JPS6299935A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To improve corrosion resistance and shelf life while maintaining the recording sensitivity and reproducing efficiency of a photomagnetic recording medium by increasing the coblt content near the surface of a recording layer than that in the inside. CONSTITUTION:A layer which consists of a resin curable by UV rays and has spiral guide grooves is formed on sheet glass and such glass is used as a disk substrate 1. SiO is depoosited by evaporation as an underlying layer 2 on the substrate 1 and in succession, the recording layer 3 consisting of an amorphous magnetic alloy and a surface layer 3a contg. Co at a high ratio are formed by binary RF sputtering using the 1st target 1 consisting of Fe, GdTb and the 2nd target consisting of Co, GdTb in succession thereto. SiO is deposited by evaporation thereon as a protective layer 4. The two disks formed in the above-mentioned manner are stuck by a hot-melt adhesive agent 5 in such a manner that protective layers 4 thereof are positioned on the inner side. The optical disk is thus manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used for erasable and rewritable high-density memory.
The present invention relates to magneto-optical recording media in the form of disks, cards, sheets, and tapes that are recorded by heating with light irradiation and can be read using the magneto-optic effect.

[Conventional technology]

As magneto-optical materials, the magnetism of rare earth transition metals makes it possible to easily form large-area thin films at temperatures near room temperature, record signals with small optical energy, and read out recorded signals with a good S/N ratio. In recent years, amorphous alloys have been actively studied as superior materials. For example, GdCo, GdF
e, TbFe, DyFe, GdTbFe.

TbDyFe, GdFeCo, TbFeCo, G
dTM;o, GdTbFeCo, etc. are known.

Among these, those containing Fp and CO as transition metals are particularly useful because they are easy to obtain perpendicular magnetic anisotropy, the key temperature for recording is appropriate, and the magneto-optical effect is large. ing. On the other hand, these magnetic amorphous alloys are easily oxidized and corroded, and have problems in long tUt storage stability as recording media.

Therefore, along with the development of an anti-corrosion iF layer to protect the recording layer,
Research is underway to improve the corrosion resistance of the recording layer itself.

[Problem that the invention seeks to solve]

When improving the corrosion resistance of the recording layer itself, among the various constituent elements mentioned above, Coi is the most excellent in corrosion resistance, and the higher the content of Coi, the better the corrosion resistance will be. Since the effect is that the Kerr rotation angle increases, it is desirable to take advantage of such properties of CO. However, when the CO content of the recording layer is high, its Curie temperature becomes high, and the optical energy required for recording becomes too large, making it impractical as a recording medium.

Therefore, despite Go's high corrosion resistance improving effect, the current situation is that its properties have not yet been fully utilized.

The present invention solves the problems listed in item L, and aims to provide a magneto-optical recording medium having a recording layer with excellent corrosion resistance while maintaining recording sensitivity and reproduction efficiency.

[Means for solving problems]

The present invention, which is capable of achieving the above objects, has a recording layer comprising an amorphous thin film of a transition metal and a rare earth element containing at least iron and cobalt, and exhibiting a magneto-optical effect, typically a Kerr effect or a Faraday effect. A magneto-optical recording medium provided on a substrate is characterized in that the content of cobalt in the vicinity of at least one surface of the recording layer is higher than in the interior thereof.

There is no particular restriction on the type of recording layer as long as it satisfies the above requirements, but its main components include, for example, GdFeCo, T
bFeCo, GdTbFeCo, TbDyFeCo
etc. can be mentioned as preferred.

The Go content of the recording layer may be distributed in such a way that it gradually increases linearly or curvedly from the inside toward the surface in the thickness direction of the recording layer, or it may be distributed only in the vicinity of the surface (surface layer) with a certain thickness. You can increase it. In the latter case, the surface layer may be provided on one or both sides of the recording layer depending on the degree of corrosion resistance required.
The total thickness of the surface layer is 1/20 to 1/2 of the entire recording layer.
The range of is appropriate.

The content ratio of Go in the entire recording layer is appropriately selected within a range that can achieve the effects described below and to an extent that does not cause a decrease in recording sensitivity, depending on the distribution state of Go in the recording layer.

The recording layer can be easily formed by, for example, sputtering method,
In various lamination methods such as vacuum evaporation method and ion blating method, the evaporation source or target consisting of the raw material components of the recording layer is divided into those containing Co and those not containing Co, and each is separated in order to scatter both during film formation. By relatively changing the magnitude of both energies applied independently and simultaneously, the ratio of the ease of scattering of the two is gradually or stepwise changed, and the proportion of Go in the scattering components is changed. This can be done by

[Effect]

The recording layer has a higher Go content near the surface than inside.
This function works to improve the oxidation and corrosion resistance of the recording layer itself.This function is achieved by the same amount of CO contained in the recording layer.
is superior to a similar effect of a recording layer in which the particles are evenly distributed throughout.

The main cause of the above effect is thought to be as follows. In other words, most of the oxidation and corrosion of the recording layer is caused by oxygen and moisture that have passed through the various layers and substrates provided outside the recording layer. This is thought to be because the Go high concentration region near the surface effectively prevents this.

In addition, the recording layer in the present invention has G in the vicinity of its surface.
Even if a large amount of O is contained, the proportion of Go in the entire recording layer can be kept low, so that the increase in the Curie temperature is small and a decrease in recording sensitivity can be suppressed.

〔Example〕

The present invention will be explained in more detail with reference to Examples below.

Example 1 An optical disc according to the present invention having the structure shown in the partially omitted membrane type sectional view of FIG. 1 was produced. First, by a method called the 2P method, an ultraviolet curable resin layer having a spiral guide groove in the shape of an S plate lath having a diameter of 200 mm and a thickness of 1.1 mm was formed, and this was used as the disk substrate 1. SiO was deposited at 900A as the base layer 2 on -L of this substrate using a diaphragm deposition system.
It was deposited to a thickness of . Subsequently, a focm square GdTb alloy chip (composition ratio 1:
The first target with 22 pieces of 1) lined up and φ1.25mm
A recording layer 3 of an amorphous magnetic alloy was formed by binary RF sputtering using a part of Ca and a second target in which the same number of GdTb alloy chips were arranged. CO content is 300W in each target and 40W in the second target.
After sputtering for 11 minutes by applying RF power of
The RF power was 170 W each to form a surface layer 3a with a high content.

The power was changed to 170W and sputtering was performed for 3 minutes. On top of that, SiO
200OA was deposited as the protective layer 4. The two discs thus produced were bonded together with a hot melt adhesive 5 so that the protective layer 4 was on the inside to produce an optical disc according to the present invention. Note that in FIG. 1, one half of the optical disc is omitted. The characteristics of this optical disc were compared with those of Comparative Examples 1 and 2 below.

Comparative Examples 1 and 2 The same method as in Example 1 was repeated except that the film forming conditions for the recording layer were as shown in the table above, and the Co content ratio of the entire recording layer was constant, and the ratio was An optical disk (Comparative Example 1) having the same part (inside) of the recording layer 3 other than the surface layer of the optical disk of Example 1 and an optical disk (Comparative Example 2) having the same surface layer 3a of the recording layer of the optical disk of Example were prepared. .

According to the analysis of ES['', the Go/(Fe4Co) values were 13 atomic % (Comparative Example 1) and 52 atomic % (Comparative Example 2), respectively.
It can be considered to be equal to Fe. Note that (Gd+Fb)/(F
e+C:o) had 173 atoms.

Using the optical discs of Example 1 and Comparative Examples 1.2, the rotation speed was 1.
When a 4 MHz pulse recording/reproducing test was conducted at 80 f rpm, the optical disc according to the present invention obtained a C/N ratio of 51 dB at a recording laser power of 7 mW. The same was true for Comparative Example 1, but only 45 dB was obtained even when recording at 10 mW in Comparative Example 2.

Next, in order to evaluate the corrosion resistance of these optical discs, they were left in a constant temperature and humidity chamber at 70°C and 85% humidity for 500 hours, and then taken out and subjected to a recording/reproduction test again.

The optical disc according to the present invention is 7ff11 almost the same as the initial version.
! In Comparative Example 1, C/N of 51 dB was obtained.
decreased to 48dB. Comparative example 2 is 45dB, same as the initial
and low. This result shows that the optical disc according to the present invention has excellent recording properties and corrosion resistance.

Example 2 An optical disk in which the Co content was increased only in the vicinity of both surfaces of each recording layer was produced in the same manner as in Example 1 except for the following three changes.

(1) φ200m+a formed by injection molding the substrate 1
A disc plate made of polymethyl methacrylate with a guide groove having a thickness of 1.2I was used.

(2) The thickness of the undercoat layer 2 (Sin) was 1200A.

(3) The film forming conditions for each recording layer 3 were changed in three steps: A4B-C.

A recording and reproducing test similar to that in Example 1 was conducted. record puff
-7mW C/N ratio 52dB gain, 70'C1
Similar values were obtained after being left for 500 hours at a humidity of 85%.

Example 3 An optical disc was produced under the same conditions as in Example 2, except that polycarbonate was used as the substrate 1 material.

This optical disc has a recording power of 71 and a C/N of 1t.
A value of 51 dB was obtained, and the same value remained even after being left at 70° C. and 85% humidity for 500 hours.

Example 4 One Tb chip was used instead of the GdTb alloy chip used as part of the first and second targets when forming the recording layer 3.
Optical discs were produced in the same manner as in Example 3 except that seven discs were arranged. With this optical disc, a C/N ratio of 50 dB was obtained with a recording power of 7, a humidity of 70'C1, 85%,
The same value remained after being left for 500 hours.

Example 5 As shown in FIG. 2, an optical disk having a structure that was extremely thin and had a recording layer with a high Co content near both surfaces and a reflective layer 7 was prepared. The substrate 1 was the same as in Example 1, and using a continuous film forming apparatus, first, as the base layer 2, SiO was deposited at 90 OA;
2118 was sequentially deposited to a thickness of 800. Next, using the same targets as in Example 1, first, +50W and 170W were applied to the first target and the second target, respectively.
W RF power for 20 seconds, then 280W, 40W R
F power for 100 seconds, +50W again, 170W
The recording layer 3 was formed by sputtering while applying RF power of 20 seconds for 20 seconds. 800 each of ZnS and SiO as the dielectric layer 6 and 500 of AI as the reflective film 7 on that hill.
Then, SiO was sequentially deposited to a thickness of 3000 nm as the 2I layer 4. Two discs thus produced were bonded together with adhesive 5 with protective film 4 on the inside to produce an optical disc according to the present invention.

Note that in FIG. 2, one half of the optical disc is omitted. The characteristics of this optical disc were compared with those of Comparative Example 3 below.

Comparative Example 3 280W for the first target, 4W for the second target
The Go
An optical disc was prepared in which the content ratio was constant and the ratio of 7 was the same as that of the central portion of the recording layer 3 of the optical disc of Example 5.

The optical disc of Example 5 had a C/N with a recording laser power of 6I.
55 dB was obtained, and the value remained constant even after being left at 70° C. and humidity 85% for 500 hours. On the other hand, in Comparative Example 3, the initial C/N was 55 dB, but at 70°C and humidity 85%,
After being left for 500 hours, it decreased to 50 dB.

Example 6 φ200mm as a substrate, 1.21! ! An optical disc was produced in the same manner as in Example 5, except that an injection molded polycarbonate product with a + thickness guide groove was used. With a recording laser power of 6111111, a C/N of 54 dB was obtained, and 7
The same value was obtained after being left for 500 hours at 0° C. and 85% humidity.

Example 7 An optical disc in which the Co content distribution gradually increases linearly from the center of the recording layer toward both surfaces was produced by the same method as in Example 6 except that the film-forming conditions for the recording layer were changed as follows. was created.

This optical disc has a recording laser power of 6 mW and a C/N of 5.
4 dB was obtained, which remained almost the same even after being left at 70° C. and 85% humidity for 500 hours.

〔Effect of the invention〕

As described in detail above, increasing the cobalt content near the surface of the recording layer from within has the effect of improving corrosion resistance and shelf life while maintaining the recording sensitivity and reproduction efficiency of the magneto-optical recording medium. .

[Brief explanation of drawings]

FIG. 1 is a partially omitted cross-sectional view of an optical disc according to the present invention manufactured according to Example 1. FIG. 2 is a partially omitted cross-sectional view of an optical disc according to the present invention manufactured according to Example 5.

Claims (1)

[Claims] 1) In a magneto-optical recording medium having on a substrate a recording layer made of an amorphous thin film of a rare earth element and a transition metal containing at least iron and cobalt, the inclusion of cobalt in the vicinity of at least one surface of the recording layer. A magneto-optical recording medium characterized in that the volume is larger than that inside the medium.