JP2960767B2 - Magneto-optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium, and more particularly, to a laminated structure of a thin film laminated on one surface of a transparent substrate.

[Prior Art] An information recording system using a magneto-optical recording medium has entered the stage of practical use, and it is necessary to provide a magneto-optical recording medium having an overwrite function and having an excellent reproduction CN ratio and excellent information preservability. It is an increasingly important technical issue.

FIG. 5 is a sectional view of a main part showing a first example of a conventionally known magneto-optical recording medium, and shows a signal surface 2 of a transparent substrate 1;
From the side of the transparent substrate 1, an enhance layer 3 made of an inorganic dielectric having a higher refractive index than the transparent substrate 1, a magneto-optical recording layer (a rare earth-transition metal based amorphous perpendicular magnetization film) 4,
A protective layer 5 made of the same material as the enhance layer 3,
Reflective layer 6 made of a metal material having high reflectivity such as aluminum
Are sequentially laminated.

This magneto-optical recording medium includes a transparent substrate 1 and a magneto-optical recording layer 4.
Since the enhancement layer 3 is provided at the interface between the transparent substrate 1 and the magneto-optical recording layer 4, the reproducing light beam is multiple-reflected between the transparent substrate 1 and the magneto-optical recording layer 4, so that the apparent Kerr rotation angle can be increased. Further, since the protective layer 5 and the reflective layer 6 are sequentially laminated on the back side of the magneto-optical recording layer 4 as viewed from the transparent substrate 1 side, the reproducing light beam transmitted through the magneto-optical recording layer 4 is reflected by the reflective layer 6. Then, the apparent Kerr rotation angle can be further increased by the Faraday effect received when the light passes through the magneto-optical recording layer 4 (reciprocating stroke). Since the playback CN ratio is proportional to the product of the car rotation angle and the reflectance,
This magneto-optical recording medium can obtain a high reproduction CN ratio.

Also, in this magneto-optical recording medium, since the metal reflective layer 6 is provided on the magneto-optical recording layer 4 with the protective layer 5 interposed therebetween, the heating section including the magneto-optical recording layer 4 has a high thermal conductivity, and The magnetic recording layer 4 is not excessively heated. Therefore, inconveniences such as deterioration of the magneto-optical recording layer 4 and deformation of the signal surface 2 of the transparent substrate 1 hardly occur, and durability against repeated recording / erasing can be improved. Of course, by adjusting the thermal conductivity of the reflective layer 6 to an appropriate value,
The recording sensitivity and the erasing sensitivity can be adjusted to values suitable for the drive.

As a known technique similar to this, Japanese Patent Application Laid-Open No. Sho 57-16
No. 9996 can be mentioned.

FIG. 6 is a sectional view of a principal part showing a second example of a conventionally known magneto-optical recording medium, and shows a signal surface 2 of a transparent substrate 1;
First, from the transparent substrate 1 side, a first protective film 11, a ferrimagnetic thin film 12 having a compensation temperature of room temperature or higher, and an in-plane magnetic layer 13
And a second protective film 14 are sequentially stacked.

In this magneto-optical recording medium, since an in-plane magnetic layer 13 is laminated on the ferrimagnetic thin film 12, the interaction between the domain wall and the in-plane magnetic layer 13 in the ferrimagnetic thin film 12 causes a large number of Blochs in the magnetic wall. The generation of lines can be suppressed, and the recording pits can be completely erased. Therefore, it is possible to directly overwrite information by an optical modulation method without using an external magnetic field.

As a known technique similar to this, Japanese Patent Application Laid-Open No. 63-24 / 1988
No. 1739 can be mentioned.

[Problem to be Solved by the Invention] The magneto-optical recording medium according to the first example of the related art has various advantages as described above, but has a disadvantage that overwriting of information is practically impossible. . According to the magnetic field modulation method, information can be overwritten in principle, but the external magnetic field sensitivity at the time of recording and erasing is poor, and in particular, a large external magnetic field (for example, , 600 [Oe] or more).

On the other hand, the magneto-optical recording medium according to the second example of the related art has an advantage that information can be overwritten by a light modulation method, but has a reflection on the back side of the ferrimagnetic thin film 12 which is a magneto-optical recording layer. Since the layers are not stacked, the reproducing light beam transmitted through the ferrimagnetic thin film 12 is applied to the transparent substrate 1.
Cannot be returned to the side, and therefore the Kerr rotation angle cannot be increased, so that there is a problem that a high reproduction CN ratio cannot be obtained. Further, since a layer made of a material having high thermal conductivity is not provided, there is a problem that durability against repeated recording / erasing is low.

The present invention has been made in order to solve the above-mentioned deficiencies of the prior art, and it is possible to overwrite information by a magnetic field modulation method, and to have a high reproduction C / N ratio and a recording / erasing sensitivity suitable for a drive. It is another object of the present invention to provide a magneto-optical recording medium having excellent durability against repeated recording / erasing.

Means for Solving the Problems In order to achieve the above object, the present invention provides a magneto-optical recording medium comprising a thin film including at least a magneto-optical recording layer on a signal surface of the transparent substrate. On the back side of the magneto-optical recording layer as viewed from the side, a ferromagnetic reflective film having a reflectance as high as possible for reproduction light and a thermal conductivity of 0.05 to 2.0 W / cm · deg was laminated.

As the ferromagnetic reflection film, (Pt, Al, Ag, Au, Cu, Rh)
At least one element selected from the group of elements and [F
e, Co, Ni] alloy thin film with at least one element selected from the group of elements is preferable, and a CoPt alloy thin film containing 60 to 95 atomic% of Pt is particularly preferable.

The magneto-optical recording layer can be formed using any known magneto-optical recording material, but a rare earth-transition metal amorphous perpendicular magnetization film is particularly preferable.

Further, it is possible to arbitrarily laminate another film in addition to the magneto-optical recording layer and the ferromagnetic reflective film, and to form an inorganic dielectric between the signal surface of the transparent substrate and the magneto-optical recording layer. A protective layer made of an inorganic material or an organic material can be provided on the surface of the ferromagnetic reflective film with an enhance layer interposed therebetween.

[Operation] When a ferromagnetic reflective film is laminated on the back surface of the magneto-optical recording layer, a magnetic interaction occurs between the magneto-optical recording layer and the ferromagnetic reflective film, and the external magnetic field sensitivity during recording and erasing is reduced. improves. Therefore, complete recording / erasing of information can be performed with a smaller external magnetic field, and overwriting of information by a magnetic field modulation method can be realized.

Also, since a ferromagnetic reflective film having the highest reflectivity to reproducing light as much as possible was used, the reproducing light beam transmitted through the magneto-optical recording layer was reflected by the ferromagnetic reflective film, and the magneto-optical recording was performed again. Can pass through the layer and return to the transparent substrate side,
The apparent Kerr rotation angle can be increased by the Faraday effect received when the reproducing light beam passes through the magneto-optical recording layer. Therefore, a high reproduction CN ratio can be obtained.

Furthermore, since a ferromagnetic reflective film having a thermal conductivity of 0.05 to 2.0 W / cm · deg is deposited on the magneto-optical recording layer, the magneto-optical recording layer is not excessively heated. Therefore, inconveniences such as deterioration of the magneto-optical recording layer and deformation of the signal surface of the transparent substrate hardly occur.
Durability against erasure can be improved. Further, the recording sensitivity and the erasing sensitivity can be set to values suitable for the drive.

Embodiment FIG. 1 is a cross-sectional view of an essential part showing an example of a magneto-optical recording medium according to the present invention. The signal surface 2 of the transparent substrate 1 is higher than the transparent substrate 1 than the transparent substrate 1 side. An enhance layer 3 made of an inorganic dielectric material having a refractive index, a magneto-optical recording layer 4,
A ferromagnetic reflective film 21 and a protective layer 22 are sequentially stacked.

The transparent substrate 1 is formed of a plastic material such as polycarbonate, polymethyl methacrylate, polyolefin, or epoxy, or a transparent material such as glass into a desired shape such as a disk shape or a card shape.

A signal pattern such as a guide groove for guiding a light beam spot and a pre-pit row representing a header signal is formed on the signal surface 2 in a fine uneven shape. In FIG. 1, a signal pattern is directly formed on one surface of the transparent substrate 1. However, a photocurable resin layer having a refractive index similar to that of the transparent substrate is formed on one surface of the transparent substrate formed in a plate shape. And the signal pattern can be transferred to the surface of the photocurable resin layer.

The enhancement layer 3 is provided for causing a reproduction light beam to cause multiple interference between the magneto-optical recording layer 4 and the transparent substrate 1 to increase an apparent Kerr rotation angle, and includes silicon, aluminum, and zirconium. , Titanium, tantalum nitride, oxide, or the like, and is made of an inorganic dielectric material having a refractive index larger than that of the transparent substrate 1, and is formed to a thickness of 600 to 1000 °. As a means for forming the layer 3, sputtering is particularly suitable.

The magneto-optical recording layer 4 is made of a rare earth-transition metal amorphous perpendicular magnetization film, a PtMnSb alloy (Heusler alloy), a laminate of a Pt film and a Co film, a Mn-Bi alloy (crystalline), an oxide, or the like. Although it can be formed using any known magneto-optical recording material, a rare earth-transition metal amorphous perpendicular magnetization film is particularly preferable.

As the rare earth-transition metal amorphous perpendicular magnetization film, a film represented by the following general formula is particularly preferable.

General formula; Tb _X Fe _(100-XYZ) Co _Y M _Z where 20 atomic% ≦ x ≦ 30 atomic% 5 atomic% ≦ y ≦ 15 atomic% 0 atomic% ≦ x ≦ 10 atomic% M is Nb, Cr , At least one element selected from Pt This perpendicular magnetization film is formed by sputtering a target formed of an alloy of Tb, Fe, Co, and an additional element M, or a sintered body containing these elements. , 200-500
It is formed to a film thickness of Å.

It is preferable that the ferromagnetic reflective film 21 has a higher reflectivity to the reproducing light than the magneto-optical recording layer 4 and has a higher reflectivity to the reproducing light as much as possible. Furthermore, 0.05-2.0W / cm
-It is formed from a material having a thermal conductivity of deg. The film thickness is formed to 200 to 400 °.

That is, according to the present invention, the reproduction light transmitted through the magneto-optical recording layer 4 is returned to the transparent substrate 1 side by the ferromagnetic reflective film 21, and the Faraday effect which is received when the incident light and the return light are transmitted through the magneto-optical recording layer 4. This increases the apparent car rotation angle, thereby improving the reproduction CN ratio. Therefore, the higher the reflectance with respect to the light for reproduction, the better the result can be obtained, and it is more preferable to use the ferromagnetic reflective film 21 having a reflectance of 70% or more with respect to the light for reproduction.

If the thermal conductivity of the ferromagnetic reflective film 21 is too low, the magneto-optical recording layer 4 is excessively heated during recording or erasing of information, and the magneto-optical recording layer 4 is deteriorated by repeating this operation (for example, The amorphous perpendicular magnetization film is likely to be crystallized, etc.), and the signal surface 2 of the transparent substrate 1 is easily deformed. On the other hand, if the thermal conductivity of the ferromagnetic reflective film 21 is too high, the temperature of the magneto-optical recording layer 4 cannot be increased to a temperature required for recording or erasing information, and the recording sensitivity is reduced, A recording / reproducing light source (eg, a laser) having a high power because a recording / reproducing error due to the remaining disappearance of the recording increases.
The inconvenience of having to mount the device occurs.

In FIG. 2, showing the thermal conductivity of the ferromagnetic reflection film 21, reduction in the reproduction output after repeating recording / erasing operation 10 ⁴ times, and the relationship between the laser power required for recording / erasing. As is apparent from this graph, the thermal conductivity as the ferromagnetic reflection film 21 is used as follows 0.05 W / cm · deg, the reproduction output after repeated recording / erasing operation 10 ⁴ times decreases rapidly It turns out that it is not practical. If a ferromagnetic reflective film 21 having a thermal conductivity of 2.0 W / cm · deg or more is used, a laser power of 10 mW (film surface) or more is required for recording / erasing information, which also makes practical use difficult. You can see that. From these data, the thermal conductivity of the ferromagnetic reflective film 21 is determined within the above range.

Specific examples of the ferromagnetic reflection film 21 include (Pt, Al, Ag, Au, C
An alloy thin film of at least one element selected from the [u, Rh] element group and at least one element selected from the [Fe, Co, Ni] element group can be given.

Even if the constituent elements are the same, the magnitude of the external magnetic field required to completely erase the recorded signal varies depending on the content ratio. FIG. 3 shows the relationship between the Pt content in the thin film and the magnetic field in the erasing direction (film thickness is 200 °), taking a CoPt alloy thin film as an example. Here, the erasing direction magnetic field is a minimum magnetic field at which recording cannot be performed when information is recorded while an external magnetic field is applied in the erasing direction, and is an external magnetic field required to completely erase a recorded signal. Represents the size of

As apparent from FIG. 3, the CoPt alloy thin film has a Pt content at which the magnetic field in the erasing direction is minimized. At the request of the drive side, the external magnetic field that can be mounted on the drive is at most 300 [Oe], and in order to safely erase the recorded signal by this external magnetic field, the Pt of the CoPt alloy thin film
It is understood that the content needs to be adjusted to 60 to 95 atomic%.

The protective layer 22 is formed of the same inorganic dielectric as the enhance layer 3 or an organic material such as a photo-curable resin. When using an inorganic dielectric as a protective layer material,
It is formed to a thickness of 500 to 2000 mm.

Hereinafter, more specific experimental examples and comparative examples will be shown, and the recording / erasing characteristics of both will be compared.

<Experimental example> The signal surface of an injection-molded polycarbonate substrate
A 0Å SiN enhancement layer, a 400Å TeFeCo amorphous perpendicular magnetization film, a 300Å PtCo ferromagnetic reflection film containing 75 at.% Of Pt, and a 1500Å SiN protective layer were sequentially sputtered, and the magneto-optical device shown in FIG. A recording medium was created.

<Comparative Example> 85
A magneto-optical recording medium shown in FIG. 5 was prepared by sequentially sputtering a 0-degree SiN enhancement layer, a 400-degree TeFeCo amorphous perpendicular magnetization film, a 200-degree SiN protective layer, and a 700-degree Al alloy reflective layer.

FIG. 4 shows the recording / erasing characteristics of the magneto-optical recording medium according to the experimental example and the recording / erasing characteristics of the magneto-optical recording medium according to the comparative example. The recording / erasing characteristics as used herein refer to a change in the reproduction CN ratio when the magnitude and direction of the external magnetic field applied during recording are changed. The horizontal axis in FIG. The size and direction are graduated, and the vertical axis represents the reproduced CN ratio.

As is clear from this figure, the magneto-optical recording medium of the comparative example does not reach the saturation value unless the external magnetic field of about 300 [Oe] is applied in the recording direction. In the magnetic recording medium, the reproduction CN ratio reaches a saturation value only by applying an external magnetic field of about 100 [Oe] in the recording direction. This indicates that the magneto-optical recording medium of the experimental example can perform perfect recording with a smaller external magnetic field. Further, the magneto-optical recording medium of the comparative example cannot make the reproduction CN ratio zero without applying an external magnetic field of 600 (Oe) or more in the erasing direction, whereas the magneto-optical recording medium of the experimental example has The reproduction CN ratio can be made zero by simply applying an external magnetic field of about 200 [Oe] in the erasing direction. This indicates that the magneto-optical recording medium of the experimental example can perform complete erasure with a smaller external magnetic field. Therefore, it can be said that the magneto-optical recording medium of the experimental example has recording / erasing characteristics in which overwriting by the magnetic field modulation method is easily performed as compared with the magneto-optical recording medium of the comparative example.

Further, the saturation value of the reproduction CN ratio is substantially the same for both the magneto-optical recording medium of the experimental example and the magneto-optical recording medium of the comparative example, and it can be seen that the saturated CN ratio has a sufficiently high CN ratio.

In the above embodiment, the enhancement layer 3 is provided between the transparent substrate 1 and the magneto-optical recording layer 4. However, when the reflectivity of the ferromagnetic reflection film 21 is high and a sufficient CN ratio can be obtained. ,
This can be omitted.

In the above embodiment, the protective layer is provided on the outermost surface of the medium.
Although 22 is provided, when a ferromagnetic reflection film 21 having excellent corrosion resistance is used, this can be omitted.

Further, in the above-described embodiment, the ferromagnetic reflective film 21 is directly laminated on the back side of the magneto-optical recording layer 4, but between the magneto-optical recording layer 4 and the ferromagnetic reflective film 21, as in the case of the enhancement layer 3. A second enhanced layer made of an inorganic dielectric material of the above.

[Effects of the Invention] As described above, according to the present invention, as far as possible from the transparent substrate side, on the back surface of the magneto-optical recording layer, the reflectance to reproduction light is as high as possible, and the thermal conductivity is 0.05 to 2.0. Since a ferromagnetic reflective film of W / cm · deg is laminated, the read / write CN ratio is high, the recording and erasing sensitivity suitable for the drive, and the
It is possible to provide a magneto-optical recording medium having excellent durability against erasing and capable of overwriting by a magnetic field modulation method.

[Brief description of the drawings]

Cross sectional view showing an example of the magneto-optical recording medium according to Figure 1 the present invention, FIG. 2 reduction in the reproduction output after repeating 10 ⁴ times the recording / erasing operation and the thermal conductivity of the ferromagnetic reflection film FIG. 3 is a graph showing a relationship between a Pt content in a PtCo thin film and a magnetic field in an erasing direction, and FIG. 4 is a magneto-optical recording according to an experimental example. FIG. 5 is a graph showing the recording / erasing characteristics of a medium and the recording / erasing characteristics of a magneto-optical recording medium according to a comparative example. FIG. 5 is a sectional view of a main part showing a first example of the prior art. It is principal part sectional drawing which shows a 2nd example. 1 ... Transparent substrate, 2 ... Signal surface, 3 ... Enhancement layer,
4 ... magneto-optical recording layer, 21 ... ferromagnetic reflection film, 22 ... protective layer.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-91132 (JP, A) JP-A-58-222455 (JP, A) JP-A-59-167864 (JP, A) 168951 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 11/10 523

Claims (7)

(57) [Claims] 1. A magneto-optical recording medium comprising a thin film including at least a magneto-optical recording layer on a signal surface of a transparent substrate. A magneto-optical recording medium comprising a laminated ferromagnetic reflective film having a thermal conductivity of 2.0 W / cm / deg. 2. A magneto-optical recording medium according to claim 1, wherein said ferromagnetic reflection film has a reflectance of 70% or more with respect to reproduction light. 3. The ferromagnetic reflective film according to claim 1, wherein at least one element selected from the group consisting of [Pt, Al, Ag, Au, Cu, Rh] and [Fe, Co, Ni]. ] A magneto-optical recording medium using an alloy thin film with at least one element selected from the group of elements. 4. The magneto-optical recording medium according to claim 1, wherein a CoPt alloy thin film containing 60 to 95 atomic% of Pt is used as said ferromagnetic reflection film. 5. The magneto-optical recording medium according to claim 1, wherein a rare earth-transition metal based amorphous perpendicular magnetization film is used as the magneto-optical recording layer. 6. The magneto-optical recording medium according to claim 1, wherein an enhanced layer made of an inorganic dielectric is provided between the signal surface of the transparent substrate and the magneto-optical recording layer. 7. A magneto-optical recording medium according to claim 1, wherein a protective layer made of an inorganic material or an organic material is provided on the surface of said ferromagnetic reflection film.