JPH02308448A - magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a large magneto-optical effect and a high recording sensitivity by successively laminating a recording layer, rare earth-iron transition metal thin film, iron transition metal thin film, and rare earth-iron transition metal thin film. CONSTITUTION:This recording medium has the rare earth-iron transition metal thin film 102 of 10 to 40nm thickness, the iron transition metal thin film 103 of 5 to 20nm thickness and the rare earth-iron transition metal thin film 104 of 10 to 40nm thickness successively formed on a transparent substrate 101. The films 102 and 104 are such ferrimagnetic films which are perpendicularly magnetized films when the films exist respectively independently. The film 103 is an intra-surface magnetized film as the simple layer. If the magneto- optical recording medium having the large film thickness of the film 103 is placed in the uniform magnetic field in the direction perpendicular to the film plane, the extremely thin parts in contact with the films 102, 104 are imparted with perpendicular magnetization by an exchange power and form intra-surface magnetized films as further from the films 102, 103. The uniformly perpendicularly magnetized film is obtd. by forming the film 103 thin.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magneto-optical recording medium in magneto-optical recording that records, reproduces and erases information using focused light such as a laser beam. This relates to the recording layer.

[Prior art] Magneto-optical recording is a recording medium in which a recording layer made of a perpendicularly magnetized film is formed on a transparent substrate such as glass or plastic, and is irradiated with focused light such as a laser beam to locally change the temperature of the recording layer. By applying a magnetic field at the same time as the magnetic field rises, perpendicular magnetic domains corresponding to the information are formed in the recording layer and information is recorded.In order to reproduce the information, the recording medium is irradiated with focused light such as linearly polarized laser light. , the reflected light or transmitted light from the medium is optically detected using a magneto-optical effect via an analyzer.

Conventionally, the recording layer of a magneto-optical recording medium used for such magneto-optical recording is TbFe5GdCo or DyFe.

GdTbFe, GdTbFeCo, NdTbF
A recording layer made of a single layer of rare earth-iron alloy thin film such as eCo5NdDyFeCo has been proposed and widely used.

[Problems to be Solved by the Invention] However, a magneto-optical recording medium having a single layer of rare earth-iron alloy thin film as a recording layer has the following drawbacks. That is, since the magneto-optical effect used for reproducing information increases in proportion to the Curie temperature of the recording layer, it is necessary to use a recording layer with a high Curie mixed carbon in order to improve the quality of the reproduced signal. However, in this case, since a high-output laser is required to record information, there is a practical limit due to problems such as the lifespan of the laser element.

In order to improve this point, as described in JP-A-57-78652, a recording layer with a low K-temperature and high coercive force and a reproducing layer with a high K-temperature and low coercive force were laminated. Magneto-optical recording media having a recording layer have been proposed. However, since the recording and reproducing characteristics of a recording medium not only change sensitively depending on the composition of each layer, but also sensitively affect the bonding state between each layer, it is difficult to mass produce recording media with stable characteristics. It is said that this is difficult.

The present invention is intended to solve the above-mentioned problems, and its purpose is to provide a magneto-optical recording medium that has a large magneto-optic effect, high recording sensitivity, and excellent productivity.

[Means for Solving the Problems] The magneto-optical recording medium of the present invention has a recording layer made of at least a ferromagnetic material on a transparent substrate, in which the recording layer has a thickness of 10 to 40 nm. It is characterized by sequentially laminating an iron group transition metal alloy thin film, an iron group transition metal thin film with a film thickness of 5 to 20 nm, and a rare earth-iron group transition metal alloy thin film with a film thickness of 10 to 40 nm.

[Operation] In magneto-optical recording, as described above, information is recorded in the recording layer as a perpendicular magnetic domain pattern. Therefore, the recording layer is required to be a perpendicularly magnetized film. On the other hand, Fe, Co, Fe
Although iron group transition metals such as Co have a large magneto-optical effect, they have not been used in magneto-optical recording media because a perpendicularly magnetized film cannot be obtained. However, as a result of our intensive efforts, it has become clear that iron-group transition metal thin films sandwiched between thin films with large perpendicular magnetic anisotropy form magnetic domains in the direction perpendicular to the film surface within a certain appropriate film thickness range. This made it possible to apply it to magneto-optical recording media. Details will be explained below.

FIG. 1 is a diagram showing the structure of a magneto-optical recording medium according to the present invention. In the figure, a rare earth-iron group transition metal thin film 102, an iron group transition metal thin film 103,
It consists of a rare earth-iron group transition metal thin film 104. Here, the rare earth-iron group transition metal thin films 102 and 104 are ferrimagnetic films that are perpendicularly magnetized films when each exists alone, and the iron group transition metal thin film 103 is an in-plane magnetized film when it is a single layer. be. Now, with this configuration, iron group transition metal thin film 1
When a magneto-optical recording medium with a thick film thickness of No. 03 is placed in a uniform magnetic field in a direction perpendicular to the film surface, it becomes magnetized as shown in FIG. 2(a). That is, the rare earth-iron group transition metal thin film 102.
A very thin portion in contact with 104 has perpendicular magnetization due to the exchange force, but as it moves away from 102 and 103, it becomes an in-plane magnetized film. ``However, the iron group transition metal thin film 103
By making it thinner, a uniform perpendicular magnetization film can be obtained as shown in FIG. 2(b). Here, for example, the rare earth-transition metal thin film 102.104 is TbFe%T b
F e Co, G d F es G d F e
Co, DyFe, DyFeCo, G d T b F
eSG d T bFeCo, TbDyFeCo, Nd
TbFeCo, NdTbFeCo% PrTbFeCo
, PrDyFeCo, TbFeCoCr, etc. can be used, and as the iron group transition metal thin film 103, Fe, Co, Ni%FeCo,
A thin film such as CoNi5 CoN1cr can be used.

The process of recording information using a magneto-optical recording medium having the above-described structure will now be described with reference to FIG. When a recording medium that is uniformly magnetized perpendicular to the film surface (Figure 3 (a)) is irradiated with focused light while applying an external magnetic field in the opposite direction to the magnetization direction, the result shown in Figure 3 (b) is irradiated with focused light. As shown, only a limited region of the rare earth-iron group transition metal thin film 102, 104 is heated to near the Curie temperature, and the magnetization disappears. At this time, the iron group transition metal thin film 103 is similarly heated, but the heated portion has in-plane magnetization because the Curie temperature is high.

Next, when the magnetic field is applied and it is cooled, as the temperature of the part that has reached the Curie temperature decreases, oppositely oriented magnetic domains are formed in the rare earth-iron group transition metal thin film 102 and 104 due to the external magnetic field, and at the same time Perpendicular magnetic domains are also formed in the group transition metal thin film 103 due to the exchange force (Fig. 3(C)).
. In this way, since recording is performed by magnetization reversal of the rare earth-iron group transition metal thin film, a highly sensitive magneto-optical recording medium can be created by using a rare earth-iron group transition metal thin film with a low Curie temperature. .

On the other hand, when reproducing information, the component of the magneto-optical effect of the iron group transition metal thin film 103 is also superimposed on the reproduced signal, so that a reproduced signal of good quality as a whole can be obtained. In addition, even if relatively high-output reproduction light is used, the temperature change in the magneto-optic effect of the iron group transition metal thin film 103 is small, so the decrease in the magneto-optic effect can be reduced, and combined with the increase in the amount of signal light, the S/N can be obtained.

Furthermore, the magnetic properties of iron-group transition metal thin films do not change rapidly with changes in composition, and in addition, they are less susceptible to corrosion than those containing rare-earth elements. The magnetic coupling state with the transition metal thin film is extremely stable and has excellent reproducibility.

[Example] Hereinafter, the present invention will be specifically explained based on Examples.

A magneto-optical recording medium constructed as shown in FIG. 4 was exploded.

That is, the substrate 401 has a diameter of 130 mm and a f of 91.2 mm.
Using polycarbonate with pregroups of 1.6 μm pitch, an 80 nm thick S+3N4 film was formed as an undercoat layer 402 on the group surface, and then a first rare earth-iron group transition metal thin film 403 was formed. d7. OD y
22. OF e 59. OCo 100 (at%) film, Fe70Co30 film as iron group transition metal thin film 404,
As the second rare earth-iron group transition metal thin film 405, T N d
7. OD y 22. OF e 59. OCo 10
．． A SI3N4 film with a thickness of 3.0 nm was laminated as a protective layer 406, and an AI film with a thickness of 30 nm was further laminated as a reflective layer 407. Next, add this to a diameter of 130m.
A magneto-optical recording medium was prepared by bonding a polycarbonate substrate 409 with a flat polycarbonate substrate 409 with a thermosetting resin adhesive layer 408 interposed therebetween. Note that the rare earth-iron group transition metal thin film 402.
403 all exhibited magnetic properties dominated by iron group transition metals at room temperature, and the Curie temperature was 130"C. Here, the film thickness d1 of the first rare earth-iron group transition metal thin film 403
, the film thickness d2 of the iron group transition metal thin film 404 and the film thickness d3 of the second rare earth-iron group transition metal thin film 405 were taken as parameters.

First, when the values of dl and d3 are fixed at 20 layers m,
Kerr history curves were compared by changing dl. Figure 5 shows the Kerr hysteresis curve when dl is 30 layers m, and the Kerr rotation angle (
The value of the ratio (squareness ratio) of the residual Kerr rotation angle) to the saturated Kerr rotation angle is as small as 0°5, which is not preferable as a magneto-optical recording medium. FIG. 6 shows the film thickness d2 of the iron group transition metal thin film 404.
It shows the changes in the saturated Kerr rotation angle (relative value) and squareness ratio. The saturated Kerr rotation angle increases as dl increases. However, the squareness ratio is 1 when dl is thinner than 10 layers m, which is preferable for a magneto-optical recording medium, but dl
It can be seen that when the film thickness becomes thicker than 10 m, the squareness ratio decreases as the film thickness increases. Like this 61 = 63
= 20 nm, dl is preferably 10 layers m or less.

Next, when di and d3 were changed, the maximum value of dl that would yield the squareness ratio l was investigated. FIG. 7 shows the results, where the horizontal axis shows the values of dl and d3, and the vertical axis shows the maximum value of dl at which a squareness ratio of 1 can be obtained. From the figure, it can be seen that as dl and d3 become thicker, dl can become thicker, and its value is di
= 63 = 10 layers m, dl = 5 nm, di = 6
When 3 = 20 nm, d2 = 20 nm. However, it can be understood from the figure that if dl exceeds 20 layers m, the squareness ratio cannot be made 1 no matter how thick di and d3 are made. In this way, when the total thickness of the three layers exceeds 60 nm, the contribution of the iron group transition metal thin film to the Kerr effect becomes relatively small, so in the present invention, the total thickness of the three layers is 60 nm.
It can be seen that the effect can be greatly exhibited when the thickness is 0 nm or less.

In Fig. 4, dl, d2, and d3 are each 25 nm,
Magneto-optical recording media with thicknesses of 10 nm and 25 nm were produced as an example of the present invention. Here, the configurations of the other media are the same as described above. At the same time, as a conventional example for comparison, in FIG. 4, the iron group transition metal thin film 404 and the second rare earth-iron group transition metal thin film 405 are not present, and the first rare earth-iron group transition metal thin film 403 is used for magneto-optical recording with a thickness of 60 nm. I also created the media. When the measurement wavelength of each medium is 780 nm, the Kerr rotation angle is 1. They were 0 degrees and 0.87 degrees.

Using these media, the recording and reproducing characteristics at a radial position of 57 mm were investigated. The medium rotation speed was 1800 revolutions per minute, the recording frequency was 3.7 MHz, and the recording bias magnetic field was 2000e. According to this, the magneto-optical recording medium of the embodiment of the present invention has a carrier-to-noise ratio (CNR) of a reproduced signal of 56.2 d.
B. The optimum recording power was 4.5 mW, whereas the medium of the comparative example had a CNR of 54.2 dB and an optimum recording power of 6°2 mW, both recording sensitivity and reproduction signal quality compared to the example of the present invention. You can see that it is inferior.

[Effects of the Invention] As described above, the present invention has the effect that a magneto-optical recording medium having a large magneto-optic effect can be provided with high productivity without impairing the sensitivity of the recording medium.

Note that this effect is not limited to the medium configuration described in the examples, but can be obtained by, for example, the composition system and composition of the recording layer, the material of the dielectric layer, the undercoat layer, the protective layer, or the type and presence or absence of the metal layer. It goes without saying that even if the above parameters are changed, the above-mentioned effect can essentially be obtained.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are diagrams showing the configuration of a magneto-optical recording medium according to the present invention. 101...Transparent substrate 102.104...Rare earth-iron group transition metal thin film 103...iron group transition metal thin film FIG. 3 is a diagram for explaining the recording process of the magneto-optical recording medium according to the present invention. FIG. 4 is a configuration diagram of a magneto-optical recording medium. 401...Substrate 402...Undercoat layer 403...First rare earth-iron group transition metal thin film 404.
...Iron group transition metal thin film 405...Second rare earth-iron group transition metal thin film 406.
...Protective layer 407...Reflection layer 408...Adhesive layer 409...Polycarbonate substrate FIG. 5 is a diagram showing the Kerr history curve of the magneto-optical recording medium according to the present invention. FIG. 6 is a diagram showing changes in the saturation Kerr rotation angle and squareness ratio with respect to the film thickness d2 of an iron group transition metal thin film. FIG. 7 is a diagram showing the maximum squareness ratio l of 62 with respect to the film thicknesses d1 and d3 of a rare earth-iron group transition metal thin film. that's all

Claims (1)

[Claims] In a magneto-optical recording medium having at least a recording layer made of a ferromagnetic material on a transparent substrate, the recording layer has a film thickness of 10 to 40 mm.
Rare earth-iron group transition metal alloy thin film with film thickness of 5 to 20 nm
1. A magneto-optical recording medium comprising a thin film of an iron group transition metal with a thickness of 10 to 40 nm and a thin film of a rare earth-iron transition metal alloy with a thickness of 10 to 40 nm.