JPS6233350A - magneto-optical disk - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a magneto-optical disk, particularly a magneto-optical disk having a protective film for protecting a magneto-optical recording medium layer.

"Prior Art" Magneto-optical disks, which use laser light to record, reproduce, and erase information, are capable of recording high-density information, as well as erasing and additionally recording information. Widely used.

As a magneto-optical recording medium of this kind of magneto-optical disk, T
b-Fe system Tb-Fe-Co system, Gd-Tb-Fe system Q
However, none of them have sufficient resistance to corrosion such as oxidation. To this end, various means have been proposed for protecting the magneto-optical recording medium layer in the magneto-optical disk.

For example, a magneto-optical recording medium is sandwiched between films filled with inert gas to prevent oxygen from being mixed in during the production of the magneto-optical recording medium, and a metal film that is easily oxidized is formed on the top layer to prevent external interference. A method has been proposed in which oxygen is used to oxidize the metal film to prevent oxygen from entering the metal film (Japanese Patent Laid-Open No. 110052/1983). Furthermore, a method has been proposed in which a reducing dielectric film is formed between the magneto-optical recording medium and the substrate to stabilize the magneto-optical recording medium by incorporating oxygen, and the presence of this dielectric film is used to prevent oxidation of the magneto-optical recording medium. (Japanese Unexamined Patent Publication No. 59-110056) also uses magneto-optical recording media.

A method of protecting with a non-porous and highly moisture-proof protective film such as Bi or Pb has been proposed (Japanese Patent Laid-Open No. 58-8
No. 0142).

However, with any of the proposed methods, it is insufficient to prevent the magneto-optical recording medium from oxidation and corrosion in an atmosphere containing atmospheric moisture, oil, and moisture. For this reason, in practical terms, when a magneto-optical recording medium is used for a long period of time in such an atmosphere, the magneto-optical recording medium deteriorates, the recording conditions change, and problems such as dropout of recorded information and C/C. Problems such as a decrease in the N ratio have not been completely resolved.

"Problems to be Solved by the Invention" This invention solves the drawbacks of protecting magneto-optical recording media in magneto-optical disks that have been proposed in the past, and uses an air-impermeable and moisture-impermeable protective film to protect magneto-optical recording media. The object of the present invention is to provide a magneto-optical disk which has excellent magneto-optical recording and reproducing characteristics, has a simple overall film structure, requires fewer film-forming steps, does not require complicated manufacturing techniques, and has excellent magneto-optical recording and reproducing characteristics.

"Structure of the Invention" In this invention, a magneto-optical recording medium layer formed on a transparent substrate made of a transparent polymer material such as glass, polycarbonate, acrylic, Evoquin, polymethylbenrane, etc. MOx or DOy or MZ
A protective film, represented by DI-ZOW, is formed to protect the magneto-optical recording medium layer.

This protective film is formed to a thickness of 100 Å to 5000 Å by high frequency sputtering or reactive sputtering, and is laminated on at least the surface of the magneto-optical recording medium layer opposite to the transparent substrate.

In this invention, M indicating the composition of the protective film is Zr or Cr.
where D is Hf or Zn, and x, y, z and W
respectively, 0.6 x f1.9. Q, 4&yfl
,9. The following conditions are set: O<z<1 and Q, 4fWf1.9.

As the magneto-optical recording medium layer, TbFe, GdCo
, TbCo.

DyCo, GdTbFe, QdFeCo, TbD
yFe, GdTbDyFe.

Rare earth transition metal alloy thin films such as TbDyFeCo, Sn, Zn, Ge, Pb, Si,
Rare earth transition metal alloy thin films containing Bi, B, Cr, etc. are used, and these thin films have a thickness of, for example, 1000
It is formed to a thickness of A by means of vacuum evaporation or sputtering.

In the protective film of this invention, X is 0.6 or less and y and W are 0, 4.
If it is less than 1.9, a homogeneous and transparent protective film cannot be obtained, and if X, y and W are larger than 1.9, there will be excess oxygen, and this excess oxygen will be used during the formation of the magneto-optical recording medium layer. , which deteriorates the magneto-optical recording and reproducing characteristics of the resulting magneto-optical disk by being mixed into the magneto-optical recording medium layer.

Furthermore, the presence of this excess oxygen prolongs the time required to reach a desired degree of vacuum in the process of forming the magneto-optical recording medium layer, reducing the productivity of the magneto-optical disk.

If the thickness of the protective film is less than 1000 A, it will not be possible to maintain air impermeability and moisture impermeability during long-term use, and the magneto-optical recording and reproducing characteristics of the resulting magneto-optical disk will deteriorate during long-term use. deteriorate in condition.

On the other hand, when the thickness of the protective film exceeds 5000 A, thermal diffusion within the protective film increases, making it necessary to increase the output of laser light during magneto-optical recording.

In this invention, basically, as shown in FIG. 1, a magneto-optical recording medium layer 2 is formed on a transparent substrate 1, and a protective film 3 is formed on this magneto-optical recording medium layer 2. . However, as shown in FIG.
-1 is formed, a magneto-optical recording medium layer 2 is formed on this first protective film 3-1, and a second protective film 3-2 is formed on this magneto-optical recording medium layer 2. It can also be taken as a thing. In the configuration shown in FIG. 2, the first protective film 3-1 reflects the information reading light that has passed through the magneto-optical recording medium layer 2, and directs this light into the magneto-optical recording medium layer 2. The effect of increasing the Kerr rotation angle of the reflected light for reading due to the Faraday effect and improving the reproduction C/N ratio can also be obtained.

``Example'' Hereinafter, the magneto-optical disk of the present invention will be described in detail based on the example and along with the manufacturing method.

Table 1 shows Examples 1 to 6 and Comparative Examples 1 to 20 corresponding to each example.
The N ratio and C/N ratio over time were shown when M was Zr and D
This is a magneto-optical disk using a protective film having a composition of Hf. A magneto-optical disk as an embodiment in which xr y, z and W and the thickness of the protective film satisfy the conditions of the present invention, x,
Comparative examples of magneto-optical disks in which y, z, and W or the thickness of the protective film do not satisfy the conditions of the present invention are shown.

In each of the Examples and Comparative Examples, as shown in FIG. 1 or 2, TbO, TbO, A magneto-optical recording medium layer 2 having a composition of 21Fe as5CoO,24 was formed to a thickness of 1000 A, and a protective film was formed on the magneto-optical recording medium layer 2 by means of high frequency sputtering while introducing high purity oxygen gas. did.

In any of the examples or comparative examples, the recording frequency was 2 MHz (RBW 30 I).
Hz) Recording was performed with a laser power of 5 mw, and reproduction was performed with a reproduction laser power of l mw. The C/N ratio when played back immediately after recording is the initial C/N ratio (dB) in Table 1.
The C/N ratio obtained by reproducing the magneto-optical disk after leaving it in an atmosphere at 60° C. and 90% RT for 1000 hours is the aged C/N ratio.

Example 1 is a case in which a protective film 3 having a composition of Zr0ts and a film thickness of 200 OA was formed directly on a transparent substrate 1 as shown in FIG. 1, and the initial C/N ratio and aging C/N ratio were each 4. .9 (dB) and 48 (dB), confirming that due to the presence of the protective film 3, a magneto-optical disk with excellent long-term durability and stable magneto-optical recording and reproducing characteristics was obtained.

Comparative Example 1 is a case in which the composition of the protective film 3 is Zr0r)3 and the protective film is formed to a thickness of 200 OA as shown in Fig. 1 under the same conditions as Example 1, and the oxygen Because of the insufficient amount of the protective film 3, a homogeneous and transparent protective film 3 cannot be obtained. For this reason, the protective film 3 no longer satisfies the conditions of non-air permeability and non-moisture permeability, and the C/N ratio over time significantly deteriorates to 36 (dB).

Table 1 Comparative Example 2 is under the same conditions as Example 1, but the composition of the protective film 3 is changed to Z.
This is a case where a protective film is formed as shown in FIG. 1 to a film thickness of 2000 A with r02.0, and oxygen is present in excess compared to the conditions of the present invention. Because this excess oxygen mixes into the magneto-optical recording medium layer during formation of the magneto-optical recording medium layer, the initial C/N ratio and the aging C/N ratio are respectively 43 (
dB) and 32 (dB), and the magneto-optical recording and reproducing characteristics have deteriorated.

Comparative Example 3 was conducted under the same conditions as Example 1, with the composition of the protective film 3 being Zr01. As shown in FIG. 1, a protective film is formed at a thickness of 500A as shown in FIG. Initial C/N ratio and aging C
/N ratios of 48 (dB) and 35 (dB), respectively, confirming that the film thickness is too thin to maintain air impermeability and moisture impermeability during long-term use.

Comparative Example 4 is a case where the protective film 3 was formed under the same conditions as in Example 1 to a thickness of 7000 A as shown in FIG. This is a case where the film thickness is thicker than the condition. The initial C/N ratio and the aging C/N ratio are 42 (dB) and 41 (dB), respectively, and the C/N ratio is generally low because the film is too thick. increases, and it is necessary to increase the output of the laser light.

Example 2 is a case in which a protective film 3 having a composition of HfOY.5 and a thickness of 2000λ was formed as shown in FIG.
/N ratio and C/N ratio over time are 5Q (dB) and 4, respectively.
9 (dB), and due to the presence of the protective film 3, a magneto-optical disk with excellent long-term durability and stable magneto-optical recording and reproducing characteristics has been obtained.

Comparative Example 5 was conducted under the same conditions as Example 2, but the composition of the protective film 3 was changed to H.
This is a case where a protective film is formed as shown in FIG. 1 with a film thickness of 2000 A as f0o,s, and oxygen is insufficient for the conditions of the present invention. Therefore, a homogeneous and transparent protective film 3 cannot be obtained, the protective film 3 no longer satisfies the conditions of air impermeability and moisture impermeability, and the initial C ratio and aging C/N ratio are 48 (dB) and 35 (dB), respectively. dB), the magneto-optical recording and reproducing characteristics deteriorate.

Comparative Example 6 is a case where the composition of the protective film 3 is HfO□0 and the protective film is formed to a thickness of 2000λ as shown in FIG. 1 under the same conditions as in Example 2. Excess oxygen is present. Because this excess oxygen is mixed into the magneto-optical recording medium layer during formation of the magneto-optical recording medium layer, the initial C/N ratio and the aging C/N ratio are each 42 (d
B) and 29 (dB), indicating that the magneto-optical recording and reproducing characteristics have deteriorated.

Comparative Example 7 is a case in which the protective film 3 is formed under the same conditions as Example 2 to a film thickness of 500 A with the composition Hf0t,s, which is thinner than the film thickness conditions of the present invention.

Initial C/N ratio and aging C/N ratio are each 48 (dB)
and 33 (dB), confirming that the film cannot maintain breathability and moisture impermeability even after long-term use due to the thin film thickness.

Comparative Example 8 is a case where the protective film 3 was formed under the same conditions as in Example 2, with the composition of Hf01.5 and a film thickness of 7000 AK as shown in FIG. This is a case where the film thickness is thicker than the condition. The initial C/N ratio and the aging C/N ratio are 41 (dB) and 40 (dB), respectively, and the C ratio is generally low because the film is too thick, and heat diffusion within the protective film 3 increases. However, it is necessary to increase the output of laser light.

Example 3 has a composition of Zr01. This is the case where a protective film 3-1.3-2 with a film thickness of 2000 A and a thickness of 2000 A is formed on a transparent substrate 1 so as to sandwich the magneto-optical recording medium layer 2 from both sides as shown in FIG. 2, and the initial C/N is A magneto-optical disk with excellent long-term durability and stable magneto-optical recording and reproducing characteristics was obtained, with both the C/N ratio and the C/N ratio over time being 52 (dB).

Comparative Example 9 was conducted under the same conditions as Example 3, with protective film 3-1.3
-2 composition is Zr0o3 and the film thickness is 2000A.
This is a case where a protective film is formed as shown in the figure, and a homogeneous and transparent protective film 3 cannot be obtained because oxygen is insufficient compared to the conditions of the present invention. For this reason, the protective film 3 no longer satisfies the conditions of air impermeability and moisture impermeability, and the initial C/N ratio and aging C/N ratio are 51 (dB) and 42 (dB), respectively.
In B), the C/N ratio particularly decreases over time.

Comparative Example 10 was conducted under the same conditions as Example 3, with protective films 3-1.
This is the case where a protective film was formed with the composition of 3-2 as ZrO2,0 to a thickness of 2000 Å as shown in FIG. 2, and oxygen was present in excess compared to the conditions of the present invention. Because this excess oxygen is mixed into the magneto-optical recording medium layer during formation of the magneto-optical recording medium layer, the initial C/N ratio and the aging C/N ratio are 42.
(dB) and 30 (dB), the magneto-optical recording and reproducing characteristics deteriorate.

Comparative Example 11 was conducted under the same conditions as Example 3, with protective films 3-1.
This is a case in which the composition of 3-2 is ZrO+, s and a protective film is formed at 500 Å in thickness as shown in FIG. 2, which is thinner than the film thickness condition of the present invention. Early C/
N ratio and C/N ratio over time are 49 (dB) and 37, respectively.
(dB), confirming that due to the thin film thickness, it is not possible to maintain air impermeability and moisture impermeability during long-term use.

Comparative Example 12 was carried out under the same conditions as Example 3, with protective films 3-1.
The composition of 3-2 is ZrO+, s, and the film thickness is 7000'A.
This is a case where a protective film is formed as shown in FIG. 2, and the film thickness is thicker than the film thickness condition of the present invention. The initial C/N ratio and the aging C/N ratio are 43 (dB) and 42 (dB), respectively, and the C/N ratio is generally low because the film is too thick, and the protective film 3-1.3-2 Thermal diffusion within the laser beam increases, requiring an increase in the output power of the laser light.

Example 4 is a case in which a protective film 3-1.3-2 having a composition of HfO+, s and a film thickness of 2000 A was formed sandwiching a magneto-optical recording medium layer as shown in FIG. The C/N ratio over time was both 52 (dB), and a magneto-optical disk with excellent long-term durability and stable magneto-optical recording and reproducing characteristics was obtained.

Comparative Example 13 was conducted under the same conditions as Example 4, with protective films 3-1.
This is a case where a protective film is formed with the composition of 3-2 as Hf0o3 and a film thickness of 2000A as shown in Fig. 2. Since oxygen is insufficient for the conditions of this invention, a homogeneous and transparent protective film is formed. I can't get 3. For this reason, the protective film 3 no longer satisfies the conditions of non-air permeability and non-moisture permeability, and the initial C/
N ratio and C/N ratio over time are 51 (dB) and 41, respectively.
(dB), the C/N ratio decreases over time.

Comparative Example 14 is a protective film 3-1.3 under the same conditions as Example 4.
This is the case where a protective film was formed as shown in FIG. 2 with a film thickness of 2000 Å using HfO2,O as the composition of -2, and oxygen was present in excess compared to the conditions of the present invention. Because this excess oxygen is mixed into the magneto-optical recording medium layer during formation of the magneto-optical recording medium layer, the initial C/N ratio and the aging C/N ratio are 43 (dB) and 29 (dB), respectively. Magneto-optical recording and reproducing characteristics have deteriorated.

Comparative Example 15 was conducted under the same conditions as Example 4, with protective films 3-1.
The composition of 3-2 was HfO, 5, and the film thickness was 50OA.
This is a case where a protective film is formed as shown in the figure, and the film thickness is thinner than the film thickness condition of the present invention. Initial C/N
ratio and temporal C/N ratio were 49 (dB) and 33 (
dB), and it is confirmed that due to the thin film thickness, it is not possible to maintain air impermeability and moisture impermeability during long-term use.

In Comparative Example 16, protective film 3-1 was prepared under the same conditions as Example 4.
．． The composition of 3-2 is HfO, 5, and the film thickness is 700OA.
This is the case where the film is formed as shown in FIG. 2, and the film thickness is thicker than the film thickness condition of the present invention.

The initial C/N ratio and the aging C/N ratio were each 43 (dB
) and 42 (dB), and because the film is too thick, C/
Since the N ratio is generally low and heat diffusion within the protective film 3 increases, it is necessary to increase the output of the laser beam.

Example 5 has a composition of Zr o, s Hf O, 501,5
This is the case where a protective film 3 with a film thickness of 2000 M is formed at 5 as shown in Fig. A magneto-optical disk having excellent long-term durability and stable magneto-optical recording and reproducing characteristics has been obtained.

Further, in Example 6, a protective film 3-1.3-2 having a composition of ZrO,5Hf6,50.5 and a film thickness of 2000 was formed as shown in FIG. 2, and the initial C/N ratio and Time C/
The N ratio is 51 (dB) in each case, and due to the presence of the protective film 3, a magneto-optical disk having excellent long-term durability and stable magneto-optical recording and reproducing characteristics can be obtained.

Comparative Example 17 was performed under the same conditions as Example 1, when the composition of the protective film 3 was SiO, and a protective film was formed to a thickness of 2000 A as shown in FIG. 1. Comparative Example 18 was performed under the same conditions as Example 3. This is the case where the composition of the protective film 3-1, 3-2 is SiO, and the protective film is formed to a thickness of 2000 mm as shown in FIG. In either case, the initial C/N ratio and the temporal C/N ratio were each 49 (dB).

52 (dB), 22 (dB), and 26 (dB), which indicates that the protective film made of this material does not satisfy the conditions of non-air permeability and non-moisture permeability, and that the protective film with the composition of the present invention is superior. shown.

Comparative Example 19 was performed under the same conditions as Example 1, when the composition of the protective film 3 was Si3N4, and a protective film was formed to a thickness of 2000 A as shown in FIG. 1. Comparative Example 20 was performed under the same conditions as Example 3. This is the case where the protective film 3-1, 3-2 has a composition of 5i3N4 and the protective film is formed to a thickness of 2,000 mm as shown in FIG.

The initial C/N ratio and the aging C/N ratio were each 49 (dB
), 53 (dB) and 21 (aB), 26
(dB), and the protective film made of this material does not satisfy the conditions of non-air permeability and non-moisture permeability, confirming that the protective film with the composition of the present invention is excellent.

Similarly, Table 2 shows Examples 6 to 11 and Comparative Examples 21 to 3G corresponding to each example.
2, and the initial C/N ratio and C/·N ratio over time are shown for these.

Example 6 has a composition of Cry. Example 7 is a case in which a protective film 3 having a thickness of 2000 A and a thickness of 2000 λ is formed as shown in FIG. 1 with a composition of Zn0o7. be.

In each example, the initial C/N ratio and the aged C/N ratio
The N ratios are 48 (dB), 50 (dB) and 48 (
dB), 50 (dB), and due to the presence of the protective film 3, a magneto-optical disk with excellent long-term durability and stable magneto-optical recording and reproducing characteristics has been obtained.

Example 8 is a case in which a protective film 3-1.3-2 having a composition of CrOx, o and a film thickness of 2000 A was formed sandwiching the magneto-optical recording medium layer 2 as shown in FIG. is a protective film 3-1゜3- whose composition is Zn0O and has a thickness of 2000A.
2 is formed by sandwiching the magneto-optical recording medium layer 2 as shown in FIG.

Initial C/N ratio and aging C/N of these Examples 8 and 9
The ratios are 51 (an), 50 (dB), and 50 (dB), respectively, and the presence of the protective film 3 indicates that a magneto-optical disk with excellent long-term durability and stable magneto-optical recording and reproducing characteristics was obtained.・Example 10 has a composition of Cro5
Protective film 3 with a film thickness of 2000A with zno,, oo8 as the first
As shown in the figure, in the case of forming only one layer, Example 11 has a composition of Cro, 5 Zn, 6,500. Film thickness 200 at B
This is a case where protective films 3-1, 3-2 of 0 A are formed sandwiching the magneto-optical recording medium layer 2, as shown in FIG.

Initial C/N ratio and aging C/N ratio of these Examples 9 and 10
The N ratio is 50 (dB), 48 (dB), 50 (dB), and 47 (dB), respectively, and due to the presence of the protective film 3, it has excellent long-term durability and has stable magneto-optical recording and reproducing characteristics. The disc is obtained.

Comparative Examples 21, 24, 27 and 30 are cases in which oxygen is insufficient compared to the conditions of the invention. Comparative Examples 21, 24, 27 and 30 are, respectively, when the protective film 3 is made of Cr0o, a for Example 6, when the protective film 3 is made of Zn0o2 for Example 7, and for Example 8. This is the case where the protective film 3-1.3-2 is made of Cr063, and the case where the protective film 3-1.3-2 is made of Zn0.2 in contrast to Example 9.

Initial C/N ratio and aging C/N ratio are 49 (dB), respectively.
, 34 (dB), 49 (dB), 33
(dB).

51 (dB), 41 (dB) and 50 (dn
), 40 (dB), a homogeneous and transparent protective film could not be obtained due to the lack of oxygen, and the conditions of air impermeability and moisture permeability of the protective film were not satisfied, resulting in poor magneto-optical recording and reproducing characteristics. It has deteriorated.

Comparative Examples 22, 25, 28, and 31 are all cases in which the thickness of the protective film is thinner than the conditions of the invention.

Comparative Examples 22, 25, 28 and 31 are Example 6.
Example 7. This is the case where the thickness of the protective film is 50 OA, which is greater than that of Examples 8 and 9.

In these comparative examples, the initial C/N ratio and the aging C/N ratio were 48 (dB) and 35 (an), respectively.

49 (dB), 32 (dB), 48 (d
B), 35 (dB).

and 49 (dB) and 34 (dn), and because the film thickness is thin, it is not possible to maintain air impermeability and moisture impermeability during long-term use, and magneto-optical recording and reproducing characteristics are insufficient. Comparative Examples 23, 26, 29, and 32 are all cases in which the thickness of the protective film is thicker than the conditions of the invention.

Comparative Examples 23, 26, 29 and 32 are respectively Example 6
．． Example 7. This is the case where the thickness of the protective film was set to 700 OA for Examples 8 and 9.

In these comparative examples, the initial C/N ratio and the aged C
/N ratio is 41 (dB), 39 (dB),
42 (aB), 41 (an), 42 (aB),
40 (dB) and 41 (dB), and because the film is too thick, the C/N ratio is generally low, and heat diffusion within the protective film increases, making it necessary to increase the output of the laser light.

Comparative Examples 33 and 34 are Example 6 and Example 8, respectively.
This is the case where the protective film is formed of SiO with a thickness of 2000 Å. The initial C/N ratio and aging C/N ratio in Comparative Examples 33 and 34 were 49 (dB) and 22, respectively.
(dB) and 52 (dB), 26 (dB)
It is confirmed that the properties of the protective film of the composition of the present invention are excellent.

In each example, the composition is Tbo2t Feo55C
Although a magneto-optical recording medium layer having an angle of Oo, z4° is used, the composition is not necessarily limited to this, and other magneto-optical recording medium layers such as a QdFeCo-based magneto-optical recording medium layer can also be used.

In each embodiment, the magneto-optical recording medium layer 2 is directly formed on the transparent substrate 1 and the protective film 3 is provided on the magneto-optical recording medium layer 2, and the protective film 3 is formed on the transparent substrate 1. 1.3
The case where the magneto-optical recording medium layer 2 is formed so as to be sandwiched by -2 has been described.

However, this invention is not limited to the configuration of each embodiment,
For example, it is also possible to realize a structure in which an ultraviolet curing resin is further applied on a protective film formed on the surface of the magneto-optical recording medium layer 2 opposite to the transparent substrate 1. Alternatively, it is also possible to realize a structure in which the magneto-optical disks constructed according to the present invention are opposed to each other, an opposing space is formed by a spacer 2, and this opposing space is filled with an inert gas.

"Effects of the Invention" As explained in detail above, according to the present invention, in a magneto-optical disk in which a magneto-optical recording medium layer is formed on a transparent substrate, at least the surface of the magneto-optical recording medium layer opposite to the transparent substrate is Composition MOx or DOy or MzDl-2
ow (M is Zr or Cr, D is Hf or Zn
) with a film thickness of 10001.9.0 (Z
(By setting the conditions of 1 and 0.4 fw-f 1.9, the magneto-optical recording medium layer is protected while maintaining air-impermeability and moisture-impermeability, and has long-term durability. It is possible to provide a magneto-optical disk that has a simple process and excellent magneto-optical recording and reproducing characteristics.

[Brief explanation of drawings]

FIGS. 1 and 2 are sectional views showing the configuration of an embodiment of the magneto-optical disk of the present invention, respectively. 1: Transparent substrate, 2: Magneto-optical recording medium layer, 3, 3-1.3
-2: Protective film.

Claims (1)

[Claims] (1) In a magneto-optical disk in which a magneto-optical recording medium layer is formed on a transparent substrate, and in which information is written and read by irradiating the magneto-optical recording medium layer with a light beam, at least The composition is MO_x or DO_y or M_zD_1_ on the surface opposite to the transparent substrate.
-_zO_w (M is Zr or Cr, D is Hf or Zn), and a protective film with a thickness of 1000 Å to 5000 Å is formed to protect the magneto-optical recording medium layer,
The x, y, z and w are each 0.6≦x≦1.9,
0.4≦y≦1.9, 0<z<1 and 0.4≦w≦1.
A magneto-optical disk characterized by being selected as No. 9.