JPH1055579A - Magneto-optical recording and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical recording and reproducing method featuring a high speed characteristic and high density in combination. SOLUTION: Magnetization domains 102 of a feather shape are recorded by irradiating a recording track 113 with a light beam along its flat part and simultaneously impressing a magnetic field thereon. The shape of the magnetization domains 102 in the flat part of the recording track 113 satisfies L<W/2 (where, W: the width of the magnetization domains, L: the length from the branch point of the fork in the angular projecting part of the fork elongating backward of the magnetization domains to the front end of the angular projecting part). The overwriting featuring the high speed characteristic and the high density in combination is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording / reproducing method, and more particularly to a high-speed and accurate magnetic-domain recording / reproducing method by reducing jitter caused by angular projections in a magnetic domain when performing overwriting by magnetic field modulation. The present invention relates to a magneto-optical recording / reproducing method suitable for performing accurate data demodulation.

[0002]

2. Description of the Related Art Magneto-optical disks are attracting attention as rewritable optical disks. In a magneto-optical disk, a recording domain is formed by a thermomagnetic effect using a perpendicular magnetization film as a recording film, and a reproducing effect is obtained by a magneto-optical effect. At the time of recording, the temperature of the magnetized film is raised to the Curie temperature by the heat of the laser beam spot, thereby losing the magnetization, and applying an external magnetic field during the cooling process to fix the perpendicular magnetization in the direction of the magnetic field. To form a magnetic domain, an external magnetic field is applied by applying a constant intensity magnetic field in the direction opposite to the initial magnetization direction of the perpendicular magnetization film, and the light modulation method that changes the intensity of the laser light pulse according to the data. Conversely, there is a magnetic field modulation method in which the laser light intensity is set to a constant value so that the temperature of the magnetic film becomes equal to or higher than the Curie temperature, and the direction of the external magnetic field is changed according to the data to be recorded.

[0003] One of the items that poses a problem in the above-mentioned magnetic field modulation method is that the shape of the magnetization domain becomes an asymmetrical arrow blade shape as shown in FIG. This is because the temperature distribution of the perpendicular magnetization film at the moment when the application direction of the recording magnetic field is reversed is reflected on the magnetization domain shape. The temperature distribution of the perpendicular magnetization film changes depending on the balance between the thermal conductivity of the perpendicular magnetization film and the linear velocity of the perpendicular magnetization film. Furthermore, as the scanning speed of the laser beam at the time of recording increases, the horn-shaped protrusion 103 extending in a forked shape extending rearward of the arrow blade shape extends. When the angular protrusion 103 of the magnetization domain 102 is long, not only does the signal amplitude during high density recording decrease,
There is a possibility that it will cause jitter during recording and reproduction.

When the scanning speed of the laser beam is as low as about 1 m / s, since the heat conduction speed of the perpendicular magnetic film is sufficiently large, the temperature distribution in the perpendicular magnetic film near the irradiation of the laser beam is small. As shown in FIG. 8, since the shape becomes substantially isotropic, the shape of the edge of the magnetization domain is substantially semicircular. Therefore, if the magnetization domain width is set to about 0.8 to 1 μm, the length of the angular projection can be set to 0.4 to 0.5 μm.
In this case, the signal band required for reproduction is narrow, and it is hard to be affected by random noise at the time of detection.
0.5 bit pitch using a laser beam spot of about m
It is discussed in the IEICE Technical Report MR87-37 (1987), pages 13 to 20, that recording and reproduction on the order of μm are possible.

However, the scanning deceleration of the laser beam is 7 m / s.
As described above, as shown in FIG. 9, the temperature distribution 50 in the perpendicular magnetization film has a tailed shape on the opposite side to the traveling direction of the laser light spot. Therefore, the edge shape of the magnetization domain becomes parabolic, and the width of the magnetization domain is 0.8 to 1 μm.
The length of the horn-shaped projections when set to about is 0.6 μm or more. In this case, the edge interval is 0.2 μm
Since a large number of dots are required, the dot pitch at which recording and reproduction can be performed is 0.7 μm or more. Further, if the width of the magnetization domain is reduced, the length of the angular protrusions is also reduced, but the reproduction signal to noise ratio required for data demodulation cannot be secured. Therefore, when the scanning speed of the laser beam is 7 m / s or more, the bit pitch achievable by the conventional technique is 0.7 μm or more. As the scanning speed is increased, the angular projections of the magnetization domain are extended, so that the bit pitch is 0.7.
It is impossible with the prior art to simultaneously satisfy the specification of μm or less and the specification of data transfer speed of 10 Mbit / s or more.

Further, the temperature distribution of the perpendicular magnetization film changes, and the position and shape of the magnetization domain also change due to fluctuations in the power and focal point temperature of the laser beam, and differences in the characteristics of the recording medium. This causes the recorded magnetization domain to remain unerased at the time of overwriting, and may cause jitter during recording and reproduction.

As described above, when the magnetic field modulation method is applied to the magneto-optical recording / reproducing system, it is important to suppress the extension of the angular projections 103 of the recording magnetization domain 102 and the increase of the remaining erase.

In the magneto-optical disk drive which realizes overwriting by the conventional magnetic field modulation method described above, a laser beam is continuously applied as a rise in the temperature of a recording film, and is applied to an optical head. The recording and erasing is realized by driving the provided magnetic field applying head in accordance with the data, but in the description of the above-described apparatus, the influence of the angular projection and the unerased portion after repeated overwriting are not described. Did not mention.

[0009]

In the above prior art, no mention is made of angular protrusions in the recording magnetization domain or fluctuations in the center position and width of the recording magnetization domain. Is difficult to apply.

It is an object of the present invention to achieve both high speed and high density by performing recording / reproduction of a magnetization domain having a fixed width and a short length of a square projection regardless of the characteristics of a recording apparatus and a recording film. An object of the present invention is to provide an overwritable magneto-optical recording / reproducing method.

Another object of the present invention is to prevent the deterioration of the signal-to-noise ratio due to unerasing after repeated overwriting using a single laser beam even when the recording apparatus is changed or the servo system of the light beam fluctuates. An object of the present invention is to provide a magneto-optical recording / reproducing method that does not occur.

[0012]

According to the magneto-optical recording / reproducing method of the present invention, as shown in FIG. 4, the width of the magnetization domain 102 which effectively contributes to the recording / reproduction of information is determined by the width of the land 104 on the recording track 113. The configuration is limited by the width. Due to the limitation of the magnetization domain width, a fixed magnetization domain width can be obtained, and the horn-shaped protrusion 103 extending bifurcated behind the arrow blade-shaped magnetization domain during magnetic field modulation recording can be separated from recording / reproducing.

Here, for example, in the case of a pit edge recording method in which information is recorded in correspondence with the edge of the magnetization domain 102, the magnetization domain width W and the recording / reproducing light spot 20 are used.
1, reproduction signal 202 and detection level 203 are shown in FIG.
It becomes as shown in. As shown in FIG. 10A, the relationship between the magnetization domain width W and the length L of the angular protrusion is the same as the conventional L>
In the case of W / 2, accurate data demodulation cannot be performed irrespective of the detection level 203 of the reproduced signal 202 of the portion corresponding to the two edges that are close to each other due to the influence of the long horn-shaped projection. On the other hand, when the relationship between the magnetization domain width W and the length L of the angular protrusions is L <W / 2 as in the present invention, FIG.
As shown in (b), the detection timing edge 204 obtained by slicing the reproduction signal 202 at the detection level 203 corresponds to a pair with the edge position of the magnetization domain 102, and accurate data demodulation can be performed even during high-speed and high-density recording. It becomes possible.

[0014]

According to the present invention, the fluctuation of the width of the recording magnetization domain due to the difference in the recording apparatus conditions and the medium characteristics can be eliminated, and the extension of the angular projection due to the improvement of the scanning speed of the laser beam can be reduced. As the overwrite characteristics are improved, higher-speed and higher-density recording can be performed.

Further, by suppressing the outflow of heat from the perpendicular magnetization film of the recording medium, recording can be performed with a lower laser power. Thus, recording can be performed on a medium that moves at a higher speed with the same laser power.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a magneto-optical disk device showing one embodiment of a magneto-optical recording / reproducing system according to the present invention, FIG. 2 is a cross-sectional view showing one embodiment of a magneto-optical recording medium to be used in the above-described embodiment,
FIG. 3 is a schematic diagram showing a temperature distribution around a laser beam at the time of recording in the above embodiment, and FIG. 4 is a diagram showing a recording magnetization domain shape in the above embodiment.

The embodiment shown in FIG. 1 shows the configuration of a magneto-optical disk recording / reproducing apparatus for one beam.
The disk 1 is, for example, a magneto-optical disk having a perpendicular magnetization film mainly composed of a TbFeCo-based element, and a cross-sectional view thereof is shown in FIG.

Reference numeral 106 denotes a substrate, which can be made of glass or a transparent resin, for example, polycarbonate, polystyrene, acryl, ultraviolet curing resin, or the like. Reference numeral 107 denotes a perpendicular magnetization film, which is a rare earth-transition metal based magneto-optical recording film, for example, T
A bFeCo-based, TbFe-based, GdFeCo-based, or the like can be used. Reference numeral 108 denotes a light shield for forming the structural band portion 112. For example, a metal thin film such as molybdenum or aluminum for shielding the laser beam 111 can be used. Substrate 10
Reference numeral 6 denotes, for example, a tempered glass having an outer diameter of φ130 mm and a thickness of about 1 mm. On this substrate 106, a metal aluminum layer having a thickness of about several hundreds of mm is formed by a vacuum evaporation method in order to form a light-shielding band 108 which also functions as a push-pull type tracking guide groove. Thereafter, a positive resist is spin-coated on the whole to form a resist layer on the metal aluminum layer. Here, a 1.6 μm pitch linear mask (line width: 0.8 μm) is exposed using a projection mask aligner, developed, and then the unmasked portion of the metal aluminum layer is etched away to remove the guide. A light-shielding band 108 that also functions as a groove is obtained. Next, a protective film 121 made of SiN having a thickness of 700 ° and having a car enhancement effect, a perpendicular magnetization film 107 made of TbFeCo having a thickness of 1000 ° and a protective film 122 made of SiN having a thickness of 1500 ° are sequentially formed by sputtering. Finally, in order to improve the sliding resistance, a protective coat 123 of about 5 μm is formed by irradiating ultraviolet rays after spin-coating an ultraviolet curable resin. By the above steps, the width of the land 104 and the width of the structural band 112 are each set to 0.
Magneto-optical disk 1 with 8 μm and track pitch of 1.6 μm
Get. A light shielding band 108 is provided on the perpendicular magnetization film 107 in the structural band.
Therefore, the recording / reproducing laser beam 111 does not arrive. Therefore, only the land portion having a width of 0.8 μm among the recorded magnetic domains is involved in recording / reproducing. Here, a metal thin film has been described as an example of the light-shielding band, but any structure may be used as long as it can shield laser light for reproduction. The disc 1 can be rotated by a spindle motor 2.

Data recording on the disk 1 is performed as follows. The semiconductor laser 3 is caused to emit light with high power by the laser drive circuit 4. The laser drive circuit 4 includes:
In response to a command from a recording / reproduction control system (not shown), light emission is performed at low power during data reproduction, and during data recording,
The semiconductor laser 3 emits light with high power so that the magnetic film reproduced by the magnetic head 5 raises the temperature of the recording film to the Curie temperature at which the magnetization of the recording film can be reversed. The configuration of the laser drive circuit 4 may be a circuit conventionally used in a write-once optical disc device.

The light beam of the semiconductor laser 3 is converted into a parallel light beam by a lens 6, passes through a beam splitter 7, is reflected in a vertical direction by a galvanometer mirror 8, and is focused on a recording film of the disk 1 by a focusing lens 9. The light is focused as a minute spot through the substrate. Assuming that the wavelength of the semiconductor laser 3 is 830 nm and the numerical aperture of the focusing lens is 0.53, the diameter of the outer periphery of the spot having a light intensity e-2 times the center of the spot (hereinafter simply referred to as the diameter of the light spot) Is about 1.6 μm. At this time, a track pitch of about 1.6 μm is considered appropriate from the viewpoints of the track separation and the push-pull tracking signal modulation. Also, since the S / N ratio of the magneto-optical signal is not very good, it is desirable to increase the width of the magnetization domain in order to increase the degree of signal modulation. However, when the width of the magnetization domain becomes 0.9 μm or more, the amount of crosstalk with an adjacent track sharply increases. Therefore, the width of the land portion 124 of the disk 1 is also set to 0.8 μm in accordance with the desired magnetization domain width. The laser beam 111 moves along the center of the land 104, that is, the track center. During recording, the Curie temperature T in the temperature distribution around the laser beam 111 as shown in FIG.
The laser beam 111 is set so that the width along the track in the region surrounded by the isotherm near c is 1 to 1.6 μm.
The recording laser beam intensity is set in advance according to the scanning speed. For example, when the scanning speed of the laser beam 111 is 7 m / s and the recording laser beam intensity is 8 mW, the Curie temperature T
The width of the region surrounded by the isotherm of c is 1.3 μm.

When the temperature of the perpendicular magnetization film is increased by the heat of the condensing spot, a modulation magnetic field corresponding to data to be recorded by the magnetic head 5 is applied to record data, that is, to form a magnetization domain. I do. As described above, in the case of recording, the temperature of the perpendicular magnetization film rises to 1.3 μm width and the Curie temperature Tc or more at the position where the 8 mW light spot is irradiated at the scanning speed of 7 m / s. As in the magnetic disk, overwriting of data, that is, recording that also serves to erase previously recorded data becomes possible over the entire unit. The magnetic head 5 is arranged so as to slightly float from the surface of the disk 1.
The distance between the magnetic head 5 and the disk 1 may be several tens of microns, which is wider than when a magnetic disk does not have an auxiliary means such as a light spot, and the head or the disk may be damaged. Crash problems are less likely. The magnetic head drive circuit 10 has a function of changing the direction of the generated magnetic field of the magnetic head 5 in accordance with the modulated recording data, and may be configured as a circuit used in a conventional magnetic disk device.

Next, reproduction of data recorded on the disk 1 will be described. The laser drive circuit 4 causes the semiconductor laser 3 to emit light at low power in accordance with a command from the recording / reproduction control system. The polarization plane of the light of the semiconductor laser 3 is in one direction, and the light is applied to the perpendicular magnetization film on the disk 1 through the same optical path as during recording. Upon playback,
Only the portion on the 0.8 μm wide land near the center of the magnetization domain 102 recorded with a 1.3 μm width is involved. Therefore, as shown in FIG. 4, the width of the magnetization domain 102 which is effectively involved in recording / reproduction can be 0.8 μm, and the length of the angular projection can be less than 0.4 μm. In addition, even if the disappearance remains due to incomplete overwriting at both ends of the 1.3 μm-wide magnetic domain 102, it can be effectively separated from the reproducing system by the effect of the light-shielding band 108. Thus, an overwrite operation without any remaining data is completed in principle. The magnetization direction of the perpendicular magnetic film overwritten as described above, with respect to the recorded data,
It is fixed upward or downward. By detecting whether these magnetization directions are up or down, "1" or "0" of the recorded data is determined. The detection is performed by using the Kerr effect, which is one of the magneto-optical effects. The Kerr effect is an effect in which the deflecting surface of the incident light rotates right and left with respect to the original deflecting surface depending on whether the magnetization direction is upward or downward. The reflected light from the perpendicular magnetization film accompanied by the rotation of the deflection surface is reflected again by the beam splitter 7 and the beam splitter 11, and is guided to the half-wave plate 12. The half-wave plate 12 has a polarization plane of 4
It is an optical element that has a function of rotating by 5 degrees. 4 polarization planes
The light rotated by 5 degrees is p-polarized by the polarizing beam splitter 13.
The light is separated into a polarization component and an s-polarization component.
The light is condensed on the photodetectors 16 and 17 at 4,15. By taking the sum of the outputs of the photodetectors 16 and 17, it is possible to detect only a change in light intensity regardless of the polarization plane rotation. Further, by taking the difference between the outputs of the photodetectors 16 and 17, a change in the magnetization direction can be detected as a signal change through rotation of the polarization plane. That is, the sum signal 18 is obtained by optically separating only the uneven pits provided in advance on the disk 1, and the difference signal 19 is obtained by optically separating only the recorded data, ie, the change in the magnetization direction of the perpendicular magnetization film on the disk 1. Can be detected. The light that has passed through the beam splitter 11 enters an automatic focus and tracking control system (not shown), and is used for detection of a focus shift signal and a track shift signal. ,
Automatic focus adjustment and tracking are performed.

In this way, even when the disk is rotated at a high speed, the angular projections of the magnetization domains are prevented from being elongated, and high-speed and high-density data recording and reproduction can be accurately performed even after repeated overwriting. . FIG. 5 is a sectional view showing a second embodiment of the magneto-optical recording medium to be used in the present invention.

The lands 104 and the structural strips 112 are formed by depositing the belts 107 on the substrate 106. Also in this case, a protective coat 123 is provided to improve sliding operation. Since the magnetization domain 102 is formed only on the perpendicular magnetization film 107, if the magnetization domain 102 is recorded so that the width of the region heated abnormally at the Curie temperature Tc during recording is larger than the width of the land 104,
The width of the magnetization domain 102 is determined by the land 104.

FIG. 6 is a schematic diagram showing the embodiment of FIG. 3 of a magneto-optical recording medium to be used in the present invention. After the low thermal conductivity material layer 109 is formed in a strip shape on the substrate 106 in the same manner as in the first embodiment of the magneto-optical recording medium, the perpendicular magnetic film 107 having a constant film thickness and the low thermal conductivity such as SiO2 are formed by continuous sputtering. A conductive material layer 109 is deposited. TbF as the perpendicular magnetization film 107
When using a rare earth transition metal compound such as eCo,
Since the thermal conductivity of the substrate 106 is at least one order of magnitude lower than the thermal conductivity of the perpendicular magnetization film 107, after forming a concave and convex groove on the substrate 106 by an etching method using a photoresist or the like, a constant value is obtained by a continuous sputtering method. It is also possible to form a perpendicular magnetic film 107 having a thickness and a low thermal conductivity material layer 109 such as SiO2. Also in this case, a protective coat 123 is provided to improve the sliding operation resistance. The laser beam 111 is applied to the land 104
In the case where recording is performed by irradiating the land, the magnetic domain is not spread outside the land 104 because the land 104 and the structural band 112 are thermally isolated by the low thermal conductivity material layer 109. Therefore, the land 104 and the structural band 112
If the magnetization domain 102 is recorded at a light intensity such that the temperature at the boundary with the temperature exceeds the Curie temperature Tc, the width of the magnetization domain 102 is determined by the land 104. In the second and third embodiments of the magneto-optical recording medium, the land portion 10 is used.
(4) The temperature of the perpendicular magnetization film easily rises at the time of recording due to the heat insulation effect of the surroundings, so that the sensitivity is improved and this is effective for high-speed recording.

In any case, the width of the magnetization domain can be determined by the width of the land.

Although the magnetic field modulation overwrite method as shown in FIG. 1 has been described as an embodiment of the present invention, the present invention is not limited to this. For example, the light modulation method described in Japanese Patent Application Laid-Open No. Sho 62-175948 may be used. Can be similarly applied. In the case of the light modulation method, due to the heat conduction of the perpendicular magnetization film,
Proceedings of the International
Symposium on Optical Memory (Proceed
ings of the International Synopium on Optical
Memory) JJAP Vol. 26 (1987) Supple.2
6-4, p. 243-248,
Problems such as teardrop domains and thermal interference between domains arise. In the conventional method, the width and length of the domain had to be controlled at the same time. However, by applying the present invention, only the domain length needs to be controlled, and high-density recording becomes easy. In addition, even when overwriting with a single beam, it is possible to prevent the unerased residue.

Further, in the above embodiment, since the axial displacement of the magnetization domain does not occur in principle, not only the erasing characteristic at the time of overwriting but also the tracking margin is improved.

[0029]

As described above, according to the present invention, it is possible to obtain a magneto-optical recording / reproducing method which is high in medium compatibility, high in recording density and capable of high-speed overwriting irrespective of the type of recording / reproducing apparatus and perpendicular magnetization film. Can be. In addition, even when a single beam is overwritten, the reproduction signal noise ratio does not deteriorate due to unerased data.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a magneto-optical disk drive showing an embodiment of a magneto-optical recording / reproducing method according to the present invention.

FIG. 2 is a sectional view showing an embodiment of a magneto-optical disk used in the embodiment.

FIG. 3 is a schematic diagram showing an isotherm at the time of recording.

FIG. 4 is a schematic diagram showing a recording magnetization domain shape in the embodiment.

FIG. 5 is a sectional view showing a second embodiment of the magneto-optical disk.

FIG. 6 is a sectional view showing a third embodiment of the magneto-optical disk.

FIG. 7 is a schematic diagram showing a magnetization domain shape.

FIG. 8 is a schematic diagram showing an isotherm at the time of recording.

FIG. 9 is a schematic diagram showing an isotherm at the time of recording.

FIG. 10 is a schematic diagram showing a relationship between a magnetization domain and a reproduction signal.

[Explanation of symbols]

102: magnetization domain, 103: prismatic projection, 104: land, 106: substrate, 107: perpendicular magnetization film, 108:
Light shielding band, 109: low thermal conductivity material, 111: laser beam, 112: structural band, 113: recording track.

Claims (2)

[Claims] 1. An optical disk medium comprising: a substrate having an uneven groove; and a perpendicular magnetic film formed on the substrate, wherein a recording track flat portion for recording information is formed along the groove. In a magneto-optical recording / reproducing method using an optical disk medium in which the thermal conductivity of the substrate is lower than the thermal conductivity of the perpendicular magnetization film, a light beam is irradiated along the recording track flat portion and simultaneously based on an input signal. A modulated magnetic field is applied to record an arrow-shaped magnetization domain, and the shape of the magnetization domain in the recording track flat portion is L <W / 2, where W: magnetization domain along the rotation direction of the optical disk medium. Width, L: a length along the optical disk rotation direction from the branch point of the fork to the tip of the square protrusion in the forked angular protrusion extending behind the magnetization domain. Magneto-optical recording and reproducing method comprising. 2. An optical disk having a perpendicular magnetization film formed on an optical disk substrate is irradiated with a light beam from the optical disk substrate side, and at the same time, a magnetic field is applied to record a magnetic domain, and the magnetic domain is reproduced by a magneto-optical effect. In the magneto-optical recording / reproducing method, the concave and convex grooves are provided on the optical disk substrate, and the thermal conductivity of the optical disk substrate is selected to be lower than the thermal conductivity of the perpendicular magnetization film. The flat portion of the concave groove of the perpendicular magnetization film is used as a recording track for recording the magnetization domain, and the length of the recording domain in the width direction of the recording track is equal to or less than the width of the recording track. A magneto-optical recording / reproducing method, characterized in that: