JP2613885B2 - Magneto-optical multilayer media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a perpendicular magnetic film used for a magneto-optical memory, a magnetic recording element, and the like, and particularly to a light having a large magneto-optical effect suitable for improving a reproduction output. The present invention relates to a magnetic multilayer medium.

[Conventional technology]

As a recording film for obtaining high reproduction output in magneto-optical recording,
For example, JP 57-78652, JP 59-168954, as described in JP-A-60-177455, a perpendicular magnetization film having a high coercive force H _C and lower Kiyuri temperature T _C, low A two-layer film in which a magnetic film having a coercive force H _C and a high Curie temperature T _C is laminated has been proposed, and an attempt has been made to obtain a perpendicular magnetization film having a high Kerr rotation angle θ _K by coupling the layers by magnetic interaction. I have.

[Problems to be solved by the invention]

In the above-mentioned conventional two-layer film recording medium, no consideration is given to the film thickness ratio of two films suitable as a magneto-optical recording film, and therefore, the recording sensitivity is higher than that of a conventional single-layer film medium of, for example, TbFeCo. And practical advantages in terms of reproduction output and the like have not been obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magneto-optical multilayer film medium having a high recording sensitivity and a high reproduction output.

[Means for solving the problem]

The above objects are achieved by a two-layer film of the above, the high H _C with respect to the film thickness of the first film having a low HT _C, the thickness of the second film having a low H _C High T _C ratio, i.e. the thickness ratio Is set to 0.01 or more and 0.3 or less, the second recording film is arranged on the side where the reproduction light is incident, and the polarities of the car hysteresis of the two films are made the same.

The film temperature of the first film is from 100 ° C. to 200 ° C. and / or from the viewpoint of recording sensitivity.
Alternatively, the compensation temperature is desirably 0 ° C. or more and 150 ° C. or less, and the coercive force is desirably greater than 1 kOe from the viewpoint of stably obtaining high-density fine bits.

As for the film characteristics of the second film, θ at high temperature
From the standpoint of preventing _K from deteriorating, its Kyrie temperature is 20
The temperature is desirably 0 ° C or higher, and more desirably 300 ° C or higher. The coercive force is desirably 1 kOe or less.

[Action]

FIG. 2 shows the Kerr rotation angle θ _K (No. 6 in the figure) and the coercive force ratio H of the two-layer recording film, with the film thickness ratio on the horizontal axis.
_It shows an example of the change (No. 7 in the figure) of _C (2) / H _C (1). Here coercivity ratio _{H C (2) / H C} (1) , the first coercive force H _C of the second recording film portion relative to the coercive force H _C (1) of the recording film portion constituting the two-layer film H _C represents the ratio of (2)
(2) / H _C (1) = 1 indicates that the two recording films are magnetically coupled by the exchange interaction, and the two films have the same coercive force.

As is clear from FIG. 2, the Kerr rotation angle of the two-layer film is
The film thickness ratio sharply increases from around 0.01, shows a high value with a gradual change to around 0.3, and sharply decreases above that.
When the thickness ratio is 0.3 or less, H _C (2) / H _C (1) =
1, which indicates that the two films are magnetically coupled by the exchange interaction.

FIG. 3 shows the car hysteresis when two recording films having different car hysteresis polarities are laminated (a) and when two recording films having the same car hysteresis polarity are laminated (b). It is. (A),
(B) In each case, the left column shows the Kerr hysteresis of the second recording film, the middle column shows the Kerr hysteresis of the first recording film, and the right column shows the Kerr hysteresis of the entire two-layer film. It has a form in which the car hysteresis of the first recording film and the second recording film is synthesized.

As is apparent from FIG. 3, even if two recording films having different Kerr hysteresis polarities are stacked, (a) complicated Kerr hysteresis as shown in the right column is obtained, and the Kerr rotation angle does not increase. On the other hand, when two recording films having the same Kerr hysteresis polarity are stacked, (b) a two-layer film having a square shape and a large Kerr rotation angle as shown in the right column is obtained.

FIGS. 2 and 3 show the film thickness of the first recording film.
A film of Tb ₂₂ Fe ₇₈ of 2000 Å was used, and Gd ₂₃ was used as a second recording film.
This is an example when a film of Tb ₅ Fe ₃₅ Co ₃₇ is used. However, even when other rare earth-iron group amorphous films and oxide films such as ferrite and garnet are selected, the absolute value of the Kerr rotation angle is different, but there is no difference in the above operation. . That is, H _C (2) / H _C (1) = 1 when the film thickness ratio is 0.3 or less, and a high θ _K is obtained when the film thickness ratio is 0.01 or more and 0.3 or less. The same can be said for the third Kerr hysteresis polarity for the other films.

〔Example〕

 Hereinafter, the present invention will be described with reference to examples.

FIG. 1 is a sectional view of a disk medium using a two-layer film of the present invention. The substrate 3 has a diameter of 130 mm and a distance between grooves of 0.6 μm.
An m-grooved polycarbonate disk was used. Using a magnetron sputter device, under an Ar pressure of 5 × 10 ⁻³ Torr and an applied high-frequency power of 1 kW, a Si ₃ N ₄ film 4 (thickness 800 mm) and a Gd ₁₅ Tb ₃ Fe ₄₁ Co as a second recording film ₄₁ film 2 (thickness 100
Å), Tb ₂₃ Fe ₇₇ film 1 as a first recording film (thickness 200
Ii), and each film was formed in the order of Si ₃ N ₄ film 5 (thickness: 1000 Å). Of the produced disc, the Kerr rotation angle theta _K is 0.8 ° as measured from the substrate side, the coercivity H _C was found to be 3 kOe.

Recording and reproduction dynamic characteristics were evaluated using a semiconductor laser beam, with a writing laser beam power of 7 mW, a reading laser beam power of 3 mW,
The recording was performed under the conditions of an external magnetic field of 300 Oe and a disk rotation speed of 2400 rpm. Carrier-to-noise ratio C / N of the reproduced output at this time
In the measurement, a high reproduction output of 60 dB was obtained at a measurement frequency of 1.77 Hz, a bandwidth Δf = 30 kHz, and a bit pitch of 1 μm.

In the present embodiment, only the rare earth-iron group amorphous film of GdTbFeCo / TbFe was used as the recording film.
In Sb / TbFe, a perpendicular magnetization film with θ _K = 1 ゜ is used, and GdFeCo / Co
In the case of -ferrite, Bu-ferrite or garnet film, a perpendicular magnetization film having θ _K = 0.7 ° was obtained, and a high reproduction output of 60 dB or more was obtained in the reproduction output.

〔The invention's effect〕

According to the present invention, it is possible to obtain a multilayer recording medium having a higher recording sensitivity and a higher reproduction output than a conventional multilayer recording medium having two recording layers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a disk medium in one embodiment of the present invention, and FIG. 2 is a Kerr rotation angle θ _K and a coercive force ratio with respect to a film thickness ratio.
FIG. 3 shows an example of a change in H _C (2) / H _C (1), and FIG. 3 shows a case where the car hysteresis polarity is different for the entire two-layer recording film and the car hysteresis of each of the two films constituting the recording film. It is the figure which showed the case (b) which is the same as. 1 ...... first recording film, 2 ...... second recording layer, 3 ...... polycarbonate substrate, 4, 5 ...... Si ₃ N ₄ film, a change in theta _K for 6 ...... thickness ratio, 7 ...... Coercive force ratio H to film thickness ratio
Change in _C (2) / H _C (1).

Claims (4)

(57) [Claims] 1. A recording medium having at least a first recording film having a low Curie temperature and a high coercive force and a second recording film having a high Curie temperature and a low coercive force. Where the ratio of the thickness of the second recording film to the thickness of the first recording film is 0.01 or more and 0.3 or less, and the Kerr hysteresis of the first and second recording films is A magneto-optical multilayer film medium having the same polarity. 2. The magneto-optical multi-layered medium according to claim 1, wherein said second recording film has a Kerr rotation angle larger than that of said first recording film. 3. The method according to claim 1, wherein the first recording film has a Curie temperature of 100 ° C.
Not less than 200 ° C and / or compensation temperature is 0 ° C or more and 150 ° C
3. A magneto-optical multi-layered medium according to claim 1, wherein the coercive force is larger than 1 kOe. 4. The method according to claim 1, wherein the second recording film has a Curie temperature of 200 ° C.
4. The magneto-optical multilayer medium according to claim 1, wherein the coercive force is 1 kOe or less.