JPH0981981A - Magneto-optic recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely reproduce the signals of the period below the diffraction threshold of light by selecting the power of a recording laser beam in recording of information according to mark lengths. SOLUTION: The magneto-optic medium 7 is moved relative to a spot SP of the reproducing laser beam like arrow (a) at the time of reproducing. At this time, the temp. in the part of the medium 7 irradiated with laser beam rises, but if the moving speed of the medium 7 is constant, the temp. distribution of the shape occurring in the intensity distribution of the laser beam, the linear speed of the medium 7 and the constitution of the medium 7 occurs and the rear end side of the spot SP becomes a high-temp. region AH. The magnetical coupling between a reproducing layer 3 and a recording layer 5 is extremely weak or cut when the temp. of this region AH exists near the Curie temp. of the intermediate layer 4. The recording marks, therefore, begin to be deformed so as to diminish the entire magnetic energy possessed by the recording marks M. Then, the high-temp. regions AH of the recording marks M recorded with the low recording laser power turns to MS when the magnetic energy in these regions are minimized. The apertures AP where the marks exclusive of the regions MS within the spot SP are readable out are obtd.

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 method for recording / reproducing information with a laser beam utilizing a magneto-optical effect, and more particularly to a magneto-optical recording method which adopts a mark length recording method.

[0002]

2. Description of the Related Art As a rewritable high-density recording method,
Using the thermal energy of the semiconductor laser, the magnetic thin film is partially heated above the Curie temperature or the compensation temperature to reduce or eliminate the coercive force of this portion, and the magnetic field is magnetized in the direction of the externally applied recording magnetic field. There is a magneto-optical recording method whose basic principle is to reverse the direction.

The structure of the magneto-optical recording medium in this case is, for example, a recording magnetic layer having an excellent magneto-optical characteristic having an easy axis of magnetization in the direction perpendicular to the film surface on one main surface of a transparent substrate made of polycarbonate or the like. It is known that a recording portion is provided by laminating (for example, a rare earth-transition metal alloy amorphous thin film), a reflection layer, and a dielectric layer, and a laser beam is emitted from the transparent substrate side to read a signal. Has been.

By the way, in an optical recording medium such as an optical disc such as a digital audio disc or a video disc for recording or / and reproducing by irradiation of light including a magneto-optical recording medium, the linear recording density is mainly S at the time of reproducing. / N, and the signal amount of the reproduced signal largely depends on the period of the pit train of the recorded signal, the laser wavelength of the reproducing optical system, and the numerical aperture of the objective lens. At present, when the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens are determined, the pit period f which is the detection limit is determined. That is, f = λ / 2NA.

Therefore, in order to increase the density of the optical disc, it is necessary to shorten the laser wavelength λ of the reproducing optical system and increase the numerical aperture NA of the objective lens. However,
In the current technology, the laser wavelength λ and the numerical aperture N. A. There is a limit to the improvement of. Therefore, for example, in magneto-optical recording and reproduction, the structure of the magneto-optical recording medium, recording,
Techniques have been developed to improve the recording density by devising a reproducing method.

For example, regarding a reproducing method, Japanese Patent Laid-Open No. 1-1
In Japanese Patent Laid-Open No. 43041 and Japanese Patent Laid-Open No. 1-143042, a magneto-optical recording medium is a three-layer film including a reproducing layer, an intermediate layer, and a recording layer magnetically coupled to each other at room temperature, and is heated in a reproducing laser spot during reproduction. By enlarging, reducing or inverting the recorded magnetic domain of the reproduced layer in the high temperature portion, the recording information is read out in a part of the reproducing laser spot, that is, in the reproducing laser spot. Proposal of technology to increase the linear recording density by reducing the interference between information pits during reproduction by enabling the effect of masking the unreadable area and reproducing signals with a period longer than the diffraction limit of light. Has been done.

On the other hand, regarding the information recording method, the information is recorded at the edge portion by changing the length of the recording mark regardless of the so-called mark position recording method of recording information depending on the presence or absence of the recording mark (magnetic domain). There is a so-called mark length recording method for increasing the recording line recording density.

[0008]

By the way, in the case of adopting a reproducing method of forming a mask area in which information is not read in a spot of a reproducing laser beam so that the linear recording density can be improved as described above, When the information is recorded by the mark length recording method, a long recording mark is not read out because a part of it is masked in the reproduction laser beam spot, and conversely C / N. The problem of reducing (S / N) arises.

The present invention also employs a mark length recording method and a reproducing method in which the linear recording density can be improved by masking a part of the mark in the reproducing laser beam spot. In the above long mark recording, the C / N (S / N) is not reduced, and the reproduction is surely performed regardless of the length of the recording mark, that is, the laser wavelength λ and the objective lens. A high-density recording information bit exceeding the recording density determined by the numerical aperture NA can be reproduced, and a long recording mark can be reproduced at the same time.

[0010]

That is, according to the present invention, the behavior of the recording mark in the method of partially enlarging, reducing or inverting the recording mark at the time of reproduction is determined by the length of the recorded mark and the laser power to be recorded. It was founded on the basis of this finding that we were found to be greatly affected by.

That is, according to the present invention, information is recorded on a magneto-optical recording medium having at least a recording layer and a reproducing layer by a mark length recording method by irradiating a recording laser, and the recording laser in recording the information. The power of is selected according to the mark length.

That is, in the present invention, the mark length recording method is utilized by utilizing the fact that the magnetic energy of the recording mark in the reproducing layer in the high temperature region within the reproducing laser spot differs depending on the recording laser power and the recording mark length. The short recording mark by minimizing the magnetic energy of the recording mark of the reproducing layer in the high temperature region in the reproducing laser spot by selecting and recording the recording laser power of each mark length when using It is possible to perform reproduction by reversing or erasing, and also to reproduce a long recording mark without reversing or erasing even when the magnetic energy is minimized. .

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of the present invention will be described with reference to the drawings.

A magneto-optical recording medium for carrying out the method of the present invention comprises:
At least a reproducing layer and a recording layer each composed of a magnetic layer are formed on a substrate. FIG.
Is a schematic sectional view of an example of this magneto-optical recording medium. In this example, a dielectric film 2, a reproducing layer 3, an intermediate layer 4 and a recording layer are sequentially formed on a substrate 1 such as a glass substrate and a transparent disk substrate such as polycarbonate. 5, the surface protective film 6 is formed. Reference numeral 7 indicates the magneto-optical recording medium as a whole.

Recording, that is, formation of information marks (magnetic domains) on the magneto-optical recording medium 7 is performed by a mark length recording method. The recording method is the same as the conventional magneto-optical recording, that is, an optical modulation recording method or a magnetic field. This can be done by the modulating magnetic field method.

On the other hand, for reproducing or reading the recorded information, the reproducing layer 3 is irradiated with a laser beam from a semiconductor laser through the transparent substrate 1, so that the magnetization signal of the reproducing layer 3 is changed to the magneto-optical effect (magnetic curve). Effect, the Faraday effect) and read out after being converted into an optical signal. At this time, the temperature distribution in the magneto-optical recording medium generated by the irradiation of this laser beam within the spot of the reproducing laser beam on the magneto-optical recording medium is utilized. A reading mode is adopted in which a specific temperature region is used as a detection region and another portion is used as a mask region. That is, when the magnetic coupling between the reproducing layer 3 and the intermediate layer 4 is broken or becomes very weak in the high temperature region within the spot of the reproducing laser light, for example, the information mark () formed on the reproducing layer 3 in the high temperature region ( Magnetic domains) are extinguished, flipped and raised, or deformed so that its magnetic energy is reduced.

In the present invention, by utilizing the fact that the magnetic energy of the recording mark differs depending on the recording laser power and the recording mark length, the recording laser power of each mark length is selected and recorded for recording. During reproduction, by minimizing the magnetic energy of the recording mark in the reproducing layer in the high temperature region within the reproducing laser beam spot, the short recording mark is reversed or erased, but the long recording mark is reversed or erased. It should not disappear.

That is, in the method of the present invention, the magnetic domain pattern within the spot diameter of the reproducing laser beam is read out by masking it, that is, masking it. However, for long recording marks, it is read in the same mark shape. Therefore, it is possible to simultaneously reproduce a signal recorded in a cycle equal to or smaller than the spot diameter of the reproduction laser beam and a long mark signal.

Further, a recording / reproducing method for a magneto-optical recording medium recorded by the method of the present invention will be described with reference to FIGS. 2 and 3 are schematic top views showing the spot sp of the reproduction laser beam L on the magneto-optical recording medium 7 and the temperature distribution due to the spot sp. Each B diagram shows the light corresponding to each part of each A diagram. FIG. 3 is a cross-sectional view schematically showing magnetization states in the reproducing layer 3, the intermediate layer 4 and the recording layer 5 of the magnetic recording medium 7 with arrows. In each of FIGS. 2 and 3B, the shaded region indicates that the magnetic coupling between the reproducing layer 3 and the intermediate layer 4 is extremely weak or is cut.

In this case, the magneto-optical recording medium 7 shown in FIG.
An information signal, that is, a recording mark M is recorded on the recording layer 5 of. This recording is based on so-called magnetic field modulation recording in which an externally applied magnetic field is modulated in accordance with the recorded information to record information while irradiating a recording laser beam with a power such that the recording layer 5 has a compensation temperature or a Curie temperature or higher. Alternatively, an optical modulation is performed in which the magnetization of the recording layer 5 is once aligned in the same direction and then the recording laser light is modulated according to the recording information while applying an external magnetic field in the opposite direction to perform the recording. According to the record.

At this time, the power of the recording laser light is controlled by controlling the power of the recording laser light in consideration of the linear velocity of the recording medium 7 so that only a predetermined area within the recording laser light spot is near the Curie temperature of the recording layer 5. A recording mark (magnetic domain) having a spot diameter or less can be formed, and as a result, a signal having a period less than the diffraction limit of light of the optical system used for this recording can be recorded.

At the time of reproduction, the magneto-optical recording medium 7 is moved relative to the spot sp of the reproduction laser light with which it is irradiated, as indicated by the arrow a in FIGS. At this time, the temperature rises in the portion of the magneto-optical recording medium 7 irradiated with the reproducing laser light, but if the linear velocity of transition of the magneto-optical recording medium 7 is constant, this spot s
Within p, the intensity distribution of the reproducing laser beam, the linear velocity of the recording medium, and the shape temperature distribution due to the structure of the recording medium are generated.
The rear end side of the spot sp is the high temperature region A _H.

By the way, at least the recording layer 5 and the reproducing layer 3
In the magneto-optical recording medium having the above-mentioned and reading the recording signal while changing the magnetization state of the reproducing layer 3, when the temperature in the high temperature region A _H is near the Curie temperature of the intermediate layer 4, the recording with the reproducing layer 3 is performed. The magnetic coupling with layer 5 is either very weak or broken.

Therefore, the recording mark M formed on the reproducing layer 3 in the high temperature region A _H within the spot sp of the reproducing laser light is deformed so as to reduce the magnetic energy.

That is, the recording mark M of the reproducing layer 3 in the high temperature region A _H has the weak magnetic coupling between the reproducing layer 3 and the recording layer 5 or is broken, so that all the recording marks M have. The recording mark begins to deform in an attempt to reduce the magnetic energy.

At this time, the deformation process of the recording mark M depends on the length of the recording mark M and the recording laser power when the recording mark M is recorded. That is, when a long recording mark or a short recording mark M recorded with a low recording laser power as shown in FIG. 2 has the minimum magnetic energy in the high temperature region A _H , the recording mark M is inverted or disappears. This area becomes the mask area Ms, and the aperture A in the spot sp where the area other than the mask area Ms can be read out.
p.

On the other hand, as shown in FIG. 3, a recording mark which has been recorded for a long time with a high recording laser power does not invert or disappear even when the magnetic energy in the high temperature portion is minimized. As a result, it is possible to reproduce a signal having a period equal to or shorter than the diffraction limit of light without impairing C / N (S / N) in a long recording mark. In FIG. 3, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and duplicate description will be omitted.

The magneto-optical recording medium used in the present invention will be described below with reference to its examples, but the magneto-optical recording medium is not limited to these examples.

[Example 1] Si, Tb, and G were placed in a sputtering chamber of a magnetron sputtering apparatus.
Each of the d, FeCo, Fe, and Al targets was placed, and a transparent substrate made of a polycarbonate substrate with a pitch of 1.35 μm provided with a track groove having a diameter of 130 mm and a thickness of 1.2 mm was mounted on the substrate holder, and the chamber was placed. The inside was evacuated by a cryopump until a high vacuum degree of 1 × 10 ⁻⁵ [Pa] or less.

After evacuation, Ar gas and N ₂ gas were introduced into the chamber until the pressure became 0.2 [Pa], and then R
Si on the substrate by F (high frequency) reactive sputtering
An N film was formed to a thickness of 70 nm to form the dielectric film 2 shown in FIG.

Then, while evacuating, the Ar gas is added to 0.2
After being introduced into the chamber until the pressure reaches [Pa], the GdFeCo film as the reproducing layer 3 of FIG. TbFeC
The o film was formed at 50 nm by continuous sputtering.

Then, while evacuating, Ar gas and N ₂ gas were introduced into the chamber until the pressure reached 0.2 [Pa], and then RF reactive sputtering was performed on the Ar gas and N ₂ gas.
A SiN film as a protective film 6 of 70 nm thick,
Then, while evacuation was performed, Ar gas was introduced into the chamber until the pressure became 0.2 [Pa], and then a metal film of Al having a thickness of 20 nm was formed to control the thermal conductivity, to manufacture a magneto-optical recording medium.

Each GdFeC in this magneto-optical recording medium
o film, TbFe film and TbFeCo film are Tb, Gd, F
Direct current power was applied to each target of eCo and Fe to form a film by co-sputtering, and the composition was adjusted by changing the power applied to each target at the time of film formation by sputtering.

The composition of the GdFeCo film as the reproducing layer 3 was set so that the compensation temperature T ₁ was 160 ° C. and the Curie temperature Tc ₁ was 320 ° C.

The composition of the TbFe film as the intermediate layer 4 has a compensation temperature T ₂ of 30 ° C. and a Curie temperature Tc ₂ of 160 ° C.
It was set to become.

The composition of the TbFeCo film as the recording layer 5 has a compensation temperature T ₃ of 30 ° C. and a Curie temperature Tc ₃ of 2.
The temperature was set to 60 ° C.

Using the magneto-optical recording medium according to Example 1, recording / reproducing characteristics by optical modulation recording were measured.

N.V. of the objective lens of the magneto-optical recording / reproducing / measuring device. A. Was 0.55, and the wavelength of the laser beam was 690 nm.

FIG. 4 is an emission waveform diagram of the recording laser during this recording. In FIGS. 4A and 4B, A, B, and C represent recording mark lengths of 0.36 μm, 0.72 μm, and 1.44 μm, respectively.
When 1 m, 1 pulse was applied, when 0.72 μm was applied, 2 pulses were applied, and when it was 1.44 μm, 6 pulses were applied, and comb-shaped light emission in consideration of thermal interference of each recording mark was used. P _L is a so-called bias power at the time of recording, Ph is the recording power.

The linear velocity of the recording medium was 8.0 m / sec, and the recording external magnetic field was 400 [Oe]. The recording conditions at this time are P _L = 3.6 mW and pulse interval To = 23 nsec.
And The measurement was performed without applying an external magnetic field during reproduction.

The length of each recording mark under such conditions is
0.36 μm, 0.54 μm, 0.72 μm, 0.90
FIG. 5 shows the measurement results of the recording laser power (Ph) dependence of the carrier level to the noise level (C / N) for μm, 1.08 μm, 1.26 μm, and 1.44 μm.

As shown in FIG. 5, even if the mark length is short or long (mark length of 0.72 μm or more), the recording laser power Ph is recorded in the recording power area (1) of FIG. For the above-mentioned reason, the reproducing operation as shown in FIG. 2 is performed for the above-mentioned reason, and it is possible to reproduce a minute recording mark with respect to the reproducing laser spot, and a sufficient C / N is obtained. It can be seen that the C / N is impaired for the long mark.

On the other hand, the C / N of a long mark (mark length of 0.72 μm or more) is markedly increased by recording the recording laser power in the recording power region (2) of FIG. It can be seen that the reproducing operation is performed by the reproducing operation as shown in FIG.

Next, FIG. 6 shows the C / N dependency on each recording mark length for the magneto-optical recording media according to the above-described Example 1 and the comparative example and the conventional example. Here, the comparative example is a magneto-optical recording medium of a type in which the recording marks are reversed or erased at the time of reproduction with respect to all the conventional recording mark lengths manufactured by the same method as in the first embodiment,
TbFeC produced by the same method as in Example 1 is different from the conventional example.
This is a magneto-optical recording medium having a single magnetic layer of o.

From FIG. 6, according to the magneto-optical recording medium of Example 1 used in the present invention, the C / N was remarkably increased for the mark length of 0.72 μm or less as compared with the conventional example. Recognize. Further, as compared with the comparative example, the C / N was not impaired for a mark length of 0.72 μm or more,
It can be seen that is obtained.

As described above, according to the information recording method of the present invention, it is possible to reproduce a minute recording mark with respect to a reproducing laser beam spot and simultaneously reproduce a long recording mark without decreasing C / N. It is a thing.

As described above, according to the magneto-optical recording method of the present invention, at least the recording layer and the reproducing layer are provided, and the reading or reproduction of information is performed by changing the magnetization state of the reproducing layer and recording the recorded signal. In the case where the reading mode is adopted, when recording the information, the recording laser power of each recording mark length is selected for each recording mark length so that the C / N (S / N) at the long recording mark is not impaired. It is possible to reproduce a signal having a period less than the diffraction limit of.

[0048]

As described above, according to the present invention, the recording marks recorded on the magneto-optical recording medium are substantially read out in the spot of the reproducing laser light, that is, the so-called aperture A, and in the spot of the reproducing laser light. Even in the case where a reproducing method in which the temperature distribution is used to limit by the mask area Ms is adopted, the C / N (S / N) is lowered due to the masking of a part of the recording mark having a long recording mark length. Therefore, it is possible to reliably reproduce a signal having a period equal to or shorter than the light diffraction limit.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of reproduction of information recorded by a recording method according to the present invention. A is a schematic top view of the magneto-optical recording medium. B is a schematic sectional view of the magneto-optical recording medium.

FIG. 3 is an explanatory diagram of reproduction of information recorded by a recording method according to the present invention. A is a schematic top view of the magneto-optical recording medium. B is a schematic sectional view of the magneto-optical recording medium.

FIG. 4 is a waveform diagram of the recording laser power of the recording method according to the present invention. A is the case where the mark length is 0.36 μm. B is the case where the mark length is 0.72 μm. C is the case where the mark length is 1.44 μm.

FIG. 5 is a diagram showing C / N dependence of recording power with respect to each recording mark length of the recording method according to the present invention.

FIG. 6 is a diagram showing C / N dependence on recording mark length in the present invention and the conventional method.

[Explanation of symbols]

 1 substrate 2 dielectric layer 3 reproducing layer 4 intermediate layer 5 recording layer 6 surface protective layer 7 magneto-optical recording medium

Claims (1)

[Claims] 1. A magneto-optical recording medium having at least a recording layer and a reproducing layer is used to record information by a mark length recording method by irradiating a recording laser beam, and the power of the recording laser beam in recording the information is adjusted. , A magneto-optical recording method which is selected according to the mark length.