JPH02199645A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve corrosion resistance by forming a protective layer of the oxide or nitride of an element the galvanyl system of which in an aq. soln. is equal to or baser than the essential element constituting a reflecting layer. CONSTITUTION:The protective layer 5 consisting of the oxide MOx or nitride MNx is provided on the reflecting layer 4. The element M of the MOx or MNx constituting the protective layer 5 is the element the galvanyl system of which in the aq. soln. is equal to or baser than the essential element R constituting the reflecting layer. There is no case in which the R is easier to be oxidized than the M and the oxidation-reduction reaction to oxidize the reflecting layer 4 does not take place between the protective layer 5 and the reflecting layer 4 if the M is equal to the R or baser than the R. The excellent weatherability and corrosion resistance are obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magneto-optical recording medium used for optical recording, and particularly to a magneto-optical recording medium of reflective film type having a reflective layer on a recording layer.

[Prior Art] Among optical memories that are high-density recording media, magneto-optical recording media are the most developed rewritable media.

As a method of improving the characteristics of this magneto-optical recording medium, a method of providing a reflective layer on the recording layer has been proposed. This method uses a combination of Kerr effect and Faraday effect to achieve high C.
It is excellent in that a /N ratio can be obtained. In this method, the reflective layer provided on the recording layer is generally made of a material with high reflectance, such as Au, Ag, Pt, Al, etc.
2. Cu, etc., but from the point of view of cost etc., Al1 and A1
Alloys are often used.

[Problems to be Solved by the Invention] When such a reflective layer is used as the outermost layer, the problem of corrosion occurs. If the reflective film does not form a passive state, the corrosion current may pass through the reflective film and corrode the recording layer, and if the reflective film is made of a material other than noble metal, corrosion of itself may also be a problem. Even if the reflective film forms a passive state, −
When pinholes are formed, corrosion current concentrates, leading to enlargement of the pinholes. This phenomenon is particularly noticeable in the presence of moisture.

An object of the present invention is to solve the above-mentioned conventional problems and provide a magneto-optical recording medium with excellent corrosion resistance.

[Means for Solving the Problems] The magneto-optical recording medium of the present invention has a recording layer, a reflective layer, a
and a magneto-optical recording medium formed by laminating protective layers in this order, wherein the protective layer is an oxide or nitride of an element whose galvanic series in an aqueous solution is equal to or less base than the main element constituting the reflective layer. Characterized by being made of things.

That is, the inventors of the present invention have made extensive studies to obtain a magneto-optical recording medium with high weather resistance that overcomes the above-mentioned conventional drawbacks, and as a result, by forming a protective layer made of a specific material on the reflective layer, The present invention was completed based on the discovery that a magneto-optical recording medium having excellent weather resistance and virtually no corrosion problems can be obtained.

The present invention will be explained in detail below.

In the magneto-optical recording medium of the present invention, examples of the substrate on which the recording layer and the like are formed include plastics such as polycarbonate and PMMA, or glass substrates on which an ultraviolet curing resin layer is formed.

The constituent material of the magneto-optical recording layer formed on such a substrate is an alloy of rare earth and transition metal, such as TbFe.
, TbFeCo, GdFeCo.

DyFeCo, GdTbFe, etc. are mainly used.

Further, oxide magnetic materials such as garnet and ferrite can also be used. The recording layer may be made of a Hayabusa layer, or may be made of two or more layers such as GdFeCo/TbFe, and the thickness of the recording layer is 250 to 500 Å.
It is preferable to set it as approximately.

Note that a transparent dielectric layer may be provided as an interference layer between the recording layer and the substrate. This interference l1I (hereinafter “
It is sometimes referred to as the "first interference layer". ) is formed for the purpose of preventing moisture permeation from the substrate and reducing noise by reducing reflectance due to interference effects. In order to obtain a sufficient interference effect, it is preferable to use a material with a high refractive index for the interference layer, and the preferable refractive index is 1.5<n<2.6. The interference layer is generally SiO2゜Sin, AJ1
203. Oxides such as Ta205, TiO2, 313N
A nitride such as 41 A 42 N or a mixture of the oxide and nitride is used. The thickness of the interference layer is adjusted based on the refractive index of the film and the wavelength of light so that its reflectance is the minimum. In normal cases, the thickness of the interference layer is 500 to 10
It is about ooA.

In the magneto-optical recording medium of the present invention, a material having a numerically high reflectance is used as a constituent material of the reflective layer formed on the recording layer, such as Au.

Ag, Pt, Cu, AJZ or an alloy thereof can be used. Among these, especially Al1 or A11.
Alloys are preferable in terms of both cost and weather resistance, and A
fL or A1 alloy with Ta and Ti.

An alloy to which at least one of Zr, Mo, Pt, V, Cr and Pd is added in an amount of about 15 atomic %, preferably about 1 to 10 atomic %, has a high reflectance and low thermal conductivity. This is extremely suitable since it is possible to form a high-performance reflective film with good C/N ratio and sensitivity. If the reflective layer is too thick, the sensitivity will decrease, and if it is too thin, the reflectance will decrease and the C/N ratio will decrease. In normal cases, the thickness of the reflective layer is about 100 to 600 mm, preferably about 200 to 600 mm.

Note that an interference layer can also be provided between the recording layer and the reflective layer. As a constituent material of this interference layer (hereinafter sometimes referred to as "second interference layer"), the same material as the first interference layer formed between the substrate and the recording layer can be used. The thickness of the second interference layer is usually about 100 to 500 mm.

In the present invention, an oxide (hereinafter referred to as 'M
Sometimes called Ox J. ) or nitride (hereinafter referred to as rMN
Sometimes it's called xJ. ) In the present invention, a protective layer consisting of MO! or MN,
Element M is the main element (hereinafter sometimes referred to as "R") whose galvanic series in an aqueous solution constitutes the reflective layer.
It is an element that is equivalent to or less base than R.

To determine the galvanic series in an aqueous solution, it is convenient to use a standard electrode potential based on a hydrogen electrode. That is, M
The potential E” (M) and the potential E of R.

(R), as long as the relationship E"(M)≦E" (R) holds true.

Specifically, the oxides of the protective layer that can be combined with the reflective layer mainly composed of A1 include An203,
MgO, Nd203. Examples of the nitride include Y202, and examples of the nitride include AflN.

The thicker the protective layer, the higher the protective effect, but if it is too thick, the sensitivity may decrease. In order to obtain sufficient protective effect and sensitivity, the thickness of the protective layer should be between 200 and 1500 mm.
A, preferably about 300 to 1000 A is appropriate.

Note that in the present invention, the interference layer, the recording layer,
To form the reflective layer and the protective layer, for example, an electron beam evaporation method, a sputtering method, or the like is used. In particular, for forming the interference layer, reactive sputtering using Ar and O2 or N2 using a metal target is excellent in terms of film formation speed, film quality, and the like.

[Function] When the element M of the oxide MO or nitride MN constituting the protective layer is an element that is more easily reduced than the main element R constituting the reflective layer, that is, when R is more easily oxidized, ,
The reflective layer becomes more easily oxidized than the protective layer, and the following oxidation-reduction reaction occurs at the interface between the reflective layer and the protective layer, and the protective layer actually becomes a factor in deteriorating the reflective layer.

M"+xe-→M R-4R""+x' e- Whether such a reaction occurs or not can be determined by considering the galvanic series in an aqueous solution, and if M is equal to or more base than R. For example, R is not more easily oxidized than M, and therefore,
No redox reaction that oxidizes the reflective layer occurs between the protective layer and the reflective layer, resulting in excellent weather resistance and corrosion resistance.

Note that the reason why an aqueous solution is assumed is that corrosion proceeds mostly through water.

[Examples] The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Example 1 A magneto-optical recording medium was prepared by sequentially laminating an interference layer 2, a recording layer 3, a reflective layer 4, and a protective layer 5 on a substrate 1, as shown in FIG.

That is, a polycarbonate substrate 1 with a diameter of 130 mm is introduced into a sputtering apparatus, and first axt o -7to
Evacuate to below rr and 20 sccm of Ar.

02 was introduced for 5 seconds, and the pressure was adjusted to 0.8 Pa. In this state, a 4 inch φ Ta target was DC sputtered with a power of 500 W, and an 800 A tantalum oxide interference layer 2 was formed at a speed of 4 A/sec. T b23 (F e9oC01
6) 77 recording layers 3 were formed on the interference layer 2 to a thickness of 300 Å.

On this recording layer 3, An is formed as a reflective layer 4.

Three types of Ta and Cu are formed with a film thickness of 300A, and
MgO, AIL20a, ZnO as f1ffi5.

A film of 5 fl of Cr2 o2 and NiO was formed to a thickness of 300 Å. Note that the standard electrode potentials of the constituent elements of the reflective layer 4 and the protective layer 5 are shown in Table 1.

Table 1 Standard electrode potential (Eo) of constituent elements of reflective layer and protective layer ("Basic Chemical Handbook MII J Chemical Society of Japan Line (1984)") The obtained magneto-optical recording medium was stored at 60°C and 85%RH. A 300-hour accelerated test was conducted to measure the drop-in error rate, and the rate of increase was determined using the following formula.

The results are shown in Table 2. vinegar.

Since there is no risk of deterioration of the reflective layer due to the increase rate of error rate in one layer, weather resistance,
Excellent corrosion resistance.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of the magneto-optical recording medium manufactured in Example 1. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Interference layer 3... Recording layer, 4... Reflective layer, 5... Protective layer. (* indicates a comparative example, others are examples of the present invention) From Table 2, the potential E of the element R constituting the reflective layer. (R) and the potential E" (M) of the element M in the protective layer. When E"(M)≦E' (R), the increase in the error rate is small, that is, the weather resistance is excellent. it is obvious. [Effects of the Invention] As detailed above, in the magneto-optical recording medium of the present invention, the protective layer has a high protective effect against the reflective layer, and the protection agent and patent attorney Tsuyoshi Shigeno

Claims (1)

[Claims] (1) In a magneto-optical recording medium in which a recording layer, a reflective layer, and a protective layer are laminated in this order on a substrate, the protective layer has a galvanic series in an aqueous solution equal to or equal to the main element constituting the reflective layer. 1. A magneto-optical recording medium comprising an oxide or nitride of an element less base than the above element.