JP2543832B2 - Magneto-optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Technical Field The present invention relates to a magneto-optical recording medium for recording and reproducing information using heat and light such as laser light.

Prior art and its problems MnBi, MnAlGe, MnS are used as recording media for magneto-optical memory.
b, MuCuBi, GdFe, TbFe, GdCo, PtCo, TbCo, TbFeCo, GdFeCo, Tb
Materials such as FeO ₃ , GdIG, GdTbFe, GdTbFeCoBi and CoFe ₂ O ₄ are known. These are formed as thin films on a transparent substrate such as plastic or glass by a method such as a vacuum evaporation method or a sputtering method. The characteristics common to these magneto-optical recording media are that the easy axis of magnetization is perpendicular to the film surface, and that the Kerr effect and the Faraday effect are large.

The requirements for such a medium are firstly that the Curie point is about 100 to 200 ° C. and the compensation point is near room temperature. Secondly, defects such as crystal grain boundaries that cause noise are relatively large. Third, it is possible to obtain a magnetically and mechanically uniform film over a relatively large area.

In response to such a demand, in recent years, among the above materials, an amorphous perpendicular magnetic thin film containing a rare earth-transition metal has attracted great attention.

However, in such a magneto-optical recording medium composed of a rare earth-transition metal amorphous thin film, when the magnetic thin film layer is stored in contact with the atmosphere, the rare earth is selectively corroded or oxidized by oxygen or water in the atmosphere. Therefore, it becomes impossible to record and reproduce information.

Therefore, in general, much research has been conducted on a structure having a protective layer on the surface of the magnetic thin film layer opposite to the substrate.

Conventionally, as a protective layer for imparting corrosion resistance such as moisture resistance, an attempt has been made to provide an inorganic vacuum vapor deposition film or resin film of silicon monoxide, silicon dioxide, aluminum nitride, silicon nitride, zinc sulfide or the like ( JP-A-58-80142) is disclosed. However, none of these is still satisfactory in terms of corrosion resistance.

Further, in a magneto-optical recording medium, it is advantageous to perform recording / reproduction from the substrate side, and a transparent substrate is used.

As the substrate for the magneto-optical disk, a resin-made substrate is preferable from the viewpoints of ease of manufacturing and handling, and among these, acrylic resin is particularly preferable from the viewpoints of transparency, productivity, economy and the like. Polycarbonate resin is preferred.

An intermediate layer made of an inorganic material is usually formed on such a resinous substrate, and a magnetic thin film layer is formed via this intermediate layer.

This intermediate layer has a function as an interference layer, has a function of improving the C / N ratio, and a function of imparting corrosion resistance to prevent deterioration of the magnetic thin film layer.

Examples of the material for such an intermediate layer include SiO and SiO _2.
Such as silicon oxide, AlN, Si ₃ N ₄ , ZnS, Si, Ge, etc. have been proposed, among which silicon oxide and zinc sulfide are
It is suitable in terms of improving the C / N ratio and corrosion resistance.

By the way, when comparing the acrylic resin and the polycarbonate resin among the above substrate materials, the acrylic resin is superior in optical uniformity, and therefore the acrylic resin is more advantageous in terms of the C / N ratio. . However, acrylic resin is inferior to polycarbonate resin in durability.

Therefore, by forming an intermediate layer of silicon oxide or zinc sulfide on the acrylic resin, the corrosion resistance is improved and the C / N ratio is also improved. In this case, zinc sulfide is advantageous in terms of C / N ratio,
Silicon oxide is advantageous in terms of corrosion resistance. However, neither is satisfactory.

On the other hand, although the polycarbonate resin is inferior to the acrylic resin in the C / N ratio, it is advantageous in terms of durability and has a great advantage that it is excellent in dimensional accuracy stability against warping and the like.

In the case of a polycarbonate resin substrate, the silicon oxide intermediate layer is superior to the zinc sulfide intermediate layer in terms of C / N ratio and corrosion resistance.

However, even in the case of the silicon oxide intermediate layer, the conventionally used film structure has insufficient C / N ratio, corrosion resistance, durability, etc., and further improvement is required.

II Object of the invention The object of the present invention is to prevent the deterioration of the magnetic thin film layer, which is excellent in corrosion resistance and durability, and which is also excellent in recording / reproducing characteristics and in stability of dimensional accuracy against warpage, etc. To provide.

III DISCLOSURE OF THE INVENTION Such an object is achieved by the present invention described below.

That is, the first invention is a magneto-optical recording medium having a magnetic thin film layer of a rare earth-transition metal on a substrate and a silicon oxide protective layer on the magnetic thin film layer, wherein the magnetic thin film in the silicon oxide protective layer is The oxygen content on the layer side is smaller than the oxygen content on the side opposite to the magnetic thin film layer, and the O / Si atomic ratio at the position of 1/4 from the surface on the side opposite to the magnetic thin film layer of the silicon oxide protective layer. Is a magneto-optical recording medium characterized by having an O / Si atomic ratio of 1.4 to 2.5 times at a position 1/4 from the surface on the magnetic thin film layer side.

A second invention is an optical device having a silicon oxide intermediate layer on a resin substrate, a rare earth-transition metal magnetic thin film layer on the intermediate layer, and a silicon oxide protective layer on the magnetic thin film layer. In the magnetic recording medium, the substrate is a polycarbonate resin, the oxygen content on the substrate side in the silicon oxide intermediate layer is larger than that on the magnetic thin film layer side, and the oxygen content on the magnetic thin film layer side in the silicon oxide protective layer is The amount is smaller than that on the side opposite to the magnetic thin film layer, and the O / Si atomic ratio in the silicon oxide intermediate layer at the position of 1/4 to 1/4 from the substrate side of the silicon oxide intermediate layer is from the magnetic thin film layer side.
1.4 of O / Si atomic ratio in silicon oxide interlayer up to 1/4
Is 2.5 times, and the O / Si atomic ratio at the position of 1/4 from the surface opposite to the magnetic thin film layer of the silicon oxide protective layer is at the position of 1/4 from the surface on the magnetic thin film layer side. The magneto-optical recording medium is characterized by having an O / Si atomic ratio of 1.4 to 2.5 times.

IV Specific Configuration of the Invention Hereinafter, the specific configuration of the present invention will be described in detail.

An embodiment of the magneto-optical recording medium of the present invention is shown in FIG.

In FIG. 1, a magneto-optical recording medium 1 of the present invention has a magnetic thin film layer 4 on a substrate 2 made of glass or resin, preferably with an intermediate layer 3 interposed particularly when the substrate is resin. A protective layer 5 is provided on the surface of the magnetic thin film layer 4.

 The protective layer 5 of the present invention is formed of a silicon oxide (SiOx) material.

The O / Si atomic ratio of the silicon oxide (SiOx) protective layer 5 is preferably 0.7 to 1.2 as an average of the entire layer.

This is because if it is less than 0.7, the recording sensitivity is poor, and if it exceeds 1.2, the corrosion resistance and durability are poor.

In such a thickness direction of the protective layer 5, there is an oxygen concentration distribution set so that the oxygen content on the magnetic thin film layer 4 side in the protective layer 5 becomes smaller than that on the opposite side to the magnetic thin film layer 4. are doing.

Such an oxygen concentration distribution in the protective layer 5 is, for example, an O / Si atomic ratio (X ₄ ) in the protective layer 5 at a position 1/4 from the surface of the protective layer 5 on the opposite side of the magnetic thin film layer 4. Is 1.4 to 2.5 times, especially 1.5 to 2.5 times, more preferably 1.6 to 2.5 times the O / Si atomic ratio (X ₁ ) in the protective layer 5 at a position 1/4 from the surface on the magnetic thin film layer 4 side. It is preferably set to 2.0 times.

If this value is less than 1.4, the corrosion resistance and durability deteriorate.

On the other hand, when it exceeds 2.5 times, the electrical characteristics mainly deteriorate. When this value is 1.6 to 2.0 times the above-mentioned preferable range, the corrosion resistance and the durability are significantly improved.

The oxygen concentration distribution as described above is provided in the protective layer 5 for the following reason.

That is, firstly, by lowering the oxygen concentration in the protective layer 5 on the magnetic thin film layer 4 side, deterioration of the magnetic thin film layer 4 described later can be effectively prevented.

Secondly, by providing the protective layer 5 with the oxygen concentration distribution as described above, deterioration of the magnetic thin film layer 4 can be prevented more effectively than in the case where the oxygen concentration distribution in the protective layer 5 is uniform. In particular, when an organic substance is used in combination with the protective film 6 which is usually formed on the surface of the protective layer 5, the effect of preventing the deterioration of the magnetic thin film layer 4 of the protective layer 5 is significantly increased.

The oxygen concentration distribution may be continuous or discontinuous.

The atomic ratio distribution of O / Si existing in the thickness direction of the protective layer 5 is measured, for example, by the method described below.

That is, first, elemental analysis is performed by SIMS (secondary ion mass spectrometry), AES, ESCA, etc. while ion-etching the protective layer 5 from the side opposite to the magnetic thin film layer 4 at a constant etching rate. Then, the time until the constituent component of the magnetic thin film layer 4 such as rare earth or transition metal is detected is measured.

By doing so, the time required for etching the film thickness of the protective layer 5 can be measured.

Based on the elemental analysis results in the protective layer 5 at the beginning of the required time or the time until 1/4 and the time from reaching 3/4 until reaching the magnetic thin film layer 4, O / Si average atoms at a predetermined position in the protective layer 5 The ratio is calculated.

Needless to say, the average O / Si atomic ratio of the entire protective layer 5 can also be calculated.

In order to form the protective layer 5 containing silicon oxide having an oxygen concentration distribution in the film thickness direction as described above, usually, a multi-source sputtering method using a target having two or more different compositions or a reactive sputtering using oxygen is used. According to the law etc.
The target may be SiO ₂ , Si or the like.

More specifically, when multi-source sputtering is used, for example, SiO ₂ and Si are used as targets, the sputtering rates of both are controlled, and film formation is performed while changing these.

When reactive sputtering is used, the oxygen concentration is controlled and changed to form a film.

Further, according to this, it is also possible to appropriately use other vapor phase film forming methods such as vapor deposition.

The protective layer 5 thus formed has a thickness of 500 to 1500.
Å, more preferably 700 to 1200 Å.

 Further, Ar or the like existing in the film forming atmosphere may be included.

In addition, a small amount of elements such as Al, Cr and Ba may be added depending on the case.

The substrate 2 is made of glass or resin, and particularly the substrate 2
When is a resin, the magnetic thin film layer 4 is preferably provided via the intermediate layer 3 made of an inorganic material.

The intermediate layer 3 of the present invention is preferably made of a silicon oxide (SiOy) material.

The O / Si atomic ratio (y ₁ ) of the silicon oxide (SiOy ₁ ) intermediate layer 3 is
0.7-1.2, more preferably 0.7-1.0 as the average of the whole layer
It is preferred that

When y ₁ is less than 0.7, the amount of reflected light decreases, which adversely affects the characteristics.

Also, if it exceeds 1.2, the apparent Kerr rotation angle decreases, and similarly the characteristics are adversely affected.

In the thickness direction of the intermediate layer 3, there is a predetermined oxygen concentration distribution so that the oxygen content on the substrate side in the intermediate layer 3 is larger than that on the magnetic thin film layer 4 side described later. .

The oxygen concentration distribution in the silicon oxide intermediate layer 3 is
For example, if the O / Si atomic ratio in the silicon oxide intermediate layer at the position of 1/4 from the substrate 2 side of the silicon oxide intermediate layer 3 is in the silicon oxide intermediate layer at the position of 1/4 from the magnetic thin film layer 4 side. 1.4-2.5 times, especially 1.5-2.5 times, more preferably 1.
It is preferably 6 to 2.0 times.

If this value is less than 1.4 times, the C / N ratio, corrosion resistance, and durability will deteriorate. On the other hand, if it exceeds 2.5 times, the electrical characteristics will mainly deteriorate. When this value becomes 1.6 to 2.0 times the above-mentioned preferable range, the C / N ratio and the durability are significantly improved.

The oxygen concentration distribution as described above is provided in the silicon oxide intermediate layer 3 for the following reason.

That is, first, by setting the refractive index of the polycarbonate resin substrate 2 (about 1.57 at 830 nm) and the oxygen concentration (value of y ₁ ) of the silicon oxide intermediate layer 3, the polycarbonate resin substrate 2 and the silicon oxide intermediate layer 3 are set. This is because reflection at the interface with and can be effectively prevented, and good recording / reproducing characteristics can be obtained.

Secondly, by lowering the oxygen concentration of the silicon oxide intermediate layer 3 on the magnetic thin film layer 4 side, Fe and Co described later can be obtained.
This is because it is possible to effectively prevent the deterioration of the magnetic thin film layer 4 containing as an essential component.

The oxygen concentration distribution may be continuous or discontinuous.

Exists in the thickness direction of the silicon oxide intermediate layer 3
The atomic ratio distribution of O / Si is measured, for example, by the method below.

That is, first, elemental distribution is performed by SIMS, AES, ESCA, etc. while ion-etching the silicon oxide intermediate layer 3 from the magnetic thin film layer 4 side at a constant etching rate. Then, the time required for reaching the polycarbonate resin substrate 2 and detecting oxygen C is measured.

By doing so, the time required to etch the film thickness of the silicon oxide intermediate layer 3 can be measured.

The average atomic ratio of O / Si at a predetermined place in the intermediate layer 3 is calculated from the elemental analysis results in the layer from the beginning of the required time to 1/4 and from the time of reaching from 3/4 to the substrate. .

Needless to say, the average O / Si atomic ratio of the entire intermediate layer 3 can be calculated.

In order to form the silicon oxide intermediate layer 3 having an oxygen concentration distribution in the film thickness direction as described above, usually, a multi-source sputtering method or an oxygen reactive sputtering method using a target having two or more different compositions is used. Good. Target is Si
O ₂ , SiO, Si or the like may be used.

Moreover, it is also possible to appropriately use other vapor deposition methods.

The film thickness of the silicon oxide intermediate layer 3 thus formed is
It is 500 to 1500Å, more preferably 700 to 1000Å.

 Further, Ar or the like existing in the film forming atmosphere may be included.

In addition, some elements such as Al, Cr and Ba may be added depending on the case.

The material of the substrate 2 on which the above-mentioned silicon oxide intermediate layer 3 is placed is polycarbonate resin.

The polycarbonate resin used in the present invention may be any of an aliphatic polycarbonate, an aromatic-aliphatic polycarbonate, and an aromatic polycarbonate, but an aromatic polycarbonate resin is particularly preferable. Of these, a polycarbonate resin made of bisphenol is preferable in terms of melting point, crystallinity, handling, and the like. Among them, the bisphenol A type polycarbonate resin is most preferably used.

The number average molecular weight of the polycarbonate resin is 10,0
It is preferably about 00 to 15,000.

The refractive index at 830 nm of such a substrate 2 is usually 1.55 to 1.59.
It is a degree.

Since recording is performed through the substrate 2, the transmittance for writing light or reading light is 86% or more.

The substrate 2 is usually disk-shaped and has a thickness of about 1.2 to 1.5 mm.

On the magnetic thin film layer formation surface of such a disc-shaped substrate,
A groove for tracking may be formed.

The depth of the groove is about λ / 8n, particularly λ / 6n to λ / 12n (where n is the refractive index of the substrate). The width of the groove is about the track width.

Then, it is usually preferable to irradiate the writing light and the reading light from the back surface side of the substrate with the magnetic thin film layer located in the concave portion of the groove as a recording track portion.

With this configuration, the write sensitivity and the read C / N ratio are improved, and the tracking control signal is increased.

Further, other shapes of the substrate may be tapes, drums, and the like.

 A magnetic thin film layer 4 is formed on the intermediate layer 3.

In the magnetic thin film layer 4 of the present invention, information is magnetically recorded by a modulated heat beam or a modulated magnetic field, and the recorded information is magnetic-optically converted and reproduced.

As a material of such a magnetic thin film layer 4, a rare earth metal such as Gd or Tb is preferably formed as an amorphous film by an alloy of a transition metal such as Fe or Co by sputtering or vapor deposition.

In this case, the total content of Fe and Co is preferably 65 to 85 at%.

And the balance is substantially rare earth metals, especially Gd and / or
Or Tb.

And, as a preferable example thereof, TbFeCo, GdFeCo, GdTb
FeCo etc.

In these magnetic thin film layers, C is contained in the range of 10 at% or less.
r, Al, Ti, Pt, Si, Mo, Mn, V, Ni, Cu, Zn, Ge, Au
Etc. may be contained.

In addition, as a rare earth element, Sc, Y, and
La, Ce, Pr, Nd, Pm, Sm, Eu, Dy, Ho, Er, Tm, Yb, Lu
Etc. may be contained.

A protective film 6 is formed on the magnetic thin film layer 4 via the above-mentioned protective layer 5.

As the material of the protective film 6, generally known various organic substances may be used.

More preferably, a radiation-curable compound cured with radiation such as electron beam or ultraviolet ray is used.

Examples of the radiation-curable compound to be used include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds having an unsaturated double bond that is sensitive to ionization energy and exhibits radical polymerizability, such as diallyl phthalate. Examples of such monomers include allylic double bonds, maleic acid, and unsaturated double bonds such as maleic acid derivatives that are crosslinked by irradiation or polymerized and dried into a molecule containing or introduced a group, an olegomer and a polymer. .

A compound having a molecular weight of less than 2000 is used as the radiation-curable monomer, and a compound having a molecular weight of 2000 to 10,000 is used as the oligomer.

These include styrene, ethylene acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol methacrylate, 1,6-hexane glycol diacrylate, 1,6-hexane glycol dimethacrylate, etc., but particularly preferred ones As, pentaerythritol tetraacrylate (methacrylate), pentaerythritol acrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (methacrylate), polyfunctional oligoester acrylate) (Aronix M-7100, M- 540
0, M-5500, M-5700, M-6250, M-6500, M-803
0, M-8060, M-8100, etc., Toa Gosei), acrylic modified urethane elastomer (Nipporan 4040), or those in which a functional group such as COOH is introduced, acrylate (methacrylate) of phenol ethylene oxide adduct. ), A compound having an acryl group (methacryl group) or ε-caprolactone-acryl group on the pentaerythritol condensed ring represented by the following general formula, _{1) (CH 2 = CHCOOCH 2} ) 3 -CCH 2 OH ( special acrylate _{A) 2) (CH 2 =} CHCOOCH 2) 3 -CCH 2 OH 3 ( special acrylate B) 3) [CH ₂ = CHCO (OC ₃ H ₆ ) _n -OCH ₂ ] _3- CCH ₂ CH ₃ (Special acrylate C) In the formula, a compound of m = 1, a = 2, b = 4 (hereinafter referred to as a special pentaerythritol condensate A), a compound of m = 1, a = 3, b = 3 (hereinafter referred to as a special pentaerythritol condensate B) , M = 1, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate C), m = 2, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate D) , And special acrylates represented by the following general formula.

_{8) CH 2 = CHCOO- (CH} 2 CH 2 O) 4 -COCH = CH 2 ( special acrylate H) _{12) AM-N n -M-} A A: acrylate M: 2 dihydric alcohol N: The dibasic acid (special acrylate L), as the radiation-curable oligomer, Ya polyfunctional oligoester acrylates represented by the following general formula Examples thereof include acrylic modified urethane elastomers, or products obtained by introducing a functional group such as COOH into these products.

Further, a radiation-curable compound obtained by subjecting a thermoplastic resin to radiation-sensitive modification may be used.

As a specific example of such a radiation curable resin, acrylic acid showing an unsaturated double bond having radical polymerizability,
Groups that crosslink or polymerize upon irradiation, such as acrylic double bonds such as methacrylic acid or their ester compounds, allyl double bonds such as diallyl phthalate, and unsaturated bonds such as maleic acid and maleic acid derivatives. Is contained or introduced in the molecule of the thermoplastic resin.

Examples of thermoplastic resins that can be modified into radiation-curable resins include vinyl chloride copolymers, saturated polyester resins, polyvinyl alcohol resins, epoxy resins, phenoxy resins, fibrin derivatives and the like.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (PVP
Olefin copolymers), polyamide resins, polyimide resins, phenol resins, spiro acetal resins, acrylic resins containing at least one hydroxyl group-containing acrylic ester and methacrylic ester as a polymerization component are also effective.

The thickness of the protective film 6 of such a radiation-curable compound is 0.
It is 1 to 30 μm, more preferably 1 to 10 μm.

If the film thickness is less than 0.1 μm, a uniform film cannot be formed, the moistureproof effect is not sufficient in an atmosphere with high humidity, and the durability of the magnetic thin film layer 4 is not improved. If it exceeds 30 μm, warpage of the recording medium or cracks in the protective film may occur due to shrinkage during curing of the resin film, which is not practical.

Such a coating film may be usually formed by combining various known methods such as spinner coating, gravure coating, spray coating and dipping. The conditions for forming the coating film at this time may be appropriately determined in consideration of the viscosity of the mixture of coating film compositions, the target coating film thickness, and the like.

In order to cure such a coating film to form a protective tank, it is sufficient to irradiate the coating film with radiation such as an electron beam and ultraviolet rays.

When using an electron beam, the radiation characteristics are acceleration voltage
It is expedient to use a radiation accelerator of 100 to 750 KV, preferably 150 to 300 KV, and to irradiate it with an absorbed dose of 0.5 to 20 megarads.

On the other hand, when ultraviolet rays are used, a photopolymerization sensitizer is usually added to the above-mentioned radiation-curable compounds.

The photopolymerization sensitizer may be a conventionally known one,
For example, benzoyl methyl ether, benzoyl ethyl ether, α-methylbenzoyl, α-chlordeoxybenzoyl and other benzoin compounds, benzophenone, acetophenone, bisdialkylaminobenzophenone and other ketones, acetolaquinone, phenanthraquinone and other quinones, benzyl disulfide. And sulfides such as tetramethylthiuram monosulfide.
The photopolymerization sensitizer is preferably in the range of 0.1 to 10% by weight based on the resin solid content.

Then, in order to cure the coating film containing such a photopolymerization sensitizer and the radiation-curable compound by ultraviolet rays, various known methods may be used.

For example, a UV bulb such as a xenon discharge tube or a hydrogen discharge tube may be used.

On such a protective film 6, a protective plate 8 is usually provided via an adhesive layer 7.

That is, the protective plate 8 is used only in the case of so-called single-sided recording in which recording / reproduction is performed only from the back surface (surface on the side where the magnetic thin film layer 4 is not provided) of the substrate 2.

The resin material of the protective plate 8 is not particularly required to have transparency, and various resins such as polyethylene, polyvinyl chloride, polystyrene, polypropylene,
Polyvinyl alcohol, methacrylic resin, polyamide,
Various types of thermoplastic resin such as polyvinylidene chloride, polycarbonate, polyacetal, fluororesin, phenol resin, urea resin, unsaturated polyester resin, polyurethane, alkyd resin, melamine resin, epoxy resin, silicon resin, etc. are used. It is possible.

Note that various inorganic materials such as glass and ceramic may be used as the protective plate 8.

The shape, dimensions, etc. of this product are substantially the same as those of the substrate 2 described above.

Such a protective plate 8 is bonded via the adhesive layer 7 as described above. The adhesive layer is usually an adhesive such as a hot melt resin and has a film thickness of about 1 to 100 μm.

On the other hand, instead of using the protective plate 8 described above, a substrate having the magnetic thin film layer 4, the protective layer 5, the protective film 6 and the like is further used.
Use both sets to face each other with both magnetic thin film layers inside.
A so-called double-sided recording type in which the adhesive layers 7 are used for bonding and writing is performed from the back side of both substrates may be used.

Further, it is preferable to provide a hard coat layer as various protective films on the back surface of the substrate 2 or the protective plate 8 (the surface on the side where the magnetic thin film layer 4 is not provided).

As the material of the hard coat layer, the protective layer film 6 described above is used.
The material may be the same as that of.

V Effect of the Invention The magneto-optical recording medium of the first invention has a silicon oxide protective layer having a predetermined oxygen concentration distribution on the magnetic thin film layer.
Therefore, deterioration of the magnetic thin film layer with time is small.

Such an effect becomes more remarkable especially when an organic protective film is formed on the protective layer.

In the magneto-optical recording medium of the second invention, the substrate is a polycarbonate resin, and in addition to the above silicon oxide protective layer, it has a silicon oxide intermediate layer having a predetermined oxygen concentration distribution on the substrate. Therefore, in addition to the above effects, the recording / reproducing characteristics are excellent, and the dimensional accuracy with respect to warpage and the like is highly stable.

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention.

Example 1 On a glass substrate having a diameter of 13 cm and a thickness of 1.2 mm, 21 at% Tb,
A 68 at% Fe, 7 at% Co, 4 at% Cr alloy thin film was deposited by sputtering to a thickness of 800 Å to form a magnetic thin film layer.

The target used was an Fe target on which Tb, Co, and Cr chips were placed.

On this magnetic thin film layer, a silicon oxide protective layer with a thickness of 1000Å
Was deposited by sputtering.

During sputtering, the target is SiO _{2 in} order to provide a predetermined oxygen concentration distribution in the silicon oxide protective layer.
Two-way sputtering using two types of Si and Si was used, and the use of these was controlled in terms of time.

After forming the layer, the elemental analysis of the layer was performed while performing ion etching. As a result, the O / Si atomic ratio (X ₁ ) from the magnetic thin film layer side to the position of 1/4 of the film thickness was 0.6. The O / Si atomic ratio (X ₄ ) from the side opposite to the layer to the 1/4 position was 1.2. The average O / Si atomic ratio (X) of the entire layer was 0.9.

On this silicon oxide protective layer, a coating composition containing the following radiation curable compound was formed as a protective film by spinner coating.

(Coating composition) Polyfunctional oligoester acrylate 100 parts by weight Photosensitizer 5 parts by weight After applying such a coating composition, it was irradiated with ultraviolet rays for 15 seconds to be crosslinked and cured to obtain a cured film.

According to this, except that the protective layer containing silicon oxide of sample No. 1 was changed to the silicon oxide protective layer shown in Table 1 below, No. 1
Various samples were prepared in the same manner as in.

For the above samples, at the initial stage and at 60 ° C and 90% RH
The bit error rate of the EFM signal after protection for 1000 hours was measured.

 Table 1 shows the results.

Example 2 A silicon oxide intermediate layer was sputtered to a thickness of 800 L on a substrate made of a bisphenol A-based polycarbonate resin (molecular weight 15000) having a diameter of 13 cm and a thickness of 1.2 mm.

During sputtering, in order to provide a predetermined concentration distribution in the silicon oxide intermediate layer, the target was Si and
A binary target using two kinds of SiO ₂ was used, and their use was controlled temporally. As a result of elemental analysis in the film after deposition, the O / Si ratio (y ₁ ) from the substrate side to the position 1/4 of the film thickness is 1.2, and from the magnetic thin film layer to the position 1/4 O /
The Si ratio (y ₄ ) was 0.6. The average O / Si ratio (y) of the entire film was 0.9.

A magnetic thin film layer similar to that in Example 1 was formed on the silicon oxide intermediate layer, and Example 1 was further formed on the magnetic thin film layer.
In the same manner as above, a silicon oxide protective layer having a predetermined oxygen concentration distribution was formed.

A protective layer similar to that of Example 1 was provided on the silicon oxide protective layer, and the same treatment was performed on the back surface of the substrate.
The sample of the second invention was used.

The following characteristic values were measured for these samples.

(1) C / N ratio (storage deterioration) Initial C / N ratio and C after storage at 60 ° C, 90% RH for 1000 hours
The amount of change in the / N ratio was measured under the following conditions.

Rotation speed 4m / sec Carrier frequency 500KHz Resolution 30KHz Recording power (830nm) 3 to 4mW Playback power (830nm) 1mW (2) Bit error rate Initial and bit of EFM signal after 1000 hours storage at 60 ℃ and 90% RH The error rate was measured.

 The results are shown in Table 2.

From the above results, the effect of the present invention is clear.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium showing an example of the present invention. DESCRIPTION OF SYMBOLS 1 ... Magneto-optical recording medium, 2 ... Substrate, 3 ... Silicon oxide intermediate layer, 4 ... Magnetic thin film layer, 5 ... Silicon oxide protective layer,
6 ... Protective film, 7 ... Adhesive layer, 8 ... Protective plate

Claims (6)

(57) [Claims] 1. A magneto-optical recording medium having a magnetic thin film layer of a rare earth-transition metal on a substrate and a silicon oxide protective layer on the magnetic thin film layer, wherein the magnetic thin film layer side in the silicon oxide protective layer is a magnetic thin film layer. The oxygen content is smaller than the oxygen content on the side opposite to the magnetic thin film layer, and from the surface of the silicon oxide protective layer on the side opposite to the magnetic thin film layer.
A magneto-optical recording medium characterized in that the O / Si atomic ratio at a position of up to 1/4 is 1.4 to 2.5 times the O / Si atomic ratio at a position of up to 1/4 from the surface on the magnetic thin film layer side. 2. Average O / of the entire layer of the silicon oxide protective layer
The magneto-optical recording medium according to claim 1, wherein the Si atomic ratio is 0.7 to 1.2. 3. The magneto-optical recording medium according to claim 1, further comprising a protective film formed of an organic material on the silicon oxide protective layer. 4. A magneto-optical device comprising a silicon oxide intermediate layer on a resin substrate, a rare earth-transition metal magnetic thin film layer on the intermediate layer, and a silicon oxide protective layer on the magnetic thin film layer. In the recording medium, the substrate is a polycarbonate resin, the oxygen content on the substrate side in the silicon oxide intermediate layer is larger than that on the magnetic thin film layer side, and the oxygen content on the magnetic thin film layer side in the silicon oxide protective layer is Is smaller than that on the side opposite to the magnetic thin film layer, and the O / Si atomic ratio in the silicon oxide intermediate layer at positions 1/4 from the substrate side of the silicon oxide intermediate layer is 1 / from the magnetic thin film layer side.
O / Si atomic ratio in the silicon oxide intermediate layer at positions up to 4 is 1.4-
2.5 times, and from the surface of the silicon oxide protective layer opposite to the magnetic thin film layer
A magneto-optical recording medium characterized in that the O / Si atomic ratio at a position of up to 1/4 is 1.4 to 2.5 times the O / Si atomic ratio at a position of up to 1/4 from the surface on the magnetic thin film layer side. 5. The average O / O of the entire layer of the silicon oxide intermediate layer
Si atomic ratio is 0.7 to 1.2, and the average O / Si atomic ratio of the entire silicon oxide protective layer is 0.7.
The magneto-optical recording medium according to claim 4, wherein the magneto-optical recording medium is 1.2. 6. The magneto-optical recording medium according to claim 4, further comprising a protective film formed of an organic material on the silicon oxide protective layer.