JP3472158B2 - 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 magneto-optical recording medium for recording / reproducing information with a laser beam by utilizing a magneto-optical effect, and more particularly to a magneto-optical recording medium utilizing a movement of a domain wall at the time of reproducing. About how to turn.

[0002]

2. Description of the Related Art In recent years, a magneto-optical disk has attracted attention as a rewritable high density recording medium. There is an increasing demand for increasing the recording density of the magneto-optical disk in order to make it a recording medium having a large capacity. The linear recording density of the optical disc is determined by the laser wavelength λ of the reproduction optical system and the numerical aperture NA of the objective lens.
, The spatial frequency during signal reproduction is NA / λ
The degree is the detectable limit. Therefore, in order to realize high density in the conventional optical disc, it is necessary to shorten the laser wavelength λ of the reproducing optical system and increase the numerical aperture NA of the objective lens. However, there is a limit in improving the laser wavelength and the numerical aperture of the objective lens. Therefore, some techniques have been proposed to improve the recording density by devising the configuration of the recording medium and the reading method.

For example, the inventors of the present invention have disclosed in Japanese Patent Laid-Open No. 6-290.
Japanese Patent No. 496 proposes a magneto-optical recording medium, a reproducing method thereof and a reproducing apparatus thereof capable of reproducing a signal having a period equal to or shorter than a circuit limit of light at a high speed without lowering the reproduction signal amplitude. That is, when a temperature distribution is formed in the reproducing layer of the magneto-optical recording medium by a heating means such as a light beam, the domain wall energy density is distributed, so that the domain wall can be moved to the lower domain wall energy.

FIG . 4 is a schematic diagram for explaining the operation of the magneto-optical recording medium and the reproducing method thereof disclosed in JP-A-6-290496. As shown in FIG. 4A, the magnetic layer of this magneto-optical recording medium has a laminated structure in which a first magnetic layer 51, a second magnetic layer 52, and a third magnetic layer 53 are sequentially laminated. The arrow 54 in each layer represents the direction of atomic spin. A domain wall 55 is formed at the boundary between the regions where the spin directions are opposite to each other.

FIG . 4B is a graph showing the temperature distribution formed on the magneto-optical recording medium during reproduction. This temperature distribution may be induced on the medium by the light beam itself irradiating for reproduction, but it is desirable to use another heating means together, and the temperature from the front side of the spot of the reproduction light beam To form a temperature distribution such that a temperature peak appears behind the spot. At the position xs, the medium temperature is the temperature Ts near the Curie temperature of the second magnetic layer.

FIG . 4C is a graph showing the distribution of the domain wall energy density σ ₁ of the first magnetic layer corresponding to the temperature distribution of FIG. 4B. When there is a gradient of the domain wall energy density σ ₁ in the x direction in this way, the force F ₁ obtained from the following formula acts on the domain wall of each layer existing at the position x.

Force F = ∂σ / ∂x This force F ₁ acts so as to move the domain wall to the lower domain wall energy. Since the first magnetic layer has a small domain wall coercive force and a large domain wall mobility, by itself, the domain wall is easily moved by this force F ₁ . However, in the region before the position xs (on the right side in the figure), the medium temperature is still lower than Ts, and the magnetic domain wall in the third magnetic layer is exchange-coupled with the third magnetic layer having a large magnetic coercive force. The domain wall in the first magnetic layer is also fixed at a position corresponding to the position.

The medium moves in the medium moving direction 58, and as shown in FIG. 4A , the domain wall 55 is moved to the position xs of the medium.
In the above, the medium temperature rises to a temperature Ts near the Curie temperature of the second magnetic layer, and the exchange coupling between the first magnetic layer and the third magnetic layer is broken. As a result, the domain wall 55 in the first magnetic layer "instantly" moves to a region of higher temperature and smaller domain wall energy density, as indicated by the dashed arrow 57.

When the domain wall 55 passes under the spot 56 of the reproducing light beam, all atomic spins of the first magnetic layer in the spot are aligned in one direction. Every time the magnetic domain wall 55 comes to the position xs as the medium moves, the magnetic domain wall 55 instantaneously moves under the spot and the directions of atomic spins in the spot are reversed to align them in one direction. As a result, as shown in FIG. 4A , the reproduction signal amplitude is always constant and maximum regardless of the recorded domain wall spacing (that is, the recording mark length), which is caused by the optical diffraction limit. Completely free from problems such as waveform interference.

As described above, according to this technique, the reproduction output does not decrease even if the linear recording density is improved, and it is possible to achieve higher density than before.

[0011]

The movement of the domain wall at this time is a phenomenon that occurs on the same track (in the track direction), and the magnetic layers are separated (that is, magnetically separated) between the tracks. Is mandatory. As a method of forming such an unclosed magnetic domain (divided domain wall), Japanese Patent Laid-Open No. 6-209496 discloses a method of using a rectangular deep groove transparent substrate and a method of magnetically irradiating the groove portion with a laser for annealing. Although a method of modifying the quality is proposed, the rectangular deep groove transparent substrate has a problem in transferability at the time of molding, and when the annealing treatment is performed, the annealing treatment portion cannot be used as the information data portion. However, there is a problem that the recording density in the track direction is reduced.

As a result of earnest studies on the above-mentioned problems, the present inventor found that the land &
We have proposed a "method of magnetically separating tracks with a land and groove substrate close to a rectangle (and narrowing the width of the land portion)" by devising the shape of a transparent substrate for groove recording. However, in this method, only the groove surface can be used as the recording surface of the magneto-optical recording medium, and the land portion cannot be used as the information data portion. Therefore, further improvement is required to increase the track density.

The present invention has been made in view of the above-mentioned problems, and by using a transparent substrate having a land portion and a groove portion on the surface, it is easy to manufacture without special magnetic cutting processing, and the land can be easily manufactured. PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium capable of performing high density recording by using both a groove portion and a groove portion as a recording surface and capable of expanding and reproducing a magnetic domain by instantaneously moving a domain wall using a temperature gradient. With the goal.

[0014]

The present invention comprises a transparent substrate,
A magneto-optical recording medium having a magnetic layer formed on the surface of this transparent substrate and capable of reproducing by expanding at least a magnetic domain by moving at least a magnetic domain wall of the magnetic layer to be reproduced, the surface of the transparent substrate consists lands and grooves, 40 the angle of and the inclined surface roughness Ra of the inclined plane Ri der following 1.2nm of the land portion
It relates to a magneto-optical recording medium characterized by being 90 degrees .

The magnetic layer has a laminated structure in which at least a first magnetic layer, a second magnetic layer and a third magnetic layer are sequentially laminated, and the first magnetic layer is relatively at ambient temperature as compared with the third magnetic layer. It is preferable that the magnetic layer has a small domain wall coercive force and a large domain wall mobility, and the second magnetic layer is a magnetic layer having a lower Curie temperature than the first magnetic layer and the third magnetic layer.

[0016]

1 is a schematic view of a cross section of a magneto-optical recording medium of the present invention cut at a right angle to the recording direction, and FIG. 2 is a view showing only a transparent substrate. The convex land portion 1 is formed on the surface of the transparent substrate 11 used in the present invention.
And a concave groove portion 2 is formed. As shown in FIG. 1, the land portion has a flat upper surface and inclined side surfaces, and the groove portion surface is a flat surface.

The angle θ of the inclined surface of the land portion is 40 to 90.
It is degree. By setting the angle θ of the inclined surface of the land portion to 40 degrees or more, when the magnetic layer 13 is deposited, a cut (discontinuous surface A) is generated in the magnetic layer at the boundary between the groove portion and the land portion, and the magnetic layer is formed. Since they are magnetically separated, no special prescription is required. Further, in order to surely perform magnetic separation, it is preferably close to 90 degrees, and preferably 60 to 90 degrees.

The widths of the land portion 1 and the groove portion 2 are preferably as narrow as possible for higher density, but cross erase (erasure of marks recorded on adjacent tracks) and crosstalk (reproduction signal from adjacent tracks). Since the influence of (mixture of) is small and the width is large enough to obtain a reproduced signal that can be used practically, it is usually 0.1 to 0.8 μm, preferably 0.3 to 0.6 μm. Further, the ratio of the land width 23 to the groove width 24 is preferably about 7: 3 to 4: 6. Further, it is preferable that the height 25 of the land portion is approximately equal to λ / (3n) (where λ is the wavelength of light and n is a natural number) at which crosstalk cancellation is possible. In order to exert the effect of magnetically separating, the larger is preferable, and it is usually 50 to 600 nm, preferably 85 to 400 nm.

According to the study by the present inventor, even in the transparent substrate having such a shape, if the surface roughness of the inclined surface 14 of the land portion is rough, it is extremely difficult for the domain wall movement reproduction to occur in the land portion. It was That is, since the size of the surface irregularities hinders the domain wall motion reproduction, the domain wall motion reproduction is occurring, but the signal level is extremely low.

Therefore, in the present invention, by setting the surface roughness Ra of the inclined surface 14 of the land portion of the transparent substrate to be 1.2 nm or less, the domain wall movement reproduction can be performed even in the land portion. The surface roughness of the inclined surface of the land portion is preferably as small as possible, and particularly preferably 0.6 nm or less.

The surface roughness Ra of the upper surface of the land portion and the surface of the groove portion is 1.2 nm or less, particularly 0.6 n.
It is preferably m or less.

An example of the layer structure of the magneto-optical recording medium of the present invention is shown in FIG. The first dielectric layer 3 is formed on the transparent substrate 11.
2, the magnetic layer 33, and the second dielectric layer 34 are sequentially stacked.

Examples of the transparent substrate used in the present invention include glass, polycarbonate, polymethylmethacrylate, and thermoplastic norbornene-based resin.

The method for molding the transparent substrate is not particularly limited, but injection molding is preferable for mass production. In this case, the surface roughness of the transparent substrate substantially reflects the surface roughness of the stamper. Therefore, the stamper is manufactured so that the surface corresponding to the land portion and the groove portion of the stamper has the surface roughness as described above. To manufacture a stamper, first
The glass master is polished, a resist is applied on the glass master to a thickness corresponding to the height 25 of the land portion, heat-treated, exposed to a predetermined pattern and cut (recorded),
It develops and forms an uneven | corrugated pattern. At this time, a resist master disk is formed in which the resist remains in the portion corresponding to the land portion.

Next, after Ni is formed by sputtering, Ni electroforming is performed, peeling and cleaning are performed, and the stamper is completed. When a transparent substrate is molded using this stamper, a transparent substrate having the same shape as the patterned resist master can be obtained. Therefore,
The surface roughness of the stamper corresponding to the upper surface and the inclined surface of the land portion of the transparent substrate is a replica of the surface roughness of the upper surface and the inclined surface of the resist, and thus the surface roughness of the resist is directly reflected.

When the groove surface is desired to be used as a land surface, the stamper thus prepared may be used as a mother to prepare a reverse stamper. In this case, the surface roughness of the stamper reflects the glass master on the upper surface of the land portion and the resist surface on the inclined surface of the land portion.

In order to control the surface roughness of the land portion, the surface roughness of the glass master is particularly important, and the surface roughness Ra of the glass master is 1.2 nm or less, particularly preferably 0.6 nm.
It is preferable to control the following.

Further, the resist material and its concentration, the resist process (resist rotation speed, resist coating amount, air supply / exhaust conditions, temperature, humidity, etc.) and exposure conditions are optimized so as to faithfully follow the surface of the glass master. It is possible to control to a predetermined surface roughness by forming a resist film and adjusting the film forming conditions of the Ni sputtered film appropriately. Especially the surface roughness of the sloped part can be adjusted by adjusting the resist material / concentration (volatility), exposure conditions and development conditions.
The surface roughness Ra can be 1.2 nm or less. Further, the angle θ of the inclined surface can be controlled by adjusting the same condition.

Further, the magnetic layer 33 may be a single layer or a laminated layer, and is not particularly limited, but the magnetic domain wall can be moved during reproduction to apparently expand the magnetic domain to reproduce. It is a layer.

For example, a three-layer structure composed of a first magnetic layer, a second magnetic layer and a third magnetic layer as shown in JP-A-6-290496 is used. Here, the first magnetic layer 331 is a magnetic layer (moving layer and reproducing layer) which has a smaller domain wall coercive force and a larger domain wall mobility than the third magnetic layer in the vicinity of the ambient temperature. The magnetic layer 332 includes a magnetic layer (switching layer) having a Curie temperature lower than that of the first magnetic layer and the third magnetic layer,
The third magnetic layer 333 is an ordinary magnetic recording layer (memory layer) having excellent storage stability of magnetic domains. Each magnetic layer is exchange-coupled with each other by continuously forming a film by a physical vapor deposition method such as sputtering or vacuum vapor deposition.

As the first magnetic layer, for example, GdCo,
GdFe, GdFeCo, NdGdFeCo, TbFe
A material for bubble memory such as rare earth-iron group amorphous alloy or garnet having a relatively small perpendicular magnetic anisotropy such as Co is preferable.

As the second magnetic layer, for example, DyC
o, TbCo, GdCo, GdFeCo, or other Co-based alloy or DyFe, GdFe, TbFe, or other Fe-based alloy magnetic layer having a Curie temperature lower than those of the first magnetic layer and the third magnetic layer 333 and a saturation magnetization value of It is preferably smaller than the third magnetic layer. Further, the Curie temperature can be adjusted by the addition amount of Co, Cr, Ti or the like.

As the third magnetic layer, for example, TbFe
Co, DyFeCo, GdFeCo, TbDyFeCo
Rare earth-iron group amorphous alloys such as Pt / Co, Pd / C
It is preferable to use a platinum group-iron group periodic structure film such as o that has a large value of saturation magnetization and magnetic anisotropy and can stably hold the magnetization state (magnetic domain).

The dielectric layers 32 and 34 are not particularly limited, but SiN, SiO ₂ , ZnS and the like are preferable.

A reflective film such as an Al alloy may be formed on the second dielectric layer 34, if necessary.

In this magnetic recording medium, an intermediate layer may be provided between the magnetic amplification layer and the recording layer.

[0037]

EXAMPLES The present invention will be described in more detail with reference to the following specific examples. However, the present invention does not exceed the gist of the invention.
The present invention is not limited to the following examples.

The surface roughness of the transparent substrate 31 and the magnetic layer 33 is determined by scanning probe microscope (SPM) NanoScop.
The measurement was performed using a tapping mode AFM of eIII (manufactured by Digital Instruments, USA). An ordinary blade tip was used as the probe, and the surface roughness was compared by the value of Ra (average center line roughness).

<Recording / Reproducing Method> In the recording / reproducing apparatus used for the measurement, as shown in FIG. 5 , a heating laser is added to the optical system of a general magneto-optical disk recording / reproducing apparatus. Reference numeral 81 is a laser light source for recording and reproduction, which has a wavelength of 6
It is arranged so that P deflection is incident on the recording medium at 35 nm. Reference numeral 82 denotes a laser light source for heating, which has a wavelength of 1.3 μm and is arranged so that P deflection is incident on the recording medium. 83 is 10 for 635 nm light
It is a dichroic mirror designed to transmit 0% and reflect 100% of 1.3 μm light. Reference numeral 84 is a deflecting beam splitter, which is designed to transmit 70% to 80% of P polarization of 635 nm light and 1.3 μm of light, and reflect 100% of S polarization. The light flux diameter of the 1.3 μm light is smaller than the aperture diameter of the objective lens 85, and the NA is smaller than that of the 635 nm light condensed through the entire aperture. Also, 87 is
It is provided to prevent 1.3 μm light from leaking into the signal detection system. It transmits 100% of 635 nm light,
It is a dichroic mirror designed to reflect 100% of 1.3 μm light.

By this optical system, a recording / reproducing spot 91 and a heating spot 92 are imaged on the recording surface of the recording medium 86 on the recording track 95 as shown in FIG. 6A . Can be made. Since the heating spot 92 has a long wavelength and a small NA, it has a larger diameter than the recording / reproducing spot 91. As a result, a desired temperature gradient as shown in FIG. 6B can be easily formed in the area of the recording / reproducing spot 91 on the recording surface of the moving medium. An isotherm 96 of the temperature Ts is also shown here.

First, the recording / reproducing laser was set to DC at 8 mW.
By modulating the magnetic field at ± 150 [Oe] while irradiating, a repeating pattern of upward magnetization and downward magnetization corresponding to the modulation of the magnetic field is formed in the cooling process after heating above the Curie temperature of the third magnetic layer. Formed. At this time, it is also possible to reduce the recording power of the recording / reproducing laser by irradiating the heating laser together.

The modulation frequency of the recording magnetic field was changed from 1 to 10 MHz, and recording was performed with a predetermined pit length and pit interval shown in each example.

The power of the recording / reproducing laser at the time of reproduction is
1mW, heating laser with the same power of 20mW
While irradiating, C / for each mark length pattern
N was measured. The temperature distribution on the medium surface at this time isFigure 6
It is as shown in (b). The reproduction principle at this time is
Similar to Kaihei 6-290496, the medium moves
Then, the medium temperature rises to Ts of the second magnetic layer,
And the exchange coupling with the third magnetic layer is broken, and the first magnetic layer
Domain wall 93 has a higher temperature and a smaller domain wall energy density.
The mark length is shortened because
Also shows the atomic spin of the first magnetic layer in the reproducing spot.
It is possible to align in all directions and the recording mark length
A constant and maximum amplitude, regardless of
The signals with the following cycles can be reproduced.

Example 1 As shown in FIG. 2, the transparent substrate 11 used in this example uses polycarbonate as a material and has a land width 23.
Is 0.6 μm and the groove width 24 is 0.4 μm. The angle θ of the inclined surface of the land is 70 degrees, and the height of the land is 25.
Is 280 nm.

In order to manufacture such a transparent substrate, a quartz glass master having an extremely smooth surface was used, and an Ar laser having a wavelength of 351 nm was used for cutting.

When the surface roughness Ra of the transparent substrate 11 was measured, it was 0.825 nm on the top surface 1a of the land portion, 1.015 nm on the bottom surface 2a of the groove portion, and the inclined surface 1b of the land portion.
Was 0.825 nm.

On this transparent substrate 11, as shown in FIG. 3, a SiN layer 32 as a first dielectric layer (interference layer) 8 is formed.
0 nm, then a GdFeCo layer 331 as a first magnetic layer (domain wall displacement layer) of 30 nm, a DyFe layer 332 as a second magnetic layer (switching layer) of 10 nm, a third magnetic layer
Of the TbFeCo layer 333 as a magnetic layer (memory layer) of
0 nm was sequentially formed by sputtering. Finally, a SiN layer 34 having a thickness of 80 nm was formed as a second dielectric layer (protective layer).

The surface roughness of the magneto-optical disk thus obtained was almost the same as the surface roughness of the transparent substrate 11.

After recording an isolated magnetic domain of 0.25 μm on the magneto-optical disk thus obtained by the magnetic field modulation method, a light beam for heating was irradiated and the magnetic domain was observed with a polarizing microscope. An unclosed magnetic domain was confirmed in both the groove and the groove.

On the "groove surface" of the magneto-optical disk thus obtained, the pit length of 0.
After continuous recording at 10 μm and a pit interval of 0.10 μm, reproduction was performed by using the above-mentioned domain wall displacement type expansion / reproduction method. A reproducibility of 0.5 dB was obtained.

Similarly, on the "land surface" of this magneto-optical disk, a pit length of 0.10 .mu.
m and a pit interval of 0.10 μm were continuously recorded, and then reproduced in the same manner. As a result, in an optical system having a wavelength of 635 nm and an NA of 0.6 (relative speed 2 m / s), C / N 38.0 was obtained.
dB was obtained with good reproducibility.

That is, according to the present invention, the magnetic separation between the tracks of the magnetic layer is realized without performing the annealing treatment and the domain wall movement occurs not only in the groove portion but also in the land portion, and both the land and the groove are formed. It has been possible to realize a domain wall motion type magneto-optical recording medium capable of recording on a disk.

Since the transparent substrate 11 can be formed by using a general-purpose substrate forming technique using polycarbonate, it is possible to avoid an increase in the cost of the medium and provide an inexpensive high density recording medium.

<Comparative Example 1> In Example 1, the surface roughness R of the inclined surface 14 of the land portion was measured.
A magneto-optical disk was produced in the same manner as in Example 1 except that a transparent substrate having a of 1.513 nm was used.

After recording an isolated magnetic domain of 0.25 μm on the thus obtained magneto-optical disk by the magnetic field modulation method, a light beam for heating was applied and the magnetic domain was observed with a polarization microscope. An unclosed magnetic domain was confirmed in both the groove and the groove.

On the "groove surface" of the magneto-optical disk thus obtained, a pit length of 0.
After continuous recording at 10 μm and a pit spacing of 0.10 μm, reproduction was carried out in the same manner as in Example 1, and a wavelength of 635
C / N of 37.5 dB was obtained with good reproducibility in an optical system of nm and NA of 0.6 (relative speed of 2 m / s).

On the other hand, similarly for the “land surface”, the pit length is 0.10 μm and the pit interval is 0.
When continuously recorded at 10 μm and then reproduced in the same manner, the reproduced signal is extremely small, and the wavelength is 635 nm and the NA is
C / N at an optical system of 0.6 (relative velocity 2 m / s)
It was 27.0 dB.

As described above, when the surface roughness Ra of the inclined surface of the land portion is 1.513 nm, the result of the magnetic domain observation shows that the division of the magnetic layer by the deep transparent rectangular substrate is realized. In other words, it was found that the reproduced signal due to the domain wall movement of a practical signal level could not be obtained on the land surface.

<Example 2> In Example 1, the resist process (mainly the viscosity and vaporization rate of the resist, the film thickness, etc.) for forming the stamper from which the transparent substrate is formed, the exposure conditions and the development conditions were changed. A transparent substrate was produced in the same manner as in Example 1 except for the above.
The surface roughness Ra of the land upper surface 1a and the inclined surface 1b of this transparent substrate were both 0.530 nm, and the surface roughness Ra of the groove 2a was 0.767 nm. A magneto-optical recording medium was prepared in the same manner as in Example 1 except that this transparent substrate was used.

After recording an isolated magnetic domain of 0.25 μm by the magnetic field modulation method on the magneto-optical disk thus obtained, a light beam for heating was applied and the magnetic domain was observed with a polarizing microscope. An unclosed magnetic domain was confirmed in both the groove and the groove.

On the "groove surface" of the magneto-optical disk thus obtained, a pit length of 0.
After continuously recording at 10 μm and a pit interval of 0.10 μm, the data was reproduced by using the above-mentioned reproduction method.
C / N of 38.5 dB was obtained with good reproducibility in an optical system of 5 nm and NA of 0.6 (relative velocity 2 m / s).

On the other hand, similarly for the "land surface", the pit length is 0.10 μm and the pit spacing is 0.
After continuously recording at 10 μm and reproducing in the same manner, an optical system with a wavelength of 635 nm and an NA of 0.6 (relative speed 2
m / s), C / N of 39.5 dB was obtained with good reproducibility.

Comparing the result of the reproduced signal with the first embodiment,
By improving the surface roughness of the land portion and the groove portion, C / N is further improved.

< Example 3 > In Example 1, the resist process (mainly the viscosity and vaporization rate of the resist, the film thickness, etc.) for forming the stamper from which the land-and-groove-shaped substrate is formed is adjusted,
Land portion upper surface 1a and land portion inclined surface (tapered portion)
A magneto-optical recording medium was prepared under the same conditions as in Example 1 except that the substrate 11 having a surface roughness Ra of 1b of 1.150 nm and a surface roughness Ra of the bottom surface 2a of the groove portion of 0.767 nm was used. .

After recording an isolated magnetic domain of 0.25 μm on the magneto-optical disk thus obtained by the magnetic field modulation method, a light beam for heating was applied and the magnetic domain was observed with a polarization microscope. An unclosed magnetic domain was confirmed in both the groove and the groove.

On the "groove surface" of the magneto-optical disk thus obtained, a bit length of 0.
After continuous recording at 10 μm and a bit interval of 0.10 μm, reproduction was performed using the domain wall displacement type expansion / reproduction method in the same manner as in Example 1, and in an optical system with a wavelength of 635 mm and NA of 0.6 (relative speed 2 m / s) C / N of 38.5 dB was obtained with good reproducibility.

On the other hand, similarly for the “land surface”, the bit length is 0.10 μm and the bit interval is 0.
After continuously recording at 10 μm and reproducing in the same manner, an optical system with a wavelength of 635 nm and an NA of 0.6 (relative speed 2
m / s), C / N of 37.0 dB was obtained with good reproducibility. Comparing the result of the reproduced signal with that of the first embodiment, the C / N in the land portion is somewhat deteriorated because the surface roughness of the land portion is large, but this is practically acceptable.

As described above, by using the rectangular substrate having such a surface roughness, the magnetic separation between the tracks can be realized without performing the annealing treatment and the "land portion" as well as the "groove portion". In this case, the domain wall movement phenomenon also occurred, and the domain wall moving type magneto-optical recording medium capable of recording on both the land and the groove could be easily realized. Since the polycarbonate substrate used can be produced by a general-purpose substrate forming technique, the cost of the medium can be prevented from increasing, and an inexpensive high-density recording medium can be provided.

< Comparative Example 2 > In Example 3 , the inclined surface (tapered portion) 1b of the land portion is used.
A magneto-optical disk was prepared in the same manner as in Example 3 except that a substrate having a surface roughness Ra of 1.305 nm was used.

After recording an isolated magnetic domain of 0.25 μm on the magneto-optical disk thus obtained by the magnetic field modulation method, a light beam for heating was applied and the magnetic domain was observed with a polarization microscope. An unclosed magnetic domain was confirmed in both the groove and the groove.

On the "groove surface" of the magneto-optical disk thus obtained, the bit length of 0.
After continuous recording at 10 μm and a bit interval of 0.10 μm, reproduction was performed using the domain wall displacement type expansion / reproduction method in the same manner as in Example 1. In an optical system with a wavelength of 635 nm and NA of 0.6 (relative speed 2 m / s). C / N of 38.5 dB was obtained with good reproducibility.

On the other hand, similarly for the “land surface”, a bit length of 0.10 μm and a bit interval of 0.
When continuously recorded at 10 μm and then reproduced in the same manner, the reproduced signal is extremely small, and the wavelength is 635 nm and the NA is
C / N at an optical system of 0.6 (relative velocity 2 m / s)
It was 35.0 dB.

From the above results, the surface roughness R of the inclined surface (tapered portion) 1b of the land portion of the polycarbonate substrate 11
When a is 1.305 nm, the result of magnetic domain observation shows that although the division of the magnetic layer by the rectangular substrate has been realized, a practical reproduction signal due to domain wall movement (of the signal level) is obtained on the land surface. There wasn't.

[0074]

The magneto-optical recording medium of the present invention is easy to manufacture because it does not require any special magnetic decoupling treatment, and both the land portion and the groove portion can be used as the recording surface, so that the track density can be improved. Is improved and higher density recording is possible. By using the magneto-optical recording medium of the present invention, it is possible to instantaneously move the domain wall by using a temperature gradient to expand and reproduce the magnetic domain.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a magneto-optical recording medium of the present invention.

FIG. 2 is a schematic cross-sectional view of a transparent substrate used in the magneto-optical recording medium of the present invention.

FIG. 3 is a cross-sectional view of a layer structure of a magneto-optical recording medium (Example 1, Example 2, Example 3 ) of the present invention.

FIG. 4 is a schematic diagram for explaining the reproduction principle of JP-A-6-209496 and the present invention.

FIG. 5 is a diagram showing a recording / reproducing apparatus used for the magneto-optical recording medium of the present invention.

FIG. 6 is a diagram showing a reproduction state of the present invention.

[Explanation of symbols]

1 land section 1a Top surface of land 1b Land slope 2 groove part 2a Groove surface 11 Transparent substrate 14 Land surface slope 13 Magnetic layer A discontinuous surface of magnetic layer 23 Land width 24 groove width 25 Land height 331 First magnetic layer 332 Second magnetic layer 333 Third magnetic layer 32, 34 Dielectric layer (interference layer or protective layer)

Claims (3)

(57) [Claims] 1. A magneto-optical device having a transparent substrate and a magnetic layer formed on the surface of the transparent substrate and capable of reproducing by expanding at least magnetic domains by moving at least the magnetic domain wall of the magnetic layer to be reproduced. In the recording medium, the surface of the transparent substrate is composed of a land portion and a groove portion, and the surface roughness Ra of the inclined surface of the land portion is 1.2 nm or less.
And a tilted surface having an angle of 40 to 90 degrees . 2. The magnetic layer has a laminated structure in which at least first, second and third magnetic layers are sequentially laminated,
The first magnetic layer is a magnetic layer having a domain wall coercive force relatively smaller than that of the third magnetic layer at the ambient temperature, and the second magnetic layer is formed from the first magnetic layer and the third magnetic layer. The magneto-optical recording medium according to claim 1, which is a magnetic layer having a low Curie temperature. 3. The magneto-optical recording medium according to claim 1, wherein the surface roughness Ra of the upper surface of the land portion and the surface of the groove portion is 1.2 nm or less.