JP2521713B2 - Magneto-optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical recording medium, particularly a magneto-optical recording medium.

(Prior Art) In the field of information processing technology, demands for further increase in recording capacity, number of times of writing, etc. of a magnetic memory have increased more and more in recent years due to rapid progress of increase and diversification of information. . Therefore, as one of the promising optical recording media, an amorphous film of a rare earth-transition metal compound (hereinafter, RE-
It is called a TM alloy layer. However, RE represents a rare earth element and TM represents a transition metal element. Has been proposed as a magneto-optical recording layer (for example, Japanese Patent Laid-Open No. 52-31703).
Or JP-A-52-109193).

These known RE-TM alloy layers are specifically Gd as RE.
(Gadolinium), Tb (terbium), Dy (dysprosium) and other rare earth elements, TM as Fe (iron) or
Co (cobalt) is the main component. This film is a so-called perpendicular magnetization film having a magnetization perpendicular to the film surface.

A magnetic recording medium using this RE-TM alloy layer as a recording layer can record a very high density of 10 ⁸ bits / cm ² by a thermomagnetic writing method using a laser beam focused to about 1 μmφ and an external magnetic field. It is known that it has a remarkably excellent feature that it is possible, and in principle, almost unlimited erasing and rewriting are possible.

This RE-TM alloy layer mainly consists of RE-Fe alloy layer and RE-Co alloy layer.
It is classified into an alloy layer.

The RE-Fe alloy layer has excellent magnetic and magneto-optical properties, and has the advantage that it is easy to form a film with a uniform distribution of properties, but it has very poor corrosion resistance, and in particular, the occurrence and development of pitting corrosion is remarkable. There is a drawback that

On the other hand, the RE-Co alloy layer is excellent in terms of corrosion resistance,
Since it is difficult to obtain a film having uniform characteristics and the Curie point is high, it is inferior to the RE-Fe alloy layer in terms of thermomagnetic writing characteristics.

Therefore, conventionally, as is well known, it has been attempted to improve not only corrosion resistance but also magnetic and magneto-optical characteristics by only adding a small amount of Co to RE-Fe. However, the addition of Co causes a rapid rise in the Curie point, and if it is added excessively, it makes thermomagnetic writing difficult, so in reality only a small amount was added. In this way, the RE-Fe-Co alloy layer obtained by adding a small amount of Co to RE-Fe has a higher magnetic and magneto-optical property than either of the RE-Fe and RE-Co alloy layers. Comparing the corrosion resistance, it was superior, but it was not as good as the RE-Fe alloy layer but could still be used for practical use.

Therefore, as a method of improving the corrosion resistance, a method of providing a protective film on the recording layer of the RE-TM film is also used. This protective film not only protects the recording layer from mechanical damage, but also protects the recording layer from direct contact with the external atmosphere such as outside air, moisture and oil, and plays a role in helping to enhance the corrosion resistance of the RE-TM film. To fulfill. However, for example, the film thickness
A 600 Å RE-Fe-Co film with a 1000 Å thickness of SiO ₂ , SiO or Si
_In the case of coating with ₃ N ₄ , the aging test was performed for 50 hours under the condition of temperature of 85 ° C and relative humidity of 85%, and it was found that many pitting corrosion occurred and the corrosion resistance was poor.

Also, as another conventional method for improving the corrosion resistance,
There is a method of adding various elements to the RE-TM film. But,
Since the addition of these elements often deteriorates the magnetic or magneto-optical characteristics, it is necessary to keep the addition amount to a small amount, but in that case, sufficient corrosion resistance cannot often be obtained. On the contrary, in order to obtain sufficient corrosion resistance, the addition amount is increased, and as a result, the magnetic or magneto-optical characteristics are sacrificed.

(Problems to be Solved by the Invention) As described above, although the RE-Fe alloy layer and the RE-Fe-Co alloy layer have excellent characteristics as a magneto-optical material, there is a problem that the corrosion resistance is extremely poor.

Further, as a method of compensating for the corrosion resistance defect, conventionally, a protective film is provided on the recording layer, or various elements are added as described above, but both methods have sufficient corrosion resistance to a practical level. There was a problem that could not be improved.

An object of the present invention is to provide a magneto-optical recording medium which has corrosion resistance sufficient for practical use and has excellent magnetic and magneto-optical characteristics.

(Means for Solving the Problems) In order to achieve this object, in the magneto-optical recording medium of the present invention, the recording layer of the magneto-optical recording medium is a RE-TM alloy layer (where RE is a rare earth element and TM represents a transition metal element), and the recording layer is composed of a multilayer film in which an inert metal layer and a RE-TM alloy layer are alternately laminated, and The layer was a film made of one kind of metal selected from the group of Rh and Ni. The multilayer film is a composition-modulated multilayer film, which is a so-called artificial lattice layer. In this case, the first and last films in the stack may be the same film or different films. These can be designed as desired depending on the design.

Further, according to a preferred embodiment of the present invention, the RE-TM alloy layer is a RE-Fe-Co alloy layer (provided that Fe represents iron and Co represents cobalt), and the amount of RF is the total amount of the alloy. 18 to 35 atomic%, and the amount of Co may be 20 atomic% or less (excluding 0 atomic%).

Further, according to a preferred embodiment of the present invention, the RM-TM alloy layer is a RE-Fe alloy layer (provided that Fe represents iron), and the RE amount is 18 to 35 atomic% of the total amount of the alloy. good.

(Operation) In the magneto-optical recording medium of the present invention, since the artificial lattice layer as the recording layer has the RE-TM alloy layer, the magneto-optical recording medium of the present invention has a good optical property as in the conventional case. In addition to having magnetic properties, this artificial lattice layer has a structure in which an RE-TM layer and an inert metal layer made of a kind of metal selected from the group of Rh and Ni are alternately laminated, so that the magneto-optical characteristics It is possible to add a large amount of an inert metal to the recording layer without fear of deterioration of the recording layer. Therefore, as can be understood from the experimental results described later, the recording formed by alloying an inert metal in the RE-TM layer. Corrosion resistance is significantly improved over that of the layer.

Embodiments Embodiments of the present invention will be described below with reference to the drawings. The present invention will be described with reference to the following specific examples, but these examples are mere examples of preferred examples, and the present invention excludes the cases where the invention is particularly limited, and the materials listed in these examples, It should be understood that the present invention is not limited to the shape, the numerical condition, and the arrangement relationship.

Example of Structure of Recording Medium FIG. 1 is a schematic cross-sectional view of an essential part showing an embodiment of a magneto-optical recording medium using the magneto-optical recording medium of the present invention to the extent that its structure can be understood. In order to avoid complication of the drawing, hatching and the like showing the cross section are partially omitted in FIG.

In FIG. 1, reference numeral 1 denotes a substrate, which is a sufficiently smooth and transparent glass substrate or resin substrate. Reference numeral 2 denotes a dielectric layer provided on the upper side of the substrate 1, which has a Kerr effect enhancement function. In the past, this dielectric layer doubled as Kerr effect enhancement and as a protective layer, so there were restrictions on the materials used,
In the present invention, since it is not necessary to consider the function as a protective layer, any material advantageous for Kerr effect enhancement may be used, and for example, a SiO film having a film thickness of 800 Å can be used.

An artificial lattice film, which is a multilayer film as the magneto-optical recording layer 3, is provided on the upper side of the dielectric layer 2. In this embodiment, the artificial lattice layer 3 is constructed as a laminated body in which the inert metal layers and the RE-TM layers 5 are alternately laminated one by one from the substrate side. This RE-TM layer 5 is formed, for example, with Tb ₃₀ (Co ₈ Fe ₉₂ ).
₇₀ (however, Tb is terbium) and the inert metal layer 4 is a single metal layer of Ni, for example. Further, in this embodiment, when the thickness of one layer of the RE-TM layer 5 is set to 90, 85, 80 and 70Å, the thickness of one layer of the inert metal layer 4 is set to 10, 1
The artificial lattice layer 3 having a thickness of 1000 Å was made by stacking 10 cycles in total corresponding to 5, 20 and 30 Å.

A disk made of a magneto-optical recording medium thus formed was rotated at a rotation speed of 900 rpm, and writing was performed on this medium by using a semiconductor laser beam of 6 mW or less on the medium surface to obtain about 1
It was confirmed that micro recording of about μm diameter was obtained and that it could endure 100,000 or more times of erasing and rewriting.

Kerr Rotation Angle Next, with respect to an example of the magneto-optical recording medium having the above-described configuration, the properties of this recording medium will be described based on the experimental results regarding the Kerr rotation angle.

FIG. 2 shows the composition of the artificial lattice layer 3 of this recording medium.
M _X {Tb ₃₀ (Co ₈ Fe ₉₂ ) ₇₀ } _100-X is a diagram showing the magnitude of the Kerr rotation angle when Ni (nickel) is used as M, and the average composition ratio is plotted on the horizontal axis. Tb not to get and the vertical axis of the inert metal layer 4 x ₃₀ (Co ₈ Fe ₉₂₎ Kerr rotation angle .theta.k / .theta.k ₀ to the Kerr rotation angle .theta.k ₀ in the case of a single layer of ₇₀ as a reference
Is shown. The average composition ratio x is a value obtained by the film thickness ratio between the RE-TM layer 5 and the inert metal layer 4, that is, the atomic density and film thickness of each film. In this figure, the solid line is the Kerr rotation angle of the medium according to the present invention including the artificial lattice layer 3 having a laminated structure, and the broken line is the Kerr rotation angle of the medium in which Ni is alloyed with the RE-TM layer shown as a comparative example. Is.

As can be understood from these experimental results, in the case of the artificial lattice layer having a laminated structure, the Kerr rotation angle decreases when Ni is excessively contained, but the average composition ratio x is around x = 30. However, the amount of decrease is small, and at this time θk / θk ₀
It can be seen that the value of is still around 0.9. Generally, the CN ratio is proportional to θk, and θk / θk ₀ = 0.9 means that the CN ratio is reduced by 10%. Normally, using a RE-Fe-Co film
A CN ratio of 50 dB can be obtained, which is 45 dB. And, the CN ratio is determined to be 45 dB or more. Therefore, 0.9 is the lower limit for maintaining the reproduction characteristics of θk / θk ₀ . The reduction of the Kerr rotation angle in the case of the laminated structure is smaller than that in the case of alloying. As described above, it is considered that the reduction of the Kerr rotation angle can be suppressed to be small because the medium of the present invention has a laminated structure rather than gold, and thus the influence of Ni on the RE-TM layer is small.

Incidentally, in the RE-Fe-Co film, when the Co is increased, the Kerr rotation angle increases, but on the other hand, the Curie point rises sharply.
If it is added excessively, thermomagnetic writing becomes difficult. for that reason,
The amount of Co in the RE-TM film is preferably 20 atomic% or less (excluding 0 atomic%).

Corrosion Resistance Next, the corrosion resistance of the magneto-optical recording medium of the present invention will be described with reference to the test results shown in FIG.

It has been conventionally known that the corrosion resistance increases as the amount of Ni added to the RE-TM layer increases. A comparative test of the corrosion resistance was conducted on the magneto-optical recording medium of the present invention, and it was confirmed that the corrosion resistance was remarkably excellent.

The recording layers of the recording medium used in this corrosion resistance test are shown in Table I below. Sample No. 1 is a conventional recording layer, and Sample Nos. 2 to 4 are media having the laminated recording layer described with reference to FIG. Sample No. 5 is a medium having a recording layer having a laminated structure of 5 periods. The thickness of the entire recording layer was set to 1000Å for all the samples.

The corrosion resistance will be described below.

Generally, the alloy layer of the magneto-optical recording medium including the RE-Fe alloy layer causes pitting corrosion in a high humidity atmosphere, and the pitting corrosion penetrates the thin film. Therefore, the light transmittance increases as the pitting corrosion increases. Therefore, the corrosion resistance can be evaluated by the magnitude of the change in light transmittance. Therefore, in this test, when the magneto-optical recording medium was kept in an atmosphere at a temperature of 85 ° C. and a relative humidity of 85%, the change with time of the light transmittance of each magneto-optical recording medium was examined. The change in the light transmittance in this case is the light transmittance T after each holding period and the light transmittance in the state before entering the atmosphere (referred to as an initial value) T _0.
The transmittance ratio T / T ₀ expressed by comparison with

FIG. 3 shows the test results for sample Nos. 1, 2, 3, 4, and 5, with the retention time (unit: time: / h) on the horizontal axis and the light transmittance on the vertical axis. .

As can be understood from the experimental results shown in FIG. 3, as compared with the recording layer (Sample No. 1) having no inert metal layer 4, an artificial lattice layer in which the Ni inert metal layer 4 is laminated. It can be understood that in the case of the magneto-optical recording medium No. 3 (Sample Nos. 2 to 4), the light transmittance ratio is reduced to about 1/100 or less. Further, as can be understood from the light transmittance of the samples (No. 2 to 5) representatively showing the Ni layer as the inactive metal layer 4, the conventional recording was performed as the content of these inactive metals increased. It can be seen that the light transmittance ratio is remarkably smaller than that of the medium for use, and thus the corrosion resistance is high. In particular, comparing Sample Nos. 2 to 4 with Sample No. 5, the transmittance of Sample No. 5 (transmittance at a holding time of 100 hours = 1 × 10 ⁻³ ) rapidly increases.

Therefore, in the example illustrated in Table I, where the thickness of the RE-TM layer 5 is a and the thickness of the inert metal layer 4 is b, sample number No. 2 is a / b = 9, No. 3 Is a / b = 85/15 ≒ 5.67, No.4 is a
/ b = 4, No. 5 has a / b = 19. Therefore, it can be seen that when a / b exceeds 9, the transmittance sharply increases.

Even in the case of the Tb ₃₀ (Co ₈ Fe ₉₂ ) ₇₀ single layer described above (Sample No. 1), since the protective film is deposited on the upper part, the corrosion resistance is superior to that without the protective film. However, pitting corrosion is unavoidable due to defects in the protective film.

Further, the above-mentioned average composition ratio x can be expressed by the following formula (1) using the film thickness ratio.

x = {b / (a + b)} × 100 = 100 / {(a / b) +1} ...
(1) θk / θk ₀ = 0.9 that can maintain the reproduction characteristics shown in FIG.
Then, the film thickness ratio when the average composition ratio x = 30 is a / b = 7/3 from the equation (1). Therefore, in order to maintain the reproduction characteristics and improve the corrosion resistance, the film thickness ratio is preferably in the range of 7/3 ≦ a / b ≦ 9.

The reason for selecting the thickness of the inert metal layer as 10 Å ≤ b ≤ 50 Å is that if the inert metal layer 4 is too thick, the number of repeating cycles becomes small and the meaning of the laminated structure becomes meaningless. This is because the magnetic properties of the RE-TM layer deteriorate as the layer becomes thicker, and further, the incident light to the RE-TM layer and the reflected light that goes out from the RM-TM layer become smaller,
This is because the reproduction characteristics deteriorate.

On the other hand, the lower limit of the thickness of the inert metal layer is 1 in principle.
It is the thickness of the atomic layer (2-3Å). However, in the apparatus used in this example, the film thickness of 10Å is the production limit. It was confirmed that the magneto-optical characteristics were good until the thickness of the inert metal layer was 10 Å, but the magneto-optical characteristics could not be confirmed when the thickness was less than 10 Å. For this reason,
The thickness of the inert metal layer is preferably in the range of 10Å ≦ b ≦ 50Å.

Therefore, if these thickness conditions are satisfied, the thicknesses a and b can be set arbitrarily within the range according to the design, and each layer or a plurality of layers constituting one artificial lattice layer 3 can be formed. The thickness may be changed for each.

Modifications The present invention is not limited to the embodiments described above, and many modifications and changes are possible within the scope of the present invention.

For example, in the above-mentioned embodiment, Tb is used as a rare earth element (RE).
However, rare earth elements other than Tb such as Dy
Even when one or more rare earth elements selected from (dysprosium), Gd (gadolinium), Nd (neodymium) and others are used, the inert metal layer 4 is made into RE.
The effect of forming a laminated structure with the -MT layer is exactly the same as in the case of Tb, and therefore a magneto-optical recording medium having excellent magneto-optical recording characteristics and high corrosion resistance can be obtained.

In addition, the effect of adding an inert metal to the RE-TM film is generally
The same applies regardless of the type of RE-TM film. Therefore, in the above-described examples, the example using the RE-Fe-Co alloy layer as the RE-TM layer has been described, but by stacking the alloy layer and the inert metal layer, it is a RE-Fe alloy layer. Also RE-Fe-
The same effect as in the case of stacking with a Co alloy layer can be expected.

Further, the inert metal layer 4 laminated to increase the corrosion resistance may be made of any one of Ni and Rh.

Further, the layers of the inactive metal layer 4 and the layers of the RE-TM layer 5 which are sequentially laminated to form the artificial lattice layer 3 may have different components for each layer or for each plurality of layers. Further, the two layers outside the artificial lattice layer 3 may be the same layer or different layers.

Further, the magneto-optical recording medium of the present invention may have a structure in which the dielectric layer 2 between the substrate 1 and the artificial lattice layer 3 is omitted, or the protective layer 6 is covered with an adhesive layer on the upper side. A structure in which a substrate layer (not shown) is provided may be used.

Further, the protective film may be an oxide film or a nitride film as in the conventional case, or a polycarbonate resin film, polyurethane, epoxy, polyimide, fluorocarbon,
It may be a layer containing polyxylene, polyvinyl, polyamide, polysulfide or other polymer material.

Further, the polycarbonate substrate has been described as an example of the substrate 1, but any other suitable material such as glass can be used, and a plate shape, a sheet shape, a tape shape, or any other suitable shape can be used. It can be shaped.

Further, the numerical values described in the above description of the embodiments are merely preferable examples, and the present invention is not limited to these values.

(Effects of the Invention) As is apparent from the above description, the magneto-optical recording medium according to the present invention has the recording layer having the laminated structure of the RE-TM layer and the inactive gold metal layer, and therefore has a conventional structure. RE active metal
Compared to the recording layer alloyed with the TM layer, the characteristics are less deteriorated and a large amount of inert metal can be mixed.
Therefore, there is an effect that the corrosion resistance is significantly improved as compared with the conventional one.

Due to the improvement of the corrosion resistance, the recording stability is remarkably improved, so that the deterioration with time of the writing and reproducing characteristics of the recording medium can be effectively controlled.

Further, since the recording layer used in the present invention has remarkably high corrosion resistance, it is possible to use as the protective layer a layer made of a polymer material which can be obtained at a low cost and which can be deposited on the recording layer by a simple method. It is possible to provide an improved, inexpensive and highly reliable recording medium.

Further, as in the conventional case, due to the nature of the recording medium itself, high-density recording is possible and the recording sensitivity is good.

In addition, the magneto-optical recording medium of the present invention has an advantage that it is possible to write and erase using a laser beam, and various restrictions on the light source used, such as those in the past, are remarkably reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a magneto-optical recording medium of the present invention. 2 to 3 are curve diagrams showing experimental results of the Kerr rotation angle and the light transmittance, which are provided for explaining the characteristics of the magneto-optical recording medium according to the present invention. 1 ... Substrate, 2 ... Dielectric layer 3 ... Recording layer (artificial lattice layer) 4 ... Inert metal layer, 5 ... RE-TM layer 6 ... Protective layer.

Claims (3)

(57) [Claims] 1. A recording layer comprising a RE-TM alloy layer (where RE represents a rare earth element and TM represents a transition metal element), and the recording layer is alternately laminated with an inert metal layer and a RE-TM alloy layer. In a magneto-optical recording medium constituted by a multi-layered film, the inert metal layer is a film made of one kind of metal selected from the group of Rh and Ni. Medium. 2. The RE-TM alloy layer is a RE-Fe-Co alloy layer (wherein Fe represents iron and Co represents cobalt), and the RE is
The amount of Co is 18 to 35 atom% of the total amount of the alloy, and the amount of Co is 20 atom% or less (however, 0 atom% is not included). The magneto-optical recording medium described. 3. The RE-TM alloy layer is a RE-Fe alloy layer (however,
Fe represents iron), and the amount of RE is based on the total amount of the alloy.
The magneto-optical recording medium according to claim 1, wherein the content is 18 to 35 atom%.