 2.1 while adjusting the mixing ratio thereof.

The composition of the GdFeCo reproducing layer is Gd ₂₈ (F
e ₆₀ Co ₄₀ ) ₇₂ at room temperature with RE rich and Ms of 220
emu / cc, compensation temperature 217 ° C, Curie temperature 3
It was at least 00 ° C. This reproducing layer was an in-plane magnetized film at room temperature and became a perpendicular magnetized film at about 140 ° C.

The composition of the TbFeCo memory layer is Tb.
₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀ was TM rich at room temperature, Ms was −230 emu / cc, and Curie temperature was 250 ° C.

This magneto-optical recording medium was evaluated in the same manner as in Experimental Example 1. The results are shown in Table 1. In this case, since the low temperature region is masked by the in-plane magnetized film, C / N
At the same time, it can be seen that crosstalk has also been improved.

Next, a magnetic super-resolution magneto-optical recording medium of a known example was prepared, and the same evaluation measurement was carried out with the same apparatus as the above-mentioned examples.

(Comparative Experiment Example 1) First, Japanese Patent Laid-Open No. 3-930
A medium similar to the medium described in No. 56 was prepared and evaluated. First, using the same film forming apparatus and film forming method as in Experimental Example 1, a SiN interference layer of 90 nm, a GdFeCo reproducing layer of 30 nm, a TbFeCoAl intermediate layer of 10 nm, and Tb were similarly formed on a glass substrate.
FeCo memory layer 40nm, SiN protective layer 70nm
Were sequentially deposited to obtain a magneto-optical recording medium of Comparative Experimental Example 1.

The composition of the GdFeCo reproducing layer is TM at room temperature.
The rich Ms was set to −180 emu / cc, and the Curie temperature was set to 300 ° C. or higher.

The composition of the TbFeCoAl intermediate layer was set to be TM rich at room temperature, Ms of -160 emu / cc, and a Curie temperature of 140 ° C.

The composition of the TbFeCo memory layer is T at room temperature.
It was set to be M rich, Ms of −150 emu / cc, and a Curie temperature of 250 ° C.

Next, using this magneto-optical recording medium, recording and reproducing characteristics were measured in the same manner as in Example 1. However, in this case, a reproducing magnetic field of 0, 200, or
The voltage was changed to 400 Oe and applied. The results are shown in Table 1.

(Comparative Experimental Example 2) Next, JP-A-3-255
A medium similar to the medium described in No. 946 was prepared and evaluated.
Using the same film forming apparatus and film forming method as in Experimental Example 1, similarly, a SiN interference layer of 90 nm, a GdFeCo reproducing layer of 30 nm, a TbFeCoAl intermediate layer of 10 nm, and a GdF were formed on a glass substrate.
The eCo auxiliary layer is 16 nm and the TbFeCo memory layer is 40 nm.
nm and a SiN protective layer having a thickness of 70 nm were sequentially formed to obtain a magneto-optical recording medium of a comparative experimental example.

The composition of the GdFeCo reproducing layer is TM at room temperature.
The rich Ms was set to -160 emu / cc, and the Curie temperature was set to 300 ° C or higher.

The composition of the TbFeCoAl intermediate layer was set so that it was TM rich at room temperature, Ms was -160 emu / cc and Curie temperature was 140 ° C.

The composition of the GdFeCo auxiliary layer is TM at room temperature.
The rich Ms was set to -160 emu / cc and the Curie temperature was set to 280 ° C.

The composition of the TbFeCo memory layer is T at room temperature.
It was set to be M rich, Ms of −150 emu / cc, and a Curie temperature of 250 ° C.

Next, using this magneto-optical recording medium, Example 1
The recording / reproducing characteristics were measured in the same manner as in. However, in this case, the initializing magnetic field in the direction perpendicular to the medium is 0, 1000, 2 before reproduction.
000 Oe and reproducing magnetic field of 0, 200, 400 Oe
The voltage was changed and applied. The results are shown in Table 1.

Therefore, in the magneto-optical recording medium of the present invention, it is possible to improve C / N or both C / N and crosstalk without applying a reproducing magnetic field or both an initializing magnetic field and a reproducing magnetic field. It has become possible to improve the linear recording density or both the linear recording density and the track density.

[0066]

[Table 1]

[0067]

According to the magneto-optical recording medium and the reproducing method of the present invention, by using a simple device (conventional device) which does not require a reproducing magnetic field and / or an initializing magnet, a magnetic domain smaller than the beam spot system can be obtained. Reproduction is possible, and the recording density is greatly improved and high density recording can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic layer structure of a magnetic layer of a magneto-optical recording medium of the present invention.

FIG. 2 is a diagram showing an information reproducing method in one form of the magneto-optical recording medium of the present invention. FIG. 6A is a diagram showing a mask region and an aperture region in a light spot on the upper surface of the medium. FIG. 6B is a diagram showing the magnetization direction state of each layer. FIG. 6C is a diagram showing a temperature distribution in the track direction.

3 (a), (b) and (c) are views for explaining the principle of masking a high temperature region in a light spot in the magneto-optical recording medium of the present invention.

FIG. 4 is a static magnetic field H applied to a recording magnetic domain transferred to a reproducing layer.
The figure which showed the effective magnetic field Hwb by leak, Hst, and Bloch domain wall energy.

FIG. 5 is a diagram showing an example of a layer structure of a magneto-optical recording medium of the present invention.

FIG. 6 is a diagram showing a known super-resolution method.

FIG. 7 is a diagram showing a known super-resolution method.

Claims (7)

[Claims] 1. A magneto-optical recording medium, a memory layer for storing information, a reproducing layer having a high Curie temperature and a low coercive force with respect to the memory layer, and a compensation temperature between room temperature and the Curie temperature of the memory layer. At least, the magnetization of the reproduction layer includes a region that is stably oriented with respect to the information stored in the memory layer in a temperature region equal to or lower than the compensation temperature of the reproduction layer. A magneto-optical recording medium which is magnetized in one direction by magnetostatic coupling with respect to the magnetization of the memory layer in the temperature region. 2. The magnetic material according to claim 1, comprising a non-metal layer such as a dielectric material, a non-magnetic metal layer, or an in-plane magnetized film for blocking exchange coupling between the reproduction layer and the memory layer. Layers are provided. 3. The reproducing layer and the memory layer according to claim 1, wherein the reproducing layer and the memory layer are ferrimagnetic rare earth-iron group element amorphous alloy thin films, and the reproducing layer has a rare earth element sublattice magnetization predominant at room temperature. The memory layer has the iron group element sublattice magnetization predominant, or both the reproducing layer and the memory layer have the rare earth element sublattice magnetization predominant. 4. The reproducing layer according to claim 1, comprising a magnetic layer containing GdFeCo as a main component. 5. The memory layer according to claim 1, wherein the memory layer is made of TbFe, TbFeCo, DyFe,
It is composed of a magnetic layer containing DyFeCo as a main component. 6. The reproducing layer according to claim 1, wherein the reproducing layer has no compensation temperature above a temperature at which the reproducing layer is magnetostatically coupled to the memory layer. 7. At least a memory layer for storing information, a high Curie temperature and a low coercive force for the memory layer, and a reproducing layer having a compensation temperature between room temperature and the Curie temperature of the memory layer, The magnetization of the reproducing layer includes a region which is oriented in a stable direction with respect to the information stored in the memory layer in a temperature region below its compensation temperature, and magnetostatic in a temperature region above its compensation temperature. In an information reproducing method of irradiating a light spot from a reproducing layer side to a magneto-optical recording medium magnetized in one direction by coupling, transferring the information accumulated in the memory layer to the reproducing layer to reproduce the information, In the high temperature portion in the irradiated light spot, the temperature of the reproduction layer is raised to a temperature exceeding the compensation temperature of the reproduction layer, thereby magnetizing the reproduction layer in the high temperature portion in one direction. The information stored in the memory layer in another area in the light spot is transferred to the reproducing layer, and the information is reproduced by detecting the magneto-optical effect of the reflected light of the light spot. Information reproduction method.