JP2990811B2 - Magneto-optical recording / reproducing method - 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 / reproducing method .

[0002]

2. Description of the Related Art When a magneto-optical recording / reproducing method is employed in which information recording pits, that is, bubble magnetic domains are formed by local heating by laser beam irradiation, and this recorded information is read out by magneto-optical interaction, that is, the Kerr effect or the Faraday effect. In order to increase the recording density of magnetic recording, the recording pits must be miniaturized. In this case, the resolution at the time of reproduction (resolution) becomes a problem. This resolution depends on the laser wavelength at the time of reproduction and the numerical aperture of the objective lens. A. Is determined by

A general magneto-optical recording / reproducing method will be described with reference to FIG. FIG. 6A shows a schematic top view of a recording pattern, for example, recording pits 4 shown with diagonal lines on lands 2 sandwiched between grooves or grooves 1 on both sides.
However, a reproducing method of a magneto-optical recording medium 3, for example, a magneto-optical disk, recorded according to, for example, binary information “1” or “0” will be described. Now, the case where the beam spot of the read laser beam on the magneto-optical recording medium 3 is a circular spot indicated by reference numeral 5 will be described. At this time, as shown in FIG. 6A, one recording pit 4
When the pit interval is selected so that only the recording pits 4 can exist, there are two modes, as shown in FIG. 6B or FIG. Therefore, when the recording pits 4 are arranged at equal intervals, the output waveform is, for example, as shown in FIG.
As shown in FIG. 7, the output becomes, for example, a sine wave output that is inverted to the positive or negative with respect to the reference level 0.

However, as shown in a schematic top view of a recording pattern in FIG. 7A, when recording pits 4 are arranged at high density, a plurality of recording pits 4
Comes in. For example, looking at three adjacent recording pits 4a, 4b, and 4c, FIGS. 7B and 7C
As shown in FIG. 7, there is no change in the reproduction output between the case where the adjacent recording pits 4a and 4b enter one beam spot 5 and the case where the recording pits 4b and 4c enter the same beam spot 5, so that the reproduction output does not change. The waveform is, for example, linear as shown in FIG. 7D, and the two cannot be distinguished.

As described above, in the conventional general magneto-optical recording / reproducing method, the recording pits 4 recorded on the magneto-optical recording medium 3
Is read out as it is, even if high-density recording, that is, formation of high-density recording pits, is possible, the S / N (C / N) problem arises due to the restriction of the resolution during reproduction. Sufficient high-density recording and reproduction cannot be performed.

[0006]

The S / N (C
/ N), it is necessary to improve the resolution (resolution) at the time of reproduction. However, this resolution is limited by the laser wavelength, the numerical aperture of the lens, and the like. In order to solve such a problem, the present applicant has previously proposed a super-resolution (super-resolution) magneto-optical recording / reproducing method (hereinafter referred to as MSR) (for example, Japanese Patent Application No. 1-222585, entitled "Optical Magnetic recording / reproducing method ").

The MSR will be described.
In R, the recording pits 4 of the magneto-optical recording medium are generated only in a predetermined temperature range at the time of reproduction by utilizing the temperature distribution due to the relative movement between the magneto-optical recording medium and the reproducing beam spot 5. As a result, the resolution of the reproduction is increased.

As examples of the MSR system, a so-called floating type reproducing system and an extinguishing type reproducing system can be considered.

First, the floating type MSR system will be described with reference to FIG. FIG. 8A is a schematic top view showing a recording pattern of the magneto-optical recording medium 10, and FIG. 8B is a schematic sectional view showing a magnetization mode. In this case, as shown in FIG. 8A, the magneto-optical recording medium 10 moves relatively to the beam spot 5 by the laser beam in the direction indicated by the arrow D. In this case, for example, as shown in FIG. 8B, it has a reproducing layer 11 composed of at least a perpendicular magnetization film and a recording layer 13, and more preferably has an intermediate layer 12 interposed between both layers 11 and 13. For example, a magneto-optical disk is used. Each layer 1 in the figure
Arrows in 1, 12, and 13 schematically show the directions of the magnetic moments. In the example shown in the figure, the downward direction is an initialized state, and the magnetic domain due to the upward magnetization in FIG. Information recording pits 4 are formed.

In such a magneto-optical recording medium 10,
The reproducing mode will be described first.
When i is applied, the reproducing layer 11 is magnetized downward in FIG. 6B and initialized. That is, the recording pits 4 disappear in the reproducing layer 11, but at this time, in the portion having the recording pits 4, the magnetization directions of the reproducing layer 11 and the recording layer 13 are maintained in opposite directions by the domain wall generated in the intermediate layer 12. The recording pit 4 is a latent image recording pit 4
Remains as 1.

On the other hand, the magneto-optical recording medium 10 has an initialization magnetic field H
A reproducing magnetic field Hr in the opposite direction to i is given at least in the reproducing section. In this state, the area having the latent image recording pits 41 initialized with the movement of the medium 10 is the beam spot 5.
When the portion that enters the lower portion and is heated by the beam irradiation shifts to the tip side below the beam spot 5, that is, to the left in FIG. 8, the tip end side of the spot 5 is indicated by hatching surrounded by a broken line a. As described above, a high-temperature region 14 substantially occurs, in which the domain wall of the intermediate layer 12 disappears, and the recording layer 1 is moved by the exchange force.
The magnetization of No. 3 is transferred to the reproducing layer 11, and the latent image recording pits 41 existing in the recording layer 13 emerge as recording pits 4 that can be reproduced on the reproducing layer 11.

Accordingly, if the rotation of the polarization plane of the beam spot 5 due to the Kerr effect or the Faraday effect due to the direction of magnetization in the reproducing layer 11 is detected, the recording pit 4
Can be read. At this time, in the low-temperature region 15 other than the high-temperature region 14 in the beam spot 5,
The latent image recording pits 41 are not raised on the reproducing layer 11, and eventually the recording pits 4 that can be read only in the narrow high-temperature region 14 shown by hatching in the beam spot 5 are present. Even when the recording density is such that a plurality of recording pits 4 enter into the beam spot 5, specifically, even in the magneto-optical recording medium 10 of high-density recording, only a single recording pit 4 can be read out. High resolution reproduction can be performed.

In order to perform such reproduction, the initialization magnetic field Hi, the reproduction magnetic field Hr, the coercive force, thickness, magnetization,
The domain wall energy or the like is high temperature region 1 in beam spot 5.
4 and the temperature of the low-temperature region 15. That is,
The coercive force of each reproducing layer 11 and recording layer 13 is represented by H _C1 and H _C3 ,
Assuming that the thickness is h ₁ and h ₃ and the saturation magnetization M _S is M _S1 and M _S3 , the condition for initializing only the reproducing layer 11 is as follows.

[0014]

## EQU1 ## Hi> H _c1 + σ _w2 / 2M _s1 h ₁

Here, σ _w2 is the reproduction layer 11 and the recording layer 13
3 shows the interface domain wall energy between the two.

The condition for maintaining the information of the recording layer 13 by the magnetic field is given by the following equation (2).

## EQU2 ## Hi <H _c3 −σ _w2 / 2M _s3 h ₃

Further, in order to maintain the domain wall by the intermediate layer 12 between the reproducing layer 11 and the recording layer 13 even after passing under the initialization magnetic field Hi, the following equation 3 is required.

H _c1 > σ _w2 / 2M _s1 h ₁

The temperature T selected in the high temperature region 14
_{In H} , the following equation 4 is required.

[Number 4] _{H c1 -σ w2 / 2M s1 h} 1 <H r <H c1 + σ w2 / 2M s1 h 1

By applying the reproducing magnetic field Hr that satisfies the equation (4), the latent image recording pits 4 of the recording layer 13 are formed on the reproducing layer 11 only in the portion where the domain wall by the intermediate layer 12 exists.
1 can be embossed as a transfer, that is, a recording pit 4.

Next, the disappearance type MSR will be described with reference to FIG. FIG. 9A is a schematic top view showing a recording pattern of the magneto-optical recording medium 10, and FIG. 9B is a schematic sectional view showing a magnetization mode thereof. 9A and 9B, FIG.
Parts corresponding to A and FIG. 8B are denoted by the same reference numerals, and redundant description is omitted. In this case, the initialization magnetic field Hi is not required.

In such a magneto-optical recording medium 10,
The reproducing mode will be described. In this case, the Curie temperature T _C2 of the intermediate layer 12 is set to be lower than the temperature in the high temperature region 14, and at this time, the external magnetic field H _r where the following equation 5 is satisfied
Thus, even in the laser beam spot 5, in the high temperature region 14, the magnetization is aligned downward in the drawing by the reproducing magnetic field Hr applied from the outside, so that the recording pits 4 in the reproducing layer 11 disappear. That is, in the annihilation type MSR system, the resolution can be improved by enabling reproduction only of the recording pits 4 in the low-temperature region 15 of the beam spot 5.

[0022]

[Number 5] _{H r> H c1 + σ w2} / 2M s1 h 1

However, in this case, various conditions such as the coercive force are set so that the recording pits 4 remain as the latent image recording pits 41 in the recording layer 13 even in the disappearing state. The magnetization of the recording layer 13, that is, the information pits 4 is transferred and maintained in a reproducible state.

According to the above-mentioned floating type and extinction type MSR system, recording pits are reproduced in a part of the reproduction laser beam spot, so that the resolution at the time of reproduction can be improved. .

However, even if the resolution at the time of reproduction is improved as described above, if the resolution at the time of recording is low, it is restricted by this, and the advantage of the MSR method cannot be fully utilized.

The present applicant has proposed a method of performing high-resolution recording by magnetic field modulation in Japanese Patent Application No. 2-39147, entitled "Magneto-optical recording method", in order to improve the resolution at the time of recording. Did.

That is, when the above-described recording pits are formed by modulating the intensity of the laser beam, recording pits having a size approximately equal to the beam diameter of the laser beam can be easily formed. If an attempt is made to form small recording pits, recording will be performed using the tip of the intensity distribution of the laser beam, and it will be difficult to control the recording power. That is, in optical modulation recording, the laser beam intensity has a Gaussian distribution, and the allowable range of laser power for forming a magnetic domain with a smaller diameter than the beam diameter is extremely narrow due to the temperature diffusion of the magneto-optical recording medium. Becomes

In the light modulation method, if the magnetic domain interval (recording pit interval) is reduced to increase the density, the temperature rise of the medium by the laser beam irradiated immediately before will increase the recording power of the next magnetic domain (recording pit). Will have an effect. That is, when random data is recorded, the optimum value of the recording power changes depending on the pattern.

Therefore, in the light modulation method, there is a limit to the improvement of the recording density, and even if the resolution at the time of reproduction is improved, the capability cannot be fully utilized.

Therefore, in the above-mentioned Japanese Patent Application No. 2-39147, signals are recorded by magnetization modulation recording on a magneto-optical recording medium capable of performing reproduction by the above-mentioned MSR method. This magnetic field modulation recording is performed by forming a recording pit, that is, a magnetic domain by a magnetic field modulated according to recording information under laser light irradiation, for example, continuous laser light, so-called DC irradiation, or pulse irradiation corresponding to the pit.

That is, in this magnetic field modulation recording, the recording layer is heated to a temperature equal to or higher than the Curie point or the compensation point by a laser beam, and in this state, an external magnetic field is applied in accordance with the recording signal while reversing the polarity. . In magnetic field modulation recording, the pit length is controlled by an external magnetic field,
It is not affected by the intensity distribution of the laser beam.

That is, assuming that the laser output is fixed as shown in FIG. 10A and an external magnetic field whose polarity is inverted with a fixed period as shown in FIG. 10B is applied.
Recording pits 4 schematically shown in C are formed with a pitch corresponding to the reversal period of the external magnetic field.

As described above, for example, by magnetic field modulation recording, if information is recorded on the magnetic recording medium 10 having at least the reproducing layer 11 and the recording layer 13 as described with reference to FIGS. 8 and 9, high-density recording becomes possible. The reproduction of the magnetic recording medium 10 on which high-density recording has been performed by the MSR method capable of performing the above-described high-resolution reproduction can improve the S / N (C / N). become.

However, as shown in FIG. 10C, the shape of the recording pit formed by the above-described magnetic field modulation recording is actually an arc shape or a crescent shape which bulges and bulges in the transition direction of the magnetic recording medium 10. Where the curve is steep.

This is because the isothermal distribution curve of the magneto-optical recording layer composed of the reproducing layer 11, the intermediate layer 12, the recording layer 13, and the like is shown in FIG.
When the point C is the center of the laser beam spot, the temperature difference between the irradiation line of the spot and the outside of the spot becomes large. It has an elliptical distribution with a major axis along the direction, and since the temperature rises on the tip side of the beam spot, the distribution has a steep curvature on the tip side, and the recording pit shape is correspondingly steep. The curved shape is a crescent shape.

When the pattern of the recording pits has a remarkable crescent shape, the S / N (C / N) is reduced. That is, the improvement in resolution inherent in the MSR method is hindered.

This reproducing state will be described with reference to FIG. FIG. 12A illustrates a floating type MSR system. In this case, a high-temperature region 1 which is a reproducible region 5w (hereinafter, referred to as a window region) of a reproducing laser spot 5 is shown.
In addition to the one recording pit 4b, the tails at both ends of the recording pit 4a adjacent to the recording pit 4b enter, thereby lowering the S / N (C / N). FIG. 12B illustrates the disappearance type MSR system. In this case, the recording pit 4 to be eliminated in the window area 14 is used.
a enters the window area 5W with a tail, and S /
N (C / N).

This phenomenon is not limited to the floating type MSR but also applies to the annihilation type MSR described with reference to FIG. 9. In this case, the low temperature region 15 below the beam spot 5 becomes the window region. In this area, not only the recording pit 4c in FIG. 12 but also the tails at both ends of the recording pit 4b adjacent thereto enter the S / N ratio.
(C / N).

The present invention solves the problem of the shape of the recording pits in the magneto-optical recording medium used in such an MSR reproduction system, and thus improves the resolution during reproduction by the MSR system, that is, the S / N ratio. (C / N) is to be improved.

In the present invention, as shown in a schematic cross-sectional view of one example in FIG. 1 , a good heat conductive material layer 22 is directly formed on at least a magneto-optical recording layer 21 comprising a reproducing layer 11 and a recording layer 13.
For magneto-optical recording media laminated indirectly or indirectly
And at least recording by magnetic field modulation is performed on the recording layer.
This recording is performed by laser light irradiation.
Change the magnetization state of the reproducing layer within a specific temperature range
While reading, a specific recording pit is read.

[0041]

According to the above-described magneto-optical recording medium, since the good thermal conductive material layer 22 is provided, its isothermal distribution curve is isotropic as shown in FIG. Since the curve is substantially a perfect circular curve, a steep curvature in the direction of relative transition with the beam spot is avoided.

Accordingly, the recording pit 4 formed by the magnetic field modulation recording has a gently curved shape as shown in FIG.

Therefore, when the recording pits 4 recorded on the magneto-optical recording medium are read out by a reproducing light beam, as shown in FIG. 3, for example, a beam spot 5 for reading (reproducing) by a laser beam is used. In the reproducible window area 5w, the original 1
Only one recording pit 4 can be present, and it is possible to prevent the end of another adjacent recording pit from entering.

By doing so, the S / N (C
/ N), and thus the reproduction resolution (resolution).

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where the present invention is applied to a magneto-optical disk will be described.

In this case, as shown in FIG. 1, a dielectric film 23 made of, for example, 800 .mu.m thick SiN or the like, a magneto-optical recording layer 21, for example, a thickness of 800 .ANG. A good thermal conductive material layer 22 made of Al of 300 ° is sequentially formed.

The magneto-optical recording layer 21 includes a reproducing layer 11, an intermediate layer 12, and a recording layer 1 similar to those described with reference to FIG. 8 or FIG.
3 can be adopted in a successively deposited manner by continuous sputtering.

It is desirable that the reproducing layer 11 has a high coercive force at room temperature as a two-layer structure with the reproducing auxiliary layer 11s. In this case, the coercive force of the reproduction auxiliary layer 11s is H _c1 ,
_Assuming that the magnetization is M _s1s and the thickness is h _1s , the above _equations 1 and 4
The term of H _c1 in is replaced as shown in the following _Expression 6,
The number 1, the σ _w2 / M _s1 h ₁ in the number 3 and number 4 sigma _{w 2}
/ (M _s1 h ₁ + M _s1s h _1s ).

[0049]

(M _s1 h ₁ H _c1 + M _s1s H _c1s ) / (M _s1 h ₁ + M _s1s h _1s )

Then, as described above, the magneto-optical recording layer 21
Is a reproduction layer 11 having a reproduction auxiliary layer 11s, and an intermediate layer 1
When the recording layer 13 has a four-layer structure, the reproducing layer 11
For example, GdFeC whose Curie point T _c1 is 300 ° C. or less
o, the reproduction auxiliary layer 11s has a Curie point T _c1s of, for example, about 120 ° C. TbFeCoAl, and the intermediate layer 12 has a Curie point T _c2.
However, the recording layer 13 can be formed of, for example, GdFeCo having a Curie point _Tc3 of, for example, about 250 ° C.

With respect to the magneto-optical recording medium having this configuration,
Linear velocity 16 m / sec, laser wavelength 780 nm, aperture diameter of objective lens When a recording pit is formed by magnetic field modulation with A of 0.53 and a mark length of 0.4 μm, the enlarged pattern of the recording pit 4 becomes as shown in FIG.

On the other hand, an enlarged pattern diagram of recording pits when recording is performed under the same conditions on a magneto-optical disk having the same configuration but not having the good heat conductive material layer 22 in FIG. As shown in FIG.

As is apparent from a comparison between FIG. 4 and FIG.
According to the magneto-optical recording medium of the present invention, the recording pits 4 are improved to have a crescent-like shape close to a gentle rectangular shape.

This is because, in the structure of the present invention, the heat radiation effect of the magneto-optical recording medium is enhanced by the provision of the good heat conductive material layer 22, whereby the laser beam spot 5 and the magneto-optical recording medium 10 are And relative recording direction (land portion) where spot 5 does not substantially hit
It can be considered that the temperature difference with respect to the width direction could be reduced, whereby the temperature distribution could be made substantially circular.

The good thermal conductive material layer 22 is made of Al
In addition, it can be made of an Al alloy, Ag, Au, Cu, or the like, and its thickness is desirably set to about 50 ° to 1200 °. This is because when the film thickness is less than 50 °, the heat radiation effect hardly occurs, and when the film thickness exceeds 1200 °, the reproducing power becomes too large.

The reading of the recording pits recorded on the magneto-optical recording medium according to the present invention can be performed by the floating type MSR method or the extinguishing type MSR method described with reference to FIGS.

In this case, the window area 5w that can be reproduced upon reading out the data, for example, the floating type M
In the SR, the S / N (C / N) can be improved because only one recording pit 4 can correspond to the window area 5w composed of the high-temperature area described in FIG.

In particular, in the disappearing type MSR, as can be seen from FIG. 12B, since the upper and lower raised areas of the window region 5W in FIG. Although the N reduction is remarkable, a significant improvement in C / N can be achieved by applying the present invention to this annihilation type MSR.

The present invention is not limited to the above-described example. For example, the floating type MS shown in FIGS.
Under the beam spot 5, a high temperature region and a low temperature region and a middle temperature region between them are taken into account by a combination method of R and annihilation type MSR, and the same operation as the annihilation type in the high temperature region is performed in the low temperature region. The recording state is maintained in the reproducing layer 11 only in the medium temperature region while maintaining the state of the medium, so that the present invention can be applied to various magneto-optical recording media applied to MSR and the like with higher resolution.

Each of the rare earth-transition metal layers constituting the magneto-optical recording layer 21 is formed of a rare earth metal and a transition metal, at least in the reproducing layer 11 to which the reproducing light is mainly irradiated during reproduction by the MSR method. It is also possible to adopt an artificial lattice structure having a repetitive lamination structure of each monoatomic layer or several atomic layers so as to make the structure less likely to cause characteristic deterioration due to mutual diffusion due to repeated heating by laser light irradiation.

[0061] by the present invention as described above lever, recording pits formed by the magnetic field modulation recording on the magneto-optical recording medium,
Since the curved shape is reduced, the S / N (C / N) is improved, that is, the reproduction resolution is improved.
By taking advantage of the reproduction of the system, it is possible to achieve sufficient high-density recording.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of a magneto-optical recording medium applied to a method of the present invention.

FIG. 2 is a diagram showing isotherms in a magneto-optical recording medium applied to the method of the present invention.

FIG. 3 is a diagram showing a relationship between recording pits formed on a magneto-optical recording medium and a reproducible area in the method of the present invention.

FIG. 4 is a pattern diagram of recording pits in a magneto-optical recording medium applied to the method of the present invention.

Continuation of the front page (56) References JP-A-62-137754 (JP, A) JP-A-58-73017 (JP, A) JP-A-2-105352 (JP, A) JP-A-2-126439 (JP) (A) JP-A-4-74328 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 11/10 506 G11B 11/10 521 G11B 11/10 523

Claims (1)

(57) [Claims] 1. A magneto-optical recording medium comprising at least a magneto-optical recording layer comprising at least a reproducing layer and a recording layer and a layer of a good heat conductive material, wherein at least the recording layer is recorded by magnetic field modulation. The recording is performed by changing the magnetization state of the reproducing layer in a specific temperature region by a laser beam irradiation in a specific temperature region by a part of a region of the laser light spot smaller than the laser light spot. A magneto-optical recording / reproducing method, which reads out recorded pits.