JPS62226449A - Optical magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve corrosion resistance and recording sensitivity by laminating the 1st intermediated layers consisting of a prescribed compd. on the surface of a photomagnetic recording layer having an axis of easy magnetization in the direction perpendicular to the film plane and the 2nd intermediate layers consisting of a compd. having the heat conductivity smaller than the heat conductivity of said layer thereon. CONSTITUTION:This optical magnetic recording medium consists of a light transmittable substrate 11, the photomagnetic recording layer 12, the 1st intermediate layers 13a, 13b, and the 2nd intermediate layers 14a, 14b. The photomagnetic recording layer 12 has the axis of easy magnetization in the direction perpendicular to the film plane, for which amorphous rare earth- transition metals such as PbFe, GdTbFe, TbFeCo, and GdTbFeCo are preferably used. The 1st intermediate layers 13a, 13b consist of at least one kind of compd. among nitrides such as AlN and Si3N4, sulfides such as ZnS, and Bi3S3, carbides such as SiC and TiC and oxides such as MgO and TiO2. The 2nd intermediate layers 14a, 14b consist of compds. having the heat conductivity smaller than the heat conductivity of the layers 13a, 13b, for example, MgF2, ZnSe, etc.

Description

[Detailed description of the invention] [Industrial application field] The present invention is directed to light such as laser light (herein referred to as light).

This invention relates to a method of manufacturing an optical magnetic recording medium in which information is recorded, reproduced, and erased using energy rays.

[Prior Art] In recent years, research and development of optical memory elements using laser light as high-density, large-capacity memories have been carried out at a rapid pace. Among these, magneto-optical recording has attracted attention as a rewritable recording method, and the optical magnetic recording medium used for this recording is highly anticipated as a rewritable optical memory element.

Conventionally, the material constituting the magneto-optical recording layer of an optical-magnetic recording medium used for such magneto-optical recording has been Mn.
Representative examples include the 1l i series, the garnet series, and the rare earth-transition total bending amorphous series. IAn
Bii has the disadvantage that it requires a high power lenser for recording due to its high Curie temperature, and it is unable to reproduce with a high S/N ratio due to the large amount of grain boundary noise. Because of its high transmittance, it had the disadvantage of requiring a high-power laser for recording. Among these, the rare earth-transition metal amorphous system has a low Curie temperature and relatively low light transmittance, and is therefore expected to compensate for the drawbacks of both.

This type of technology will be described in more detail below with reference to the drawings.

FIG. 3 is a schematic cross-sectional view of a typical conventionally used optical magnetic recording medium.

In Figure 3, 11 is polymethyl methacrylate (P
It is a light-transmitting substrate made of plastic such as MMA), polycarbonate (PC), or glass, and plate-shaped substrates of various shapes such as donut shapes are generally used. 1
For the reasons mentioned above, rare earth-transition metal amorphous systems such as TbFe, GdTbFe, and TbFeCo are currently widely used.

Recording, reproducing, and erasing on such an optical magnetic recording medium is generally performed as follows.

First, the recording medium is magnetized in a certain direction perpendicular to the substrate 11, and then a laser beam is spot-irradiated from the substrate 11 side. The magnetization direction may be any desired direction as long as it is constant. The laser beam irradiated onto the substrate II passes through the substrate 11 and reaches the magneto-optical recording layer 12 . As a result, light is absorbed in the laser beam irradiated portion of the magneto-optical recording layer 12, and due to a local temperature rise, this portion reaches the Curie point or more of the layer-constituting material, and the magnetization disappears. At this time, when a magnetic field is applied in the opposite direction to the magnetization direction to the part where the magnetization has disappeared, the magnetization in that part is reversed, and an inverted magnetic domain is formed whose magnetization direction is different from the part not irradiated with the laser beam, and information is transmitted. Records will be made. To erase a record, the recorded portion of the magneto-optical recording layer 12 is raised above one Curie point by re-irradiation with laser light, and by applying magnetization in the opposite direction to that during recording to the portion, recording of the magnetization direction is started. This is done by returning to the previous state.

In addition, for reproduction of recording, a laser beam whose power is lowered to such an extent that the temperature of the magneto-optical recording layer 12 does not rise above one Curie point is irradiated from the base material 11 side, and the magnetization direction of the recorded portion is changed using the magnetic Kerr effect. This is done by reading.

However, in such optical magnetic recording, the magneto-optical recording layer 12 is easily affected by the base material in terms of oxidation, corrosion, etc. Especially when an organic resin is used as the substrate, the magneto-optical recording layer 12 During the formation of the layer 12, oxygen, moisture, etc. adsorbed on the substrate +1 may be taken into the magneto-optical recording layer 12, causing deterioration of the magnetic properties. Furthermore, if the formed optical magnetic recording medium is stored in a high temperature and high humidity atmosphere for a long time, the magnetic properties will deteriorate due to oxygen and moisture penetrating the substrate 11 and entering the magneto-optical recording layer 12. However, there were problems such as an increase in errors during recording and playback and a deterioration in signal quality.

Therefore, in order to solve such problems and obtain an optical magnetic recording medium with excellent recording sensitivity, storage environment characteristics, etc., in order to reduce the influence of the substrate 11 on the magneto-optical recording layer 12,
An intermediate layer between the magneto-optical recording layer 12 and the substrate 11! (Problem to be solved by the invention) However, when an intermediate layer with excellent corrosion prevention effect is provided, the thermal conductivity of is often relatively high, and the thermal energy absorbed by the magneto-optical recording layer I2 by laser beam irradiation is released to the intermediate layer, causing a temperature drop in the magneto-optical recording layer 12, resulting in a decrease in recording sensitivity. There was a drawback. If you want to improve recording sensitivity,
This requires a laser beam with higher power, but there is a limit to its power both economically and due to the durability of the recording medium.

When a material with low thermal conductivity is used as the material for the intermediate layer, its corrosion prevention effect is insufficient, and the corrosion resistance of the recording medium is often not improved as much as expected.

The present invention has been made in view of the above problems, and its purpose is to provide an optical magnetic recording medium that exhibits corrosion resistance equivalent to or higher than that of known optical recording media that exhibit high corrosion resistance, and that also has improved recording sensitivity. The goal is to provide recording media.

[Means for Solving the Problems] The optical magnetic recording medium of the present invention which achieves the above object comprises a magneto-optical recording layer having an axis of easy magnetization in a direction perpendicular to the film surface on a transparent substrate. In an optical magnetic recording medium comprising:
A first intermediate layer made of a compound of at least one of nitride, sulfide, carbide, and oxide is laminated on the surface of the magneto-optical recording layer, and the first intermediate layer is further laminated on the surface of the first intermediate layer. It is characterized in that a second intermediate layer made of a compound having a lower thermal conductivity than the intermediate layer is laminated.

[Embodiments of the Invention] The present invention will be described in detail below. FIG. 1 is a schematic cross-sectional view of one embodiment of the optical magnetic recording medium of the present invention.

In the optical magnetic recording medium shown in FIG. 1, numeral 11 is a transparent base material made of various materials such as glass, PMMA, polycarbonate, etc., and its shape is not particularly limited.

12 is a magneto-optical recording layer having an axis of easy magnetization in the direction perpendicular to the film surface, and its material is TbFe, Gd'"bF
Rare earth-transition metal amorphous systems such as e, TbFcCo, and GdTbFe1;o are preferably used. Of course, it is also possible to use the MnBi yarn mentioned above, garnet type, etc.

+3a and 13b laminated on both surfaces of the magneto-optical recording layer 12
The film is the first intermediate layer, and is made of a material with excellent film quality that sufficiently protects the magneto-optical recording layer 12 from external oxidation, corrosion, etc. First intermediate layer 13a, 1
3b are each independently AIN, Si3N4, ZrN
%GrN, nitrides such as TiN, ZnS, i2
Sulfides such as S3, SiG, Tie, Zn
Carbides such as C, MgO, Ti02, ZrO2, S
It consists of at least one compound of oxides such as iO and Si02.

The first intermediate layer 13a +3 when viewed from the magneto-optical recording layer 12
The films 14a and 14b laminated on the outer surface of each layer b are the second intermediate layer, and in order to reduce the escape of heat from the magneto-optical recording layer 12, each film has a thermal conductivity higher than that of the adjacent first intermediate layer. Made of material with low thermal conductivity. For example, MgF
2, fluorides such as BiF3, Zn5e, Ge
Sc, selenide such as Ca5a%GaSe%InSe3, organic material such as Teflon, PTFE (polytetrafluoroethylene), TM01 (tetramethoxysilane), trichloroethylene, or ZnS, SiO, SiO2, Zr02, etc. used in the first intermediate layer. One or more compounds are appropriately selected from materials having low thermal conductivity depending on the material of the first intermediate layer.

The film thicknesses of the first intermediate layer and the second intermediate layer are set in consideration of protective function, film quality, thermal conductivity, and the like.

Generally, the thickness of the first intermediate layer is preferably about 100 to 1000 layers, and the thickness of the second intermediate layer is preferably about iooλ to 3000 layers. Note that, if the protective function of the first intermediate layer is sufficient, it is preferable that the thickness of the second intermediate layer is thicker than that of the first intermediate layer in terms of recording sensitivity.

In the optical magnetic recording medium of the present invention, the first intermediate layer mainly has a function of protecting the magneto-optical recording layer from oxidation and corrosion, and the second intermediate layer mainly has a function of protecting the magneto-optical recording layer from heat during recording. It has the function of preventing diffusion. Therefore, the optical magnetic recording medium of the present invention maintains the same level of corrosion resistance as the conventional recording medium due to the first intermediate layer, and in some cases, the synergistic effect of the first intermediate layer and the second intermediate layer Therefore, corrosion resistance exceeding this level may be exhibited. Furthermore, the second intermediate layer allows thermal energy to be used effectively and improves recording sensitivity.

FIG. 2 is a schematic sectional view showing another embodiment of the present invention. 1
1.12.13a, 13b, 14a, 14
b are the same layers as above. However, since the optical magnetic recording medium of this embodiment uses the Kerr effect and the Faraday effect for reproduction, it is better not to make the film thickness of the magneto-optical recording layer 12 too thick. degree is preferred. Reference numeral 15 denotes a reflective layer made of a material with high light reflection ability such as silver, Ag, Cu, or AI, and its thickness is preferably about 400 to 1,000 layers.

■6 is a protective layer for further improving the oxidation resistance of the magneto-optical recording layer 12, and is made of an organic polymer film or an inorganic or metal material such as oxide, sulfide, nitride, or carbide. be done. In the present invention, although it is not necessarily necessary to provide the protective layer 16, oxidation and corrosion of the magneto-optical recording layer 12 can be more effectively prevented by providing it.

As shown in Figures 1 and 2, when the first and second intermediate layers are provided on both sides of the magneto-optical recording layer, they can sufficiently prevent oxygen, moisture, etc. from entering from both sides of the recording layer. However, depending on the degree of corrosion resistance required, the first and second intermediate layers may be provided only on one side.

Note that in the optical magnetic recording medium of the present invention, the substrate 11 on which tracking groups (guide grooves) are formed
When using the second intermediate layer 14a on the substrate side 11, it is preferable to make the film thickness of the second intermediate layer 14a thicker than the depth of the group. As a result, the substrate 11 is completely covered with the second intermediate layer 14a, making it difficult for oxygen and moisture to enter the magneto-optical recording layer 12 from the substrate 11, further improving storage stability.

Each layer in the optical magnetic recording medium of the present invention can be formed by resistance heating evaporation, electron beam evaporation, sputtering, CVD.
It can be formed using a method such as a method, an ion blating method, or the like.

[Examples] The present invention will be described in more detail below with reference to Examples.

Example 1 An optical magnetic recording medium similar to that illustrated in FIG. 1 was prepared. Disk-shaped polycarbonate substrate Ill
Then, as the second intermediate layer 14a, a SiO thin film having a thickness of 800 nm was formed by electron beam evaporation. 7. On top of that, the first intermediate layer 13a has a film thickness of 300. An nS thin film was formed by sputtering.

On top of that, as a magneto-optical recording layer 12, a film thickness of 1000 Tb is formed.
A FeCo thin film was formed by sputtering. Furthermore, a ZnS thin film with a thickness of 500 and an SiO thin film with a thickness of 3000 were formed as the first intermediate layer 13b and the second intermediate layer 14b by the same method as described above, thereby producing the optical magnetic recording medium of this example. I got it.

Comparative Example 1 The second intermediate layer 14a was not provided, and the first intermediate layer 13a had a thickness of 8
00 ZnS thin film and second intermediate layer +4
b is not provided, and the first intermediate layer 13b is made of Zn with a film thickness of 3000.
A conventional optical magnetic recording medium was prepared in the same manner as in Example 1 except that the thin film was replaced with a thin film.

The recording media of Example 1 and Comparative Example 1 were rotated at 1800 rpm, a semiconductor laser (wavelength: 830 RAM) was pulsed at a frequency of 2 MHz, and recording was performed at a duty ratio of 50%. The recording power at this time was 7.5 mW. When these were reproduced with Ilz at a reproduction power of 2 mW and a bandwidth of 30, the C/N value was 51 dB (Example 1)
, 50 dB (Comparative Example 1).

Next, the image recording medium was left in an atmosphere with a temperature of 45° C. and a relative humidity of 95%, and a storage test was conducted.

The coercive force t(co) before being left unused and the coercive force Ilc after being left unused for 500 hours are measured, and the ratio of the coercive force after being left to that before being left unused!
The storage stability was evaluated by calculating Ic/1lco (the larger the ratio, the better the storage stability).

As shown in Table 1, tic/1lco-0,95(
Example 1) and 0.85 (Comparative Example 1). In addition, 50
Even after standing for 0 hours, no changes in appearance such as cracks were observed in the recording medium of Example 1, but the occurrence of cranks was observed in the recording medium of Comparative Example 1.

Also, from the relationship between the C/N value and the recording laser power, the recording laser power (Pw) when the C/N value is saturated
When approximated as sensitivity, Pw = 7 mW in the example and Pw = 7.5 mW in the comparative example. (The smaller the recording laser power, the better the sensitivity.) Example 2 An optical magnetic recording medium similar to that illustrated in FIG. 2 was prepared. Disk-shaped polycarbonate J, (plate 1
1, SiO with a film thickness of 900 as the second intermediate layer +4a
A thin film was formed by electron beam evaporation, and a ZnS thin film having a thickness of 300 nm was formed by sputtering as the first intermediate layer 13a. Furthermore, the first intermediate layer 13b has a film thickness of 300. The nS thin film is used as the second intermediate layer 14b with a thickness of 110
After forming a SiO thin film with a thickness of 800 mm as the reflective layer 15, a SiO thin film of 0.0 mm is formed using the same method as described above. A thin film was formed by electron beam evaporation. Finally, a SiO thin layer 11!2 having a thickness of 3000 is formed as the protective layer 16 by electron beam evaporation, and the second intermediate layer 14a is not provided, and the first intermediate layer 13a is The film thickness l
The same method as in Example 2 was used except that the second intermediate layer +4b was not provided and the first intermediate layer +3b was a ZnS thin film with a thickness of 1300 mm. A magnetic recording medium was created.

The recording media of Example 2 and Comparative Example 2 were recorded and reproduced in the same manner as in Example 1, and Ilc/Hco was measured. As a result, (
:/N-55dB, Hc/Hco-0,94 (Example 2
), (:/N-54dB, llc/Hco・O,
aO (Comparative Example 2) was obtained.

The recording laser power Pw required for saturation of the C/N value is Pw = 6 mW in Example 2, and Pw = 6.8 mW in Comparative Example 2.
It was W.

Examples 3 to 6 Four types of optical magnetic recording media were prepared in the same manner as in Example 1 except that the first intermediate layer and the second intermediate layer were changed as shown in Examples 3 to 6 in Table 1. Created.

Examples 7 to IO Four types of optical magnetic recording media were prepared in the same manner as in Example 1 except that the first intermediate layer and the second intermediate layer were changed as shown in Examples 7 to 10 in Table 1. Created.

The recording media of Examples 3 to 10 were recorded and reproduced in the same manner as in Examples, and the C/N value and coercive force ratio were 11c/1lc.
The storage stability was evaluated by determining o. The results are shown in Table 1. Errors during playback did not increase for all recording media.

Further, as shown in Table 1, the recording laser power Pw required for saturation of the C/N value is smaller than that of the comparative example, which indicates that the recording sensitivity is excellent.

〔Effect of the invention〕

As explained in detail above, the present invention has corrosion resistance equal to or higher than that of known recording media that exhibit excellent corrosion resistance, and has minimal deterioration in magnetic properties and error rate.
Furthermore, it has become possible to provide an optical magnetic recording medium with improved recording sensitivity.

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views showing one embodiment of the optical magnetic recording medium of the present invention, and FIG. 3 is a schematic cross-sectional view of a conventional optical magnetic recording medium. DESCRIPTION OF SYMBOLS 11... Substrate, 12... Magneto-optical recording layer, 13a, +3b --- First intermediate layer, 1
4a, 14b---Second intermediate layer, 15...
...Reflection layer, 16...Protective layer.

Claims (2)

[Claims] (1) In an optical magnetic recording medium comprising a magneto-optical recording layer having an axis of easy magnetization perpendicular to the film surface on a transparent substrate, nitrides, sulfides,
A first intermediate layer made of a compound of at least one of carbides and oxides is laminated, and a second intermediate layer made of a compound having a thermal conductivity lower than that of the first intermediate layer is further disposed on the surface of the first intermediate layer. An optical magnetic recording medium comprising a stack of layers. (2) The optical magnetic recording medium according to claim 1, wherein the first intermediate layer and the second intermediate layer are laminated on both sides of the magneto-optical recording layer.