JPH07334877A - Magneto-optical recording medium and information reproducing method of the medium - Google Patents

Abstract

(57) [Summary] [Object] To provide a magneto-optical recording medium and an information reproducing method capable of reproducing a recording mark having a light diffraction limit or less with high signal quality with a simple structure. [Structure] An in-plane magnetized film at room temperature, which is mainly composed of GdFeCo and which satisfies the following conditions: Gd _x (Fe _100-y Co _y ) _100-x , 24 ≦ x ≦ 32,
20 ≦ y ≦ 50 Curie temperature lower than the first magnetic layer and the second magnetic layer, Gd
A third magnetic layer mainly composed of FeCo and satisfying the following: Gd _p (Fe _100-q Co _q ) _100-p , 25 ≦ p ≦ 50,
0 ≦ q ≦ 20 Magneto-optical recording in which a perpendicular magnetic film made of a rare earth-iron group element amorphous alloy and a second magnetic layer having a Curie temperature lower than that of the first magnetic layer are laminated in this order on the substrate. A medium and an information reproducing method using the medium.

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 by using a light beam and a method for reproducing information on the medium, and more particularly to an optical recording medium capable of increasing the density of the medium. The present invention relates to a magnetic recording medium and an information reproducing method for 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 disk such as this 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 reproduction light wavelength 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 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 laser wavelength due to problems such as element efficiency and heat generation.
Further, if the numerical aperture of the objective lens is increased, not only the processing of the lens becomes difficult, but also a mechanical problem occurs such that the distance between the lens and the disk becomes too short and the disk collides with the disk. 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, a medium configuration as shown in FIG. 19 is proposed as a super-resolution technique for realizing a recording density higher than the optical resolution of reproduction light. ing. FIG. 19 (a) shows a cross-sectional view of an optical disc, which is an example of super-resolution technology. Substrate 20 is usually a transparent material such as glass or polycarbonate and has pre-concentric or spiral grooves (group 6) to form guide tracks. 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 a substrate 20. The interference layer 43 is a protective layer to enhance the Kerr effect.
44 is used for protection of 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 magnetic domains depending on whether the magnetization of this layer is upward or downward with respect to the film surface. The reproducing layer 41 is made of a material having a large saturation magnetization Ms and a small perpendicular magnetic anisotropy, and has a composition in which the rare earth element sublattice magnetization is dominant. FIG. 20 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 perpendicular magnetic anisotropy Ku
And the magnitude relationship of 2πMs ² is reversed, and the film becomes a perpendicular magnetization film. Figure 20 shows the static characteristics of the playback layer alone.
When it is laminated with 42, an exchange coupling force with the memory layer 42 acts, so that it becomes a perpendicular magnetic film at a lower temperature Tth, and the magnetization direction of the reproducing layer 41 when it becomes a perpendicular magnetic film is exchange coupled with the memory layer 42. It will be the direction you did. When information reproducing light is radiated from the substrate 20 side to a disk having such a medium structure, the temperature gradient at the center of the data track becomes as shown in Fig. 19 (c). As shown in 19 (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 because it becomes an in-plane magnetized film, and the recording domain retained in the memory layer 42 is masked. It becomes invisible. On the other hand, in the portion above Tth, the reproducing layer 41 is a perpendicularly magnetized film, and the magnetization direction is the same as the recorded information due to 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. In addition, JP-A-3-93058 and JP-A-3-93058
In the super-resolution reproduction method disclosed in the 4-255946 publication, the method shown in FIG.
As shown in, a medium including a reproducing layer 31, a third magnetic layer (hereinafter referred to as an intermediate layer) 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 to mask the magnetic domain information of the memory layer 33, and then the light spot 2 is irradiated. 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. (By forming the rear mask 5), the magnetic domain information of the memory layer 33 is transferred only in the middle temperature region to reduce the effective size of the reproducing 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 methods, 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.

[0004]

However, in the super-resolution reproducing method disclosed in Japanese Patent Laid-Open No. 6-124500, only the front mask 4 is used. Therefore, when 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. In addition, JP-A-3-93058 and JP-A-3-93058
According to the method disclosed in Japanese Patent Laid-Open No. 4-255946, while the resolution can be increased without degrading the signal quality, the magnetization of the reproducing layer 31 must be aligned in one direction prior to the information reproduction, and therefore the initialization magnet 21 for that purpose. Is required to be added to the conventional device.

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.

[0007]

The above-mentioned object of the present invention is to form at least a first magnetic layer, a third magnetic layer and a second magnetic layer on a substrate in the above-mentioned order. In the magneto-optical recording medium, the first magnetic layer and the third magnetic layer are in-plane magnetized films at room temperature, and the first magnetic layer is GdF.
It is composed mainly of eCo and satisfies the following: Gd _x (Fe _100-y Co _y ) _100-x , 24 ≦ x ≦ 32 (atomic%), 20 ≦ y
≦ 50 (atomic%), the third magnetic layer is composed mainly of GdFeCo, and satisfies the following: Gd _p (Fe _100-q Co _q ) _100-p , 25 ≦ p ≦ 50 (atomic%), 0 ≤q
≦ 20 (atomic%), the second magnetic layer is a perpendicular magnetization film made of a rare earth-iron group element amorphous alloy, and the Curie temperature of the second magnetic layer is higher than the Curie temperature of the first magnetic layer. It is also achieved by setting it to be lower than the Curie temperature of the third magnetic layer.

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 And the third magnetic layer is an in-plane magnetized film at room temperature, and the first magnetic layer is
GdFeCo is the main constituent and satisfies the following Gd _x (Fe _100-y Co _y ) _100-x , 24 ≦ x ≦ 32 (atomic%), 20 ≦ y
≦ 50 (atomic%), the third magnetic layer is composed mainly of GdFeCo, and satisfies the following: Gd _p (Fe _100-q Co _q ) _100-p , 25 ≦ p ≦ 50 (atomic%), 0 ≤q
≦ 20 (atomic%), the second magnetic layer is a rare earth-iron group element amorphous alloy perpendicular magnetization film, information is accumulated and the Curie temperature of the second magnetic layer is the first magnetic layer. In an information reproducing method for reproducing information recorded by using a light beam on a magneto-optical recording medium lower than the Curie temperature of the magnetic layer and higher than the Curie temperature of the third magnetic layer, from the first magnetic layer side. Irradiating a light beam, leaving the first magnetic layer in the low temperature portion within the spot of the light beam as an in-plane magnetized film,
Information accumulated in the second magnetic layer in the first magnetic layer by exchange-coupling the first magnetic layer as a perpendicular magnetization film with the second magnetic layer in a portion other than the low temperature portion in the spot. Is recorded and the reflected light of the light beam is detected to reproduce the information stored in the second magnetic layer.

[0009]

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 are formed on a substrate 20. A second magnetic layer (hereinafter referred to as a memory layer) 13 and a protective layer 15 are laminated in this order. The substrate 20 is usually made of a transparent material such as glass or 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 , SiO, ZnS, MgF ₂
A transparent dielectric material such as

The protective layer 15 is used for protecting the magnetic layer, and the same material as the interference layer 14 is used.

Since the interference layer 14 and the protective layer 15 are irrelevant to the essence of the present invention, they may be omitted in the structure.
Further, detailed description is omitted here. Although not shown in FIG. 1, a hard coat material such as an ultraviolet curable resin may be further applied to the protective layer 15 in order to protect the film or use the magnetic field head for magnetic field modulation overwrite.

The reproducing layer 11 is a layer responsible for reproducing the magnetization information held in the memory layer 13, is an in-plane magnetized film at room temperature, and has a magnetic characteristic that becomes a perpendicular magnetized film at a predetermined temperature or higher between room temperature and Curie temperature. Prepare The reproducing layer 11 is located closer to the incidence of light than the intermediate layer 12 and the memory layer 13, and the Curie temperature is at least higher than that of the intermediate layer 12 and the memory layer 13 so that the Kerr rotation angle does not deteriorate during reproduction. . The reproducing layer 11 is preferably a rare earth-iron group element amorphous alloy having a small perpendicular magnetic anisotropy, specifically GdFeCo. Further, a light rare earth metal such as Nd, Pr or Sm may be added to this to increase the Kerr rotation angle at a short wavelength. Preferably, the one having a compensation temperature between room temperature and Curie temperature is desirable. Incidentally, this compensation temperature is near the Curie temperature of the intermediate layer 12 described later, that is, the intermediate layer 12
The Curie temperature is set to -50 ° C to + 100 ° C, more preferably -20 ° C to + 80 ° C.

The intermediate layer 12 is provided for the following three purposes.

(1) At room temperature, the domain wall energy between the reproducing layer 11 and the memory layer 13 is relaxed, and the reproducing layer 11 serves as 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 exchange coupling between the reproducing layer 11 and the memory layer 13 is broken.

To achieve these ends, the intermediate layer 12
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 reproduction layer 11 at the middle temperature portion in the light spot during reproduction, and small enough to cut the exchange coupling force at the maximum temperature portion. , Specifically, it should be 100 ℃ or more and 220 ℃ or less, more preferably 180 ℃ or more.
℃ or less is good. The material of the intermediate layer 12 is, for example, a rare earth-iron group amorphous alloy, specifically GdFeCo. Further, in order to reduce the Curie temperature, a non-magnetic element such as Cr, Al, Si, Cu may be added.

The memory layer 13 is a layer for holding recorded information and has a size of 1 u.
It is necessary to be able to stably hold a small magnetic domain of m 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, such as TbFeCo or Dy.
FeCo, TbDyFeCo and other rare earth-iron group amorphous alloys, garnet, or platinum group-iron group periodic structure film, for example Pt / C
o, Pd / Co, and platinum group-iron group alloys such as PtCo, PdCo
And so on.

The reproducing layer 11, the intermediate layer 12 and the memory layer 13 are
Elements such as l, Ti, Pt, Nb and Cr may be added to improve the corrosion resistance. 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.

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 such 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 laser light intensity so that only a predetermined area within the light spot becomes Tc3, and as a result, a signal with a period less than the light diffraction limit 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-A-62-1
It uses a medium having the structure described in 75948 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 is performed 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 direction opposite to the writing layer. When the temperature of the medium is raised 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 If the temperature is raised only to the temperature Tl corresponding to Pl, 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, considering the time when the medium is irradiated with the laser of Ph, the portion forming the recording magnetic domain is heated to Th, but since the temperature distribution at this time is two-dimensionally widened. , Even if you raise the laser to Ph, be sure to surround the magnetic domain
There is a portion 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.

As another recording method, the above-mentioned magnetic field modulation recording can be mentioned. 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 domains, The width forming the magnetic domains must always be constant. Therefore, in this case, unless some measures are taken, there is a region where the magnetization direction is random 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 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 the state of spots and the magnetization state of each magnetic layer when the disk moves rightward while irradiating the optical disk of the present invention with laser light. At this time, 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 front 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, FIGS. 3 and 4, and both layers have a 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 of the reproducing layer 11
If the energy that directs the magnetization of the reproducing layer 11 in the vertical direction by the exchange coupling force from the memory layer 13 via Ku1, the saturation magnetization Ms1, and the intermediate layer 12 is Ew13, (Equation 1) 2πMs ² > Ku + Ew13 The magnetization of the reproducing layer 11 is oriented in the film plane. In particular, since the saturation magnetization of the intermediate layer 12 is larger than that of the reproducing layer 11 and the in-plane anisotropy is strong, the interface domain wall energy between the memory layer 13 which is a perpendicular magnetic film and the reproducing layer 11 which is an in-plane magnetic film is The intermediate layer 12 has an absorbing effect. 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 where the intermediate layer 12 is not provided, and the magnetization of the memory layer 13 is not transferred. Form the front mask 4.

Next, when the medium temperature rises due to the irradiation of the spot 2, the saturation magnetization Ms of the reproducing layer 11 and the intermediate layer 12 gradually decreases. In particular, in the case of the present invention, both the compensation temperature of the reproducing layer 11 and the Curie temperature of the intermediate layer 12 are close to about 200 ° C., so that the saturation magnetization sharply decreases with increasing temperature of the medium. Therefore, the medium has a predetermined temperature Tth.
And (2) 2πMs ² <Ku + Ew13, the reproducing layer 11 becomes a perpendicularly magnetized film and at the same time exchange-couples with the memory layer 13, so that the magnetic domain held in the memory layer 13 is transferred to the reproducing layer 11. Form aperture 3 When the temperature further rises and becomes higher than the Curie temperature Tc2 of the intermediate layer 12, the exchange coupling force between the reproducing layer 11 and the memory layer 13 disappears. At this temperature, the reproducing layer 11 has the rare earth element sublattice magnetization predominant, and the composition is adjusted in advance so that the memory layer 13 has the iron group element sublattice magnetization predominant (that is, antiparallel). Then, the magnetic domain transferred to the reproducing layer 11 at a temperature of Tc2 or less 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 in the opposite direction. Will join. Also reproduction layer
Since 11 is also close to the compensation temperature, the influence of the demagnetizing field of the reproducing layer 11 itself is small, so that the reproducing layer 11 transferred from the memory layer 13
Domain cannot contract the Bloch domain wall energy and contracts and inverts. 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 in which the magnetic domains cannot exist in the reproducing layer and are aligned in the same direction. This part 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 domains 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.

FIG. 5 is a plan view showing a process in which a recording magnetic domain of the reproducing layer 11 transferred from the memory layer 13 (hereinafter simply referred to as a recording magnetic domain) contracts in a high temperature region when a light spot moves. And FIG. For the sake of simplicity, Fig. 5 shows the shrinking process of one recording domain. In addition, 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 sublattice magnetization, and the reproducing layer 11 is the RE-rich magnetic material. As the layers and the memory layer 13, the TM-rich magnetic layer is described as an example. 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 where 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,
An effective magnetic field Hwb due to Bloch domain wall energy and a static magnetic field Hd from the inside of the medium are applied. Hwi works to stably hold the recording magnetic domain 1 of the reproducing layer, but Hw
A force acts on b 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) The coercive force Hc1 of the reproducing layer 11 apparently becomes large due to the exchange coupling force from the memory layer 13, so that 3)
Holds, and it becomes possible to stably transfer the magnetization information of the memory layer 13 and accurately reproduce the recorded information.

Hwi is represented by (Equation 4), where σwi is the interfacial 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. However, when the light spot (Equation 4) Hwi = σwi / 2Ms1h1 moves and enters the high temperature region 5, Hwi reaches the vicinity of the Curie temperature of the intermediate layer 12 and σwi sharply decreases.
i decreases. Therefore, the reproducing layer 11 returns to the original state of small coercive force (Equation 5), and 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 σwb, and the radius of the recording magnetic domain 1 of the reproducing layer 11 is r (Equation 6) , And acts in the direction to shrink the recording domain 1 (Fig. 6).

(Equation 6) Hwb = σwb / 2Ms1r Therefore, if Hwb-Hd becomes positive (sign +) 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 is in the high temperature region.
When it enters 5, it contracts and reverses, and finally, as shown in Fig. 5 (c), all the magnetization is oriented in the erasing direction.

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 the low temperature in-plane magnetized film region (front mask), and the apertures in other regions. Area 3 is reached, and recording magnetic domains (recording marks) with a period below the detection limit can be detected.

A conventional super-resolution method is disclosed in Japanese Patent Laid-Open No. 4-2559.
As described in 47, the external magnetic field Hr is used to form the mask according to the relationship of (Equation 8).

(Equation 8) Hr> Hc1 + Hwi In the present invention, since 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, the external magnetic field is unnecessary.

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 in more detail. Hd of (Equation 7) is composed of a leakage magnetic field Hleak from the surrounding erase magnetization, a static magnetic field Hst from the 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.

The first method of shrinking the recording magnetic domain 1 more easily in the high temperature region is to reduce the Hleak to reduce the recording magnetic domain 1.
This is a method of reducing the magnetic field that prevents the reversal of. Hlea
k is the saturation magnetization of the reproducing layer 11 around the recording magnetic domain to be eliminated
If s1 ″ and the radius of the recording magnetic domain 1 are r, they are roughly expressed by (Equation 10).

(Formula 10) Hleak = 4πMs1 ″ h1 / (h1 + 3 / 2r) In (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. Figures 8 (a) to 8 (c) show the temperature dependence of Ms of GdFeCo with different compensation temperatures. The maximum temperature on the medium during reproduction depends on the reproducing power, but the maximum temperature shown in the figure is generally shown. Is about 160 ~
Since the temperature reaches 220 ° C and the middle temperature region is lower by about 20 to 60 ° C, Ms1 "is large in the cases as shown in Figs. 8 (b) and 8 (c). Therefore, Hleak becomes large. When a composition having a compensation temperature between room temperature and Curie temperature is used for the reproducing layer 11 as shown in Fig. 8 (a), Ms in the middle temperature and high temperature regions can be reduced and Hd can be reduced. When used in the reproducing layer 11, the compensation temperature strongly depends on the composition of the rare earth element (Gd) as shown in FIG. 8, so that the reproducing layer 11 is mainly composed of the magnetic layer containing GdFeCo.
When used in, it is desirable to set the Gd amount to 25 to 35 at%.

The second method is the static magnetic field H from the memory layer 13.
This is a method of increasing st to a negative value to promote the reversal of the recording magnetic domain 1. Hst in (Equation 7) is maintained as it is when the recording magnetic domain 1 contracts depending on whether the reproducing layer 11 and the memory layer 13 are of the parallel type or the anti-parallel type when the high temperature region is entered from the exchange coupling region. Decides how to work. This is for the following reason.

As shown in FIG. 7, the exchange coupling force follows the direction of the TM sublattice magnetization having a strong exchange force, and the magnetostatic coupling force follows the direction of the entire magnetization. FIG. 7 (a) shows an anti-parallel type in which the reproducing layer 11 is RE-rich and the memory layer 13 is TM-rich. In this case, when the intermediate layer 12 reaches the Curie temperature and the exchange coupling is broken, the memory layer is The magnetic domain 1 tries to reverse the magnetization due to the magnetostatic coupling force with 13 (Hs
t is negative). On the contrary, as shown in Fig. 7 (b), in the case of the parallel type (both layers show the case of TM rich), the magnetostatic coupling force acts in the direction to maintain the exchange coupling state (Hst is Be positive). Therefore, in order to invert the recording magnetic domain 1, it is desirable to adopt an anti-parallel type configuration.

Specifically, for example, the reproducing layer 11 and the memory layer 13
Is assumed to be ferrimagnetic, and the types of dominant sublattice magnetization may be reversed. For example, the reproducing layer 11 and the memory layer 13 are composed of a rare earth (RE) iron group (TM) element alloy,
11 is a magnetic layer having a rare earth element sublattice magnetization predominant (RE-rich), and memory layer 13 is an iron group element sublattice magnetization predominant (TM) at room temperature.
Rich). The anti-parallel structure needs to be achieved at least at the temperature at which 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). Doctoral dissertation, March 1993. "Research on the magnetism and magneto-optical effect of rare earth-iron group amorphous alloy thin films and their composite films", see Kobayashi Tadashi, P40-41). Hst is
It is proportional to the saturation magnetization Ms2 of the memory layer (Equation 11).

(Equation 11) Hst∝Ms2 Therefore, it is desirable to increase Ms2 so that the stability of recorded information does not deteriorate and the erase magnetization does not reverse.

Further, the static magnetic field Hst from the memory layer 13 described above is used.
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 that is magnetically oriented in the erasing direction is always generated, and this becomes the rear mask 5. 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 domain 1 above is 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. As described above, when the magneto-optical recording medium of the present invention is used, the magnetization of the memory layer 13 can be optically aligned in a uniform direction in the high temperature region 5 of the light spot without applying an external magnetic field during reproduction. Can be masked to.

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) 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 pregroove having a pitch of 1.6 μm were set at a distance from the target. After fixing 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 1x10-5 Pa or less was obtained. After evacuating and introducing Ar gas into the chamber until the pressure reached 0.4 Pa, the SiN interference layer was 90 nm and the Gd ₂₈ (Fe ₆₀ Co ₄₀ ) ₇₂ reproduction layer was ₄₀ n.
An m, Gd ₃₇ Fe ₆₃ intermediate layer having a thickness of 10 nm, a Tb 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 obtain a medium having the structure shown in FIG. At the time of depositing each SiN dielectric layer, N ₂ 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. The reproduction layer of Gd ₂₈ (Fe ₆₀ Co ₄₀ ) ₇₂ has a rare earth element sublattice magnetization predominance at room temperature, a saturation magnetization Ms of 225 emu / cc, a compensation temperature of 217 ° C, and a Curie temperature of 300 ° C or higher. .

The Gd ₃₇ Fe ₆₃ intermediate layer has a rare earth element sublattice magnetization predominant at room temperature, a saturation magnetization Ms of 470 emu / cc, and a Curie temperature of 190 ° C.

The Tb ₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀ memory layer was set so that the iron group element sublattice magnetization was dominant at room temperature, the saturation magnetization Ms was 250 emu / cc, and the Curie temperature was 270 ° C.

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, using this magneto-optical recording medium, recording / reproducing characteristics were measured. The measurement was performed using an optical head with an NA of 0.53 for the objective lens and a laser wavelength of 780 nm, a linear velocity of 9 m / s, and a recording power of 10 mW. After first erasing the entire surface of the medium,
The laser was modulated at a frequency of 11.3MHz to record a mark of 0.40um in length, and the change in C / N was measured when the reproducing power was changed from 0.8mW to 4.4mW. 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 oriented almost in the plane of the film. Therefore, the mark recorded in the memory layer is masked by the reproducing layer, so that C / N hardly occurs. Playback power 2.0 to 2.8
When raised to about mW, the medium temperature area in the playback spot,
That is, the aperture is formed and the magnetic domain of the memory layer is transferred to the reproducing layer, so that C / N increases. The shape of the aperture at this time was the conventional in-plane film shown in FIG.
It is almost the same as the super-resolution of the two-layer structure, and the super-resolution phenomenon occurs, but the size and position of the aperture are not optimal, so only about 36 dB can be obtained as C / N. When the reproducing power is further raised to 3.2 to 4.0 mW, the part where the intermediate layer reaches the Curie temperature appears in the spot, that is,
A rear mask is formed. Then the aperture shape is shown in Fig. 2.
As shown in, the optimum shape for the spot was obtained, so a C / N of 45 dB 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, the laser modulation frequency at the time of recording was changed to 5.8, 9.0, 11.3, and 15 MHz (corresponding to mark lengths of 0.78, 0.50, 0.40, and 0.30 um) for the same medium, and the C / N ratio was changed. The mark length dependence was investigated. The results are shown in Fig. 10. As shown in the drawing, 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 land and groove, recording a signal with a mark length of 0.78um on the land part and measuring the carrier level (CL), then tracking the adjacent groove. The carrier level at the time of application (measured as CG) was measured and expressed as the ratio CL / CG. In other words, since the experiment is conducted assuming that data is recorded on both the land and the groove, the effective track pitch is 0.8um. The result at this time is shown in FIG.
As is clear from the figure, the crosstalk is -28 dB in the optimum reproducing power range of 3.2 to 4.0 mW for this medium.
It is suppressed to some extent, which shows that this medium is also effective for narrowing the track pitch.

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

(Experimental Example 2) An SiN interference layer of 90 nm and Gd _x (Fe) was formed on a polycarbonate substrate by the same apparatus and method as in Experimental Example 1.
₆₀ Co ₄₀ ) _100-x reproducing layer 40 nm, Gd _p Fe _100-p intermediate layer 10 nm,
A Tb 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 deposited to form a medium having the same structure as that shown in FIG. However, this time, the Gd contents x and p of the reproduction layer and intermediate layer respectively
Was changed variously, and the change in the characteristics for each composition was investigated.

Under the same conditions as in Experimental Example 1, each sample had a length of 0.
Gd content x in playback layer when recording 40um mark x
Figure 12 shows the relationship between (at%) and C / N. For example, looking at the curve when the Gd content p (at%) of the intermediate layer is 30, it is an upwardly convex curve having a maximum value near x = 30. This is x
Is smaller, the in-plane anisotropy of the reproducing layer is smaller because the saturation magnetization Ms of the reproducing layer is smaller, that is, the temperature at which the magnetization becomes perpendicular due to exchange coupling with the memory layer is lower, and the effect of the front mask is weakened. , C / N is expected to decrease. Conversely, if x is too large, the front mask is too strong and the intermediate layer reaches the Curie temperature before the aperture is sufficiently opened, which again deteriorates the C / N. 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 Gd content p of the intermediate layer increases, the optimum value of x decreases. Therefore, as shown in Fig. 12, the peak position of C / N shifts as p changes. As will be described later, in a conventional two-layer super-resolution medium that uses an in-plane magnetized film, it is about 37 dB for a mark length of 0.40 um.
Since the C / N is obtained, it can be seen that a superior super-resolution effect is obtained by the medium of the present invention by comparison with this. In order to ensure high reliability of information reproduction, C / N is 43
Since it is necessary to obtain dB or more, the Gd content x (at%) in the reproducing layer in the super-resolution medium of the present invention is 24 ≦ x ≦ 32.
Can be said to be in the range. Further, in order to secure higher reliability, it is desirable to obtain C / N of about 45 dB, and for that purpose, it is more desirable to set in the range of 26≤x≤30.

Next, crosstalk was measured for each medium in this experimental example by the same method as in Experiment 1. The results are shown in Figure 13. For example, looking at the curve when the Gd content p (at%) of the intermediate layer is 30, it is a downwardly convex curve with a maximum value near x = 30. This is because when the x 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 when reproducing in the groove This is because when the x is small, the effect of the front mask is small, and when the groove is reproduced, it is easily affected by the crosstalk. Therefore, regarding crosstalk, there is an optimum value where the two are most balanced. As will be described later, considering that a similar experiment is performed on a TbFeCo single layer disc, a crosstalk of about -22 dB occurs, and when x ≧ 24, the effect of the front mask appears in the super-resolution medium of the present invention. . This means that the optimum Gd content x (at%) of the reproducing layer from the viewpoint of C / N is as described above.
In the range of 1, the front mask is formed and it can be said that the effect is also exerted on crosstalk.

Next, the same data was applied to the intermediate layer Gd content p (at%)
10 and 11 in the form of a dependency on.

FIG. 14 shows the C / N data, which has a convex curve similar to FIG. This is because when the intermediate layer Gd content is small, the in-plane anisotropy is small and the Curie temperature rises at the same time, so increasing the reproducing power until the intermediate layer reaches the Curie temperature causes the aperture to spread too much in the spot. If the resolution does not improve, and the Gd content in the intermediate layer is high, the Curie temperature of the intermediate layer will be reached with low power,
This is due to insufficient exchange coupling with the memory layer.
Similar to the case where the reproduction layer Gd content is dependent, in order to ensure high reliability of information reproduction, considering the range where C / N is 43 dB or more, the effect of the magneto-optical recording medium of the present invention can be obtained. Can be said to be in the range of 20≤p≤50. Also, in order to secure C / N of about 45 dB for higher reliability,
The range of 30 ≦ p ≦ 45 is more desirable.

However, looking at the crosstalk data in FIG. 15, it can be seen that the crosstalk greatly changes with respect to the Gd content in the intermediate layer. This is because the Gd content of the intermediate layer affects both the in-plane anisotropy and the reduction of the reproducing power, and thus has a great influence on the effect of the front mask. According to the results in Fig. 15, the crosstalk is not necessarily improved in the composition where C / N is 43 dB or more. Based on the -22 dB obtained with the TbFeCo single layer disc, when p ≧ 25, The effect of the front mask is obtained.

From the above results, the Gd content p (at%) of the intermediate layer of the present invention is preferably set to 25≤x≤50, and more preferably 30≤x≤45. Table 1 shows some of the data obtained in this experimental example.

Also, in this experimental example, for comparison, all the samples were tested with the thicknesses of the reproducing layer and the intermediate layer being 40 nm and 10 nm, respectively. Considering the masking effect of the reproducing layer,
The thickness of the reproducing layer 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, in view of the power required for recording / reproducing information, it is desirable that the thickness of the entire magnetic layer is suppressed to 200 nm or less.

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) A SiN interference layer having a thickness of 90 nm and Gd _x (Fe) was formed on a polycarbonate substrate by the same apparatus and method as in Experimental Example 1.
_100-y Co _y ) _100-x 40-nm reproducing layer, Gd _p Fe _100-p 10n intermediate layer
m, Tb ₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀ 30 nm memory layer, ₇₀ n SiN protective layer
Films of m were formed in order, and a medium having the same structure as in FIG. 1 was prepared. However, this time, the Co content y (at%) of the reproduction layer was variously changed with respect to the Gd contents x and p of the reproduction layer and the intermediate layer obtained in Experimental Example 2.

The Co content in the GdFeCo alloy affects various physical property values, and in this case, the items having a large influence are the perpendicular magnetic anisotropy Ku and the Curie temperature Tc. The role of the reproducing layer in the present invention is to increase the Kerr effect in the aperture portion in addition to the mask effect already described. In other words, the Kerr rotation angle obtained when a perpendicularly magnetized film is irradiated with a polarized beam is generally higher in a material with a higher Curie temperature, and the quality of the reproduction signal is higher. It is desirable to set it higher. When the amount of Co in the GdFeCo alloy is reduced, the Curie temperature tends to decrease, so it is desirable to add some Co to the reproducing layer. In this experimental example, Gd ₂₄ (Fe ₈₀ Co ₂₀ ) ₇₆ was used for the reproducing layer. As shown in Table 1, the C / N of 42 dB was obtained even for the mark of 0.40 um, and it was confirmed that the effect of the present invention was obtained. However, in the playback layer
When the Co content was reduced to 19 at% or less, the C / N was lowered to 39 dB due to the lower Curie temperature.

On the other hand, if the Co content of the reproducing layer is too large, the perpendicular magnetic anisotropy is lowered, so that the reproducing layer is unlikely to transition to the perpendicular magnetization film even when heated by a laser, that is, exchange coupling with the memory layer. Becomes weaker and C / N decreases. Table 1 shows the results when Gd ₃₂ (Fe ₅₀ Co ₅₀ ) ₆₈ was used for the reproducing layer.
In this way, a C / N of 42 dB was obtained for the 0.40um mark. However, when the Co content in the reproducing layer was increased to 51 at% or more, the C / N was reduced to 38 dB due to insufficient exchange coupling in the aperture part.

From the above results, the reproduction layer of the present invention
The Co content y (at%) is preferably set to 20 ≦ y ≦ 50.

(Experimental Example 4) A SiN interference layer having a thickness of 90 nm and Gd _x (Fe) was formed on a polycarbonate substrate by the same device and method as in Experimental Example 1.
_100-y Co _y ) _100-x reproducing layer 40 nm, Gd _p (Fe _100-q Co _q ) _100-p intermediate layer 10 nm, Tb ₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀ memory layer 30 nm, SiN protective layer Films having a thickness of 70 nm were sequentially formed to prepare a medium having the same structure as that shown in FIG. However, this time, the Co content q (at%) of the intermediate layer was variously changed with respect to the Gd content x, p and the Co content y of each of the reproduction layer and the intermediate layer obtained in Experimental Examples 2 and 3. It was

The Co content of the intermediate layer is related to the Curie temperature, which is one of the important factors determining the reproducing power for the medium. For example, when the linear velocity is 9m / s, the playback power is
If it is 4 mW or more, the laser power required for erasing data is required to be 7 mW or more because of the power margin. Further, since the laser is pulse-lighted during the optical modulation recording, a recording power of about 13 mW is required and the reliability of the drive device is significantly limited. Therefore, the laser power at the time of reproducing information is 4 mW or less, preferably 3 mW or less. For that purpose, the Curie temperature of the intermediate layer must be 220 ° C or lower.

The data shown in Table 1 shows that Gd ₄₅ (Fe ₈₀ C
o ₂₀ ) ₅₅ . Co content of the middle layer is 20 at%
At that time, the Curie temperature is 220 ° C, which enables highly reliable information reproduction. However, if the Co content exceeds 20 at%, the reproducing power becomes high, and the reliability of the drive device is significantly impaired.

In this experimental example, the case where GdFeCo is used for the intermediate layer is explained, but if only the Curie temperature is considered, the Curie temperature can be improved by adding a non-magnetic element such as Al and Cr for the purpose of improving the corrosion resistance. Therefore, even if Co is added at 20 at% or more, the same Curie temperature can be obtained by adding the nonmagnetic element. However, in this case, the addition of the non-magnetic element will impair the properties as a magnetic body as a whole, and the addition of Co will reduce the perpendicular magnetic anisotropy. Therefore, replacement with the memory layer at the aperture portion is required. This weakens the coupling and makes it difficult to obtain a playback signal with good S / N. From the above, the intermediate layer in the present invention is Gd _p (Fe
_100-q Co _q ) _100-p is the main component, and the Co content q (at%) is preferably set to 0 ≤ q ≤ 20 even when other elements are added.

(Experimental Example 5) Next, the same apparatus as in Experimental Example 1,
Method to form SiN interference layer on polycarbonate substrate by 90nm, Gd
_x (Fe _100-y Co _y ) _100-x reproducing layer 40nm, Gd _p (Fe _100-q Co _q )
_100-p intermediate layer 10 nm, Tb _a (Fe _100-b Co _b ) _100-a memory layer 3
A 0 nm thick SiN protective layer and a 70 nm thick SiN protective layer were formed in this order to prepare a medium having the same structure as in FIG. However, this time, Experimental Example 2,
Gd content x, p of each of the reproduction layer and the intermediate layer obtained in 3 and 4,
The Tb content a (at%) and the Co content b (at%) of the memory layer were variously changed with respect to the Co content y and q.

FIG. 16 shows the Tb content a (at%) and C / N of the memory layer.
(Mark length 0.40um). However, the Co content b (at%) of the memory layer at this time is almost equal to the Curie temperature.
It is changed according to the Tb content so as to be constant at 270 ° C.

As can be seen from the figure, the composition margin of the memory layer viewed from C / N is sufficiently wide, and a substantially constant C / N is obtained within the range of 18 ≦ a ≦ 31. When the Tb content a is 18 at% or less, the saturation magnetization becomes 250 emu / cc or more (iron group element sublattice magnetization dominance), so the influence of the demagnetizing field becomes strong, and even smaller magnetic domains (microdomains) inside the magnetic domains. ) Is formed or the shape of the magnetic domain is distorted and the noise component increases, so that C / N deteriorates. On the other hand, when the Tb content a is 31 at% or more, the saturation magnetization is 200 emu / cc or more (rare earth element sublattice magnetization dominant) and the compensation temperature is 200 ° C or more. In this case, since the compensation temperature of the memory layer is higher than the Curie temperature of the intermediate layer, the memory layer at the temperature at which the exchange coupling with the reproducing layer is broken has a rare earth element sublattice magnetization predominance. 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 fades next, and the C / N decreases.

The results of FIG. 16 and the conventional in-plane magnetized film were used.
Comparing the data in the super-resolution magneto-optical recording medium having the two-layer structure, it can be said that the effect of the magneto-optical recording medium of the present invention is obtained in the range of 14 ≦ a 3 ≦ 33. In addition, in order to secure C / N of 42 dB or more to improve reliability, 16 ≦
The range of a ≤ 32 is more preferable. Furthermore, in order to obtain stable C / N from the composition margin, 18 ≤ a ≤ 31
Is more desirable.

(Experimental Example 6) Next, the same apparatus as in Experimental Example 1,
Method to form SiN interference layer on polycarbonate substrate by 90nm, Gd
_x (Fe _100-y Co _y ) _100-x reproducing layer 40nm, Gd _p (Fe _100-q Co _q )
_100-p intermediate layer 10 nm, Tb _a (Fe _100-b Co _b ) _100-a memory layer 3
A 0 nm thick SiN protective layer and a 70 nm thick SiN protective layer were formed in this order to prepare a medium having the same structure as in FIG. However, this time, Experimental Example 2,
Gd content of each of the reproducing layer and the intermediate layer obtained in 3, 4, and 5 x,
The Co content b (at%) of the memory layer was variously changed with respect to p, Co content y, q, and Tb content a of the memory layer. An example of the results is shown in Table 1.

The Co content of the memory layer is related to the Curie temperature, which is an important parameter that determines the laser power during recording. Further, considering the storage stability of information on the medium, the Curie temperature of the memory layer needs to be high to some extent. From these facts, the Curie temperature of the memory layer is preferably about 180 to 280 ° C. Therefore, in order to secure this Curie temperature in the range of the Tb content described in Experimental Example 5, the Co content b (at%) is preferably set to 14 ≦ b 2 ≦ 45.

(Experimental Example 7) Next, the same apparatus as in Experimental Example 1 was used.
Method to form SiN interference layer on polycarbonate substrate by 90nm, Gd
₂₈ (Fe ₆₀ Co ₄₀ ) ₇₂ Playback layer 40 nm, Gd ₃₇ Fe ₆₃ Intermediate layer 10 nm,
Tb ₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀ memory layer 30 nm, SiN protective layer 70 nm in sequence, and Al heat dissipation layer 60 nm to improve thermal characteristics are shown in Fig. 17. Created the medium of composition. 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. 18 shows the recording power dependence of carriers and noise when magnetic field modulation recording is performed on the medium of this experimental example. Thus, according to this experimental example, a good C / N of 44 dB was obtained even for a minute mark (0.40 um) even when magnetic field modulation recording was performed, and the super-resolution of the object of the present invention It turns out that it can exert an effect.

(Experimental Example 8) A SiN interference layer of 90 nm and Gd ₂₈ (F) was formed on a polycarbonate substrate by the same device and method as in Experimental Example 1.
e ₆₀ Co ₄₀ ) ₇₂ Playback layer 40 nm, Gd ₃₇ Fe ₆₃ Intermediate layer 10 nm, Dy ₂₅
A (Fe ₇₀ Co ₃₀ ) ₇₅ memory layer and a SiN protective layer having a thickness of 30 nm and 70 nm, respectively, were sequentially deposited to form a medium having the same structure as in FIG.

In the present experimental example, DyFeCo was used as the memory layer instead of TbFeCo. However, good results similar to those in Experiment 1 were obtained for both C / N and crosstalk.
It was confirmed that it is not limited to the FeCo 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 SiN interference layer on a polycarbonate substrate by 90 nm, Tb
_{A 20} (Fe ₈₀ Co ₂₀ ) ₈₀ memory layer and a SiN protective layer having a thickness of 80 nm and 70 nm, respectively, were sequentially formed. That is, a single-layer disk having 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 Figure 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 Figure 10
As shown in Fig. 7, it is clear that when the mark length is as large as 0.78um, sufficient C / N is obtained, but when the cutoff frequency of the optical system is exceeded, the resolution sharply decreases.

Also in the crosstalk measurement, the effective track pitch of 0.8 um is narrow with respect to the reproduction spot, and in the case of a single-layer disc, there is no mask effect.
As shown in Fig. 11, only crosstalk of about -22 dB was obtained.

(Comparative Experimental Example 2) The same device as in Experimental Example 1,
Method to form SiN interference layer on polycarbonate substrate by 90nm, Gd
₂₈ (Fe ₆₀ Co ₄₀ ) ₇₂ Reproduction layer 70 nm, Tb ₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀ Memory layer 30 nm, SiN protective layer 70 nm
A medium having the same structure as the above was created.

First, the mark length was added to the medium created in this experimental example.
A 0.40um mark was recorded, and the dependence of carrier and noise on the reproducing power was measured. The results are shown in Figure 9. in this way,
Since the medium of the present experimental example also has a super-resolution effect by using the in-plane magnetized film at a low temperature, the carrier level increases in the range of the reproducing power of 0.8 to 2.8 mW as in the medium of the experimental example 1. However, in the two-layer super-resolution medium of this 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 experimental example 1 is 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 Figure 10
As shown in, although the resolution in the high frequency range is higher than that of the single-layer disc, the disc of Experimental Example 1 is selected because the rear mask has no effect and the positional relationship between the aperture and the spot is not optimal. The resolution is inferior in comparison.

However, with respect to crosstalk, the front mask has a great influence and the rear mask has no relation. Therefore, as shown in FIG. 11, -30d equivalent to that of the medium of Experimental Example 1 was obtained.
A crosstalk of about B was obtained.

[0101]

[Table 1]

[0102]

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. 7 (a) 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 (b) 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.

8 (a), (b) and (c) are diagrams showing changes in magnetization with temperature 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 the mark length dependence of C / N.

FIG. 11 is a diagram showing the reproduction power dependence of crosstalk.

FIG. 12 is a graph showing the dependence of C / N on the reproduction layer Gd content in the present invention.

FIG. 13 is a diagram showing the dependence of crosstalk in the reproducing layer Gd content in the present invention.

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

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

FIG. 16 is a view showing the dependency of C / N on the memory layer Tb content in the present invention.

FIG. 17 is a configuration diagram of another embodiment of the present invention.

FIG. 18 is a diagram showing recording power dependence of carriers and noise when magnetic field modulation recording is performed on the medium of the present invention.

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

FIG. 20 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.

21 (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 (6)

[Claims] 1. 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 And the third magnetic layer is an in-plane magnetized film at room temperature, the first magnetic layer is mainly composed of GdFeCo, satisfying the following Gd _x (Fe _100-y Co _y ) _100-x , 24 ≦ x ≤ 32 (atomic%), 20 ≤ y
≦ 50 (atomic%), the third magnetic layer is composed mainly of GdFeCo, and satisfies the following: Gd _p (Fe _100-q Co _q ) _100-p , 25 ≦ p ≦ 50 (atomic%), 0 ≤q
≦ 20 (atomic%), the second magnetic layer is a perpendicular magnetization film made of a rare earth-iron group element amorphous alloy, and the Curie temperature of the second magnetic layer is higher than the Curie temperature of the first magnetic layer. And a Curie temperature of the third magnetic layer which is lower than the Curie temperature of the third magnetic layer. 2. The magnetization of 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. Are aligned in one direction above the Curie temperature of the third magnetic layer. 3. The TbFeCo mainly composed of TbFeCo according to claim 1, wherein Tb _a (Fe _100-b Co _b ) _100-a , 14 ≦ a ≦ 33 (atomic% ), 14 ≦ b
≦ 45 (atomic%). 4. The method according to claim 1, wherein the second magnetic layer is mainly composed of DyFeCo. 5. The first magnetic layer according to claim 1, wherein the first magnetic layer has a compensation temperature, and the compensation temperature is near the Curie temperature of the third magnetic layer. 6. 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 And the third magnetic layer is an in-plane magnetized film at room temperature, the first magnetic layer is mainly composed of GdFeCo, satisfying the following Gd _x (Fe _100-y Co _y ) _100-x , 24 ≦ x ≤ 32 (atomic%), 20 ≤ y
≦ 50 (atomic%), the third magnetic layer is composed mainly of GdFeCo, and satisfies the following: Gd _p (Fe _100-q Co _q ) _100-p , 25 ≦ p ≦ 50 (atomic%), 0 ≤q
≦ 20 (atomic%), the second magnetic layer is a rare earth-iron group element amorphous alloy perpendicular magnetization film, information is accumulated and the Curie temperature of the second magnetic layer is the first magnetic layer. In an information reproducing method of reproducing information recorded by using a light beam on a magneto-optical recording medium lower than the Curie temperature of the magnetic layer and higher than the Curie temperature of the third magnetic layer, from the first magnetic layer side. Irradiating the light beam, leaving the first magnetic layer in the low temperature portion in the spot of the light beam as an in-plane magnetized film, and perpendicularly magnetizing the first magnetic layer in the portion other than the low temperature portion in the spot. The film is exchange-coupled with the second magnetic layer, the information accumulated in the second magnetic layer is transferred to the first magnetic layer, and the second reflected light of the light beam is detected. To reproduce the information stored in the magnetic layer Information reproducing method according to claim.