JPH087384A - Magneto-optical information recording/reproducing apparatus - Google Patents

Abstract

PURPOSE:To improve the recording densities of a magneto-optical disc device, a magneto-optical tape device, etc., and increase a recording capacity. CONSTITUTION:A magneto-optical recording medium 112 in which magnetic domains appear or disappear by the application of an external magnetic field 109 is employed. The initialization directions of adjacent tracks on the recording medium are opposite to each other. At the time of reproduction, a reproducing magnetic field whose direction is the magnetizing direction of the recording mark of the track to be reproduced is applied for the reproduction. As a result, a reproduction crosstalk from the adjacent track can be suppressed, so that a track density can be increased. Further, an apparatus which facilitates the reproduction from a ROM type recording medium and a RAM type recording medium with the same principle can be provided.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In an information recording / reproducing apparatus using a magneto-optical effect, such as an optical disk device, an optical tape device,
In order to improve the recording density, it is a direct method to reduce recording marks carrying information, that is, magnetic domains, and to form them close to each other. On the other hand, the reproduction signal from the magneto-optical recording medium is determined by the shape and size of the light spot, the shape and size of the recording mark, the rotation angle of the polarization plane of the medium, etc., but the recording linear density in the track direction is increased to perform recording. When the mark length and the recording mark interval are shortened, the amplitude of the reproduction signal is reduced in a portion where short recording marks are continuous with a narrow spacing, and the local S / N ratio is deteriorated in that portion. . When the recording density in the direction orthogonal to the track is increased,
Leakage of playback signals from adjacent tracks (playback cross /
(Talk) increases, and the error in restoring the reproduced signal to information increases together with the deterioration of the S / N ratio.

In order to increase the recording density, for example, a method using a magnetic super-resolution recording medium constituted by laminating a reproducing layer 301, a coupling layer 302 and a recording layer 303 in this order as shown in FIG. It is disclosed in Japanese Patent Laid-Open No. 3-93056. The reproducing layer 301, the coupling layer 302, and the recording layer 303 are perpendicular magnetization films having an easy axis of magnetization in the direction normal to the magnetic film surface, and have different coercive forces and Curie temperatures. At room temperature, the coupling layer 302 has magnetism, and the recording layer 303 and the reproducing layer 301 are magnetically coupled by exchange coupling to transfer the magnetic domain of the recording layer 303 to the reproducing layer 301. A reproducing light spot 3 is formed on the magneto-optical super-resolution magnetic film.
When 05 is irradiated and the coupling layer 302 loses magnetism by exceeding the Curie temperature, the coupling between the reproducing layer 301 and the recording layer 303 is broken, and the magnetization of the reproducing layer 301 is oriented in the external magnetic field direction.
By the above operation, the recording mark 3 in which a part of the reproducing layer 301 heated in the spot 305 is recorded on the recording layer 303
Since 06 is not transferred and the mask region 304 is formed, the effective diameter of the light spot 305 in the scanning direction is reduced, and the apparent resolution of the optical system is improved.
However, even when this method is used, the improvement effect cannot be expected with respect to the resolution in the track orthogonal direction. Further, with this method, it is difficult to make the density of the ROM type recording medium as high as that of the RAM type recording medium.

[0004]

The intensity distribution of the light spot used for recording / reproduction in an optical disk device, an optical tape device, etc. has a Gaussian distribution and has a spread. Therefore, when the track density is increased, the reproduction cross from the adjacent track is reproduced.・ Talk increases. Therefore, there is a limit in increasing the track density without reducing the light spot diameter in the optical disk device.

SUMMARY OF THE INVENTION An object of the present invention is to improve the recording density of a magneto-optical information recording / reproducing apparatus by enabling a format with a narrow track interval, which has been impossible in the past.

[0006]

In order to solve the above problems, the present invention scans a recording mark composed of magnetic domains formed on a recording medium using a laser beam as a light source with a light spot formed by converging the laser beam. In a magneto-optical information recording / reproducing apparatus for recording / reproducing information by using a recording medium in which a magnetic domain on the recording medium appears or disappears by application of an external magnetic field, means for detecting a track position on the recording medium, It is characterized by further comprising means for applying a magnetic field in a direction reversed for each adjacent track to the light spot scanning portion on the recording medium at the time of reproducing information based on the track position detection result.

Based on the track position detection result, the magnetic field applying means applies a magnetic field equal to the magnetization direction of the recording mark of the track being scanned on the recording medium and opposite to the magnetization direction of the recording mark of the adjacent track. It is means for applying to the light spot scanning portion on the recording medium at the time of reproducing information.

Further, the magneto-optical recording medium is characterized in that it is composed of perpendicularly magnetized films having locally different effective coercive forces.

[0009]

The magnetic domain in the perpendicularly magnetized film has a lower limit on the size of the structure capable of stably existing, and this size is determined by the physical property values such as magnetostatic energy and domain wall energy.
When the magnitude and direction of the magnetic field applied from the outside is changed, magnetic domains with a magnitude smaller than a predetermined value in the magnetic film cannot exist stably and disappear, or conversely, unstable magnetic domains are generated. It becomes possible to exist stably. The present invention is characterized by improving the track density by utilizing the appearance and disappearance phenomena of these magnetic domains. That is, in a recording medium in which the magnitude of the magnetic field in which magnetization reversal occurs when an external magnetic field is applied is locally reversed, by reversing the initialization direction of adjacent tracks, the recording mark magnetic domain in the adjacent track disappears. A magnetic field is applied to selectively cause only the magnetic domains of the recording mark of the track being reproduced to appear.
As a result, reproduction cross talk from the adjacent track is suppressed and the recording density is improved.

[0010]

EXAMPLE First, the operation principle of a RAM type recording medium utilizing magnetic domain transfer between two layers of perpendicularly magnetized films having different coercive forces will be described. The recording layer 203 and the reproducing layer 202 are perpendicularly magnetized films having an easy axis of magnetization in the normal direction of the recording film.
The coercive force of the recording layer 203 is larger than the coercive force of 2.

FIG. 2 shows a normal state in which the magnetic domain of the recording mark 204 of the recording layer 203 is completely transferred to the reproducing layer 202. FIG. 2A shows the reproduction layer 2 at this time.
2 is a diagram showing a magnetic domain distribution of No. 02, a shaded portion indicates a magnetic domain facing downward on the paper surface, and a non-hatched portion indicates a magnetic domain facing upward on the paper surface.
2B shows the recording film 20 on the cut surface 201 of FIG.
The state of the cross section of No. 6 is shown. When no reproducing magnetic field is applied, the recording layer 203 and the reproducing layer 202 are magnetically coupled by exchange coupling, and the magnetic domain of the recording mark 204 of the recording layer 203 is transferred to the reproducing layer 202. Further, the initialization directions of the adjacent tracks are opposite to each other, and all tracks are initialized over the entire track width.

Then, in FIG. 3, let us consider a case where a reproducing magnetic field is applied to this recording medium. The application direction of the reproducing magnetic field is equal to the magnetization direction of the recording mark of the track n being reproduced, and also equal to the initialization direction of the adjacent tracks n-1 and n + 1. FIG. 3A is a diagram showing the magnetic domain distribution of the reproducing layer 202 at this time. The shaded portion represents the magnetic domain facing downward on the paper surface, and the non-hatched portion represents the magnetic domain facing upward on the paper surface, and FIG. 3B shows FIG. The state of the cross section of the recording film at the cut surface 201 of FIG. From the recording layer 203 to the reproducing layer 2 by applying a reproducing magnetic field.
When the magnetic domain is not transferred to the reproduction layer 202, the reproduction layer 202
Since the magnetization of the recording layer 203 and the magnetization of the recording layer 203 face each other, the potential energy at that portion rises by the amount of the interface domain wall energy. However, at the same time, the domain wall in the reproducing layer 202 disappears to reduce the domain wall energy. Furthermore, the magnetostatic energy is also reduced by the magnetization being directed in the direction of the reproducing magnetic field. Therefore, if the size of the magnetic domain, the interface domain wall energy, the domain wall energy, and the value of magnetization are appropriately selected so that the potential energy is reduced as a whole, the transfer of the magnetic domain in the direction opposite to the reproducing magnetic field direction is limited. It becomes possible. In other words, this means that the effective coercive force of the reproducing layer 202 in the portion where the recording mark exists in the recording layer 203 is smaller than that in the other portion. As described above, by applying the reproducing magnetic field equal to the magnetization direction of the recording mark of the track n being scanned, the magnetic domain of the track n being scanned appears and the adjacent tracks n-1, n
The +1 magnetic domain disappears. However, in order to allow the magnetic domains to appear and disappear stably, the ratio of the area of the recording marks 204 to the area of the entire track should not exceed 50%.
Further, in order to prevent reproduction cross talk from the tracks n + 2 and n−2, the track interval must be wider than 1/3 of the diameter of the light spot 205 and must be smaller than the diameter of the light spot 205. The effect of densification according to the invention is reduced.

Next, the operation principle of the ROM type recording medium by the single layer film in which the effective coercive force of the recording film is locally changed will be described. The recording film 206 is a perpendicularly magnetized film having an easy axis of magnetization in the film surface normal direction, and the recording mark 204 is the recording film 20.
The effective coercive force of 6 is represented by the locally reduced portion. In order to reduce the effective coercive force, it is possible to provide a minute concavo-convex structure on the recording medium, or to partially strongly heat the recording medium to relax the crystal structure in the recording film. . The method of relaxing the crystal structure in the recording film is suitable for the write-once type ROM, and in the structure with the minute concavo-convex structure, the same RO as the conventional CD is used.
Suitable for mass production of M-type magneto-optical disk,
In either case, the ROM type recording medium and the RAM type recording medium can be reproduced by the same principle.

FIG. 4 shows a normal state in which the magnetic domains of all the recording marks 204 are completely exposed.
FIG. 4A is a diagram showing a magnetic domain distribution of the recording film 206 at this time. A hatched portion indicates a magnetic domain facing downward on the paper surface, and a non-hatched portion indicates a magnetic domain facing upward on the paper surface, and FIG. 4B illustrates FIG. 4) a magnetic domain in the cross section of the recording film 206 on the cut surface 201,
Similarly, (c) shows the distribution of coercive force on the cut surface 201. The initialization directions of adjacent tracks are opposite to each other, and all tracks are initialized over the entire track width.

Now, consider the case where a reproducing magnetic field is applied to this recording medium in FIG. The application direction of the reproducing magnetic field is equal to the magnetization direction of the recording mark of the track n being reproduced, and also equal to the initialization direction of the adjacent tracks n-1 and n + 1. FIG. 5A is a diagram showing the magnetic domain distribution at this time,
The shaded portions indicate the magnetic domains facing downward on the paper surface, and the non-hatched portions indicate the magnetic domains facing upward on the paper surface. FIG. 5B is a magnetic domain of the cross section of the recording film 206 in the cut surface 201 of FIG. 5A, and FIG. The distribution of coercive force on the cut surface 201 is shown. Figure 5
As shown in (c), by applying a reproducing magnetic field exceeding the magnitude of the coercive force of the recording mark portion, the magnetic domain of the track n during scanning appears and the adjacent tracks n-1, n +.
The magnetic domain of 1 disappears.

As described above, by reversing the initialization direction of the adjacent tracks and applying the reproducing magnetic field in an appropriate direction, the magnetic domains of the adjacent tracks are erased and the reproducing cross talk from the adjacent tracks can be suppressed. As a result, the recording density can be increased beyond the limit of the conventional track density, which was limited by the light spot diameter. However, in order to prevent reproduction cross talk from the tracks n + 2 and n-2, the track interval must be wider than 1/3 of the diameter of the light spot 205, and the light spot 2
If the diameter is not smaller than the diameter of 05, the effect of increasing the density according to the present invention becomes small.

Next, referring to FIG. 1, an embodiment of the present invention using the magneto-optical recording medium described in FIGS. 2 to 5 will be described. It is assumed that the ID information indicating the track position on the recording medium is previously recorded on this recording medium by phase pits or the like at the time of manufacturing.

Recording of information is performed with an initialization operation of uniformly magnetizing a track for recording, prior to an operation of forming a recording mark on the recording medium 112. Optical head 1
Reference numeral 00 narrows laser light from a built-in laser light source (not shown) onto the recording medium 112, and scans the recording medium 112 with a light spot (not shown). At the same time, the optical head 100 converts the polarization state of the reflected light on the recording medium 112 into an electric signal, and generates a reproduction signal 10 having an amplitude proportional to the intensity of polarization components orthogonal to each other. The reproduced signal 10 thus obtained is given to the differential amplifier 101 and the adder 102,
Each is converted into a magneto-optical reproduction signal 11 and a reflected total light amount signal 13. The reflected total light amount signal 13 is sent to the ID recognition unit 106, where the ID data 14 indicating the track number being scanned is obtained from the ID information recorded on the recording medium 112.
The overall control unit 107 that controls the entire recording / reproducing apparatus recognizes the track position on the recording medium 112 from the ID data 14. Next, the overall control unit 107 drives the magnetic field control unit 108 through the magnetic field direction control signal 15 so as to generate the magnetic field in the initialization direction of the track, and operates the electromagnet 109. The magnetic field application direction at the time of initialization must be reversed between adjacent tracks. For example, consecutive integer track numbers are assigned to adjacent tracks, even-numbered tracks are upward in FIG. 1, and odd-numbered tracks are It is defined as downward in FIG. The initialization operation is completed by the overall control unit 107 giving an instruction to the laser driver 111 to cause the laser light source to emit light at a high power level and continuously heat the scanning portion to uniformly magnetize the track. To do.

The formation of the recording mark is performed subsequent to the above-mentioned initialization operation. First, the overall control unit 107 drives the magnetic field control unit 108 through the magnetic field direction control signal 15 to operate the electromagnet 109 so as to generate a magnetic field in the magnetization direction of the recording mark of the track according to the track number. The magnetic field application direction during recording must be reversed between adjacent tracks, and must be opposite to the magnetic field application direction during initialization of the tracks. According to the example of the initialization operation, the even numbered tracks are downward in FIG. 1 and the odd numbered tracks are upward in FIG. The recording user data 20 is converted by the encoder 110 according to the modulation rule, and the converted recording code string 16 is transmitted to the laser driver 111. The laser driver 111 intermittently causes the laser light source in the optical head to emit light according to the recording code sequence 16 and partially heats the recording medium 112 to form magnetic domains. Further, by heating a recording film (not shown) on the recording medium 112 stronger than usual,
It is also possible to perform recording on a write-once ROM type recording medium of the type that relaxes the crystal structure in the recording film described in the above.

Information is reproduced by irradiating a light spot on the recording medium 112 by the optical head 100 while applying a magnetic field in the magnetization direction of the magnetic domain of the recording mark of the track to be reproduced, that is, the initialization direction of the adjacent track. This is done by scanning over 112. The overall control unit 107 drives the magnetic field control unit 108 through the magnetic field direction control signal 15 so as to generate a magnetic field in the reproduction direction of the track to be reproduced, and operates the electromagnet 109. The magnetic field application direction during reproduction must be reversed between adjacent tracks, and must be the same as the magnetic field application direction when a recording mark is formed on the track to be reproduced. As described above, the magnetic domain on the recording medium 112 appears or disappears by applying the external magnetic field, and the magnetic domain of the recording mark on the track adjacent to the track being scanned does not exist. In this state, the magneto-optical reproduction signal 11 is input to the equalizer 103, subjected to waveform equalization processing if necessary, and transmitted to the demodulator 104. Demodulator 1
In 04, the reproduction code string 12 corresponding to the recording mark is generated in consideration of the polarity of the reproduction signal 10 while referring to the magnetic field direction control signal 15. In the decoder 105, the reproduction code string 12 output from the demodulator 104 is inversely converted according to the conversion rule corresponding to when recording, and the final reproduction user data 21
Is output.

[0021]

According to the present invention, even if the track density is increased for the purpose of improving the recording density in the optical disk device, the optical tape device, etc., the reproduction cross talk from the adjacent track can be suppressed. As a result, it becomes possible to format a track with a narrow track interval, which was not possible to reproduce information in the past, and it is possible to increase the recording density and increase the amount of recorded information. Further, it is possible to provide an apparatus capable of reproducing the ROM type recording medium and the RAM type recording medium by the same principle.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating an embodiment of the present invention.

FIG. 2 is a first explanatory diagram illustrating an operation of a RAM type recording medium according to the present invention.

FIG. 3 is a second explanatory diagram illustrating the operation of the RAM type recording medium according to the present invention.

FIG. 4 is a first explanatory diagram for explaining the operation of the ROM type recording medium in the present invention.

FIG. 5 is a second explanatory diagram for explaining the operation of the ROM type recording medium in the present invention.

FIG. 6 is an explanatory diagram illustrating an operation principle of a conventional magnetic super-resolution medium.

[Explanation of symbols]

10: reproduction signal, 14: ID data, 15: magnetic field direction control signal, 21: reproduction user data, 100: optical head, 106: ID recognition unit, 107: overall control unit, 10
8: magnetic field control unit, 109: electromagnet, 202: reproduction layer, 2
03: recording layer, 204: recording mark, 205: light spot, 206: recording film.

Front page continuation (72) Inventor Takeshi Maeda 1-280, Higashi Koigokubo, Kokubunji, Tokyo Inside Hitachi Central Research Laboratory

Claims (10)

[Claims] 1. A magneto-optical information recording / reproducing apparatus for recording / reproducing information by scanning a recording mark composed of a magnetic domain formed on a recording medium using a laser beam as a light source, with a light spot formed by converging the laser beam. Using a recording medium in which magnetic domains on the recording medium appear or disappear by the application of an external magnetic field,
Means for detecting a track position on the recording medium, and means for applying a magnetic field in a direction reversed for each adjacent track to the light spot scanning portion on the recording medium at the time of information reproduction based on the track position detection result. A magneto-optical information recording / reproducing apparatus having: 2. A magneto-optical information recording / reproducing apparatus according to claim 1, wherein the magnetic field applying means is equal to and adjacent to a magnetization direction of a recording mark of a track being scanned on the recording medium based on the track position detection result. A magneto-optical information recording / reproducing apparatus, which is means for applying a magnetic field in a direction opposite to a magnetization direction of a recording mark of a track to the optical spot scanning portion on the recording medium at the time of reproducing information. 3. The magneto-optical information recording / reproducing apparatus according to claim 1, wherein the magnetic field applying means records the magnetic field in a direction reversed for each adjacent track based on the track position detection result at the time of information recording. A magneto-optical information recording / reproducing apparatus, characterized in that it is means for applying to the light spot scanning portion above. 4. The magneto-optical information recording / reproducing apparatus according to claim 1, wherein the magnetic field applying means records the magnetic field in the direction reversed for each adjacent track based on the track position detection result. A magneto-optical information recording / reproducing apparatus, which is means for applying to the light spot scanning portion on the recording medium at the time of initialization. 5. The magneto-optical information recording / reproducing apparatus according to claim 1, wherein the magneto-optical recording medium is composed of perpendicularly magnetized films having locally different effective coercive forces. A characteristic magneto-optical information recording / reproducing apparatus. 6. The magneto-optical information recording / reproducing apparatus according to claim 1, wherein the magneto-optical recording medium is composed of at least two layers of perpendicularly magnetized films having different coercive forces. Magneto-optical information recording / reproducing device. 7. A perpendicular magnetic film in the magneto-optical information recording / reproducing apparatus according to claim 1, wherein the magneto-optical recording medium relaxes its crystal structure to locally reduce the coercive force. A magneto-optical information recording / reproducing apparatus comprising: 8. The magneto-optical information recording / reproducing apparatus according to claim 1, wherein a fine concavo-convex structure is provided on the magneto-optical recording medium to locally reduce the coercive force. A magneto-optical information recording / reproducing apparatus comprising a magnetized film. 9. The magneto-optical information recording / reproducing apparatus according to claim 1, wherein the diameter of the light spot is 1 to 3 times the track pitch. Magnetic information recording / reproducing apparatus. 10. The magneto-optical information recording / reproducing apparatus according to claim 1, wherein a ratio of an area of a recording mark portion to an area of an entire track of the recording medium is 50.
% Or less, a magneto-optical information recording / reproducing apparatus.