JPS63146256A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To increase the recording capacity per sheet of disk by increasing continuously the (y) value of a magnetic film having a composition of Rex(M1-yCoy)1-x formed on a substrate toward the inner circumferential part from the outer circumferential part of the disk to continuously increase the Curie temperature and reducing the shortest recording bit length. CONSTITUTION:A magneto-optical disk contains a composition where the (y) value of a magnetic thin film 13 formed on a substrate having a constitution Rex(M1-yCoy)1-x changes continuously up to 0.01 from 0.25 toward the outer circumferential part from the inner circumferential part within an area used for recording/reproducing jobs. Here Re shows a rare earth metal group with M showing an element of a transition metal group. In other words, the Curie temperature is increased owing to a fact that the (y) value is increases as the film 13 moves toward the inner circumferential part from the counter circumferential part of the disk. Thus the increase of temperature is suppressed at the inner circumferential part in a reproduction mode. As a result, the signals can be reproduced with large reproduction power and the maximum limit of the signal output is obtained to give the design limit of a device.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magneto-optical disk used for recording information and characterized by a thin film structure.

BACKGROUND OF THE INVENTION In recent years, as the information society has progressed, there has been a strong desire to put rewritable large-capacity magneto-optical disks into practical use. Among these, magneto-optical memory, which has attracted particular attention, has recently been confirmed to have excellent characteristics as a digital memory.

By the way, due to constraints such as the Curie temperature, which is the main factor that determines the recording sensitivity, the Kerr rotation angle, which determines the quality of the reproduced signal, and film fabrication at low temperatures, magneto-optical thin film materials are made of rare earth transition metal amorphous magnetic materials. The body is used. This rare earth transition metal includes one or more of Fe, Co, and Ni, as well as Gd and Tb.
, D7, and an alloy of one or more rare earth elements.

Specifically, TbFe, GdTbFe, TbFeCo
etc.

However, these magnetic thin films have a larger Kerr rotation angle than other magnetic materials, but the angle is 0.3 to 0.
6 degrees, and a sufficient signal-to-noise ratio cannot be obtained. Specifically, when a magneto-optical disk is used as a digital memory, a problem arises (in other words, if the bit length is sufficiently larger than the optical beam spot diameter used for recording and reproduction, a sufficient signal-to-noise ratio is not achieved). On the other hand, when the recorded bit length becomes approximately the same as the optical beam spot diameter, the signal-to-noise ratio deteriorates rapidly. Therefore, since the signal-to-noise ratio limits high-density recording, it is necessary to obtain an even larger signal-to-noise ratio in order to improve the recording density.

In order to eliminate such drawbacks, in the structure of magneto-optical disks, K Sin,
ZnS, Si3N4. AIN! V) A method using a thin film with a high refractive index has been proposed. This uses multiple reflections caused by a dielectric thin film to increase the Kerr rotation angle. Therefore, the thickness of the dielectric thin film is set to λ/4n, where its refractive index is n1 and the laser wavelength used for recording and reproduction is λ.

However, the structure using these dielectric thin films causes a decrease in light emissivity and an increase in light energy absorption rate.

Therefore, although an improvement in recording sensitivity can be expected, similar energy absorption occurs during reproduction as well. However, since the Kerr rotation angle of magnetic thin films deteriorates due to high temperatures, it is necessary to reduce the light intensity during reproduction.

When the laser input power during reproduction is Io, the reflectance of the magneto-optical disk is R1, and the Kerr rotation angle is θ, the signal-to-noise ratio S/N for shot noise is S/N +x: σ cosin 2θk... ...(1
). In the magneto-optical disk structured using the dielectric thin film described above, as the Kerr rotation angle θ increases, ! . ,
This resulted in a decrease in H and no significant S/N improvement was obtained.

Problems to be Solved by the Invention In magneto-optical disks, the limit of high-density recording is determined by the signal-to-noise ratio as described above. Therefore, it has been easily considered that by reducing the amount of optical energy absorption, the light intensity during reproduction can be increased and a large signal-to-noise ratio can be obtained (for example, Japanese Patent Laid-Open No. 74844/1983).

By the way, there are two types of disk rotation methods: an angular velocity-based method and a linear velocity-based method. Generally, disk drives for data files use an angular velocity construction method due to the need for high-speed access. Therefore, when the amount of optical energy absorption is reduced in order to obtain a large signal-to-noise ratio, the recording sensitivity also decreases, causing the following problems. In other words, in the angular velocity-based method, a high-power laser is required for recording at the outer periphery of the disk where the linear velocity is high. However, it is essential to use a semiconductor laser in terms of the device size and cost of the drive, and as a result, the number of rotations of the disk is severely restricted, resulting in the problem that the necessary data transfer rate cannot be obtained.

Means for Solving the Problem In order to solve this problem, the magneto-optical disk of the present invention is provided with Re! (Ml-aCoa),-! The value of y in the above equation ranges from 0.26 to 0.01 as the magnetic thin film formed on the substrate has the structure shown in FIG. It has a composition that changes continuously.

Function Generally speaking, in magneto-optical disks, as the recording bit length becomes shorter, the reproduced signal becomes smaller. When recording is performed while rotating the disk at a constant angular velocity, the recording bit length becomes shorter at the inner periphery and longer at the outer periphery. The shortest recording bit length is determined because a sufficient signal-to-noise ratio can be obtained when the shortest pulse width is recorded at the innermost circumference.

On the other hand, since the medium movement speed increases at the outer periphery, it is necessary to increase the optical input power during recording and erasing. In other words, the number of rotations of the disk is determined based on the recording sensitivity constraint that sufficient recording can be performed with the maximum input power that can be used with a semiconductor laser.

Therefore, at the inner circumference of the disk, the magnitude of the signal output limits the device design, and at the outer circumference of the disk, the recording sensitivity limits the device design.

The present invention relates to Re engineering (Ml-A Coa), -! By increasing the value of y (increasing the amount of Co) as the magnetic film, expressed by It is possible to suppress the rise in the signal output, enable signal reproduction with large reproduction power, and obtain the maximum signal output that limits device design. Furthermore, since the Curie temperature is lower in the outer circumference, recording sensitivity is improved and high speed rotation of the disk can be maintained. As a result, compared to conventional magneto-optical disks, the recording density and recording capacity can be increased without causing a decrease in data transfer speed.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a magneto-optical disk in one embodiment of the present invention. In FIG. 1, 11 is a substrate made of plastic, glass, or metal, 12.14 is a protective film made of SiOx or MqO, 13 is TbO, 21 (Fe1-y"y"
) 0.79.

FIG. 2 shows the T of the magneto-optical disk in one embodiment of the present invention.
FIG. 3 is a diagram showing the relationship between the Curie temperature and the Co concentration in the radial direction of a magnetic film having a composition of bO,21(C'yFe1-y)0.79. It can be seen from FIG. 2 that the Curie temperature changes when the amount of Co 2 is changed. Therefore, by changing the amount of Co and continuously changing the Curie temperature from 160 degrees to 230 degrees as shown in Figure 2 within the range used for recording and reproduction, it is possible to change heat conduction continuously. .

Next, a method for manufacturing the magneto-optical disk of this example will be described. FIG. 3 shows the configuration of a magnetic film manufacturing apparatus. In FIG. 3, 31 is a substrate holder, 32 is a substrate made of plastic or glass, and 33 is Tb0.21.
``The evaporation source that evaporates 0.79, 24 is a Co chip.

A magnetic film having a varying Co concentration as shown in FIG. 2 is formed using an evaporation apparatus equipped with an electron beam evaporation source shown in FIG.

After first evacuation to 2X10-' Torr,
- Substrate 32 with a diameter of 130m + 11φ attached to the da 31
The position from the evaporation source 33 can be adjusted while rotating at 60 rpm. A magnetic film having the composition distribution shown in FIG. 2 can be obtained using a film forming apparatus having these configurations.

First, the protective film 12 is formed on the substrate 11 by vapor deposition or sputtering, then the magnetic film 13 is formed in 1000 times by the method described above, and the protective film 14 is formed by the same method as the protective film 12.

Next, FIG. 4 shows the recording and reproducing characteristics of the magneto-optical disk having the magnetic film of this example.

FIG. 4a shows a characteristic diagram of this embodiment, and FIG. 4a shows a characteristic diagram of a conventional configuration. Recording was performed by recording a 4.5 MHz signal while rotating the disk at 3000 rpm.

Therefore, the recording domain length is 1.0μ at the innermost periphery than the conventional one.
The outermost circumference of 0.8 μm, which is shorter than m, is 2.0 μm.

In the conventional structure, the signal-to-noise ratio (C/N) at the innermost circumference is 50.
．． However, in this example, the signal-to-noise ratio (C/N) s2. odB
can be obtained. In FIG. 4, the solid line A indicates the recording laser power, and the dotted line B indicates the signal-to-noise ratio.

Effects of the Invention The present invention provides Re, (Co-a) formed on a substrate.
By continuously increasing the value of y of the magnetic film having a composition of , -8 from the outer circumference toward the inner circumference, the Curie temperature is continuously increased, thereby reducing the recording sensitivity in the outer circumference. The signal-to-noise ratio of the inner circumferential portion is improved without causing a problem, and as a result, the minimum recording bit length can be shortened, and the recording capacity per disc can be increased.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view showing the configuration of a magneto-optical disk in an embodiment of the present invention, and FIG. 2 shows the Co concentration and
A characteristic diagram showing the relationship between IJ and temperature; FIG. 3 is a schematic side view showing the configuration of a magnetic film manufacturing apparatus for realizing the magneto-optical disk of the present invention; and FIG. 4 is a recording diagram in one embodiment of the present invention. FIG. 3 is a reproduction characteristic diagram. 11...Substrate, 12.14...Protective film, 13...Magnetic film, 31...Substrate holder, 32...Substrate, 33...TbFe
Evaporation source, 34...Co chip. Name of agent: Patent attorney Toshio Nakao, 1 person//--
-Basic version 13- Sho 1 Biomembrane Figure 1 Figure 2 0.1 ? 7.2 633
06 θ (Ritan board central force, R'J1 34--Co chip, 33-Tb 7"a vaporized R'J1 34-- Co chip, Qi) (b) Distance battle between circular center D and others

Claims (2)

[Claims] (1) A magnetic thin film laminated on a disk-shaped substrate rotated at a constant angular velocity is
．． 15<x<0.28, 0.01<y<0.25) (wherein Re is at least one element from the rare earth metal group, M
represents at least one element of the transition metal group), and the value of y decreases from the inner circumference to the outer circumference at least within the area used for recording and reproduction. magneto-optical disk. (2) The magneto-optical disk according to claim 1, wherein Re is Tb and M is Fe (0.17<x<0.26, 0.05<y<0.2).