JPH05217226A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide a magneto-optical recording medium capable of recording with satisfactory characteristics in a smaller bias magnetic field than the conventional one. CONSTITUTION:This magneto-optical recording medium has 1st and 2nd magnetic substance layers on the substrate in a contact state. The 1st layer has >=10 kOe coercive force and is made of an amorphous rare earth element- transition metal alloy having a higher transition metal content than that of a compensation compsn. The 2nd layer has lower coercive force at room temp. than the 1st layer and a higher Curie temp. than the 1st layer and is made of an amorphous rare earth element-transition metal alloy. This recording medium has higher recording sensitivity to a bias magnetic field than the conventional one, electromagnets for generating a bias magnetic field can be miniaturized and electric power consumed by driving a magneto-optical disk can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording, reproducing and erasing information by using laser light.

[0002]

2. Description of the Related Art Conventionally, information is recorded by forming magnetic domains perpendicularly magnetized in a magnetic thin film by heat from a laser beam and an external magnetic field, and information is recorded by using the Kerr effect or Faraday effect by the recording mark. The magneto-optical recording method for reproducing information has been put into practical use as a highly reliable high-density information recording method capable of repeating recording and erasing. Although many kinds of magnetic alloys have been proposed as the magnetic film used for the recording film of the magneto-optical recording medium used for this purpose, especially transition metals such as Fe and Co and T are used.
An amorphous alloy thin film mainly composed of a heavy rare earth metal such as b, Dy, or Gd has a Curie temperature within a range suitable for recording.
Since it is amorphous, it is most often used because it does not generate grain boundary noise during reproduction, can form a perpendicular magnetization film easily by a method such as sputtering, and can obtain a relatively large magnetic-optical Kerr effect. Has been.

In this magneto-optical recording medium, in order to prevent deterioration of recording characteristics due to oxidation of the magnetic film over time, and to amplify the magneto-optical Kerr effect in order to obtain a sufficient reproduction signal output and CN ratio, A method of providing transparent dielectric layers on both sides of the magnetic layer or on the side of the magnetic layer on which laser light is incident,
Further, a method of providing a reflective layer and utilizing the Faraday effect of light transmitted through the magnetic layer is also widely used. By these methods, a magneto-optical recording medium having high reliability and good recording characteristics can be obtained.

[0004]

Recording and reproduction on a magneto-optical recording medium are performed by irradiating laser light while applying a bias magnetic field. However, in the conventional magneto-optical recording film, in order to perform sufficient recording and erasing, 3
A bias magnetic field of 00 Oe or more is required,
There is a drawback that the electromagnet that generates the bias magnetic field of the magneto-optical disk device for performing reproduction and erasure becomes large, and the power consumption of the entire device also becomes large. for that reason,
A recording medium having good sensitivity to a bias magnetic field has been desired.

In general, a rare earth-transition metal amorphous alloy has a small saturation magnetization when the composition thereof is in the vicinity of the compensating composition, and the demagnetizing field when magnetized in the direction perpendicular to the film surface of the recording film is small. Recording can be performed in a magnetic field. However, the recording domain formed when recording with a small bias magnetic field is unstable, and the shape of the recording mark is not good. Therefore, the reproduced signal from the recording mark recorded in this manner has a high noise level, a low CN ratio, large jitter, and other good recording characteristics cannot be obtained.

The problem to be solved by the present invention is that it has good sensitivity to a bias magnetic field, good recording mark shape, excellent recording domain stability, and low reproduction signal noise level. , A high CN ratio and a small jitter are provided.

[0007]

In order to solve the above problems, the present invention provides a rare earth-transition metal having a coercive force of 10 kOe or more on a substrate and a composition on the transition metal side of a compensating composition. A first magnetic layer made of an amorphous alloy;
In contact with this, a second magnetic layer made of a rare earth-transition metal amorphous alloy having a coercive force at room temperature lower than that of the first magnetic layer and a Curie temperature higher than that of the first magnetic layer is provided. A magneto-optical recording medium characterized by the above.

FIG. 1 is a schematic diagram showing the temperature dependence of the coercive force of the first magnetic layer and the second magnetic layer.

Further, this second magnetic layer is magnetized in the same direction as the magnetization direction of the recording mark at the time of recording on the first magnetic layer at the initialization stage, and thereafter, recording, reproduction, It is characterized in that the direction of its magnetization is not changed in all the processes of erasing. In the present invention, recording of information and reproduction of a recorded signal are performed in the first magnetic layer, so that the first magnetic layer is formed on the laser beam incident side of the second magnetic layer, that is, a transparent substrate in general. Since the laser beam is incident through the first magnetic layer, the first magnetic layer must be located on the substrate side with respect to the second magnetic layer. The state of recording on this recording film is shown in FIG.

According to the present invention, since the recording domain formed in the first magnetic layer is stabilized by the exchange coupling force with the magnetic moment of the second magnetic layer, a small bias magnetic field is applied. Even when recording is performed, a recording domain with a good shape is formed, recording noise is low,
Further, a recording film having a high CN ratio and a small jitter and good recording characteristics can be obtained.

The substrate used in the present invention is, for example,
Examples thereof include substrates such as polycarbonate, polymethylmethacrylate, and amorphous polyolefin in which guide grooves are directly formed in resin or glass, substrates in which guide grooves are formed on a flat plate of glass or resin by a photopolymer method, and the like.

The rare earth-transition metal amorphous alloy used in the first and second magnetic layers of the present invention is, for example, T
bFeCo, DyFeCo, TbFe, GdTbFeC
o, NdDyFeCo, TbCo, etc., and those obtained by adding other metals to these amorphous alloys for the purpose of improving oxidation resistance can also be used.

As described above, the rare earth-transition metal alloy used in the first magnetic layer is preferably close to the compensating composition on the transition metal side, and specifically, the coercive force of 10 kOe or more is preferable. Further, the rare earth-transition metal alloy used for the second magnetic layer preferably has a sufficiently high Curie temperature so that reversal of magnetization does not occur during recording on the first magnetic layer. It is preferably 300 ° C. or higher. However, the second magnetic layer should have a small coercive force at room temperature in order to facilitate the initialization of aligning the magnetization direction with the recording side direction of the first magnetic layer when manufacturing the recording medium. Need to use. Specifically, it is preferably 5 kOe or less.

In practical use, the two magnetic layers of the present invention are provided on both sides of the magnetic layer for the purpose of preventing the deterioration of the characteristics due to oxidation and for enhancing the Kerr effect to obtain a reproduced signal with a large output. A structure with an inorganic dielectric layer,
Further, it is used in a structure provided with a reflective layer.

An inorganic dielectric having high transparency is used for the dielectric layer. Examples of the material include SiN _x and Si
O _x , AlSiON, AlSiN, AlN, AlTi
N, Ta ₂ O ₅ , ZnS and the like can be mentioned, but among them, S
iN _x is preferred. The refractive index of these dielectric layers is 1.8 to
A range of 2.5 is preferred.

Examples of the material of the reflective layer include Al and alloys of Al with other metals. Al, Al-Ti alloys and Al-Cr alloys are preferable.

The dielectric layer, magnetic layer and reflective layer are formed by physical vapor deposition (P, P, etc.) such as sputtering or ion plating.
VD), chemical vapor deposition (CVD) such as plasma CVD, or the like.

The magneto-optical recording medium thus formed may be used alone or may be used by laminating two substrates so that the substrates are on the outside.

[0019]

EXAMPLES The magneto-optical recording medium according to the present invention will be described below with reference to specific examples.

(Embodiment) FIG. 3 is a cross-sectional view of a magneto-optical recording medium according to this embodiment. As shown in FIG. 3, the recording medium of this embodiment has a first dielectric layer on a transparent substrate. A body layer, a first magnetic body layer and a second magnetic body layer that are recording layers, a second dielectric layer, and a reflective layer are sequentially laminated in the thickness direction.

The magneto-optical recording medium of the present invention was prepared by forming each thin film by magnetron sputtering on a polycarbonate substrate having a groove and a preformat and having a diameter of 86 mm. First, as the first dielectric layer, S having a thickness of 100 nm was formed by RF sputtering using Ar mixed with N ₂ and Si as a sputtering gas.
An iN film was formed. Next, a 15 nm thick Tb ₂₁ Fe ₇₀ Co ₉ film was formed by the DC sputtering method as the first magnetic layer of the recording film, and a 15 nm thick Tb ₁₅ Fe ₇₀ layer was formed as the second magnetic layer.
A Co ₁₅ film was formed. In addition, a second 20 nm SiN layer
In the same manner as the first magnetic layer as the dielectric layer of
Further, a film of Al ₉₅ Ti ₄ having a thickness of 50 nm was laminated by a DC sputtering method as a reflection layer.

Separately, the first magnetic layer and the second magnetic layer were separately formed on a glass substrate, and their magnetic characteristics were measured using a vibrating sample magnetometer. The coercive forces of the first magnetic layer and the second magnetic layer were 14 kOe and 2 kOe, respectively. The Curie temperatures were 200 ° C and 320 ° C, respectively.

(Evaluation) The magneto-optical recording medium manufactured by the above method was initialized by using an electromagnet in a magnetic field of 5 kOe. This magneto-optical recording medium was measured using a magneto-optical disk recording characteristic evaluation device. Laser wavelength 830
Recording was performed under the conditions of nm, rotation speed 1,800 rpm, recording frequency 2.9 MHz, pulse width 90 ns, and recording laser power 8 mW. FIG. 4 shows the dependency of the CN ratio on the recording magnetic field strength in this case.
It was shown to.

From FIG. 4, C of the magneto-optical recording medium of this embodiment is shown.
It can be seen that the N ratio is saturated with an external magnetic field of about 100 Oe.
It is presumed that this is because during recording, even if the applied bias magnetic field strength is small, a well-formed recording mark is formed on the recording film, and thus recording noise is low.

Comparative Example Each layer was laminated on the same polycarbonate substrate as in the example. Of these layers, the recording film is different from the case of the embodiment, only Tb ₂₁ Fe ₇₀ Co ₉ having the same composition as that of the first magnetic layer is formed to a thickness of 30 nm.
No magnetic layer was provided. On the other hand, the composition of the other layers,
The film thickness and the stacking order were exactly the same as in the example.

The magneto-optical disk recording characteristic evaluation apparatus for the above-mentioned magneto-optical recording medium was used to measure the recording magnetic field strength dependency of the CN ratio under the same method and conditions as in Example, and the results are shown in FIG.
It was shown to.

From FIG. 4, C of the magneto-optical recording medium of this comparative example is shown.
It can be seen that a bias magnetic field of about 300 Oe or more is required to saturate the N ratio. It is presumed that this is because when the bias magnetic field strength applied at the time of recording is small, the shape of the formed recording mark is defective and the recording noise becomes large.

[0028]

According to the present invention, it is possible to manufacture a magneto-optical recording medium which can obtain good recording characteristics even when recording is performed in a low bias magnetic field. Therefore, the electromagnet that generates the bias magnetic field can be downsized, and the power consumption of the magneto-optical disk drive can be reduced.

[Brief description of drawings]

FIG. 1 is a table showing temperature dependence of coercive force of a first magnetic layer and a second magnetic layer.

FIG. 2 is an explanatory diagram showing directions of magnetization of first and second magnetic layers when recording is performed on the recording film of the present invention.

FIG. 3 is a sectional view showing a layer structure of a magneto-optical recording film according to an example of the present invention.

[Explanation of symbols]

 1 Substrate 2 1st Dielectric Layer 3 1st Magnetic Layer 4 2nd Magnetic Layer 5 2nd Dielectric Layer 6 Reflective Layer

FIG. 4 is a table showing the bias magnetic field strength dependence of the CN ratio when recording is performed on the magneto-optical recording media of the example of the present invention and the comparative example.

Claims (4)

[Claims] 1. A first magnetic layer made of a rare earth-transition metal amorphous alloy having a coercive force of 10 kOe or more and having a composition on the transition metal side of a compensating composition, on a substrate,
In contact with this, a second magnetic layer made of a rare earth-transition metal amorphous alloy having a coercive force at room temperature lower than that of the first magnetic layer and a Curie temperature higher than that of the first magnetic layer is provided. A magneto-optical recording medium characterized by the above. 2. The magneto-optical recording according to claim 1, wherein the magnetization direction of the second magnetic layer is perpendicular to the film surface and is constant in all processes of recording, reproducing and erasing. Medium. 3. The magneto-optical recording medium according to claim 2, wherein the magnetization direction of the second magnetic layer is the same as the magnetization direction of the recording mark of the first magnetic layer. 4. The magneto-optical recording medium according to claim 1, wherein the first magnetic layer is located closer to the substrate than the second magnetic layer is.