JPH05101471A - Magneto-optical recording and reproducing method - Google Patents

Abstract

PURPOSE:To provide a recording and reproducing method which performs a one shot reproduction, automatically erases the recording right after a reproduction, has a simple magnetic layer constitution of the magneto-optical recording medium and reproduces images with a ultra high resolution. CONSTITUTION:During a recording, information recording pits 11, which include spacial frequency components that are more than the cutoff spacial frequency, are recorded against a magneto-optical recording medium 10. During a reproduction, a reproduction light power is selected so as to form a high temperature region 13 within a reproduction light spot 12 which erases information recording pits 11 and only the information recording pits 11 in the low temperature region 14, that excludes the high temperature 13 within the reproduction light spot 12, are reproduced by a magneto-optical effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magneto-optical recording / reproducing system,
In particular, it relates to a magneto-optical recording / reproducing system for performing super-resolution reproduction on a magneto-optical recording medium on which high density recording is performed.

[0002]

2. Description of the Related Art In a magneto-optical recording / reproducing method in which an information recording pit, that is, a bubble magnetic domain is formed by local heating by irradiating a laser beam and the recorded information is read by a magneto-optical interaction, that is, Kerr effect or Faraday effect, In order to increase the recording density of recording, the recording pits must be miniaturized, but in this case, the resolution at the time of reproduction becomes a problem. This resolution is determined by the laser wavelength during reproduction and the numerical aperture NA of the objective lens, and the recording density is limited by the so-called cutoff spatial frequency 2NA / λ.

An ordinary general magneto-optical recording / reproducing system will be described with reference to FIG. FIG. 5A shows a schematic top view of a recording pattern. For example, a recording pit 24 shown by hatching a land portion 22 sandwiched by grooves or grooves 21 on both sides is binary information "1" or "0". Of the magneto-optical recording medium 10 recorded according to
The reproducing method will be described.

A magneto-optical recording medium 1 for reading laser light now
Consider a case where the beam spot on 0 is a circular spot indicated by reference numeral 26. At this time, as shown in FIG. 5A, one recording pit 24 is formed in one beam spot 26.
If the pit interval is selected so that only the recording pits 24 can exist, there are two modes of whether or not the recording pits 24 are present in the spot 6, as shown in FIG. 5B or 5C. Therefore, when the recording pits 24 are arranged at equal intervals, the output waveform thereof is, for example, a sine wave output that is inverted with respect to the reference level 0 as shown in FIG. 5D.

However, as shown in the schematic top view of the recording pattern in FIG. 6A, when the recording pits 24 are arranged at a high density, a plurality of recording pits 24 come into the beam spot 26. Looking now at, for example, three adjacent recording pits 24a, 24b, 24c, FIG.
B and FIG. 6C, one beam spot 26
Since the reproduction output does not change between the case where the adjacent recording pits 24a and 24b enter and the case where the adjacent recording pits 24b and 24c enter, the reproduction output waveform is shown in FIG.
As shown in D, for example, they become linear and the two cannot be distinguished.

As described above, in the conventional general magneto-optical recording / reproducing system, since the recording pits 24 recorded on the magneto-optical recording medium 10 are read out as they are, high density recording, that is, formation of high density recording pits. Even if it is possible, S / N (C / N) is imposed due to the limitation of the resolution during playback.
The above problem occurs, and sufficient high density recording / reproduction cannot be performed.

In order to solve such a problem of S / N (C / N), it is necessary to improve the resolution at the time of reproduction, but this resolution is restricted by the laser wavelength, the numerical aperture of the lens, etc. There is a problem that is. In order to solve such a problem, the present applicant has previously proposed a super resolution (super resolution) magneto-optical recording / reproducing system (hereinafter referred to as MSR).
(For example, JP-A-3-88156, JP-A-3-93058, and JP-A-3-97140).

The MSR will be described.
In R, the temperature distribution due to the relative movement of the magneto-optical recording medium and the reproducing beam spot 26 is used to generate the recording pits 24 of the magneto-optical recording medium only in a predetermined temperature region during reproduction. As a result, the resolution of reproduction is increased.

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

First, the embossing type MSR system will be described with reference to FIG. FIG. 7A is a schematic top view showing a recording pattern of the magneto-optical recording medium 10, and FIG. 7B is a schematic cross-sectional view showing its magnetization mode. In this case, as shown in FIG. 7A, the magneto-optical recording medium 10 is moved relative to the beam spot 26 of the laser beam in the direction indicated by the arrow D. In this case, for example, as shown in FIG. 7B, a reproducing layer 31 including at least a perpendicular magnetization film,
And a recording layer 33, and more preferably both layers 31 and 33.
A magneto-optical recording medium 10 having an intermediate layer 32 interposed therebetween, for example, a magneto-optical disk is used. The solid arrow in the figure schematically shows the direction of the magnetic moment. In the illustrated example, the downward direction is the initial state, that is, the binary “0” or “1”, and the magnetic domain due to the upward magnetization is shown in the figure. Then, the information recording pits 24 are formed at least in the recording layer 33 as binary "1" or "0".

In such a magneto-optical recording medium 10,
The reproducing mode will be described. First, the initialization magnetic field H is externally applied.
i is applied to magnetize the reproducing layer 31 downward in the figure to initialize it. That is, the recording pits 24 disappear in the reproducing layer 31, but at this time, the magnetization directions of the reproducing layer 31 and the recording layer 33 are held in opposite directions by the domain wall generated in the intermediate layer 32 in the portion having the recording pits 24. Therefore, the recording pit 24 remains as the latent image recording pit 41.

On the other hand, the magneto-optical recording medium 10 has an initializing magnetic field H
A reproducing magnetic field Hr opposite to i is applied at least in the reproducing section. In this state, the area having the latent image recording pits 41 initialized along with the movement of the medium 10 is the beam spot 2
6 goes down and moves to the left side of the tip side view under the beam spot 26, the beam irradiation time becomes substantially long. Therefore, as shown by a broken line a on the tip side of the spot 26, as shown in FIG. A high temperature region 34 is generated, and this region 3
In 4, the magnetic domain wall of the intermediate layer 32 disappears, the magnetization of the recording layer 33 is transferred to the reproducing layer 31 by the exchange force, and the latent image recording pits 41 existing in the recording layer 33 can be reproduced in the reproducing layer 33. It emerges as a pit 24.

Therefore, if the rotation of the plane of polarization of the beam spot 26 due to the Kerr effect or Faraday effect due to the direction of magnetization in the reproducing layer 31 is detected, the recording pit 24 can be read. At this time, in the low temperature region 36 other than the high temperature region 34 in the beam spot 26, the latent image recording pits 41 are not raised in the reproducing layer 31, and the record pits 24 are readable only in the narrow high temperature region 34. As a result, even when a plurality of recording pits 24 enter the beam spot 26, that is, the magneto-optical recording medium 10 for high density recording.
Also in the above, only a single recording pit 24 can be read out and high resolution reproduction can be performed.

Next, the extinction type MSR 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 cross-sectional view showing its magnetization mode. 8A and 8B, portions corresponding to those of FIGS. 7A and 7B are denoted by the same reference numerals, and redundant description will be omitted. In this case, the initialization magnetic field Hi is not required.

In this case, the intermediate layer 3 in the high temperature region 34
For example, the laser beam power and the material of the intermediate layer 32 are selected so that the Curie point is 2 or more. by this,
In the high temperature region 34 in the laser beam spot 26, the magnetization is aligned downward in the drawing by the reproducing magnetic field Hr applied from the outside, and the recording pit 2 in the reproducing layer 31 is aligned.
Make 4 disappear. On the other hand, various conditions such as coercive force of the recording layer 33 are set so that the recording pits 24 remain as the latent image recording pits 41 in the recording layer 33 even when the magnetization of the intermediate layer 32 disappears.

On the other hand, in the low temperature region 34, the reproducing layer 31 is
The magnetization of the recording layer 33, that is, the recording pit 24 is transferred and held in a reproducible state. That is, in the disappearance type MSR system, the recording pits in the low temperature region 36 of the beam spot 26 can be reproduced to improve the resolution.

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

However, as described above, these MS
In the R method, the magnetic layer of the magneto-optical recording medium needs to have a multi-layered structure, the structure is complicated, and the degree of freedom in selecting materials may be low.

On the other hand, in a normal general magneto-optical recording medium, the recorded information remains as it is without being erased when the recorded information is reproduced, so that the reproduction is required only once.
After that, when it is desired to erase the recorded contents for the purpose of maintaining confidentiality, a special degausser is used or the recording track is erased.

[0020]

The present invention requires, in particular, only one reproduction, but after this one reproduction,
In a magneto-optical recording medium used when it is necessary to erase recorded information, a simple magnetic layer structure is adopted without using a complicated magnetic layer of the magneto-optical recording medium as in the above-mentioned MSR system, and super resolution is adopted. There is provided a recording / reproducing method capable of reproducing.

[0021]

FIG. 1 shows a schematic explanatory view of an example of a magneto-optical recording / reproducing method of the present invention. The present invention is shown in FIG.
As shown in FIG.
Information recording pits 11 containing a spatial frequency component equal to or higher than the cutoff spatial frequency are recorded, and at the time of reproduction, selected as reproduction optical power for forming a high temperature region 13 in the reproduction optical spot 12 where the information recording pits 11 disappear. Then, only the information recording pit 11 in the low temperature region 14 excluding the high temperature region 13 in the reproducing light spot 12 is reproduced by the magneto-optical effect.

[0022]

The magneto-optical recording / reproducing method of the present invention utilizes the temperature distribution on the magneto-optical recording medium 10 generated in the reproducing light spot 12. In FIG. 1A, 10 is an information recording pit 1 including a spatial frequency component higher than the cutoff spatial frequency.
1 (11A, 11B ...) In the magneto-optical recording medium, when the magneto-optical recording medium 10 moves in the traveling direction indicated by the arrow a in FIG. The temperature rises due to the irradiation, and due to the relationship of heat conduction, a temperature distribution occurs such that the region slightly ahead of the center of the reproducing light spot 12 having the highest irradiation intensity has the highest temperature.

FIG. 1B is an enlarged schematic sectional view taken along the line CC in FIG. 1A. The solid arrow h indicates the magneto-optical recording medium 1
The magnetic moment in 0 is schematically shown, the temperature distribution due to the irradiation of the spot 12 described above is shown by a solid line t, and the light intensity distribution of the reproducing light spot 12 is shown by a solid line s. At this time, by appropriately selecting the relative transition speed of the magneto-optical recording medium 10 to the spot 12, the reproducing optical power, and the like, a high temperature region 13 above a predetermined temperature and a low temperature below a predetermined temperature within the spot 12 are selected. The area occupied by each of the areas 13 and 14 can be selected so that the area 14 is generated and only one of the plurality of information recording pits in the spot 12 exists in the low temperature area 13.

In particular, in the method of the present invention, since the reproducing optical power is selected so that the information recording pit 11B disappears in the high temperature region 13 generated in the spot 12 during reproduction, this high temperature region 13 is used as a mask. Of the plurality of information recording pits in the spot 12, only one information recording pit 11A in the low temperature area 14 can be reproduced by the magneto-optical effect.

Since the information pits are magnetized in the high temperature region 13 as described above, the magneto-optical recording medium 10 is automatically initialized immediately after the reproduction. That is, the reproduction is performed only once, and thereafter the recorded contents are erased without requiring a special erasing operation.

[0026]

EXAMPLES Each example of the magneto-optical recording / reproducing method of the present invention will be described below with reference to FIGS. In each of these examples, a laser beam is applied to a predetermined position of the magneto-optical recording medium 10 by, for example, a condenser lens 16 as shown in the block diagram of one example of the recording / reproducing apparatus for carrying out the method of the present invention. At the same time, the reflected light is read out to perform recording / reproduction. In this example, the external magnetic field Hex is applied to the magneto-optical recording medium 10 by the magnetic field generating means 9 during recording or, in some cases, during reproduction.

The magneto-optical recording medium 10 is composed of, for example, a transparent substrate 1 made of polycarbonate or the like, a dielectric layer 2 made of SiN or the like and having a thickness of 1100 Å, a magnetic layer 3 made of TbFeCo or the like and having a thickness of 300 Å, or the like. A dielectric layer 4 made of SiN or the like and having a thickness of, for example, 450 Å, and a thermal control layer 5 made of Al or the like and having a thickness of, for example, 700 Å are sequentially deposited by sputtering or the like.

In such an apparatus structure, first, high density recording having a frequency component higher than the cutoff spatial frequency is performed on the magneto-optical recording medium 10.

A reproducing method for the magneto-optical recording medium 10 will be described with reference to FIG. In FIG. 1, in order to erase the information recording pits, the temperature is raised above the Curie temperature at which the magnetization disappears in the high temperature region 13. As described above, high-density recording is performed on the recording track 8 of the magneto-optical recording medium 10, and the reproduction light spot 1
For example, two information recording pits 11A and 11B are inserted in the area 2.

At this time, when the magneto-optical recording medium 10 is moved in the traveling direction indicated by the arrow a by the irradiation of the reproducing light,
As described above, the temperature rises due to the irradiation of the reproduction light, and due to the heat conduction relationship, a temperature distribution occurs such that the region slightly ahead of the center of the reproduction light spot 12 has the highest temperature.

In this case, as shown by the solid line t in FIG. 1B, this temperature rise causes a certain region including a part of the spot 12 to be higher than the Curie temperature Tc of the magnetic layer 3, that is, the magnetization disappears. The reproduction optical power is selected so that the magnetization disappearing region 15 is obtained. That is, in the spot 12, a high temperature region 13 which is a part of the magnetization disappearing region 15 and where the magnetic layer 3 has a Curie temperature or higher, and a low temperature region 14 which is lower than the Curie temperature are generated. Further, only one information recording pit 11A exists on the recording track 8 in the low temperature area 14, and the low temperature area 1 exists in the high temperature area 13.
For example, the transfer speed of the magneto-optical recording medium 10 or the material and thickness of the magnetic layer 3 and the thermal control layer 5 are appropriately selected so that only the pits 11B that have passed through 4 enter.

As described above, by inserting the information recording pits 11B among the plurality of information recording pits in the spot 12 into the high temperature region 13 having the Curie temperature or higher, the magnetization can be eliminated, that is, masked. Only one information recording pit 11A can be read by the magneto-optical effect, and super resolution reproduction can be performed with a simple magneto-optical recording medium structure.

After reproduction, the read information recording pits 11A enter the high temperature region 13 due to the movement of the magneto-optical recording medium 10, so that recording and erasing are automatically performed immediately after reproduction, and no special information is recorded. The initialization can be performed without providing any means, and in the case where the recorded information needs to be erased after the reproduction, the recording / reproducing apparatus can be simplified.

Next, another example of the magneto-optical recording / reproducing method of the present invention will be described with reference to FIGS. 3A and 3B. In FIGS. 3A and 3B, portions corresponding to those in FIGS. 1A and 1B are designated by the same reference numerals, and redundant description will be omitted. In this example, high temperature region 1
The temperature of the magneto-optical recording medium 10 in 3 is set so as to be equal to or higher than the so-called magnetization reversal temperature at which the magnetization directions are aligned in the direction of the external magnetic field and lower than the Curie temperature. The magnetic field shown in FIG. An external magnetic field Hex is applied by the generating means 9.

Also in this case, the reproduction light spot 1
2 has two information recording pits 11A and 11B, the temperature of the magneto-optical recording medium 10 is gradually increased by the irradiation of the reproducing light, as indicated by the solid line t in FIG. 3B.
The power of the reproducing light is selected so that the magnetization reversal temperature Tr at which the magnetization is aligned in the direction of the external magnetic field Hex is equal to or higher than a certain range, and the maximum temperature is not equal to or higher than the Curie temperature. At this time, in the magnetization reversal region 16 having the magnetization reversal temperature Tr or higher, the magnetization is aligned in the direction of the external magnetic field Hex.

In this case, in the reproducing light spot 12, there is only one information recording pit 11A in the low temperature region 14 below the magnetization reversal temperature Tr, and in the high temperature region 13 included in the magnetization reversal region 16. The transfer speed of the magneto-optical recording medium 10, the material of the magnetic layer 3, etc. are selected so that the other information recording pits 11B enter.

With such a structure, the information recording pits 11B in the reproducing light spot 12 are always aligned with the magnetization in the same direction as the external magnetic field Hex regardless of the information, and the information of the information recording pits 11A is recorded. A change in the magneto-optical effect can be obtained according to the direction of magnetization corresponding to
In other words, only this information recording pit 11A can be read and super resolution reproduction can be performed.

Also in this case, the read information recording pit 11A enters the high temperature region 13 as the magneto-optical recording medium 10 moves, and the external magnetic field H is generated here.
Since the magnetization direction is aligned with ex, the information recording pit 11 is automatically erased after reproduction. Therefore, when it is necessary to erase the recorded information for the purpose of maintaining confidentiality after the reproduction, it is not necessary to provide any erasing means, and the recording / reproducing apparatus can be simplified.

Next, another example of the magneto-optical recording / reproducing method of the present invention will be described with reference to FIGS. 4A and 4B. 4A and 4B, portions corresponding to those in FIGS. 1A and 1B are designated by the same reference numerals, and redundant description will be omitted.

In this case, as in the example described with reference to FIG. 3, the magneto-optical recording medium 10 in the high temperature region 13 is set to have a magnetization reversal temperature or higher. Especially, the maximum temperature is the Curie of the magnetic layer 3. The case where the magnetization disappearing region 15 is formed in a part of the magnetization switching region 16 at the temperature or higher is shown. As described above, even in the case where the magnetization disappearing region 15 in which the magnetization disappears at the Curie temperature or higher exists in the magnetization reversal region 16, the magnetization disappearing region 15 and the magnetization disappearing region 15 are formed as in the example described in FIG. In the high temperature region 13 in the spot 12 overlapping a part of the magnetization switching region 16, the magnetization of the information recording pit 11B is aligned with the external magnetic field Hex or disappears, and the information recording pit 1 in the low temperature region 14 is magnetized.
1A will be masked. Therefore, even in this case, it is possible to reproduce only one information recording pit 11A among the plurality of information recording pits in the spot 12, and it is possible to perform high-density reproduction with super-resolution.

Also in this case, the information recording pit 11A is initialized by passing through the magnetization reversal region 16 so that the magnetization is aligned in the same direction as the external magnetic field Hex, as in the example described with reference to FIG. It will be. Therefore,
Similar to the above example, when it is necessary to erase the recorded information after performing the reproduction only once, the recording / reproducing apparatus can be simplified.

In the example described with reference to FIGS. 3A and 3B above, the reproduction output was measured while changing the reproduction light power. First, with respect to the magneto-optical recording medium 10 having the structure described in FIG. 2, a linear velocity of 7 m / s, 10 MHz (recording wavelength of 0.7 μm).
m, mark length 0.35 μm), and high density recording was performed.

On the other hand, the reproducing light power is 1.5 mW.
However, no reproduction output was obtained. This is shorter than this because the cutoff recording wavelength λ, which is the reciprocal of the cutoff frequency, is λ = 780 nm, the numerical aperture NA is 0.53, and the cutoff spatial frequency λ / 2NA = 0.74 μm. This is because it is not possible to replay the recording of the 0.7 μm wavelength.

Next, when the reproducing optical power was raised to 3.0 mW and reproducing was performed by the magnetic field generating means 9 while applying the external magnetic field Hex of 300 Oe, a reproducing output of C / N = 35 dB was obtained.

After this reproducing operation, when reproducing was carried out by the same method as the above-mentioned condition, no reproduced output was obtained.
This is because the information pits have been magnetized and initialized by the external magnetic field, as described above with reference to FIG.

That is, in this case, by applying a reproducing magnetic field and substantially increasing the power of the reproducing light as compared with the conventional method, the magneto-optical recording medium having a simple magnetic layer structure can be made super-magnetic. It is possible to record and reproduce resolution,
When the reproducing operation is performed only once, particularly when it is necessary to erase the recorded information after the reproducing, the recording can be erased without providing any erasing means, and the device can be simplified.

The method of the present invention is not limited to the above-described embodiment, but various other device configurations and reproducing methods such as the case where the direction of the external magnetic field Hex is reversed in the example described in FIGS. 3 and 4, for example. Can be taken.

[0048]

As described above, according to the magneto-optical recording / reproducing method of the present invention, in particular, only one reproduction is required, but thereafter, it is necessary to erase the recorded contents for confidentiality protection. In using a special degausser,
Since the recorded information is automatically erased after the reproduction without taking the trouble of erasing the recording track, it is possible to simplify the recording / reproducing apparatus.

Furthermore, super-resolution recording / reproduction with a cut-off spatial frequency or higher can be performed, and the magnetic layer of the magneto-optical recording medium can be used as a magneto-optical recording medium used in a conventional recording / reproducing method such as the MSR system. In comparison, a much simpler configuration can be adopted.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an example of a magneto-optical recording / reproducing method of the present invention.

FIG. 2 is a block diagram of an example of an apparatus for carrying out the magneto-optical recording / reproducing method of the present invention.

FIG. 3 is an explanatory diagram of an example of a magneto-optical recording / reproducing method of the present invention.

FIG. 4 is an explanatory diagram of an example of a magneto-optical recording / reproducing method of the present invention.

FIG. 5 is a diagram showing conventional magneto-optical recording / reproducing.

FIG. 6 is a diagram showing conventional magneto-optical recording / reproducing.

FIG. 7 is an explanatory diagram of a relief type MSR.

FIG. 8 is an explanatory diagram of an extinction type MSR.

[Explanation of symbols]

 1 substrate 2 dielectric layer 3 magnetic layer 4 dielectric layer 5 thermal control layer 8 recording pit 9 magnetic field generating means 10 magneto-optical recording medium 11 information recording pit 12 reproducing light spot 13 high temperature region 14 low temperature region 15 magnetization disappearing region 16 magnetization Inversion area

Claims (1)

[Claims] 1. An information recording pit containing a spatial frequency component equal to or higher than a cutoff spatial frequency is recorded on a magneto-optical recording medium at the time of recording, and the information recording pit disappears in a reproduction light spot at the time of reproduction. Magneto-optical recording / reproducing characterized in that only the information recording pits in the low temperature region in the reproducing light spot excluding the high temperature region are reproduced by the magneto-optical effect by selecting the reproducing optical power for forming the high temperature region to be reproduced. Method.