JP2827869B2 - Reproduction method of magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reproducing a magneto-optical recording medium, and more particularly to a method for reproducing a magneto-optical recording medium suitable for high-density recording.

[0002]

2. Description of the Related Art In a conventional magneto-optical recording medium, there is known a method of improving a linear density by masking a portion other than a recording mark to be read at the time of reproduction (Japanese Patent Laid-Open No. 3-93056, Nikkei Electronics No. 539). (1991) p.223). The above technique uses an exchange-coupled multilayer film and is called an iris technique or an MSR technique. In this method, 3
FAD that uses a medium having a recording film having at least two layers and masks a recording mark in a portion that has become relatively high in temperature by reproduction light.
There are two types of RAD systems, in which a medium composed of two or more recording films is used, and a recording mark is masked at a portion other than a portion which has become relatively high in temperature by reproduction light.

In the FAD system, in order to cut the exchange coupling force between the reproducing layer closest to the light irradiation side and the recording layer for data recording farthest from the light irradiation side during reproduction, the Curie temperature is placed between the two layers. However, it is necessary to sandwich an intermediate layer lower than both layers.

[0004] In the case of the RAD method, it is necessary to align the magnetization of the recording film closest to the light irradiation side in one direction before reproducing, so that an initialization magnetic field is required.

[0005]

In the conventional FAD medium, the exchange coupling force between the reproduction layer closest to the light irradiation side and the data recording layer farthest from the light irradiation side is cut during reproduction. For this purpose, an intermediate layer having a lower Curie temperature than both layers must be interposed between the two layers, and at least three recording films are required. Further, in the FAD system, only the portion where the exchange coupling force between the recording layer and the reproducing layer is cut by being heated by the reproducing light can be masked, and the crosstalk from the adjacent track is not so effective.

According to the present invention, the Curie temperature is lower than the upper and lower layers.
It is an object of the present invention to provide a reproducing method for a magneto-optical recording medium that does not need to sandwich an intermediate layer and can realize a FAD reproducing method.

[0007]

SUMMARY OF THE INVENTION The present invention provides two layers or three layers.
With more than one recording film, and the recording film closest to the light irradiation side
The coercive force during light irradiation is higher than the coercive force during light irradiation of other recording films.
The magnetization state of the recording film on which information has been recorded can be transferred to the recording film closest to the light irradiation side in a predetermined temperature range, and the magnetization state of the recording film closest to the light irradiation side is set to an external bias. If the recording film has a configuration that can be changed by a magnetic field and has three or more recording films, the recording film having the characteristic that the Curie temperature of the recording film farthest to the light irradiation side is lower than the Curie temperature of the other recording films using the formed magneto-optical recording medium, wherein said information in a predetermined temperature range rather smaller than the coercive force of the recording film is recorded, the closest serial to the irradiation side of the light
While applying a bias magnetic field larger than the coercive force of the recording film, irradiating light with a spot diameter larger than the recording bit,
A reproducing method for a magneto-optical recording medium, characterized by reproducing only recorded information in a low-temperature area in a traveling direction of the light spot.

The coercive force at the time of light irradiation of the recording film having two or three or more recording films and being closest to the light irradiation side is reduced.
The magnetization state of the recording film on which information is recorded can be transferred to a recording film that is smaller than the coercive force of the other recording film at the time of light irradiation and is closest to the light irradiation side in a predetermined temperature region, and the light irradiation In the configuration in which the magnetization state of the recording film closest to the recording film side can be changed by an external bias magnetic field, and when there are three or more recording films, the Curie temperature of the recording film furthest to the light irradiation side is set to another recording film. Using a magneto-optical recording medium on which a recording film having a characteristic lower than the Curie temperature is formed, the maximum coercive force of the recording film in which the information is recorded from room temperature to the Curie temperature is smaller than the maximum coercive force , and the light irradiation side Keep the recording film closest to
The larger bias field than the magnetic force, is irradiated with light of a larger spot diameter than the recording bit while applying to a portion other than the recording bit to be reproduced in the recording bit to be the reproduction to reproduce only the recording information of the recording bits A method for reproducing a magneto-optical recording medium characterized by the following.

This reproducing method can be realized by applying a bias magnetic field to a coil having a hole at the center of a core by adjusting the hole of the core to a reproducing light spot.

The magneto-optical recording medium used in the present invention is characterized in that the interface domain wall energy density of the plurality of recording films decreases as the recording film on the light irradiation side becomes smaller.

Further, the thickness of the recording film on the light irradiation side of the adjacent recording film among the plurality of recording films is smaller than the thickness of the interface magnetic wall formed at the interface between the adjacent recording films.

[0012]

[Action] In the above-mentioned temperature region, the recording film 15 shown in the recording film 2 of the magnetization state is transferred to the serial Rokumaku 1 or 5 shown in FIG. 1
The fact that it is possible to transfer the magnetization states in serial Rokumaku 13, the bias magnetic field is that of being able to reverse the only the magnetization of the recording film 1 or the recording film 13 in the bias magnetic field direction. Since the inverted bias magnetic field of the recording layer 1 or the recording film 13 by the temperature varies, if Shiteyare reproduced by applying a bias magnetic field such that only when the temperature of the recording film 1 is increased by the reproduction beam is reversed, there Is masked, and the same as the iris technology of the FAD system can be performed with a two-layer recording film or with three or more recording films without an intermediate layer having a relatively low Curie temperature.

When transferring the magnetization state of a certain recording film to another recording film, it is necessary to punch through the interface domain wall generated at the interface of the recording film to the recording film on the side where the magnetization state is transferred. The interface domain wall moves toward the recording film having a low interface domain wall energy density, and punches through the recording film having a low interface domain wall energy density. Also, regardless of the magnitude of the interface domain wall energy density, if the recording film is thinner than the thickness of the interface domain wall that would occur in the recording film, the interface domain wall punches through the recording film. Therefore, if an exchange-coupling multilayer film is manufactured under such conditions, it is shown in FIG.
The magnetization state of the to the recording film 2 is transferred to the recording film 1. Or figure
The magnetization state of the recording film 15 shown in 5 can be transferred to the recording film 13.

In this magneto-optical recording medium, the bias magnetic
Irradiating the light of the reproduction power while applying the field
Closest to the light irradiation side in the high temperature area
The magnetization of the film is reversed and masked, which is the same as in iris technology.
It becomes possible. Alternatively, in this magneto-optical recording medium, if a bias magnetic field is applied around a recording mark to be reproduced and a portion other than the recording mark to be reproduced is masked, the same operation as the iris technique can be performed. At this time, the magnitude of the bias magnetic field can be applied to such an extent that the information on the recording film 2 shown in FIG. 1 or the recording film 15 shown in FIG. 5 does not disappear. In this case, since the recording mark of the adjacent track can be masked, the crosstalk of the adjacent track can be reduced. A coil with a hole in the center of the core will have a smaller magnetic field at that hole than around it. Therefore, when the reproduction is performed by aligning the hole of the coil with the center of the reproduction light spot, the recording mark around the center of the reproduction light spot is masked, and the same operation as the iris technique can be performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of a disk using a two-layer film according to the present invention. It is obtained by sequentially forming an interference film 4, a recording film 1, a recording film 2, and a protective film 5 on a substrate 3.

As an example, the substrate 3 has a diameter of 130 m.
m, a polycarbonate substrate having a track pitch of 1.6 μm, and a silicon nitride film as an interference film 4 on the substrate 3
80 nm, recording film 1 GdFeCo film 30 nm, recording film 2
Then, a TbFeCo film of 100 nm and a silicon nitride film of 80 nm as a protective film 5 were sequentially formed. Curie temperature of GdFeCo film is 310 ℃, interface domain wall energy density at room temperature is 1.0 er
g / cm ² . The Curie temperature of the TbFeCo film is 150
The interface domain wall energy density at ℃ and room temperature is 2.3 erg / cm ² . Thereby, punch-through of the interface domain wall from the TbFeCo film to the GdFeCo film can be caused.

As another example, as a recording film 1, a TbFeCo film is 20 nm, and as a recording film 2, a composition of the recording film 1 is slightly different from that of the recording film 1.
A 100 nm bFeCo film was fabricated. The other films are the same as in the above example. The Curie temperature of the TbFeCo film of the recording film 1 is 300 ° C, and the interface domain wall energy density at room temperature is
2.7 erg / cm ² . The Curie temperature of the TbFeCo film of the recording film 2 is 150 ° C., and the interface domain wall energy density at room temperature is 2.3 erg / cm ² . In this case, since the thickness of the interface domain wall which is supposed to be formed by the recording film 1 is thinner, punch-through of the interface domain wall from the recording film 2 to the recording film 1 occurs.

As another example, GdDyFeCo is used as the recording film 1.
A recording film having a thickness of 30 nm and a recording film 2 having a TbFeCo film having a thickness of 100 nm was produced. The other films are the same as in the above example.
The Curie temperature of the GdDyFeCo film is 400 ° C., and the interface domain wall energy density at room temperature is 1.8 erg / cm ² . The Curie temperature of the TbFeCo film is 150 ° C, and the interface domain wall energy at room temperature is 2.3
erg / cm ² . Near the Curie temperature of the TbFeCo film, Gd
The effective anisotropic magnetic field of the DyFeCo film is 1 kOe and the bias magnetic field
At 400 Oe, this film does not reverse magnetization.

As another example, GdTbFeCo is used as the recording film 1.
A recording film having a thickness of 30 nm and a recording film 2 having a TbFeCo film having a thickness of 100 nm was produced. The other films are the same as in the above example.
The Curie temperature of the GdTbFeCo film is 250 ° C., and the interface domain wall energy density at room temperature is 1.5 erg / cm ² . The Curie temperature of the TbFeCo film is 150 ° C., and the interface domain wall energy density at room temperature is 2.3 erg / cm ² . As a result, the TbFeCo film
Punch-through of the interface domain wall to the GdFeCo film can be caused.

The above paragraphs 0016, 0017, 001
The four types of magneto-optical recording media shown in FIGS.
The playback was performed in the manner shown in FIG. 7.4MHz dut at 9.42m / s
When recording was performed at y50% and the bias magnetic field 6 was reproduced at 5000 e and the reproduction power was 2.0 mW, the recording mark 10 of the recording film 1 was masked in the high-temperature region 9 and the mask was reversed. As a result, each magneto-optical recording medium has a C / N of about 53 dB.
was gotten. This is about 8 dB larger than the conventional magneto-optical recording medium or the case where no bias magnetic field 6 is applied. At this time, the laser wavelength is 680 nm.

The above four types of magneto-optical recording media were reproduced by the method shown in FIG. Except for a part of the light reproduction spot 8 (about the size of the recording mark), a bias magnetic field 11 was applied to perform reproduction. The recording conditions are the same as before. The bias magnetic field 11 is applied by a permanent magnet and has a magnitude of about 2 kOe. With each magneto-optical recording medium, a C / N of about 54 dB was obtained. This is 9 dB lower than the conventional magneto-optical recording medium or the case where no bias magnetic field 11 is applied.
About big. When examining the crosstalk of adjacent tracks,
This is about 5 dB better than the conventional magneto-optical recording medium or the case where no bias magnetic field 11 is applied.

The above four types of magneto-optical recording media were reproduced by the method shown in FIG. A coil 12 having a hole in the center of the core at a part (about the size of a recording mark) of the reproduction light spot 8
And a magnetic field is applied by the coil 12,
Played. The recording conditions are the same as before. With each magneto-optical recording medium, a C / N of about 53 dB was obtained.
This is about 8 dB larger than a conventional magneto-optical recording medium or a case where no magnetic field is applied by the coil 12. Examining the crosstalk of the adjacent tracks, it was found that the crosstalk was 5d compared to the conventional magneto-optical recording medium or the case where no magnetic field was applied by the coil 12.
B was better.

FIG. 5 shows the structure of a disk using the three-layered film of the present invention. The interference film 4, the recording film 13, and the recording film 1 are provided on the substrate 3.
4, the recording film 15 and the protective film 5 are sequentially formed.

As an example, the substrate 3 has a diameter of 130 m.
m, a polycarbonate substrate having a track pitch of 1.6 μm, and a silicon nitride film as an interference film 4 on the substrate 3
80 nm, the GdFeCo film as the recording film 13 is 30 nm, the GdTbFeCo film as the recording film 20 is 20 nm, and the recording film 15 is T
The bFeCo film is 100 nm, and the silicon nitride film is 80
nm was sequentially formed.

The Curie temperature of the GdFeCo film of the recording film 13 is
The interface domain wall energy density at 310 ° C and room temperature is 1.0 erg / cm
² The Curie temperature of the GdTbFeCo film of the recording film 14 is 250 ° C., and the interface domain wall energy density at room temperature is 1.5.
erg / cm ² . The Curie temperature of the TbFeCo film of the recording film 15 is 150 ° C., and the interface domain wall energy density at room temperature is
2.3 erg / cm ² . Thereby, the TbFeC of the recording film 15 is
o From the film to the GdTbFeCo film of the recording film 14, the Gd of the recording film 14
Punch-through of the interface domain wall from the TbFeCo film to the TbFeCo film of the recording film 13 can be caused. The Curie temperature of the recording film 14 is higher than the Curie temperature of the recording film 15.

As another example, TbFeCo is used as the recording film 13 .
A 20 nm thick film, a 40 nm thick GdTbFeCo film as the recording film 14 , and a TbFeCo film slightly different in composition from the recording film 13 as the recording film 15 .
Timing of making 100nm film. The other films are the same as in the above example. The Curie temperature of the TbFeCo film of the recording film 13 is 300 ° C., and the interface domain wall energy density at room temperature is 2.7 erg / cm ² at room temperature.
The Curie temperature of the GdTbFeCo film of the recording film 14 is 250
The interface domain wall energy density at 1.5 ° C. and room temperature is 1.5 erg / cm ² . The Curie temperature of the TbFeCo film of the recording film 15 is
The interface domain wall energy density at 150 ° C. and room temperature is 2.3 erg / cm ² at room temperature. In this case, since the interface domain wall to the recording film 13 is thinner than the thickness of the interface domain wall that should be formed, punch-through of the interface domain wall from the recording film 14 to the recording film 13 occurs. Further, since the interface domain wall energy density of the recording film 14 is smaller than that of the recording film 15, punch-through of the interface domain wall from the recording film 15 to the recording film 14 occurs. As a result, from the recording film 15 to the recording film 13
Transcription to occurs. The Curie temperature of the recording film 14 is higher than the Curie temperature of the recording film 15.

The magneto-optical recording medium having the above two types of three-layer recording films was reproduced in the same manner as the two-layer recording film shown in FIG. When recording was performed at a linear velocity of 9.42 m / s and a duty of 7.4 MHz at 7.4 MHz, and reproduction was performed with a bias magnetic field of 500 Oe and a reproduction power of 2.0 mW, a C / N of about 53 dB was obtained with each magneto-optical recording medium. This is about 8 dB larger than the conventional magneto-optical recording medium or the case where no bias magnetic field is applied. At this time, the laser wavelength is 680 nm.

The magneto-optical recording medium having the above two types of three-layer recording films was reproduced in the same manner as the two-layer recording film shown in FIG. The recording conditions are the same as before. The bias magnetic field is applied by a permanent magnet and has a magnitude of about 2 kOe. For each magneto-optical recording medium, C of about 54 dB
/ N was obtained. This is about 9 dB larger than a conventional magneto-optical recording medium or a case where no bias magnetic field is applied. Examination of the crosstalk between adjacent tracks revealed that the crosstalk was improved by about 5 dB as compared with the conventional magneto-optical recording medium or when no bias magnetic field was applied.

The magneto-optical recording medium having the two types of three-layer recording films was reproduced in the same manner as the two-layer recording film shown in FIG. The recording conditions are the same as before. With each magneto-optical recording medium, a C / N of about 53 dB was obtained. This is about 8 dB larger than a conventional magneto-optical recording medium or a case where no magnetic field is applied by a coil. Examination of the crosstalk of the adjacent track showed that it was improved by about 5 dB compared to the conventional magneto-optical recording medium or the case where no magnetic field was applied by a coil.

[0030]

According to the present invention described above, according to the present invention, only uses the recording film two layers, or the upper Curie temperature
The iris technology of the FAD system can be realized with three or more recording films that do not use an intermediate layer lower than the lower layer. In addition, by applying a bias magnetic field to a portion other than a portion of the reproduction light spot, the iris technology can be realized, and crosstalk between adjacent tracks can be reduced. Further, by using a coil having a hole in the center of the core, a bias magnetic field can be easily applied to a portion other than a part of the reproduction light spot. With these techniques, the density of the magneto-optical recording medium can be increased, and a large-capacity optical disk can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a disk according to an embodiment of the present invention.

FIG. 2 shows a disc reproducing method according to an embodiment of the present invention.

FIG. 3 shows a disc reproducing method according to an embodiment of the present invention.

FIG. 4 shows a disc reproducing method according to an embodiment of the present invention.

FIG. 5 is a sectional view of a disk according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 1st recording film 2 2nd recording film 3 board | substrate 4 interference film 5 protective film 6 bias magnetic field 7 disk moving direction 8 reproduction light spot 9 high temperature area 10 recording mark 11 bias magnetic field applied to other than a part of reproduction light spot 12 Coil with hole at center of core 13 First recording film 14 Second recording film 15 Third recording film 16 Substrate 17 Interference film 18 Protective film

Claims (5)

(57) [Claims] An optical recording medium having two or three or more recording films,
The coercive force during light irradiation of the recording film closest to the irradiation side of
The magnetization state of the recording film on which information is recorded can be transferred to the recording film closest to the light irradiation side in a predetermined temperature region, which is smaller than the coercive force at the time of light irradiation of the recording film, and can be transferred to the light irradiation side. In a configuration in which the magnetization state of the closest recording film can be changed by an external bias magnetic field, and when there are three or more recording films,
Using a magneto-optical recording medium on which a recording film having a characteristic in which the Curie temperature of the recording film farthest to the light irradiation side is lower than the Curie temperature of the other recording films is formed, the information is recorded in the predetermined temperature region. has been rather smaller than the coercive force of the recording film, the closest recording layer to the irradiation side of the light
Irradiating light with a spot diameter larger than the recording bit while applying a bias magnetic field larger than the coercive force of the recording medium, and reproducing only recorded information in a low-temperature region in the traveling direction of the light spot. A method for reproducing a recording medium. 2. An optical recording medium having two or three or more recording films,
The coercive force during light irradiation of the recording film closest to the irradiation side of
The magnetization state of the recording film on which information is recorded can be transferred to the recording film closest to the light irradiation side in a predetermined temperature region, which is smaller than the coercive force at the time of light irradiation of the recording film, and can be transferred to the light irradiation side. In a configuration in which the magnetization state of the closest recording film can be changed by an external bias magnetic field, and when there are three or more recording films,
The information is recorded from room temperature to the Curie temperature using a magneto-optical recording medium on which a recording film having a characteristic in which the Curie temperature of the recording film furthest to the light irradiation side is lower than the Curie temperature of the other recording films is formed. It was rather smaller than the coercivity of the recording film, most irradiation side of the light
The larger bias field than the coercive force near the recording film is irradiated with light of a larger spot diameter than the recording bit while applying to a portion other than the recording bit to be reproduced in the recording bit to be the reproduction, recording of the recording bit A method for reproducing a magneto-optical recording medium, which reproduces only information. 3. The reproducing method for a magneto-optical recording medium according to claim 2 , wherein the bias magnetic field is applied by adjusting a coil having a hole in the center of the core with the hole of the core to a reproducing spot. . 4. The magneto-optical medium according to claim 1, wherein the interface magnetic wall energy density of the two or three or more recording films decreases toward the recording film on the light irradiation side. How to play. 5. A recording film on the light irradiation side of an adjacent recording film among the two or three or more recording films, wherein a thickness of an interface magnetic wall formed at an interface between the adjacent recording films is thinner. A method for reproducing a magneto-optical recording medium according to claim 1.