JPH103702A - Magneto-optical recording medium and its reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to make a linear recording density and the recording density in a radial direction to be high regardless of the numerical aperture of a lens and the laser wavelength of a reproduction optical system and to enable sufficient correspondence to the higher recording density. SOLUTION: First and second magneto-optical recording films 3, 5 which consist of amorphous alloys of rare earth metal-transition metals and have the axes of easy magnetization in a direction perpendicular to the film planes are laminated via a second dielectric substance film 4 on a transparent substrate 1. These magneto-optical recording films are so formed as to have the relation Tr <Tcomp1 <Tc2 when the compensation temp. of the second magneto-optical recording film 5 is defined as room temp. or below, the Curie temp. thereof as Tc2 , the compensation temp. of the first magneto- optical recording film 3 as Tcomp1 and the room temp. as Tr . The film thickness of the second magneto-optical recording film 5 is specified to >=15nm, the film thickness of the first magneto-optical recording film 3 to 3 to 15nm and the film thickness of the first dielectric substance film 4 to 1 to 15nm. The magnetization at the room temp. of the second magneto-optical recording film 5 is preferably specified to >=50emu/ cc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magneto-optical recording medium having a plurality of magneto-optical recording films and a reproducing method therefor. More specifically, the present invention relates to a magneto-optical recording medium capable of increasing the recording density by controlling the direction of the partial magnetization of each magneto-optical recording film, and a reproducing method therefor.

[0002]

2. Description of the Related Art As a rewritable recording medium, the thermal energy of a semiconductor laser is used to partially raise the temperature of a magnetic thin film beyond the Curie point or a compensation temperature, and the coercive force in this portion is extinguished to apply externally. There is a magneto-optical recording medium in which information is recorded by reversing the direction of magnetization in the direction of a recording magnetic field to be read, and the information is read out using a magneto-optical effect.

This magneto-optical recording medium has a magneto-optical recording film having an easy axis of magnetization in a direction perpendicular to the film surface on one main surface side of a transparent substrate made of, for example, transparent polycarbonate and having excellent magneto-optical characteristics. In general, a recording section is formed by laminating a recording layer, a reflection layer, and a dielectric film. The magneto-optical recording film is generally a rare earth metal-transition metal amorphous alloy thin film.

In order to reproduce the information signal of such a magneto-optical recording medium, a laser beam is irradiated from the transparent substrate side as reproduction light, and the phenomenon that the polarization plane of the laser light is rotated by the magneto-optical recording film is performed. To detect. The case where the rotation of the polarization plane is viewed by reflected light is called a Kerr effect, and this rotation angle is called a Kerr rotation angle.

[0005]

By the way, not only in the above-described magneto-optical recording medium but also in an optical recording medium such as a digital audio disk and a video disk,
High recording density is required.

As one means for increasing the recording density, there is a method of improving the linear recording density. However, this linear recording density is mainly determined by the SN ratio at the time of reproduction, and there is a limit.

As another means for increasing the recording density, there is a method of shortening the period of a pit row representing information.
At present, the pit period f serving as the detection limit is determined by the following equation (1).

F = λ / 2N. A. (Equation 1) In Equation 1, λ represents the laser wavelength of the reproducing optical system.
A. Denotes the numerical aperture of the objective lens.

That is, in order to increase the recording density,
The wavelength λ of the laser light of the reproducing optical system is shortened, and the numerical aperture N.P. A. Must be increased, but these improvements have their limitations. The signal amount of the reproduced signal greatly depends on the period of the pit row of the recorded information signal, the laser wavelength of the reproducing optical system, and the numerical aperture of the objective lens.

Further, as one of means for increasing the recording density, a method of reducing the recording density in the radial direction of the optical recording medium can be considered. Is highly likely to be read out at the same time, and the SN ratio of the reproduced signal is lowered, which is not preferable.

Therefore, the present invention has been proposed in view of the conventional situation, and the linear recording density and the radial recording density can be increased regardless of the numerical aperture of the lens or the laser wavelength of the reproducing optical system. It is an object of the present invention to provide a magneto-optical recording medium which is made possible and which can sufficiently cope with high recording density and a reproducing method therefor.

[0012]

In a rare earth metal-transition metal amorphous alloy generally used as a material for a magneto-optical recording film, the overall magnetization direction is the same as the partial magnetization of the transition metal in the opposite direction. It is observed as a difference in partial magnetization of rare earth metals. That is, the direction of the entire magnetization matches the direction of the partial magnetization of the transition metal (so-called transition metal-dominant magnetization state) or the direction of the partial magnetization of the rare earth metal (so-called rare-earth metal dominant magnetization state). Will be done. In addition, since the partial magnetization of the rare earth metal is more dependent on temperature than the partial magnetization of the transition metal, depending on the composition of the alloy, the entire magnetization direction may be changed from the direction of the partial magnetization of the rare earth metal to the partial magnetization of the transition metal. There may be a temperature that is reversed in the direction, a so-called compensation temperature.

Further, when, for example, two magneto-optical recording films are laminated via a dielectric film, only when the direction of the partial magnetization of the transition metal in the upper and lower magneto-optical recording films is parallel, The magneto-optical recording film can cause a phenomenon of rotating the plane of polarization of light. This is the same even when two or more magneto-optical recording films are formed.

When two layers of magneto-optical recording films are stacked with a dielectric film interposed therebetween, the directions of the magnetizations thereof are made uniform in the same direction by magnetostatic coupling.
Therefore, the upper and lower layers are in a transition metal dominant magnetization state, and if the entire magnetization direction matches the direction of the partial magnetization of the transition metal in both the upper and lower layers, the direction of the partial magnetization of the transition metal in the upper and lower layers is aligned in the same direction. Are parallel to each other, and the above-mentioned phenomenon can be caused, and a sufficient signal amount can be obtained. Conversely, if one is a transition metal dominant magnetized state and the other is a rare earth metal dominant magnetized state, the direction of the partial magnetization of the transition metal in the upper and lower layers is in the opposite direction, becomes antiparallel, and causes the above phenomenon. Is substantially difficult, and a sufficient signal amount cannot be obtained.

Therefore, the present inventors have found out the following contents in consideration of the above.

That is, in a magneto-optical recording medium in which a plurality of magneto-optical recording films are laminated on a transparent substrate with a dielectric film interposed therebetween, a material having a compensation temperature lower than room temperature may be used as the uppermost magneto-optical recording film. And a transition metal dominant magnetization state at a temperature equal to or higher than room temperature, so that the direction of the entire magnetization coincides with the direction of the partial magnetization of the transition metal, and magneto-optical recording other than the uppermost magneto-optical recording film The film is formed from a material having a compensation temperature equal to or higher than room temperature, and only at the temperature equal to or higher than the compensation temperature, the magneto-optical recording film other than the magneto-optical recording film, which is the uppermost layer, becomes a transition metal-dominant magnetization state, and the direction and transition of the entire magnetization The direction of the partial magnetization of the metal is made to match.

As described above, in a magneto-optical recording film having a plurality of layers laminated with a dielectric film interposed therebetween, the direction of the entire magnetization is aligned in the same direction by magnetostatic coupling. At this time, in the magneto-optical recording medium, at a temperature lower than the compensation temperature of the magneto-optical recording film other than the magneto-optical recording film serving as the uppermost layer,
The overall magnetization direction of the uppermost magneto-optical recording film coincides with the direction of the partial magnetization of the transition metal, and the other magnetization directions of the magneto-optical recording film are the same as the direction of the partial magnetization of the rare earth metal. Matches. As a result, the directions of the partial magnetizations of the transition metals of these magneto-optical recording films are not aligned and are antiparallel. On the other hand, at a temperature equal to or higher than the compensation temperature of the magneto-optical recording film other than the magneto-optical recording film as the uppermost layer, the overall magnetization direction of the magneto-optical recording film as the uppermost layer is the same as the direction of the partial magnetization of the transition metal. The direction of the entire magnetization of the magneto-optical recording film also coincides with the direction of the partial magnetization of the transition metal. As a result, the directions of the partial magnetizations of the transition metals of these magneto-optical recording films are aligned and parallel.

Therefore, when the reproducing light is irradiated from the substrate side to reproduce the information of the magneto-optical recording medium, the compensation temperature of the magneto-optical recording film other than the uppermost magneto-optical recording film in the spot of the reproducing light. Only in the portion having the above temperature, the direction of the partial magnetization of the transition metal of the laminated magneto-optical recording film becomes parallel, and information can be sufficiently reproduced only in this portion. This indicates that the temperature of the region where the temperature is equal to or higher than the compensation temperature of the magneto-optical recording film other than the magneto-optical recording film serving as the uppermost layer and the compensating temperature of the magneto-optical recording film other than the magneto-optical recording film serving as the uppermost layer in the reproduction light. The reproducible range can be determined according to the size, and it is possible to sufficiently cope with high-density recording.

That is, the magneto-optical recording medium of the present invention comprises a rare earth metal-transition metal amorphous alloy on a transparent substrate,
A magneto-optical recording film having a plurality of layers having an easy axis of magnetization perpendicular to the film surface is laminated via a dielectric film, and the compensation temperature of the uppermost magneto-optical recording film is lower than room temperature. the Curie temperature of the magnetic recording film T _c2, other compensation temperature of the magneto-optical recording film T _comp1, when the room temperature and T _r,
T _r <T _comp1 <T _c2 , the thickness of the uppermost magneto-optical recording film is 15 nm or more, and the thickness of the other magneto-optical recording films is 3 nm to 15 nm.
The thickness of the dielectric film is 1 nm to 15 nm.

In the magneto-optical recording medium of the present invention, the magnetization at room temperature of the magneto-optical recording film as the uppermost layer is 50.
It is preferably at least emu / cc.

The reproducing method of the present invention is a reproducing method of reproducing information by irradiating the magneto-optical recording medium of the present invention with reproducing light from the transparent substrate side. In the temperature range _lower than the compensation temperature T _comp1 of the magneto-optical recording film other than the magneto-optical recording film, the direction of the partial magnetization of the transition metal in the magneto-optical recording film as the uppermost layer and the The direction of the partial magnetization of the transition metal in at least one layer is antiparallel, and the uppermost layer of the magneto-optical recording film other than the uppermost layer of the reproducing light has a compensation temperature T _comp1 or higher. In the portion where the temperature of the recording film is equal to or lower than the Curie temperature T _c2 ,
The direction of the partial magnetization of the transition metal in the magneto-optical recording film as the uppermost layer is parallel to the direction of the partial magnetization of the transition metal in at least one of the other magneto-optical recording films. It is characterized in that the rotation of the polarization plane is detected and the information of the magneto-optical recording film as the uppermost layer is reproduced.

When information is reproduced in this manner, it is preferable to suppress an external magnetic field at least in the vicinity of the spot of the reproduction light so as not to hinder the magnetostatic coupling of the plurality of magneto-optical recording films. .

In the magneto-optical recording medium of the present invention, by interposing a dielectric film between a plurality of magneto-optical recording films,
The direction of the magnetization of the entire stacked magneto-optical recording film is aligned in the same direction by magnetostatic coupling.

Therefore, in the magneto-optical recording medium of the present invention, if the thickness of the magneto-optical recording film as the uppermost layer is less than 15 nm, a sufficient magnetostatic coupling force is generated with respect to other magneto-optical recording films. Becomes difficult, which is not preferable.

Further, in the magneto-optical recording medium of the present invention,
It is difficult to make the thickness of the magneto-optical recording film other than the magneto-optical recording film to be less than 3 nm less than 3 nm. This is not preferable because the interaction cannot be sufficient.

Further, the thickness of the dielectric film is set to 1 nm to 15 n.
Outside the range of m, it is difficult to exert a sufficient magnetostatic coupling force between a plurality of laminated magneto-optical recording films, which is not preferable.

In the magneto-optical recording medium of the present invention, the material for forming the uppermost magneto-optical recording film is as follows.
A rare earth metal-transition metal amorphous alloy containing at least Tb and Fe is preferable, and other materials for forming the magneto-optical recording film are rare earth metals containing at least Gd and Fe.
Transition metal amorphous alloys are preferred.

In the magneto-optical recording medium of the present invention, a magneto-optical recording film composed of a rare earth metal-transition metal amorphous alloy on a transparent substrate and having an easy axis of magnetization perpendicular to the film surface is formed of a dielectric material. The compensation temperature of the uppermost magneto-optical recording film is lower than room temperature, the Curie temperature of the magneto-optical recording film is T _c2 , and the compensation temperature of the other magneto-optical recording films is T _comp1, when the room temperature and T _r, T _r <T
_comp1 <to have a relation of T _c2, and the thickness of the magneto-optical recording film comprising a top layer and above 15 nm, which other film thickness of the magneto-optical recording film and 3 nm to 15 nm, thickness of the dielectric film Is set to 1 nm to 15 nm, the overall magnetization directions of the uppermost magneto-optical recording film and the other magneto-optical recording films are aligned in the same direction by magnetostatic coupling.

In order to reproduce the information on the magneto-optical recording medium, even if the reproducing light is irradiated from the substrate side, compensation of the magneto-optical recording film other than the uppermost magneto-optical recording film in the spot of the reproducing light is performed. At a temperature lower than the temperature, the uppermost magneto-optical recording film shows a transition metal-dominant magnetization state, and the other magneto-optical recording films show a rare earth metal-dominant magnetization state. The direction of the overall magnetization of the recording film matches the direction of the partial magnetization of the transition metal, and the direction of the overall magnetization of the other magneto-optical recording film matches the direction of the partial magnetization of the rare earth metal. . That is, the direction of the partial magnetization of the transition metal of these magneto-optical recording films is antiparallel, and in this portion, the rotation phenomenon of the polarization plane of the reproduction light is not substantially detected, and specifically, the apparent Since there is no temporal change in the car rotation angle, a sufficient signal amount cannot be obtained, and information is not reproduced.

On the other hand, in a portion of the reproduction light spot other than the uppermost layer of the magneto-optical recording film other than the compensation temperature of the magneto-optical recording film, the uppermost layer of the magneto-optical recording film changes the magnetization state in which the transition metal dominates. Since the other magneto-optical recording films also show the transition metal dominant magnetization state, the direction of the overall magnetization of the uppermost magneto-optical recording film and the direction of the partial magnetization of the transition metal match, Other directions of the magnetization of the magneto-optical recording film and the direction of the partial magnetization of the transition metal coincide with each other.
That is, the direction of the partial magnetization of the transition metal of these magneto-optical recording films is parallel, and the rotation phenomenon of the polarization plane of the reproduction light is detected only in this portion. A sufficient signal amount is obtained by reading as a change, and information is reproduced.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings. Here, an example of a magneto-optical recording medium having a two-layer magneto-optical recording film will be described.

As shown in FIG. 1, the magneto-optical recording medium of the present embodiment has a first dielectric film 2 on one main surface 1a side of a transparent substrate 1.
The first magneto-optical recording film 3, the second dielectric film 4, the second magneto-optical recording film 5, the third dielectric film 6, and the reflective film 7 are sequentially laminated.

The transparent substrate 1 may be any material as long as it is used as a substrate for this type of magneto-optical recording medium, such as transparent polycarbonate or glass.

The first dielectric film 2 may be formed of a material used for a dielectric film of this type of magneto-optical recording medium, such as silicon nitride, and its thickness is, for example, about 80 nm. good.

Further, the third dielectric film 6 may be formed of a material used for the dielectric film of this type of magneto-optical recording medium, such as silicon nitride, and has a thickness of, for example, 20 nm.
It should just be about.

Further, the reflective film 31 may be formed of a material such as aluminum which is used for a reflective film of this type of magneto-optical recording medium, and its thickness may be, for example, about 60 nm.

In the magneto-optical recording medium of the present embodiment, the first magneto-optical recording film 3 is formed of a rare earth metal-transition metal amorphous alloy having a compensation temperature equal to or higher than room temperature. The range is 15 nm, for example, 9 nm.

Further, the second magneto-optical recording film 5 serving as the uppermost layer
Is formed of a rare earth metal-transition metal amorphous alloy having a compensation temperature lower than room temperature, and has a thickness of 15 nm or more, for example, 20 nm.

Then, the rare earth metal-transition metal amorphous alloy forming the first magneto-optical recording film 3 is _cured by setting the Curie temperature of the second magneto-optical recording film 5 as the uppermost layer to T _c2 , the compensation temperature of the magneto-optical recording film 3 T _comp1, when the room temperature and T _r, assumed to have a relation of _{T r <T comp1 <T c2} . Further, the magnetization at room temperature of the second magneto-optical recording film 5 as the uppermost layer is set to 50 emu / cc or more. The rare earth metal forming the first magneto-optical recording film 3
The transition metal amorphous alloy preferably contains at least Gd and Fe, and the second magneto-optical recording film 5 preferably contains at least Tb and Fe.

Further, the first magneto-optical recording film 3, the second
The second dielectric film 4 sandwiched between the magneto-optical recording films 5 may be formed of a material used for a dielectric film of this type of magneto-optical recording medium, such as silicon nitride, and has a thickness of 1 nm to 1 nm.
The range may be 5 nm, for example, 5 nm.

In order to reproduce information from the magneto-optical recording medium of this embodiment, a reproducing light such as a laser beam is made incident from the transparent substrate 1 side, and the reproducing light is transmitted through the first and second magneto-optical recording films 3 and 5. Is detected as a temporal change of the apparent Kerr rotation angle.

At this time, in the magneto-optical recording medium of the present embodiment, the first magneto-optical recording film 3 is formed of a material having a compensation temperature of room temperature or higher, and the compensation temperature T is higher than room temperature.
_At a temperature lower than _comp1 , the first magneto-optical recording film 3 shows a rare-earth metal-dominant magnetization state, the overall magnetization direction matches the direction of the rare-earth metal partial magnetization, and the compensation temperature T _comp1 At the above temperature, the first magneto-optical recording film 3 shows a transition metal-dominant magnetization state, and the direction of the entire magnetization coincides with the direction of the partial magnetization of the transition metal. Since the second magneto-optical recording film 5, which is one of the uppermost layers, is formed of a material having a compensation temperature lower than room temperature,
If the temperature is equal to or higher than the room temperature, the transition metal is predominantly magnetized regardless of the temperature, and the direction of the entire magnetization coincides with the direction of the partial magnetization of the transition metal.

In the magneto-optical recording medium of this embodiment,
Since the second dielectric film 4 is disposed between the first magneto-optical recording film 3 and the second magneto-optical recording film 5, the first magneto-optical recording film 3 and the second magneto-optical recording The overall magnetization direction of the film 5 is aligned in the same direction by magnetostatic coupling.

Therefore, when the magneto-optical recording medium of this embodiment is irradiated with the reproducing light, the first and second magneto-optical recording films 3 and 3 are formed at a temperature _lower than the compensation temperature T _comp1 as shown in FIG. 5, the partial magnetizations of the transition metals indicated by arrows M ₁ and M ₂ are not aligned in the same direction, are antiparallel, and have a compensation temperature T _comp1.
Only in the portions having the above temperatures, as shown in FIG. 1, arrows M ₁ ,
The partial magnetizations of the transition metal indicated by M ₂ are aligned in the same direction and become parallel.

FIG. 3 schematically shows this as a whole. In the magneto-optical recording medium of this example, since the second magneto-optical recording film 5 exhibits a transition metal-dominant magnetization state regardless of the temperature at room temperature or higher, the second magneto-optical recording film 5 On the other hand, information is recorded by a combination of a transition metal dominant magnetization state indicated by an upward arrow in a frame having dots and a transition metal dominant magnetization state indicated by a downward arrow having a hatching in the frame. The recording mark 8 indicating information is the magnetization indicated by an upward arrow.

Then, the transparent substrate 1 is placed on the magneto-optical recording medium.
When the reproduction light is irradiated from the side and the reproduction light spot 9 is aligned with the recording mark 8,
At a temperature _{equal to} or higher than the compensation temperature T _{comp1 of} the first magneto-optical recording film 3, the second
Second heating portion 9b is formed of not heated only to a first heating part 9a and a temperature below the compensation temperature T _comp1 which is heated to a temperature below the Curie temperature T _c2 of the magneto-optical recording film 5. The reason why the intensity of the reproducing light spot is adjusted as described above is to prevent the information recorded on the second magneto-optical recording film 5 from being erased by the reproducing light.

At this time, since the first magneto-optical recording film 3 shows a magnetized state in which the rare earth metal is dominant or a transition metal is dominant depending on the temperature, as shown in FIG. 9 and the second heating portion 9b in the reproduction light spot 9, the rare earth metal dominant magnetization state indicated by an upward arrow in the frame and the downward arrow having a hatching in the frame having dots. There is a rare earth metal dominant magnetization state noted.

In the first magneto-optical recording film 3, the first heating portion 9a of the reproducing light spot 9
There is a transition metal dominant magnetization state marked by an upward arrow in the frame with dots and a transition metal dominant magnetization state marked by a down arrow with hatching in the frame.

Further, as described above, the overall magnetization directions of the first magneto-optical recording film 3 and the second magneto-optical recording film 5 are aligned in the same direction by magnetostatic coupling.

That is, in the portion where the reproduction light spot 9 is not irradiated and the second heated portion 9b of the reproduction light spot 9 which is a temperature _lower than the compensation temperature T _comp1 , the first magneto-optical recording film 3 has an overall structure. The direction of the magnetization matches the direction of the partial magnetization of the rare-earth metal, and in the second magneto-optical recording film 5, the direction of the overall magnetization matches the direction of the partial magnetization of the transition metal. Therefore, in these portions, it is impossible to detect a substantial rotation of the polarization plane of the reproduction light, specifically, a temporal change of the apparent Kerr rotation angle, and a sufficient signal amount cannot be obtained. It is impossible to reproduce information recorded on the second magneto-optical recording film 5.

On the other hand, in the first heated portion 9a of the reproducing light spot 9 having a temperature _{equal to} or higher than the compensation temperature T _{comp1 and lower} than the Curie temperature T _{c2 of} the second magneto-optical recording film 5, the first magneto-optical recording is performed. In the film 3, the direction of the overall magnetization coincides with the direction of the partial magnetization of the transition metal, and also in the second magneto-optical recording film 5, the direction of the overall magnetization coincides with the direction of the partial magnetization of the transition metal. Therefore, in this part, the rotation of the polarization plane of the reproduction light, specifically, the temporal change of the Kerr rotation angle is detected,
A sufficient signal amount is obtained, and the information recorded on the second magneto-optical recording film 5 is reproduced.

Therefore, when the reproducing light spot 9 is scanned on the magneto-optical recording medium of the present embodiment as shown by the arrow m in the figure, the recording mark 8 becomes the first heating portion 9a in the reproducing light spot 9.
The information of the recording mark 8 is reproduced only when the recording mark 8 is entered.

That is, in the magneto-optical recording medium of this embodiment, the readable area has a compensation temperature and a temperature not lower than the compensation temperature in the spot of the reproduction light regardless of the numerical aperture of the lens or the laser wavelength of the reproduction optical system. It is determined by the size of the area, and the effective spot diameter can be reduced by masking unnecessary parts in the spot, preventing the mixing of unnecessary leakage signals, improving the resolution, and affecting the crosstalk. Can be removed. Therefore, it is possible to reproduce a signal having a period equal to or less than the diffraction limit of light without requiring signal processing such as maximum likelihood compounding or an external magnetic field at the time of reproduction, thereby increasing the linear recording density and the radial recording density. Is possible,
It can sufficiently cope with high recording density.

Further, since information is reproduced from the magneto-optical recording medium of the present embodiment by the above-described method, information can be reproduced at a high SN ratio even when high-density recording is performed.

Furthermore, unlike a conventional magneto-optical recording medium having a plurality of magneto-optical recording films, the information of the uppermost magneto-optical recording film is transferred to another magneto-optical recording film, and the transferred light is recorded. Since the information on the magnetic recording film is not reproduced, the thickness of the magneto-optical recording film other than the magneto-optical recording film, which is the uppermost layer, can be made relatively thin, and the thickness of the entire magneto-optical recording medium can be reduced. Since it can be made relatively thin, productivity is also improved.

[0056]

EXAMPLES Next, in order to confirm the effects of the present invention, the following experiments were conducted.

Experimental Example 1 First, the relationship between the direction of the partial magnetization of the transition metal of the magneto-optical recording film and the apparent Kerr rotation angle of the polarization plane of the reproduction light was investigated. That is, the first of the magneto-optical recording medium as described above
The magneto-optical recording medium is manufactured by changing the film thickness of the magneto-optical recording film of Example 1. In each magneto-optical recording medium, the direction of the partial magnetization of the transition metal of the first magneto-optical recording film and the second magneto-optical recording film is changed. Are parallel and anti-parallel, the apparent Kerr rotation angle of the polarization plane of the reproduction light and a figure of merit obtained by multiplying the Kerr rotation angle by the reflectance are obtained by a computer.

At this time, the value of the complex refractive index of the first and second magneto-optical recording films for the reproduction light having a wavelength of 780 nm is N ₊ (= n ₊ + ik) for the clockwise circularly polarized light.
₊ ) And N ₋ (= n ₋ + ik) for left-handed circularly polarized light.
_- ), The values shown in Table 1 were used according to the magnetization state. In Table 1, the direction toward the transparent substrate is referred to as downward, and the direction toward the reflective film is referred to as upward.

[0059]

[Table 1]

FIG. 4 shows the results. In FIG. 4, the horizontal axis represents the thickness of the first magneto-optical recording film, and the vertical axis represents an arbitrary unit. Further, the solid line in FIG. 4 indicates the Kerr rotation angle when the direction of the partial magnetization of the transition metal of the first and second magneto-optical recording films is parallel,
The broken line in FIG. 4 indicates the figure of merit in this case, and the dashed line in FIG. 4 indicates the Kerr rotation angle when the direction of the partial magnetization of the transition metal of the first and second magneto-optical recording films is antiparallel. 4 show the figure of merit in this case.

As is clear from the results shown in FIG. 4, when the thickness of the first magneto-optical recording film is a certain value, the transition metals of the first and second magneto-optical recording films have parallel magnetization directions. Indicates a Kerr rotation angle of a certain magnitude, and when the direction of the partial magnetization of the transition metal of the first and second magneto-optical recording films is antiparallel, the apparent Kerr rotation angle becomes substantially zero. It turns out that it is. Although the thickness of the first magneto-optical recording film may be changed in design depending on the thickness conditions of other films, it is preferably in the range of 3 nm to 15 n in the present invention.
It is considered that the range of m can cover the conditions in various magneto-optical recording media.

That is, when reproducing information from the magneto-optical recording medium of the present invention, if a heated region having a temperature equal to or higher than the compensation temperature at which the direction of the partial magnetization of the transition metal is aligned in the reproduced light spot,
It was confirmed that information was reproduced only in this area.

Experimental Example 2 Next, the relationship between the recording magnetic domain diameter (recording magnetic domain diameter) for recording information on the magneto-optical recording film as the uppermost layer and the strength of the leakage magnetic field generated from this recording magnetic domain was examined. That is,
The thickness of the second dielectric film of the magneto-optical recording medium having the above-described configuration is set to 5 nm, and the thickness of the second magneto-optical recording film is set to 20 nm.
nm, and the magnetization of the second magneto-optical recording film at room temperature was 100 emu / cc. Then, the leakage magnetic field at a predetermined recording magnetic domain diameter in the second magneto-optical recording film was calculated by changing the recording magnetic domain diameter. Equation 1 shows the calculation formula of the leakage magnetic field.

[0064]

(Equation 1)

FIG. 5 shows the results. In FIG. 5, the horizontal axis indicates the recording magnetic domain diameter (radius from the center of the recording magnetic domain), and the vertical axis indicates the leakage magnetic field. The curve indicated by A in FIG. 5 shows the result when the recording magnetic domain diameter in the second magneto-optical recording film is 0.2 μm, and the curve indicated by B in FIG. 5 shows the result when the recording magnetic domain diameter is 0.5 μm, and the curve indicated by C in FIG. 5 shows the result when the recording magnetic domain diameter in the second magneto-optical recording film is 1 μm, and the curve indicated by D in FIG. Shows the results when the recording magnetic domain diameter in the second magneto-optical recording film is 2 μm.

As can be seen from the results shown in FIG. 5, it was confirmed that the smaller the recording magnetic domain diameter, the stronger the leakage magnetic field can be obtained. The coercive force of the first magneto-optical recording film is no more than 20
Since it was about 00 Oe, it was confirmed that the magnetic domain information was sufficiently transferred to the first magneto-optical recording film even when the recording magnetic domain diameter was relatively large, 2 μm.

That is, in the magneto-optical recording medium of the present invention, the overall magnetization directions of the first and second magneto-optical recording films are aligned in the same direction by magnetostatic coupling, and Was sufficiently transferred to the first magneto-optical recording film.

Experimental Example 3 Next, the relationship between the temperature and the apparent Kerr rotation angle in an actual magneto-optical recording medium was investigated. That is, a glass substrate is used as a transparent substrate, and a 80-nm-thick silicon nitride film (refractive index: 1.92) is formed thereon as a first dielectric film.
Was formed by sputtering, the rare earth metals were simultaneously sputtered film thickness 9nm of Gd and Fe ₈₀ Co ₂₀ alloy as the first magnetooptical recording film - forming a transition metal amorphous alloy film, further a second dielectric film the silicon nitride film having a film thickness of 5nm is formed by sputtering, the second thickness 20nm as a magneto-optical recording film Tb and Fe ₈₀ Co ₂₀ alloy simultaneously sputtered rare earth metals as - to form a transition metal amorphous alloy film And a third dielectric film thereon having a thickness of 2
A 0-nm silicon nitride film was formed by sputtering, and finally a 60-nm-thick aluminum film was formed as a reflective film by sputtering to manufacture a magneto-optical recording medium having the above-described configuration. The composition of the rare earth metal-transition metal amorphous alloy forming the first magneto-optical recording film has a compensation temperature of 120 ° C.

Then, while changing the temperature of this magneto-optical recording medium, the apparent change in the Kerr rotation angle when the transparent substrate was irradiated with reproduction light having a wavelength of 780 nm was measured.
FIG. 6 shows the results. 6, the horizontal axis indicates the magneto-optical recording medium temperature, and the vertical axis indicates the apparent Kerr rotation angle. Needless to say, no external magnetic field was applied during the measurement.

As is clear from the results shown in FIG. 6, in the temperature range lower than 120 ° C., which is the compensation temperature of the rare earth metal-transition metal amorphous alloy forming the first magneto-optical recording film,
The Kerr rotation angle was zero, and it was confirmed that the rotation of the polarization plane of the reproduction light was not substantially detected.

On the other hand, in the temperature range of 120 ° C. or more of the compensation temperature of the rare earth metal-transition metal amorphous alloy forming the first magneto-optical recording film, the Kerr rotation angle becomes a certain value,
It was confirmed that the rotation phenomenon of the polarization plane of the reproduction light was sufficiently detected.

That is, in a temperature range of less than 120 ° C. of the compensation temperature of the first magneto-optical recording film, the first magneto-optical recording film shows a rare earth metal-dominant magnetization state, and the second magneto-optical recording film shows a transition state. Since the magnetization state is dominated by the metal, the direction of the partial magnetization of the transition metal becomes antiparallel, and it was confirmed that information could not be reproduced. At the same time, when the compensation temperature of the first magneto-optical recording film is equal to or higher than 120 ° C., the first magneto-optical recording film shows a transition metal-dominant magnetization state, and the second magneto-optical recording film also has a transition metal-dominant state. In this case, the direction of partial magnetization of the transition metal became parallel, and it was confirmed that information could be reproduced.

FIG. 7 shows the result of investigation of the coercive force-magnetization curve at room temperature of the second magneto-optical recording film of this magneto-optical recording medium. The horizontal axis in FIG. 7 indicates external magnetization,
The vertical axis indicates magnetization.

As is apparent from the results shown in FIG. 7, even when the external magnetization is zero, the residual magnetization is more than ± 200 emu / cc even when the measurement offset is taken into consideration. It was confirmed that it had a sufficient size.

Accordingly, from the above results, in the magneto-optical recording medium of the present invention, when the reproducing light is irradiated from the transparent substrate side, the temperature is lower than the compensation temperature of the magneto-optical recording film other than the magneto-optical recording film as the uppermost layer. The rotation of the polarization plane of the reproduction light is substantially not detected in the region where the temperature of the reproduction light is detected, and the reproduction of the information is impossible. The phenomenon is sufficiently detected, the information can be reproduced, and the compensating temperature of the magneto-optical recording film other than the magneto-optical recording film having the reproducible area as the uppermost layer and the magneto-optical recording as the uppermost layer in the spot of the reproduction light. It is determined by the size of the area where the temperature is equal to or higher than the compensation temperature of the magneto-optical recording film other than the film, and the linear recording density and the radial recording density can be increased, and it is possible to sufficiently cope with the high recording density. It was confirmed that there was.

Experimental Example 4 Next, thermomagnetic recording was performed on a magneto-optical recording medium to which the present invention was applied, and this was reproduced to evaluate a reproduced signal. In addition,
In this experimental example, a polycarbonate substrate in which guide grooves having a period of 0.95 μm are spirally formed was used as a substrate, and a silicon nitride film having a thickness of 80 nm (refractive index: 1) was formed thereon as a first dielectric film. .92) by sputtering, and a thickness of 8.5 nm as a first magneto-optical recording film.
Of Gd and Fe ₈₀ Co ₂₀ alloy simultaneously sputtered rare earth metal - transition metal amorphous alloy film is formed, further the silicon film having a film thickness of 3nm is formed by sputtering as the second dielectric film, a second light Film thickness 2 as magnetic recording film
At the same time sputtered rare earth metal Tb and Fe ₈₀ Co ₂₀ alloy 0 nm - transition metal amorphous alloy film is formed, a third dielectric film as film thickness 27nm of silicon nitride film is formed by sputtering thereon, Finally, a 50 nm-thick aluminum film was formed as a reflective film by sputtering to manufacture a magneto-optical recording medium having the above-described structure. The composition of the rare earth metal-transition metal amorphous alloy forming the first magneto-optical recording film has a compensation temperature of 130 ° C.

Next, the magneto-optical recording medium is set to a laser wavelength of 6
The evaluation was performed using a differential detection optical system having an objective lens of 85 nm and a numerical aperture of 0.55. That is, while applying a magnetic field having a strength of 24 kA / m perpendicularly to the surface of the magneto-optical recording medium, D
After irradiating a C laser beam with an intensity of 6 mW to initialize the magnetization information of the magneto-optical recording film (hereinafter referred to as erasing), 24
What is the time of erasing at a linear velocity of 5 m / s while applying a magnetic field of kA / m perpendicular to the surface of the magneto-optical recording medium and turning on / off a DC laser beam at a peak intensity of 8 mW. Irradiation was performed by scanning in the reverse direction, and a single-frequency carrier signal was recorded as information on the magneto-optical recording film.

FIG. 8 shows a plot of the carrier signal level to noise ratio (hereinafter referred to as CNR) of the recorded information with respect to the spatial frequency (1 / (mark length × 2)). The vertical axis indicates CNR, the horizontal axis indicates spatial frequency, and the results are indicated by solid lines. At this time, the setting of the spectrum analyzer used for the measurement was such that the resolution bandwidth was 30 k.
Hz and the video bandwidth is 10 Hz. For comparison, the CNR with respect to the spatial frequency of the current standard magneto-optical recording medium is also shown by a broken line in FIG.

The cut-off spatial frequency of this optical system is 1.7 × 10 ⁶ / m. Comparing the CNR at this value, the magneto-optical recording medium to which the present invention is applied is the current standard magneto-optical medium. The value is larger than that of the recording medium, and it can be seen that the signal is obtained even in the optical frequency band. That is, it was confirmed that in the magneto-optical recording medium to which the present invention was applied, it was possible to increase the density in the linear recording density direction.

Experimental Example 5 Subsequently, the amount of leakage from adjacent signals in the magneto-optical recording medium used in Experimental Example 4 was measured. That is, on the magneto-optical recording medium used in Experimental Example 4, a single-frequency carrier signal having a mark length of 0.6 μm was recorded on a predetermined track, and each track adjacent to both sides of this track was internally recorded with the same recording power. A single-frequency carrier signal having a mark length of 0.65 μm on the peripheral side and a mark length of 0.55 μm on the outer peripheral side is recorded. The smaller one of the leak signal level differences (hereinafter, referred to as CTL) was measured. FIG. 9 shows the result of measuring the change in CTL while changing the recording power. In FIG. 9, the horizontal axis shows the magnitude of the recording power, and the vertical axis shows the value of CTL. At this time, the intensity of the reproduction light was 2.0 mW.

The value of CTL has a sufficient difference of 30 dB or more even in the case of the smaller difference in the leakage signal level. In the magneto-optical recording medium to which the present invention is applied, it is possible to increase the density in the radial direction. It was confirmed that there was.

That is, from the results of Experimental Examples 4 and 5, it was confirmed that in the magneto-optical recording medium of the present invention, it was possible to increase the recording density in the linear recording density direction and the radial direction.

[0083]

As is apparent from the above description, in the magneto-optical recording medium of the present invention, the overall magnetization directions of the uppermost magneto-optical recording film and the other magneto-optical recording films are magnetostatic. When aligned with the same direction due to the coupling, when irradiating the reproduction light to reproduce this, in the portion of the reproduction light spot below the compensation temperature of the magneto-optical recording film other than the uppermost magneto-optical recording film, Since the uppermost magneto-optical recording film shows a transition metal-dominant magnetization state and the other magneto-optical recording films show a rare earth metal-dominant magnetization state, the direction of the partial magnetization of the transition metal in these magneto-optical recording films Are antiparallel, and no information is reproduced in this portion. On the other hand, in the portion of the reproduction light spot other than the compensation temperature of the magneto-optical recording film other than the magneto-optical recording film as the uppermost layer, the magneto-optical recording film as the uppermost layer shows a transition metal-dominant magnetization state. Since the magneto-optical recording films also exhibit a transition metal-dominant magnetization state, the direction of the partial magnetization of the transition metal in these magneto-optical recording films is parallel, and information is reproduced only in this portion.

Therefore, in the magneto-optical recording medium of the present invention, the rewritable area of the magneto-optical recording film other than the uppermost layer is irrespective of the numerical aperture of the lens or the laser wavelength of the reproducing optical system. The linear recording density and the radial recording density are determined by the temperature and the size of the area where the temperature is equal to or higher than the compensation temperature of the magneto-optical recording film other than the uppermost magneto-optical recording film in the reproduction light spot. It is possible to sufficiently cope with higher recording density.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part showing a magneto-optical recording medium to which the present invention is applied.

FIG. 2 is an enlarged sectional view of a main part showing a magneto-optical recording medium to which the present invention is applied.

FIG. 3 is a schematic diagram showing a state in which a magneto-optical recording medium to which the present invention is applied is irradiated with reproduction light.

FIG. 4 is a characteristic diagram showing a relationship between a film thickness of a first magneto-optical recording film, a Kerr rotation angle, and a figure of merit.

FIG. 5 is a characteristic diagram showing a relationship between a recording magnetic domain diameter and a leakage magnetic field.

FIG. 6 is a characteristic diagram showing a relationship between a magneto-optical recording medium temperature and an apparent Kerr rotation angle.

FIG. 7 is a characteristic diagram showing an external magnetic field-magnetization curve.

FIG. 8 is a characteristic diagram showing a relationship between a spatial frequency and a CNR.

FIG. 9 is a characteristic diagram showing a relationship between recording power and CTL.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 transparent substrate, 2 first dielectric film, 3 first magneto-optical recording film, 4 second dielectric film, 5 second magneto-optical recording film, 6 third dielectric film, 7 reflective film

Claims (3)

[Claims] 1. A magneto-optical recording film comprising a rare earth metal-transition metal amorphous alloy and a plurality of magneto-optical recording films having an easy axis in a direction perpendicular to the film surface laminated on a transparent substrate via a dielectric film. In the magneto-optical recording medium, the compensation temperature of the uppermost magneto-optical recording film is lower than room temperature, the Curie temperature of the magneto-optical recording film is T _c2 , the compensation temperature of the other magneto-optical recording films is T _comp1 , the when the T _r, have the relationship _{T r <T comp1 <T c2} , the thickness of the magneto-optical recording film serving as the uppermost layer is at 15nm or more, the film thickness of the magneto-optical recording film other than this 3 nm to 15 nm
Wherein the thickness of the dielectric film is 1 nm to 15 nm. 2. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording film as the uppermost layer has a magnetization at room temperature of 50 emu / cc or more. 3. A multi-layer magneto-optical recording film comprising a rare earth metal-transition metal amorphous alloy and having an easy axis of magnetization perpendicular to the film surface is laminated on a transparent substrate via a dielectric film. , the compensation temperature of the magneto-optical recording film made of a top layer is less than room temperature and the Curie temperature of the magneto-optical recording film T _c2, other magneto-optical recording the compensation temperature T of the film _comp1, at room temperature and T _r Occasionally, has a relation of _{T r <T comp1 <T c2} , the thickness of the magneto-optical recording film serving as the uppermost layer is at 15nm or more, which the thickness of the magneto-optical recording film other than the be 3nm~15nm A reproducing method of reproducing information from a transparent substrate by irradiating the magneto-optical recording medium having a dielectric film with a thickness of 1 nm to 15 nm with reproducing light; The compensation temperature T _{comp1 of the} magneto-optical recording film other than the upper magneto-optical recording film is not In the portion where the temperature is full, the direction of the partial magnetization of the transition metal in the magneto-optical recording film as the uppermost layer and the direction of the partial magnetization of the transition metal in at least one of the other magneto-optical recording films are anti-parallel. A portion of the reproduction light spot having a temperature range _{equal to} or higher than the compensation temperature T _comp1 of the magneto-optical recording film other than the uppermost magneto-optical recording film and _{equal to} or _lower than the Curie temperature T _{c2 of} the uppermost magneto-optical recording film. In this case, the direction of the partial magnetization of the transition metal in the uppermost magneto-optical recording film and the direction of the partial magnetization of the transition metal in at least one of the other magneto-optical recording films are parallel to each other. A reproducing method for a magneto-optical recording medium, comprising: detecting rotation of a polarization plane of light to reproduce information of a magneto-optical recording film as an uppermost layer.