JPH0547055A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To eliminate the need for initializing magnets exclusive for external magnetic fields at the time of recording by laminating a reproducing layer and a recording layer so to be exchange bonded and the recording layer and a bias layer so as to be magnetostatically bonded, thereby the bias layer is not allowed to invert in magnetization under max. temp. in the recording, erasing and reproducing stages. CONSTITUTION:The reproducing layer 1, the recording layer 2 and the bias layer 4 are successively laminated from the incident side of a layer 8 in such a manner that the reproducing layer 1 and the recording layer 2 are mainly exchange bonded and that the recording layer 2 and the bias layer 4 are mainly make magnetostatically bonded. Amorphous RE-TM films, etc., are applicable as the reproducing layer 1 and the recording layer 2. RE-TM films, etc., which are not inverted in magnetization by recording, erasing and reproducing operations and have the sensitivity lower than the sensitivity of the recording layer 2 are used as the bias layer 4. The combined thickness of the reproducing layer 1 and the recording layer is reduced to the extent at which the sufficient inversion in magnetization is induced by the irradiation with a laser of a recording level. The bias layer 4 may be as thick as to locally generate a magnetization distribution when locally heated by the irradiation with the laser and to generate a leaking magnetic field on the outside of the bias layer 4.

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 magneto-optical recording medium capable of recording / reproducing / erasing information.

[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 such magneto-optical recording, information is recorded / erased / reproduced by a laser beam spot narrowed by a lens, so that the upper limit of the recording density is given by the wavelength of the laser. It is possible to record / reproduce with a sufficient C / N (carrier noise ratio) using a semiconductor laser with a wavelength of 830 to 780 nm, which is currently widely used, at a track pitch density of about 1.6 μm. As long as a laser, a recording medium and a recording method are used, a recording density higher than this cannot be obtained.

In order to solve such a problem, a method of shortening the laser wavelength to reduce the beam spot diameter has been studied. However, as a semiconductor laser that can be mounted on a magneto-optical disk drive, a semiconductor laser having a sufficient output power for magneto-optical recording has not yet been put into practical use. In addition, SHG (Second Harmo
A method of halving the wavelength using a nic generation) element has been studied, but there are problems that high power is not output and high-speed modulation is difficult.

A method of performing high density recording by using the wavelength of the existing semiconductor laser as it is, for example, nikkei el
electronics 1991.3.4 No. 521p. 9
2 is reported. This uses a recording medium composed of an exchange coupling two-layer film of a reproducing layer and a recording layer, and irradiates a laser from the reproducing layer side. In this medium, first, recording is performed by applying a recording magnetic field Hex while irradiating a high power beam as in the case of an ordinary magneto-optical recording medium. In this case, the recording layer
The magnetization of both the reproducing layers is reversed. After that, an initialization magnetic field Hini is applied to the medium at room temperature to cause only the reproduction layer to remagnetize and be initialized. Reproduction is performed by continuously irradiating a beam having a reproduction power level. At this time, the temperature of the laser-irradiated portion of the medium rises, and the coercive force of the reproducing layer decreases. Therefore, if there is a recording bit in the recording layer at that position, the reproducing layer is regenerated by the exchange force from the recording layer. A signal is detected by causing magnetization reversal. When this method is used, the temperature of the track adjacent to the track being reproduced is small, so that the reproducing layer remains initialized and does not generate a signal. Therefore, conventionally
It is possible to record with a track width narrower than the limited distance of 1.6 μm due to crosstalk from adjacent tracks.

However, this method requires an initialization magnet in addition to the ordinary recording magnet. Since the exchange force between rare earth-transition metal magnetic thin films, which is an ordinary magneto-optical recording material, is several kOe, the initializing magnet that overcomes it and reverses the magnetization of the reproducing layer becomes large, making it difficult to miniaturize the device. Become. Further, immediately after the reproduction, since the magnetic domains transferred to the reproduction layer remain on the reproduction track, there is a drawback that the density can be increased only in the radial direction of the disc.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and achieves high density in both the radial direction and the circumferential direction of a disk without the need for an initialization magnet. It is an object of the present invention to provide a magneto-optical recording medium that can be used. [Constitution of Invention]

[0008]

A magneto-optical recording medium according to a first aspect of the present invention comprises a reproducing layer, a recording layer, and a magnetic layer.
And a reproducing layer, a recording layer, and a bias layer, which are laminated in this order from the laser incident side, wherein the reproducing layer and the recording layer are laminated so that exchange coupling is the main. It is characterized in that the recording layer and the bias layer are laminated such that magnetostatic coupling is the main, and the magnetization is not reversed at a temperature lower than the maximum temperature reached by the bias layer in the recording / erasing / reproducing process.

The magneto-optical recording medium according to the second aspect has a reproducing layer, a recording layer, and a bias layer made of a magnetic material, and an optical layer in which the reproducing layer, the recording layer, and the bias layer are laminated in this order from the laser incident side. In a magnetic recording medium, a reproducing layer and a recording layer are laminated so that exchange coupling is the main, a recording layer and a bias layer are laminated so that magnetostatic coupling is the main, and
The magnetization of the bias layer does not reverse at a temperature lower than the maximum temperature reached in the erasing / reproducing process, and the magnetization of the bias layer decreases from room temperature to TR when the maximum temperature TR of the medium reached during reproduction is set. When it has characteristics, the bias layer is magnetized in the direction opposite to the magnetization direction of the reproducing layer,
When the magnetization of the bias layer has a characteristic of increasing from room temperature to TR, the bias layer is magnetized in the same direction as the magnetization direction of the reproducing layer.

FIG. 1 is a sectional view showing an embodiment of a magneto-optical recording medium according to the present invention. In FIG. 1, 1 is a reproduction layer,
Reference numeral 2 is a recording layer, 3 is an intermediate layer, 4 is a bias layer, 5 is a protective layer, 6 is an interference layer, 7 is a substrate, and 8 is a laser beam.

As the reproducing layer 1 and the recording layer 2, Gd and T are used.
b, Dy represented by heavy rare earth elements (HRE) or HRE partially replaced by light rare earths (LRE) such as Nd and Pd, and transition metal elements represented by Fe and Co (TM) ) An amorphous RE-TM film consisting of
The i-substituted garnet film, the Whistler alloy film or the like which has been conventionally used as the recording layer of the magneto-optical recording medium can be applied. Further, the bias layer 4 is made of a material that does not cause magnetization reversal by recording / erasing / reproducing operations, for example, a RE-TM film having a lower sensitivity than the recording layer, B
An i-substituted garnet film, a Whistler alloy film, a FeBN film or the like is used.

The sensitivity lower than that of the recording layer means that the Curie temperature of the bias layer is higher than the Curie temperature of the recording layer, the thickness of the bias layer is thicker than the recording layer, the intermediate layer is the recording layer, This means that the bias layer has a thermal conductivity smaller than that of the bias layer, has a heat insulating function, and the temperature of the bias layer does not rise as much as that of the recording layer during laser irradiation, or a combination thereof.

It is preferable that the total thickness of the reproducing layer and the recording layer is thin enough to cause magnetization reversal when a recording level laser is irradiated. The bias layer may have a thickness that can generate sufficient Hb during laser irradiation. Here, Hb means a leakage magnetic field generated outside the bias layer by locally heating the bias layer by laser irradiation and generating a local magnetization distribution.

An initialization layer may be laminated adjacent to the bias layer so that exchange coupling is predominant. At this time, the exchange force acting from the initializing layer to the bias layer is HeIB, the exchange force acting from the bias layer to the initializing layer is HeBI, the coercive force of the bias layer is HcB, the coercive force of the initializing layer is HcI, and the bias layer. Letting the leakage magnetic field felt by the magnetic field be HaB and the leakage magnetic field sensed by the initialization layer be HaI, H at a temperature lower than the maximum temperature reached by the bias layer during the recording / erasing / reproducing process.
eIB + HaB is the same as the magnetization direction of the bias layer,
The bias layer and the initialization layer may be selected so that the following expression (1) is established in the bias layer and the following expression (2) is established in the initialization layer. HcB <| HeIB + HaB | ... (1) HcI> | HeBI + HaI | ... (2)

The initialization layer may be thick enough not to hinder the temperature rise of the recording medium due to laser irradiation. Further, it is preferable that the Curie temperature of the bias layer is lower than the maximum temperature reached by the bias layer at the time of reproduction because a large change in the leakage magnetic field distribution can be obtained.

The intermediate layer 3 is provided to eliminate the exchange force between the recording layer 2 and the bias layer 4. In addition, the protective layer 5
Is provided for scratching the medium,
The interference layer 6 is provided in order to enhance the reproduced signal by causing multiple interference when the laser beam is irradiated. The intermediate layer 3, the protective layer 5, and the interference layer 6 are Si-N, Si-O, and Zr- used in a usual magneto-optical recording medium.
Metal compound materials such as O, Al-O, Al-N, Zn-S, and Ti-O, metal compound materials to which a metal element or the like is added for purposes other than the present invention such as enhancing the protective function, and plasma polymerized films. Any non-magnetic material such as an organic material may be used as long as it has the translucency required for carrying out the present invention with respect to the wavelength of the laser used. Further, the intermediate layer 3 and the protective layer 5 do not necessarily have to have a light-transmitting property.

The reproducing layer 1, the recording layer 2, and the bias layer 4 may each be a single layer or a multilayer as long as they do not depart from the scope of the present invention. By providing an intermediate layer having a higher thermal conductivity than the reproducing layer, the recording layer, and the bias layer, it is possible to control the temperature rise of each layer so that the exchange force and the leakage magnetic field are appropriate. Further, by using a transparent dielectric layer as an intermediate layer, it is possible to play a role as an interference layer such as increasing the Kerr rotation angle and controlling the absorptance of each layer.

Further, the minimum requirement for the present invention is the reproducing layer 1, the recording layer 2 and the bias layer 4, and if the recording layer 2 and the bias layer 4 are laminated so that magnetostatic coupling is the main, they are intermediate. The layer 3 is not always necessary, and the intermediate layer 3 may be a recording layer whose surface is modified by oxidation or the like. Furthermore, as long as the reproducing layer 1 and the recording layer 2 are laminated so that exchange coupling is the main, another layer may exist between them. Also, the protective layer 5 and the interference layer 6 are not essential.

The substrate 7 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 8 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 first aspect of the present invention, the leakage magnetic field (excluding the external magnetic field Hex) sensed by the reproducing layer is set to Ha.
When the exchange force acting from the recording layer to the reproducing layer is represented by Hewr, it is preferably larger than the minimum value and smaller than the maximum value of Hewr + Har 'in the reproduction beam spot during Hex reproduction. This external magnetic field is not always necessary, and may be applied only during reproduction or may be applied during the entire recording / erasing / reproducing process.

The leakage magnetic field (excluding the external magnetic field Hex) sensed by the recording layer is obtained through the first and second aspects.
Is Haw ′, and the exchange force acting on the recording layer from the reproducing layer is He.
When rw and the coercive force of the recording layer are Hcw, an external magnetic field satisfying the following equation (3) may be applied to the recording layer during irradiation of the recording beam to assist the recording process. Hex + Haw '> Herw + Hcw (3) This external magnetic field may be applied only during the recording operation or continuously during the recording / reproducing operation as long as the reproducing operation can be sufficiently performed.

[0022]

In the magneto-optical recording medium according to the present invention, the reversed magnetic domain of the recording layer which has already been recorded according to desired recording information is transferred to the reproducing layer by laser irradiation during reproduction, and when the medium is cooled after the reproduction is completed, High density magneto-optical recording is performed by re-inverting the magnetic domain of the reproducing layer by the leakage magnetic field from the bias layer or both the bias layer and the initializing layer. Hereinafter, the recording / reproducing process in the first aspect of the present invention will be described in detail.

FIG. 2 shows the temperature dependence of the coercive force and exchange force of a typical recording layer and reproducing layer of the recording medium of the present invention. Figure 2
Where Hcw is the coercive force of the recording layer, Hcr is the coercive force of the reproducing layer, Hewr is the exchange force acting on the reproducing layer from the recording layer, and Hr
erw is the exchange force acting on the recording layer from the reproducing layer, Ta is room temperature, TR is the temperature of the medium during reproduction, and TW is the temperature of the medium during recording. In this case, the recording layer has a RE-rich composition without compensation temperature, and the reproducing layer has a TM-rich composition. FIG. 3 shows temperature dependence of coercive force and magnetization of a typical bias layer of the recording medium of the present invention.

FIG. 4 shows a reproducing operation when the magnetization of the recording layer is downward in the medium having the recording layer and the bias layer having the magnetic characteristics shown in FIGS. 2 and 3 and performing the operation of the first mode. It shows the position distribution of the medium temperature and the magnetic field sensed by the reproducing layer during operation. FIG. 4A shows the medium temperature, and TcB is the Curie temperature of the bias layer. The laser moves in the direction indicated by the arrow at the top of FIG. FIG. 4D shows the direction of magnetization of each layer. Reference numeral 1 is a reproducing layer, 2 is a recording layer, 3 is an intermediate layer, 4 is a bias layer, and arrows indicate the directions of magnetization of the layers.

FIG. 4B shows the exchange force Hewr acting on the reproducing layer from the recording layer and the leakage magnetic field HB from the bias layer.
And the position distribution of the sum of the externally applied magnetic field Hex is shown. Figure 4
(C) shows the position distribution of HB + Hex and the magnitude of the magnetic field for reversing the magnetization of the reproducing layer. In (b) and (c), the direction of the magnetic field for reversing the magnetization of the reproducing layer to the upper side in FIG. Since the recording layer is RE-rich and the reproducing layer is TM-rich, in the case of FIG. 4D, an interface magnetic wall exists between the reproducing layer and the recording layer and the exchange layer Hewr always acts on the reproducing layer. ing.

When the bias layer having the magnetic characteristics as shown in FIG. 3 is used, the leakage magnetic field generated by the bias layer is as shown in FIG.
As shown in (b), the distribution has a trapezoidal shape with shoulders when the temperature reaches TcB. The external magnetic field Hex is applied in the direction of shifting the HB distribution to the negative side. When the reproducing beam passes over the medium, as shown in FIG. 4 (c), the magnitude of HB + Hex at the center of the laser spot is a magnetic field Hcr-He for reversing the magnetization of the reproducing layer upward.
It becomes larger than wr and the magnetization of the reproducing layer is reversed. In the cooling process after passing through the laser, | HB + Hex | becomes larger than the magnetic field | Hcr + Hewr | for re-reversing the magnetization of the reproducing layer downward at the peripheral portion of the laser spot, and the reproducing layer is magnetized again. After passing through the laser, the state returns to that shown in FIG.

| HB + Hex | is | Hcr + Hewr |
Since the condition of being larger than the above condition is also established in the peripheral portion in the laser traveling direction (right side of FIG. 4C), the laser traveling is not affected by the initialization state of the magnetization of the reproducing layer. Along with this, the magnetization of the reproducing layer is reversed in the order of bottom->top-> bottom, and after passing through the laser, the state as shown in FIG.

The same thing will be described with reference to FIG. 5 when the magnetization of the recording layer is upward. Similar to Figure 4,
(A) is the temperature distribution, (b) is the magnetic field distribution, and (c) is the magnetization state of each layer. In the case of the magnetization state as shown in (c), there is no interface domain wall between the recording layer and the reproducing layer, and at the center of the laser spot, the magnitude of HB + Hex is a magnetic field for reversing the magnetization of the reproducing layer upward. The condition of becoming larger than Hcr + Hewr is not satisfied, and nothing happens (FIG. 5 (b)). Further, when the magnetization of the reproducing layer is upward, as shown in FIG. 5B, | HB + Hex | is a magnetic field that re-inverts the magnetization of the reproducing layer downward at the periphery of the laser spot in the traveling direction. It becomes larger than | Hcr + Hewr |, and the magnetization of the reproducing layer is aligned downward before passing through the spot central portion.

As shown in FIGS. 4 and 5, when reproducing is performed in the magneto-optical recording medium of the present invention, the recording layer is magnetized downward at the center of the reproduction spot regardless of the magnetization state of the reproduction layer. When the recording layer has an upward magnetization, the magnetization of the reproducing layer is inverted, and when the recording layer has an upward magnetization, the magnetization of the reproducing layer is downward. After passing through the laser spot, the magnetization of the reproducing layer is always downward.

The recording process using the above recording medium will be described with reference to FIG. Similar to FIG. 4D, FIG. 6 shows the magnetization state of each layer by an arrow, and when an inverted magnetic domain is formed in each layer, a vertical line is drawn at the position of the domain wall. Reference numeral 1 is a reproducing layer, 2 is a recording layer, 3 is an intermediate layer, and 4 is a bias layer.

FIG. 6A shows an initial magnetized state at room temperature Ta. When pulse irradiation with a high-power laser is performed on this, the medium temperature rises to Tw shown in FIGS. 2 and 3, and the magnetizations of the bias layer and the recording layer disappear at the center of the laser spot.
The magnetization state is as shown in (b). At this time, the external magnetic field He
When x is applied in the direction indicated by an arrow beside (b), an inverted magnetic domain is formed in the recording layer 2. The relationship between the magnetic properties at this time is that the leakage magnetic field sensed by the recording layer excluding the external magnetic field Hex is H
aw ′, Hex + Haw ′> Herw + Hcw in the recording layer in the recording beam spot.

Is satisfied. After the laser irradiation, when the medium temperature becomes close to TR in the cooling process, the magnetization of the reproducing layer is inverted upward as shown in FIG. 4, and the magnetic domain of the recording layer is transferred to the reproducing layer. After that, in the cooling process up to Ta, if the state of the peripheral portion of FIG. 4C is maintained, the state becomes a magnetization state in which the inverted magnetic domain is formed only in the recording layer as shown in FIG. 5D.

However, in the recording process, it suffices that an inverted magnetic domain is formed in the recording layer, and the magnetization of the reproducing layer may be in any state. This is because the initial magnetization state of the reproducing layer does not affect the reproducing process as shown below. Further, since the self-leakage magnetic field of the recording layer is in the same direction as Hex in the figure, Hex is not always necessary if the self-leakage magnetic field is large. The erasing process can be performed in the same manner as this recording process.

Next, the reproducing process will be described with reference to FIG.
Similar to FIGS. 4D and 6, FIG. 7 shows the magnetization state of each layer by an arrow, and when an inverted magnetic domain was formed in each layer, a vertical line was drawn at the position of the domain wall. 1 is a reproduction layer, 2
Is a recording layer, 3 is an intermediate layer, 4 is a bias layer, and 8 is a reproducing beam. The playback beam moves from left to right.

FIG. 7A shows the state of magnetization at room temperature, and FIG.
Inversion magnetic domains generated according to the above process exist in the recording layer. For the sake of explanation, it is assumed that the magnetization of the reproducing layer is uniformly magnetized downward. When the reproducing level laser is irradiated, the medium temperature rises to TR, and the magnetization disappears at the center of the laser spot in the bias layer (FIG. 7B).

When the reproducing beam passes through the region where the inverted magnetic domain does not exist in the recording layer, the magnetization of the reproducing layer remains downward at the center of the laser spot as shown in FIG. When the reproducing laser beam hits the inverted magnetic domain of the recording layer, the magnetization of the reproducing layer is reversed at the center of the laser spot and in the region where the magnetization of the recording layer is upward. As it is (Fig. 7)
(C)).

When the reproducing laser beam is just above the inversion magnetic domain of the recording layer, the magnetization of the reproducing layer is inverted only at the center of the laser spot (FIG. 7 (d)). When the laser beam slightly passes over the inversion domain of the recording layer, the magnetization of the reproducing layer starts to be reinverted in the rear part of the laser spot (peripheral part in FIG. 6) (FIG. 7 (e)). When the laser beam passes over the reversed magnetic domain of the recording layer, the reproducing layer is all magnetized in the downward direction and returns to the initial magnetized state (FIGS. 7F and 7G).

Whatever the initial magnetization state of the reproducing layer is, once it is aligned downward at the peripheral portion in the direction of travel of the laser beam, as shown in FIGS. The steps (g) to (g) are the same. In the central portion of the laser spot, the reproducing layer also has the reversing magnetic domain in the region having the reversing magnetic domain in the recording layer, so that the above reproducing process is the same as the reproducing process of the usual magneto-optical recording medium when viewed from the laser beam side. Next, the recording / erasing process in the second aspect of the present invention will be described in detail. Also in the second mode, the recording layer and the bias layer have the magnetic characteristics shown in FIGS.

FIG. 8 shows a reproducing operation when the magnetization of the recording layer is downward in the medium having the recording layer and the bias layer having the magnetic characteristics shown in FIGS. 2 and 3 and performing the operation of the second mode. It shows the position distribution of the medium temperature and the magnetic field sensed by the reproducing layer during operation.

FIG. 8A shows the medium temperature, TcB shows the Curie temperature of the bias layer, the solid line shows the temperature of the reproducing layer, and the dotted line shows the temperature of the bias layer. A phase difference occurs in the temperature distribution between the reproducing layer and the bias layer because the reproducing layer, the recording layer, and the bias layer are thick, or due to the heat insulating action of the intermediate layer. FIG. 8B shows the distribution of the exchange force Hewr acting from the recording layer to the reproducing layer and the leakage magnetic field HB from the bias layer.

FIG. 8D shows the direction of magnetization of each layer. Similar to FIG. 4D, 1 is a reproducing layer, 2 is a recording layer, 3 is an intermediate layer, 4 is a bias layer, and arrows indicate the directions of magnetization of the layers. Since the recording layer is RE-rich and the reproducing layer is TM-rich,
In the case of FIG. 8D, an interface domain wall exists between the reproducing layer and the recording layer, and the exchange force Hewr always acts on the reproducing layer.

FIG. 8C shows HB + Hex, and a magnetic field Hcr-Hewr for reversing the magnetization of the reproducing layer upward from the state of FIG. 8D, and remagnetization reversing the magnetic field Hcr-Hewr. Magnetic field required to return to the state- | Hcr + He
The distribution of wr | is shown. Here, the magnetization of the reproducing layer is shown in FIG.
The direction of the magnetic field to be inverted above (d) was set to be positive. The laser moves in the direction shown by the arrow in the upper part of FIG.

When the bias layer having the magnetic characteristics as shown in FIG. 3 is used, the leakage magnetic field generated by the bias layer is as shown in FIG.
As shown in (b), the trapezoidal distribution has a shoulder when the temperature reaches TcB. The external magnetic field Hex is shown in FIG.
When applied upward in (d), the distribution of Hex + HB is as shown in FIG. 8 (c). When the reproducing beam passes over the medium, at the center of the laser spot, the magnitude of HB + Hex is the magnetic field Hc for reversing the magnetization of the reproducing layer upward.
It becomes larger than r-Hewr, and the magnetization of the reproducing layer is reversed.

However, after the center of the laser spot has passed, at the peripheral portion of the laser spot, | HB + Hex | causes a magnetic field | Hcr for reversing the magnetization of the reproducing layer downward.
It becomes larger than + Hewr |, the magnetization of the reproducing layer is inverted again, and after the laser passes, the state returns to the state shown in FIG. 8D.

The same thing will be described with reference to FIG. 9 when the magnetization of the recording layer is upward. Similar to FIG.
(A) is the temperature distribution, (b) is the magnetic field distribution, and (c) is the magnetization state of each layer. In the case of the magnetization state as shown in (c), there is no interface domain wall between the recording layer and the reproducing layer, and at the center of the laser spot, the magnitude of HB + Hex is a magnetic field for reversing the magnetization of the reproducing layer upward. The condition of becoming larger than Hcr + Hewr is not satisfied, and the magnetization reversal does not occur. However, after the center of the laser spot has passed, the condition that HB + Hex | becomes larger than the magnetic field | Hcr + Hewr | that re-inverts the magnetization of the reproducing layer downward at the peripheral portion of the laser spot is satisfied.

In order to establish the operation shown in FIGS. 8 and 9, the laser travels on the track in the vicinity of the peak of HB rather than in the vicinity of the lowest Hcr, that is, near the highest temperature in the recording layer. Must be backwards with respect to direction. Since the peak of HB is often near the highest temperature in the bias layer, the position on the track where the highest temperature in the bias layer is
It is preferable that the recording layer is located rearward with respect to the laser traveling direction on the track rather than the position where the temperature is highest.

FIG. 10 shows a recording process using the above recording medium.
Will be explained. FIG. 10 shows the state of magnetization of each layer by arrows, as in FIG. 6, and the reference numerals shown therein are also the same as in FIG. Further, when a reversed magnetic domain was formed, a vertical line was drawn at the position of the domain wall.

FIG. 10A shows an initial magnetized state at room temperature Ta. When a pulse of a high-power laser is applied to this, the medium temperature rises to Tw shown in FIGS. 2 and 3, the magnetization disappears in the high temperature portion of both the recording layer and the reproducing layer, and the maximum temperature T
At max, the magnetization state is as shown in (b). At this time, when an external magnetic field Hex is applied in the direction indicated by the arrow beside (b), an inverted magnetic domain is formed in the recording layer. The relationship between the respective magnetic characteristics at this time is that the leakage magnetic field sensed by the recording layer excluding the external magnetic field Hex is Haw ′, and within the recording beam spot,
Hex + Haw ′> Herw + Hcw in the recording layer

Is established. After the laser irradiation, when the medium temperature becomes close to TR in the cooling process, the magnetization of the reproducing layer is inverted upward as shown in FIG. 8, and the magnetic domain of the recording layer is transferred to the reproducing layer. Thereafter, in the cooling process up to Ta, Hex + Har '> Hcr + Hewr is established in the reproducing layer, the reproducing layer is remagnetized and reversed, and when returning to room temperature, it becomes as shown in FIG. The erasing process can be performed in the same manner as this recording process.

Next, the reproducing process will be described with reference to FIG. 11, the state of magnetization of each layer is shown by an arrow, as in FIG. 7, and the reference numerals shown therein are also the same as in FIG. 7. Further, when a reversed magnetic domain was formed, a vertical line was drawn at the position of the domain wall. The reproduction beam moves from left to right.

FIG. 11A shows a state of magnetization at room temperature, in which the reversed magnetic domain generated according to the process of FIG. 10 exists in the recording layer. The magnetization of the reproducing layer is uniformly magnetized downward. When the reproducing level laser is irradiated, the medium temperature rises to TR, and the medium disappears in the high temperature portion deviated from the center portion of the laser spot in the bias layer (FIG. 11B).

When the reproducing beam passes through the region where the reversed magnetic domain does not exist in the recording layer, the magnetization of the reproducing layer remains downward at the center of the laser spot as shown in FIG. When the reproducing laser beam hits the reversed magnetic domain of the recording layer, the reproducing layer magnetization is reversed only in the central portion of the laser spot and in the region where the recording layer magnetization is downward, and the magnetization direction of the other portions is reversed. Remains the same (Fig. 11)
(C)).

When the reproducing laser beam reaches just above the inversion magnetic domain of the recording layer, the magnetization of the reproducing layer is inverted only in the central portion of the laser spot (FIG. 11 (d)). When the laser beam slightly passes over the inversion domain of the recording layer, the leakage magnetic field from the bias layer causes a re-inversion of the magnetization of the reproducing layer in the rear portion of the laser spot (see FIG. 9). 11 (e)). When the laser beam passes over the reversed magnetic domain of the recording layer, the reproducing layer is entirely magnetized in the downward direction and returns to the initial magnetized state at room temperature (FIGS. 11F and 11G). In the central portion of the laser spot, the reproducing layer also has the reversing magnetic domain in the region having the reversing magnetic domain in the recording layer, so that the above reproducing process is the same as the reproducing process of the usual magneto-optical recording medium when viewed from the laser beam side.

By using this recording medium, high-density magneto-optical recording can be realized. That is, even if the recording bits are formed in the recording layer with a bit density such that the crosstalk is large in ordinary magneto-optical recording and a sufficient reproduction signal output cannot be obtained,
When reproducing, magnetic domains in regions other than the central portion of the laser spot are not transferred onto the reproducing layer, and adjacent recording bits are not detected as a signal, so crosstalk does not occur. In addition, since the recording medium of the present invention aligns (initializes) the magnetization of the reproducing layer downward after passing through the reproducing laser spot, another high density recording medium (nikkei electr).
onics 1991.3.4 No. 521p. 92), which does not require an initialization magnet different from Hex, and can realize higher density in the disc track direction, which was not possible with the above high-density recording medium.

In the above description, the reproducing layer and the recording layer have a composition combination such that the interface domain wall is not generated when the magnetization directions are opposite, but the interface domain wall is not generated when the magnetization direction is the same. Even in such combinations, the same recording / reproducing can be performed by changing the magnetization direction of the bias layer according to the transfer direction of the magnetic domain.

As shown in FIG. 3, when a bias layer having a magnetic characteristic with a low Curie temperature is used, the medium is heated to TcB or higher during the reproducing / recording process, and the bias layer undergoes magnetization reversal. There is a possibility that the leakage magnetic field distribution shown in will not be obtained. To prevent the magnetization reversal of the bias layer,
Increase the thickness of the bias layer to provide a temperature difference in the thickness direction,
The surface of the bias layer opposite to the recording layer is kept at a low temperature, or a thermal diffusion layer such as an Al film is provided on the surface of the bias layer opposite to the recording layer, and the surface provided with the thermal diffusion layer is kept at a low temperature. Or an exchange coupling two-layer film with a high Curie temperature and magnetization reversal that is hard to reverse magnetization, or a combination of the above three methods.

In the method using the exchange coupling two-layer film with the initializing layer, the initializing layer does not undergo magnetization reversal in all the processes of recording, reproducing and erasing, and the exchange force exerted on the bias layer causes recording, erasing and reproducing. In all the steps of (3), the bias layer is laminated so as to be large enough not to cause magnetization reversal.

Typical magnetic characteristics of the bias layer and the initialization layer of the recording medium of the present invention are shown in FIGS. In these figures, HcI is the coercive force of the initialization layer, HcB is the coercive force of the bias layer, HeIB is the exchange force acting from the initialization layer to the bias layer, HeBI is the exchange force acting from the bias layer to the initialization layer, TR is the medium temperature during reproduction, TW is the medium temperature during recording, MsI is the magnetization of the initialization layer, and MsB is the magnetization of the bias layer. The bias layer has a TM-rich composition and the initialization layer has a RE-rich composition having a compensation temperature. When the magnetization of each layer is in the opposite direction, the interface domain wall is not generated and is stable.

As is clear from FIG. 12, since HeIB is larger than HcB at all temperatures and the magnetization direction of the bias layer is aligned with the direction of the initialization layer, no inversion domain can be formed in the bias layer. Even if the leakage magnetic field HaB from other magnetic layers including the externally applied magnetic field Hex is in the direction of inverting the bias layer, | HaB | <| HeIB | and HcB <| HaB + HeIB |

As long as the following is true, the bias layer does not undergo magnetization reversal. Since an exchange force may act between the initialization layer and the bias layer, even if the bias layer and the initialization layer have a combination in which the interface domain wall does not exist when the magnetizations are in the same direction, the magnetizations are reversed. The combination may be such that the interface domain wall does not exist when facing.

FIG. 14 shows a typical sectional structure of the magneto-optical recording medium of the present invention when an initialization layer is used. Reference numeral 1 is a reproducing layer, 2 is a recording layer, 3 is an intermediate layer, 4 is a bias layer, 5 is a protective layer, 6 is an interference layer, 7 is a substrate, and 9 is an initialization layer. Either the bias layer or the initialization layer may be stacked first. However, the bias layer is preferably closer to the recording layer from the viewpoint of applying a larger leakage magnetic field to the recording layer and the effect of suppressing the temperature rise of the initialization layer and preventing the magnetization reversal of the bias layer.

FIG. 15A shows the magnetization direction of each layer in the case of the first mode. Note that the reference numerals are the same as in FIG.
Is the same as. When the temperature distribution shown in FIG. 15B is generated, the magnetization distribution of the initialization layer is as shown in FIG. 15C, and the magnetization distribution of the bias layer is as shown in FIG. 15D. At this time, the leakage magnetic field of the initialization layer tends to prevent the magnetization reversal of the bias layer, and can assist the reversal prevention action by the exchange force. Further, since the initialization layer is far from the recording layer and the magnetization distribution is gentler than that of the bias layer, the leakage magnetic field from the initialization layer that the recording layer feels is small in size and has a gentle distribution. The direction is opposite to the leakage magnetic field.

Therefore, the leakage magnetic field from the bias layer and the initialization layer becomes the same as that in FIG. 4C, and by appropriately selecting Hex, the recording / reproducing process similar to that shown in FIGS. Can be realized. If the magnitude of the leakage magnetic field from the initializing layer to the recording layer and the reproducing layer is sufficiently large, FIG.
The external magnetic field that shifts the leakage magnetic field from the bias layer to the positive side can be replaced with the leakage magnetic field generated from the initialization layer. Thus, the composition of the initialization layer is preferably such that the interface domain wall is not generated when the magnetization is in the opposite direction to that of the bias layer.

FIG. 16A shows the magnetization direction of each layer in the case of the second mode. Note that the reference numerals are the same as those in FIG.
It is similar to (a). When the temperature distribution as shown in FIG. 16B is generated, the magnetization distribution of the initialization layer is as shown in FIG.
The magnetization distribution of the bias layer is as shown in (d). At this time, similarly to the first aspect, the leakage magnetic field of the initialization layer tends to prevent the magnetization reversal of the bias layer, and can assist the reversal prevention action by the exchange force. Further, since the initialization layer is far from the recording layer and the magnetization distribution is gentler than that of the bias layer, the leakage magnetic field from the initialization layer that the recording layer feels is small in size and has a gentle distribution. The direction is opposite to the leakage magnetic field.

Therefore, the leakage magnetic field from the bias layer and the initialization layer becomes the same as that in FIG. 8C, and by appropriately selecting Hex, the recording / reproducing process similar to that shown in FIGS. Can be realized. If the magnitude of the leakage magnetic field from the initialization layer to the recording layer and the reproducing layer is sufficiently large,
The external magnetic field that shifts the leakage magnetic field from the bias layer as shown in (b) to the positive side can be replaced with the leakage magnetic field generated from the initialization layer. Thus, the composition of the initialization layer is preferably such that the interface domain wall is not generated when the magnetization is in the opposite direction to that of the bias layer.

[0066]

EXAMPLES Examples of the present invention will be described below. (Example-1)

On the Si wafer, a 100 nm thick Si--N interference layer, 25 was formed by magnetron sputtering.
nm thick Tb _0.29 (Fe _0.9 Co _0.1 ) _0.71 recording layer, 15
nm thick Si-N intermediate layer, 200 nm thick Tb _0.16 (Fe
_0.95 Co _0.05 ) _0.84 bias layer, 200 nm thick Tb _0.22
(Fe _0.5 Co _0.5 ) _0.78 initialization layer, 20 nm thick Si-
N protective layers were sequentially laminated. The dielectric layer was formed by reactive sputtering of a Si ₃ N ₄ target, and the magnetic layer was formed by ternary simultaneous sputtering of Tb, Fe and Co. Bias layer is TM
Rich, the initialization layer was RE rich. Bias layer,
Both the initialization layer had perpendicular magnetic anisotropy, and its magnetic characteristics were as shown in FIGS. The bias layer has a magnetization of 160 emu / cc at room temperature, a Curie temperature of 150 ° C., a coercive force of 2 kOe at room temperature, and the initialization layer has a magnetization of 100 emu / c at room temperature.
c, compensation temperature 120 ° C., Curie temperature 400 ° C. or higher, room temperature coercive force 3 kOe. The recording layers are stacked to evaluate the generated leakage magnetic field, and have a coercive force of 5 kOe at room temperature.
The Curie temperature was 170 ° C. The leakage magnetic field generated by this bias layer was calculated by numerical calculation. 1.6μ
When the leakage magnetic field sensed at the position of the recording layer was calculated from the temperature distribution when 6 mW laser light of wavelength 830 nm focused on m was continuously irradiated at a linear velocity of 8 m / s, the leakage magnetic field distribution from the bias layer was The shape is as shown in (b), the shoulder part is 325 Oe, the bottom part is 64 Oe, and the shoulder width is about 200 nm.
Met. Further, the sum of the leakage magnetic fields from the initialization layer has a distribution as shown in FIG. 4B, but is negatively biased by the gentle leakage magnetic field distribution based on the gradual magnetization change of the initialization layer. The shoulder area 20
It was 5 Oe, the bottom portion was -40 Oe, and the shoulder width was about 200 nm. In addition, when the magneto-optical recording characteristics of the recording layer were examined, it was found that the threshold value of the recording magnetic field changed by about 300 Oe due to the presence of the bias layer and the initialization layer, and a leakage magnetic field of about 300 Oe at the peak value was generated. Was done. Further, the exchange force acting from the initialization layer to the bias layer is always larger than the coercive force of the bias layer up to the Curie temperature of the bias layer, and the external magnetic field in the direction of reversing the bias layer is 15 mW and 160 nsec in the range of -1 kOe to 500 Oe. Even when the recording operation by pulse irradiation was performed, the inversion domain was not formed in the bias layer. (Example-2)

On a glass disk substrate without a groove having a thickness of 1.2 mm, 1 was formed by a magnetron sputtering method.
00nm thick Si-N interference layer, 200nm thick Tb
_0.195 (Fe _0.9 Co _0.1 ) _0.805 reproducing layer, 200 nm thick Tb _0.16 (Fe _0.95 Co _0.05 ) _0.84 bias layer, 20
0 Tb _0.22 (Fe _0.5 Co _0.5 ) _0.78 initialization layer, 2
A 0 nm thick Si-N protective layer was sequentially laminated. Dielectric layer is S
Reactive sputtering of i ₃ N ₄ target, magnetic layer is Tb
And Fe and Co were simultaneously sputtered. The bias layer and the initialization layer are the same as those in the first embodiment. Both the recording layer and the reproducing layer had perpendicular magnetic anisotropy, and the magnetic characteristics were as shown in FIG. The reproducing layer has a coercive force of 6 kOe at room temperature and a Curie temperature of 400 ° C or higher, the recording layer has a coercive force of 15 kOe at room temperature and a Curie temperature of 200 ° C, and the exchange force acting on the reproducing layer from the recording layer is 2.5 kOe at room temperature. The intersection with the magnetic force was 90 ° C.

A magnetic field of 1 kOe was applied downward to the recording medium at a linear velocity of 8 m / s in FIG. 6 to irradiate a recording pulse of 10 mW and 160 ns, and the recording layer had a bit interval of 0.6 μm.
A recording magnetic domain having a track interval of 0.6 μm was formed. When a magnetic field of 100 Oe was applied downward in FIG. 7 to perform reproduction with a power of 5 mW, reproduction could be performed without crosstalk. (Example-3)

A sample having the same medium structure as in Example 2 was prepared, in which only the thickness of the reproducing layer and the recording layer was set to 150 nm. The exchange force acting from the recording layer to the reproducing layer was 4 kOe at room temperature, and the intersection with the coercive force of the reproducing layer was 140 ° C. This recording medium was recorded downward in FIG. 7 in an applied magnetic field of 100 Oe at a linear velocity of 8 m / s at 15 mW and 160 ns and reproduced at 6 mW in the same applied magnetic field. Recording magnetic domains with a bit interval of 0.6 μm and a track interval of 0.6 μm could be reproduced without crosstalk. (Example-4)

A sample having the same medium structure as in Example 2 except that the thickness of the bias layer was 300 nm was prepared. This recording medium is directed upward in FIG. 7 in a magnetic field of 800 Oe, at a linear velocity of 8 m / s, to an erasing level of continuous irradiation of 8 mW of 160 ns and 15 mW.
By irradiating the signal with the pulse irradiation of the recording level, we could realize the optical power modulation overwrite which can record / erase only by selecting the irradiation power without changing the magnitude of the external magnetic field. Furthermore, when a magnetic field of 200 Oe was applied downward in FIG. 7 and reproduction was performed with a power of 7 mW, a bit interval of 0.6 μm and a track interval of 0.6 μm.
The recording domain of μm could be reproduced without crosstalk. (Example-5)

On a glass disk substrate without a groove having a thickness of 1.2 mm, 1 was formed by a magnetron sputtering method.
00nm thick Si-N interference layer, 200nm thick Tb
_0.195 (Fe _0.9 Co _0.1 ) _0.805 recording layer, 200 nm thick Tb _0.254 (Fe _0.7 Co _0.3 ) _0.746 recording layer, 15
nm thick Si-N intermediate layer, 200 nm thick (Gd _0.5 Tb
_0.5 ) _0.225 (Fe _0.5 Co _0.5 ) _0.775 Bias layer,
A 20 nm thick Si-N protective layer was sequentially laminated. The dielectric layer is reactively sputtered with a Si ₃ N ₄ target, and the magnetic layer is T
It was created by ternary simultaneous sputtering of b, Fe and Co.
The reproducing layer has a coercive force of 6 kOe at room temperature and a Curie temperature of 400 ° C or higher, and the recording layer has a coercive force of 15 kOe at room temperature and a Curie temperature of 2
It was 00 ° C. The exchange force acting from the recording layer to the reproducing layer is 2.5 kOe at room temperature, and the intersection with the coercive force of the reproducing layer is 9
It was 0 ° C. The bias layer has a room temperature magnetization of 100 emu / cc,
The compensation temperature was 110 ° C., the Curie temperature was 400 ° C. or higher, and the coercive force at room temperature was 10 kOe.

The recording medium magnetized as shown in FIG. 10A was recorded by applying a magnetic field of 800 Oe downward in FIG. 10 at a linear velocity of 8 m / s and irradiating a recording pulse of 10 mW and 160 ns. The layer has a bit interval of 0.6 μm and a track interval of 0.
A recording magnetic domain of 6 μm was formed. When a magnetic field of 150 Oe was applied upward in FIG. 11 and reproduction was performed with a power of 5 mW, reproduction could be performed without crosstalk. (Example-6)

On a glass disk substrate without a groove having a thickness of 1.2 mm, 1 was formed by a magnetron sputtering method.
00 nm thick Si-N interference layer, 150 nm thick Tb
_0.195 (Fe _0.9 Co _0.1 ) _0.805 reproducing layer, 200 nm thick Tb _0.254 (Fe _0.7 Co _0.3 ) _0.746 recording layer, 15
nm thick Si-N intermediate layer, 200 nm thick (Gd _0.5 Tb
_0.5 ) _0.175 (Fe _0.97 Co _0.03 ) _0.825 bias layer,
200 nm thick (Gd _0.5 Tb _0.5 ) _0.225 (Fe _0.5 C
o _0.5 ) _0.775 initializing layer and a 20 nm thick Si-N protective layer were sequentially laminated. The reproducing layer had a coercive force of 6 kOe at room temperature and a Curie temperature of 400 ° C. or higher, and the recording layer had a coercive force of 15 kOe at room temperature and a Curie temperature of 200 ° C. The exchange force acting from the recording layer to the reproducing layer was 4 kOe at room temperature, and the point of intersection with the coercive force of the reproducing layer was 140 ° C. The bias layer has a room temperature magnetization of 150 emu / cc, a Curie temperature of 210 ° C., and a room temperature coercive force of 1.3 kOe. The initialization layer has a room temperature magnetization of 100 emu / cc, a compensation temperature of 110 ° C., a Curie temperature of 400 ° C. or higher, and a room temperature coercive force. It was 10 kOe. This recording medium was magnetized as shown in FIG. 16A, and recording operation was performed at a linear velocity of 8 m / s at 15 mW and 160 ns in the downward applied magnetic field of 500 Oe in FIG. , Track spacing 0.6 μm
Recording magnetic domains were formed. This is 10 upwards in FIG.
With a power of 6 mW in an applied magnetic field of 0 Oe, reproduction was possible without crosstalk.

[0075]

According to the present invention, high-density magneto-optical recording is possible without requiring an initialization magnet other than an external magnetic field at the time of recording, and high-density recording can be performed in the disc track direction. It is possible to easily increase the storage capacity of the magneto-optical disk.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a magneto-optical recording medium according to the present invention.

FIG. 2 is a diagram showing the coercive force of the recording layer and the reproducing layer, and the temperature dependence of the exchange force acting between these layers.

FIG. 3 is a diagram showing temperature dependence of coercive force and magnetization of a bias layer.

FIG. 4 is a diagram showing the position distribution of the sum of the medium temperature, the leakage magnetic field, the exchange force and the coercive force of the reproducing layer when the magnetization directions of the recording layer and the reproducing layer are the same in the first mode.

FIG. 5 is a diagram showing the position distribution of the sum of the medium temperature, the leakage magnetic field, the exchange force and the coercive force of the reproducing layer when the magnetization directions of the recording layer and the reproducing layer are different in the first mode.

FIG. 6 is a diagram showing a magnetization state of each layer in the recording process in the first mode.

FIG. 7 is a diagram showing a magnetization state of each layer in the reproducing process in the first mode.

FIG. 8 is a diagram showing a position distribution of the sum of the medium temperature, the leakage magnetic field, the exchange force and the coercive force of the reproducing layer when the magnetization directions of the recording layer and the reproducing layer are the same in the second mode.

FIG. 9 is a diagram showing the position distribution of the sum of the medium temperature, the leakage magnetic field, the exchange force and the coercive force of the reproducing layer when the magnetization directions of the recording layer and the reproducing layer are different in the second mode.

FIG. 10 is a diagram showing a magnetization state of each layer in the recording process in the second mode.

FIG. 11 is a diagram showing a magnetization state of each layer in the reproducing process in the second mode.

FIG. 12 is a diagram showing the coercive force of the bias layer and the initialization layer, and the temperature dependence of the exchange force acting on each of these layers.

FIG. 13 is a diagram showing temperature dependence of magnetization of a bias layer and an initialization layer.

FIG. 14 is a sectional view showing an example of a magneto-optical recording medium when an initialization layer is used.

FIG. 15 is a diagram showing a position distribution of medium temperature, magnetization of an initialization layer, and magnetization of a bias layer in the first mode.

FIG. 16 is a diagram showing a position distribution of medium temperature, magnetization of an initialization layer, and magnetization of a bias layer in a second mode.

[Explanation of symbols]

1; reproducing layer, 2; recording layer, 3; intermediate layer, 4; bias layer, 5; protective layer, 6; interference layer, 7; substrate, 8; laser beam, 9; initialization layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yumi Mizusawa 70 Yanagimachi, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Toshiba Yanagimachi Factory

Claims (2)

[Claims] 1. A magneto-optical recording medium having a reproducing layer, a recording layer, and a bias layer each made of a magnetic material, wherein the reproducing layer, the recording layer, and the bias layer are laminated in this order from the laser incident side. Layered so that exchange coupling is the main with the recording layer,
A magneto-optical device characterized in that the recording layer and the bias layer are laminated so that the magneto-static coupling is mainly present, and the magnetization is not reversed at a temperature lower than the maximum temperature reached by the bias layer in the recording / erasing / reproducing process. recoding media. 2. A magneto-optical recording medium having a reproducing layer, a recording layer, and a bias layer made of a magnetic material, wherein the reproducing layer, the recording layer, and the bias layer are laminated in this order from the laser incident side. Layered so that exchange coupling is the main with the recording layer,
The recording layer and the bias layer are laminated such that magnetostatic coupling is the main, and the bias layer does not undergo magnetization reversal at a temperature equal to or lower than the maximum temperature reached in the recording / erasing / reproducing process,
When the maximum temperature TR of the medium reached at the time of reproduction is set, when the magnetization of the bias layer has a characteristic of decreasing from room temperature to TR, the bias layer is magnetized in the direction opposite to the magnetization direction of the reproduction layer. A magneto-optical recording medium, wherein the bias layer is magnetized in the same direction as the magnetization direction of the reproducing layer when the magnetization of the bias layer increases from room temperature to TR.