JPH0731831B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used in magneto-optical memories, magnetic printing, display elements, etc., and can be read using a magneto-optical effect such as a magnetic Kerr effect or a Faraday effect. The present invention relates to improvements in magnetic recording media.

[Conventional technology]

Conventionally, MnBi and MnCu have been used as magnetic recording layers for magneto-optical recording media.
Polycrystalline thin films such as Bi, GdFe, GdCo, TbFe, DyFe, GdTbF
e, GdFeCo, TbFeCo, TbDyFe, GdTbCo, GdTbFeCo, GdTbF
Amorphous thin films such as eGe and single crystal thin films such as GdIG are known.

Of these thin films, the film forming properties when manufacturing a large area thin film, the writing efficiency for writing signals with small photothermal energy, and the reading efficiency for reading written signals with a good S / N ratio, etc. Considering this, recently, the amorphous thin film is considered to be excellent for a magneto-optical recording medium.

[Problems to be solved by the invention]

However, in general, an amorphous magnetic material has poor corrosion resistance and is corroded in an atmosphere containing moisture to cause deterioration of magnetic properties. In particular, in the structure where a reflective layer is provided on the back surface of the magnetic recording layer or an interference layer and a reflective layer are provided for the purpose of improving the S / N ratio, it is necessary to effectively use the Faraday effect. Is usually limited to 500Å or less, so that the corrosion resistance becomes worse. In order to eliminate such defects, Si and C have been conventionally used in the magnetic recording layer.
Disks with an air sandwich structure or a laminated structure in which elements such as r, Ti, Ni, and Co are added, various protective layers are provided on the magnetic recording layer, or the magnetic recording layer is sealed with an inert gas. Although magneto-optical recording media have been proposed, none of them have been satisfactory in terms of holding effect.

An object of the present invention is to provide a magneto-optical recording medium which has no magneto-optical effect and recording sensitivity as compared with the conventional recording medium and has more excellent corrosion resistance.

[Means for solving problems]

The magneto-optical recording medium of the present invention is a magneto-optical recording medium having at least a magnetic recording layer on a substrate, characterized by being provided with a corrosion prevention layer made of SrF ₂ .

The corrosion preventing layer made of SrF ₂ in the magneto-optical recording medium of the present invention is laminated on one side or both sides of the magnetic recording layer having a magneto-optical effect, in direct contact with or through various auxiliary layers described later, a substrate or the like. It is possible to extremely effectively suppress the corrosion of the magnetic recording layer due to oxygen, water, etc. originally contained in each auxiliary layer or the like.

This corrosion prevention layer is preferably laminated in direct contact with the magnetic recording layer. This is because, when the auxiliary layer is laminated via the auxiliary layer, when the auxiliary layer (particularly, one made of an organic substance) contains water, oxygen, or the like, corrosion due to these cannot be prevented.

The corrosion-preventing layer made of SrF ₂ may contain various additive substances within the range not hindering the achievement of the object of the present invention. This corrosion prevention layer can be formed by a known film forming method such as vacuum deposition or sputtering. Its thickness is generally 20
Corrosion resistance can be improved at about 4000Å.

The magneto-optical recording medium of the present invention can have any structure, for example, an air sandwich structure or a laminated structure. In this structure, the reflection layer, the antireflection layer, the heat insulation layer,
An auxiliary layer such as a layer in which index marks and tracking marks are written is provided as needed.

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view of one embodiment of the magneto-optical recording medium of the present invention. This magneto-optical recording medium is composed of Sr on a transparent substrate 1.
The corrosion prevention layer 2 made of F ₂ is laminated, and further, the magnetic recording layer 3 having a magneto-optical effect and the protective layer 4 are sequentially laminated on the layer 2, and the corrosion prevention layer 2 is present. Therefore, it has excellent corrosion resistance.

Materials for the substrate 1, the magnetic recording layer 3 and the protective layer 4 are not particularly limited, but as the substrate 1, polycarbonate, acrylic resin, glass or the like is usually used.

The magnetic recording layer 3 is a combination of one or more elements from the group of rare earth elements such as Gd, Tb, Dy and Ho and one or more elements from the group of transition metal elements such as Fe, Co and Ni. (For example,
GdFe, TbFe, GdFeCo, and GdTbFeCo films) can be preferably used because they have excellent recording and reproducing characteristics, and can be formed by a film forming method such as vacuum deposition or sputtering. The thickness of these films is usually 300-5000Å.

Particularly, it is preferable that the coercive force of the magnetic recording layer 3 is 100 to 1000 Oe because the recording and reproducing characteristics are good.

Since the protective layer 4 has a function of preventing corrosion against oxygen, moisture, etc., and since it is an outermost layer, it is desirable to have resistance to external force as well, and therefore, for example, an inorganic material such as an oxide, a sulfide, or a nitride, or a metal. Alternatively, an organic polymer film or the like may be used.

FIG. 2 is a schematic sectional view showing another embodiment of the magneto-optical recording medium of the present invention. In this magneto-optical recording medium, a corrosion prevention layer 5 made of SrF ₂ and a reflective layer 6 were formed between the magnetic recording layer 3 and the protective layer 4 of the magneto-optical recording medium shown in FIG. It has a structure.

In this way, the corrosion prevention layers 2 and 5 made of SrF ₂ arranged on both sides of the magnetic recording layer 3 suppress the erosion of oxygen and water on both sides of the magnetic recording layer 3, and the protective layer 4 synergistically. By exerting such a function, extremely excellent corrosion resistance is provided. Therefore, this magneto-optical recording medium also has a structure in which the reflective layer 6 is provided in order to improve the reproduction efficiency by utilizing the Faraday effect in addition to the Kerr effect, and the thickness of the magnetic recording layer 3 is as described above. Although it is usually about 50 to 500 Å, the progress of corrosion of the magnetic recording layer 3 is significantly suppressed, and this magneto-optical recording medium is very excellent in practical use.

〔The invention's effect〕

The magneto-optical recording medium of the present invention has superior corrosion resistance to the conventional recording medium, and has no discoloration in terms of recording characteristics, thus extending the period of practical use. It has become possible. Further, as will be apparent from the examples described later, the magneto-optical recording medium of the present invention is practically preferable because there is no need to change the recording conditions because the S / N and coercive force of the magneto-optical recording medium maintain a substantially constant value during the usable period. It is a thing.

Example 1 A glass plate having a diameter of 200 mm and a thickness of 1.15 mm provided with a pre-group of 50 μm in thickness by a photo-curing resin layer was used as a substrate, and SrF ₂ (film thickness 15
00Å) was electron beam evaporated. Next, GdTbFe (film thickness 160Å) is formed by sputtering using a high frequency sputtering device.
To form a magnetic recording layer. On top of this, a corrosion prevention layer of SrF ₂ (thickness 2000 Å) was formed in the same manner as the above corrosion prevention layer. On top of that, Al (film thickness 500
Å) is deposited, and then SiO (film thickness 4000) is used as a protective layer.
Å) was deposited. Further, a protective glass plate of the same type as the substrate was attached to the protective layer using an adhesive to manufacture the magneto-optical recording medium of the present invention.

Comparative Example 1 A magneto-optical recording medium was produced in the same manner as in Example 1 except that SiO layers having the same optical film thickness of these layers were provided instead of the two corrosion prevention layers of Example 1.

Comparative Example 2 Instead of the two corrosion prevention layers of Example 1, an AlN layer, which is generally considered to have a high corrosion prevention ability, was provided so that the optical thicknesses of these two layers were equal to each other. A magneto-optical recording medium was produced in the same manner as in Example 1.

Comparative Examples 3, 4, 5 In the same manner as in Example 1 except that, instead of the two corrosion preventing layers of Example 1, the following corrosion preventing layers having the same optical film thickness of these layers were provided, respectively. A recording medium was produced.

Comparative Example No. 2 Components of Two Corrosion Inhibiting Layers 3 GdF ₃ 4 LaF ₃ 5 CeF ₃ The corrosion resistance of the magneto-optical recording medium of Example 1 and proportional 1 to 5 was evaluated. For the evaluation, the magneto-optical recording medium was placed in a constant temperature and humidity chamber at 45 ° C and 95%, and an acceleration test was performed to examine changes with time in coercive force and S / N ratio.

The S / N ratio was measured using a semiconductor laser with a wavelength of 830 nm while rotating the magneto-optical recording medium at 1800 rpm.
Recording was performed at mW, a duty ratio of 50%, and a recording frequency of 4 MHz, and this was reproduced by using the same semiconductor laser with a reproduction output of 2 mW.

The acceleration test results of the coercive force change are shown in FIG. 3 (Example 1 and Comparative Example 1) and FIG. 5 (Comparative Examples 3, 4, 5), and the acceleration test result of the S / N change is shown in FIG. 4 ( This is shown in Example 1 and Comparative Examples 1 and 2).

In these figures, the values of coercive force and S / N ratio are
It is standardized by the initial value. The initial values of each are shown below.

As is clear from the test results, it was confirmed that the magneto-optical recording medium of the present invention having the corrosion-preventing layer made of SrF ₂ has high corrosion resistance, and that the practical use range of the recording medium is 30% of the coercive force.
It can be seen that the practical period can be longer than that of the conventional magneto-optical recording medium if the reduction or the S / N is reduced by 3 dB. Further, the magneto-optical recording media of Comparative Examples 1 and 2 gradually deteriorate in characteristics and become unusable, whereas Comparative Example 3
The magneto-optical recording media of Nos. 5 to 5 are characterized in that their characteristics hardly change for a certain period of time after production, and the characteristics rapidly deteriorate after a certain period of time. As shown in FIG. 3, the magneto-optical recording medium of the present invention shows almost no change in the characteristics for a certain period of time as compared with the comparative example, and the deterioration of the characteristics after the lapse of this period gradually progresses. is there. Therefore, according to the present invention,
Recording / reproduction can be performed under certain optimum conditions until the life of the medium is exhausted, and the written information is lost by taking backup measures until the life expires and the magnetic characteristics are lost. It also has the effect of never disappearing.

[Brief description of drawings]

1 and 2 each show an embodiment of a magneto-optical recording medium according to the present invention. 3 and 5 show changes with time of the coercive force of the magneto-optical recording medium, and FIG. 4 shows the S / N of the magneto-optical recording medium.
Shows the change with time. 1 ... Substrate 2,5 ... Corrosion preventive layer made of fluoride of rare earth element 3 ... Magnetic recording layer 4 ... Protective layer 6 ... Reflective layer 7,10 ... Coercive force or S / N of Example 1 Curves showing changes over time in the ratio 8, 11 ... Curves showing coercive force of the comparative example 1 or S / N ratios over time 9, 12 showing changes in the coercive force or S / N ratios of the comparative example 2 with time Curve 13 ... Curve showing coercive force change over time of Comparative Example 3 ... Curve showing coercive force change over time of Comparative Example 4 ... Curve showing coercive force change over time of Comparative Example 5

Front Page Continuation (72) Inventor Yoichi Osato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-59-110052 (JP, A)

Claims (1)

[Claims] 1. A magneto-optical recording medium having at least a magnetic recording layer on a substrate, wherein a corrosion preventing layer made of SrF ₂ is provided.