JP3328989B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable magneto-optical recording medium, and more particularly to a magneto-optical recording medium for reading a recording signal while changing a magnetization state of a reproducing layer.

[0002]

2. Description of the Related Art A magneto-optical recording medium is a rewritable optical recording medium, and has excellent repeated erasing / writing durability and erasing ratio as compared with a phase change type optical recording medium and the like, and is a portable large-capacity recording medium. Attention has been paid.

The magneto-optical recording medium employs a recording / reproducing method in which recording bits are formed by local heating by laser light irradiation, and the recording bits are read out by the Kerr effect. The interval between recording bits can be made much smaller than the laser spot diameter by adjusting the laser light irradiation power, the intensity of the recording magnetic field, etc., but the reading is performed at the laser wavelength at the time of reproduction. And the numerical aperture of the lens. That is, the laser wavelength λ of the reproducing optical system and the numerical aperture N.P. A. Is determined, the bit period f (= λ / 2 · N.
A. ) Is decided.

Therefore, in order to increase the density of an optical disc, the basic idea is to shorten the laser wavelength of the reproducing optical system or increase the numerical aperture of the objective lens. However, with the current technology, there is a limit to the improvement of the laser wavelength and the numerical aperture of the objective lens. Therefore, a technology for improving the recording density by another method has been developed.

As one of the methods for such high density, for example, Japanese Patent Application Laid-Open No. 1-143041,
Japanese Patent Publication No. 143042 proposes a system (MSR disk) in which information bits (magnetic domains) are partially enlarged, reduced, or eliminated during reproduction to improve reproduction resolution. In this method, the recording magnetic layer is an exchange-coupling multilayer film composed of a reproducing layer, an intermediate layer, and a recording layer, and the magnetic domain of the reproducing layer heated by the reproducing light beam at the time of reproduction is enlarged, reduced, or expanded at a high temperature portion. By erasing, interference between information bits during reproduction is reduced, and a signal having a period equal to or longer than the diffraction limit of light can be reproduced.

[0006]

The MSR disk is
As described above, the magnetic domain of the reproducing layer heated by the reproducing light beam at the time of reproducing is enlarged, reduced or erased at a high temperature portion to apply an optical mask in the beam spot to narrow the detection area. The spatial resolution is improved and the recording density is increased.

[0007] The MSR disk is a FAD (Front A).
Percentage Detection) and RAD
(Rear Aperture Detection)
The method is roughly divided into two types. In the FAD system, a heated portion in the beam spot is demagnetized in the direction of the reproducing magnetic field to act as an optical mask. On the other hand, in the RAD method, the reproducing layer is DC-demagnetized by the initialization magnet in advance, and only the heated portion in the beam spot is set as the detection area.

In both types, in the detection area within the beam spot, the recording magnetic domain of the recording layer is transferred to the reproducing layer by the exchange coupling force through the intermediate layer and the information is read.

The intermediate layer controls the exchange coupling force between the reproducing layer and the recording layer, or cuts off the exchange force between the reproducing layer and the recording layer at a temperature higher than the Curie temperature of the intermediate layer to mask the reproducing layer. It plays a role in generating.

The Curie temperature of the intermediate layer is, for example, as disclosed in
Japanese Patent No. 229432 discloses that the temperature is preferably 60 ° C. or more and 200 ° C. or less. However, according to experiments performed by the present inventors, as the Curie temperature of the intermediate layer was lowered, the C / N ratio gradually decreased.
And the C / N suddenly dropped at a certain point. If the Curie temperature of the intermediate layer is increased in order to improve C / N, the reproduction power for causing MSR is increased, and the margin of the reproduction power becomes narrow, which is not practical.

As the Curie temperature of the intermediate layer decreases, C
The reason for the decrease in / N is that the exchange coupling between the reproducing layer and the recording holding layer is weakened as the Curie temperature is lowered, and that the difference between the so-called mask area and the environmental temperature is reduced, and the influence of thermal fluctuations. And the like.

The present inventors strengthen the exchange coupling between the reproducing layer and the recording holding layer by means for improving the perpendicular magnetic anisotropy of the magnetic layer by etching the underlying layer before forming the reproducing layer. It was found that, although the exchange coupling was strengthened, good transfer from the recording holding layer to the reproducing layer after passing through the mask area was not performed, and C / N deteriorated.

An object of the present invention is to make it possible to obtain a high-resolution MSR medium with high productivity by finding a structure that enhances the transferability from the recording holding layer to the reproducing layer as compared with the related art. .

[0014]

Means for Solving the Problems In view of the above-mentioned situation, the present inventors have made intensive studies, and as a result, before forming a reproducing layer (substrate side), recording was performed by adding an in-plane magnetized film. The present inventors have found that the recording magnetic domain is transferred from the layer to the reproducing layer stably with good reproducibility, and that the allowable amount of the Curie temperature of the intermediate layer is widened. Thus, the present invention has been completed.

That is, the present invention provides a first magnetic film, a second magnetic film, and a third magnetic film magnetically coupled to each other on a transparent substrate.
When the Curie temperatures of the first, second, and third magnetic films are Tc1, Tc2, and Tc3, respectively, Tc3, Tc1>Tc2> room temperature, and the first magnetic layer The present invention relates to a magneto-optical recording medium capable of reproducing while deforming magnetic domains, wherein an in-plane magnetized film is added before forming a first magnetic film.

Hereinafter, the present invention will be described in detail.

The magnetic layer of the magneto-optical recording medium of the present invention has a multilayer structure as shown in FIG. 1, for example. The first magnetic film, the second magnetic film, and the third magnetic film are magnetically coupled to each other, and their respective Curie temperatures are set to Tc1 and Tc2.
And Tc3, Tc1, Tc2> Tc3. The first and third magnetic films are perpendicular magnetic films, and an in-plane magnetic film is added before forming the first magnetic film (on the substrate side).

The first magnetic film has a large coercive force at room temperature,
Any perpendicular magnetization film having a small coercive force at Tc2 may be used. For example, GdFeCo, GdTbFeCo, Gd
dDyFeCo and the like. If necessary, a material to which Cr, Ti, Ta or the like is added to increase the corrosion resistance or Nd or the like is added to correspond to a short wavelength laser can be used.

The method of adding the in-plane magnetized film may be any method. For example, the in-plane magnetized film is formed by changing the ratio of the rare earth element at the initial stage of the growth of the first magnetic film, A gas can be mixed into a sputtering gas to form an in-plane magnetized film by reactive sputtering, or an alloy thin film containing a ferromagnetic metal such as Fe, Co, or Ni can be used as the in-plane magnetized film. . The magnitude of the saturation magnetization of the in-plane magnetization film is not particularly limited, but is preferably 200 to 600 emu / cc.

The thickness of the first magnetic layer is preferably from 200 to 600 angstroms. Further, the thickness of the added in-plane magnetic film is preferably from 10 to 300 angstroms.

The second magnetic layer is composed of Tc3, Tc1>Tc2>
There is no particular limitation on a magnetic thin film that satisfies room temperature, but preferably, 100 ° C <Tc2 <200 ° C, magnetization <
100 emu / cc. The thickness of the second magnetic layer is 50
~ 200 Å is preferred.

The third magnetic layer may be any perpendicular magnetic film having a sufficiently large coercive force at a temperature between room temperature and Tc2. For example, TbFeCo, DyFeCo, NdDyF
eCo and the like. The thickness of this layer is 200-80
0 Å is preferred.

The reason why the transferability is stabilized with good reproducibility by adding an in-plane magnetic film to the first magnetic layer is currently under study and the details are unknown, but the in-plane magnetic film is provided on the surface of the first magnetic layer. This is presumably because the presence of reduces the domain wall energy in the first magnetic layer and allows the magnetic domain to exist stably in this layer. However, such a guess is
It does not affect the present invention at all.

The structure of the magneto-optical recording medium of the present invention comprises a first magnetic film, a second magnetic film, a third magnetic film, and a first magnetic film which are magnetically coupled to each other on the transparent substrate. It is not particularly limited as long as it is constituted by the in-plane magnetized film added to
A dielectric film such as silicon nitride may be interposed between the transparent substrate and the magnetic film, or a protective film or a metal film such as Al may be laminated on the magnetic film.

The third magnetic film may be composed of two to five layers in order to further add a function such as light modulation overwrite.

The transparent substrate is sufficiently transparent in the wavelength region of the laser to be used, and if the characteristics of the medium substrate such as mechanical characteristics are satisfied, glass, polycarbonate,
It is not particularly limited, such as amorphous polyolefin.

If there is a dielectric film between the transparent substrate and the magnetic film, the dielectric film is formed under conditions that are as dense as possible, or etching is performed after the dielectric film is formed, so that the recording layer and the recording layer are recorded. Even when the exchange coupling force of the holding layer is increased, the transferability is not sacrificed, so that the C / N can be improved.

[0028]

【Example】

Example 1 A magneto-optical recording medium as shown in FIG. 2 was manufactured. Polycarbonate
A dielectric layer 2 made of silicon nitride on a bone substrate 1
(Film thickness: 800 angstroms), and after etching in an argon gas, in-plane magnetized film 3 of GdFeCo (film thickness: 40 angstroms, magnetization: 3)
50 emu / cc (room temperature), Curie temperature: 350 ° C. or higher), first magnetic film 4 made of GdFeCo (thickness: 3)
A second magnetic film 5 made of TbFeCoSi (thickness: 100 angstroms, coercive force: 3 kOe, Tc2: 140 ° C.), and a third made of TbFeCo. Magnetic film 6 (thickness: 400 Å,
Coercive force:> 12 kOe, Tc3: 260 ° C.), and a silicon nitride layer 7 (film thickness: 800 Å) and an aluminum layer 8 (film thickness: 200 Å) were formed. As a comparative example, a sample without the in-plane magnetized film 3 was also manufactured.

Next, this magneto-optical recording medium is set in a recording / reproducing apparatus, and while rotating at a linear velocity of 5.5 m / sec, a laser beam having a wavelength of 780 nm is applied to a 33% duty.
5.7m while modulating at 7.1MHz at the tee
Recording was performed with W laser power. The bias magnetic field at the time of recording was 250 Oe.

A bias magnetic field of 300 Oe (H
When the laser power was reproduced at 1.6 mW while applying r), the value of C / N became 46.5 dB.

When the C / N was measured under the same conditions in the comparative example, it was 39 dB, and a good C / N was not obtained.

Many recording magnetic domains of 1.4 μm were written on both recording media, and the Carr effect was measured at 90 ° C. by irradiating 780 nm light from the substrate side. After applying a magnetic field until the recording magnetic domain of the first magnetic film 4 is erased within a range where the recording magnetic domain of the third magnetic film 6 does not disappear, the magnetic field is lowered. It was confirmed that the recording magnetic domain of the third magnetic film 6 was transferred to the first magnetic film 4, and in the comparative example having no in-plane magnetization film 3, no transfer was performed at zero magnetic field, and the magnetic field was further reduced in the recording direction. Was transferred over 5 kOe.

Therefore, the difference in C / N between the two recording media is
When the laser power was irradiated at 1.6 mW while applying a bias magnetic field (Hr) of 300 Oe in the erasing direction, the region of the second magnetic film 5 exceeding the Curie temperature in the comparative example returned to room temperature. However, it was clear that the cause was not completely restored, and the effect of the present invention became clear.

Example 2 A magneto-optical recording medium as shown in FIG. 2 was manufactured in the same manner as in Example 1. However, the etching step in argon gas after forming the dielectric layer 2 (thickness: 800 Å) was omitted. Thereafter, the in-plane magnetic film 3 made of GdFeCo (film thickness: 25 Å, magnetization: 330 emu)
/ Cc (room temperature), Curie temperature: 350 ° C or higher), Gd
First magnetic film 4 made of FeCo (thickness: 300 angstroms, magnetization: 20 emu / cc (room temperature), Tc
1: 340 ° C.), second magnetic film 5 made of TbFeCoSi (film thickness: 100 Å, coercive force: 5 kO)
e, Tc2: 110 ° C.), third magnetic film 6 made of TbFeCo (thickness: 400 Å, coercive force:>
12 kOe, Tc3: 260 ° C.), a silicon nitride layer 7 (film thickness: 800 Å), and an aluminum layer 8 (film thickness: 200 Å). As in Example 1, for comparison, a comparative example in which the in-plane magnetized film 3 was omitted was also manufactured.

Next, this magneto-optical recording medium is set in a recording / reproducing apparatus, and while rotating at a linear velocity of 5.5 m / sec, a laser beam having a wavelength of 780 nm is applied to a 33% duty.
5.5m while modulating at 7.1MHz at the tee
Recording was performed with W laser power. The bias magnetic field at the time of recording was 250 Oe.

In the erase direction, a bias magnetic field (H
When the laser power was reproduced at 1.5 mW while applying r), the value of C / N became 45 dB.

When the C / N was measured under the same conditions in the comparative example, it was 32 dB, and a good C / N was not obtained.

A large number of 1.4 μm recording magnetic domains were written on both recording media, and the Carr effect was measured at 80 ° C. by irradiating 780 nm light from the substrate side. After applying a magnetic field until the recording magnetic domain of the first magnetic film 4 is erased within a range where the recording magnetic domain of the third magnetic film 6 does not disappear, the magnetic field is lowered. It was confirmed that the recording magnetic domain of the third magnetic film 6 was transferred to the first magnetic film 4, and in the comparative example having no in-plane magnetization film 3, no transfer was performed at zero magnetic field, and the magnetic field was further reduced in the recording direction. Was transferred over 4 kOe.

From the above description, it has been clarified that the addition of the in-plane magnetic film improves transferability. In the second embodiment, when the Curie temperature of the intermediate layer is set to 130 ° C. or higher, good transferability can be obtained without the in-plane magnetized film 3. However, in the second embodiment, the second magnetic film 5 as the intermediate layer can be obtained. Curing temperature is set as low as 110 ° C, so regeneration power is 1.2 ~ 2.5
A C / N of 40 dB or more was obtained at mW, and a considerably large reproducing power margin was obtained with respect to a power of -2.8 mW at which the recording layer began to be erased.

[0040]

The in-plane magnetized film provided on the magneto-optical recording medium of the present invention reduces the domain wall energy of the recording magnetic domain while maintaining good perpendicular magnetic anisotropy of the first magnetic layer. Even if the Curie temperature of the second magnetic film is low, good transferability and exchange coupling force can be provided. Therefore, the curable temperature of the second magnetic film can be selected in a considerably wide range, so that a sufficient reproducing power margin can be obtained, and the curable temperature of the third magnetic film cannot be controlled. And the recording durability is not deteriorated repeatedly. Further, when the fourth magnetic film is a two- to five-layer film to add a light modulation overwrite function, a reasonable medium design is possible.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of the structure of a magneto-optical recording medium according to the present invention.

FIG. 2 is a sectional view showing an example of the structure of the magneto-optical recording medium of the present invention.

Claims (1)

(57) [Claims] A first magnetic film, a second magnetic film, and a third magnetic film magnetically coupled to each other on a transparent substrate, wherein the first, second, and third magnetic films are provided; When the Curie temperatures of the films are Tc1, Tc2, and Tc3, respectively, Tc3, Tc3
In a magneto-optical recording medium which satisfies c1>Tc2> room temperature and is capable of reproducing while deforming a magnetic domain of the first magnetic layer, an in-plane magnetic film is added before forming the first magnetic film. Magneto-optical recording medium.