JPH07153133A - Recording and reproducing method for magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain good reproducing waveforms by disposing >=1 auxiliary light beams around reproducing light and having a mask part expanded as compared with the case of irradiation with the reproducing light alone by the thermal interference effect of these auxiliary light beams. CONSTITUTION:The Curie temps. of respective layers; a reproducing layer, cut layer and recording layer are respectively >=300 deg.C, 140 deg.C and 240 deg.C and the coercive forces of the respective layers are respectively 300Oe, 12kOe and 20kOe. While the width of the mask (temp. region exceeding the Curie temp. of the cut layer) within the beam spot (a range where the light intensity is >=1/e<2> the max. value) of the reproducing light is 0.8mum, this width evidently increases up to 1.2mum in the case of the presence of the auxiliary light beams if the reproducing light 1 is set at 2.4mW and a calculation of the heat distribution in the state that there are no auxiliary light beams and the state where the auxiliary light beams 6 of 2.0mW are arranged apart 1mum on both sides of the reproducing is executed. The distortion of the reproducing waveforms are not generated if there are the auxiliary light beams.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Magneto-optical recording media have been put to practical use as high-density, low-cost rewritable information recording media. In particular, a medium using a recording layer of an amorphous alloy of a rare earth element and a transition metal shows very excellent characteristics. The magneto-optical disk is a recording medium having a very large capacity, but further increasing the capacity is desired as the amount of information in society increases. The recording density of this optical disk is usually determined by the size of the spot diameter of the reproduction light.

Since the size of the spot diameter can be made smaller as the wavelength of the laser becomes shorter, studies are being made to shorten the wavelength of the laser, but it is extremely difficult. On the other hand, in recent years, so-called super-resolution technology has been attempted to obtain a resolution higher than that determined by the laser wavelength by various means. One of them is a super-resolution using the magneto-optical disk and the exchange coupling force between the multilayer films.
(Magnetically induced super resolution, MSR) has been reported.

One form of this system uses a medium composed of three layers, which are exchange-coupled with each other, a reproducing layer having a small coercive force, a switching layer having a low Curie temperature, and a recording layer having a high Curie temperature and a high coercive force. FIG. 3 is a view from above of a medium for showing a recording / reproducing system using this medium. When the medium is heated by reproducing light while applying a reproducing magnetic field, the medium is exchanged at a high temperature portion (mask portion) 2. The bond is broken.

Since the reproducing layer alone has a small coercive force, in the high temperature portion 2, the magnetization uniformly points in the direction of the reproducing magnetic field and the recorded bits are erased. As a result, the low temperature part (aperture part)
Only 3 is played, and as a result the playback range is narrowed,
The same effect as when the reproduction light is narrowed down can be obtained, and high density recording bits can be reproduced. The erased recorded bits are recorded when the medium temperature becomes low and the exchange coupling is restored.
It is restored by being transferred from the recording layer.

Since the medium is rotating, the maximum temperature portion is slightly behind the maximum light intensity portion, and the mask portion 2 is located behind the reproduction beam spot 1 and the aperture portion 3 is formed.
Can be forward For this reason, this method detects the signal at the front of the reproduction light spot, and
It is called tion FAD. On the other hand, as a method of improving the capacity of the magneto-optical disk, PWM (pulse width modulatio
n) Adopting records. In PWM recording, information is stored as the length of the recording magnetic domain. At the time of reproduction, the end of the magnetic domain is detected and information is reproduced according to the interval.

According to this method, the PP that has been conventionally used
About 1.5 compared to M (pulse position modulation)
A doubled capacity increase can be expected. Conventionally, in optical modulation recording, it has been difficult to record a magnetic domain with an accurate length due to the problem of thermal diffusion during recording, but in recent years, it has been put to practical use by improving the recording method and the like.

[0008]

Even when FAD is used, the capacity becomes larger when such PWM recording is adopted as the recording method. The present inventors have adopted such FAD and P
As a result of studying recording / reproduction of a combination of WM recording, FA
When PWM recording is performed with D, when a long bit (long magnetic domain) is reproduced, waveform distortion occurs such that the signal becomes larger as it goes backward, which has a great influence on jitter (edge detection error). I found a thing.

Since there is no recording of long bits in PPM recording, this distortion is not a problem, but in PWM recording, there is always a recording of long bits, which is a fatal problem. Also,
In FAD, basically, crosstalk was not reduced and the track pitch could not be reduced to increase the capacity.

[0010]

SUMMARY OF THE INVENTION The gist of the present invention is that in the mask portion where the medium temperature is raised to a specific temperature or higher by the reproducing light, the magnetization always points in the same direction, and the change in the reproduced signal is caused by the specified value. When the signal is recorded / reproduced using a magneto-optical recording medium in which the intersymbol interference of the signal at the time of reproduction is reduced as compared with the normal reproduction by obtaining it from the aperture below the temperature of In the reproducing method of the magneto-optical recording medium, one or more auxiliary lights are provided in the above, and the mask portion is enlarged by a thermal interference effect of the auxiliary light as compared with a case where only the reproducing light is irradiated. Exist.

The present invention will be described in more detail below. In order to investigate the cause of waveform distortion in a long bit, an FAD reproduction waveform of a magnetic domain having a length of 1.5 μm and a width of 1.0 μm was analyzed based on the analysis of the state of heat distribution. FIG. 2 is a reproduction waveform diagram showing the result. In FIG. 2, L1 is the width in the mask portion,
L2 is the maximum width of the recording magnetic domain. L1 = 0 is a reproduced waveform when there is no mask.

As shown in FIG. 3, it has been found that the cause of the distortion of the reproduced waveform is that the width of the mask portion is narrower than the width of the recording magnetic domain. The width mentioned here refers to the width in the direction perpendicular to the traveling direction of the reproduction light. When L1 <L2, that is, when the width of the mask is narrow, the signal from the recording magnetic domain in the part not covered by the mask is detected little by little behind the reproduction light and gradually increases, and the reproduction signal strength increases behind the long bit. This was the cause of the loss.

In order to prevent this phenomenon, the mask width L1 may be made larger than the maximum width L2 of the recording magnetic domain, which can be achieved by increasing the reproducing light or reproducing magnetic field. However, since the increase in the mask width causes the mask to expand in the reproduction light traveling direction at the same time, the low temperature region (aperture portion) involved in the reproduction of the signal change is driven to the end of the reproduction spot, and the reproduction signal is significantly reduced. Bring

Further, in such high power reproduction,
There is a risk that the temperature near the center of the reproduction light will rise sharply and destroy the recorded information itself. Therefore, in the present invention, the mask width is increased by arranging the auxiliary light having the thermal interference effect around the reproduction light. FIG. 1 is a diagram showing an example of a recording / reproducing system according to the present invention.

As shown in FIG. 1, the auxiliary light 6 is arranged on both sides of the reproduction light 1 in a direction perpendicular to the traveling direction 4 of the reproduction light 1 (only on one side in some cases), or the reproduction light 1 is arranged. It is preferable to arrange it behind the reproduction light 1 with respect to the traveling direction 4. When they are arranged on both sides of the reproduction light 1, they may be located slightly back and forth along the traveling direction 4 with respect to the reproduction light 1.

This arrangement is used in order to concentrate the temperature of the mask portion 2 behind the reproducing beam spot and to raise the temperature of the aperture portion 3 in front of the reproducing beam spot 1 as little as possible. Is. By providing such auxiliary light, the heat distribution in the reproduction beam spot 1 changes, and the width of the mask portion can be enlarged without significantly reducing the aperture portion 3.

Providing the auxiliary light on both sides of the reproduction light is a preferable mode because the width of the aperture portion 3 is reduced, and the effect of reducing crosstalk can be obtained. In this case, it is preferable that the auxiliary light is applied to an adjacent track or an intermediate area (a groove in the case of land recording) between the tracks. The effect of enlarging the mask is also obtained when the auxiliary light is arranged behind the reproduction light. In this case, there is an advantage that only one auxiliary light is required. It is naturally possible to arrange the auxiliary light on both sides and the rear of the reproduction light.

Since the auxiliary light is intended to improve the heat distribution, it does not need to be accurately focused on the medium. In addition, a slight misalignment is allowed. Therefore,
The complication of the drive caused by providing the auxiliary light does not occur so much. As a method of actually irradiating the auxiliary light, a method of splitting the reproducing light can be considered, but other than that, a laser array or a completely independent optical system can be used. It is also possible to use a light emitting diode instead of a laser.

The FAD medium preferably used in such a recording / reproducing method includes the following.
A magnetic layer, which is composed of three layers of a reproducing layer, a cutting layer, and a recording layer, exchange-coupled with each other is provided on a substrate. When the Curie temperatures of the reproducing layer, the cutting layer, and the recording layer are Tc1, Tc2, and Tc3, respectively, it is preferable that they are all 50 ° C. or higher and satisfy the relationship of Tc1> Tc2, Tc3> Tc2.

Examples of the material used for the substrate include polycarbonate and glass. Gd in the playback layer
FeCo, GdTbFeCo, or the like is used. TbFe, TbFeCo, DyFe or the like is used for the cutting layer.
TbFeCo, TbDyFeCo, or the like is used for the recording layer.

It is a preferable mode that both sides of the magnetic layer are sandwiched by protective films made of a dielectric material such as Si nitride, Al nitride and Ta oxide. At this time, it is preferable that the protective film on the side irradiated with light has a thickness near the minimum reflectance due to the interference effect of light.

[0022]

【Example】

Example 1 On a 1.2 mm thick polycarbonate substrate, a 75 nm oxide Ta dielectric film, a 30 nm GdFeCo reproducing layer, 1
0 nm TbFe cutting layer (Curie temperature 120 ° C.), 4
A 0 nm TbFeCo recording layer and an 80 nm Si nitride protective layer were sequentially provided, and a 5 μm ultraviolet curable resin was provided thereon. Reproduction wavelength is 780 nm, NA = 0.55, linear velocity 1
It was set to 0 m / s.

Curie temperatures of the reproducing layer, the cutting layer and the recording layer are 300 ° C. or higher, 140 ° C. and 240 ° C., respectively.
The coercive force of each layer is 300 Oe, 12 kOe, 20 kO, respectively.
It was e. The heat distribution was calculated with the reproducing light of 2.4 mW and no auxiliary light and the condition of 2.0 mW of auxiliary light placed 1 μm apart on both sides of the reproducing layer.

As a result, the width of the mask (the temperature region exceeding the Curie temperature of the cutting layer) within the beam spot of reproducing light (the range of the light intensity being 1 / e ² or more of the maximum value) is 0.8 μm.
On the other hand, in the case of the auxiliary light, it increased to 1.2 μm. Track pitch 1.2 μm, recording domain length 1.
When the reproduced waveform and crosstalk were measured with a recording domain width of 5 μm and a recording domain width of 1.0 μm, the reproduced waveform was greatly distorted so that the signal became stronger at the rear when there was no auxiliary light. Such distortion did not occur. The intensity of the reproduction signal was 0.8 when the case where there was no auxiliary light was 1. The crosstalk was -21 dB when there was no auxiliary light, but was -28 dB when there was auxiliary light.

Example 2 Using the same disk as in Example 1, 2.0 mW of auxiliary light was placed 1 μm behind the reproduction light. As a result, the width of the mask was 1.0 μm. The reproduced signal was not distorted, and the reproducing light intensity was 0.9. The crosstalk was -23 dB. Comparative Example The same disk as in Example 1 was used, and the reproducing light was set to 3.0 mW in the state where the auxiliary light was not irradiated. As a result, the width of the mask was 1.1 μm.

Although the reproduced signal was not distorted, the reproduced light intensity was 0.3. The crosstalk was -22 dB.

[0027]

By using the recording / reproducing method for the magneto-optical recording medium of the present invention, it is possible to obtain a good reproducing waveform that can be used for PWM recording in the super-resolution medium by FAD, and also reduce crosstalk. It is possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a recording / reproducing system according to the present invention.

FIG. 2 is a diagram showing a change in a reproduced waveform due to a change in a width of a mask portion.

FIG. 3 is a diagram showing a conventional FAD medium recording / reproducing system.

[Explanation of symbols]

 1 reproducing light 2 mask part 3 aperture part 4 moving direction of reproducing light 5 recording magnetic domain 6 auxiliary light

Claims (3)

[Claims] 1. In a mask portion where the medium temperature is raised to a specific temperature or higher by reproducing light, its magnetization always points in the same direction, and a change in a reproduction signal is obtained from an aperture portion whose temperature is lower than the specific temperature. , When performing signal recording / reproduction using a magneto-optical recording medium in which the intersymbol interference of signals during reproduction is reduced as compared with normal reproduction, one or more auxiliary lights are placed around the reproduction light. A reproducing method of a magneto-optical recording medium, wherein the mask portion is enlarged by a thermal interference effect of the auxiliary light as compared with a case where only the reproducing light is irradiated. 2. The size of the reproduction beam spot is defined as a range in which the light intensity is 1 / e ² (e is a natural logarithm) or more of the maximum intensity, and the reproduction light of a mask portion in the reproduction beam spot is further defined. The auxiliary light having a thermal interference effect such that L is increased is arranged around the reproduction light, where L is a maximum width in a direction perpendicular to the relative traveling direction with respect to the medium.
A recording / reproducing method for the magneto-optical recording medium according to. 3. The recording / reproducing method for a magneto-optical recording medium according to claim 1, wherein a recording method in which information is stored according to the length of the recorded magnetic domain is used.