JPH10241224A - Method for recording/reproducing magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent recorded information from being destroyed just before and just after recording even when high reproducing power is emitted at the reproducing time. SOLUTION: In this method for recording/reproducing a magneto-optical recording medium by applying the reproducing magnetic field of a magnetic field intensity Hr (Hr>Hw) different from a recording magnetic field of the magnetic field intensity Hw at the information reproducing time and reproducing it by using a reproducing beam of a beam intensity Pr, the reproducing beam of the beam intensity Pr is changed to the beam of the beam intensity Pr' lower than the intensity Pr in the state applying the magnetic field intensity Hr until just before recording the information. Thereafter, the magnetic field intensity Hr is changed to the recording magnetic field of the magnetic field intensity Hw different from the intensity Hr. Further, the beam of the beam intensity Pr' is changed to a recording beam, and the recording is performed in this state. After the recording is ended, after the magnetic field intensity Hw is changed to the magnetic field intensity different from the intensity Hw, the recording beam is changed to the beam of the beam intensity Pr', and further is changed to the reproducing beam of the beam intensity higher than the intensity Pr'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording / reproducing a magneto-optical recording medium capable of optical intensity modulation overwriting.

[0002]

2. Description of the Related Art Magneto-optical recording media capable of storing high-density data and capable of processing information at a high speed have attracted attention as audio and image applications and computer memories. Read-only CDs (compact discs) are rapidly becoming popular for audio and computer use. Also, a write-once type, in which information can be written only once, and a rewritable type, in which information can be repeatedly rewritten, are gradually becoming popular in the market. In particular, a rewritable type magneto-optical recording medium is capable of repeating information rewriting many times, and is becoming popular mainly as an external memory of a computer.

[0003] In a normal magneto-optical recording medium, in principle, rewriting of information requires two operations of erasing and recording the previous information, and the information is recorded over the previous information as in magnetic recording ( Overwrite) alone cannot be rewritten,
The drawback is that the information transfer speed is reduced accordingly. In order to solve this drawback, an optical modulation overwrite medium which is rewritable by overwriting information using a multilayer film has been invented (Japanese Patent Laid-Open No. 62-175948). Further, it was invented that an initializing layer which plays a role of an initializing magnetic field, which was initially required for this overwrite medium, was added to the recording film (Japanese Patent Application Laid-Open No. 3-219449), and practical use has recently started. .

On the other hand, in order to record more information on one magneto-optical recording medium, information is recorded at a higher density.
There is an increasing demand for reproduction, and various studies have been made on how to achieve this. For this purpose, first, a method of reducing the light source wavelength of the reproducing head to make the reproducing light beam spot smaller to enable reproduction of information recorded at high density is conceivable. However, the wavelength of a semiconductor laser usually used as a light source of an optical head is limited, and a short-wavelength laser has a problem in that the shape, output, and the like of laser light are insufficient.

Therefore, information recorded at a higher density is read out without changing the wavelength of the light source and the size of the reproducing light beam spot, and the magnetically super-resolution (Magnetically Induced) in which the apparent resolution is improved. Super Resolution
A technique called “MSR” has been proposed and is receiving attention. This is because the temperature distribution in the light beam spot and the magnetic coupling force, coercive force, and the magnitude of magnetization of the magnetic multilayer film, which are caused by the combination of the temperature rise due to the reproduction light and the rotational movement of the recording medium, change with temperature. In combination, a part of the signal of the light beam spot is masked. As a result, the area of the opening that is effective for reproduction becomes smaller than the spot diameter, and higher-density information can be reproduced. The MSR method includes a FAD method (Front Aperture Detecti) that masks a high-temperature portion in a light beam spot.
on) and RAD method (Rear Aperture
Detection), and there are various methods such as a method in which a high-temperature portion becomes an effective opening, and a higher-temperature portion therein is masked again to realize a very small opening. According to such an MSR method, the reproduction resolution can be improved beyond the limit of the optical system, and the recording density in the linear density direction can be improved.

In a magneto-optical recording medium capable of optical intensity modulation overwriting, the beam intensity is used for recording and reproducing information.
High level (PH) and low level (PL) of recording power
And reproduction power (Pr) between three levels. This means that a normal magneto-optical recording medium has one more level than the two levels of reproducing power and recording power. Usually, there is an upper limit to the power that a semiconductor laser can emit, and the allowable width (power margin) of each level becomes narrower in a recording medium that can be overwritten, so that the allowable upper limit of the reproducing power also becomes lower. Since the CN ratio (carrier noise ratio) of the reproduction signal can be increased as the intensity of the reproduction power increases, the upper limit of the reproduction power is preferably higher. However, a recording medium capable of overwriting is disadvantageous in this respect. Also, in magnetic super-resolution reading, in order to utilize the temperature difference between the room temperature and the periphery of the reproducing light beam spot, it is necessary to increase the reproducing power, especially compared to a normal medium. The overwritable recording medium has a low reproduction power upper limit for the above-described reason, and it is practically difficult to achieve both high transfer speed and high density in combination with magnetic super-resolution reading. .

In order to solve this problem, the present inventors conducted magneto-optical recording by performing reproduction while applying a magnetic field having a magnetic field strength Hr different from the magnetic field strength Hw at the time of recording as shown in FIG. A recording and reproducing method for improving the upper limit of the reproducing power Pr of the medium was invented (Japanese Patent Application No. 8-222).
007 and Japanese Patent Application No. 9-26383). Japanese Patent Application 8
The recording / reproducing method of -222007 discloses that the magnetization direction of the memory layer is reversed by the exchange coupling force exerted from the recording layer and the information is hard to be broken. Apply an external magnetic field. Since the magnetization of the memory layer is less likely to be reversed, the upper limit of the reproducing power is improved. Further, in Japanese Patent Application No. 9-26383, in a temperature rising process at the time of reproduction, information of a memory layer is transferred to a recording layer side by a reproducing magnetic field of a magnetic field strength Hr to eliminate a domain wall between the memory layer and the recording layer. Improve the upper limit of the reproduction power. That is the method. By adopting such a method, it has become possible to reproduce even overwriteable recording media with high reproducing power. In addition,
FIG. 4 will be described later.

[0008]

In a normal magneto-optical recording / reproducing apparatus, the beam intensity is the reproducing power (reproducing power) except when recording or erasing is performed.
When recording is performed, first, a recording magnetic field having a magnetic field strength Hw is applied, then the beam intensity is modulated according to the recording data, and recording is performed. After the recording is completed, the beam intensity is changed from the recording beam intensity PH to the reproducing beam intensity. After returning to Pr, the recording magnetic field is turned off. Since it usually takes time to change the applied magnetic field, a recording magnetic field is applied to the medium before and after such recording. However, in the case of the above-described prior art shown in FIG. 3, if the magnetic field is similarly switched from the reproducing magnetic field having the magnetic field strength Hr to the recording magnetic field having the magnetic field strength Hw for recording, the allowable upper limit of the reproducing power is reduced. It has been found that a problem arises in that information already recorded is destroyed before and after recording (period a in FIG. 3).

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. It is an object of the present invention to provide a high-intensity beam during reproduction even before and after recording. It is an object of the present invention to provide a recording and reproducing method for a magneto-optical recording medium that does not destroy recorded information.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for reproducing information on a magneto-optical recording medium having at least two layers of a memory layer and a recording layer and capable of light intensity modulation and overwriting. A reproducing magnetic field having a predetermined magnetic field strength Hr was applied, and the reproducing magnetic field was applied immediately before recording information on a magneto-optical recording medium for performing reproduction using a reproducing beam having a predetermined beam intensity Pr. In this state, the reproducing beam is changed to a beam intensity Pr ′ lower than the beam intensity Pr, and then the reproducing magnetic field is changed to a recording magnetic field having a magnetic field intensity Hw different from the magnetic field intensity Hr. Beam intensity Pr
The recording beam is changed to a recording beam having a higher beam intensity, thereby performing recording. After the recording is completed, the recording beam is maintained at a beam having the beam intensity Pr ′, and the recording magnetic field is changed to a beam intensity different from the magnetic field intensity Hw. After the change to the magnetic field, the beam intensity is changed to a beam intensity higher than the beam intensity Pr ′. Further, the present invention applies a reproducing magnetic field of a predetermined magnetic field strength Hr at the time of reproducing information to a magneto-optical recording medium capable of overwriting light intensity modulated having at least two layers of a memory layer and a recording layer, In a magneto-optical recording medium in which reproduction is performed using a reproduction beam having a predetermined beam intensity Pr, the reproduction beam is applied with a beam intensity lower than the beam intensity Pr in a state where the reproduction magnetic field is applied until immediately before information is recorded. After changing the reproducing magnetic field to a recording magnetic field having a magnetic field intensity Hw different from the magnetic field intensity Hr, changing the beam to a recording beam having a beam intensity higher than the beam intensity Pr of the reproducing beam. After that, after recording, the recording beam is maintained at the beam intensity Pr ′, and the recording magnetic field is reproduced at the magnetic field intensity Hr. After returning to the field, and changes to the high the beam intensity Pr than the beam intensity Pr '.

If a magnetic field having a magnetic field strength Hr is applied during reproduction and a magnetic field having a magnetic field strength Hw is applied during recording, the upper limit of the reproducing power is reduced, and thus the already recorded information is destroyed before and after recording. There is a risk. for that reason,
In the state where the recording magnetic field is applied, it is necessary to lower the intensity of the irradiated beam.

Therefore, in the present invention, reproduction is performed by applying a magnetic field of a magnetic field strength Hr at the time of reproduction, and at the time of recording, immediately before recording information, the beam intensity is adjusted in a state where the magnetic field of the magnetic field Hr is applied. The beam intensity is changed from Pr to a lower beam intensity Pr ', and then the magnetic field intensity Hr is changed to a magnetic field intensity Hw different from the magnetic field intensity Hr, and recording is performed in that state. After the recording is completed, the magnetic field intensity Hw is changed to a magnetic field intensity different from the magnetic field intensity Hw, and then the beam intensity is changed to the beam intensity Pr ′.
To a higher beam intensity.

Further, in the present invention, the beam intensity is changed from the beam intensity Pr to a beam intensity Pr ′ lower than the beam intensity Pr in a state where the magnetic field intensity Hr is applied immediately before recording information, Then the magnetic field strength Hr
Is changed to a magnetic field strength Hw different from the magnetic field strength Hr, recording is performed in that state, and after the recording is completed, after returning from the magnetic field strength Hw to the magnetic field strength Hr, the beam strength is changed from the beam strength Pr ′. The beam intensity is returned to Pr. By doing so, it is possible to improve the upper limit of the reproduction beam without destroying information already recorded before and after recording.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a sectional view showing an example of the configuration of a magneto-optical recording medium used in the method of the present invention. This magneto-optical recording medium includes a dielectric layer 2, a memory layer 3, an intermediate layer 4, and a recording layer 5 sequentially laminated on a substrate 1.
And a dielectric layer 6 as a protective layer.

As the substrate 1, for example, a disk-shaped glass substrate with a tracking groove (track pitch 1.2 μm) having a thickness of 1.2 mm and a diameter of 130 mm is used. The dielectric layer 2 is formed of SiN and has a thickness of 70 nm. The memory layer 3 is made of TbFeCo,
It has a thickness of nm. The intermediate layer 4 is made of GdFeCo and has a thickness of 10 nm. The recording layer 5 is TbD
It is made of yFeCo and has a thickness of 40 nm. The dielectric layer 6 is formed of SiN and has a thickness of 70 nm. The memory layer 3 has a TM (Transition Metal) rich composition, and the recording layer 5 has a RE (Rare earth: rare earth) rich composition having a compensation temperature between room temperature and Curie temperature.

FIG. 2 is a conceptual diagram of a recording / reproducing apparatus used for recording / reproducing a magneto-optical recording medium used in the method of the present invention.
The disk 10 is rotated by the driving device 21. Recording and reproduction of information are performed by irradiating a laser beam focused from the optical pickup 22 onto the disk surface. The optical pickup 22 is moved in the radial direction of the disk by the coarse movement motor 23 to change the radial position at which information is recorded and reproduced. Further, the magnet 24 generates a magnetic field in order to apply a magnetic field perpendicular to the disk surface when recording / reproducing information. When an electromagnet is used as the magnet 24, the strength and direction of the magnetic field can be switched by changing the current. When a permanent magnet is used as the magnet 24, the switching of the magnetic field can be performed by changing the distance between the permanent magnet and the disk 10 and the direction of the magnet.

The initialization magnet 25 is a magnet that generates a magnetic field for aligning the magnetization direction of the recording layer of the overwritable magneto-optical recording medium, and the medium always passes through this magnetic field during one rotation. It has become. When an overwritable medium having an initialization layer is used as the disk 10, this initialization magnetic field is unnecessary. Number of rotations of the disc,
The radial position at which the laser beam is irradiated, the intensity of the irradiated beam, the intensity of the applied magnetic field, and the like are controlled by the controller 20.

FIG. 3 is a diagram showing a laser beam intensity and a magnetic field intensity during recording / reproducing in the present invention. In the figure, PH is a high level (recording power) during information recording, and PL is
Is a low level (erasing power) at the time of recording, Pr is a beam intensity (reproduction power) at the time of reproduction, and Pr 'is a beam intensity immediately before and immediately after information recording (Pr>Pr').
Hw is the magnetic field strength at the time of recording information (recording magnetic field), and Hr is the magnetic field strength at the time of reproducing information (reproducing magnetic field). Note that FIG.
Although the case where Hr> Hw has been described, there may be a case where Hr <Hw.

As shown in FIG. 3, in the present invention, when information is reproduced, a reproducing magnetic field having a predetermined magnetic field strength Hr different from the recording magnetic field is applied, and reproduction is performed using a reproducing beam having a predetermined beam intensity Pr. In the magneto-optical recording medium to be performed, immediately before information is recorded, the reproducing power P
r, the reproducing magnetic field is changed to the recording magnetic field of the magnetic field intensity Hw, and the beam intensity is changed to the recording beam (PH) higher than the reproducing power Pr.
, PL), and information is recorded in this state. After the recording is completed, the beam intensity is maintained at Pr ', and after changing the recording magnetic field to a magnetic field having an intensity different from the magnetic field intensity Hw, the recording intensity is changed from Pr'. Switch to a higher beam intensity to reproduce information. In this case, the magnetic field whose recording magnetic field is changed after the recording is completed may be a reproducing magnetic field having a magnetic field strength Hr. Further, after changing the recording magnetic field after the recording to a magnetic field having a strength different from the magnetic field strength Hw, Pr ′ is switched to a beam strength higher than Pr ′, and the beam intensity may be the reproduction power strength Pr. Good.

In such a recording / reproducing method, when a recording magnetic field is applied to the medium surface immediately before and after recording, the beam intensity applied to the medium surface is lower than the reproducing power Pr. 'So that the information already recorded will not be destroyed.

FIG. 4 is a diagram showing a laser beam intensity and a magnetic field intensity at the time of recording / reproducing in the conventional method. When shifting from the information reproducing state to the recording state, first, the reproducing magnetic field (including the case where the intensity is zero) is changed to the recording magnetic field, and then the beam intensity is changed to the recording beam (PH) higher than the reproducing power Pr.
, PL), the information is recorded in this state, and after the recording is completed, the beam intensity is returned to Pr and the reproduction of the information is started.
The recording magnetic field is changed to a reproducing magnetic field after returning the beam intensity to Pr. Usually, switching of the magnetic field requires a longer time (several ms to several tens of ms) than switching of the beam intensity. Therefore, such a procedure is taken to ensure that the recording magnetic field is applied during recording.

Next, the present invention will be compared with a conventional example using specific examples.

EXAMPLE The disk shown in FIG. 1 was set in a recording / reproducing apparatus. The light source wavelength of the recording / reproducing apparatus was 780 nm, and the numerical aperture (NA) of the objective lens was 0.55. An initialization magnetic field for generating a magnetic field of 4 KOe is mounted on the medium surface. The rotation speed of the disk is set to 3600 rpm, and a signal of a frequency of 5 MHz is applied to a position of a radius of 30 mm by PH = 9.0
Recording was performed with a recording power of 300 Oe (mW, PL = 4.0 mW) and a recording magnetic field (the same direction as the initialization magnetic field). When this data was reproduced at a reproduction power of 1.0 mW, the C / N was 53 dB. When the reproducing magnetic field was 300 Oe, the upper limit of the reproducing power was 2.0 mW. C / at playback power of 2.0 mW
N was 55.5 dB. When the reproducing power exceeds 2.0 mW, the C / N suddenly decreases, and the reproducing power is reduced to 1.0
Even if the power was reduced to mW, the original C / N was not obtained, and it was considered that a part of the recorded mark was destroyed by the temperature rise due to the reproduction light. The same mark was recorded again with the same power, and reproduction was performed while applying a reproducing magnetic field of 1500 Oe in the same direction as the recording magnetic field. The upper limit of the reproducing power in this case is 2.5 mW
Met. By applying a magnetic field, the upper limit of the reproducing power is improved. C / N at reproduction power of 2.5 mW
Is 56.5 dB, and the C / N can be increased by setting the reproduction power high.

In the case where recording / reproducing is performed on the sector having this radius on the disk by the method of the present invention, the recording / reproducing apparatus comprises: Reproduction is performed with a reproduction power Pr = 2.2 mW. At this time, the reproducing magnetic field Hr = 1500 Oe is applied. 2. The beam intensity is reduced to Pr '= 1.5 mW. 3. The reproducing magnetic field is switched to the recording magnetic field Hw = 300 Oe. 4. Recording is performed on the sector in which information is to be recorded. The overwrite recording can be performed by modulating the laser power into two values of 9 mW and 4 mW according to the recording information. 5. After recording, set the beam intensity to Pr '= 1.5 mW
Return to 6. The recording magnetic field Hw is switched to the reproducing magnetic field Hr = 1500 Oe. 7. Raising the beam intensity to the reproduction power Pr = 2.2 mW,
It is assumed that information can be reproduced. Recording and reproduction are performed according to the following procedure.

In this case, the reproducing magnetic field Hr is always applied while the reproducing beam having the intensity of Pr = 2.2 mW is irradiated on the medium, and the information already recorded before and after the sector to be recorded is destroyed. I never did.

When the same recording is performed by the conventional method Reproduction is performed with a reproduction power Pr = 2.2 mW. At this time, the reproducing magnetic field Hr = 1500 Oe is applied. 2. The reproducing magnetic field is switched to the recording magnetic field Hw = 300 Oe. 3. Recording is performed on the sector in which information is to be recorded. The overwrite recording can be performed by modulating the laser power into two values of 9 mW and 4 mW according to the recording information. 4. After the recording is completed, the beam intensity is returned to Pr = 2.2 mW, and the information can be reproduced. 5. The recording magnetic field Hw is switched to the reproducing magnetic field Hr = 1500 Oe. Recording and reproduction are performed according to the following procedure.

In this case, immediately before and after recording, Pr = 2.2 with the recording magnetic field Hw = 300 Oe applied.
It means that the medium is irradiated with the reproducing beam having the intensity of mW. Since the upper limit of the reproduction power of the medium No. under Hr = 300 Oe is 2.0 mW, if there is information already recorded in the sectors before and after the sector to be recorded, the information will be destroyed.

Actually, when recording was performed on only one sector of the disk by this procedure, destruction of information was observed over about half the circumference of the disk before and after the sector. In order to prevent such information destruction by the conventional recording / reproducing method, the reproducing power must be set so as not to exceed 2.0 mW at which the information is not destructed under the recording magnetic field. In addition, the C / N obtained during reproduction is reduced.

[0028]

As described above, the recording / reproducing method for a magneto-optical recording medium according to the present invention is applicable to a magneto-optical recording medium having at least two layers of a memory layer and a recording layer and capable of light intensity modulation and overwriting. In a magneto-optical recording medium that applies a reproducing magnetic field of a predetermined magnetic field strength Hr at the time of reproducing information and performs reproduction using a reproducing beam of a predetermined beam intensity Pr, immediately before recording information, With the reproducing magnetic field applied, the reproducing beam is changed to a beam intensity Pr ′ lower than the beam intensity Pr, and then the reproducing magnetic field is changed to a recording magnetic field having a magnetic field intensity Hw different from the magnetic field intensity Hr. The beam is changed to a recording beam having a beam intensity higher than the beam intensity Pr of the reproduction beam, thereby performing recording. After the recording is completed, the recording beam is changed to the beam intensity. After maintaining the beam at a degree Pr ′ and changing the recording magnetic field to a magnetic field having a strength different from the magnetic field strength Hw, then changing the beam to a beam having a beam intensity higher than the beam strength Pr ′, or Since the recording beam was changed to the beam having the beam intensity Pr ', and the recording magnetic field was returned to the reproducing magnetic field having the magnetic field intensity Hr, then the beam intensity was changed to the beam intensity Pr higher than the beam intensity Pr'. Even when a high reproduction power is applied to the magneto-optical recording medium during reproduction, the information already recorded before and after recording is not destroyed, and good recording and
Reproduction can be performed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a configuration of a magneto-optical recording medium used in a method of the present invention.

FIG. 2 is a conceptual diagram of an example of a recording / reproducing apparatus used in the method of the present invention.

FIG. 3 is a diagram showing a recording and reproducing beam intensity and a magnetic field intensity according to the method of the present invention.

FIG. 4 is a diagram showing a beam intensity and a magnetic field intensity during recording and reproduction according to a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Dielectric layer, 3 ... Memory layer, 4 ... Intermediate layer, 5 ... Recording layer, 6 ... Dielectric layer, PH ... High level of recording beam (recording power), PL ... Low level of recording beam (Erasing power), Pr: intensity of reproducing beam (reproducing power), Hr: magnetic field intensity of reproducing magnetic field, Hw: magnetic field intensity of recording magnetic field.

Claims (2)

[Claims] 1. A magnetic field intensity Hr determined at the time of reproducing information for a magneto-optical recording medium having at least two layers of a memory layer and a recording layer and capable of light intensity modulation and overwriting.
In a magneto-optical recording medium in which a reproducing magnetic field is applied and reproduction is performed using a reproducing beam having a predetermined beam intensity Pr, the reproducing beam is applied in a state where the reproducing magnetic field is applied until immediately before information is recorded. After changing the beam intensity to a beam intensity Pr 'lower than the beam intensity Pr, and then changing the reproducing magnetic field to a recording magnetic field having a magnetic field intensity Hw different from the magnetic field intensity Hr, the beam is changed to a beam higher than the beam intensity Pr of the reproducing beam. After the recording is completed, the recording beam is maintained at the beam intensity Pr ′, and the recording magnetic field is changed to a magnetic field having a different intensity from the magnetic field intensity Hw. After that, the beam intensity is changed to a beam intensity higher than the beam intensity Pr ′. 2. A predetermined magnetic field strength Hr at the time of reproducing information for a magneto-optical recording medium having at least two layers of a memory layer and a recording layer and capable of light intensity modulation and overwriting.
In a magneto-optical recording medium in which a reproducing magnetic field is applied and reproduction is performed using a reproducing beam having a predetermined beam intensity Pr, the reproducing beam is applied in a state where the reproducing magnetic field is applied until immediately before information is recorded. After changing the beam intensity to a beam intensity Pr 'lower than the beam intensity Pr, and then changing the reproducing magnetic field to a recording magnetic field having a magnetic field intensity Hw different from the magnetic field intensity Hr, the beam is changed to a beam higher than the beam intensity Pr of the reproducing beam. After changing the recording beam to a recording beam having a high intensity, the recording is performed, and after the recording is completed, the recording beam is maintained at the beam having the beam intensity Pr ′, and after returning the recording magnetic field to the reproducing magnetic field having the magnetic field intensity Hr, A recording / reproducing method for a magneto-optical recording medium, wherein the beam intensity Pr is changed to a beam intensity Pr higher than the beam intensity Pr '.