JPH0863809A - Magnetooptical recording medium and information reproducing method therefor - Google Patents

Abstract

PURPOSE: To achieve high density recording by specifying the compositions of first to third magnetic layers and the difference between the compensation temperature of the first magnetic layer and the Curie point of the third magnetic layer. CONSTITUTION: An interference layer 14, a first magnetic layer (reproduction layer) 11, a third magnetic layer (intermediate layer) 12, a second magnetic layer (memory layer) 13 and a protective layer 15 are formed sequentially on a substrate 20. The reproduction layer 11 is composed of an amorphous alloy of rare earth-iron group elements having a compensation temperature between the room temperature and Curie point in which the rare earth element sublattice magnetization prevails under the room temperature. The memory layer 12 is formed of a vertical magnetization film of a rare earth-iron group element amorphous alloy having Curie point higher than the temperature of the interference layer but lower than that of the intermediate layer. They are formed such that the difference between the compensation temperature of the reproduction layer 11 and the Curie point of the intermediate layer 12 satisfies a specified value. This structure increases the line density and the traffic density thus realizing high density recording.

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 for optically recording and reproducing information using a light beam, and an information reproducing method for the medium, and in particular, enables high density recording of the medium. The present invention relates to a magneto-optical recording medium and a method for reproducing information from the medium.

[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 make it 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 the 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 disc, 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 wavelength of the laser because of problems such as the efficiency of the element and heat generation.
Increasing the numerical aperture of the objective lens not only makes it difficult to process the lens, but also causes mechanical problems such as collision between the lens and the disk because the distance between the lens and the disk becomes too short. 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 recording medium disclosed in Japanese Unexamined Patent Publication No. 6-124500, FIG. 24 shows a super-resolution technique for realizing a recording density higher than the optical resolution of reproducing light.
A medium structure as shown in (1) has been proposed. Figure 24 (a)
FIG. 3 shows a cross-sectional view of an optical disc which is an example of super-resolution technology. The substrate 20 is usually a transparent material such as glass or polycarbonate, and is provided with a concentric or spiral groove (group 6) in advance to form a guide track. Record information is recorded along the land and / or group. An interference layer 43, a first magnetic layer (hereinafter referred to as a reproduction layer) 41, a second magnetic layer (hereinafter referred to as a memory layer) 42, and a protective layer 44 are laminated in this order on the substrate 20. Since the interference layer 43 enhances the Kerr effect, the protective layer 44
Is used to protect the magnetic layer. The arrow in the magnetic layer indicates the direction of iron group element sublattice magnetization in the film.
The memory layer 42 is, for example, a film having a large perpendicular magnetic anisotropy such as TbFeCo or DyFeCo, and the recorded information is retained by forming a magnetic domain depending on whether the magnetization of this layer is upward or downward with respect to the film surface. The reproducing layer 41 is a material having a large saturation magnetization Ms and a small perpendicular magnetic anisotropy, and is composed of a composition in which the rare earth element sublattice magnetization is dominant. FIG. 25 shows an example of static characteristics of the reproduction layer 41. Although it is an in-plane magnetized film at room temperature, the saturation magnetization Ms gradually decreases as the temperature rises, and when it reaches a predetermined temperature, the magnitude relationship between the perpendicular magnetic anisotropy Ku and 2πMs ² is reversed, so that the film becomes a perpendicular magnetized film. FIG. 25 shows the static characteristics of the reproducing layer alone, but when laminated with the memory layer 42, the exchange coupling force with the memory layer 42 acts to lower the temperature T.
At th, the layer becomes a perpendicular magnetic film, and the direction of the iron group element sublattice magnetization of the reproducing layer 41 at the time of becoming the perpendicular magnetic film is the direction of exchange coupling with the memory layer 42. When a disk having such a medium structure is irradiated with light for reproducing information from the substrate 20 side, the temperature gradient at the center of the data track becomes as shown in FIG. 24 (c). As shown in 24 (b), there is a Tth isotherm in the spot. Then, as described above, the reproducing layer 41 does not contribute to the polar Kerr effect (forms the front mask 4) in the portion below Tth since it becomes an in-plane magnetized film, and the recording magnetic domain held in the memory layer 42 is masked. It becomes invisible. On the other hand, Tt
In the portion of h or more, the reproducing layer 41 is a perpendicular magnetization film, and the direction of the iron group element sublattice magnetization is the same as the recorded information due to the exchange coupling from the memory layer 42. As a result, the recording magnetic domain of the memory layer 42 is transferred only to the portion of the aperture 3 which is smaller than the size of the spot 2, so that super-resolution is realized.

Further, in the super-resolution reproducing method disclosed in JP-A-3-93058 and JP-A-4-255946, as shown in FIG. 26, a reproducing layer 31 and a third magnetic layer (hereinafter referred to as an intermediate layer) are used. A medium composed of 32) and a memory layer 33 is used. Prior to information reproduction, the magnetization direction of the reproduction layer 31 is aligned in one direction by the initialization magnetic field 21 and the memory layer 33 is formed.
After the magnetic domain information is masked, the light spot 2 is irradiated, and in the temperature distribution of the medium generated at that time, the reproducing layer 31 is maintained in the initialized state (forms the front mask 4) in the low temperature region, and the intermediate layer 32. In the high temperature region above the Curie temperature Tc2, the reproducing layer 31 is forcibly oriented in the direction of the reproducing magnetic field 22 (rear mask 5 is formed), and the magnetic domain information of the memory layer 33 is transferred only in the intermediate temperature region. By reducing the effective size of the spot, the recording mark 1 below the diffraction limit of light can be reproduced, 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 super-resolution reproducing method disclosed in Japanese Patent Laid-Open No. 6-124500, only the front mask 4 is used. Therefore, if the area of the mask is widened to increase the resolution, the aperture 3 There was a problem that the signal quality was sacrificed due to the position of the point deviating from the center of the spot. Further, in the methods disclosed in JP-A-3-93058 and JP-A-4-255946, although the resolution can be increased without degrading the signal quality, the magnetization of the reproducing layer 31 is unidirectionally prior to the information reproduction. They must be aligned, which necessitates the addition of magnets to the conventional device to generate the initializing magnetic field 21.

As described above, the conventional super-resolution reproduction method is
There are problems that the resolution cannot be sufficiently increased, the magneto-optical recording / reproducing apparatus becomes complicated, the cost becomes high, and the size reduction is difficult.

In order to solve such a problem, 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 makes a recording mark having a light diffraction limit or less with a high signal quality. An object of the present invention is to provide a reproducible magneto-optical recording medium and an optical information reproducing method using the medium.

[0011]

The above object of the present invention is to provide a magneto-optical recording medium in which at least a first magnetic layer, a third magnetic layer and a second magnetic layer are laminated in this order on a substrate. The first magnetic layer is made of a rare earth-iron group element amorphous alloy, and has a rare earth sublattice magnetization predominance at room temperature,
The second magnetic layer has a compensation temperature between room temperature and Curie temperature, the second magnetic layer is a perpendicular magnetic film made of a rare earth-iron group element amorphous alloy, and the Curie temperature of the second magnetic layer is Curie of the first magnetic layer. The temperature is lower than the Curie temperature of the third magnetic layer and higher than the Curie temperature of the third magnetic layer, and the relationship between the compensation temperature Tcomp1 of the first magnetic layer and the Curie temperature Tc3 of the third magnetic layer is −20 (° C.) ≦ Tcomp1 ( C) -Tc3 (C) <8
It is achieved by setting the temperature to 0 (° C).

A magneto-optical recording medium comprising at least a first magnetic layer, a third magnetic layer and a second magnetic layer laminated on a substrate in the above-mentioned order, wherein the first magnetic layer is rare earth-iron. A rare earth element sublattice magnetization dominant at room temperature, a compensation temperature between room temperature and Curie temperature, and the second magnetic layer has a perpendicular magnetization composed of a rare earth-iron group element amorphous alloy. In the film, the Curie temperature of the second magnetic layer is lower than the Curie temperature of the first magnetic layer and higher than the Curie temperature of the third magnetic layer, and the compensation temperature T of the first magnetic layer is
The following relationship between comp1 and the Curie temperature Tc3 of the third magnetic layer −20 (° C.) ≦ Tcomp1 (° C.) − Tc3 (° C.) ≦ 8
In an information reproducing method of irradiating a magneto-optical recording medium satisfying 0 (° C.) with a light beam to reproduce recorded information, the light beam is irradiated from the side of the first magnetic layer, and The magnetization of the first magnetic layer in the low temperature portion is magnetized in one direction, and the first magnetic layer is exchange-coupled with the second magnetic layer as a perpendicular magnetization film in a portion other than the low temperature portion in the spot. This is achieved by transferring the information stored in the second magnetic layer to the magnetic layer and reproducing the information stored in the second magnetic layer by detecting the reflected light of the light beam.

[0013]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view of an optical disk according to this embodiment. As shown in FIG. 1, in the optical disk used in this embodiment, an interference layer 14, a first magnetic layer (hereinafter referred to as a reproduction layer) 11, a third magnetic layer (hereinafter referred to as an intermediate layer) 12, and a first magnetic layer 12 are provided on a substrate 20. A two magnetic layer (hereinafter referred to as a memory layer) 13,
The protective layer 15 is laminated in this order. The substrate 20 is usually made of glass or a transparent material such as polycarbonate. Each of these layers can be deposited by continuous sputtering using a magnetron sputtering device, continuous vapor deposition, or the like. The interference layer 14 is provided to enhance the magneto-optical effect, and is made of, for example, Si ₃ N ₄ , AlN, SiO ₂ , Si.
Transparent dielectric materials such as O, ZnS, MgF ₂ are used. The protective layer 15 is used to protect the magnetic layer, and the same material as the interference layer 14 is used. Interference layer 1
4 and the protective layer 15 have nothing to do with the essence of the present invention, a detailed description thereof will be omitted here. Although not shown in FIG. 1, a hard coat material such as an ultraviolet curing resin may be further applied to the protective layer 15 in order to protect the film or use a magnetic field modulation overwrite magnetic head.

The reproducing layer 11 is a layer for reproducing the magnetization information held in the memory layer 13 and is an in-plane magnetized film at room temperature.
It has a magnetization characteristic of forming a perpendicular magnetization film at a predetermined temperature or higher between room temperature and Curie temperature. The reproduction layer 11 is the intermediate layer 1
2. Located closer to the incidence of light than the memory layer 13,
The Curie temperature is set to be higher than at least the intermediate layer 12 and the memory layer 13 so as not to deteriorate the Kerr rotation angle during reproduction. The reproducing layer 11 is, for example, a rare earth-iron group element amorphous alloy having small perpendicular magnetic anisotropy, such as GdFeCo.
GdFeCo, GdDyFeCo, etc. GdFeCo
It is preferable that the material mainly containing is because the Curie temperature is high, the coercive force is low, and the recording magnetic domain easily contracts in the high temperature region, which is the main point of the present medium. Specifically, GdFeCo
Is desirable. Further, a light rare earth metal such as Nd, Pr or Sm may be added to this in order to increase the Kerr rotation angle at a short wavelength.

Next, the purpose of providing the intermediate layer 12 is the following three. (1) At room temperature, the domain wall energy between the reproducing layer 11 and the memory layer 13 is relaxed to help the reproducing layer 11 to become an in-plane magnetized film. As a result, this also contributes to the reduction of the thickness of the reproducing layer. (2) When the temperature reaches a predetermined temperature or higher, it transits to the perpendicular magnetization film together with the reproducing layer 11, and mediates exchange coupling from the memory layer 13 to the reproducing layer 11. (3) Above the Curie temperature of the intermediate layer 12, the regeneration layer 11
The exchange coupling between the memory layer 13 and the memory layer 13 is broken.

In order to achieve these objects, the intermediate layer 1
2 is located between the reproducing layer 11 and the memory layer 13 and has a Curie temperature higher than room temperature and lower than the Curie temperatures of the reproducing layer 11 and the memory layer 13. The Curie temperature of the intermediate layer 12 is large enough to mediate the exchange coupling force from the memory layer 13 to the reproducing layer 11 at the middle temperature portion in the light spot at the time of reproducing,
It is small enough to break the exchange coupling force at the highest temperature part, and specifically, it is preferably 80 ° C or higher and 220 ° C or lower, and more preferably 110 ° C or higher and 180 ° C or lower. Examples of the material for the intermediate layer 12 include rare earth-iron group amorphous alloys such as TbFe, TbFeCo, GdFe, and GdFeC.
o, GdTbFeCo, GdDyFeCo, DyFe,
DyFeCo and TbDyFeCo are preferable. Further, in order to reduce the Curie temperature, a non-magnetic element such as Cr, Al, Si, Cu may be added. When the reproducing layer is used as an in-plane magnetized film at low temperature to mask the low temperature region, the in-plane anisotropy at room temperature is higher than that of the reproducing layer in order to enhance the in-plane magnetic anisotropy of the reproducing layer at low temperature. It is more desirable that the saturation magnetization Ms at room temperature is larger than the Ms at room temperature of the reproducing layer.

The memory layer 13 is a layer for holding recorded information,
It is necessary to be able to stably hold minute magnetic domains of 1 μm or less. As a material of the memory layer 13, a material having a large perpendicular magnetic anisotropy and capable of maintaining a stable magnetization state, for example, Tb
Rare earths such as FeCo, DyFeCo, TbDyFeCo-iron group amorphous alloy, garnet, or platinum group-
An iron group periodic structure film such as Pt / Co or Pd / Co, or a platinum group-iron group alloy such as PtCo or PdCo may be used.

The reproducing layer 11, the intermediate layer 12 and the memory layer 13 may be added with elements such as Al, Ti, Pt, Nb and Cr for improving the corrosion resistance. Further, a layer having good thermal conductivity such as Al, AlTa, AlTi, AlCr, or Cu may be provided for improving thermal conductivity. 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.

Recording of a data signal on the optical disk of the present invention is performed by moving the medium and simultaneously modulating the laser power while applying a magnetic field in a fixed direction (optical modulation recording).
Alternatively, the external magnetic field is modulated while irradiating the laser light having a constant power so that the memory layer 13 has a Curie temperature around Tc3 (magnetic field modulation recording). In the former case, a recording magnetic domain smaller than the light spot diameter can be formed by adjusting the intensity of the laser light so that only a predetermined area in the light spot becomes Tc3, and as a result, a signal with a period less than the diffraction limit of light is recorded. You can do it. In the latter case, a small recording magnetic domain can be formed by setting the modulation frequency of the magnetic field to a high frequency as compared with the relative velocity (linear velocity) between the light spot and the medium.

Further, as is clear from the mechanism described later, in order for the super-resolution of the present invention to function stably, the magnetization around the recording mark must be oriented in the opposite direction to the mark. In the most general optical modulation recording, 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 reversed. In this 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 under the conventional optical modulation recording.

Another method of optical modulation recording is optical modulation overwrite. This is JP 62
No. 175948 uses a medium having a structure as described above and does not require an erasing operation prior to recording. In addition to a memory layer that holds recorded information, this medium includes a write layer whose magnetization is oriented in one direction prior to recording. When recording on this medium,
The laser intensity is modulated between Ph and Pl (Ph> Pl) according to the recorded information while applying a constant magnetic field in the opposite direction to the writing layer. 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 Temperature Tl equivalent to Pl
If the temperature is raised only up to this, the magnetization direction of the memory layer becomes the same as that of the writing layer. This process occurs independently of prerecorded magnetic domains. Here, the medium is Ph
Considering when the laser is irradiated, the temperature of the portion forming the recording magnetic domain is raised to Th. However, since the temperature distribution at this time is two-dimensionally widened, the laser is raised to Ph. Even if it does, there is always a portion around the magnetic domain where the temperature rises only up to Tl. Therefore, there is a portion having the opposite magnetization around the recording magnetic domain. That is, the super-resolution of the present invention operates stably even under the conventional optical modulation overwrite recording. Still another recording method is the above-mentioned magnetic field modulation recording. This is to change the direction of the external magnetic field in an alternating manner while irradiating the laser with high power DC, but in order to record new information without leaving the history of the previously recorded magnetic domain, The width forming the magnetic domains must always be constant. Therefore, in this case, there is a region where the magnetization direction is random around the recording magnetic domain unless some measures are taken,
The super-resolution of the present invention will not operate stably. Therefore, when performing magnetic field modulation recording, the recording area should be initialized with a power larger than the normal recording power before shipment of the medium or prior to the first recording, or the land or groove should be recorded. It is necessary to completely initialize the magnetization of both of them.

FIG. 2 shows a state of spots and a magnetization state of each magnetic layer when the disc moves rightward while irradiating the optical disc of the present invention with a laser beam.
FIG. 2 shows a case where the disk is moving at about 9 m / s, and since heat is accumulated by laser irradiation, the position where the film temperature is maximum is behind the center of the laser spot. .

First, the temperature of the medium on the leading edge side with respect to the traveling direction of the spot 2 has not risen so much from room temperature. The temperature dependence of the saturation magnetization Ms of the reproducing layer 11 and the intermediate layer 12 is as shown in, for example, FIG. 3 and FIG. 4, and both layers have large saturation magnetization Ms in the low temperature region of the spot and the perpendicular magnetic anisotropy. Ku is small. At this time, the perpendicular magnetic anisotropy Ku1 of the reproducing layer 11, the saturation magnetization Ms1, and the exchange coupling force from the memory layer 13 via the intermediate layer 12 cause the reproducing layer 11 to move.
When the energy for orienting the magnetization in the vertical direction is Ew13, the magnetization of the reproducing layer 11 is oriented in the film plane when (Equation 1) 2πMs1 ² > Ku1 + Ew13. In particular, the saturation magnetization of the intermediate layer 12 depends on the reproduction layer 11
Since the in-plane anisotropy is even larger than that, the intermediate layer 12 has a function of absorbing the interfacial domain wall energy between the memory layer 13 which is the perpendicular magnetization film and the reproducing layer 11 which is the in-plane magnetization film. Therefore, by inserting the intermediate layer 12, the direction of magnetization is in the film plane even when the film thickness of the reproducing layer 11 is smaller than that in the case without the intermediate layer 12, and the magnetization of the memory layer 13 is not transferred. The front mask 4 is formed.

Next, when the medium temperature rises due to the irradiation of the spot 2, the saturation magnetization M of the reproducing layer 11 and the intermediate layer 12 is increased.
s becomes smaller and smaller. Particularly in the case of the present invention, since the compensation temperature of the reproducing layer 11 and the Curie temperature of the intermediate layer 12 are close to each other, the saturation magnetization of both rapidly decreases as the temperature of the medium rises. Therefore, when the medium reaches a predetermined temperature Tth and (Equation 2) 2πMs1 ² <Ku + Ew13, the reproducing layer 11 becomes a perpendicular magnetization film and at the same time exchange-couples with the memory layer 13, so that the magnetic domain held in the memory layer 13 becomes It is transferred to the reproduction layer 11 to form the aperture 3. When the temperature further rises, the Curie temperature T of the intermediate layer 12
When it becomes higher than c2, the magnetization of the intermediate layer 12 disappears, and the exchange coupling force between the reproducing layer 11 and the memory layer 13 disappears. Consider a case where the reproducing layer 11 has a rare-earth element sublattice magnetization dominant at this temperature and the memory layer 13 has an iron-group element sublattice magnetization dominant (that is, antiparallel). Then, the magnetic domain transferred to the reproducing layer 11 at a temperature of Tc2 or lower loses the exchange coupling force from the memory layer 13 which holds the magnetic domain, and at the same time, the magnetostatic coupling force from the memory layer 13 is reversed. Will join. Further, since the reproducing layer 11 is also close to the compensation temperature, the influence of the demagnetizing field of the reproducing layer 11 itself is small. Therefore, the magnetic domain of the reproducing layer 11 transferred from the memory layer 13 does not resist the Bloch domain wall energy and contracts and inverts. Resulting in. That is, in the spot 2 where the temperature is raised to the Curie temperature Tc2 or higher of the intermediate layer 12, there is a region where magnetic domains cannot exist in the reproducing layer and are aligned in the same direction. This portion is the rear mask 5. The process of forming this rear mask results from the change in the balance of energy related to the interaction between the magnetic layers.
In particular, the mask is formed without applying an external magnetic field for reproduction.

The behavior of the magnetic domain transferred to the reproducing layer 11 in the process of moving from the aperture portion to the rear mask will be described in more detail.

In FIG. 5, the recording magnetic domain of the reproducing layer 11 transferred from the memory layer 13 (hereinafter simply referred to as recording magnetic domain).
6A and 6B are a plan view and a cross-sectional view showing a process in which a light spot contracts in a high temperature region when the light spot moves. 1 for simplicity in FIG.
The contraction process of two recording magnetic domains is illustrated. Further, in FIG. 5, a rare earth iron group ferrimagnetic material is assumed as the magnetic material,
The white arrow 30 indicates the entire magnetization, the black arrow 31 indicates the iron group sub-lattice magnetization, the reproduction layer 11 is the RE-rich magnetic layer, and the memory layer 13 is the TM-rich magnetic layer. 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.

FIG. 5A shows a state in which the recording magnetic domain 1 is in the aperture area. In the recording magnetic domain 1, in addition to the effective magnetic field Hwi due to the exchange coupling force from the memory layer 13, the effective magnetic field Hwb due to the Bloch domain wall energy,
The static magnetic field Hd from the inside of the medium is applied. Hwi functions to stably hold the recording magnetic domain 1 of the reproducing layer,
A force acts on wb and Hd in the direction of expanding or 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 3) is required before the recording magnetic domain 1 reaches the high temperature region 5. (Equation 3) | Hwb-Hd | <Hc1 + Hwi (T <Th-mask) where Th-mask is the boundary temperature of the high temperature region 5.

The coercive force Hc1 of the reproducing layer 11 is determined by the memory layer 1
The exchange coupling force from 3 apparently increases the value, so that (Equation 3) can be easily established, and the magnetization information of the memory layer 13 can be stably transferred to accurately reproduce the recorded information.

Hwi is represented by (Equation 4), where σwi is the interface domain wall energy between the reproducing layer 11 and the memory layer 13, Ms1 is the saturation magnetization of the recording magnetic domain 1 of the reproducing layer 11, and h1 is the film thickness of the reproducing layer. . (Equation 4) Hwi = σwi / 2Ms1h1 When the light spot further moves and enters the high temperature region 5, Hw
When i reaches near the Curie temperature of the intermediate layer 12, σwi rapidly decreases and Hwi decreases. Therefore, the reproduction layer 11
Returns to its original low coercive force (Equation 5),
The Bloch domain wall 8 of the recording magnetic domain 1 easily moves. (Equation 5) | Hwb−Hd |> Hc1 + Hwi (T> Th-mask) Hwb is the Bloch domain wall energy of the reproducing layer 11 σw
b, the radius of the recording magnetic domain 1 of the reproducing layer 11 is represented by (Equation 6), and the recording magnetic domain 1 acts in a direction of contracting (FIG. 6). (Equation 6) Hwb = σwb / 2Ms1r Therefore, when Hwb−Hd becomes positive (sign is +) and becomes (Equation 7), the recording magnetic domain 1 contracts. (Equation 7) Hwb-Hd> Hc1 + Hwi (T> Th-mask) Thus, as shown in FIG. 5B, the recording magnetic domain 1 contracts and inverts when it enters the high temperature region 5, and finally FIG. As shown in c), the magnetizations are all oriented in the erase direction.

That is, as shown in FIG. 2, in the high temperature region 5 in the light spot 2, the reproducing layer 11 is always a perpendicular magnetization film oriented in the erasing direction, and therefore 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 the low temperature in-plane magnetized film region (front mask). In the region 3, the recording magnetic domain (recording mark) having a period less than the detection limit can be detected. In the conventional super-resolution method, the mask is formed by using the external magnetic field Hr according to the relationship of (Equation 8) as described in Japanese Patent Laid-Open No. 4-25947. (Equation 8) Hr> Hc1 + Hwi In the present invention, the external magnetic field is not necessary because the mask is formed by changing the magnitude of the effective magnetic field Hw−Hd inside the medium instead of the external magnetic field Hr.

Next, the method of making the effective magnetic field Hw-Hd positively dominant at high temperature, that is, contracting the recording magnetic domain 1 will be described more specifically. Hd in (Equation 7) is composed of a leakage magnetic field Hleak from surrounding erase magnetization, a static magnetic field Hst from magnetization of the memory layer 13, and the like, and is represented by (Equation 9). (Equation 9) Hd = Hleak ± Hst Among these, Hleak works in the direction of expanding the recording magnetic domain 1 as shown in FIG. A first method for more easily contracting the recording magnetic domain 1 in the high temperature region is to reduce Hleak to reduce the magnetic field that prevents the reversal of the recording magnetic domain 1.
Hleak is roughly expressed by (Equation 10) when the saturation magnetization of the reproducing layer 11 around the recording magnetic domain to be erased is Ms1 ″ and the radius of the recording magnetic domain 1 is r. (Equation 10) Hleak = 4πMs1 ″ h1 / (h1 + 3) / 2r) (Formula 10), the recording domain radius r and the reproducing layer film thickness h1 are
Since it cannot be easily changed, it is necessary to reduce Ms1 ″. In such a case, a material having a compensation temperature between room temperature and the Curie temperature may be selected for the reproducing layer. At the compensation temperature, the magnetization becomes small. Therefore, Hleak can be reduced.As an example, a case where GdFeCo is used for the reproducing layer 11 will be described.FIGS.8A to 8C show the temperature dependence of Ms of GdFeCo having different compensation temperatures. The maximum temperature on the medium during reproduction depends on the reproduction power, but generally the maximum temperature shown in the figure reaches approximately 160 to 220 ° C, and the medium temperature range is 20 to 6 ° C.
Since the region is low by about 0 ° C., Ms1 ″ is large in the case of FIGS. 8B and 8C. Therefore, Hlea
k becomes large. When a composition having a compensation temperature between room temperature and the Curie temperature as shown in FIG. 8A is used for the reproducing layer 11, Ms in the middle temperature and high temperature regions is reduced and Hlea increases.
k can be reduced. Reproducing layer 1 of GdFeCo
When used for No. 1, since the compensation temperature strongly depends on the composition of the rare earth element (Gd) as shown in FIG.
When a magnetic layer containing o is used as the reproducing layer 11, the Gd amount is 2
It is desirable to set it to 4 to 32 at%.

The second method is to increase the static magnetic field Hst from the memory layer 13 to a negative value to promote the reversal of the recording magnetic domain 1. In Equation (7), Hst is the recording magnetic domain 1 depending on whether the reproducing layer 11 and the memory layer 13 are of the parallel type or the anti-parallel type at the time of entering the high temperature region from the exchange coupling region.
Is determined to work in a contracting direction or to be kept as it is. This is for the following reason.

As shown in FIG. 7, the exchange coupling force follows the direction of the iron group sublattice magnetization having a strong exchange force, and the magnetostatic coupling force follows the direction of the overall magnetization. FIG. 7A shows an anti-parallel type in which the reproducing layer 11 has a rare earth element sublattice magnetization dominant and the memory layer 13 has an iron group element sublattice magnetization dominant. In this case, the intermediate layer 12 is near the Curie temperature. And the exchange coupling is broken, the magnetostatic coupling force with the memory layer 13 tries to reverse the magnetization of the recording magnetic domain 1 (Hst becomes negative). On the contrary, as shown in FIG. 7B, in the case of the parallel type (both layers show the case where the iron group element sublattice magnetization is dominant in the figure), the magnetostatic coupling force is the direction in which the exchange coupling state is maintained. Work (Hst becomes positive).

Therefore, in order to invert the recording magnetic domain 1,
It is desirable to use an anti-parallel type configuration. Specifically, for example, the reproducing layer 11 and the memory layer 13 may be made to be ferrimagnetic, and the types of dominant sub-lattice magnetization may be reversed. For example, the reproducing layer 11 and the memory layer 13 are made of a rare earth (RE) iron group (TM) element alloy, and the reproducing layer 11
Is a magnetic layer in which the rare-earth element sublattice magnetization is dominant, and is a memory layer 13.
Has a predominant iron group element sublattice magnetization at room temperature. The anti-parallel structure needs to be achieved at least at the temperature when the recording magnetic domain 1 contracts (in the above-mentioned middle temperature to high temperature region 5).

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). Ph.D. thesis, March 1993. "Study on magnetism and magneto-optical effect of rare earth-iron group amorphous alloy thin films and composite films thereof", see Tadashi Kobayashi, p. 40-41). H
st is proportional to the saturation magnetization Ms2 of the memory layer (Equation 1)
1). (Equation 11) Hst∝Ms2 Therefore, it is desirable to increase Ms2 so that the stability of the recorded information does not deteriorate and the erase magnetization does not reverse.

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 12) where R is the reversal domain radius. (Equation 12) Hwb ′ = σwb / 2Ms1R Therefore, the condition that the erase magnetization is not inverted by Hst is (Equation 13). (Equation 13) Hwb '> Hst The recording magnetic domains 1 above are easily inverted to the erased state 2
One of the two methods-a method for reducing Hleak and a method for increasing Hst negatively-may be used alone, but the super-resolution effect is best exhibited when the two methods are used in combination.

Next, the medium structure that satisfies these conditions will be described below.

In order to produce a rear mask in the spot, the intermediate layer must reach the Curie temperature in the hottest part of the spot as described above. The laser power for information reproduction is usually set to about 4 mW or less on the surface of the medium, and if it is higher than that, the margin for the laser power during recording becomes small. At this time, considering that the temperature reached by irradiation with the reproducing power is about 220 ° C., the Curie temperature of the intermediate layer must be 220 ° C. or lower. On the contrary, the rear mask should be generated only in a part of the spot, and if the intermediate layer reaches the Curie temperature without laser irradiation, the front mask or the aperture is not formed and the signal cannot be reproduced. . Since the temperature inside the magneto-optical recording / reproducing apparatus usually rises to about 50 to 60 ° C., stable information reproduction cannot be performed unless the Curie temperature of the intermediate layer is 80 ° C. or higher. Therefore, the Curie temperature of the intermediate layer is 80 to 220.
Must be in the range of ° C.

In order for the rear mask to be stably formed when the intermediate layer reaches a temperature near the Curie temperature, it is necessary that Hleak is small as described above. Hleak is the saturation magnetization Ms1 ″ around the recording magnetic domain as shown in (Equation 10).
Since Ms1 ″ must be small, the above condition is satisfied when the reproducing layer is near the compensation temperature when the intermediate layer reaches near the Curie temperature.

Next, another condition for forming the rear mask, Hst, will be considered. Hst is a magnetostatic coupling force that acts on the reproducing layer from the recording magnetic domain of the memory layer when the intermediate layer reaches a temperature near the Curie temperature. When the memory layer and the reproducing layer are anti-parallel, Hst works in the direction of inverting the transferred magnetic domain to form the rear mask, but in the case of the parallel type, it works in the direction of hindering the formation of the rear mask. This means that, for example, when the memory layer is iron group sublattice magnetization dominant, the reproducing layer is rare earth element sublattice magnetization dominant at a temperature near the Curie temperature Tc3 of the intermediate layer.
That is, the effect of Hst is greater when the compensation temperature Tcomp1 of the reproducing layer is higher than the Curie temperature Tc3 of the intermediate layer.

As described above, in order to reduce the magnetic domain holding effect by Hleak and increase the magnetic domain contraction effect by Hst, the compensation temperature Tcomp of the reproducing layer is set.
When 1 is set to be slightly higher than the Curie temperature Tc3 of the intermediate layer, the rear mask can be formed most stably. On the other hand, when Tcomp1 becomes low, the effect of Hst to shrink the magnetic domain becomes small, so that the rear mask cannot be stably formed and the quality of the reproduced signal deteriorates.
On the contrary, if Tcomp1 is too high, Ms1 ″ becomes large, so that Hleak is also large, and even if the intermediate layer reaches the Curie temperature, the magnetic domain of the reproducing layer does not easily shrink, so that the quality of the reproducing signal also deteriorates. Tc3
The effect of the present invention is maximized when the temperature is set to about several tens of degrees, specifically, -20 ° C or higher and 80 ° C or lower.

As described above, when the magneto-optical recording medium of the present invention is used, the magnetic orientation in the high temperature region 5 of the light spot can be uniformly oriented without applying an external magnetic field during reproduction, and the magnetization of the memory layer 13 is magnetized. Can be optically masked.

With the mechanism as described above, in the magneto-optical recording medium of the present invention, the most efficient super-resolution, that is, only the vicinity of the center of the information reproducing spot contributes to the information reproduction, so that high reproduction signal quality is expected. Moreover, the front mask can be formed by further optimizing the film characteristics, and the super-resolution method that is strong against crosstalk from adjacent tracks is realized without adding new parts such as an external magnetic field to the conventional reproducing device. It is possible. 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.

(Experimental Example 1) Si, Gd, Tb, Fe and Co targets were attached to a DC magnetron sputtering apparatus, and a glass substrate having a diameter of 130 mm and a polycarbonate substrate with a pregroove having a pitch of 1.6 μm were separated from the target. After being fixed to a substrate holder installed at a position of 150 mm, the inside of the chamber was evacuated by a cryopump until a high vacuum of 1 × 10 ⁻⁵ Pa or less was obtained. Ar gas 0.4Pa while evacuating
The SiN interference layer to 90 nm and the Gd ₂₈ (Fe ₆₀ Co ₄₀ ) ₇₂ reproducing layer to ₄₀ n.
m, Gd ₃₇ Fe ₆₃ intermediate layer 10 nm, Tb ₂₀ (Fe ₈₀ C
o ₂₀ ) ₈₀ nm memory layer 30 nm, SiN protective layer ₇₀ n
m was sequentially formed into a film to obtain the medium having the structure shown in FIG. At the time of forming each SiN dielectric layer, N2 gas was introduced in addition to Ar gas, and reactive sputtering was performed so that the refractive index became 2.1 while adjusting the mixing ratio. Gd ₂₈ (F
The e ₆₀ Co ₄₀ ) ₇₂ reproducing layer has a predominant rare earth element sublattice magnetization at room temperature, a saturation magnetization Ms1 of 180 emu / cc, a compensation temperature Tcomp1 of 215 ° C., and a Curie temperature of 300.
℃ or above. The Gd ₃₇ Fe ₆₃ intermediate layer has a predominant rare earth element sublattice magnetization at room temperature and a saturation magnetization Ms3 of 450 em.
The u / cc and Curie temperature Tc3 were set to 190 ° C. The Tb ₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀ memory layer has an iron group element sublattice magnetization predominant at room temperature and a saturation magnetization Ms2 of −25.
The Curie temperature Tc2 was set to 0 emu / cc and 270 ° C. Hereinafter, the polarity of the saturation magnetization will be described as positive when the rare earth element sublattice magnetization is dominant and negative when the iron group element sublattice magnetization is dominant.

After recording a magnetic domain with a mark length of 0.78 μm on this magneto-optical recording medium, the magnetic domain was observed with a polarization microscope while irradiating light with a semiconductor laser of 830 nm. It was confirmed that when the laser power was increased, the recording magnetic domain contracted in the central portion (high temperature region) of the light spot 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. NA of the objective lens is 0.5
3, an optical head with a laser wavelength of 780 nm was used, and the linear velocity was 9 m / s and the recording power was 10 mW. First, after erasing the entire surface of the medium, the laser is modulated at a frequency of 11.3 MHz to record a mark having a length of 0.40 μm.
The change in C / N when the reproducing power was changed from 0.8 mW to 4.4 mW was measured. The results are shown in Fig. 9.

In the magneto-optical recording medium of the present invention, when the reproducing power is 1.0 mW or less, the temperature of the medium does not rise sufficiently, so that the magnetization of the reproducing layer is almost in-plane. Therefore, the mark recorded in the memory layer is masked by the reproducing layer, so that C / N hardly occurs. When the reproducing power is increased to about 2.0 to 2.8 mW, an intermediate temperature region, that is, an aperture is formed in the reproducing spot and the magnetic domain of the memory layer is transferred to the reproducing layer, so that the C / N increases. The shape of the aperture at this time is almost the same as the super-resolution of the conventional two-layer structure using the in-plane film shown in FIG. 24. Although the super-resolution phenomenon occurs, the size and position of the aperture are optimized. Since it is not, the C / N is 36
Only about dB can be obtained. Furthermore, the reproduction power is 3.2 to
When the temperature is increased to 4.0 mW, a portion where the intermediate layer reaches the Curie temperature appears in the spot, that is, a rear mask is formed. Then, the aperture shape becomes the optimum shape for the spot as shown in FIG. 2, so that the C / N is 45d.
B was obtained. When the reproducing power exceeds 4.0 mW, the maximum temperature exceeds the Curie temperature of the memory layer, the recorded data is destroyed, and the C / N decreases.

Next, in order to further support the formation of the rear mask in the magneto-optical recording medium of the present invention, the amplitude of the reproduced signal and the DC level were measured. The carrier of FIG.
The noise is the same data as shown above, and it can be seen that when the recording mark length is 0.4 μm and the reproducing power exceeds 3 mW, the carrier level sharply rises and a rear mask is formed.

Amplitude and DC level are 0.8 μm for the same medium
Is obtained from the reproduction signal when the mark is recorded, and the erasing side has a positive sign in the DC level. In the case of a conventional optical disc, the aperture shape does not change even if the reproduction power is changed. Therefore, if the power is such that the memory layer does not reach the Curie temperature, the relationship between the reproduction signal amplitude and the reproduction power is It becomes a straight line that passes through the origin.
Further, the recording mark is not recorded in the full width of the spot, and since the erased portions remain on both sides of the mark, even if recording is performed so that the duty cycle of the recording mark is 50%, The DC level of the reproduction signal does not become 0, but is offset to the erase side (positive side in FIG. 10). From the above, the relationship between the amplitude and the DC level and the reproduction power is a straight line having a positive inclination and passing through the origin. Alternatively, if the reduction in the Kerr rotation angle of the reproducing layer due to the increase in power is at a level that cannot be ignored, the curve becomes slightly upward depending on the degree. However, in the case of the super-resolution disc of the present invention, the straight line does not pass through the origin and the inclination changes near the reproducing power of 3 mW. This is considered as follows.

When the reproducing power is 0.5 mW or less, the temperature of the reproducing layer does not reach the transition temperature from the in-plane magnetized film to the perpendicular magnetized film even at the highest temperature. Is in the plane, that is, in a masked state, so that both the amplitude and the DC level are 0. When the power exceeds 0.5 mW, a part of the reproducing layer in the spot becomes a perpendicular magnetization film, and as the power is further increased, the aperture expands. Therefore, both the amplitude and the DC level suddenly increase with a slope larger than the proportional relationship with the reproducing power. Increase. However, when the reproducing power exceeds 3 mW, a rear mask starts to be formed in the spot, and the magnetization of the rear mask is aligned in the erasing direction. Although this portion contributed to the signal reproduction before the appearance of the rear mask, it is masked in the erasing direction as the rear mask appears and does not contribute to the signal reproduction. Therefore, the DC level rapidly increases in the erasing direction with the reproduction power of 3 mW as a boundary, and the reproduction signal amplitude decreases. From the above results, the behavior of the rear mask in the super-resolution disc of the present invention is supported.

FIG. 11 shows the result of examining the dependence of the reproducing magnetic field in order to confirm that the super-resolution effect of the present invention occurs without applying a reproducing magnetic field from the outside. This is a plot of the change in C / N at the time when the reproducing magnetic field was changed while reproducing a signal with a reproducing power of 3.2 mW after recording a mark of 0.4 μm on the disk by the same method as described above. is there. As you can see from this figure,
Stable C / of 45 dB in the range of reproducing magnetic field ± 200 Oe
N has been obtained.

Next, the laser modulation frequencies during recording on the same medium were set to 5.8, 9.0, 11.3 and 15 MHz (mark lengths 0.78, 0.50, 0.40 and 0.3, respectively).
(Corresponding to 0 μm), and the dependence of C / N on the mark length was investigated. Results are shown in FIG. As shown in the figure,
Good spatial frequency characteristics were obtained with the recording medium of the present invention.

Next, crosstalk with adjacent tracks (hereinafter referred to as crosstalk) was measured. This is because after erasing the entire surface of both the land and the groove, a signal with a mark length of 0.78 μm is recorded on the land portion by the above method and the carrier level (this is CL) is measured, and then tracking is performed on the adjacent groove. The carrier level (when this is CG) is measured when applied, and their ratio CL
Expressed as / CG. That is, since the experiment is performed assuming that data is recorded on both the land and the groove, the effective track pitch is 0.8 μm. The result at this time is shown in FIG. As is apparent from the figure, the optimum reproduction power for this medium is 3.2 to 4.0 m.
In the range of W, the crosstalk is suppressed to about -28 dB, which shows that this medium is effective for narrowing the track pitch.

All the data shown above were measured without applying an initializing magnetic field, and good results were obtained for high-density recording marks using the same device as the conventional information recording / reproducing device. In addition, C / N under the optimum conditions and crosstalk under the same reproducing power are summarized in Experimental Example 1 in Table 1.

(Experimental Example 2) A SiN interference layer having a thickness of 90 nm was formed on a polycarbonate substrate by the same apparatus and method as in Experimental Example 1.
A GdFeCo reproducing layer having a thickness of 40 nm, a GdFeCo intermediate layer having a thickness of 10 nm, a TbFeCo memory layer having a thickness of 30 nm, and a SiN protective layer having a thickness of 70 nm were sequentially formed to form a medium having the same structure as in FIG. However, this time, by changing the composition of each of the reproducing layer and the intermediate layer, the saturation magnetization, the compensation temperature, and the Curie temperature of each layer were changed, and the change in the characteristics with respect to each physical property value was investigated.

FIG. 14 shows the relationship between the saturation magnetization Ms1 (emu / cc) of the reproducing layer and C / N when a mark having a length of 0.40 μm was recorded on each sample under the same conditions as in Experimental Example 1. For example, the saturation magnetization Ms3 (emu / cc) of the intermediate layer
Looking at the curve when is 100, it is an upwardly convex curve having a maximum value near Ms1 = 260. This is because when the saturation magnetization Ms1 of the reproducing layer is small, the in-plane anisotropy of the reproducing layer becomes small, that is, the temperature at which the magnetization becomes perpendicular due to exchange coupling with the memory layer becomes low, and the effect of the front mask weakens. It is considered that the C / N will decrease. On the other hand, if Ms1 is too large, the front mask is too strong and the intermediate layer reaches the Curie temperature before the aperture is opened sufficiently, so that the C / N is deteriorated. The effect of the front mask is determined by the balance relationship between the in-plane anisotropies of the reproducing layer and the intermediate layer. When the in-plane anisotropy of the reproducing layer becomes weak, the in-plane anisotropy of the intermediate layer must be increased. That is, as the saturation magnetization Ms3 of the intermediate layer increases, the optimum value of Ms1 decreases. Therefore, as shown in FIG. 14, the peak position of C / N shifts as Ms3 changes. As described later, the conventional 2 using the in-plane magnetized film
In the super-resolution medium having a layered structure, a C / N of about 37 dB is obtained for a mark length of 0.40 μm.
By comparison with this, it can be seen that the medium of the present invention has an excellent super-resolution effect. In order to secure high reliability of information reproduction, it is necessary to obtain C / N of 43 dB or more. Therefore, the saturation magnetization Ms1 of the reproduction layer in the super-resolution medium of the present invention at room temperature is 20 ≦ Ms1. It can be said that it is in the range of ≦ 340 (rare earth element sublattice magnetization dominant). Further, in order to secure higher reliability, it is desirable to obtain C / N of about 45 dB.
It is more desirable to set in the range of ≦ Ms1 ≦ 260.

Next, crosstalk was measured for each medium in this experimental example in the same manner as in Experimental example 1. The results are shown in Fig. 15. For example, the saturation magnetization Ms3 (e of the intermediate layer
Looking at the curve when mu / cc) is 100, Ms
The curve is a convex curve with a minimum value around 1 = 260. This is because when the Ms1 is large for the same intermediate layer composition, the in-plane anisotropy of the reproducing layer is too large and the effect of the front mask is too strong, and the carrier level at the land does not rise, so that the reproducing at the groove is performed. It is difficult to make a difference with
This is because when s1 is small, the effect of the front mask is small and the effect of crosstalk is likely to occur during groove reproduction. Therefore, regarding crosstalk, there is an optimum value where the two are most balanced. As will be described later, considering that the same experiment is performed on a TbFeCo single layer disc, the crosstalk is about -22 dB. Therefore, assuming that the level at which the crosstalk improving effect of the present invention sufficiently appears is -25 dB, Of C / N
From the point of view of the above, the front mask is formed in the range of the optimum saturation magnetization Ms1 of the reproduction layer, and it can be said that the front mask is also effective against crosstalk.

Next, the same data is applied to the saturation magnetization Ms of the intermediate layer.
16, in the form of a dependency on 3 (emu / cc),
Shown in 17. FIG. 16 shows C / N data, which has a convex curve similar to FIG. This is because when the saturation magnetization Ms3 of the intermediate layer is small, the in-plane anisotropy is small, and therefore when the reproducing power is increased until the intermediate layer reaches the Curie temperature, the aperture becomes too wide in the spot and the resolution cannot be improved. Conversely, when the saturation magnetization Ms3 of the intermediate layer is large, exchange coupling with the memory layer is not sufficiently performed before the intermediate layer reaches the Curie temperature. Similar to the case of the saturation magnetization of the reproducing layer, considering the range in which C / N is 43 dB or more in order to ensure high reliability of information reproduction, the effect of the magneto-optical recording medium of the present invention can be obtained. It can be said that the range is −200 ≦ Ms3 ≦ 700. However, looking at the crosstalk data in FIG. 17, it can be seen that the crosstalk greatly changes with respect to the saturation magnetization Ms3 of the intermediate layer. This is because the saturation magnetization of the intermediate layer greatly affects the effect of the front mask. According to the result of FIG. 17, the crosstalk is not necessarily improved in the composition in which C / N of 43 dB or more is obtained, and when -25 dB is used as the reference as in the previous case, the front mask is obtained when Ms3 ≧ −150. The effect of is obtained. That is, the saturation magnetization Ms3 of the intermediate layer for achieving good C / N is −150 ≦ Ms3 ≦ 700.
It is good to Also, better crosstalk is required to further reduce the track pitch,
If the crosstalk is -30 dB or less, 200≤Ms3
≦ 700. Also, for higher reliability, 45
To secure C / N of about dB, 200 ≦ Ms3 ≦
A range of 550 is more desirable. From the above results, the saturation magnetization Ms3 of the intermediate layer of the present invention is −150 ≦ Ms3 ≦ 70.
It is preferable to set it to 0, more preferably 200 ≦ Ms3
It is preferable that ≦ 700. More preferably, 200 ≦
Ms3 ≦ 500 is good. Table 1 shows some of the data obtained in this experimental example.

Next, in order to support the above-mentioned rear mask forming mechanism, the experimental results obtained in this experimental example will be expressed from different viewpoints. 18 and 19 are diagrams showing the relationship between the saturation magnetization of the reproducing layer and the intermediate layer used in this experimental example, and the respective compensation temperatures and Curie temperatures. The relationship between the saturation magnetization, the compensation temperature, and the Curie temperature is not always the same depending on the combination of the compositions of GdFeCo, but in this experimental example, the characteristics were changed by changing the Gd amount without changing the Co content too much. The curves are as shown in FIGS. In the C / N data shown in FIG. 14, although the peak position was shifted due to the saturation magnetization of the intermediate layer, the horizontal axis represents the compensation temperature of the reproducing layer and the Curie temperature of the intermediate layer based on FIGS. Difference (ΔT = Tcomp1-T
When rewritten as c3), a curve having substantially the same peak position is obtained as shown in FIG.

As described above, in the formation of the rear mask of the present invention, the magnetization direction and magnitude of the reproducing layer and the memory layer when the intermediate layer reaches the Curie temperature and the exchange coupling between the reproducing layer and the memory layer is broken. Heavily depends on. In this experimental example, the composition of the memory layer is constant, and the composition has a dominant iron group element sublattice magnetization at room temperature. Therefore, whether or not the rear mask is formed depends on the characteristics of the reproducing layer.

Within the range of 0 ≦ ΔT ≦ 60, the reproducing layer has not yet reached the compensation temperature when the intermediate layer reaches the Curie temperature, and the rare earth element sublattice magnetization is dominant, so that the iron group element sublattice magnetization is dominant. The magnetostatic coupling force from a certain memory layer works in a direction to assist the formation of the rear mask. Further, since the saturation magnetization of the reproducing layer itself is small, the leakage magnetic field from the periphery of the magnetic domain is small, and a mask can be easily formed. As a result, a high C / N can be obtained.

When ΔT becomes smaller and becomes negative, that is, when the intermediate layer reaches the Curie temperature, the reproducing layer has already exceeded the compensation temperature and has the iron group element sublattice magnetization predominant. Since the binding force acts in a direction to prevent the magnetic domains transferred to the reproducing layer from contracting, it becomes difficult to form a mask, and the C / N gradually decreases.
On the other hand, if ΔT is too large, the saturation magnetization of the reproducing layer when the exchange coupling is broken is too large, and the magnetic domain tends to be preserved by the leakage magnetic field, so that the rear mask is not formed and the C / N also decreases. .

From these results, it is possible to secure C / N of 43 dB or more because the characteristics of the reproducing layer and the intermediate layer are −20 ≦ Tc.
In the case of omp1−Tc3 ≦ 80, more preferably, C / N of 45 dB or more is obtained when 0 ≦ Tcomp1−Tc3 ≦ 50.

Also, in this experimental example, for comparison, the thicknesses of the reproducing layer and the intermediate layer were 40 nm and 1 respectively for all samples.
The experiment was performed with 0 nm, but considering the masking effect of the reproducing layer, the reproducing layer thickness may be 20 nm or more. The thickness of the intermediate layer may be 3 nm or more in view of the function of breaking the exchange coupling between the reproducing layer and the memory layer at the Curie temperature or higher. Further, in the memory layer, magnetic domains are stably stored, so that if the film thickness is 10 nm or more, a medium realizing the effect of the present invention can be obtained. On the contrary, when viewed from the power required for recording and reproducing information, the total film thickness of the magnetic layer is 200 n.
It is desirable to keep it below m. Therefore, the film thickness does not depart from the idea of the present invention as long as it is within the above-mentioned range.

(Experimental Example 3) Next, the same apparatus as in Experimental Example 1,
Method to form a 90 nm SiN interference layer on a polycarbonate substrate.
m, GdFeCo reproducing layer 40 nm, GdFeCo intermediate layer 10 nm, TbFeCo memory layer 30 nm, Si
An N protective layer having a thickness of 70 nm was sequentially formed to prepare a medium having the same structure as that shown in FIG. However, this time, the saturation magnetization (emu / cc) of the memory layer was variously changed with respect to the optimum film characteristics of each of the reproducing layer and the intermediate layer obtained in Experimental Example 2. FIG. 21 shows the relationship between the saturation magnetization of the memory layer and C / N (mark length 0.40 μm). As you can see from the figure,
The composition margin of the memory layer viewed from C / N is wide enough,
An almost constant C / N is obtained in the range of −300 ≦ Ms2 ≦ 200. The saturation magnetization of the memory layer is -300 emu /
When it exceeds cc (iron group element sublattice magnetization predominant), the influence of the demagnetizing field of the memory layer itself becomes strong, and even smaller magnetic domains (microdomains) are formed inside the magnetic domains, or the shape of the magnetic domains is distorted. As a result, the noise component increases and C / N deteriorates. On the contrary, the saturation magnetization of the memory layer is 200 emu / c
Above c (rare earth element sublattice magnetization predominant), the compensation temperature of the memory layer becomes 200 ° C. or higher, which is higher than the Curie temperature of the intermediate layer, so the memory at the temperature at which the exchange coupling with the reproducing layer is broken. The layer becomes predominantly the rare earth sublattice magnetization. Then, the magnetostatic coupling force exerted on the reproducing layer from the memory layer has the same direction as the exchange coupling force at a low temperature, so that the magnetic domains transferred to the reproducing layer act in the direction of hindering reversal by the rear mask. Therefore, the super-resolution effect decreases next and C / N decreases.

From the results of FIG. 21, it can be said that a high C / N of 43 dB or more can be obtained in the range of −350 ≦ Ms2 ≦ 250 by the super-resolution effect in the magneto-optical recording medium of the present invention. Further, in order to obtain a stable C / N in view of the composition margin, the range of −300 ≦ Ms2 ≦ 200 is more desirable.

(Experimental Example 4) Next, the same apparatus as in Experimental Example 1,
Method to form a 90 nm SiN interference layer on a polycarbonate substrate.
m, Gd ₂₈ (Fe ₆₀ Co ₄₀ ) ₇₂ reproducing layer 40 nm, Gd
₃₇ Fe ₆₃ Intermediate layer 10 nm, Tb ₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀
A memory layer having a thickness of 30 nm and a SiN protective layer having a thickness of 70 nm were formed in this order, and a heat dissipation layer of Al having a thickness of 60 nm was formed to improve thermal characteristics. It is already known that the addition of the heat dissipation layer improves the linear velocity dependence of the thermal characteristics. In the present invention, the addition of the heat dissipation layer also improves the linear velocity dependence of the recording and reproducing power. This effect can be obtained by the optical modulation recording described in Experimental Examples 1 to 6, but the same effect can be obtained by the magnetic field modulation recording method. Also, in the case of magnetic field modulation recording, it is known that the shape of the recording mark becomes arcuate (so-called arrow mark) according to the temperature distribution shape of the medium at the time of recording. This has the effect of reducing the curvature of the part.

FIG. 23 shows the recording power dependence of carriers and noise when magnetic field modulation recording is performed on the medium of this experimental example. As described above, according to the present experimental example, even when the magnetic field modulation recording is performed, even if a minute mark (0.40 μm) is recorded,
It was found that a good C / N of 4 dB was obtained, and the effect of super-resolution, which is the object of the present invention, can be exhibited.

(Experimental Example 5) A SiN interference layer having a thickness of 90 nm was formed on a polycarbonate substrate by the same apparatus and method as in Experimental Example 1.
Gd ₂₈ (Fe ₆₀ Co ₄₀ ) ₇₂ reproduction layer 40 nm, Gd ₃₇ F
An e ₆₃ intermediate layer having a thickness of 10 nm, a Dy ₂₅ (Fe ₇₀ Co ₃₀ ) ₇₅ memory layer having a thickness of 30 nm, and a SiN protective layer having a thickness of 70 nm were sequentially formed to form a medium having the same structure as in FIG.

In this experimental example, TbFeCo was used as the memory layer.
Although DyFeCo was used instead of, the same good results as in Experiment 1 were obtained for both C / N and crosstalk, confirming that the gist of the present invention is not limited to the TbFeCo memory layer.

Next, in order to further clarify the effect of the present invention, a similar experiment was performed with a conventionally known medium structure and a comparison was made.

(Comparative Experimental Example 1) An apparatus similar to Experimental Example 1,
Method to form a 90 nm SiN interference layer on a polycarbonate substrate.
m, Tb ₂₀ (Fe ₈₀ Co ₂₀ ) _{80 80} nm memory layer, S
An iN protective layer having a thickness of 70 nm was sequentially formed. That is,
A single-layer disc using only the memory layer used in Experimental Example 1 as a magnetic layer was prepared. First, a mark having a mark length of 0.40 μm was recorded on the medium prepared in this experimental example, and the reproduction power dependence of carrier and noise was measured. The results are shown in Fig. 9. As described above, although the carrier level increases as the reproducing power increases, the slope is gentle because the masking effect as seen in the medium of the present invention cannot be obtained. Next, marks of various sizes were recorded on the medium of this experimental example, and the spatial frequency characteristics were measured. The result is as shown in FIG.
Sufficient C / N when the mark length is as large as 0.78 μm
However, it is understood that the resolution sharply decreases when the cutoff frequency of the optical system is exceeded.

Also, in the crosstalk measurement, at an effective track pitch of 0.8 μm, it is narrow with respect to the reproduction spot, and in the case of a single-layer disc, there is no masking effect. Therefore, as shown in FIG. I only got a good amount of crosstalk.

(Comparative Experimental Example 2) An apparatus similar to Experimental Example 1,
Method to form a 90 nm SiN interference layer on a polycarbonate substrate.
m, Gd ₂₈ (Fe ₆₀ Co ₄₀ ) ₇₂ reproduction layer 70 nm, Tb
_{A 20} (Fe ₈₀ Co ₂₀ ) ₈₀ memory layer having a thickness of 30 nm and a SiN protective layer having a thickness of 70 nm were sequentially formed to form a medium having the same structure as that shown in FIG.

First, a mark having a mark length of 0.40 μm was recorded on the medium prepared in this experimental example, and the reproduction power dependence of carrier and noise was measured. The results are shown in Fig. 9. As described above, even in the medium of this experimental example, since the super-resolution effect is obtained by using the in-plane magnetized film at a low temperature, the reproduction power is 0.8 to
In the range of 2.8 mW, the carrier level increases as in the medium of Experimental Example 1. However, in the double-layered super-resolution medium of the present experimental example, the rear mask does not appear even when the reproducing power is further increased to 3 mW or more, so that a sharp increase in carriers as in the medium of the experimental example 1 is not seen. I can't.

Next, marks of various sizes were recorded on the medium of this experimental example, and the spatial frequency characteristics were measured. The result is shown in Figure 1.
As shown in FIG. 2, although the resolution in the high frequency range is higher than that of the single-layer disc, the disc of Experimental Example 1 does not have the effect of the rear mask and the positional relationship between the aperture and the spot is not optimal. The resolution is inferior to that of.

However, with respect to crosstalk, the front mask has a great influence and the rear mask has no relation. Therefore, as shown in FIG.
Crosstalk of about 30 dB was obtained.

[0079]

[Table 1]

[0080]

As described above in detail, when the magneto-optical recording medium and the information reproducing method for the medium of the present invention are used, a simple apparatus (similar to the prior art) which does not require a reproducing magnetic field and / or an initializing magnetic field. It is possible to reproduce magnetic domains smaller than the beam spot system by using the device), and it is possible to achieve high density recording by significantly improving the linear recording density or both the linear density and the track density.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram for explaining the mechanism of super-resolution in the present invention.

FIG. 3 is a diagram showing a saturation magnetization curve of the first magnetic layer of the present invention.

FIG. 4 is a diagram showing a saturation magnetization curve of a third magnetic layer of the present invention.

5 (a), (b) and (c) are diagrams showing a reproducing state of the magneto-optical recording medium of the present invention.

FIG. 6 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. 7A is a diagram showing a stable magnetization direction when an exchange coupling force and a magnetostatic coupling force predominantly act on an antiparallel type layer structure, and FIG. 7B is a parallel type layer. The figure which showed the direction of stable magnetization when each exchange coupling force and magnetostatic coupling force act predominantly about a structure.

FIGS. 8A, 8B and 8C are diagrams showing magnetization temperature changes for GdFeCo having different compensation temperatures.

FIG. 9 is a diagram showing reproduction power dependence of carrier and noise.

FIG. 10 is a diagram showing reproduction power dependence of carrier, noise, amplitude, and DC level.

FIG. 11 is a diagram showing the dependence of C / N on the reproducing magnetic field.

FIG. 12 is a diagram showing the mark length dependency of C / N.

FIG. 13 is a diagram showing reproduction power dependence of crosstalk.

FIG. 14 is a diagram showing the dependence of C / N on the reproducing layer Gd content in the present invention.

FIG. 15 is a diagram showing the dependence of crosstalk in the reproducing layer Gd content in the present invention.

FIG. 16 is a diagram showing the dependence of C / N in the present invention on the content of the intermediate layer Gd.

FIG. 17 is a diagram showing the dependency of crosstalk in the intermediate layer Gd content in the present invention.

FIG. 18 is a diagram showing the relationship between the saturation magnetization of the reproducing layer and the compensation temperature in the present invention.

FIG. 19 is a diagram showing the relationship between the saturation magnetization of the intermediate layer and the Curie temperature in the present invention.

FIG. 20 is a graph showing the relationship between the difference between the reproducing layer compensation temperature and the Curie temperature of the intermediate layer and C / N.

FIG. 21 is a diagram showing the dependency of C / N on the content of the memory layer Tb in the present invention.

FIG. 22 is a configuration diagram of another embodiment of the present invention.

FIG. 23 is a diagram showing the recording power dependence of carriers and noise when magnetic field modulation recording is performed on the medium of the present invention.

24 (a), (b) and (c) are principle diagrams of a two-layer constitution super resolution using a conventional in-plane magnetized film.

FIG. 25 is a diagram showing static characteristics of a single magnetic layer having a two-layer structure super-resolution using a conventional in-plane magnetized film.

26 (a), (b) and (c) are principle diagrams of a three-layer structure super resolution using a conventional perpendicular magnetization film.

[Explanation of symbols]

 1 recording mark 2 reproducing spot 3 aperture 4 front mask 5 rear mask 6 groove 7 land 11 reproducing layer 12 intermediate layer 13 memory layer 14 interference layer 15 protective layer 16 heat dissipation layer 20 substrate

Claims (11)

[Claims] 1. A magneto-optical recording medium in which at least a first magnetic layer, a third magnetic layer and a second magnetic layer are laminated in this order on a substrate, wherein the first magnetic layer is a rare earth-iron group element Consisting of a crystalline alloy, with a rare earth element sublattice magnetization predominant at room temperature, having a compensation temperature between room temperature and Curie temperature, the second magnetic layer is a rare earth-iron group element amorphous alloy perpendicular magnetization film, The Curie temperature of the second magnetic layer is lower than the Curie temperature of the first magnetic layer and higher than the Curie temperature of the third magnetic layer, the compensation temperature Tcomp1 of the first magnetic layer and the Curie temperature of the third magnetic layer. The following relationship with Tc3 −20 (° C.) ≦ Tcomp1 (° C.) − Tc3 (° C.) ≦ 8
A magneto-optical recording medium characterized in that 0 (° C.) is established. 2. The first magnetic layer according to claim 1, wherein the first, second and third magnetic layers are exchange-coupled at a temperature between room temperature and the Curie temperature of the third magnetic layer, and the magnetization of the first magnetic layer is: At the Curie temperature of the third magnetic layer or higher, they are aligned in one direction. 3. The saturation magnetization Ms1 of the first magnetic layer according to claim 1, wherein the saturation magnetization Ms1 of the first magnetic layer at room temperature is 20 ≦ Ms1 (emu / c).
c) ≦ 340. 4. The third magnetic layer according to claim 3, wherein the first magnetic layer contains Gd, Fe, and Co. 5. The saturation magnetization Ms2 of the second magnetic layer according to claim 1, wherein when the rare earth element sublattice magnetization is dominant at room temperature, Ms2 (emu / cc).
≦ 250, and Ms2 (emu / cc) ≦ 350 when the iron group element sublattice magnetization is dominant at room temperature. 6. The method according to claim 5, wherein the second magnetic layer contains Tb, Fe and Co. 7. The method according to claim 5, wherein the second magnetic layer contains Dy, Fe and Co. 8. The saturation magnetization Ms3 of the third magnetic layer according to claim 1, when the rare earth element sublattice magnetization is dominant at room temperature, Ms3 (emu / cc).
≦ 700, and Ms3 (emu / cc) ≦ 150 when the iron group element sublattice magnetization is dominant at room temperature. 9. The third magnetic layer according to claim 8, wherein the third magnetic layer contains Gd and Fe. 10. The Curie temperature Tc3 of the third magnetic layer according to claim 1, wherein 80 (° C.) ≦
Tc3 (° C) ≤ 220 (° C). 11. A magneto-optical recording medium comprising at least a first magnetic layer, a third magnetic layer and a second magnetic layer laminated in this order on a substrate, wherein the first magnetic layer is a rare earth-iron group. A perpendicular magnetization film made of an elemental amorphous alloy, having a rare earth element sublattice magnetization dominant at room temperature, a compensation temperature between room temperature and Curie temperature, and the second magnetic layer being a rare earth-iron group element amorphous alloy. The Curie temperature of the second magnetic layer is lower than the Curie temperature of the first magnetic layer and higher than the Curie temperature of the third magnetic layer, and the compensation temperature Tcomp1 of the first magnetic layer and the Curie temperature of the third magnetic layer are The following relationship between the Curie temperature Tc3 and −20 (° C.) ≦ Tcomp1 (° C.) − Tc3 (° C.) ≦ 8
In an information reproducing method of irradiating a magneto-optical recording medium having a temperature of 0 (° C.) with a light beam to reproduce recorded information, the light beam is irradiated from the first magnetic layer side, and The magnetization of the first magnetic layer in the low temperature portion is magnetized in the in-plane direction, and the first magnetic layer is exchange-coupled with the second magnetic layer as a perpendicular magnetization film in a portion other than the low temperature portion in the spot, Information stored in the second magnetic layer is transferred to the first magnetic layer, and the information stored in the second magnetic layer is reproduced by detecting the reflected light of the light beam. How to play.