JPH11126386A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the quality of a reproduced signal by making a coercive force expressing the stability of the preservation of the recorded domain of a recording magnetic layer in the radial direction of a recording track maximum at the center of the track or the neighboorhood of the center and making the force gradually smaller as a place is sepatrated from the center. SOLUTION: In order to make a coercive force expressing the stability of the preservation of the recorded domain of a recording magnetic layer in the radial direction of a recording track maximum at the center of the recording track or the neighboorhood of the center and to make the force gradually smaller as the place is sepatrated from the center, the coercive force is made gradually smaller as the place is separated from the center of the recording track by making the track surface of the center of the recording track or the neighboorhood the center roughly parallel with respect to the back of a substrate and making the inclination with respect to the back of the substrate of the recording track surface larger as the place is separated from the center and, moreover, by making the surface roughness of the center of the track or the neighboorhood of the center maximum and by making the surface roughness smaller as the place is separated from the center.

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 with a laser beam, and more particularly to a magneto-optical recording medium capable of high-density recording of the medium.

[0002]

2. Description of the Related Art As one of large-capacity memories in which information can be rewritten, a magneto-optical recording medium that performs reproduction and recording using a laser beam has attracted attention. Since the beam waist diameter is determined by the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens, the magneto-optical recording medium can detect a spatial frequency of about 2 NA / λ during signal reproduction. However, the demand for further increasing the capacity of the magneto-optical recording medium is increasing. For the purpose of satisfying this requirement, that is, in order to increase the recording density of the magneto-optical recording medium to a density exceeding the diffraction limit determined by the wavelength λ and the numerical aperture NA, the recording medium configuration and reading method are devised to reduce the recording density. Improved techniques are being developed.

The following is an example of a magneto-optical recording medium in which the recording density is increased to a minute recording magnetic domain length exceeding the optical diffraction limit. For example, JP-A-3-93058 and JP-A-6-12
No. 4500, a signal is recorded on a recording holding layer of a multilayer film having a reproducing layer and a recording holding layer which are magnetically coupled to each other, and the recording layer is heated by irradiating a laser beam to raise the temperature of the reproducing layer. A signal reproducing method for reading a signal recorded on a recording holding layer in an area while transferring the signal has been proposed (see FIG. 4).

According to this method, an area (aperture) where a spot diameter of a reproducing laser is heated by the laser to reach a transfer temperature and a signal is detected.
Can be limited to a smaller area, so that intersymbol interference during reproduction can be reduced, and a signal having a pit period equal to or less than the optical detection limit λ / 2NA can be reproduced.

As another example, JP-A-6-290496 has been proposed as a magneto-optical recording medium, a reproducing method, and a reproducing apparatus which compensate for the disadvantages of the super-resolution magneto-optical recording / reproducing method.

In Japanese Patent Application Laid-Open No. 6-290496, a magneto-optical recording medium comprising a multilayer film composed of at least three layers utilizing magnetic exchange coupling is used to reduce the reproduction signal amplitude below the optical detection limit. A magneto-optical recording medium, a reproducing method, and a reproducing apparatus capable of reproducing a signal having a period of at a high speed and greatly improving a recording density and a transfer speed are proposed.

That is, a temperature distribution is given to the read / write mark by the attached heating device, and the temperature distribution and the temperature dependence of the domain wall energy in the read / write mark induce a pressure on the domain wall to move into the read light spot. (See FIG. 5). As a result, the domain wall instantaneously moves into the reproduction light spot, the direction of the atomic spins in the reproduction light spot is reversed, and all are aligned in one direction, and the reproduction signal amplitude is the distance between the recorded domain walls (that is, the recording mark). Regardless of the length, the amplitude is always constant and maximum, and the problem of waveform interference and the like due to the optical diffraction limit is completely eliminated. The above-mentioned reproducing method will be referred to as a domain wall moving magnetic domain expansion reproducing method.

[0008]

The super-resolution magneto-optical recording / reproducing system and the domain wall moving magnetic domain enlarging / reproducing system are both reproducing systems which exceed the optical diffraction limit. Is based on the premise that minute recording magnetic domains exceeding the diffraction limit are formed. The recording of a minute magnetic domain exceeding the diffraction limit can be roughly classified into two methods, an optical modulation recording method and a magnetic field modulation recording method.

In the case of the light modulation recording system, the tip of the Gaussian intensity distribution of the laser light is used. Recording is performed by generating a temperature distribution region exceeding the diffraction limit and exceeding a minute recording temperature on the recording medium and modulating the intensity of the laser beam under a constant applied magnetic field.

On the other hand, in the magnetic field modulation recording method, a laser beam is irradiated so that the temperature distribution formed by the laser beam formed on the recording medium always becomes the same distribution (for example, continuous irradiation of the laser beam at a recording power). Recording is performed by modulating an external magnetic field. At this time, by setting the modulation speed of the magnetic field to be high, it is possible to record a minute magnetic domain.

In the light modulation recording method and the magnetic field modulation recording method as described above, a recording magnetic domain having a shape reflecting a temperature distribution by a laser beam showing a Gaussian intensity distribution is formed. That is, in the optical modulation recording method, a recording magnetic domain is formed in a circular or elliptical shape, and in the magnetic field modulation recording method, an arrow-shaped recording magnetic domain is formed.

[0012] Such a recording magnetic domain having an arc shape is particularly useful in a super-resolution magneto-optical recording / reproducing method for realizing a reproducing method exceeding the optical diffraction limit and a domain wall moving magnetic domain enlarging / reproducing method. At the time of reproduction, it adversely affects reproduction signal quality. In the following, with reference to the drawings, an explanation will be given of the influence of the arrow-shaped recording magnetic domain on the reproduction signal quality. FIGS. 6 and 7 are schematic diagrams for explaining the influence of the arc-shaped recording magnetic domain on the reproduction signal quality in the super-resolution magneto-optical recording / reproducing system, and FIGS. 8 and 9 in the domain wall moving magnetic domain enlarging / reproducing system.

In the super-resolution magneto-optical recording / reproducing method,
For example, when a small magnetic domain is recorded by a magnetic field modulation recording method as shown in FIG. 6, since the magnetic domain shape is an arrow feather shape, a plurality of recording magnetic domains are provided in an aperture area which plays a role of reproducing recorded magnetic domain information. And adversely affect the reproduced signal.

On the other hand, in the domain wall moving domain expansion / reproducing system as shown in FIG. 8, since the recording magnetic domain has an arc shape, the movement of the domain wall and the phenomenon of magnetic domain expansion are unlikely to occur, and the rise and fall of the reproduction signal are caused. The decline slows down.
In this reproducing method, when the isotherm of the temperature at which the domain wall can be moved (domain wall moving temperature) covers the entire domain wall forming the recording domain shape by heating the medium, the domain wall moves and expands the domain. To play the information. Therefore, when the arcuate shape of the domain wall of the recording magnetic domain intersects with the shape of the isotherm of the domain wall moving temperature as shown in FIG. 8, the stage at which the isotherm starts to contact the recording magnetic domain (the isothermal line shown by the solid line in the drawing) Line), the movement of the domain wall and the expansion of the magnetic domain lead to an increase in the domain wall energy,
It will be difficult. When the isotherm moves to the position indicated by the broken line in the figure, the entire domain wall moves. Such a phenomenon can be said not only when recording is performed by the magnetic field modulation recording method but also when recording is performed by the light modulation recording method. Then, in the reproduction of the recording magnetic domain by the magnetic field modulation recording method as shown in FIG. 8, before a sufficient reproduction signal by an arbitrary recording magnetic domain is obtained, a reproduction spot or an isotherm of a domain wall moving temperature is formed in the next recording magnetic domain. Ingress,
The information of the latter recorded magnetic domain is also reproduced, which affects reproduction characteristics.

In view of the above-mentioned problems, an object of the present invention is to provide a magneto-optical recording medium which achieves a higher recording density in accordance with the miniaturization of the recording magnetic domain, and in particular, the reproduction signal quality from the viewpoint of the recording magnetic domain shape. Is achieved.

[0016]

The above object is achieved by the following means.

That is, according to the present invention, in the radial direction of the recording track, the coercive force indicating the stability of storage of the recording magnetic domain of the recording magnetic layer is maximized at or near the center of the recording track, and as the distance from the center increases, This invention proposes a magneto-optical recording medium characterized in that the coercive force gradually decreases, and in the radial direction of the recording track, the recording track surface at or near the center of the recording track is substantially parallel to the back surface of the substrate. As the distance from the center or the vicinity of the center increases, the inclination of the recording track surface with respect to the back surface of the substrate increases, and in the radial direction of the recording track,
By increasing the surface roughness at or near the center of the recording track and decreasing the surface roughness as the distance from or near the center increases, the coercive force increases as the distance from the center or near the center decreases. , Which gradually decreases.

According to the present invention, as shown in FIG. 1, the coercive force indicating the stability of storage of the recording magnetic domain of the recording magnetic layer is maximized at or near the center of the recording track in the radial direction of the recording track. By gradually decreasing the coercive force as the distance increases, it becomes possible to reduce the degree of the arc shape of the recording magnetic domain shape as compared with when the coercive force distribution is not provided.

Therefore, in the reproduction of the recording magnetic domain according to the present invention, in the case of the super-resolution magneto-optical recording / reproducing method, the influence of the signal reproduction by a plurality of recording magnetic domains can be suppressed as shown in FIG. The recording magnetic domain area to be reproduced is larger than in the conventional example, and the signal quality can be improved with an increase in the signal amplitude. In the case of the domain wall displacement magnetic domain expansion reproduction method, as shown in FIG. 9, the influence of signal reproduction by a plurality of recording magnetic domains can also be suppressed, and the rise and fall of the reproduction signal should be steeper than in the conventional example. And improve the signal quality. The effect that the rising and falling edges of the reproduction signal of the present invention obtained by the domain wall displacement magnetic domain expansion reproduction method become steeper also exerts the same effect in the normal reproduction method, and leads to an improvement in signal quality due to an improvement in jitter. .

The formation of the recording magnetic domain having a small degree of arc shape is achieved, for example, by forming a recording film on a substrate having a cross-sectional shape as shown in FIGS. That is, by forming a recording film on a substrate having a cross-sectional shape as shown in FIGS. 2 and 3, the distribution of the coercive force in the radial direction of the recording track has a maximum at or near the center of the recording track. As shown, the coercive force gradually decreases as the distance from the center of the track increases, and a recording magnetic domain having a small degree of arc shape is formed, thereby achieving the object of the present invention.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

[0022]

【Example】

Example 1 FIG. 1 shows a cross-sectional shape of a substrate used in this example.
0 is shown. A stamper for manufacturing a substrate having a sectional shape as shown in FIG. 10 could be manufactured by using a conventional master stamper manufacturing method. However, in order to increase the inclination of the concave portion (so-called groove portion) on the substrate with respect to the back surface of the substrate as the distance from the center or near the center of the radial concave portion of the track increases, the center portion of the concave portion must be The exposure is controlled by adjusting the exposure amount to the end. In the present embodiment, since a positive photoresist made of a quinonediazide-based photosensitizer and a novolak resin was used as the resist layer, the exposure was adjusted so that the exposure amount was gradually reduced from the center to the end of the concave portion of the resist master. A resist master was prepared. A stamper was manufactured from the resist master, and a substrate was manufactured from the stamper.

The substrate used in this example was manufactured by injection molding using polycarbonate (PC). The track pitch is 1.1 μm and the groove depth is 0.3 μm. When a magnetic film is formed on this substrate, it is possible to break magnetic coupling between adjacent recording tracks. The width of the flat portion of the groove portion parallel to the back surface of the substrate is 0.3 μm, and is located near the center of the groove portion. Then, it is inclined with respect to the back surface of the substrate by a width of 0.3 μm outward from the flat portion located near the center of the groove portion. The gradient increases toward the outside of the groove portion. In this embodiment, polycarbonate (PC) is used for the injection molded substrate, but polymethyl methacrylate (PMMA), amorphous polyolefin (APO), or the like may be used as a molding material. Also,
A so-called 2P molded substrate made of an ultraviolet effect resin can also be used.

A recording film as proposed in JP-A-6-290496 was formed on the substrate thus prepared by sputtering. As the recording film, the first
Dielectric layer (SiN), first magnetic layer (GdFe), second magnetic layer (TbFe), third magnetic layer (TbFeC)
o), a second dielectric layer (SiN) is sequentially laminated. As each dielectric layer, besides the above-mentioned dielectric layer, for example, a transparent dielectric material such as AlN, SiO ₂ , SiO, ZnS, MgF ₂ or the like can be used. Each magnetic layer may be made of various magnetic materials including the above magnetic materials. For example, Pr, Nd, Sm, G
One or more rare earth metal elements such as d, Tb, Dy, and Ho are 10 to 40 at%, and Fe, Co,
One or two or more transition metals such as Ni
It can be constituted by a rare earth-transition metal amorphous alloy composed of ９０90% at%. In order to improve corrosion resistance, Cr, Mn, Cu, Ti, Al, Si, Pt,
A small amount of an element such as In may be added.

Information is recorded in the groove portion of the above-described magneto-optical recording medium, and the C / N ratio (carrier level versus noise level) is measured using a measuring device having a heating laser added to the optical system of the magneto-optical disk recording / reproducing device. Ratio) was measured. Recorded information was a laser power of 3.5 mW (λ = 680 nm, NA
= 0.55) while irradiating a laser beam of 20
0 Oe was modulated, and a carrier signal was written at a disk rotation speed of 2 m / sec, a recording frequency of 5 MHz, and 0.2 μm. For information reproduction, λ = 680 nm, NA = 0.5
5. When the laser power is 2 mW, the C of 50 dB
/ N ratio was obtained.

The recording medium recorded with the 0.2 μm mark length was observed for its magnetic domain shape by MFM (magnetic force microscope). From the obtained MFM observation image, the distance from the start position of the recording magnetic domain to the position where the magnetic domain width of the recording magnetic domain shows the maximum value, or the position where the magnetic domain width starts to show the maximum value is d, and the length of the maximum width of the recording magnetic domain width is When 1 (see FIG. 13),
d / 1 × 100 = 6 (%) Example 2 The substrate used in this example was the same as that used in Example 1.

A recording film as proposed in JP-A-6-124500 was formed on the substrate by a sputtering method. As a recording film, a first dielectric layer (Si
N), a first magnetic layer (GdFeCo), a second magnetic layer (TbFeCo), and a second dielectric layer (SiN). As each dielectric layer, in addition to the above-described dielectric layer, for example, AlN, SiO ₂ , SiO, ZnS, Mg
Transparent dielectric material, such as F ₂ can be used. Each magnetic layer may be made of various magnetic materials including the above-described magnetic materials. For example, Pr, Nd, S
one or two or more rare earth metal elements such as m, Gd, Tb, Dy, and Ho are 10 to 40 at%;
One or more transition metals such as Co and Ni may be composed of a rare earth-transition metal amorphous alloy composed of 90 to 60 at%. In addition, Cr, Mn, Cu, Ti, Al, Si,
Elements such as Pt and In may be added in small amounts.

Information was recorded in the groove portion on the above-described magneto-optical recording medium, and the C / N ratio (the ratio of carrier level to noise level) was measured. Recorded information is laser power 3.5m
While irradiating a laser beam of W (λ = 680 nm, NA = 0.55), the external magnetic field 2000e is modulated to generate a carrier signal at a disk rotation speed of 2 m / sec, a recording frequency of 2.5 MHz, and a recording mark length of 0.4 μm. I wrote it. When information was reproduced at λ = 680 nm, NA = 0.55, and laser power of 2 mW, a C / N ratio of 47 dB was obtained.

With respect to the recording medium recorded with the mark length of 0.4 μm, the shape of the recorded magnetic domain was observed by MFM (magnetic force microscope). At this time, d / 1 × 100 = 5 (%). [Embodiment 3] The cross-sectional shape of the substrate used in this embodiment is shown in FIG.
It is shown in FIG. A stamper for manufacturing a substrate having a sectional shape as shown in FIG. 11 can be manufactured by using a conventional master stamper manufacturing method. However, in order to reduce the surface roughness of the concave portion (so-called groove portion) on the substrate as the distance from the center or near the center of the concave portion in the radial direction of the track decreases, the surface roughness (Ra> A large glass master (1 nm) is used, and the exposure is adjusted from the center to the end of the recess. In this embodiment, since a positive type photoresist made of a quinonediazide-based photosensitizer and a novolak resin was used as the resist layer, the exposure was adjusted so that the exposure amount gradually decreased from the center to the end of the concave portion of the resist master. A master was produced. A stamper was manufactured from the resist master, and a substrate was manufactured from the stamper.

The substrate used in this example was manufactured by injection molding using polycarbonate (PC). The track pitch is 1.1 μm and the groove depth is 0.3 μm. When a magnetic film is formed on this substrate, it is possible to break magnetic coupling between adjacent recording tracks. The surface roughness of the groove portion is Ra =
The roughness is the coarsest at 0.95 nm, and the surface roughness gradually decreases to about Ra-0.35 nm toward the outside of the groove portion. In this embodiment, polycarbonate (PC) is used for the injection molded substrate, but polymethyl methacrylate (PMMA), amorphous polyolefin (APO)
Etc. may be used as a molding material. Also, a so-called 2P molded substrate made of an ultraviolet curable resin can be used.

A recording film similar to that of Example 1 was formed on the substrate manufactured as described above, information was recorded in the groove portion, and a heating laser was added to the optical system of the magneto-optical disk recording / reproducing apparatus. The C / N ratio (ratio of carrier level to noise level) was measured using a measuring device. Recorded information was a laser power of 3.5 mW (λ = 680 nm, NA = 0.
55) Apply an external magnetic field of 200
The carrier signal was written by e-modulation at a disk rotation speed of 2 m / sec, a recording frequency of 5 MHz, and a recording mark length of 0.2 μm. Information is reproduced by λ = 680 nm, NA =
48d at 0.55, laser power 2mW
The C / N ratio of B was obtained.

The recording medium recorded with the mark length of 0.2 μm had a recording magnetic domain d / 1 × 100 = 4 (%) by MFM (magnetic force microscope). Example 4 The substrate used in this example was the same as that used in Example 3.

A recording film similar to that of Example 2 was formed on the substrate manufactured as described above, information was recorded in the groove portion, and the C / N ratio (the ratio of carrier level to noise level) was measured. . Recorded information is a laser power of 3.5 mW (λ
(680 nm, NA = 0.55) while modulating the external magnetic field 200 Oe to write a carrier signal at a disk rotation speed of 2 m / sec, a recording frequency of 2.5 MHz, and a recording mark length of 0.4 μm. When information was reproduced at λ = 680 nm, NA = 0.55, and laser power of 2 mW, a C / N ratio of 45 dB was obtained.

With respect to the recording medium recorded with the mark length of 0.4 μm, the shape of the recorded magnetic domain was observed by MFM (magnetic force microscope). At this time, d / 1 × 100 = 28 (%)
Met. Comparative Example 1 A film was formed in the same manner as in Examples 1 and 3, except that a substrate having the cross-sectional shape shown in FIG. 12 was manufactured using a conventional master stamper manufacturing method.
A measurement was made. The track pitch was 1.1 μm and the groove depth was 0.3 μm. At this time, the C / N ratio was 3 dB and d / 1 × 100 = 28 (%). Comparative Example 2 A film was formed in the same manner as in Examples 2 and 4, except that a substrate having the cross-sectional shape shown in FIG. 12 was manufactured using a conventional master stamper manufacturing method.
A measurement was made. The track pitch was 1.1 μm and the groove depth was 0.3 μm. At this time, the C / N ratio was 44 dB and d / 1 × 100 = 27 (%).

[0035]

According to the magneto-optical recording medium of the present invention, in the case of the super-resolution magneto-optical recording / reproducing method, the influence of signal reproduction by a plurality of recording magnetic domains can be suppressed. The area is larger than in the conventional example, and the signal quality can be improved as the signal amplitude increases. In the case of the domain wall displacement magnetic domain expansion reproduction method, the effect of signal reproduction by a plurality of recording magnetic domains can be suppressed, and the rise and fall of the reproduction signal can be made steeper than in the conventional example. Enable improvements.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view and a coercive force distribution diagram of a magneto-optical recording medium showing one example of the present invention.

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

FIG. 3 is a schematic sectional view of a magneto-optical recording medium showing another example of the present invention.

FIG. 4 is a principle diagram of a super-resolution magneto-optical recording / reproducing method.

5 (a) to 5 (c) are principle diagrams of a domain wall moving magnetic domain enlarging reproduction method.

FIG. 6 is an explanatory diagram of a conventional super-resolution magneto-optical recording / reproducing phenomenon of arrow-shaped magnetic domains.

FIG. 7 is an explanatory diagram of a super-resolution magneto-optical recording / reproducing phenomenon of a recording magnetic domain according to the present invention.

FIG. 8 is an explanatory diagram of a domain wall moving magnetic domain expansion reproduction phenomenon of a conventional arrow feather-shaped magnetic domain.

FIG. 9 is an explanatory view of a domain wall moving magnetic domain expansion reproduction phenomenon of a storage magnetic domain according to the present invention.

FIG. 10 is a schematic cross-sectional view of a substrate used for a magneto-optical recording medium of Examples 1 and 2.

FIG. 11 is a schematic cross-sectional view of a substrate used for a magneto-optical recording medium of Examples 3 and 4.

FIG. 12 is a schematic cross-sectional view of a substrate used for a magneto-optical recording medium of Comparative Examples 1 and 2.

FIG. 13 is a top view of a recording magnetic domain.

Claims (3)

[Claims] In the radial direction of a recording track, the coercive force indicating the stability of recording magnetic domain preservation of the recording magnetic layer is maximized at or near the center of the recording track, and as the distance from the center increases, the coercive force increases. A magneto-optical recording medium characterized by becoming gradually smaller. 2. The recording track surface at or near the center of the recording track in the radial direction of the recording track is substantially parallel to the back surface of the substrate, and the recording track surface increases as the distance from the center or near the center increases. 2. The magneto-optical recording medium according to claim 1, wherein the tilt of the magneto-optical recording medium with respect to the back surface of the substrate increases. 3. The recording track according to claim 1, wherein the surface roughness at the center or near the center of the recording track is maximized in the radial direction of the recording track, and the surface roughness decreases as the distance from the center or near the center increases. Magneto-optical recording medium.