JPH02246034A - Magneto-optical disk medium - Google Patents

Abstract

PURPOSE:To improve the recording sensitivity of a magnetic film by providing a dielectric layer having specific thermal conductivity as at least one of protective layers on a substrate for the magnetic layer. CONSTITUTION:The medium consists of a glass substrate 1, photopolymer 2, base protective film 3 consisting of SnO2, magnetic layer 4 such as TbFeCo and a protective film 5 of Tb-SiO2 same as in conventional medium. The base protective film 3 is a dielectric material comprising SnO2 with <=3W/cm.K thermal conductivity. By using the base protective film of dielectric material (SnO2) with such low thermal conductivity, the magnetic layer 4 of the magneto- optical disk can maintain large heat insulation, so that the recording sensitivity can be enhanced.

Description

[Detailed Description of the Invention] [Summary] Regarding a magneto-optical disk medium, particularly a magneto-optical disk medium that can be made highly sensitive, a 3W/magneto-optical disk is coated on a substrate for the purpose of improving the recording sensitivity of the magnetic film of the magneto-optical disk. The structure includes a magnetic layer including at least one protective layer of a dielectric material having a thermal conductivity of cm·K or more.

[Industrial application field]

The present invention relates to a magneto-optical disk medium, and in particular, has a high sensitivity [Prior Art] Unlike a magnetic disk, a conventional magneto-optical disk cannot be overwritten, and thus has a slow data transfer speed. Currently, one possible method for high-speed transfer using a magneto-optical disk is to rotate the disk at high speed. However, since recording on magneto-optical disks is thermomagnetic recording, good recording cannot be achieved unless the recording sensitivity is increased when the disk rotates at high speeds. Therefore, higher sensitivity is required.

[Problem to be solved by the invention]

Magneto-optical disks that rotate at high speeds for high-speed transfer perform writing and reproduction at more than twice the rotation speed of conventional disks. A particular problem with high-speed rotation is that even if the magnetic layer is heated, it is easily cooled down, so the magnetic layer is not heated sufficiently. Naturally, increasing the laser power will result in sufficient heating, but the output of semiconductor lasers currently in use is limited to 10 mW.

Furthermore, in order to substantially increase the amount of light absorbed by the magneto-optical recording layer in the base protective film for higher sensitivity, [absorption (A
%> = ioo% - (Reflectance (R%) + Transmittance (T%)
)], it is necessary to reduce the reflectance. In order to reduce the reflectance, it is sufficient to increase the refractive index of the underlying protective film. However, since magneto-optical disks use a rare earth-transition metal alloy that is easily oxidized as a magnetic layer, the protective effect cannot be reduced. Currently, Tb-3in□ is considered to be the most suitable protective film material for the magnetic layer, but this protective film cannot reduce the reflectance to 25% or less, so it is disadvantageous for achieving high sensitivity.

In view of the above-mentioned problems, an object of the present invention is to increase the recording sensitivity of a magneto-optical disk magnetic film.

[Means to solve the problem]

According to the present invention, the above problem can be solved by applying 3 W/am on the substrate.
The problem is solved by a magneto-optical disk medium characterized by comprising a magnetic layer having at least one protective layer made of a dielectric material having a thermal conductivity of K or less.

Furthermore, according to the present invention, the above-mentioned problem is solved by an optical device characterized in that a Tb-3in□ layer as a base protective layer, a dielectric and magnetic layer having a refractive index of 2 or more, and a Tb 5iOz layer are sequentially formed on a substrate. This problem is solved by magnetic disk media.

In the present invention, it is preferable for at least one of the sandwiched protective layers that protect the magnetic layer from both sides to be a Tb-3I02 layer in view of the protective effect.

In the present invention, the above-mentioned protective layer means a so-called base protective film or upper protective film that protects a magnetic layer as a magneto-optical recording layer, and according to the structure of the magneto-optical disk of the present invention: (1) Substrate/ Dielectric film/magnetic layer/Tb-3102 film■ Substrate/dielectric film/magnetic layer/dielectric film■ Substrate/'rb 5
102 film/magnetic layer/dielectric film■ Substrate/Tb-3in□
Possible examples include film/high refractive index protective film/magnetic layer/Tb-3iO3 film.

The substrate is preferably a glass-photopolymer or plastic substrate, and the dielectric film has a thermal conductivity of 3 W/Cm·K or less.

The magnetic layer is made of TbFeCo, GdFeCo, G
dTbCo etc. are used.

Further, in order to make the protective effect more effective, it is preferable that the protective film of the magnetic layer is the lowermost layer and the uppermost protective layer is a Tb-3I[+2 film. That is, in the case of the above configuration (■), ■' substrate/Tb-3102 film/dielectric film/magnetic M/Tb
-3in□ film, ■If the configuration is ■'substrate/Tb-3iO□ film/dielectric film/magnetic layer/dielectric film/Tb-3in□ film■, ■'substrate/Tb- 3in□ film/magnetic layer/dielectric film/Tb
-3 inch □ film.

[For production]

According to the present invention, by using a dielectric material with low thermal conductivity or high refractive index as the sandwiching layer of the magnetic layer, it is effective in keeping the magnetic layer warm or improving the recording sensitivity, thereby enabling high-speed rotation of the disk.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a sectional view of a magneto-optical disk medium according to the present invention.

In FIG. 1, 1 is a glass substrate, 2 is a photopolymer with a thickness of about IJM, 3 is an underlying protective film made of SnO□ with a thickness of about 1100 nm, and 4 is a TbFe film with a thickness of about 50 nrn.
A magnetic layer made of Co or the like, and 5 a Tb-3tOz protective film having a thickness of about 1100 nm, similar to the conventional one.

The base protective film 3 made of 5n02 of the magneto-optical disk shown in FIG. 1 has a thermal conductivity of 2.9 W/Cm·K and 3 W.
/Cm·K or less. FIG. 3 shows the recording and reproducing characteristics of a magneto-optical disk medium obtained by using a dielectric film (SnO□) with low thermal conductivity as an underlying protective film. Second
The figure shows a conventional example (disc rotation speed is 1800 rpm).
m, recording frequency 1. OMHz.

The magnetic field was set to 3000e). These figures show that the method of the present invention using SnO□ as the underlying protective film (Tb-3iO3
(using Tb-3iOz as the upper protective film) improves the recording sensitivity by about 40% compared to the conventional case where Tb-3iOz is used as both protective films.

In FIGS. 2 and 5, the solid line indicates CNR (carrier to noise ratio), the dashed line indicates second harmonic/noise, and the broken line indicates noise level.

From the relationship between CNR and recording laser power and the relationship between second harmonic/noise ratio and recording laser power shown in Figures 2 and 5, record the maximum point of CNH and the minimum point of second harmonic/noise. Laser power may be used.

In the conventional magneto-optical disk configuration, the recording laser power is 3
The CNR saturates above ~4 mW, while the harmonics/noise reaches its minimum value at a recording laser power of about 4.6+nW.

Therefore, the recording sensitivity of the conventional magneto-optical disk is 4.6 mW.

On the other hand, in the configuration of the magneto-optical disk of the present invention, the CNR is saturated at a recording laser power of 2 to 3 m11 or more, while the second harmonic/noise ratio is approximately 2.8 mW at the recording laser power.
becomes the minimum value.

The recording sensitivity of the magneto-optical disk of the present invention is 2.81'llll.
It is 1l. In addition, in FIG. 2 and FIG. 5, the recording and reproducing characteristics were obtained as follows. First, 1-aoorpm
A single frequency signal of LOMHz was recorded on a magneto-optical disk rotating at a recording frequency of 1.0 MHz using an external magnetic field of 3000e and by changing the recording laser power.

For playback, use a spectrum analyzer with a bandwidth of 30KH.
z, with a carrier-to-noise ratio (C/N) of 1°OMHz.
ratio) obtains a CNR of approximately 55 dBm.

In addition, a dielectric film with low thermal conductivity (3W/Cm・K or less) is
Table 1 shows the results using nO□O instead.

The first margin below shows the upper protective film SnO, and the lower protective film is the conventional Tb
Table 2 shows the recording sensitivity when -3iDz.

Table 2 (*) Bulk value: In the case of a thin film of 1100n or less, it may differ from the bulk value (00) Estimated value The above dielectric film was produced by RF sputtering with an output Q of 1klli and a pressure of 5pa (Ar gas ). Table 1 shows that even if TiO□, ZrO□, etc. are used instead of SnO□, compared to the conventional Tb-3i[l□, both
% or more (approximately 17% to 39%).

Next, as a second embodiment, when both the base protective film 3 and the top protective film are made of SnO□, and in the third embodiment and the first embodiment described above, the base protective film is SnO□ and the top protective film is When the conventional Tb-3+Oz is used, the recording sensitivity is 2.
Considering that the output power was 3 mW and the ratio to the conventional one was 40, the second embodiment achieved the highest sensitivity. This is thought to be because the upper and lower portions of the magnetic layer are made of Sn[l□, which has a low thermal conductivity, so that heat escape is minimized.

Next, as a fourth example, glass-photopolymer/Tb
-3hot (underlying protective film) /51102 (high refractive index dielectric film) /magnetic layer /Tb-5+[]z The recording and reproducing characteristics are shown. This result was almost the same as that shown in FIG. 3 above. On the other hand, if we look at the lifespan (Figure 4),
Conventional Tb-3in. Comparing the method of the present invention with the method of the present invention, it can be seen that the disk of the present invention has a protective effect equivalent to that of the conventional case using only Tb-3iO2.

In addition, the results of examining other materials for the high refractive index dielectric film shown in Table 3 are almost the same as those in Table 1 above, and all films achieve high sensitivity, with a refractive index of 2. If the above film is used, the sensitivity will surely be improved by 10% or more when compared with the conventional Tb-3iO□. Regarding the protective effect, Tb
If -3iO□ is used, the life will not deteriorate. That is, recording sensitivity can be further improved by selecting a dielectric material having a thermal conductivity of 3 W/cmk or less as shown in Table 1 and a material having a refractive index of 2 or more shown in Table 3. It seems possible to do so.

Incidentally, FIG. 5 shows a sectional view of the disk of the present invention. Fifth
In the figure, the same reference numerals as in FIG. 1, including the Sn02 film 6, indicate the same materials.

Margin Table 3 below [Effects of the Invention] As explained above, according to the present invention, the heat retention effect of the magnetic layer of the magneto-optical disk medium is increased, so that recording sensitivity is increased and high sensitivity can be achieved.

[Brief explanation of drawings]

Fig. 2 is a cross-sectional view of a magneto-optical recording medium for explaining the present invention in detail, Fig. 2 is a diagram showing the recording and reproducing characteristics of the magneto-optical recording medium of the present invention, and Fig. 3 is a diagram showing the recording and reproducing characteristics of the magneto-optical recording medium of the present invention. FIG. 4 is a cross-sectional view showing another magneto-optical recording medium of the present invention, and FIG. 5 shows the recording and reproducing characteristics of a conventional magneto-optical recording medium. It is a diagram. DESCRIPTION OF SYMBOLS 1...Glass substrate, 2...Photopolymer 3...Underlying protective film, 4...Magnetic layer, 5.
-Tb-310z protective film, 5.5n02 film.

Claims (1)

[Claims] 1. A magneto-optical disk medium comprising a magnetic layer having at least one protective layer made of a dielectric material having a thermal conductivity of 3 W/Cm·K or less on a substrate.