JPS61202352A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To improve a shelf life by providing an intermediate layer formed by dispersing an Se compd. into a dielectric material. CONSTITUTION:This photomagnetic recording medium is laminated with at least the intermediate layer 2 and a photomagnetic recording layer 3 on a light transmittable substrate material 1 and has the intermediate layer formed by dispersing the Se compd. into the dielectric material. The effective temp. increase of the layer 3 is not possible if the film thickness of the intermediate layer 2 formed by dispersing the Se compd. into the dielectric material is too large or too small and therefore the intermediate layer is preferably formed to about 0.005-0.5mum thickness and is more particularly preferably set at the thickness at which the intermediate layer exhibits an antireflection function. The dielectric material constituting such layer 2 is, for example, an oxide such as SiO, SiO2 or ZrO2, nitride such as AlN, Si3N4, ZrN or CrN or sulfide such as ZnS or Bi2S3. The volumetric ratio of the Se compd. with respect to the dielectric material, when designated as (q), is preferably made in a q=5-90% range. The absorption of light increases at the value of (q) exceeding 5% and the medium is thermally unstable and such instability is disadvantageous in terms of recording sensitivity when the value is below 5%.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the recording of information using light such as laser light (the light here refers to energy rays of various wavelengths including the above-mentioned laser light). -Relates to optical and magnetic recording media for reproducing and erasing.

[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 materials constituting the magneto-optical recording layer of the optical-magnetic recording medium used for such magneto-optical recording include Mn.
Representative examples include B1 type, garnet type, and rare earth-transition metal amorphous type. MnB1
The disadvantage of the garnet system is that it requires a high-power laser for recording due to its high Curie temperature, and that reproduction with a high S/N ratio cannot be achieved 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 a relatively low light transmittance, so it is 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, 1 is polymethyl methacrylate) (P
It is a light-transmitting base material made of plastic such as PMA), polycarbonate (PC), or glass, and plate-like substrates of various shapes such as donut shape are generally used. 2
is an intermediate layer made of 5iO1Si02, Al1%ZnS, etc. 3 is a magneto-optical recording layer, which is currently made of TbFe, for example, for the reasons mentioned above.

Rare earth-transition metal amorphous systems such as GdTbFe and TbFeCo are widely used.

Recording/reproduction number erasing in 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 1, and then a spot of laser light is irradiated from the substrate 1 side.

The magnetization direction may be any desired direction as long as it is constant. The laser beam irradiated onto the substrate 1 passes through the substrate 1 and the intermediate layer 2 and reaches the magneto-optical recording layer 3 . As a result, light absorption occurs in the laser beam irradiated portion of the magneto-optical recording layer 3.

Due to the local temperature rise of the magneto-optical recording layer 3 due to absorption in the layer, the magneto-optical recording layer 3 in the laser beam irradiated area reaches the Curie point or more of the layer constituting material, and the magneto-optical recording layer 3 is irradiated with the laser beam. The magnetization of the part disappears. At this time, when a magnetic field is applied in a direction opposite to the magnetization direction to the part of the magneto-optical recording layer 3 where the magnetization has disappeared, the magnetization of the part is reversed, resulting in an inverted magnetic domain whose magnetization direction is different from that of the part not irradiated with the laser beam. is formed in the area irradiated with the laser beam, and information is recorded. To erase the recording, the recorded portion of the magneto-optical recording layer 3 is irradiated with laser light again to raise the temperature of the portion above the Curie point E.
During such recording and erasing, the intermediate layer 2
By setting the thickness of the layer to a thickness that exhibits an anti-reflection function for the wavelength of the laser light used,
The temperature increase of the magneto-optical recording layer 3 can be made extremely effective for recording and erasing.

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 3 does not rise beyond the Curie point is irradiated from the substrate l side, and the direction of magnetization of the recorded portion is changed using the magnetic Kerr effect. This is done by reading out.

However, among the various materials constituting the intermediate layer 2 and the magneto-optical recording layer 3, the above-mentioned rare earth-transition metal amorphous system, which is commonly used as the material constituting the magneto-optical recording layer 3, has the above-mentioned excellent features. However, since its thermal conductivity is relatively high, the thermal energy absorbed by these layers 2 and 3 by laser beam irradiation is mainly released from the substrate 1 side, resulting in a temperature drop in the recording layer 3. However, there is a drawback that recording sensitivity decreases as a result. In order to improve the recording sensitivity, a laser beam with higher power is required, but there is a limit to the power due to economic reasons and the durability of the recording medium. It is possible to reduce heat dissipation by using a material with low thermal conductivity for the intermediate layer, but the conventionally used materials such as SiO and Si
O2, AIM.

It has been difficult to suppress heat radiation using materials such as ZnS.

Furthermore, when an organic resin is used as the substrate 1, this heat dissipation problem is serious, and since the coefficient of thermal expansion of the organic resin is generally smaller than that of the material constituting the intermediate layer, the difference in the coefficient of thermal expansion between the two causes This results in the problem of cracks.

In addition, as one method for improving the recording sensitivity, for example, as shown in FIG. One possibility is to use this effect to increase the apparent Kerr rotation angle, but it is said that the magneto-optical recording layer 3 is generally easily oxidized if left in a high-temperature, high-humidity atmosphere in the presence of oxygen. There are also disadvantages, especially when the layer is made thinner, which increases errors during recording and reproduction and deteriorates the signal, and there is a natural limit to the improvement of recording sensitivity by making the layer thinner. Ta.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned points, and the main purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional example, improve recording sensitivity, and reduce cracking. The object of the present invention is to provide a novel optical magnetic recording medium that prevents the occurrence of cracks, especially in the intermediate layer.

Another object of the present invention is to provide a novel optical magnetic recording medium that also has excellent storage stability.

[Means for solving the problem] As a result of intensive research to achieve the above object, the inventors of the present invention found that the above object was achieved by providing an intermediate layer formed by dispersing Se compounds in a dielectric material. The present invention has been completed based on the discovery that the present invention is extremely effective.

That is, the present invention provides an optical magnetic recording layer, characterized in that at least an intermediate layer and a magneto-optical recording layer are laminated on a transparent substrate, and the intermediate layer is formed by dispersing a Se compound in a dielectric material. It is a recording medium.

[Embodiments of the invention] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing a basic aspect of the optical magnetic recording medium of the present invention.

In Fig. 1, 1 is the aforementioned glass, PMMA, P
The substrate is a light-transmitting substrate made of various materials such as C, and in this example, it is a disk-shaped substrate, but its shape is not particularly limited and can be any desired shape.

2 is an intermediate layer made by dispersing a Se compound in a dielectric according to the present invention, and 1 is preferably a thin film made of the following material, for example, #! The thickness is not particularly limited, but the magneto-optical recording layer 3 may be too thick or too thin.
Since the temperature cannot be raised efficiently, the thickness of 0.005
The dielectric material constituting such an intermediate layer 2 is preferably set to a thickness of about 0.5 - 0.5 -, and is particularly preferably set to a thickness that exhibits an anti-reflection function, such as, for example, Sin, 5i
07, Oxides such as ZrO□, All, Si3N4
, ZrN, nitrides such as CrN, ZnS,
Specific examples include sulfides such as Bi253. Among them, 5iO1S Mi07, ZrO2, AIN,
One or more dielectrics selected from the group consisting of Si3N4, ZrM and ZnS are preferably used.

The Se compound dispersed in the dielectric is ZnSe.
, GeSe, CaSe, GaSe, 5nSe,
Specific examples include In7Se3.5eed, among which one or more Se compounds selected from the group consisting of ZnSe, GeSe, In7Se3 and 5eed are preferably used.

The intermediate layer 2 made of such a dielectric material and Se compound differs depending on the wavelength of the light used (specifically, the above-mentioned laser light, etc.), but if the light absorption rate becomes too large, the magneto-optical Since the temperature of the recording layer 3 cannot be raised efficiently and the object of the present invention cannot be fully achieved, it is preferable that the absorption rate is 10% or less at the wavelength of the light used, and also for good recording. In order to do this, it is preferable to configure the intermediate layer 2 so that it does not change thermally in the recording temperature range (usually about 50 to 300 degrees Celsius).
It is preferable to disperse the Se compound in the dielectric material within a range where light absorption is small and does not change thermally. Specifically, when the volume ratio of the Se compound to the dielectric material is q, q = 5 ~ The value of q is preferably in the range of 30%; when q exceeds 5%, light absorption increases, and when q is below 5%, it is thermally unstable and disadvantageous in terms of recording sensitivity.

3 is a magneto-optical recording layer, the material of which is TbFe,
GdTbFe, TbFeCo, GdTbFeCa
A rare earth-transition metal amorphous system such as the following is preferably used. Of course, it is also possible to use the aforementioned MnB1 type, garnet type, etc.

5 is a protective layer for preventing oxidation of the magneto-optical recording layer 3, and is made of an organic polymer film, or an inorganic material such as an oxide or sulfide, or a metal material.

In the present invention, it is not necessarily necessary to provide the protective layer 5, but by providing it, oxidation and corrosion of the magneto-optical distribution/armor layer 3 can be prevented, making the present invention even more effective. I can do it.

The intermediate layer 2, the magneto-optical recording layer 3 and the protective layer 5 are placed on a substrate l.
)1. The method of laminating the layers is not particularly limited, but specifically, for example, a vapor deposition method.

Typical examples include film forming methods such as a CVD method, a sputtering method, and an ion blating method.

As mentioned above, during recording, laser light is irradiated from the substrate 1 side, and most of the optical energy of the irradiated light is absorbed in the magneto-optical recording layer 3, converted into thermal energy, and at the same time, the substrate 1 and the protective layer are irradiated with laser light. Heat diffuses towards 5.
Therefore, in order to improve recording sensitivity, it is considered effective to efficiently convert optical energy into thermal energy and to suppress thermal diffusion from the magneto-optical recording layer 3.

To evaluate the recording sensitivity of such an optical magnetic recording medium, for example, the recording power of the recording light is varied while rotating the L-recording medium at a desired rotational speed (usually a constant value). After performing recording, the threshold recording power is determined by measuring the reproduction CAM, and the results are compared. Recording power and playback C/H
For example, the relationship between the It remains almost constant. The recording power when this CAH is almost constant is the threshold recording power (Pw), and the smaller Pw is, the higher the recording sensitivity is, so the recording sensitivity of the recording medium is evaluated by finding the threshold recording power (Pw). It is possible to do so. As shown in the Examples below, the optical magnetic recording medium of the present invention has a smaller Pw and superior recording sensitivity than conventional media. The cause of such recording sensitivity increase H is not clear, but it is assumed that one of the reasons is that Se compounds are stable against heating in the recording temperature range and have low thermal conductivity. .

In addition, organic materials generally have low thermal conductivity, and using such organic materials as substrates (including coating substrates with organic resin layers laminated on glass, etc.) is extremely effective for preventing heat diffusion. However, it has been difficult to use because it has a high hygroscopicity and has an adverse effect on the storage stability of the recording medium, or it causes cracks, especially in the intermediate layer 2. However, in the optical magnetic recording medium of the present invention, such a rack did not occur.The fact that the Se compound applied to the present invention has a low thermal conductivity
It is assumed that this is one of the reasons for solving the crack problem.

[Example] Hereinafter, the present invention will be explained in more detail based on Examples.

[Example 1] An optical magnetic recording medium similar to that illustrated in FIG. 1 was prepared.

AIN and Zn5e on the disk-shaped glass substrate IF
An intermediate layer 2 in which Zn5e was dispersed in AIM as a dielectric was formed by a binary sputtering method using two targets. The film thickness is 9008, and Zn5 for AIM.
The volume ratio q of e was set to q=50%. On top of that, a TbFeCo thin film with a thickness of 10QOA was formed as a magneto-optical recording layer 3 by sputtering, and further on top of this a TbFeCo thin film with a thickness of 3000A was formed as a protective layer 5! A thin film of 1lii3N was formed by sputtering to obtain an optical magnetic recording medium on the water side.

This recording medium was rotated at 1800 rpm, using a semiconductor laser with a recording frequency of I MHz, and a duty ratio of 50%.
The threshold recording power (Pa) was determined from the relationship between the recording power and the CAH when recording was performed. The result is the first
As shown in the table, Pw was 7.51-.The reproduction conditions (ie, C/N measurement conditions) at this time were a reproduction power of 2- and a band width of 30 KHz.

Next, record the E recording medium at a temperature of 45°C and a relative humidity of 95% RH.
A storage test was conducted by leaving the product in an atmosphere of The coercive force Hco before standing and the coercive force f(c) after standing for 500 hours were measured, and the ratio of coercive force He/Hco after standing to that before standing was calculated to evaluate the storage stability (the larger the ratio, the better the storage The measurement results are shown in Table 1.As shown in Table 1, Hc/Hco = 0.93.Even after being left for 500 hours, the recording medium No cracks were observed.

[Comparative Example 1] A conventional optical magnetic recording medium having the same structure as Example 1 was prepared in the same manner as Example 1, except that the intermediate layer 2 was an AIM thin film with a thickness of 900 mm.

With respect to this recording medium, recording and reproduction were performed in the same manner and under the same conditions as in Example 1, and the threshold recording power (Pw) was determined. The results are shown in Table 1.

Pa had 91 approvals.

In addition, a storage test was conducted under the same conditions as in Example 1, and Hc/
I asked for Hco. The results are shown in Table 1.
Hc/Hco =0.90.

As is clear from the results of Example 1 and Comparative Example 1,
In the optical magnetic recording medium of the present invention provided with the intermediate layer 2 made of a dielectric material with a Se compound dispersed therein, a decrease in threshold recording power was achieved, and an improvement in recording sensitivity was observed. Furthermore, as is clear from the results of the storage test, it had excellent storage stability.

[Examples 2 to 8] Various dielectrics and Se compounds shown in Examples 2 to 8 in Table 1 were used, except that intermediate M2 was constructed.

Various optical magnetic recording media having the same configurations as in Example 1 were produced in the same manner as in Example 1 (Examples 2 to 8).

For these recording media, the threshold recording puff (Pw) and the coercive force ratio He/Hc were determined in the same manner as in Example 1.

The recording sensitivity and storage stability of these media were evaluated. The results are shown in Table 1.

As is clear from the results in Table 1, in the optical magnetic recording medium of the present invention provided with the intermediate layer 2 made of a dielectric material with a Se compound dispersed therein, the laser power required for recording is reduced, and the recording sensitivity is improved. Significant improvements have been made. Also, 4
Even after being left in a high-temperature, high-humidity atmosphere of 5° C. and 85% RH for a long time, almost no change in coercive force was observed, and the storage stability was extremely excellent. Of course, no cracks were observed in these recording media.

[Effects of the Invention] As explained above, the present invention provides a novel optical magnetic recording that improves recording sensitivity, prevents the occurrence of cracks, particularly in the intermediate layer, and also has excellent storage stability. It is now possible to provide media.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing the basic aspect of the optical magnetic recording medium of the present invention, FIG. 2 is a diagram showing the relationship between recording power and reproduction CAM, and FIGS. 3 and 4 are respectively conventional FIG. 1 is a schematic cross-sectional view of an example optical magnetic recording medium. 1--Substrate 2-m-Intermediate layer 3--Magneto-optical recording 1j4-m-Reflection layer 5--Protective layer

Claims (3)

[Claims] (1) An optical magnetic recording medium characterized in that at least an intermediate layer and a magneto-optical recording layer are laminated on a transparent base material, and the intermediate layer is formed by dispersing a Se compound in a dielectric material. . (2) The Se compound is ZnSe, GeSe, In_2
The optical magnetic recording medium according to claim 1, characterized in that it is one or more Se compounds selected from the group consisting of Se_3 and SeCd. (3) The intermediate layer is SiO, SiO_2, ZrO_2
, AIN, Si_3N_4, ZrM, and ZnS.