JPH0354748A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To efficiently realize high-density/high-speed recording by providing a recording layer of an org. composite film comprising a metal magnetic film having >=0.1deg Kerr rotation and <=400 deg.C Curie point and containing one or more kinds of org. material having the weight-average mol.wt. of <500. CONSTITUTION:The recording medium has recording layers 12, 22 of org. composite films comprising metal magnetic films having axes of easy magnetization perpendicular to the film plane, >=0.1deg Kerr rotation and <=400 deg.C Curie point and containing one or more kinds of org. material having the weight-average mol.wt. of <500 by 0.001 - 10wt.%. By using the composite magnetic layers comprising metal thin films and one or more kinds of org. material having the weight mean mol.wt. of <500 as the recording layers 12, 22, thermal conductivity of the medium can be decreased and thereby, high-density/high-speed recording can be performed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to optical recording media, particularly magneto-optical recording media.

More specifically, the present invention relates to a novel magneto-optical recording medium that allows easy control of the shape of recording magnetic domains in a recording medium layer and is suitable for high-density recording and high-speed data transfer.

[Conventional technology]

In recent years, various recording technologies capable of high-density recording have been developed as information processing capacity increases. In particular, rewritable magneto-optical disks that utilize the so-called magneto-optic effect are viewed as promising. Such recording media such as magneto-optical disks are
A perpendicularly magnetized thin film with an axis of easy magnetization mainly perpendicular to the disk surface is formed on a substrate such as glass or resin, and information is written using thermomagnetic writing using a laser beam on the magnetic thin film. During reproduction, the magnetic information stored in the recording medium is read out by detecting the rotation of the polarization plane of the reflected light or transmitted light from the magnetic thin film due to the magneto-optic effect.

In recent years, rare earth transition metal amorphous films or amorphous films of alloys thereof have become mainstream as perpendicularly magnetized thin films for storing information. Such materials include Gd
Examples include Fe, NdFe, Dyke, TbFe, etc., and in addition, Sr, Gd, Co as a third element.
It is also known that the recording characteristics can be improved by forming a multi-component alloy by adding .

Typically, the production of this non-quality rare earth/transition metal alloy thin film is
Bulletin of the Japan Institute of Metals Vol. 24 No. 7 (1985) p581
~p587 and Trikebbs “Magneto-Optical Disk J (1
986) as described on pages 43 to 81,
This is accomplished by vacuum evaporation, DC two-pole sputtering, three-pole sputtering, high-frequency sputtering, Planar magnetron sputtering, and the like.

[Problem to be solved by the invention]

However, although magneto-optical recording media with the above-mentioned metal thin film as a recording layer have received great attention and expectations as high-density recording media, there remain several serious issues that need to be overcome before industrialization. .

In other words, the major problem is that the shape of the recording magnetic domain is teardrop-like as shown in Figure 2, making it difficult to position the bit edges and control the magnetic domain width, making it difficult to further improve the recording density, and eventually increasing the speed of recording. This was a major hindrance to the realization of transfer.

Although various efforts have already been made to address this issue,
I have not yet been able to overcome it. For example, in order to overcome the above problems, it is desirable to (a) improve the heating efficiency of the medium, that is, have low thermal conductivity, and (b) have a low Curie point, but there are still metals that fully meet these requirements. The reality is that thin film materials have not yet been obtained.

Therefore, an object of the present invention is to provide a magneto-optical recording medium that allows efficient high-density and high-speed recording.

[Means to solve the problem]

In view of the current situation, the present invention has conducted various studies to develop a recording film material with low thermal conductivity, and has discovered that the above object can be achieved by compounding an organic substance into the recording layer of a magneto-optical recording medium. This is the completion of the present invention.

That is, the present invention has an axis of easy magnetization in a direction perpendicular to the film surface,
And Kerr rotation axis is 0.1 degree or more, Curie point is 400℃
The present invention relates to an organic composite magneto-optical recording medium characterized by having a recording layer made of an organic composite film containing one or more organic substances having a weight average molecular weight of less than 500 in the following metal magnetic film.

The magnetic gold film used in the magneto-optical recording medium of the present invention has an axis of easy magnetization perpendicular to the film surface, and has a rotation angle of 0.1 degree or more, preferably 0.2 degree or more, and a Curie It is required that the temperature is below 400°C. In other words, CoC'r, CoNiP used for perpendicular magnetic recording
Thin film materials such as these have a high Curie point, are difficult to perform thermomagnetic writing using semiconductor laser light, and are not practical as magneto-optical recording media, so they are excluded.

According to the present invention, a magneto-optical film that enables high-density and high-speed recording is obtained by using a magnetic film, which is a composite of one or more organic substances having a weight average molecular weight of less than 500, in a continuous metal thin film as described above, as a recording layer. A recording medium is provided.

In the magneto-optical recording medium of the present invention, an appropriate amount of an organic substance and a metal element are composited without deteriorating the original magneto-optical properties of the metal thin film, and the recording layer is formed by the action of the composite organic substance. Thermal conductivity can be reduced. In other words, by reducing thermal conductivity, unnecessary bulging of the recording magnetic domain can be prevented, and minute recording magnetic domains whose shapes are precisely controlled can be formed at high density, making high-density and high-speed recording possible. Ta. Furthermore, according to the present invention, heating efficiency is also improved, so even if a semiconductor laser with limited output is used as a light source, writing can be performed in a short time.

Conventionally, it has been proposed to use Ta, 05, or the like, which has a low thermal conductivity, as a protective film as a means to prevent heat conduction of the medium. However, these methods do not improve the thermal characteristics of the recording film itself on which information is actually recorded, and cannot prevent the recording magnetic domain from becoming teardrop-shaped. Furthermore, no protective film material has been found that satisfies the characteristics required for a protective film, such as transmittance, refractive index, and protective properties, and has sufficiently low thermal conductivity. These conventional proposals are essentially different from the present invention, which makes it possible to reduce the thermal conductivity of the recording film itself, but if the present invention is applied to a protective film, it will be possible to reduce the thermal conductivity of the recording film itself. It is also possible to further reduce the thermal conductivity of the overcoat material used.

On the other hand, as optical recording media on which information is recorded by laser beam heating, in addition to the magneto-optical type, phase change type or perforated type optical disks using organic thin films, chalcogenite-based materials, etc. are known. Although the present invention mainly relates to magneto-optical recording media, the present invention can also be applied to other heat mode optical recording media, especially those in which materials with high thermal conductivity such as alloys are used in the recording media. It can be applied to increase recording sensitivity.

The metal magnetic film material that can be used in the present invention has an axis of easy magnetization perpendicular to the film surface, that is, has positive perpendicular magnetic anisotropy energy, and has a Curie temperature suitable for thermomagnetic writing using a semiconductor laser. Alternatively, it is preferable to have a compensation temperature.

Such materials are generally preferred to be rare earth-transition metal amorphous alloys, but may also be in crystalline form. Examples of these include GdFe, TbFe,
GdCo, DyFe, GdTbFe, TbDyF
e, TbFeCo, NdDyFe, NdDyFeC
o, GdTbCo, GdTbFeCo, GdFeB
i, GdTbFeCe; or Bi,
Ni, Pt, Ta, In, Cr, Ti, Sr
, to which additional elements such as Ce are added; MnBi,
PtCo, PtMnSb, MnCuB5MnAIC
Examples include e.

Although there are no particular restrictions on the organic substance that can be used in the present invention, it is preferable that it satisfies the following conditions.

1) Light absorption is small in the practical wavelength range 2) Does not act as an oxidizing agent for rare earths and transition metals 3) Melting point is at least higher than the Curie point of the recording film 4> Does not exhibit optical activity that may cause noise Furthermore, when manufacturing an organic composite film by vacuum evaporation, it is desirable that the organic substance be fixed at room temperature in order to control the amount of organic substance added. It is possible to combine organic substances into a film using a method.

The amount of the organic substance added can be in the range of 0.001 to 10% by weight, preferably in the range of 0.01 to 5% by weight, although it depends on the type of organic substance.

The amount of organic matter added is 0. When the amount is less than 0.01% by weight, almost no decrease in thermal conductivity according to the present invention is observed;
If the amount is at least % by weight, the above effects are generally observed.

Furthermore, if the amount of organic substance added exceeds IO weight %, the corrosion resistance of the resulting recording film decreases, which poses a problem. When the content is 5% by weight or less, the deterioration in corrosion resistance is alleviated, and a recording film that best meets the purpose of the present invention can be obtained.

The weight average molecular weight of the organic material used in the present invention is less than 500. Organic substances with a weight average molecular weight of less than 500 have extremely low absorption in the practical wavelength range, and therefore have a great advantage in that they can be combined without worrying about deterioration of magneto-optical properties.

The lower limit of the molecular weight is preferably one that is solid at room temperature, and one with a weight average molecular weight of 100 or more.

The film thickness is 100 to 2000 mm as a recording layer of a magneto-optical recording medium.
A range of people is preferred.

As the substrate on which the thin film is formed, a transparent substrate made of polycarbonate, polyolefin, glass, or the like, or one on which a transparent base layer of nitride, oxide, or the like is formed can be used.

Further, a protective film or the like may be further formed on the recording layer by sputtering or the like to form a multilayer structure as shown in FIG. 1, for example. When creating such a multilayer structure, materials that can be used for the protective film, reflective film, etc. include Cu, AI, and Ti.
, Pt, Au, Ni, Mn, Bi, Cr,
Metals such as Ag, Sn, AIN, SI3N4,
AISIN, CeF2, MgF2, LaF,,
CaF2, NaF, ZnS, Sin,
Sh02,CeF,, AIF,, Ta,Os,
CoFe,O. , Y3Fes[]+2,3i,Fe
Dielectric materials such as 5+2+ (BIY) 3F'eSoi can be mentioned.

[For production]

The magneto-optical recording medium according to the present invention has the following characteristic effects 1) to 5).

1) The denseness and surface smoothness of the film are increased by the action of organic substances, and the medium noise during reading is reduced.

2> Heat conduction in the film is suppressed by the action of the organic substance, improving the heating efficiency of the writing laser beam and increasing the writing speed.

3) Because heat conduction is small, it is possible to prevent heat from propagating to areas not irradiated by the laser beam, and a minute recording magnetic domain is formed faithfully to the trajectory of the writing laser beam, making it possible to increase the recording density. Become.

4) Shortening of writing time due to 2> above and 3) above
Due to the increase in linear recording density, high-speed data transfer on magneto-optical disks becomes possible with conventional writing laser output and disk rotation speed.

5) The effect of 1) above can be obtained without impairing the magneto-optical properties.

〔Example〕

The present invention will be explained in more detail using Examples below.
The present invention is not limited to the following examples.

Film Formation Method Using a vacuum evaporation apparatus equipped with an electron gun, crucibles for rare earth metals, transition metals, and organic substances were set, and ternary simultaneous evaporation was performed. Resistance heating was used in part as the evaporation source for organic matter.

Table 1 shows the organic substances used in this example.

Table 1 Table 1 (continued) Table 1 (continued) ? Metal carbon analyzer (manufactured by Horiba, BMIA-110)
) to 1000-1350℃, and the generated C
Quantification was carried out by either the method of quantifying O■, CD, UV absorption method, or fluorescent X-ray method.

Metal assembly analysis ICP method (manufactured by Nippon Jarrell Ash Co., Ltd., ICAP-5)
75 type).

Measurement of film thickness: Measurement was performed using a stylus-type step measuring device or a repeating reflection interferometer.

Measurement of magneto-optical properties Kerr rotation angle (θk), coercive force (Hc), and Curie point (TC) were measured using a Kerr effect measuring device (JASCO K-250).
) was measured.

Corrosion resistance test 0. After uniformly spraying the 1N NaC] solution onto the membrane surface,
A standing test was conducted in an environment of 60° C. and 90% RH for 100 hours continuously, and the area ratio of the corroded portion of the film before and after was determined using an image analysis device. Evaluation was made on the following three levels based on the area ratio of the corroded portion after being left for 100 hours.

A: less than 30% B: less than 60% C: 60% or more Measurement of thermal conductivity Measurement was performed using a laser flashco method on samples coated on polyimide and PET films with a film thickness of 1 to 5 μm.

Membrane structure and surface shape The fine structure, non-quality, surface shape, etc. of the membrane were observed using a transmission electron microscope (JEOL 2000FX) and a field emission scanning electron microscope (Hitachi S-4000). .

The results are shown in Table 2, along with the metal composition of the product of the present invention, the organic substances used (the numbers shown in Table 1), the coating method, the thermal conductivity, and a comparative example in which no organic substances were included.

First, the thermal conductivity of all the samples decreased due to the addition of organic substances. In addition, the rotation angle per force is 0.30 to 0.30 depending on the metal assembly.
±0.02 if the metal assemblies are equal within a range of 0.42 degrees
It was almost constant within the range of degrees.

The coercive force was 5 kG or more, and the Curie point was in the range of 150 to 200°C. No deterioration of magneto-optical properties (decrease in force/rotation angle, decrease in coercive force, and increase in Curie point) due to the addition of organic substances was observed within the range of addition amount of 5% by weight or less.

OthersGdTbFeCo, GdTbFe, NdDy
FeCo, NdDyFe, TbFe (N
o. 16 to 19), similar effects due to the addition of organic substances were observed.

Table 2 Table 2 (Continued) (Note) K1 Composition ratio of each metal when the total amount of metal in the film is 100 Book 2 Organic composite rare earth transition metal alloy obtained by the present invention as above the value at 25°C It has been found that by using a film as a recording layer, the thermal conductivity of the film is reduced, so that a magneto-optical recording medium capable of high-density and high-speed recording can be provided.

4,

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a general magneto-optical recording medium, and FIG. 2 is a diagram schematically showing the shape of recording magnetic domains written on a conventional medium. 1.2: Recorded magnetic domain with teardrop shape due to high thermal conductivity of the medium 3: Beam scanning direction 4: Difference in domain width when beam irradiation time differs 5, 6: Ideal recording domain shape 7 : Misalignment of bit edge 11.21: Substrate 12.22: Recording layer 13, 23: Protective layer 14.24: Base layer 15: Encapsulant layer

Claims (1)

[Scope of Claims] 1. A metal magnetic film having an axis of easy magnetization perpendicular to the film surface, a Kerr rotation axis of 0.1 degrees or more, and a Curie point of 400°C or less, with a weight average molecular weight of 500°C or less. less than 1 organic matter
1. A composite magneto-optical recording medium comprising a recording layer made of an organic composite film containing at least one species. 2. The magneto-optical recording medium according to claim 1, wherein the main component of the metal magnetic film is one or more selected from rare earth metals and transition metal elements. 3. The metal magnetic film contains at least one rare earth element selected from Tb, Gd, Nd, and Dy, and Fe,
Claim 1 containing either or both of Co.
Or magneto-optical recording medium according to 2.