JPH11195253A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a recording density and a transfer rate by specifying the surface roughness of the substrate of either a land part or a groove part and dividing a first magnetic layer by these land parts or groove parts. SOLUTION: A magnetic layer 14 in which first to third magnetic layers are successively laminated is provided on a rectangular substrate 11 on which a land width 12 and a groove width 13 are alternately provided. The magnetic wall coercive force of the first magnetic layer is smaller at the vicinity of an ambient temp. than that of the third magnetic layer and the degree of the movement of the magnetic wall is large and the Curier temp. of the second magnetic layer is lower than those of the first and third magnetic layers. The surface roughness Ra of the rectangular substrate 11 dividing the first magnetic layer of either the land width 12 or the groove width 13 is made to be >=1.2 nm and, preferably, these parts are applied to an annealing process. Thus, the magnetic wall moving type magneto-optical recording medium suited for a superhigh density recording is obtained with a low cost by a simple technique.

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 capable of recording at a very high density by utilizing the movement of a domain wall during reproduction.

[0002]

2. Description of the Related Art As a rewritable high-density recording medium,
2. Description of the Related Art Magneto-optical disks have attracted attention in recent years, and there is an increasing demand for higher recording densities of magneto-optical disks to produce large-capacity recording media. The linear recording density of an optical disc largely depends on the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens, and the spatial frequency at the time of signal reproduction is at the limit of about NA / λ. Therefore, in order to realize a higher density in a conventional optical disk, 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. For this reason, several techniques have been proposed to improve the recording density by devising the configuration of the recording medium and the reading method.

[0003] For example, the applicant of the present invention disclosed in
As described in Japanese Patent No. 0496, a magneto-optical recording medium, a reproducing method, and a reproducing apparatus capable of reproducing a signal having a period equal to or less than the diffraction limit of light at a high speed without reducing the reproduced signal amplitude are proposed. . As described in the publication, when a temperature distribution is formed on a reproducing layer of a magneto-optical recording medium by a heating means such as a light beam, a distribution occurs in a domain wall energy density. Can be moved. As a result, the reproduced signal amplitude is always constant and maximum regardless of the interval between recorded domain walls (that is, the recording pit length). That is, the inevitable decrease in the reproduction output accompanying the improvement in the linear recording density is greatly improved, and the density can be further increased.

[0004]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 6-290.
According to No. 496, the movement of the domain wall is a phenomenon that occurs on the same track (in the track direction), and it is essential that the magnetic layers be separated (that is, magnetically separated) between the tracks. . As a method of creating such an unclosed magnetic domain (divided domain wall), Japanese Patent Laid-Open No.
290496 discloses a method using a rectangular deep groove substrate,
A method of magnetically altering the groove by annealing and irradiating the groove with a laser has been proposed, but for a rectangular deep groove substrate,
When transferring at the time of molding, the bottom portion of the rectangular groove of the stamper cannot be transferred cleanly, and if the land portion of the substrate becomes U-shaped, there is a problem of transferability that a sufficient dividing effect cannot be obtained. In addition, annealing requires high-temperature processing such as irradiation with a high-power laser, and the magnetic properties are deteriorated when annealing with such a high-power laser is performed. (The magnetic layer is degraded)
Since the area of the portion spreads out of the track depending on the temperature distribution of the laser, there is a problem that the area that can be used as an information data portion is substantially reduced and the track density is reduced.

Accordingly, an object of the present invention is to provide a domain wall displacement type magneto-optical recording medium in which tracks are magnetically separated by the shape of a land or a groove without using deep groove forming or annealing. I do.

[0006]

A magneto-optical recording medium according to the present invention is a magneto-optical recording medium in which at least first, second and third magnetic layers are sequentially laminated. The layer is a magnetic layer (moving layer and reproducing layer) having a smaller domain wall coercive force and a larger domain wall mobility than the third magnetic layer near the ambient temperature, and the second magnetic layer is A magnetic layer (switching layer) having a lower Curie temperature than the first magnetic layer and the third magnetic layer. The third magnetic layer is a normal magnetic recording layer (memory layer) having excellent storage stability of magnetic domains. In the film configuration disclosed in Japanese Patent Application Laid-Open No. 6-290496, the substrate surface roughness Ra of a track to be magnetically separated out of a land portion or a groove portion is 1.2 n.
m or more, preferably 1.5 nm or more.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In order to magnetically divide a magnetic layer between tracks, the magnetic layer in the divided region may be changed from a perpendicular magnetization film to an in-plane magnetization film or a non-magnetic film. The inventor of the present invention has made intensive studies in view of this point. As a result, the crystal growth state of the magnetic layer formed differs depending on the surface state of the substrate on which the magnetic layer is formed, that is, the roughness of the substrate surface. It has been found that when the surface roughness Ra is 1.2 nm or more, the magnetic layer becomes an in-plane magnetized film or a non-magnetic film, and has reached the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view for explaining the magneto-optical recording medium of the present invention. The substrate 11 has a land 1
2 (projection) and groove 13 (concave), and one of the land and groove (here, tentatively groove 13) is a track for the purpose of track separation. The surface roughness Ra of the track (land or groove) for the purpose of dividing the track is set to 1.2 nm.
Or more, preferably 1.5 nm or more,
Since the crystal growth state (that is, magnetic properties) of the magnetic layer 141 formed thereon by sputtering is different from that of the other portion 142 (becomes an in-plane recording film or a non-magnetic film), as a result, the magnetic layer 14 is made magnetic. It becomes possible to separate them.

[0010] Incidentally, the surface roughness Ra of the portion of the substrate not intended to be divided is less than 1.2 nm, preferably 0.6 n
m or less. Further, the difference between the surface roughness of the substrate surface of the track for the purpose of division and the surface roughness of the substrate of the normal data track is preferably 0.4 nm or more, and particularly when the difference is 1.0 nm or more, the effect of the division is large. It is.

Further, the portion 14 in which the magnetic characteristics are deteriorated
By annealing 1 with a low power laser,
The dividing effect is further improved.

The track width is not particularly limited. However, in order to increase the track density, the narrower the track (the groove portion 13 in FIG. 1) for the purpose of division is, the better.

In the present invention, the shapes of the land portion and the groove portion are not particularly limited.
-290496
Further, various shapes such as a trapezoidal shape as shown in FIG. 1 are possible.

Here, the surface roughness of the substrate 11 reflects the surface roughness of the stamper in the case of an injection-molded substrate.

The manufacturing procedure of the stamper is as follows. First, a glass master is polished, a resist is coated thereon, exposed to desired specifications, cut, and then developed. Next, a Ni film is formed by sputtering, Ni electroforming is performed, and peeled and washed is a stamper. Therefore, usually, the surface roughness of the resist surface is reflected on the surface roughness of the stamper. However, when cutting is performed on the land and groove recording substrate up to the glass master, the surface roughness of the groove surface becomes the surface roughness of the glass master.

As described above, the surface roughness of the stamper reflects the surface roughness of the resist surface or the glass master, and the resist surface is optimized by optimizing the resist material and the resist process. ,
It is possible to obtain a desired surface roughness.

The surface roughness of the substrate 11 was measured using a tapping mode AFM of a scanning probe microscope (SPM) “NanoScope III” (trade name, manufactured by Digital Instruments, USA). The probe used a normal blade tip, and the surface roughness was compared by the value of Ra (average center line roughness).

FIG. 2 is a schematic sectional view showing another example of the substrate shape of the magneto-optical recording medium of the present invention.

The transparent substrate 21 is composed of land portions 22 (convex portions) and groove portions 23 (concave portions). The land portions 22 are tracks whose purpose is to divide the magnetic layer between the tracks. Ra is 1.2 nm or more, preferably 1.5 nm or more.

FIG. 3 is a sectional view showing the layer structure of the magneto-optical recording medium of the present invention. On a transparent substrate 31, a first dielectric layer 32, a magnetic layer 33, and a second dielectric layer 34 are sequentially laminated.

As the transparent substrate 31, for example, glass,
Polycarbonate, polymethyl methacrylate, thermoplastic norbornene-based resin, and the like can be used.

The magnetic layer 33 may be a single layer or a multilayer, and is not particularly limited.
It is preferable that it has a layer configuration disclosed in Japanese Patent Application Laid-Open No. 6-206. That is, at least the first, second, and third magnetic layers are sequentially stacked, and the first magnetic layer 331 has a domain wall coercive force relatively near the ambient temperature near the third magnetic layer 333. The second magnetic layer 332 is a magnetic layer (switching layer) having a lower Curie temperature than the first magnetic layer and the third magnetic layer 333. ), The third magnetic layer 3
33 is a magnetic recording layer (memory layer) having excellent storage stability of magnetic domains.

Each magnetic layer is exchange-coupled or magnetostatically coupled to each other by continuous film formation by physical vapor deposition such as sputtering or vacuum vapor deposition.

As the first magnetic layer 331, for example, G
Rare earth-iron group amorphous alloys having relatively small magnetic anisotropy, such as dCo-based, GdFe-based, GdFeCo-based, and TbCo-based alloys, and materials for bubble memories such as garnet are preferable.

As the second magnetic layer 332, for example, C
o-based or Fe-based alloy magnetic layer with Curie temperature of 1st
It is preferable that the magnetic layer is smaller than the magnetic layer 331 and the third magnetic layer 333 and has a saturation magnetization value smaller than that of the third magnetic layer 333. The Curie temperature can be adjusted by the amount of Co, Cr, Ti, or the like.

As the third magnetic layer 333, for example, T
Rare earth-iron group amorphous alloys such as bFeCo, DyFeCo and TbDyFeCo, and platinum group-iron group periodic structure films such as Pt / Co and Pd / Co have large values of saturation magnetization and magnetic anisotropy, Magnetic domains) are preferred.

The dielectric layers 32 and 34 are not particularly limited, but are preferably made of SiN, SiO ₂ , ZnS or the like.

The separation between the tracks of the magnetic layer can be further improved by utilizing the surface roughness of the substrate and annealing the tracks to be separated after forming the magnetic layer with a laser or the like. Regarding the annealing conditions, the magnetic layer is already almost magnetically divided due to the difference in the surface roughness of the substrate, so that a dividing effect can be expected with a low power or a narrow beam width. As a result, a decrease in track density can be suppressed without reducing the area that can be used as the information data portion, as compared with the case where annealing is performed by a high-power laser as shown in the conventional example. The apparatus for annealing is not particularly limited, but a laser used for recording / reproduction can be used as it is, or a general-purpose optical disk cutting machine or the like can be used.

[0029]

EXAMPLES The present invention will be described in more detail with reference to specific examples below, but the present invention is not limited to the following examples as long as it is within the scope of the gist.

Example 1 FIG. 1 is a schematic sectional view of the substrate shape of a magneto-optical recording medium of the present invention, and FIG. 3 is a sectional view of the layer structure of the magneto-optical recording medium of the present invention.

In FIG. 1, the polycarbonate substrate 11
Has a land width 12 of 0.6 μm and a groove width 13 of 0.1 μm.
This is a land and groove substrate having a thickness of 3 μm, a groove depth 15 of 85 nm, and a taper angle 16 of 45 degrees. The surface roughness Ra of the upper surface of the land portion 12 of the substrate 11 was measured to be 0.53
It was 0 nm. The surface roughness Ra of the upper surface of the groove 13 was measured and found to be 1.513 nm.

As described above, the land portion 12 and the groove portion 13
As shown in FIG. 3, an SiN layer as a first dielectric layer (interference layer) 32 is formed on a substrate manufactured by changing the surface roughness of the substrate.
0 nm, and then the first magnetic layer (domain wall moving layer) 331
The GdFeCo layer is 30 nm, the DyFe layer is 10 nm as the second magnetic layer (switching layer) 332, and the third
A TbFeCo layer as a magnetic layer (memory layer) 333 of
0 nm was sequentially formed by sputtering. Finally, an 80 nm-thick SiN layer was formed as the second dielectric layer (protective layer) 34.

On both sides of the land and the groove of the magneto-optical disk obtained in this way, a magnetic field modulation method of 0.2 μm
After recording the isolated magnetic domain of
Magnetic domain observation was performed with a polarizing microscope. As a result, unclosed magnetic domains were confirmed in the land portions, but no magnetic domains were observed in the groove portions. That is, 0.
It was confirmed that the film was unable to record an isolated magnetic domain of 2 μm, and the magnetic layer was magnetically separated by the groove portion.

The pit length of 0.10 μm was formed on the land surface of the magneto-optical disk thus obtained by a normal magnetic field modulation method.
m and a pit interval of 0.10 μm continuously, and then the method described in JP-A-6-290496, that is, the first method is performed while moving the light beam relative to the disk.
Forming a temperature distribution having a gradient with respect to the moving direction of the spot of the light beam on the disk, and adjusting the temperature distribution to a temperature region higher than at least the Curie temperature of the second magnetic layer. By moving the domain wall formed in the first magnetic layer by making a temperature distribution having
When reproduction is performed using a method of reproducing recorded information by detecting a change in the polarization plane of the reflected light of the light beam (hereinafter referred to as a “domain wall displacement type expansion reproduction method using a temperature gradient of a magnetic layer”), In an optical system with a wavelength of 680 nm and NA of 0.6 (relative velocity of 2 m / s), C / N of 40.0 dB was obtained.

That is, by using the polycarbonate substrate 11 having the above shape, the magnetic layer is magnetically separated between the tracks without performing an annealing process or the like, and the reproduction of the domain wall displacement type magneto-optical recording medium can be easily realized. did. Since such a polycarbonate substrate 11 can be manufactured by a general-purpose substrate forming technique, an increase in the cost of the medium can be avoided, and an inexpensive high-density recording medium can be provided.

Example 2 FIG. 2 is a schematic sectional view of the substrate shape of the magneto-optical recording medium of the present invention, and FIG. 3 is a sectional view of the layer structure of the magneto-optical recording medium of the present invention.

The polycarbonate substrate 21 has a land width of 2
2 is 0.3 μm, the groove width 23 is 0.6 μm, the groove depth 25 is 85 nm, and the taper angle 26 is about 70 °. When the surface roughness Ra of the upper surface of the land portion 22 of the substrate 21 was measured, it was 1.255 m. The surface roughness Ra of the upper surface of the groove 13 was measured and found to be 0.825 nm.

In FIG. 3, the polycarbonate substrate 2
A magnetic layer and a dielectric layer were formed on 1 under the same conditions as in Example 1.

After recording an isolated magnetic domain of 0.2 μm on the magneto-optical disk obtained in this way by a magnetic field modulation method, a heating light beam was applied, and the magnetic domain was observed with a polarizing microscope. As a result, unclosed magnetic domains were confirmed in the groove portions, but no magnetic domains were observed in the land portions. That is, it was confirmed that the land portion was a film in which recording of a 0.2 μm isolated magnetic domain was impossible, and the magnetic layer was magnetically separated by the land portion.

A pit length of 0.10 was formed on the groove surface of the magneto-optical disk thus obtained by a normal magnetic field modulation method.
.mu.m and a pit interval of 0.10 .mu.m continuously, and then reproduced using the "domain wall displacement type expansion reproduction method utilizing the temperature gradient of the magnetic layer" in the same manner as in Example 1.
C / N of 39.0 dB was obtained in an optical system with a nm of 0.6 and a NA of 0.6 (relative speed of 2 m / s).

That is, by using the polycarbonate substrate 21 having the above shape, the magnetic layer is magnetically separated between the tracks without performing an annealing process or the like, and the reproduction of the domain wall displacement type magneto-optical recording medium can be easily realized. did. Since such a polycarbonate substrate 21 can be manufactured by a general-purpose substrate forming technique, an increase in the cost of the medium can be avoided and an inexpensive high-density recording medium can be provided.

Comparative Example 1 In Example 1, the surface roughness R of the upper surface of the groove 13 was
Example 1 was the same as Example 1 except that a substrate having a of 0.825 nm was used.

After recording an isolated magnetic domain of 0.2 μm on the magneto-optical disk obtained in this way by a magnetic field modulation method, a magnetic beam was observed with a polarizing microscope by applying a heating light beam. As a result, magnetic domains were confirmed in both the land portion and the groove portion.

The pit length of 0.10 μm was formed on the land surface of the magneto-optical disk thus obtained by a normal magnetic field modulation method.
m and pit spacing of 0.10 μm continuously, and then reproduced using the “domain wall displacement type expansion reproducing method using the temperature gradient of the magnetic layer” as in Example 1. The reproduced signal was very small. In an optical system with a wavelength of 680 nm and NA of 0.6 (relative speed of 2 m / s), only 24.0 dB was obtained in C / N.

When a recording / reproducing experiment was performed on the groove surface under the same conditions as above, the reproduced signal was similarly small, and only 19.0 dB was obtained in C / N.

As described above, when the polycarbonate substrate having the above shape was used, the magnetic layer was not magnetically separated, so that domain wall motion was extremely unlikely to occur, and a practical reproduced signal could not be obtained.

Example 3 In Example 2, after forming the magneto-optical recording medium, only the lands were annealed with a low laser power.
The annealing conditions were a laser having a wavelength of 680 nm and a NA of 0.6, and the spot width was 0.25 μm slightly smaller than the land width.
m and power were 2 mW. Incidentally, the laser power required for magnetically separating the magnetic layer only by annealing has a wavelength of 680 nm, NA of 0.6, a spot diameter of about 1 μm, and a power of 8 to 10 mW.

On both sides of the land and the groove of the magneto-optical disk obtained in this way, a magnetic field modulation method of 0.2 μm
After recording the isolated magnetic domain of
Magnetic domain observation was performed with a polarizing microscope. As a result, unclosed magnetic domains were confirmed in the groove portions, but no magnetic domains were observed in the land portions. That is, 0.2
It was confirmed that the film was not able to record an isolated magnetic domain of μm, and that the magnetic layer was magnetically separated by the land portion.

A pit length of 0.10 was formed on the groove surface of the magneto-optical disk thus obtained by a normal magnetic field modulation method.
.mu.m and a pit interval of 0.10 .mu.m continuously, and then reproduced using the "domain wall displacement type expansion reproduction method utilizing the temperature gradient of the magnetic layer" in the same manner as in Example 1.
C / N of 41.0 dB was obtained in an optical system with a nm and NA of 0.6 (relative speed of 2 m / s).

The reason why the C / N ratio was improved as compared with Example 2 was that noise was reduced by the annealing treatment. That is, by adding the annealing treatment to Example 2, the magnetic separation of the magnetic layer was further ensured, and the magnetic layer was suitable as a domain wall displacement type magneto-optical recording medium.

Example 4 In Example 1, the surface roughness Ra of the upper surface of the groove portion 13 was changed.
Was set to 1.315 nm, and was the same as Example 1.

After recording an isolated magnetic domain of 0.2 μm on the magneto-optical disk obtained as described above by a magnetic field modulation method, a heating light beam was applied, and the magnetic domain was observed with a polarizing microscope. As a result, unclosed magnetic domains were confirmed in the land portions, but no magnetic domains were observed in the groove portions.
That is, it was confirmed that the groove portion was a film in which it was impossible to record a 0.2 μm isolated magnetic domain, and the magnetic layer was magnetically separated by the groove portion.

The pit length of 0.10 μm was formed on the land surface of the magneto-optical disk thus obtained by a normal magnetic field modulation method.
m and a pit interval of 0.10 μm continuously, and then reproduced using the “domain wall displacement type expansion reproduction method using the temperature gradient of the magnetic layer” in the same manner as in Example 1.
In an optical system having a m of 0.6 and a NA of 0.6 (relative speed of 2 m / s), C / N of 37.0 dB was obtained. The reason why C / N is slightly reduced as compared with Example 1 is that the dividing effect by the groove is reduced.

As described above, by using the polycarbonate substrate having the above shape, the magnetic layer was magnetically separated between the tracks without performing the annealing treatment, and the reproduction of the domain wall displacement type magneto-optical recording medium was easily realized. . Since the polycarbonate substrate can be formed by a general-purpose substrate forming technique, an increase in the cost of the medium can be avoided and an inexpensive high-density recording medium can be provided.

Comparative Example 2 In Example 1, the surface roughness Ra of the upper surface of the groove portion 13 was changed.
Was set to 1.115 nm, except that Example 1 was used.

After recording an isolated magnetic domain of 0.2 μm on the magneto-optical disk thus obtained by a magnetic field modulation method, a heating light beam was applied, and the magnetic domain was observed with a polarizing microscope. As a result, magnetic domains were confirmed in both the land portion and the groove portion.

A pit length of 0.10 μm was formed on the land surface of the magneto-optical disk thus obtained by a normal magnetic field modulation method.
m and pit spacing of 0.10 μm continuously, and then reproduced using the “domain wall displacement type expansion reproducing method using the temperature gradient of the magnetic layer” as in Example 1. The reproduced signal was very small. In an optical system having a wavelength of 680 nm and an NA of 0.6 (relative speed of 2 m / s), only C / N of 33.0 dB was obtained.

When a recording / reproducing experiment was conducted on the groove surface under the same conditions as above, the reproduced signal was smaller.
The C / N was 30 dB or less.

As described above, when the polycarbonate substrate having the above shape was used, the magnetic layer was not magnetically separated, so that domain wall movement was extremely unlikely to occur, and a practical reproduced signal could not be obtained.

[0060]

As described above, according to the magneto-optical recording medium of the present invention, the magneto-optical recording medium disclosed in Japanese Patent Application Laid-Open No. 6-290496 (the domain wall displacement type expansion utilizing the temperature gradient of the magnetic layer). The magnetic separation between tracks, which has been indispensable in the formation of the recording method and the transfer speed by the reproduction method, is improved by a simple method of controlling the surface shape (surface roughness) of the land or groove. This can be achieved by using the magnetic recording medium, and at the same time, a domain wall displacement type magneto-optical recording medium suitable for ultra-high density recording can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a substrate shape of a magneto-optical recording medium (Examples 1 and 4) of the present invention.

FIG. 2 is a schematic sectional view showing a substrate shape of a magneto-optical recording medium (Examples 2 and 3) of the present invention.

FIG. 3 shows a magneto-optical recording medium of the present invention (Examples 1, 2, 3,
It is sectional drawing which showed the layer structure of 4).

[Explanation of symbols]

 11, 21, 31: polycarbonate substrate 14, 142, 24, 33: magnetic layer 141: magnetic layer with degraded magnetic properties 331: first magnetic layer 332: second magnetism Layer 333: Third magnetic layer 32, 34: Dielectric layer 12, 22: Land (land width) 13, 23: Groove (groove width) 15, 25: Groove Depth 16, 26 ... taper angle

Claims (2)

[Claims] 1. Magneto-optical recording in which at least first, second and third magnetic layers are sequentially laminated on a substrate on which land portions (convex portions) and groove portions (concave portions) are alternately arranged. A first magnetic layer formed of a magnetic layer having a smaller domain wall coercive force and a larger domain wall mobility than the third magnetic layer at a temperature near an ambient temperature; The magnetic layer is a magneto-optical recording medium composed of a magnetic layer having a lower Curie temperature than the first magnetic layer and the third magnetic layer. A magneto-optical recording medium, wherein the first magnetic layer is separated by a land or groove having a substrate surface roughness of 2 nm or more. 2. After the formation of the magnetic layer, the substrate surface roughness Ra is 1.
2. The magneto-optical recording medium according to claim 1, wherein a portion of 2 nm or more is annealed.