JPH06290496A - Magneto-optical recording medium, reproducing method and reproducing device - Google Patents

Abstract

PURPOSE:To greatly improve a recording density and transfer speed and to miniaturize the reproducing device by enabling the reproduction of signals of periods below the diffraction threshold of light at a high speed without lowering the amplitude of the reproduced signals. CONSTITUTION:A first magnetic layer 11, a second magnetic layer 12 and a third magnetic layer 13 are successively laminated. This first magnetic layer 11 is relatively smaller in the coercive force of magnetic walls than the third magnetic layer and is larger in the mobility of the magnetic walls. The second magnetic layer 12 is lower in Curie temp. than the first magnetic layer and the third magnetic layer. Further, a fourth magnetic layer may be formed between the first magnetic layer and the second magnetic layer. The magnetic walls 15 are moved backward by heating TS.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording / reproducing information with a laser beam by utilizing the magneto-optical effect, and more particularly to a magneto-optical recording which enables high density recording of the medium. The present invention relates to a medium, a reproducing method, and a reproducing device.

[0002]

2. Description of the Related Art As a rewritable high density recording system,
Using the thermal energy of a semiconductor laser to write magnetic domains in a magnetic thin film to record information, using the magneto-optical effect,
Attention has been paid to a magneto-optical recording medium for reading this information.
Further, in recent years, there is an increasing demand for increasing the recording density of this magneto-optical recording medium to make it a recording medium having a larger capacity.

The linear recording density of an optical disk such as a magneto-optical recording medium greatly depends on the laser wavelength of the reproducing optical system and the numerical aperture of the objective lens. That is, since the diameter of the beam waist is determined when the laser wavelength λ of the reproduction optical system and the numerical aperture NA of the objective lens are determined, the spatial frequency during signal reproduction is 2
NA / λ is the limit of detection.

Therefore, in order to realize high density in the conventional optical disk, it is necessary to shorten the laser wavelength of the reproducing optical system and increase the numerical aperture NA of the objective lens.
However, there is a limit to the improvement of the laser wavelength and the numerical aperture of the objective lens. Therefore, a technique for improving the recording density by devising the configuration of the recording medium and the reading method has been developed.

For example, in Japanese Patent Laid-Open No. 3-93058, signal recording is performed on a recording holding layer of a multilayer film having a reproducing layer and a recording holding layer which are magnetically coupled,
A signal reproducing method has been proposed in which, after aligning the magnetization directions of the reproducing layer, laser light is irradiated to heat the reproducing layer, and the signal recorded in the recording holding layer is read while being transferred to a temperature rising region of the reproducing layer.

According to this method, the area where the laser is heated by the laser to reach the transfer temperature and the signal is detected can be limited to a smaller area with respect to the spot diameter of the reproducing laser. It is possible to reduce inter-interference and reproduce a signal having a period less than the diffraction limit of light.

[0007]

However, in the magneto-optical reproducing method described in Japanese Patent Laid-Open No. 3-93058, the signal detection area that is effectively used becomes smaller than the spot diameter of the reproducing laser. It has a drawback that the signal amplitude is greatly reduced and a sufficient reproduction output cannot be obtained.

Further, the magnetization of the reproducing layer must be aligned in one direction before being irradiated with laser light. Therefore, it is necessary to add a reproducing layer initialization magnet to the conventional device. Therefore, the reproducing method has problems that the magneto-optical recording device is complicated, the cost is high, and it is difficult to reduce the size.

The present invention has been made to solve the problems of the prior art. That is, the object of the present invention is to
A magneto-optical recording medium and a reproducing method capable of reproducing a signal having a period equal to or shorter than the light diffraction limit at high speed without lowering the reproduction signal amplitude, greatly improving the recording density and the transfer speed, and enabling downsizing of the reproducing apparatus. And to provide a playback device.

[0010]

The above object can be achieved by the present invention described below.

The first magneto-optical recording medium of the present invention is a magneto-optical recording medium in which at least a first magnetic layer, a second magnetic layer and a third magnetic layer are sequentially laminated, and the first magnetic layer comprises: At a temperature near the ambient temperature, it is composed of a perpendicular magnetic film having a domain wall coercive force relatively smaller than that of the third magnetic layer and a large domain wall mobility, and the second magnetic layer comprises the first magnetic layer and the third magnetic layer. Magnetic layer having a lower Curie temperature than the magnetic layer of
The magnetic layer is a perpendicular magnetization film, which is a magneto-optical recording medium.

The second magneto-optical recording medium of the present invention is a magneto-optical recording medium in which at least first, fourth, second and third magnetic layers are sequentially laminated, and the first magnetic layer The layer is composed of a perpendicularly magnetized film having a domain wall coercive force relatively smaller than that of the third magnetic layer at a temperature near the ambient temperature, and the second magnetic layer includes the first magnetic layer and the third magnetic layer. The magnetic layer has a Curie temperature lower than that of the magnetic layer, the third magnetic layer is a perpendicular magnetization film, the fourth magnetic layer is higher than the second magnetic layer, and the first magnetic layer is higher than the second magnetic layer. A perpendicular magnetic film having a lower Curie temperature and having a domain wall coercive force relatively smaller than that of the third magnetic layer at a temperature of at least the Curie temperature of the second magnetic layer. And a magneto-optical recording medium.

The first reproducing method of the present invention is the first reproducing method of the present invention.
A method of reproducing recorded information from a magneto-optical recording medium, the method comprising irradiating a light beam from the side of the first magnetic layer while moving the light beam relative to the medium, and applying the light beam onto the medium. By forming a temperature distribution having a gradient with respect to the moving direction of the spot and making the temperature distribution a temperature distribution having at least a temperature region higher than the Curie temperature of the second magnetic layer, the first magnetic layer is formed. The reproducing method is characterized in that the formed domain wall is moved and the change in the polarization plane of the reflected light of the light beam is detected to reproduce the recorded information.

The second reproducing method of the present invention is the second reproducing method of the present invention.
A method of reproducing recorded information from a magneto-optical recording medium, the method comprising irradiating a light beam from the side of the first magnetic layer while moving the light beam relative to the medium, and applying the light beam onto the medium. A temperature distribution having a gradient with respect to the moving direction of the spot is formed, and the temperature distribution is higher than at least the Curie temperature of the second magnetic layer and has a temperature region near the Curie temperature of the fourth magnetic layer. By setting the temperature distribution, the domain walls formed in the first and fourth magnetic layers are moved, the change of the polarization plane of the reflected light of the light beam is detected, and the recorded information is reproduced. This is the playback method.

The reproducing apparatus of the present invention is a reproducing apparatus for reproducing recorded information from the magneto-optical recording medium of the present invention, and comprises a heating means capable of forming a temperature distribution having a gradient with respect to the moving direction of the spot of the light beam. It is a reproducing apparatus characterized by having.

[0016]

1 is a schematic view for explaining the operation of the magneto-optical recording medium and the reproducing method thereof according to the present invention.

FIG. 1A is a schematic sectional view of the magneto-optical recording medium of the present invention. The magnetic layer of this medium comprises a first magnetic layer 11, a second magnetic layer 12, and a third magnetic layer 13 which are sequentially stacked. The arrow 14 in each layer represents the direction of atomic spin. A domain wall 15 is formed at the boundary between regions where the spin directions are opposite to each other. The recording signal of this recording layer is also shown as a graph on the lower side.

FIG. 1B is a graph showing the temperature distribution formed on the magneto-optical recording medium of the present invention. This temperature distribution may be induced on the medium by the light beam itself irradiating for reproduction, but it is desirable to use another heating means together, and the temperature from the front side of the spot of the reproduction light beam To form a temperature distribution such that a temperature peak appears behind the spot. Here, at the position x _s , the medium temperature is a temperature T _s near the Curie temperature of the second magnetic layer.

FIG. 1C shows the temperature distribution of FIG.
Domain wall energy density σ of the corresponding first magnetic layer₁ The distribution of
It is a graph shown. In this way, domain wall energy is dense in the x direction.
Degree σ ₁ If there is a gradient of, the domain wall of each layer existing at the position x
On the other hand, the force F calculated from the following formula₁ Works.

[0020]

[Equation 1] This force F ₁ acts so as to move the magnetic domain wall to the lower domain wall energy. Since the first magnetic layer has a small domain wall coercive force and a large domain wall mobility, by itself, the domain wall is easily moved by this force F ₁ . However, in the region before the position x _s (on the right side in the figure), the medium temperature is still lower than T _{s, and the} medium is exchange-coupled with the third magnetic layer having a large domain wall coercive force. The magnetic domain wall in the first magnetic layer is also fixed at a position corresponding to the magnetic domain wall position.

In the present invention, as shown in FIG. 1A, when the domain wall 15 is at the position x _s of the medium, the medium temperature rises to a temperature T _s near the Curie temperature of the second magnetic layer,
The exchange coupling between the first magnetic layer and the third magnetic layer is broken. As a result, the domain wall 15 in the first magnetic layer moves "instantaneously" to a region having a higher temperature and a smaller domain wall energy density, as indicated by a dashed arrow 17.

When the domain wall 15 passes under the spot 16 of the reproducing light beam, the atomic spins of the first magnetic layer in the spot are all aligned in one direction. Then, every time the domain wall 15 comes to the position x _s with the movement of the medium, the domain wall 15 momentarily moves under the spot, the direction of atomic spins in the spot is reversed, and all are aligned in one direction. As a result, as shown in FIG. 1A, the reproduction signal amplitude is always constant and the maximum amplitude regardless of the recorded domain wall spacing (that is, the recording mark length), which is caused by the optical diffraction limit. It is completely free from problems such as waveform interference.

However, since the moving speed of the domain wall is not infinite, the time τ required for the domain wall to pass under the spot is τ.
However, it is necessary to ensure that the distance corresponding to the shortest recording mark length does not become longer than the time t _min required for the medium to move (see FIG. 2).

FIG. 3 shows the present invention based on the above-described principle operation,
It is a schematic diagram which compares with a usual conventional method. In this figure, (a1) to (a7) and (b1) to (b7) are
The state where the reproducing spot 31 moves on the information track 36 in which the magnetic domains 33 having different recording mark lengths are formed is shown. Further, (a8) and (b8) are graphs of the reproduced signals obtained.

In the conventional reproducing method, the maximum amplitude of the reproduced signal cannot be obtained (b8) unless the reproducing spot 31 itself is completely within one magnetic domain on the information track 36 (b2). On the other hand, in the present invention, the reproducing spot 31 and the temperature profile are relatively moved in the same direction 32 so that the portion immediately before the reproducing spot 31 becomes the critical temperature T _s of the second magnetic layer. Therefore, immediately before the reproducing spot 31 contacts the domain wall 34, the temperature of the portion of the domain wall 34 becomes the critical temperature Ts, the domain wall 34 moves in the reverse direction 35, and the reproducing spot 31 completely enters the recording mark. The state becomes the state (a2), and the maximum amplitude of the reproduction signal is instantaneously obtained (a8).

In the conventional reproducing method, the magnetic domain 3
If 3 is smaller than the spot diameter, the reproduction spot 3
The whole 1 does not fit in the magnetic domain (b3 to b7), and the obtained reproduction signal becomes unclear (b8). On the other hand, in the present invention, when the reproducing spot 31 is almost in contact with the domain wall of the recording mark, the domain wall sequentially moves backward in the reverse direction (a
3 to a7), an extremely clear reproduction signal can be obtained (a
8).

Although the magneto-optical recording medium of the present invention having the first to third magnetic layers has been described above, in the present invention, as shown in FIG. 1
It may be provided between the magnetic layer 41 and the second magnetic layer 42. The fourth magnetic layer 44 has a Curie temperature higher than that of the second magnetic layer and lower than that of the first magnetic layer, and at least at a temperature equal to or higher than the Curie temperature of the second magnetic layer. The perpendicular magnetic film has a domain wall coercive force relatively smaller than that of the third magnetic layer. The fourth magnetic layer is for further inducing a force sufficient to move the domain wall in the first magnetic layer.

[0028] As shown in FIG. 4 (a) (b), also in the fourth magneto-optical recording medium comprising a magnetic layer, the temperature T _s near the Curie temperature of the second magnetic layer at the position x _s By this, the exchange coupling between the fourth magnetic layer and the third magnetic layer can be broken, and the domain walls in the first and fourth magnetic layers can be moved.

FIG. 4C is a graph showing the distribution of the domain wall energy density σ ₁ of the _first magnetic layer and the domain wall energy density σ ₄ of the fourth magnetic layer corresponding to the above temperature distribution. When there is a gradient of the domain wall energy density σ ₁ in the x direction in this way, the force F _i acts on the domain wall of each layer existing at the position x as described above, and this force F _i is the domain wall energy. The domain wall is moved to the lower side of.

On the other hand, in order to read the recording at high speed, it is necessary to move the domain wall at high speed. Therefore, it is necessary to apply a large force to the domain wall. In general, the temperature dependence of the domain wall energy density increases as it approaches the Curie temperature. Therefore, when the temperature gradient is given in the temperature range near the Curie temperature, the gradient of the domain wall energy density in the x direction can be increased and a large force can be applied to the domain wall. However, in order to detect the change in the plane of polarization of the reflected light from the first magnetic layer, the temperature in the irradiation region of the spot of the reproduction light beam is sufficiently lower than the Curie temperature of the first magnetic layer. Must be

Here, as shown in FIG. 4, if a fourth magnetic layer 44 having a lower Curie temperature is provided adjacent to the side opposite to the light beam incident side of the first magnetic layer, reproduction is performed. In the irradiation region of the spot of the light beam, the temperature gradient can be given in a temperature range sufficiently lower than the Curie temperature of the first magnetic layer and near the Curie temperature of the fourth magnetic layer.
As a result, a large force acts on the domain wall in the fourth magnetic layer,
The force due to the exchange interaction with the fourth magnetic layer is also applied to the domain wall in the first magnetic layer, and a large force acts.

Further, if the fourth magnetic layer is provided with a gradient of the Curie temperature in the film thickness direction such that the Curie temperature becomes lower as it gets closer to the second magnetic layer, x is accompanied by the temperature gradient in the x direction. Since it is possible to sequentially form the constituent portion of the fourth magnetic layer immediately below the Curie temperature, it is necessary to move the domain wall x
A relatively large force can be applied over the entire range of directions.

[0033]

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

FIG. 5 is a schematic sectional view showing an embodiment of the layer structure of the magneto-optical recording medium of the present invention. In this aspect, the dielectric layer 55, the first magnetic layer 51, the second magnetic layer 52, the third magnetic layer 53, and the dielectric layer 54 are sequentially stacked on the transparent substrate 56.

As the transparent substrate 56, for example, polycarbonate, glass or the like can be used. Dielectric layer 5
5 includes, for example, Si ₃ N ₄ , AlN, SiO ₂ ,
Transparent dielectric materials such as SiO, ZnS, MgF ₂ can be used. Finally, the dielectric layer 54 is formed again as a protective film.
The same thing can be used for. Each of these layers can be deposited and formed by, for example, continuous sputtering using a magnetron sputtering device, continuous vapor deposition, or the like. In particular, each magnetic layer is formed continuously without breaking the vacuum,
They are exchange-coupled with each other.

In addition to this structure, Al, AlTa,
A metal layer made of AlTi, AlCr, Cu or the like may be added to adjust the thermal characteristics. Further, a protective coat made of a polymer resin may be applied. Alternatively, the substrates after the film formation may be attached.

In the above medium, each magnetic layer 51-53
May be composed of various magnetic materials. For example, Pr, Nd, Sm, Gd, Tb, Dy, H
Rare earth-iron composed of one or two or more rare earth metal elements such as o and 10 to 40 at% and one or two or more iron group elements such as Fe, Co and Ni from 90 to 60 at% It may be composed of a group amorphous alloy.
Further, in order to improve the corrosion resistance, etc., Cr, Mn, C
You may add a small amount of elements, such as u, Ti, Al, Si, Pt, In.

In the case of a heavy rare earth-iron group amorphous alloy, the saturation magnetization can be controlled by the composition ratio of the rare earth element and the iron group element. Also, the Curie temperature can be controlled by the composition ratio, but in order to control the Curie temperature independently of the saturation magnetization, a material in which a part of Fe is replaced with Co is used as the iron group element, and the replacement amount is set. A control method can be used more preferably. That is, by substituting 1 at% of Fe with Co, a Curie temperature rise of about 6 ° C. can be expected. Therefore, using this relationship, the addition amount of Co is adjusted so as to obtain a desired Curie temperature. It is also possible to lower the Curie temperature by adding a small amount of a non-magnetic element such as Cr or Ti. Alternatively, the Curie temperature can be controlled by using two or more kinds of rare earth elements and adjusting the composition ratio thereof.

Besides, materials such as garnet, a platinum group-iron group periodic structure film, or a platinum group-iron group alloy can also be used.

The first magnetic layer is, for example, GdC.
A rare earth-iron group amorphous alloy having small perpendicular magnetic anisotropy such as o, GdFeCo, GdFe, and NdGdFeCo, or a material for bubble memory such as garnet is preferable.

As the third magnetic layer, for example, TbFe
Rare earths such as Co, DyFeCo, TbDyFeCo-
An iron group amorphous alloy, a platinum group-iron group periodic structure film such as Pt / Co, Pd / Co, or the like, which has a large perpendicular magnetic anisotropy and can stably maintain a magnetized state is desirable.

To record a data signal on the magneto-optical recording medium of the present invention, the external magnetic field is modulated while moving the medium while irradiating a laser beam having a power such that the third magnetic layer has a Curie temperature or higher. Or by modulating the laser power while applying a magnetic field in a fixed direction. In the latter case, if the intensity of the laser light is adjusted so that only a predetermined region within the light spot is near the Curie temperature of the third magnetic layer, a recording magnetic domain having a diameter smaller than the diameter of the light spot can be formed. It is possible to record signals with a period less than the diffraction limit of.

Further, FIG. 6 shows the structure of the medium provided with the fourth magnetic layer. In this aspect, on the transparent substrate 66,
The dielectric layer 65, the first magnetic layer 61, the fourth magnetic layer 64,
The second magnetic layer 62, the third magnetic layer 63, and the dielectric layer 64 are sequentially stacked. The material and manufacturing method of each layer are the same as those described with reference to FIG.

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

First, an example of a magneto-optical recording medium having first to third magnetic layers as shown in FIG. 5 will be described below.

<Example 1> B-doped Si, and Gd, Dy, and T were added to a DC magnetron sputtering apparatus.
After attaching each target of b, Fe and Co and fixing the polycarbonate substrate with the guide groove for tracking to the substrate holder, vacuum the chamber with a cryopump until a high vacuum of 1 × 10 ⁻⁵ Pa or less is achieved. Exhausted. While evacuating, Ar gas was introduced into the chamber until the pressure reached 0.3 Pa, and the SiN layer as the interference layer was formed to a thickness of 800 Å while rotating the substrate.
Subsequently, a GdCo layer as the first magnetic layer is 300 angstroms, and a DyFe layer as the second magnetic layer is 100 angstroms.
Angstroms, and a TbFeCo layer as a third magnetic layer were sequentially formed to 400 angstroms. Finally, a SiN layer having a thickness of 800 Å was formed as a protective layer.
At the time of forming the SiN layer, N ₂ gas was introduced in addition to Ar gas, and the film was formed by DC reactive sputtering. Each magnetic layer is
A DC power was applied to each target of Gd, Dy, Tb, Fe, and Co to form a film.

The composition of each magnetic layer was adjusted so that all were in the vicinity of the compensation composition, and the Curie temperature was 30 for the first magnetic layer.
0 ° C or higher, 70 ° C for the second magnetic layer, 20 ° C for the third magnetic layer
The temperature was set to about 0 ° C.

In this medium, a dielectric layer 72, a magnetic layer 73, and a dielectric layer 74 are laminated on a substrate 71 as shown in a sectional shape in FIG. 100
It is formed in a rectangular shape of 0 angstrom. For this reason,
The magnetic layer 72 laminated on the land 76 is substantially separated at the guide groove 75. Actually, although a film is deposited on the step portion and the magnetic layer is connected to the magnetic layer, the film thickness is very thin compared to other portions, and thus the coupling at the step portion can be ignored. In the present invention, magnetically separating each information track from each other also includes such a state. When the reversed magnetic domain is formed over the land 76 in the full width, an unclosed domain wall 77 is formed at the boundary of the magnetic domain on the land 76, as shown in FIG. 7B. Such a domain wall 77 can be easily moved even if it is moved in the track direction, since the domain wall 77 on the side of the track is not generated or disappears.

The recording / reproducing characteristics of the thus obtained magneto-optical recording medium were measured.

In the recording / reproducing apparatus used for the measurement, as shown in FIG. 8, a heating laser is added to the optical system of a general magneto-optical disk recording / reproducing apparatus. Reference numeral 81 is a laser light source for recording and reproduction, which has a wavelength of 780 nm and is arranged so that P deflection is incident on the recording medium. 8
2 is a laser light source for heating, the wavelength is 1.3 μm,
Similarly, it is arranged so that P deflection is incident on the recording medium. No. 83 transmits 100% of 780 nm light, and
It is a dichroic mirror designed to reflect 100% of 3 μm light. Reference numeral 84 is a deflecting beam splitter, which has 780 nm light, 1.3 μm light, and P deflection of 70
It is designed to be -80% transparent and 100% S-polarized. The light flux diameter of the 1.3 μm light is made smaller than the aperture diameter of the objective lens 85, and the NA is made smaller than that of the 780 nm light which is condensed after passing through all the opening portions. Also, 87 is 1.3 μm light,
This is provided to prevent leakage into the signal detection system. It transmits 100% of 780 nm light and 1 μm of 1.3 μm light.
It is a dichroic mirror designed to reflect 100%.

With this optical system, on the recording surface of the recording medium 86, as shown in FIG. 9A, on the land 95 between the guide grooves 94, the recording / reproducing spot 91 and the heating spot 91 are formed. Can be imaged with the spot 92. Since the heating spot 92 has a long wavelength and a small NA, it has a larger diameter than the recording / reproducing spot 91. As a result, a desired temperature gradient as shown in FIG. 9B can be easily formed in the area of the recording / reproducing spot 91 on the recording surface of the moving medium. Where temperature T
The isotherm 96 of _s is also shown. For recording and reproduction, the medium speed is 5m
It was performed by driving at / sec.

First, the recording / reproducing laser was set to DC at 8 mW.
By modulating the magnetic field at ± 150 Oe while irradiating, a repeating pattern of upward magnetization and downward magnetization corresponding to the modulation of the magnetic field was formed in the cooling process after heating the Curie temperature of the third magnetic layer or higher. . At this time, it is also possible to reduce the recording power of the recording / reproducing laser by irradiating the heating laser together.

The modulation frequency of the recording magnetic field was changed from 1 to 10 MHz, and a pattern having a mark length in the range of 2.5 to 0.25 μm was recorded.

The power of the recording / reproducing laser at the time of reproduction is set to 1 mW, and the laser for heating is simultaneously irradiated with the power of 20 mW, and C /
N was measured. The temperature distribution on the medium surface at this time is shown in FIG.
It is as shown in (b).

The result of this measurement is shown by the graph line a in FIG. For comparison, the measurement result by the conventional super-resolution reproducing method described in Japanese Patent Laid-Open No. 3-93058 in the figure is shown as a graph line b, and the measurement result by the normal reproducing method in which the super-resolution phenomenon does not occur is shown in the graph. Shown as line c.

According to the reproducing method of the present invention, even if the mark length becomes short, the reversal of all the magnetization in the reproducing spot is detected, so that it is only possible to reproduce a signal having a period below the diffraction limit of light. As a result, the dependency of C / N on the mark length is almost eliminated.

In the medium of this example, the manner in which the domain wall of the first magnetic layer moved due to the temperature gradient was confirmed by direct observation with a polarizing microscope, as described below.

First, a sample having the same structure as in Example 1 but having the magnetic layers laminated in the opposite order was prepared. A magnetic domain pattern was formed on this sample by the same recording method as in Example 1. This was observed with a polarizing microscope from the film surface side, that is, the first magnetic layer side.

Next, this sample was irradiated with a condensing laser for heating to form a temperature distribution almost similar to that in Example 1 within the field of view of the polarization microscope.

In this state, a magnetic field of about 500 Oe was applied to the sample. As a result, it was observed that only the circular region corresponding to the temperature distribution was oriented in the direction of the external magnetic field. This is because the first magnetic layer and the third magnetic layer are formed in this region.
It means that the exchange coupling with the magnetic layer is broken.

Next, the application of the magnetic field was stopped and the sample was slowly moved in the track direction. Then, it was observed that each time the boundary of the magnetic domain formed on the track entered the above-mentioned circular bond cutting region, the moving magnetic domain expanded toward the center of the circular region.

It was observed that when the irradiation of the heating laser was stopped, the magnetic domain pattern stored in the third magnetic layer was transferred to the first magnetic layer.

From the above, it was confirmed that the domain wall of the first magnetic layer moved to the high temperature side due to the temperature gradient in the region where the bond with the third magnetic layer was broken.

Example 2 A magneto-optical recording medium was prepared by forming a thin film on a polycarbonate substrate in the same manner with the same film forming apparatus and film forming method as in Example 1. However, the following three points were changed in this example.

First, the accelerated irradiation of Ar ions was applied to the substrate surface before film formation. Secondly, Si that was the interference layer was used.
That is, the accelerated irradiation treatment of Ar ions was applied to the film surface after forming the N layer. The surface condition was smoothed by these treatments. Thirdly, the film thickness of the first magnetic layer is set to 20
It was changed to 00 angstrom. These changes independently contribute to the improvement of the domain wall mobility of the first magnetic layer.

When the recording / reproducing characteristics of this medium were measured by the same method as in Example 1, the same good results as in Example 1 were obtained. Furthermore, the linear velocity of the medium during reproduction is 20 m / s.
Even when the reproduction speed was increased to ec, the reproduction characteristics did not deteriorate.

Example 3 A magneto-optical recording medium was prepared by forming a thin film on a polycarbonate substrate in the same manner by using the film forming apparatus and the film forming method similar to those in Example 1.

However, in this embodiment, as the substrate,
A prepit was formed and the guide groove had a U-shaped cross section. Therefore, the laminated magnetic layers are not geometrically divided at the guide groove portion.

A high-power laser was irradiated onto the guide groove portion of this medium to anneal the entire magnetic layer of the guide groove portion. As a result, the magnetic layer in the portion of the guide groove was altered to become an in-plane film, and the coupling between the magnetic layers of the tracks adjacent to each other was separated via the guide groove. When the recording / reproducing characteristics of this medium were measured by the same method as in Example 1, Example 1
The same good result was obtained.

Further, when the recording / reproducing characteristics of the above medium were measured by the same method as in Example 1 without performing the above-mentioned annealing treatment, the noise was increased as compared with the result of Example 1, but The reproduction of a signal with a period below the diffraction limit was sufficiently possible. In this medium, since there is a magnetic domain surrounded by a closed domain wall, the operation became unstable when moving the domain wall in the direction of expanding this domain, and noise increased.

As another method for breaking the coupling between the magnetic layers of adjacent tracks, patterning by etching may be performed.

<Example 4> Using the medium of Example 1, the recording / reproducing characteristics were evaluated by a recording / reproducing apparatus almost the same as in Example 1.

However, the positional relationship between the recording / reproducing spot and the heating spot was changed as shown in FIG. That is, the recording / reproducing spot was arranged on the front slope of the temperature distribution induced by the heating laser with respect to the moving direction of the medium.

When the medium moves and passes through the position shown by S in the figure, the first magnetic layer and the third magnetic layer are recombined, and the first magnetic layer and the third magnetic layer are combined. The magnetization orientation state is transferred. When the domain wall of the third magnetic layer passes the position indicated by S, the domain wall remains at the position indicated by S of the first magnetic layer,
This domain wall instantaneously moves backward. When the recording / reproducing spots are arranged as described above, the movement of the domain wall at this time is detected.

With this arrangement, the critical temperature T indicated by S
_Since the shape of the isotherm of _s and the shape of the domain wall of the magnetic domain formed by the magnetic field modulation method substantially match, the domain wall can be moved more stably.

Comparative Example 1 The recording / reproducing characteristics of the medium of Example 1 were measured by an ordinary magneto-optical disk recording / reproducing apparatus to which a heating laser was not added.

When the reproducing characteristics were examined by the same method as in Example 1 except that the laser for heating was not irradiated,
Good C / N was obtained by increasing the reproducing power to about 3 mW. However, compared with the results of Example 1, the C / N was low by about 5 dB at each mark length. This is because the temperature of the medium does not rise in the front part of the reproducing spot, the domain wall moves from the middle of the reproducing spot, and the entire spot cannot be effectively used as in the first embodiment.

Next, examples of the magneto-optical recording medium having the first to fourth magnetic layers as shown in FIG. 6 will be given below.

<Embodiment 5> B-doped Si, and Gd, Tb, and F were added to a DC magnetron sputtering apparatus.
After attaching each target of e, Co and Cr and fixing the polycarbonate substrate with the guide groove for tracking to the substrate holder, vacuum the chamber with a cryopump until a high vacuum of 1 × 10 ⁻⁵ Pa or less is achieved. Exhausted.

Ar gas was supplied at 0.3 Pa with the vacuum exhausted.
It was introduced into the chamber until it became, and the SiN layer as the interference layer was formed to a thickness of 800 Å while rotating the substrate. Subsequently, a GdCoCr layer as the first magnetic layer is 300 angstroms, and a GdFc layer as the fourth magnetic layer.
An eCr layer was formed in the order of 300 angstroms, a TbFeCr layer was formed in the order of 100 angstrom as the second magnetic layer, and a TbFeCo layer was formed in the order of 400 angstrom as the third magnetic layer. Finally, a SiN layer having a thickness of 800 Å was formed as a protective layer. At the time of forming the SiN layer, N ₂ gas was introduced in addition to Ar gas, and the film was formed by DC reactive sputtering. Each magnetic layer is composed of Gd, Tb, Fe, Co, Cr
DC power was applied to each of the targets to form a film.

The composition of each magnetic layer is adjusted so that all are in the vicinity of the compensation composition, and the Curie temperature is 30 for the first magnetic layer.
0 ° C or above, 170 ° C for the fourth magnetic layer, 7 ° C for the second magnetic layer
The temperature was set to 0 ° C. and the temperature of the third magnetic layer was set to about 200 ° C. This medium has a cross-sectional shape as shown in FIG. 7, as in the first embodiment.

The recording / reproducing characteristics of the magneto-optical recording medium thus obtained were measured in the same manner as in Example 1. However, the DC irradiation laser power during recording was 10 mW, and the heating laser power during reproduction was 25 mW.
As in the case of Example 1, the measurement result was a good result indicated by the graph line a in FIG. 10.

Furthermore, the linear velocity of the medium during reproduction is set to 20 m.
The reproduction characteristics did not deteriorate even when the reproduction was performed at a speed up to / sec.

The movement of the domain wall of the first magnetic layer due to the temperature gradient was confirmed by direct observation with a polarization microscope as in Example 1.

<Example 6> A magneto-optical recording medium was prepared by forming a thin film on a polycarbonate substrate in the same manner by using the same film forming apparatus and film forming method as in Example 5.

However, in the present embodiment, the inside of the fourth magnetic layer is formed of the first, second and third constituent layers in order from the first magnetic layer side, and the Curie of each constituent layer is formed. Temperature in order,
180 ℃, 160 ℃, 140 ℃, the film thickness in order 20
0 Å, 400 Å, 800
As the angstrom, in the fourth magnetic layer, a stepwise Curie temperature gradient was provided in the film thickness direction. GdFeCoCr was used as the material.

The first magnetic layer has a Curie temperature of 30.
200 angstrom GdFeCoCr layer at 0 ° C,
The second magnetic layer is TbFeCo with a Curie temperature of 120 ° C.
The Cr layer has a thickness of 200 Å, and the third magnetic layer has a Curie temperature of 200 ° C. and the TbFeCoCr layer has a thickness of 600 Å.

The composition of each magnetic layer is adjusted so that the composition ratio of the rare earth element and the iron group element is adjusted so as to be in the vicinity of the compensation composition, the addition amounts of Co and Cr are adjusted, and the Curie temperature is set as described above. did.

The recording / reproducing characteristics of this medium were measured by the same method as in Example 5, and the same good result as in Example 5 was obtained. Furthermore, the linear velocity of the medium during reproduction is 30 m / s.
Even when the reproduction speed was increased to ec, the reproduction characteristics did not deteriorate.

In this example, a temperature gradient in the track direction of about 120 ° C. to 180 ° C. was formed in the area of the recording / reproducing spot on the recording surface of the medium during reproduction. In this case, in the range of 120 ° C. to 140 ° C., a large force acts on the domain wall of the third constituent layer of the fourth magnetic layer, and 140 ° C.
In the region of from 160 to 160 ° C., a large force acts on the domain wall of the second constituent layer of the fourth magnetic layer, and in the region of from 160 ° C. to 180 ° C., the domain wall of the first constituent layer of the fourth magnetic layer. A large force acts. Therefore, the domain wall existing from the first magnetic layer to the fourth magnetic layer can be moved with a relatively large force over the entire area of the recording / reproducing spot, and the reproducing operation of the present invention can be performed. Can be performed more stably and at high speed.

<Embodiment 7> A magneto-optical recording medium was prepared by forming a thin film on a polycarbonate substrate in the same manner by using a film forming apparatus and a film forming method similar to those in Example 5.

However, in this embodiment, as the substrate,
A prepit was formed and the guide groove had a U-shaped cross section. Therefore, the laminated magnetic layers are not geometrically divided at the guide groove portion.

The magnetic layer and other components were the same as in Example 5 except that the composition ratio of the fourth magnetic layer was changed as described below.

The fourth magnetic layer is a sample (1) in which the composition ratio of Gd of GdFeCr is adjusted so that the iron group element sublattice magnetization is dominant at room temperature, and the rare earth element sublattice magnetization is dominant at room temperature. A sample (2) having a composition having a compensation temperature below the Curie temperature and a sample (3) having a composition having a rare earth element sublattice magnetization dominant at room temperature and having no compensation temperature below the Curie temperature were prepared. It was made. The Curie temperature of each sample was adjusted to 170 ° C. by adjusting the Cr addition amount.

The guide groove portion of each of these samples was irradiated with a high-power laser to anneal the entire magnetic layer of the guide groove portion. As a result, the magnetic layer in the guide groove portion was magnetically deteriorated, and the coupling between the magnetic layers of the tracks adjacent to each other via the guide groove was broken.

Next, the recording / reproducing characteristics were measured by the same method as in Example 5, and at the linear velocity of 5 m / sec, good results similar to those in Example 5 were obtained for each sample.

However, when the linear velocity was increased to 30 m / sec for reproduction, the sample (1) had a C / N of 5 dB.
To some extent. On the other hand, in the sample (2), C /
Almost no decrease in N was observed, and in sample (3), there was only a decrease of about 2 dB.

This is because the composition of the rare earth element sublattice magnetization dominant at room temperature, especially the composition having the compensation temperature below the Curie temperature has a larger temperature dependence of the domain wall energy near the Curie temperature, and It is considered that this is because a larger force can be applied to the domain wall by the gradient.

The present invention is not limited to the embodiments described above. As another possible example, a method is conceivable in which the optical head is left as it is and the temperature distribution on the medium is adjusted by another means. For example, it is conceivable to use the core of the flying head used for magnetic field modulation recording as a heat source, or to dispose another suitable heating element near the reproducing laser irradiation area of the medium. However, in this case, it is necessary to take care so that the positional relationship between the temperature position that is the movement start position of the domain wall and the reproduction spot does not change at a frequency close to the frequency of the reproduction signal.

[0100]

As described in detail above, according to the magneto-optical recording medium, the reproducing method, and the reproducing apparatus of the present invention, a signal having a period less than the diffraction limit of light can be transmitted at high speed without lowering the reproduction signal amplitude. With this, it is possible to greatly improve the recording density and the transfer speed, and it is possible to downsize the reproducing apparatus.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the concept of a reproducing method of the present invention when using a magneto-optical recording medium having first to third magnetic layers. (A) shows the cross section of the medium in the reproducing state, and schematically shows the spin alignment state of each magnetic layer. (B) shows the temperature distribution on the medium at the position shown in (a). (C) schematically shows the distribution of the domain wall energy density at the same position and the distribution of the force acting on the domain wall accordingly.

FIG. 2 is a graph showing the relationship between the time τ required for the domain wall to pass under the spot and the time t _min required for the medium to move a distance corresponding to the shortest recording mark length.

FIG. 3 is a schematic diagram comparing the method of the present invention with a conventional conventional method.

FIG. 4 is a diagram schematically showing a concept of a reproducing method of the present invention when using a magneto-optical recording medium having first to fourth magnetic layers.

FIG. 5 is a schematic cross-sectional view showing one embodiment of the layer structure of the magneto-optical recording medium of the present invention.

FIG. 6 is a schematic cross-sectional view showing one embodiment of the layer structure of the magneto-optical recording medium of the present invention.

FIG. 7 is a diagram showing a cross-sectional shape of a magneto-optical recording medium in an example.

FIG. 8 is a schematic diagram showing a recording / reproducing apparatus used in Examples.

FIG. 9 is a schematic diagram showing a reproduction state in an example.

FIG. 10 is a graph showing C / N obtained in the examples.

FIG. 11 is a schematic diagram showing a reproduction state in the example.

[Explanation of symbols]

 11 First Magnetic Layer 12 Second Magnetic Layer 13 Third Magnetic Layer 14 Direction of Atomic Spin 15 Domain Wall 16 Optical Beam Spot for Reading 17 Domain Moving Direction 18 Medium Moving Direction

Claims (10)

[Claims] 1. A magneto-optical recording medium in which at least first, second and third magnetic layers are sequentially laminated, said first magnetic layer comprising:
Is composed of a perpendicular magnetic film having a domain wall coercive force smaller and a domain wall mobility larger than that of the third magnetic layer at a temperature near the ambient temperature. A magneto-optical recording medium comprising a magnetic layer and a magnetic layer having a Curie temperature lower than that of the third magnetic layer, wherein the third magnetic layer is a perpendicular magnetization film. 2. The magneto-optical recording medium according to claim 1, wherein the first magnetic layer is magnetically separated from each other between the information tracks. 3. A magneto-optical recording medium in which at least first, fourth, second and third magnetic layers are sequentially laminated,
The first magnetic layer has the third magnetic layer at a temperature near ambient temperature.
Of the perpendicular magnetic film having a domain wall coercive force relatively smaller than that of the first magnetic layer and the second magnetic layer of which the Curie temperature is lower than that of the first magnetic layer and the third magnetic layer. , The third magnetic layer is a perpendicular magnetization film, the fourth magnetic layer has a Curie temperature higher than that of the second magnetic layer and lower than that of the first magnetic layer, and at least the A magneto-optical recording medium comprising a perpendicular magnetic film having a domain wall coercive force relatively smaller than that of the third magnetic layer at a temperature equal to or higher than the Curie temperature of the second magnetic layer. 4. The magneto-optical recording medium according to claim 3, wherein the fourth magnetic layer has a Curie temperature gradient in the film thickness direction such that the Curie temperature becomes lower as it gets closer to the second magnetic layer. 5. The magneto-optical recording medium according to claim 3, wherein the fourth magnetic layer is made of a rare earth-iron group element amorphous alloy and has a composition in which the rare earth element sublattice magnetization is dominant. 6. The magneto-optical recording medium according to claim 5, wherein the fourth magnetic layer has a compensation temperature at a temperature equal to or lower than the Curie temperature. 7. The magneto-optical recording medium according to claim 3, wherein the first and fourth magnetic layers are magnetically separated from each other between the information tracks. 8. A method for reproducing recorded information from the magneto-optical recording medium according to claim 1 or 2, wherein the first magnetic layer side is provided while moving a light beam relative to the medium. Temperature to form a temperature distribution having a gradient with respect to the moving direction of the spot of the light beam on the medium, and the temperature distribution has a temperature region having a temperature region higher than at least the Curie temperature of the second magnetic layer. A reproducing method characterized in that the domain wall formed in the first magnetic layer is moved by the distribution, and a change in the polarization plane of the reflected light of the light beam is detected to reproduce the recorded information. 9. A method of reproducing recorded information from the magneto-optical recording medium according to claim 3.
Irradiating the light beam from the side of the first magnetic layer while moving the light beam relative to the medium to form a temperature distribution having a gradient with respect to the moving direction of the spot of the light beam on the medium. The temperature distribution has a temperature region that is at least higher than the Curie temperature of the second magnetic layer and has a temperature region near the Curie temperature of the fourth magnetic layer, so that the first and fourth magnetic layers have the same temperature distribution. A reproducing method characterized in that the formed domain wall is moved, and a change in the polarization plane of the reflected light of the light beam is detected to reproduce the recorded information. 10. A reproducing apparatus for reproducing recorded information from the magneto-optical recording medium according to claim 1, wherein the temperature distribution has a gradient with respect to a moving direction of a spot of a light beam. A reproducing apparatus having a heating means capable of forming a film.