JPH0589536A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve a recording density by providing a recording layer recorded with magneto-optical information and a reproducing layer for reproducing the magneto- optical information of the recording layer and forming this reproducing layer of any one kind among 4 kinds of materials. CONSTITUTION:Inversion magnetic domains are formed in the recording layer 1 when the recording layer is pulsively irradiated with a laser beam of a recording level while a magnetic field is kept impressed thereto with a magnetic fixed from the outside. The reproducing layer 2 is formed of the material which makes phase transition from antiferromagnetism to ferromagnetism with an increase in temp., the spin rearrangement material, the magnetic anistoropy of which changes from an intra-surface direction to a perpendicular direction with respect to the substrate surface, the material which makes phase transition from ferromagnetism to antiferromagnetism with an increase in temp., and the spin rearrangement material, the magnetic anistropy of which changes from a perpendicular direction to an intra- surface direction with respect to the substrate surface. The inversion magnetic domains of the reproducing layer are made smaller than the inversion magnetic domains of the recording layer in such a case and can be made smaller than a laser spot. The recording density is thus increased.

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable magneto-optical recording medium capable of recording / reproducing / erasing information, and more particularly to a magneto-optical recording medium capable of high density recording.

[0002]

2. Description of the Related Art Magneto-optical recording technology for recording / reproducing / erasing information by irradiating a magnetic thin film having perpendicular magnetic anisotropy with a laser is known to have a high recording density and a medium exchange capability. It has been put into practical use as a memory technology that has both the characteristics such as the magnetic property and the rewritability of data that the magnetic recording technology has.

In magneto-optical recording, recording / erasing / reproduction is performed by a laser beam spot narrowed down by a lens, so that the recording density is limited by the wavelength of the laser beam and the numerical aperture of the focusing lens. The latter is determined based on the requirements such as output and laser life, and the requirements such as disk skew tolerance.

Currently used 830 to 780 nm
Recording with sufficient C / N using semiconductor lasers with
The track pitch is about 1.6 μm and the recording density is 10 ⁷ ~ 10 ⁸ bit / cm ² Is.
Further, as long as the existing laser, recording medium and recording method are used, it is impossible to obtain a recording density higher than this.

On the other hand, as the computing speed of computers and the amount of information are increasing, the demand for increasing the recording capacity of the memory is unavoidable, and further improvement in recording density is strongly demanded. In order to meet such requirements, methods of shortening the laser wavelength to reduce the beam spot diameter have been studied. However, a semiconductor laser that can be mounted in a magneto-optical disk drive in a short wavelength region and has an output power sufficient for magneto-optical recording has not yet been put into practical use. In addition, SHG (Second Ha)
using an rmonic Generation) element,
A method of halving the wavelength has been studied, but there are problems that high power cannot be obtained and high-speed modulation is difficult.

As a method for high density recording using the wavelength of the existing semiconductor laser as it is, MSR (Magnetic S
upper resolution) technology has been proposed (nikkei elect
ronics 1991.3.4 No.521 p92, and ohta et. al.: MO
RIS '91 Technical Digest p.91). This technology is RAD
(Rear Aperture Detection) method and FAD (Front Aperture)
e Detection). The RAD method is
A medium in which a recording layer and a reproducing layer are exchange-coupled and laminated is irradiated with a light beam having a recording power level to form a reversed magnetic domain in the recording layer, and the reproducing layer is initialized, and then a light beam having a reproducing power level is irradiated. Then, the coercive force of the reproducing layer of this heating portion is made lower than the exchange force applied from the recording layer to the reproducing layer, and a magnetic domain smaller than the recording magnetic domain is transferred to the reproducing layer for reproduction. In the FAD method, a medium in which a recording layer and a reproducing layer are laminated via an intermediate magnetic layer having a low Curie point is irradiated with a light beam having a recording power level to form inverted magnetic domains in the recording layer and the reproducing layer. The exchange power applied from the recording layer to the reproducing layer is eliminated by irradiating with a light beam at the reproducing power level and heating, and the intermediate magnetic layer is set to the Curie point or higher. This is a technique in which the magnetic force is made equal to or less than the external magnetic field at the time of reproduction and the reversed magnetic domain in the reproduction layer in this portion is erased to reproduce the magnetic domain in the portion irradiated with the reproduction beam other than the erased portion. RAD method, FAD
In both methods, the main purpose is to reduce the coercive force of the reproducing layer to less than the effective magnetic field applied to the reproducing layer during reproduction by heating during irradiation of the reproducing beam. These methods have traditionally limited distances of 1.
Since recording can be performed with a track width narrower than 6 μm, high recording density can be obtained. In addition, the FAD method can also be packed and recorded in the track direction.

However, the RAD method requires an initialization magnet in addition to the ordinary recording magnet. The exchange force between rare earth-transition metal magnetic thin films, which are ordinary magneto-optical recording materials, is several KOe.
Therefore, the initializing magnet that overcomes it and reverses the magnetization of the reproducing layer becomes large, and it is difficult to downsize the device. Immediately after reproducing, the magnetic domains transferred to the reproducing layer remain on the reproducing track, so that the density can be increased only in the radial direction of the disc.

On the other hand, in the FAD method, since the recording bits of the recording layer are transferred to the reproducing layer in the cooling process after laser irradiation, the initialization magnet like the RAD method is unnecessary. However, it has drawbacks that the medium structure is complicated and that a magnetic field must be applied during reproduction. In addition, since there is a portion above the Curie point where there is no signal in the intermediate layer near the center of the laser spot, there is also the problem that a sufficiently large reproduced signal cannot be obtained.

Further, in the above-mentioned MSR technique, it is difficult to make a medium because it is necessary to strictly control the exchange force between the recording layer and the reproducing layer with respect to the film temperature. In addition, since the coercive force of the reproducing layer needs to be less than the exchange force from the recording layer (RAD method) or less than the magnetic field applied during reproduction (FAD method) by heating to the extent of beam irradiation at the reproducing power level, It is difficult to use a film material having large magnetic anisotropy as the reproducing layer, and the reproducing magnetic domain shape is likely to be disturbed.

Further, since the reproducing power is set lower than the recording power, the reproducing power cannot be set so high in order to obtain sufficient recording sensitivity. Due to this, the film temperature at which the coercive force of the reproducing layer drops below the effective magnetic field during reproduction must be set to a temperature that is considerably close to the memory operating temperature. Therefore, the conventionally proposed MSR technology has a drawback that it is difficult to secure a practically sufficient margin because the memory operating temperature range where a stable MSR operation can be obtained is narrow.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to achieve the first object.
Another object of the present invention is to provide a magneto-optical recording medium that does not require an initialization magnet and has a simple medium structure, which enables high density of the magneto-optical recording medium. Secondly, it is to provide a magneto-optical recording medium that is easy to manufacture and that can obtain a stable reproducing magnetic domain shape. Thirdly, it is to provide a magneto-optical medium capable of stable reproduction with a wide operating temperature margin even when the film temperature at which the coercive force of the reproducing layer is equal to or less than the effective magnetic field is set at the time of reproduction. [Constitution of Invention]

[0012]

The present invention firstly has a recording layer in which magneto-optical information is recorded and a reproducing layer for reproducing magneto-optical information in the recording layer, and has a recording power level. To form a recording magnetic domain in the recording layer, and to irradiate a reproducing power level optical beam to transfer a magnetic domain smaller than the recording magnetic domain into the reproducing layer. A recording medium and a reproducing layer are irradiated with a power level optical beam to form a recording magnetic domain, and a reproducing power level optical beam is irradiated to erase a part of the recording magnetic domain in the reproducing layer. A magneto-optical recording medium, wherein the reproducing layer (a) is a material that undergoes a phase transition from antiferromagnetism to ferromagnetism as the temperature rises, and (b) magnetic anisotropy is in-plane with respect to the substrate surface. Spin-rearrangement material that changes in the vertical direction from (c) changes from ferromagnetic to antiferromagnetic as the temperature increases. It is formed of any one of a material that undergoes a transition and (d) a spin reorientation material whose magnetic anisotropy changes from a direction perpendicular to the surface of the substrate to an in-plane direction. Provided is a magneto-optical recording medium characterized in that the temperature is lower than the Curie point of the recording layer and higher than the temperature reached by the recording medium during reproduction.

Secondly, there is provided a magneto-optical recording medium having a recording layer on which magneto-optical information is recorded and a reproducing layer on which the magneto-optical information on the recording layer is transferred, wherein the recording layer has a recording power level. A recording magnetic domain array is formed therein by being irradiated with a light beam, and a leakage magnetic field is supplied to the reproducing layer by being irradiated with a light beam having a reproducing power level. Provided is a magneto-optical recording medium in which a recording magnetic domain is transferred.

Thirdly, it has a recording layer for recording magneto-optical information and a reproducing layer for reproducing the magneto-optical information of the recording layer, and irradiates a recording power level optical beam for recording. A recording magnetic domain is formed in the layer, and a reproducing power level optical beam is irradiated to transfer a magnetic domain smaller than the recording magnetic domain into the reproducing layer, or a recording power level optical beam is irradiated. A magneto-optical recording medium in which a recording magnetic domain is formed in the recording layer and the reproducing layer, and a reproducing power level optical beam is irradiated to erase a part of the recording magnetic domain in the reproducing layer.

The reproducing layer has a compensation point above the memory operating temperature, and the coercive force of the reproducing layer is set to be smaller than the magnetic field applied from the recording layer to the reproducing layer at a temperature above this compensation point. There is provided a magneto-optical recording medium characterized by the above. Hereinafter, the present invention will be described in detail.

First, the first aspect will be described. Figure 1
FIG. 1 is a diagram showing a typical sectional configuration of a magneto-optical recording medium according to a first aspect of the present invention. In FIG. 1, 1 is a recording layer,
2 is a reproduction layer and 3 is a substrate.

Here, the recording layer 1 has the same function as the recording layer of a general magneto-optical recording medium, and while applying a magnetic field from the outside to the recording layer 1, a recording level laser beam is pulsed. By irradiating, an inverted magnetic domain is formed.

As described above, the reproducing layer 2 includes (a) a material that undergoes a phase transition from antiferromagnetic to ferromagnetic as the temperature rises, and (b) magnetic anisotropy is in-plane with respect to the substrate surface. From the perpendicular direction to the substrate surface, and (d) a material that undergoes a phase transition from ferromagnetic to antiferromagnetic as the temperature rises; It is formed of one of the spin rearrangement materials that changes inward. When the reproducing layer is made of the material (a) or (b), the reversal domain does not exist in the reproducing layer at room temperature. When reproducing is performed with laser power such that the temperature of the reproducing layer rises above the phase transition temperature or the spin rearrangement temperature, the exchange interaction or the leakage magnetic field from the recording layer occurs only in the portion where the temperature rises. Thus, the magnetization direction of the recording layer is transferred to the reproducing layer, and the signal recorded in the recording layer is read. In this case, the reversal magnetic domain of the reproducing layer can be made smaller than that of the recording layer and smaller than the laser spot, and it becomes possible to perform high density recording in the radial direction and the circumferential direction of the disc. The density can be significantly increased.

When the reproducing layer is made of the material (c) or (d), the magnetization direction of the recording layer is transferred to the reproducing layer by the exchange interaction or the leakage magnetic field from the recording layer. ing. A light having such a power that the temperature at the center of the spot is higher than the phase transition temperature or the spin rearrangement temperature and lower than the Curie point of the recording layer is applied to such a reproducing layer. Upon irradiation, the transferred magnetization is erased only in the portion heated to that temperature. The reproduction of the signal is performed in a region where such a beam of light is irradiated and the transferred magnetization remains. In this case, signal interference is less likely to occur even if the reversed magnetic domain spacing is narrower than in the conventional case, so that the signal density in the circumferential direction of the disk can be increased as compared with the conventional case. Therefore, also in this case, the recording density can be increased.

Next, the second mode will be described. Since the transfer of the magnetic domain from the recording layer to the reproducing layer in this mode is basically performed by utilizing the leakage magnetic field generated from the recording layer, the recording layer and the reproducing layer are laminated via the exchange force. It is not necessary to control the exchange force with respect to the film temperature even if they are laminated through the exchange force.
The direction of the leakage magnetic field at the time of transfer is opposite to the direction of the initial magnetization of the recording layer regardless of whether the recording layer has a compensation point or not.

The reproducing layer may or may not have a compensating point, but the Curie point of the reproducing layer is preferably set lower than the compensating point or Curie point of the recording layer, and the coercive force of the reproducing layer at the time of reproducing. Form a portion smaller than the sum of the leakage magnetic field of the recording layer and the reproducing magnetic field applied as necessary.

In this embodiment, it is preferable to irradiate the medium with a recording optical beam and then apply an initializing magnetic field to the medium before reproducing. In the case where the initializing magnetic field is applied in this way, an inverted magnetic domain may be formed in the reproducing layer during recording. When no initializing magnetic field is applied,
It is necessary to prevent a magnetic domain larger than the transfer magnetic domain from being formed in the reproducing layer. Therefore, a material having a compensation point is used as the recording layer, and the reversal magnetization direction of the recording layer and the initial magnetization direction of the reproducing layer match. To select the magnetization direction.

When no erasing operation is required in the magneto-optical drive, it is not necessary to install an initialization magnetic field applying source in the drive, which is advantageous in miniaturizing the drive. Even in this case, initialization can be performed outside the drive, and rewriting operation in a broad sense is possible. The magnitude of the initializing magnetic field is set to be smaller than the coercive force of the recording layer and larger than the coercive force of the reproducing layer at room temperature or operating temperature.

The reversal magnetic field of each layer at the time of initialization is determined only by the coercive force of each layer if the recording layer and the reproducing layer are laminated without interposing the exchange force, so that the initialization magnetic field can be easily set and the reproducing layer can be easily set. The coercive force can be set to a relatively large value, and a film material having a large perpendicular magnetic anisotropy can be used for the reproducing layer. Therefore, the shape of the transfer magnetic domain is excellent.

According to the magneto-optical recording medium of this aspect, high density recording can be performed with the current laser wavelength as it is, the medium can be easily formed as compared with the conventional technique, and the perpendicular magnetic field as a reproducing layer is changed. Since it is possible to use a film material having a large directionality,
It is possible to provide a high-density magneto-optical recording medium having a low reproduction price and high reproduction signal quality.

Next, the third mode will be described. In this mode, as described above, the reproducing layer has the compensation point above the memory operating temperature. Further, the coercive force of the reproducing layer is set to be smaller than the transfer magnetic field or the erasing magnetic field applied from the recording layer to the reproducing layer at a temperature above the compensation point. Therefore, the compensation point of the reproduction layer may be set according to the required value of the memory operating temperature.

According to the medium having such a configuration, the RAD
In both cases of the FAD method and the FAD method, a required operating temperature margin can be obtained by using a reproducing layer having a compensation point above the memory operating temperature, and stable MSR reproducing operation characteristics can be obtained. Further, this mode is not limited to the conventional MSR technique of performing the contraction transfer of the magnetic domain by utilizing the exchange force, and the magnetic domain is produced by utilizing the leakage magnetic field generated from the recording layer and applied to the reproducing layer without utilizing the exchange force. The present invention can be applied to the case where the reduction transfer is performed, and in that case, the same action and effect are obtained. In addition, it is preferable to set the compensation point of the reproducing layer to a temperature equal to or higher than the upper limit of the required value of the memory operating temperature described above in order to obtain stable operating temperature characteristics.

[0028]

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

FIG. 2 is a sectional view showing an example of a magneto-optical recording medium according to the first aspect of the present invention. 1 is a recording layer, 2
Is a reproducing layer, 3 is a substrate, 4 is a protective layer, 5 is an interference layer, and 6 is a laser beam.

The recording layer 1 is a heavy rare earth element (HRE) typified by Gd, Tb, and Dy, or N in HRE.
an amorphous film composed of a rare earth element (RE) partially substituted with a light rare earth (LRE) such as d or Pd and a transition metal element (TM) represented by Fe or Co, a Bi-substituted garnet film,
What is conventionally used as a recording layer of a magneto-optical recording medium such as a Whistler alloy film can be used.

As the reproducing layer 2, a material exhibiting an antiferromagnetic-ferromagnetic phase transition or a material exhibiting spin rearrangement is used. In the former case, the phase transition temperature is set lower than the Curie point of the recording layer and higher than the temperature reached by the recording medium during reproduction. The phase transition may be a transition from antiferromagnetism to ferromagnetism or a transition from ferromagnetism to antiferromagnetism as the temperature rises. As a concrete material,
For example, FeRh or FeRh having a phase transition temperature of 80 to 200 ° C. to which Ir and Co are added, MnSb or MnSb to which Bi and Cr are added, and HfTa.
There are Fe and the like.

When a spin rearrangement material is used for the reproducing layer, the spin rearrangement temperature is set lower than the Curie point of the recording layer and higher than the temperature reached by the recording medium during reproduction. The change in anisotropy due to spin rearrangement may be either perpendicular to the film surface or perpendicular to the film surface with increasing temperature. As a specific material, if RE is a rare earth metal, the spin rearrangement temperature is room temperature or higher.
B, RE (FeCo) B, REFeCo and the like. It is preferable that the total thickness of the reproducing layer and the recording layer is thin enough to cause magnetization reversal in the recording layer when a recording level laser is irradiated.

The protective layer 1 and the interference layer 4 are made of Si-N, Si-O, Zr-O, Al- used in a usual magneto-optical recording medium.
Metal compound materials such as O, Al-N, Zn-S, and Ti-O, metal compound materials to which metal elements or the like are added for the purpose other than the present invention such as enhancing the protective function, organic material such as plasma polymerized film Any material may be used as long as it is formed of a non-magnetic material such as, and has a translucency necessary for recording / reproducing operation with respect to the wavelength of the laser used. Further, the protective layer 4 does not need to have a light-transmitting property. Also,
The recording layer 1 and the reproducing layer 2 may each be a single layer or a multilayer, as long as they do not depart from the spirit of the present invention. Further, the minimum requirement for the present invention is the recording layer 2 and the reproducing layer 3, and the protective layer 1 and the interference layer 4 may be omitted. The substrate 5 can be widely selected from materials conventionally used as optical disk substrates such as glass, polycarbonate, polymethylmethacrylate, and polyolefin. The wavelength and the spot diameter of the laser beam 6 are preferably micron size or submicron size for the purpose of the present invention. An external magnetic field Hex may be applied when reproducing the above magneto-optical recording medium. The Hex applying means may be an electromagnet or a permanent magnet.

In the medium of this aspect, the laser irradiation during reproduction causes the temperature of the reproducing layer to exceed the phase transition temperature and generate magnetization, so that the reversed magnetic domain of the recording layer which has already been recorded according to desired recording information is reproduced. It is reproduced by being transferred to a layer, and when the medium is cooled and the temperature of the reproducing layer falls below the phase transition temperature after the completion of reproducing, the magnetic domains on the reproducing layer disappear, which is utilized for high density magneto-optical recording.・ Play. The recording / reproducing process will be described in detail below.

FIG. 3 shows the temperature dependence of the magnetization of a typical recording layer and reproducing layer of the recording medium of the present invention, M _SW is the recording layer magnetization, and M _SR is the reproducing layer magnetization. Ta is room temperature, T _CR is the phase transition temperature of the reproducing layer, and T _CS is the Curie point of the recording layer. The reproduction layer shows such characteristics
This is the case of a material that undergoes a phase transition from antiferromagnetism to ferromagnetism as the temperature rises, or a spin rearrangement material whose magnetic anisotropy changes from the in-plane direction to the perpendicular direction with respect to the substrate surface.

The recording process of this medium is performed in the same manner as the conventional magneto-optical recording medium. For example, by applying high-power laser irradiation to a temperature above the Curie point of the recording layer or to a temperature at which the coercive force of the recording layer is sufficiently small, application from outside including leakage magnetic fields and demagnetizing fields from other layers An inverted magnetic domain is formed by the magnetic field. After the reversed magnetic domain is formed, when it is cooled to room temperature, the reproducing layer has antiferromagnetism or has in-plane magnetization with respect to the substrate surface, and therefore, the reversed magnetic domain does not exist on the reproducing layer.

Next, the reproducing process of such a medium will be described. FIG. 4 schematically shows the relationship between the reproduction laser spot and the recording bit. Reference numeral 11 represents a reversed magnetic domain of the recording layer, 12 represents a laser spot, and 13 represents a reversed magnetic domain transferred to the reproducing layer. Magnetization occurs inside the equal T _CR line in the portion irradiated with the laser light as shown in FIG. 3, and therefore the magnetization state of the recording layer is transferred to the reproducing layer by the exchange coupling interaction. By properly selecting the medium layer structure, T _CR , reproduction power, etc., the inversion domain of the reproduction layer can be made smaller than that of the recording layer and smaller than the laser spot, as shown in FIG. 4B. .. According to the conventional reproducing method, when recording is performed with the reversed magnetic zone filled,
As shown in (a), two recorded bits are reproduced, and inter-signal interference occurs. However, in the medium of this aspect,
As shown in FIG. 4B, there is no inter-signal interference. Also,
Since the reverse magnetic domain is not transferred on the adjacent track,
In the conventional reproducing method, crosstalk does not occur in the medium of this aspect even when recording is performed at a track pitch such that signals of adjacent tracks are also reproduced and crosstalk occurs. Therefore, in the medium of this aspect, it is possible to perform high-density recording / reproducing in both the radial direction and the circumferential direction of the disc,
It is possible to achieve higher density than the conventional MSR technology.

Next, as the reproducing layer 2, a material that undergoes a phase transition from ferromagnetic to antiferromagnetic as the temperature rises, or a spin whose magnetic anisotropy changes from a direction perpendicular to the substrate surface to an in-plane direction. The case where the rearrangement material is used will be described in detail. FIG. 5 shows typical magnetic properties of such a reproducing layer material. Similar to FIG. 3, the transition temperature is indicated by T _CR .

Even in the case of the recording medium using such a reproducing layer, the recording process is performed in the same manner as the conventional magneto-optical recording medium. For example, by applying high-power laser irradiation to a temperature above the Curie point of the recording layer or to a temperature at which the coercive force of the recording layer becomes sufficiently small, application from outside including leakage magnetic fields and demagnetizing fields from other layers An inverted magnetic domain is formed in the recording layer by the magnetic field. After the inverted magnetic domain is formed, when it is cooled to room temperature, the reproducing layer becomes ferromagnetic around T _CR or has a magnetization in the direction perpendicular to the substrate surface. Inversion domain is also formed on the reproducing layer by the exchange coupling interaction with.

Next, the reproducing process of such a medium will be described. FIG. 6 is a schematic diagram showing the relationship between the reproduction beam spot, the equal T _CR line, and the recording bit of the recording layer. Reference numeral 21 is an inverted magnetic domain of the recording layer, 22 is a laser spot, and 23 is an equal T _CR line. Strictly speaking, since there is thermal diffusion at a finite speed in the reproducing layer, the phase of the equal T _CR line of the reproducing layer is delayed by d as compared with the laser beam as shown in the figure. Since the inside of the equal T _CR line (the hatched portion in the figure) has antiferromagnetism or magnetic anisotropy in the in-plane direction with respect to the substrate surface, the signal transferred from the recording layer is present in this region. The contributing magnetization disappears. Then, the detection of the signal is performed in the direction of the magnetization of the non-hatched portion in the laser beam. According to such a medium, by choosing such a suitably media layer structure and T _CR or reproducing power, the reproducing beam spot and equal T _CR
When the relationship between the lines and the recording bits of the recording layer is as shown in FIG. 6, even if the reversed magnetic domain interval of the recording layer is reduced to the distance d, no inter-signal interference occurs. When the reversed magnetic domain of the interval d is reproduced by the conventional method, the laser spot is applied to the two reversed magnetic domains, and interference between signals occurs. Therefore, even in such a medium, there is little interference between signals, and high-density recording / reproducing can be performed in the circumferential direction of the disk. However, since there is a transferred reversal magnetic domain on the adjacent track of the reproducing layer, the reversal magnetic domain interval in the disk radial direction cannot be narrower than that of the conventional one.

The external magnetic field H _ex is essentially unnecessary,
It may be applied at the time of recording in order to generate a recording magnetic domain at the time of recording. The function of transferring the magnetic domain of the recording layer to the reproducing layer does not have to be the exchange coupling effect, and may be the leakage magnetic field generated from the recording layer, for example.

Next, an example corresponding to the second mode will be described. FIG. 7 is a schematic configuration diagram showing an example of the magneto-optical recording medium according to the second aspect, 32 is a disk substrate, and the multilayer film 31 is formed on this substrate 32. 33 is a focusing lens, 34 is a recording / reproducing laser beam, 35 is a recording / reproducing applied magnetic field source, 36 is an initializing magnetic field source, 3
Reference numeral 7 indicates a spindle motor for rotating the disk.

The multilayer film 31 is composed of the reproducing layer 41 and the recording layer 4.
2 is laminated in that order from the light beam irradiation side. An intermediate layer 43 is provided between the reproducing layer and the recording layer to block the exchange force therebetween. Middle layer 43
May be any non-magnetic material, as long as the exchange force does not act between the recording layer and the reproducing layer. The intermediate layer 43 is not essential, and it is not necessary to provide it if a sufficiently large leakage magnetic field can be obtained without providing it.
As other films, for example, an interference layer may be provided between the substrate and the reproducing layer, and a protective film or a reflective film may be provided on the recording layer.

FIG. 8 is a diagram showing an example of thermomagnetic characteristics of the recording layer and the reproducing layer in this embodiment. The horizontal axis represents the film temperature (T), Ta is the operating temperature of the disk, T _CR is the Curie point of the reproducing layer, T _compW is the compensation point of the recording layer, and T _CW
Represents the Curie point of the recording layer, H _ini is the initializing magnetic field, H _CR is the coercive force of the reproducing layer, H _CW is the coercive force of the recording layer, and M is
_SW represents the magnetization of the recording layer. The characteristics of Fig. 8 are amorphous.
It can be realized with a heavy rare earth-transition metal alloy (RE-TM) film material, for example, a GdTbCo film or TbF film as a recording layer.
An eCo film or the like can be used, and DyF is used as the reproducing layer.
An eCo film, a GdDyFeCo film or the like can be used.

The film thickness of the recording layer 42 is preferably thin enough to obtain sufficient recording sensitivity and thick enough to generate a sufficient leakage magnetic field, preferably about 50 to 300 nm. The thickness of the reproducing layer 41 is preferably thick enough that the magnetic domains of the recording layer cannot be seen through during reproduction and thin enough that the heat of the laser is sufficiently applied to the recording layer during recording, preferably about 25 to 100 nm. These layers 41 to 43 can be formed using a commonly used thin film forming technique, and for example, a magnetron sputtering method can be used.

Next, the initialization and recording / reproducing operation of the medium having such a configuration will be described. After each layer is formed, the initial magnetization directions of the recording layer and the reproducing layer are adjusted, for example, in the directions of arrows in FIG. 7 (both the recording layer and the reproducing layer are upward in FIG. 7). Then, the spindle motor 37 is driven to rotate the disk and irradiate the laser beam 34 through the focusing lens 33 at the reproduction level (P _R ) to focus and track. At this time, since no inversion magnetic domain is formed in the recording layer, no leakage magnetic field is generated from the recording layer.

In this state, the magnetic field applying source 35 is energized to supply the recording magnetic field (H _W ) upward in FIG. The direction of H _W is the direction in which the recording magnetic domain is formed in the recording layer, and the direction in which the recording magnetic domain is not formed in the reproducing layer. When the recording level (P _W ) laser beam modulated by the information signal is pulsed while applying this H _W , the film temperature of both the recording layer 42 and the reproducing layer 41 rises to near T _CW , and recording is performed. The coercive force (H _CW ) of the layer drops below H _W. And
Recording magnetic domains are formed in the heated region in the recording layer 42 that satisfies H _CW <H _W.

When the magnetization in the recording layer 42 changes spatially, a leakage magnetic field is generated from the recording layer 42. At this time, the position where the reproducing layer 41 reaches the Curie point (T _CR ) is the recording layer 42. Since it is outside of the magnetization reversal part, the reproducing layer hardly feels the leakage magnetic field from the recording layer at the position of T _CR . After the magnetization reversal portion is formed in the recording layer 42, the recording pulse is turned off or the medium is separated from the laser spot to cool the medium. In the cooling process, the reproducing layer 41 has its Curie point ( When it reaches the vicinity of (T _CR ), it is transferred to the reproducing layer with the magnetic domain of the recording layer being contracted.

FIG. 9 is a diagram schematically showing this transfer process, where (a) is the spatial distribution of the magnetization (M _SW ) of the recording layer,
(B) is the distribution of the leakage magnetic field (H _l ) generated from the recording layer due to (a), and (c) is the distribution of the coercive force (H _CR ) of the reproducing layer. The arrow shown in the upper part of FIG. 9 indicates the approximate position of the laser spot. When the recording layer becomes less than T _compW in the cooling process after irradiation with the recording laser, the magnetization distribution in the recording layer is as shown in (a) in the recording portion (-M _SW ) and the non-recording portion (+ M _SW ). become. H based on this magnetization distribution
Considering that the area of the + M _SW region is larger than the area of the -M _SW region in the direction perpendicular to the track, the _l distribution is near the -M _SW position as shown in (b). The distribution is large only in. On the other hand, H _CR is smaller than H _{1 at the} position heated near T _CR . Magnetization is transferred to a portion where H _CR is lower than the vector sum of H ₁ and H _ex (the transfer area is indicated by an arrow in FIG. 3C, for example), and the size of this transfer magnetic domain is determined by the recording layer. It is smaller than the size of the recording magnetic domain in 42. That is, the magnetic domains having a high recording density could be transferred to the reproducing layer 41.

In order to actually perform high-density recording, it suffices to perform recording so that inter-signal interference and crosstalk become large when recording on the recording layer 42. Since the magnetic domain transferred to the reproducing layer 41 is smaller than the magnetic domain formed in the recording layer, interference between signals and crosstalk are reduced during reproduction.

The magnetic domains transferred to the reproducing layer 41 can be reproduced as they are without initializing, but the following merits can be expected by initializing. The transferred magnetic domain array disappears when the medium passes through the initializing magnetic field supply source 36 (the magnetic domain in the recording layer is preserved as it is), but when the reproducing level beam is irradiated again, the distribution of the irradiation part is changed. As shown in FIG. 9, magnetic domains are transferred to the reproducing layer, and high density reproducing can be performed. Once the magnetic field passes through the initializing magnetic field 36, the magnetic domain of the adjacent track remains lost during reproduction, and the problem of crosstalk disappears. Further, when _performing the erasing operation, the direction of H _ex is the opposite direction to that at the time of recording, that is, the reversal direction of the reproducing layer 41.
At the time of erasing, a magnetization reversal portion is formed in the reproduction layer 41 along the track, and recording and transfer cannot be performed again unless this is initialized. Therefore, it is preferable that the initialization magnetic field supply source 36 is provided. However, when the erasing operation is not required, the high density recording information can be reproduced without the initialization magnetic field. In such a case, it is advantageous for downsizing the drive, and such a case becomes possible when a recording layer having a compensation point is used. On the other hand, when the initializing magnetic field is used, the recording layer may have no compensation point. This is because the distributions shown in FIGS. 9A and 9B can be realized even by using a recording layer having no compensation points. However, in this case, since the reversal direction of the recording layer and the reversal direction of the reproducing layer coincide with each other, transfer does not occur in the cooling process after recording but only in the reproducing process after initialization. That is, when a recording layer having no compensation point is used, the presence of an initializing magnetic field is essential for high density reproduction. In any case where the initialization magnetic field is used, the magnitude of the initialization magnetic field is set to be smaller than the coercive force (H _CW ) of the recording layer and larger than the coercive force (H _CR ) of the reproducing layer at the memory operating environment temperature. It is good, and it is not necessary to set it in consideration of the exchange force, which is simple. At the same time, since H _CR can be set near H _ini , H _CR can be set relatively large. That is, since the reproducing layer having a large perpendicular magnetic anisotropy can be used, the shape of the magnetic domain transferred to the reproducing layer is good and a high reproduced signal quality can be obtained.

Next, an example corresponding to the third mode will be described. FIG. 10 is a schematic configuration diagram showing an example of the magneto-optical recording medium according to the third aspect, 52 is a disk substrate, and the multilayer film 51 is formed on this substrate 52. 53
Is a focusing lens, 54 is a recording / reproducing laser beam, 55 is a recording / reproducing applied magnetic field (H _ex ) supply source, 56 is an initializing magnetic field (H _ini ) supply source, and 57 is a spindle motor for rotating a disk.

The multilayer film 51 is composed of the reproducing layer 61 and the recording layer 6.
2 is laminated in that order from the light beam irradiation side. Although not shown in FIG. 10, the substrate 52 and the reproduction layer 6
It is preferable that an interference layer be provided between the recording layer 62 and the recording layer 62 in order to obtain a higher reproduction signal strength, and that a protective layer be provided on the recording layer 62 in order to improve the medium life. ..

As the film material, both the recording layer 62 and the reproducing layer 61 are amorphous / rare earth (RE) -transition metal (T) composed of rare earths such as Gd, Tb, Dy and transition metals such as Fe and Co.
M) An alloy film can be used, and a commonly used thin film forming technique such as magnetron sputtering can be used for film formation.

FIG. 11 is a diagram showing an example of thermomagnetic characteristics of the recording layer and the reproducing layer used in this embodiment. The horizontal axis of FIG. 11 is the film temperature, Ta is the memory operating temperature, and T _compR
Is the compensation point of the reproducing layer, T _copy is the magnetization transfer temperature when a magnetic field is not applied during reproduction, T _CW is the Curie point of the recording layer, and T _CR
Is the Curie point of the reproduction layer. T _compR is the required T
It is set according to the margin for a, for example, 50 ° C.
Is set to.

H_CRIs the coercive force of the reproducing layer, and T_compRso
Divergence and T_CRSharply decreases towards
It is a characteristic that H_CWIs the coercive force of the recording layer, H_exg
Is the exchange force applied from the recording layer to the reproducing layer. H_exg
And H_CRThe temperature at which and are equal is T_copyAnd T_copyLess than
Then H_CRIs H_exgIs set larger than. T_copythat's all
And T_CRAnd T_CWH in the temperature range below the lower temperature_CR
Is H_exgAnd the magnetization of the recording layer is transferred to the reproducing layer.
To be copied. H_iniIs the same direction as the initial magnetization of the reproducing layer
Is applied to Ta and the magnitude of Ta is
Chosen to be satisfied. H_CR+ H_exg≤H_ini≤H_CW-H_{exg '}  Where H_{exg '}Is the exchange force applied from the reproducing layer to the recording layer
Is. In this example, the recording layer 62 has a compensation point of Ta or more.
I chose a composition that has no
It may be used as a recording layer.

When a material having a TM-rich composition with no compensation point is used as the recording layer 62, the directions of initial magnetization of the medium are opposite to each other in the recording layer 62 and the reproducing layer 63, as shown in FIG. The direction of initial magnetization of the recording layer is opposite to the direction of the recording magnetic field.

When a material having an RE-rich composition having no compensation point is used as the recording layer 62, the directions of initial magnetization of the medium are the same in the recording layer 62 and the reproducing layer 61, and the direction of initial magnetization of the recording layer 62 is the same. Is opposite to the direction of the recording magnetic field. In this case, the direction of the recording magnetic field is such that the magnetization reversal of the reproducing layer is obstructed.
The magnetization of the reproducing layer can be reversed by the exchange force in the cooling process after the irradiation of the aluminum. Even when a recording magnetic field that does not cause reversal is applied, if the recording magnetic field and the applied magnetic field at the time of reproduction are made different, the magnetic domain transfer at the time of reproduction can be achieved, so there is no problem in carrying out MSR reproduction.

When a material having a compensation point is used for the recording layer 62, the directions of initial magnetization of the medium are the same in the recording layer 62 and the reproducing layer 61, and the directions of magnetization of the recording layer and recording magnetic field are the same. And are in the same direction.

FIG. 11 shows an example in which T _CW is set lower than T _CR , but there is no particular restriction on the magnitude relationship between them,
T _CW may be set to such an extent that the magnetization of the recording layer is sensitively reversed when the recording beam is irradiated, and T _CR is set so that the coercive force of the reproducing layer is sufficiently reduced when the reproducing beam is irradiated.

Next, the initialization and recording / reproducing operation of the medium having such a structure will be described. After each layer is formed, the initial magnetization directions of the recording layer and the reproducing layer are aligned in the directions of arrows in FIG. 10 (in FIG. 10, the recording layer is upward and the reproducing layer is downward). Then, the spindle motor 37 is driven to rotate the disk, and the recording magnetic field is applied downward by H _ex in FIG. After irradiating the laser beam 54 on the disc through the focusing lens 53 and taking servos such as focusing and tracking, the recording power level (P _W ) beam modulated by the information signal is emitted. Irradiate the pulsed light. In the P _W light irradiation portion of the medium, the temperature rises near T _CW , and the reversed magnetic domain is formed in the recording layer 62 in the portion where H _CW has dropped below the recording magnetic field. This magnetic domain is formed based on the principle of the above-mentioned MSR technique, and at a high density such that inter-signal interference and crosstalk become too large when reproduced as it is as in a normal magneto-optical recording medium. Whether or not the reproducing layer is also inverted by the recording magnetic field depends on the magnitude relationship between H _CR near T _CW and the recording magnetic field, which may be either, and the recording layer 62 may be formed in the portion where the inverted magnetic domain is formed in the recording layer. A domain wall is formed at the interface between the reproducing layer 61 and the reproducing layer 61, and H _exg acts on the reproducing layer 61.
Inversion magnetic domains are formed in the reproducing layer in the portion where H _CR is less than the vector sum of H _exg and the recording magnetic field. At this point, the size of the magnetic domain formed in the reproducing layer may be larger or smaller than that of the magnetic domain in the recording layer. When the recording pulse is cut off or the medium is cooled away from the laser spot, both H _CR and H _CW rise, and the formed magnetic domain is fixed.

Next, the medium passes through H _ini , the magnetic domains in the recording layer 62 are preserved as they are, the magnetic domains in the reproducing layer 61 are erased, and only the magnetization state of the reproducing layer returns to the initial magnetization state.
An interface domain wall is formed at the interface between the recording layer 62 and the reproducing layer 61 in the portion where the inverted magnetic domain exists in the recording layer, and no interface domain wall is formed in the portion where no magnetic domain exists. H _exg acts on the reproducing layer where the interface magnetic wall is formed, but H _CR
Is set to be larger than H _exg , the reproduction layer 61
Preserves its magnetized state. Next, the MSR reproducing operation is performed, but the reproducing optical head may be the same as or different from the recording optical head. Here, a case where the same head is used will be described.

The medium that has passed through H _ini again travels under the beam 54 and is irradiated with a light beam having a reproduction power level (P _R ). The light intensity of P _R is the reproduction layer 61 near the center of the spot.
Is set so as to rise above T _copy .
Here, the meaning of being around T _copy or higher means that when H _ex is used to apply a magnetic field during reproduction, the magnetization is transferred at a portion where H _CR is less than or equal to the vector sum of H _exg and the reproducing magnetic field. That is, even if the temperature of the reproducing layer does not reach the T _copy shown in FIG. 11, the magnetic domain transfer occurs.

The magnetization of the recording layer is transferred to the reproducing layer in the part where H _CR is lower than the sum of H _exg and the reproducing magnetic field, and only the information signal of this transferred part is detected as the reproducing signal. High density recording / reproduction can be performed substantially.

Next, for the purpose of clarifying the effect of this embodiment, using a medium having a reproducing layer having no T _{comp R} above Ta, which was prepared for comparison with the medium having the characteristics shown in FIG.
The reproducing operation characteristics were compared by changing a. The recording layer of the comparative medium has the same characteristics as in FIG. 11, and the reproducing layer is T
_The RE rich film without _compR was used, and T _copy was matched.

The recording conditions were examined in advance for each medium, recording magnetic domains of the same size and the same pattern were formed in the recording layer, the reproducing layer was initialized, and then the reproducing operation was performed by changing Ta and reproducing. The relationship between the signal CN ratio and P _R was investigated. When the magnetic domain pattern formed in the recording layer is reproduced as it is as a pattern with large intersymbol interference, the reproduction CN ratio is 25.
It becomes about dB. When this was reduced and transferred to the reproducing layer and reproduced, when the Ta was 0 ° C., the CN ratio of both the medium of the present invention and the medium for comparison was 40 dB or more.

Next, by changing Ta, the reproduction CN ratio was examined to find the maximum P _R for each Ta. Figure 12 shows P _{R in} this case
It is a figure which shows the relationship between Ta and Ta. In FIG. 12, (A)
Shows the results obtained using the magneto-optical medium of this embodiment,
(B) shows the results obtained using the medium for comparison. ×
The mark means that the maximum CN ratio did not reach 30 dB. As is apparent from FIG. 12, it is understood that the use of the magneto-optical medium of this aspect makes it possible to set P _R to be large and the Ta margin is significantly wider than that of the medium for comparison. It was also confirmed that the maximum CN ratio obtained in the region where Ta is 0 ° C. or higher is larger in (A) than in (B). T
_{Even if the copy} is the same, the _case where T _compR is in the playback layer (A) is T
_The reproduction characteristic is superior to that of (B) without _{compR because} the reproduction layer with T _compR has T _copy more than Ta.
At a temperature region, H _CR is because with stable transfer characteristics against variations of P _R and the reproducing magnetic field in order to satisfactorily ensure the condition that is greater than the reproducing magnetic field and H _exg, T
_{This is because in} the reproducing layer without _compR , when P _R or the reproducing magnetic field changes, the temperature at which H _CR balances with the sum of H _exg and the reproducing magnetic field greatly changes.

In the above-described embodiment, R among MSR techniques is used.
Although the case where the AD method is adopted has been described, the present invention has the same effect when the FAD method is adopted. FA
In the case of method D, instead of the medium shown in FIG.
As shown in FIG. 5, a medium in which a magnetic intermediate layer 63 having a low Curie point is provided between the reproducing layer 61 and the recording layer 62 is used, and after the recording magnetic domains are formed in the recording layer 62 and the reproducing layer 61, initialization is performed. Without heating, the reproducing beam is irradiated to heat the magnetic intermediate layer 63 to the Curie point or higher, and the magnetization of the reproducing layer 61 of this heating portion is initialized by the reproducing magnetic field to reproduce the reproducing layer 6 other than the initializing portion.
It is sufficient to perform the operation of reproducing the magnetic domain in No. 1 and even in such a case, a stable MSR reproducing operation can be performed by using a film having T _compR of Ta or more in the reproducing layer.

In addition to the MSR technique of transferring and reproducing magnetic domains by utilizing the exchange force between the recording layer and the reproducing layer, for example, a leakage magnetic field applied from the recording layer to the reproducing layer is used. Also in the technique of reducing and transferring the magnetic domain by using the film having T _compR of Ta or more as the reproducing layer according to the present invention, the reproducing operation with a reliable operating temperature margin can be performed.

In the above embodiments, R is used as the recording layer and the reproducing layer.
Although the example using the E-TM film has been described, the present invention can be carried out without being particularly limited to a material, and other than the RE-TM film, for example, a Pt / Co multilayer film, a garnet film and the like are also included in the present invention. It can be used in a range that does not deviate from the gist of.

[0071]

According to the present invention, there is provided a magneto-optical recording medium capable of densifying the magneto-optical recording medium with a simple medium structure without requiring an initializing magnet. Further, there is provided a magneto-optical recording medium which can be easily manufactured and can obtain a stable reproducing magnetic domain shape. Further, it is possible to provide a magneto-optical medium capable of stable reproduction with a wide operating temperature margin even when the film temperature at which the coercive force of the reproducing layer is equal to or lower than the effective magnetic field is set at the time of reproduction.

[Brief description of drawings]

FIG. 1 is a sectional view showing a typical configuration of a magneto-optical recording medium according to a first aspect of the present invention.

FIG. 2 is a sectional view showing an embodiment of a magneto-optical recording medium according to the first aspect of the present invention.

FIG. 3 is a material for the reproducing layer, which undergoes a phase transition from antiferromagnetic to ferromagnetism with increasing temperature, or a spin rearrangement material whose magnetic anisotropy changes from an in-plane direction to a perpendicular direction with respect to the substrate surface. FIG. 6 is a diagram showing temperature dependence of magnetization of a recording layer and a reproducing layer in the case of.

[4] reversed magnetic domain and a laser beam spot of the recording layer in the case of using the material characteristics shown in FIG. 3 as a reproduction layer, etc. T _CR
The figure which shows the relationship with a line.

FIG. 5 is a reproduction layer made of a material that undergoes a phase transition from ferromagnetic to antiferromagnetic as the temperature rises, or a spin rearrangement material whose magnetic anisotropy changes from a direction perpendicular to the substrate surface to an in-plane direction. The figure which shows the temperature dependence of the magnetization of a reproducing layer when it uses.

Reversal magnetic domain 6 in the case of using the material characteristics shown in FIG. 5 as the reproducing layer recording layer and the laser beam spot, etc. T _CR
The figure which shows the relationship with a line.

FIG. 7 is a schematic configuration diagram showing an embodiment of a magneto-optical recording medium according to the second aspect of the invention.

FIG. 8 is a diagram showing an example of thermomagnetic characteristics of a magneto-optical medium used in the second aspect of the present invention.

FIG. 9 is a diagram for explaining the principle of the second aspect of the present invention.

FIG. 10 is a schematic configuration diagram showing an embodiment of a magneto-optical recording medium according to the third aspect of the present invention.

FIG. 11 is a diagram showing an example of thermomagnetic characteristics of the magneto-optical medium used in the third aspect of the present invention.

FIG. 12 is a diagram for explaining the effect of the third aspect of the present invention.

FIG. 13 is a sectional view showing an optical recording medium according to another embodiment of the third aspect of the present invention.

[Explanation of symbols]

1, 42, 62 ... recording layer, 2, 41, 61 ... reproducing layer,
3, 32, 52 ... Substrate, 4 ... Protective layer, 5 ... Interference layer, 6,
34, 54 ... Laser beam, 43, 63 ... Intermediate layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junsei Ashida 70 Yanagimachi, Saiwai-ku, Kawasaki-shi, Kanagawa Toshiba Yanagimachi Factory

Claims (3)

[Claims] 1. A recording layer in which magneto-optical information is recorded, and a reproducing layer for reproducing magneto-optical information in the recording layer, wherein the recording layer is irradiated with a recording power level optical beam. To form a recording magnetic domain and irradiate a reproducing power level optical beam to transfer a magnetic domain smaller than the recording magnetic domain into the reproducing layer, or irradiate a recording power level optical beam. A recording magnetic domain is formed in the recording layer and the reproducing layer, and a reproducing power level optical beam is formed.
A magneto-optical recording medium for erasing a part of a recording magnetic domain in a reproducing layer by irradiating the reproducing layer, wherein the reproducing layer (a) has a phase transition from antiferromagnetic to ferromagnetic as the temperature rises. , (B) a spin reorientation material whose magnetic anisotropy changes from an in-plane direction to a perpendicular direction with respect to the substrate surface, (c) a material that undergoes a phase transition from ferromagnetic to antiferromagnetic as the temperature rises, (D) The magnetic layer is formed of any one of spin-rearrangement materials whose magnetic anisotropy changes from the direction perpendicular to the substrate surface to the in-plane direction, and the phase transition temperature or the rearrangement temperature thereof is the recording layer. The magneto-optical recording medium is characterized in that it is lower than the Curie point of and higher than the temperature reached by the recording medium during reproduction. 2. A magneto-optical recording medium having a recording layer on which magneto-optical information is recorded and a reproducing layer on which the magneto-optical information of the recording layer is transferred, wherein the recording layer is a light beam of a recording power level. Is irradiated with a recording magnetic domain array and is irradiated with a light beam having a reproduction power level to supply a leakage magnetic field to the reproduction layer, and the reproduction layer is recorded by the leakage magnetic field of the recording layer. A magneto-optical recording medium in which magnetic domains are transferred. 3. A recording layer having a recording layer for recording magneto-optical information and a reproducing layer for reproducing the magneto-optical information of the recording layer, wherein the recording layer is irradiated with a recording power level optical beam. A recording magnetic domain and irradiating a reproducing power level optical beam to transfer a magnetic domain smaller than the recording magnetic domain into the reproducing layer, or irradiating a recording power level optical beam. A recording magnetic domain is formed in the recording layer and the reproducing layer, and a reproducing power level optical beam is formed.
A magneto-optical recording medium for erasing a part of a recording magnetic domain in a reproducing layer by irradiating a recording medium, wherein the reproducing layer has a compensation point above a memory operating temperature, and at a temperature above this compensation point. A magneto-optical recording medium, wherein the coercive force of the reproducing layer is set smaller than the magnetic field applied from the recording layer to the reproducing layer.