JP3332905B2 - Method and apparatus for reproducing magneto-optical recording medium - Google Patents

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 and the like for recording and reproducing information by a laser beam utilizing a magneto-optical effect, and more particularly to a magneto-optical recording capable of high-density recording of the medium. a reproducing method and reproducing apparatus of the medium.

[0002]

2. Description of the Related Art As a rewritable high-density recording method,
Using the thermal energy of the semiconductor laser, write magnetic domains on the magnetic thin film to record information, and use the magneto-optical effect,
Attention has been paid to a magneto-optical recording medium for reading this information.
In recent years, there has been a growing demand for increasing the recording density of this magneto-optical recording medium to produce a recording medium having a larger capacity.

[0003] The linear recording density of an optical disk such as a magneto-optical recording medium greatly depends on the laser wavelength of a reproducing optical system and the numerical aperture of an objective lens. That is, when the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens are determined, the beam waist diameter is determined.
About NA / λ is the limit of detection.

[0004] Therefore, in order to realize a higher density in a 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. For this reason, techniques for improving the recording density by devising the configuration of the recording medium and the reading method have been developed.

For example, in JP-A-3-93058, signal recording is performed on a recording holding layer of a multilayer film having a reproducing layer and a recording holding layer that are magnetically coupled.
A signal reproducing method has been proposed in which the magnetization direction of the reproducing layer is aligned, heated by irradiating a laser beam, and the signal recorded on the recording holding layer is read while being transferred to a temperature rising region of the reproducing layer.

According to this method, the area of the spot diameter of the reproducing laser which is heated by the laser to reach the transfer temperature and the signal is detected can be limited to a smaller area. Interference is reduced, and a signal having a period equal to or less than the diffraction limit of light can be reproduced.

[0007]

However, in the magneto-optical reproducing method described in JP-A-3-93058, the signal detection area used effectively is smaller than the spot diameter of the reproducing laser. There is a disadvantage 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 the laser beam is irradiated. Therefore, it is necessary to add a magnet for initializing the reproducing layer to the conventional device. For this reason, the reproducing method has problems that the magneto-optical recording device is complicated, the cost is high, and miniaturization is difficult.

The present invention has been made to solve such problems of the prior art. That is, the object of the present invention is:
A method of reproducing a magneto-optical recording medium that can reproduce a signal having a period equal to or less than the diffraction limit of light at a high speed without lowering the reproduction signal amplitude, can greatly improve the recording density and transfer speed, and can reduce the size of the reproducing apparatus. And a playback device.

[0010]

The above object is achieved by the present invention described below.

[0011]

The reproduction method of the present invention contributes to reproduction of information.
The domain wall moving layer on which the domain wall moves
A memory layer for holding the domain, and a domain wall moving layer and a memory layer.
A barrier layer disposed between and having a lower Curie temperature than both layers
Wherein the domain wall motion layer is smaller than the memory layer.
Method of reproducing information from magneto-optical recording medium having coercive force
In, irradiating a light beam to the magneto-optical recording medium, relatively moving the medium and the light beam, forming a temperature distribution having a gradient with respect to the moving direction of the spot of the light beam on the medium, In the region above the Curie temperature of the barrier layer
In the above, the data was transferred from the memory layer to the domain wall motion layer.
The domain wall of the recording domain is generated by the gradient of the temperature distribution.
The recording magnetic domain is moved on the domain wall motion layer by force to
A reproducing method for a magneto-optical recording medium, which enlarges and detects a change in a polarization plane of reflected light of the light beam to reproduce the information.

[0013] The playback apparatus of the present invention contributes to the playback of information.
The domain wall moving layer on which the domain wall moves
A memory layer for holding the domain, and a domain wall moving layer and a memory layer.
A barrier layer disposed between and having a lower Curie temperature than both layers
At room temperature, the recording magnetic domain of the memory layer
Transferred to the moving layer, wherein the domain wall moving layer is
Information from magneto-optical recording media with smaller domain wall coercivity
An apparatus for reproducing and means for irradiating a light beam to said medium, the movement direction of the light beam spot on the medium
Heating means for forming a temperature distribution having a gradient with respect to the direction
And a means for relatively moving the medium and the light beam, and means for detecting a change in the polarization plane of the reflected light of the light beam and reproducing the recorded information. .

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram for explaining the operation of a magneto-optical recording medium according to the present invention and its reproducing method.

FIG. 1A is a schematic sectional view of a magneto-optical recording medium according to the present invention. The magnetic layer of this medium has a first magnetic layer 11 as a reproducing layer, a second magnetic layer 12 as an intermediate layer,
A third magnetic layer 13 as a recording layer is sequentially laminated.
Arrows 14 in each layer indicate the directions of atomic spins. The domain wall 15 is located at the boundary between the regions where the spin directions are opposite to each other.
Are formed. The recording signal of this recording layer is also shown as a graph on the lower side.

FIG. 1B is a graph showing a 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 being irradiated for reproduction, but it is desirable to use another heating means together with the temperature distribution from the near side of the spot of the light beam for reproduction. To form a temperature distribution such that a temperature peak comes after the spot. Here in the position x _s, the medium temperature is in the temperature T _s near the Curie temperature of the second magnetic layer.

FIG. 1C shows a graph corresponding to the temperature distribution of FIG.
The domain wall energy density σ of the corresponding first magnetic layer₁ Distribution
It is a graph shown. Thus, the domain wall energy density in the x direction
Degree σ ₁ , The domain wall of each layer at the position x
On the other hand, the force F calculated from the following equation₁ Works.

[0018]

(Equation 1) This force F ₁ acts to move the domain wall to a lower domain wall energy. The first magnetic layer, since the domain wall coercive force is small domain wall mobility is large, alone, readily domain wall is moved by the force F _1. However, in the region before the position x _s (right side in the figure), the medium temperature is still lower than T _{s and} the region is exchange-coupled with the third magnetic layer having a large domain wall coercive force. The domain wall in the first magnetic layer is also fixed at a position corresponding to the position of the domain wall.

In the present invention, as shown in FIG. 1 (a), the domain wall 15 is in the position x _s of the medium, it increased the medium temperature to a temperature T _s near the Curie temperature of the second magnetic layer,
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 “instantly” to a region where the temperature is higher and the domain wall energy density is smaller, as indicated by the dashed arrow 17.

When the domain wall 15 passes below the spot 16 of the reproducing light beam, all the atomic spins of the first magnetic layer in the spot are aligned in one direction. Each time the magnetic wall 15 with the movement of the medium comes to a position x _s, and moves under the spot domain wall 15 is momentarily aligned in all one direction inverted atomic spins in the spot. As a result, as shown in FIG. 1A, the amplitude of the reproduced signal is always constant and maximum regardless of the interval between the recorded magnetic domain walls (that is, the length of the recording mark), and is due to the optical diffraction limit. This completely eliminates 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 make sure that the time required for the medium to move a distance corresponding to the shortest recording mark length is not longer than t _min (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 normal conventional method. In this figure, (a1) to (a7) and (b1) to (b7)
This shows a state in which the reproducing spot 31 moves on the information track 36 on which the magnetic domains 33 having different recording mark lengths are formed. (A8) and (b8) are graphs of the obtained reproduced signal.

In the conventional reproducing method, the maximum amplitude of the reproduced signal cannot be obtained (b8) unless the reproducing spot 31 is completely in 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, just before the portion of the reproducing spot 31 are the manner becomes critical temperature T _s of the second magnetic layer. Therefore, immediately before the reproducing spot 31 is attached to the domain wall 34, the temperature of the domain wall 34 reaches 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 (a2), and the maximum amplitude of the reproduced signal is obtained instantaneously (a8).

In the conventional reproducing method, the magnetic domain 3
If 3 is smaller than the spot diameter, the reproduction spot 3
1 does not fall within the magnetic domain (b3 to b7), and the obtained reproduced signal becomes unclear (b8). On the other hand, in the present invention, when the reproducing spot 31 substantially crosses the domain wall of the recording mark, the domain wall sequentially moves backward in the reverse direction.
3-a7), a very clear reproduced signal is obtained (a
8).

As described above, the magneto-optical recording medium of the present invention having the first to third magnetic layers has been described. In the present invention, as shown in FIG. The magnetic layer 44 may be provided between the first magnetic layer 41 and the second magnetic layer 42. The fourth magnetic layer 44 has a Curie temperature higher than the second magnetic layer, lower than 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 inducing a force sufficient to move the domain wall in the first magnetic layer.

[0026] 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 doing so, the exchange coupling between the fourth magnetic layer and the third magnetic layer is cut, and the domain wall 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-mentioned temperature distribution. When the gradient of the domain wall energy density σ ₁ exists in the x direction in this manner, the force F _i acts on the domain wall of each layer existing at the position x as described above, and the force F _i is The domain wall is moved to the lower side of.

On the other hand, in order to read a record at a high speed, it is necessary to move the domain wall at a high speed. Therefore, it is necessary to apply a large force to the domain wall. Generally, the temperature dependence of the domain wall energy density increases as the temperature 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 a change in the plane of polarization of the reflected light from the first magnetic layer, the irradiation area of the spot of the reproducing light beam has a temperature sufficiently lower than the Curie temperature of the first magnetic layer. Must be

Here, as shown in FIG. 4, if the fourth magnetic layer 44 having a lower Curie temperature is provided adjacent to the first magnetic layer on the side opposite to the light beam incident side, the reproduction In the irradiation area of the light beam spot, a 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.

Furthermore, if the fourth magnetic layer is provided with a Curie temperature gradient in the film thickness direction such that the Curie temperature becomes lower as approaching the second magnetic layer, the x-direction temperature gradient is increased. Since the components of the fourth magnetic layer immediately below the Curie temperature can be sequentially formed in the direction x, it is necessary to move the domain wall x
A relatively large force can be exerted over the entire range of directions.

[0031]

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 embodiment, a dielectric layer 55, a first magnetic layer 51, a second magnetic layer 52, a third magnetic layer 53, and a dielectric layer 54 are sequentially stacked on a transparent substrate 56.

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

Further, in this structure, Al, AlTa,
A thermal property may be adjusted by adding a metal layer made of AlTi, AlCr, Cu, or the like. Further, a protective coat made of a polymer resin may be provided. Alternatively, a substrate after film formation may be attached.

In the above medium, each of the magnetic layers 51 to 53
Can be made of various magnetic materials, for example, Pr, Nd, Sm, Gd, Tb, Dy, H
Rare earth-iron composed of 10 to 40 at% of one or more rare earth metal elements such as o, and 90 to 60 at% of one or more iron group elements such as Fe, Co, and Ni It can be constituted by a group III amorphous alloy.
In order to improve corrosion resistance, Cr, Mn, C
Elements such as u, Ti, Al, Si, Pt, and In may be added in small amounts.

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

In addition, materials such as garnet, a platinum group-iron group periodic structure film, and a platinum group-iron group alloy can be used.

As the first magnetic layer, for example, GdC
O, GdFeCo, GdFe, NdGdFeCo, and the like, a rare earth-iron group amorphous alloy having a small perpendicular magnetic anisotropy, and a material for bubble memory such as garnet are desirable.

As the third magnetic layer, for example, TbFe
Rare earths such as Co, DyFeCo, TbDyFeCo
It is desirable to use a material that has a large perpendicular magnetic anisotropy and can stably maintain the magnetization state, such as an iron group amorphous alloy or a platinum group-iron group periodic structure film such as Pt / Co and Pd / Co.

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

FIG. 6 shows the structure of a medium provided with a fourth magnetic layer. In this embodiment, on the transparent substrate 66,
A dielectric layer 65, a first magnetic layer 61, a fourth magnetic layer 64,
A second magnetic layer 62, a third magnetic layer 63, and a 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 unless it exceeds the gist of the present invention.

First, an embodiment 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, T
b, Fe, and Co targets were attached, and a polycarbonate substrate having a guide groove for tracking was fixed to a substrate holder. Then, the inside of the chamber was evacuated with a cryopump until a high vacuum of 1 × 10 ⁻⁵ Pa or less was obtained. Exhausted. An Ar gas was introduced into the chamber until the pressure became 0.3 Pa while the vacuum was evacuated, and an SiN layer serving as an interference layer was formed to 800 Å while rotating the substrate.
Subsequently, a GdCo layer was formed as a first magnetic layer with a thickness of 300 Å, and a DyFe layer was formed as a second magnetic layer with a thickness of 100 Å.
An Angstrom and a TbFeCo layer were sequentially formed as a third magnetic layer to a thickness of 400 Angstrom. Finally, a 800 Å-thick SiN layer was formed as a protective layer.
When 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
DC power was applied to each target of Gd, Dy, Tb, Fe, and Co to form a film.

The composition of each magnetic layer is adjusted so that it is all close to the compensation composition.
0 ° C. or higher, the second magnetic layer is 70 ° C., and the third magnetic layer is 20 ° C.
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 view in FIG. 100
It is formed in a rectangular shape of 0 Å. For this reason,
The magnetic layer 72 stacked on the land 76 is substantially separated at the guide groove 75. Actually, a small amount of film is deposited on the step portion and the magnetic layer is connected, but since the film thickness is extremely thin as compared with other portions, the coupling at the step portion can be ignored. In the present invention, magnetically separated from each other between the information tracks includes such a state. When a reversed magnetic domain is formed on the land 76 over the entire width, an unclosed domain wall 77 is formed at the boundary of the magnetic domain on the land 76 as shown in FIG. 7B. Even if such a domain wall 77 is moved in the track direction, the domain wall 77 on the side of the track is not generated and disappears, so that it can be easily moved.

The recording and reproduction characteristics of the magneto-optical recording medium thus obtained 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 denotes a recording / reproducing laser light source having a wavelength of 780 nm and arranged so that P-polarized light enters the recording medium. 8
2 is a laser light source for heating, the wavelength is 1.3 μm,
Similarly, they are arranged so that P-polarized light enters the recording medium. 83 transmits 100% of 780 nm light, and
This is a dichroic mirror designed to reflect 100% of 3 μm light. Reference numeral 84 denotes a deflecting beam splitter.
It is designed to transmit 〜80% and reflect S-polarization 100%. The luminous flux diameter of the 1.3 μm light is smaller than the aperture diameter of the objective lens 85, and the NA is smaller than that of the 780 nm light that is condensed through all the openings. In addition, 87 has 1.3 μm light,
It is provided so as not to leak into the signal detection system, and transmits 100% of 780 nm light and 1.3 μm light.
This is a dichroic mirror designed to reflect 00%.

With this optical system, on the recording surface of the recording medium 86, as shown in FIG. Can be formed 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. Thus, 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
Also shown is the isotherm 96 of _s . For recording / reproducing, the medium has a linear velocity of 5m.
/ Sec.

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

The modulation frequency of the recording magnetic field was varied 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 was 1 mW, and the laser for heating was simultaneously irradiated at a power of 20 mW.
N was measured. The temperature distribution on the medium surface at this time is shown in FIG.
It is as shown in (b).

The measurement result is shown by a graph line a in FIG. For comparison, the measurement result by the conventional super-resolution reproduction method described in JP-A-3-93058 in the figure is shown as a graph line b, and the measurement result by the normal reproduction method without super-resolution phenomenon is shown in the graph. Shown as line c.

According to the reproducing method of the present invention, the reversal of all magnetizations in the reproducing spot is detected even if the mark length is shortened. And the mark length dependence of C / N is almost eliminated.

Incidentally, in the medium of the present embodiment, the manner in which the domain wall of the first magnetic layer moves due to the temperature gradient was confirmed by direct observation with a polarizing microscope as described below.

First, a sample having the same configuration as that of the first embodiment and having the magnetic layers laminated in reverse order was manufactured. 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, from the first magnetic layer side.

Next, this sample was irradiated with a condensing laser for heating to form a temperature distribution substantially similar to that of Example 1 within the field of view of the polarizing 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
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, each time the boundary of the magnetic domain formed on the track enters the above-described circular coupling / cutting region, it was observed that the moved magnetic domain expanded toward the center of the circular region.

When the irradiation of the heating laser was stopped, it was observed that 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 moves to the high temperature side due to the temperature gradient in the region where the coupling with the third magnetic layer has been cut.

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

First, the substrate surface before film formation was subjected to an accelerated irradiation treatment of Ar ions.
This means that accelerated irradiation of Ar ions was applied to the film surface after the N layer was formed. By these treatments, the surface state was smoothed. Third, the thickness of the first magnetic layer is set to 20
That is, it was changed to 00 angstroms. These changes independently contribute to the improvement of the domain wall mobility of the first magnetic layer.

The recording / reproducing characteristics of this medium were measured by the same method as in Example 1. As a result, the same good results as in Example 1 were obtained. Further, the linear velocity of the medium during reproduction is set to 20 m / s
Even when reproduction was performed at a high speed up to ec, the reproduction characteristics did not decrease.

Example 3 A magneto-optical recording medium was produced by forming a thin film on a polycarbonate substrate in the same manner as in Example 1 using the same film forming machine and method.

However, in this embodiment, the substrate is
A pre-pit was formed, and a guide groove having a U-shaped cross section was used. For this reason, the laminated magnetic layers are not divided in shape at the guide grooves.

The medium was irradiated with a high-output laser at the guide groove portion to anneal the entire surface of the magnetic layer at 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 adjacent tracks was cut off via the guide groove. The recording and reproduction characteristics of this medium were measured by the same method as in Example 1.
The same good results as those described above were obtained.

When the recording / reproducing characteristics of the medium were measured by the same method as in Example 1 without performing the annealing treatment described above, the noise increased compared to the result of Example 1, but the light Reproduction of a signal having a period equal to or less than the diffraction limit was sufficiently possible. In this medium, since a magnetic domain surrounded by a closed magnetic domain wall exists, the operation becomes unstable when the magnetic domain wall is moved in a direction in which the magnetic domain is enlarged, and noise increases.

As another method of breaking the coupling between the adjacent track and the magnetic layer, patterning by etching may be performed.

Example 4 Using the medium of Example 1, the recording / reproducing characteristics were evaluated using the same recording / reproducing apparatus 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 is arranged on the slope in front of the moving direction of the medium in the temperature distribution induced by the heating laser.

When the medium moves and passes through the position indicated by S in the figure, the first magnetic layer and the third magnetic layer are combined again, and the first magnetic layer is connected to the third magnetic layer. The magnetization orientation state is transferred. When the domain wall of the third magnetic layer passes through the position indicated by S, the domain wall is left at the position indicated by S of the first magnetic layer,
This domain wall momentarily moves backward. If 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 substantially matches the shape of the domain wall of the magnetic domain formed by the magnetic field modulation method, the domain wall can be moved more stably.

<Comparative Example 1> Using the medium of Example 1, the recording / reproducing characteristics were measured by a normal magneto-optical disk recording / reproducing apparatus to which a heating laser was not added.

The reproduction characteristics were examined in the same manner as in Example 1 except that the heating laser was not irradiated.
By increasing the reproducing power to about 3 mW, a good C / N was obtained. However, as compared with the result of Example 1, the C / N was about 5 dB lower at each mark length. This is because the temperature of the medium does not increase at the front of the reproducing spot, and the domain wall moves from the middle of the reproducing spot, so that the entire spot cannot be used effectively as in the first embodiment.

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

<Embodiment 5> A B-doped Si and Gd, Tb, F
e, Co, and Cr targets were attached, and the polycarbonate substrate on which the guide groove for tracking was formed was fixed to the substrate holder. Then, the inside of the chamber was evacuated with a cryopump until a high vacuum of 1 × 10 ⁻⁵ Pa or less was obtained. Exhausted.

Ar gas is maintained at 0.3 Pa
The SiN layer serving as an interference layer was formed to a thickness of 800 Å while rotating the substrate. Subsequently, a GdCoCr layer was formed as a first magnetic layer at 300 Å, and a GdFr layer was formed as a fourth magnetic layer.
An eCr layer was formed in order of 300 angstroms, a second magnetic layer was formed of a TbFeCr layer of 100 angstroms, and a third magnetic layer of a TbFeCo layer was formed of 400 angstroms. Finally, a 800 Å-thick SiN layer was formed as a protective layer. When 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
A DC power was applied to each of the targets to form a film.

The composition of each magnetic layer is adjusted so as to be close to the compensation composition, and the Curie temperature is set to 30 for the first magnetic layer.
0 ° C. or higher, fourth magnetic layer at 170 ° C., second magnetic layer at 7 ° C.
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.

The recording / reproduction 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 a result of the measurement, as in the case of Example 1, a good result indicated by a graph line a in FIG. 10 was obtained.

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

The manner in which the domain wall of the first magnetic layer moves due to the temperature gradient was confirmed by direct observation with a polarizing 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 as in Example 5, using a film forming machine and a film forming method.

However, in this embodiment, the inside of the fourth magnetic layer is formed of the first, second and third constituent layers in order from the side of the first magnetic layer, and the Curie of each constituent layer is formed. Temperature in order,
180 ° C., 160 ° C., 140 ° C.
0 angstroms, 400 angstroms, 800
As the angstrom, the fourth magnetic layer had a graded Curie temperature gradient in the film thickness direction. GdFeCoCr was used as a material.

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

The composition of each magnetic layer is adjusted so as to be close to the compensation composition by adjusting the composition ratio of the rare earth element and the iron group element, adjusting the amounts of Co and Cr added, and setting the Curie temperature 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 results as in Example 5 were obtained. Further, the linear velocity of the medium during reproduction is set to 30 m / s.
Even when reproduction was performed at a high speed up to ec, the reproduction characteristics did not decrease.

In this embodiment, at the time of reproduction, a temperature gradient in the track direction of about 120 ° C. to 180 ° C. was formed in the recording / reproducing spot area on the recording surface of the medium. In this case, in the region from 120 ° C. to 140 ° C., a large force acts on the domain wall of the third constituent layer of the fourth magnetic layer, and
A large force acts on the domain wall of the second constituent layer of the fourth magnetic layer in the range of from 160 ° C. to 160 ° C., and in the range of 160 ° C. to 180 ° C., it acts on the domain wall of the first constituent layer of the fourth magnetic layer. Large force acts. Therefore, the domain wall existing from the first magnetic layer to the fourth magnetic layer can be moved by 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 a higher speed.

Example 7 A magneto-optical recording medium was prepared by forming a thin film on a polycarbonate substrate in the same manner as in Example 5, using a film forming machine and a film forming method.

However, in this embodiment, the substrate is
A pre-pit was formed, and a guide groove having a U-shaped cross section was used. For this reason, the laminated magnetic layers are not divided in shape at the guide grooves.

The structure of the magnetic layer and others 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 was composed of a sample (1) in which the composition ratio of Gd of GdFeCr was adjusted to have a composition in which the iron group element sublattice magnetization was dominant at room temperature, and a sample in which the rare earth element sublattice magnetization was 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 in which rare earth element sublattice magnetization is dominant at room temperature and no compensation temperature exists below the Curie temperature. Produced. The Curie temperature of each sample was adjusted to 170 ° C. by adjusting the amount of Cr added.

In these samples, a high-output laser was applied to the guide groove portions, and the entire magnetic layer in the guide groove portions was annealed. As a result, the magnetic layer in the portion of the guide groove was magnetically altered, and the coupling between the magnetic layers of the tracks adjacent to each other via the guide groove was broken.

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

However, when the linear velocity is increased to 30 m / sec for reproduction, the sample (1) has a C / N of 5 dB.
To some extent. On the other hand, in sample (2), C /
The decrease in N was hardly observed, and in the sample (3), the decrease was only about 2 dB.

This is because the composition having a predominant rare earth element sublattice magnetization at room temperature, especially the composition having a compensation temperature equal to or lower than the Curie temperature has a large temperature dependence of the domain wall energy near the Curie temperature, It is considered that 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 of adjusting the temperature distribution on the medium by another means while leaving the optical head in the conventional state can be considered. For example, it is conceivable to divert the core of the flying head used for magnetic field modulation recording as a heat source, or to arrange another appropriate heating element near the laser irradiation area for reproduction of the medium. However, in this case, care must be taken so that the positional relationship between the temperature position at which the domain wall starts to move and the reproduction spot does not fluctuate at a frequency close to the frequency of the reproduction signal.

[0098]

As described above in detail, according to the reproducing method and the reproducing apparatus of the magneto-optical recording medium of the present invention, a signal having a period equal to or less than the diffraction limit of light can be transmitted at a high speed without reducing the reproduced signal amplitude. , The recording density and transfer speed can be greatly improved, and the size of the reproducing apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a concept of a reproducing method of the present invention when a magneto-optical recording medium having first to third magnetic layers is used. (A) shows a cross section of the medium in a reproducing state, and schematically shows a spin orientation 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 a relationship between a time τ required for a domain wall to pass under a spot and a time t _min required for a medium to move a distance equivalent to the shortest recording mark length.

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

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

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

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

FIG. 7 is a diagram illustrating a cross-sectional shape of a magneto-optical recording medium according to an example.

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

FIG. 9 is a schematic diagram showing a reproduction state in the embodiment.

FIG. 10 is a graph showing C / N obtained in an example.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 1st magnetic layer 12 2nd magnetic layer 13 3rd magnetic layer 14 Direction of atomic spin 15 Domain wall 16 Reproduction-like light beam spot 17 Moving direction of domain wall 18 Moving direction of medium

Claims (3)

(57) [Claims] 1. A domain wall moving layer that contributes to reproduction of information and in which a domain wall moves, a memory layer that holds recording magnetic domains according to information, and is disposed between the domain wall moving layer and the memory layer; A method for reproducing information from a magneto-optical recording medium having a domain wall coercive force smaller than that of the memory layer, wherein the magnetic domain wall moving layer includes a blocking layer having a lower Curie temperature, and irradiating the magneto-optical recording medium with a light beam; And relatively moving the light beam, forming a temperature distribution having a gradient with respect to the moving direction of the spot of the light beam on the medium, in the region above the Curie temperature of the blocking layer, from the memory layer The domain wall of the recording magnetic domain transferred to the domain wall motion layer is moved on the domain wall motion layer by the force generated by the gradient of the temperature distribution to enlarge the recording magnetic domain, and the polarization of the reflected light of the light beam is increased. The method of reproducing a magneto-optical recording medium for reproducing said information by detecting a change in the surface. 2. A domain wall moving layer which contributes to reproduction of information and in which a domain wall moves, a memory layer which holds a recording magnetic domain according to information, and is disposed between the domain wall moving layer and the memory layer; The magnetic domain of the memory layer is transferred to the moving layer at room temperature, and the domain wall moving layer transfers information from a magneto-optical recording medium having a smaller domain wall coercive force than the memory layer. A reproducing device for irradiating the medium with a light beam; heating means for forming a temperature distribution having a gradient with respect to a moving direction of a spot of the light beam on the medium; A reproducing apparatus comprising: means for relatively moving; and means for detecting a change in the polarization plane of reflected light of the light beam and reproducing recorded information. 3. The reproducing apparatus according to claim 2, wherein said heating means and said irradiation means are separated.