JP3112504B2 - 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 magneto-optical recording medium capable of overwriting information by a light intensity modulation method.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Application Laid-Open No. Sho 62-1759
As described in JP-A-48-48, a recording layer for performing thermomagnetic recording and magneto-optical reading on a substrate and an auxiliary layer exchange-coupled to the recording layer are provided. A magneto-optical recording medium capable of writing has been proposed.

FIG. 8 is a cross-sectional view schematically showing the film structure of this type of magneto-optical recording medium, wherein 21 is a magneto-optical recording medium, 22 is a substrate, 23 is a recording layer, and 24 is an auxiliary layer. ing. The recording layer 23 is formed of a perpendicular magnetization film having a higher coercive force at room temperature than the auxiliary layer 24 and a lower Curie point than the auxiliary layer 24, as exemplified in the coercive force-temperature characteristic diagram of FIG. Is done. On the other hand, the auxiliary layer 24 is formed of a perpendicular magnetization film having a lower coercive force at room temperature than the recording layer 23 and having a higher Curie point than the recording layer 23 as illustrated in FIG.

The mechanism of overwriting in this type of magneto-optical recording medium will be described below, taking a so-called parallel type magneto-optical recording medium as an example.

FIG. 10 is an explanatory diagram of a drive for performing overwriting of the light intensity modulation method, and shows a read level,
A laser 25 capable of intensity modulation to three values of an erasing (L) level and a recording (H) level, a magnet 26 for applying a bias magnetic field during recording, and an initialization magnet 27 for overwriting are provided.

The L level laser is set to a value capable of heating the recording layer 23 to the Curie temperature, and the H level laser is set to a value capable of heating the auxiliary layer 24 to the Curie temperature. The bias magnetic field applying magnet 26 is formed of a magnet that generates a magnetic field weaker than the initializing magnet 27, is arranged to face the laser 25, and applies a magnetic field in one direction, for example, an upward magnetic field to the magneto-optical recording medium 21. The initialization magnet 27 is formed of a magnet that generates a magnetic field stronger than the bias magnetic field application magnet 26, and is disposed upstream of the set position of the bias magnetic field application magnet 26 in the rotation direction of the magneto-optical recording medium 21. A downward magnetic field is applied to the magneto-optical recording medium 21.

In the recording state, the parallel type magneto-optical recording medium 21 has a recording layer 2 as shown in FIG.
3 and the magnetization of the auxiliary layer 24 are directed upward, and in the erased state, as shown in FIG.
Both the magnetization of the recording layer 23 and the magnetization of the auxiliary layer 24 become downward.

A magneto-optical recording medium 2 on which information has already been written
When 1 is mounted on the above-mentioned drive and driven to rotate, the magnetization of the auxiliary layer 24 is aligned downward by the downward magnetic field at the stage of passing through the initialization magnet 27. That is, the state of FIG. 11A is changed from the state of FIG. 11A to the state of FIG. 11C in the recording unit, and the state of FIG.
In the state shown in FIG. 11C, the partial magnetization of each of the layers 23 and 24 is in the opposite direction, so that the interface domain wall 27 is generated.

After passing through the initialization magnet 27, when the laser 25 is irradiated with L level laser light at the stage where the laser 25 and the bias magnetic field applying magnet 26 are set, the medium temperature rises, The Curie point of the recording layer 23 is almost reached. At this time, the magnetization state of FIG.
11B, the magnetization state shown in FIG. 11C becomes unstable under the influence of the interface domain wall 27, and the recording layer 23 becomes instable.
Is reversed, and the state shifts to a stable state shown in FIG.

In this state, even if the medium comes out of the laser beam irradiation part and the medium temperature drops, the magnetization state in FIG. 11B is stable, and the state before overwriting is shown in FIGS.
Erasure is performed regardless of the state of (c).

When the laser 25 emits H-level laser light, the temperature of the medium rises and reaches the L-level temperature. At the stage when the medium reaches the L-level temperature, the two magnetization states shown in FIGS. 11B becomes the magnetization state as shown in FIG. When the temperature further rises and reaches near the Curie point of the auxiliary layer 24, the state shown in FIG. At this temperature, since the coercive force of the auxiliary layer 24 is small, the magnetization of the auxiliary layer 24 is reversed by the influence of the external magnetic field, and the state shown in FIG.

In this state, when the medium comes out of the laser beam irradiating section and the medium temperature drops to a temperature near the L level, the magnetization of the recording layer 23 is changed to the auxiliary layer 24 as shown in FIG.
Appear by imitating the partial magnetization of the auxiliary layer 24 due to the exchange coupling. Even if the medium temperature drops to room temperature, FIG.
The magnetization state is stable, and the state before overwriting is shown in FIG.
Regardless of the state of FIG. 11B or FIG. 11C, information is recorded.

[0013]

As described above, this type of magneto-optical recording medium performs overwriting by utilizing the exchange coupling force acting between the recording layer 23 and the auxiliary layer 24. Regarding erasure and erasure, those having a large exchange coupling force are preferable. On the other hand, a magneto-optical recording medium having a large exchange coupling force requires a large initialization magnet for initializing the auxiliary layer 24, and the device becomes large.
There are various disadvantages that the dynamic characteristics of the head are deteriorated and the interface domain wall is not stable when there is no external magnetic field, and the recording magnetic domain is easily lost. Therefore, in this type of magneto-optical recording medium, the exchange coupling force acting between the recording layer 23 and the auxiliary layer 24 is reduced to such an extent that the recording and erasing characteristics are not impaired and the above disadvantages do not occur. Need to adjust to the value.

However, when the recording layer 23 and the auxiliary layer 24 (generally, an amorphous alloy containing a rare earth element and a transition metal as a main component are used) are directly laminated as in a conventional magneto-optical recording medium, The exchange coupling force is much larger than expected, and an initialization magnet of at least about 5 to 6 [KOe] is required. In addition, the recording magnetic domains are apt to disappear in proportion thereto.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages of the prior art, and provides a magneto-optical recording medium capable of reducing the size of an initialization magnet and realizing stable recording. The purpose is to do.

[0016]

According to the present invention, there is provided a magneto-optical recording medium comprising a recording layer and an auxiliary layer on a substrate.
Force is higher than the room temperature coercive force of the auxiliary layer; and
Compare the Curie point of the recording layer with the Curie point of the auxiliary layer.
In addition, an intermediate layer made of a magnetic oxide having an easy axis of magnetization in the film surface direction was provided between the recording layer and the auxiliary layer.

As a specific material of the intermediate layer, a magnetic oxide mainly containing an oxide of at least one element selected from the group consisting of [iron, cobalt, chromium, manganese, nickel] is particularly suitable. .

[0018]

In order to control the exchange coupling force acting between the recording layer and the auxiliary layer, the thickness of the intermediate layer is particularly important. If the thickness of the intermediate layer is 1000 ° or more, the recording and erasing of information is adversely affected. Therefore, the thickness of the intermediate layer is preferably 1000 ° or less.

[0020]

When an intermediate layer made of a magnetic oxide having an easy axis of magnetization in the film surface direction is provided between the recording layer and the auxiliary layer, the exchange coupling force acting between the recording layer and the auxiliary layer is reduced. be able to. Therefore, the size of the initialization magnet for initializing the auxiliary layer can be reduced, and the device can be downsized and the dynamic characteristics of the head can be improved. In addition, even when there is no external magnetic field, the interface domain wall can be stabilized, and the recording magnetic domain is hardly lost.

[0021]

【Example】

<First Embodiment> As shown in FIG. 1, an ultraviolet curable resin layer 2 on which a preformat pattern (not shown) is transferred is brought into close contact with one surface of a glass disk 3 by a so-called 2P method, and a preformat pattern is formed. , A transparent substrate 4 was prepared.

Next, on the preformat pattern of the transparent substrate 4, a film thickness of about 85
0 ° silicon nitride dielectric enhancement layer 5 and a thickness of about 3
A recording layer 6 made of an amorphous alloy of terbium-iron-cobalt having a thickness of about 00 °, an intermediate layer 7 made of an iron oxide having a non-stoichiometric composition having a thickness of about 200 °, An auxiliary layer 8 made of a cobalt amorphous alloy and a protective layer 9 made of silicon nitride having a thickness of about 1000
The disk single plate 10 shown in FIG. 1 was produced.

Finally, the two disk single plates 10 manufactured as described above are laminated concentrically with the respective layers 5 to 9 inside, thereby manufacturing a magneto-optical disk 11 having an air sandwich structure shown in FIG. did. In this figure, reference numeral 1
Reference numeral 2 denotes an inner peripheral spacer, 13 denotes an outer peripheral spacer, and 14 denotes an air gap formed between the respective disk single plates 10.

<Second Embodiment> A transparent substrate 15 made of polycarbonate having a preformat pattern (not shown) formed on one surface was prepared by injection molding.

Next, on the preformat pattern of the transparent substrate 15, from the transparent substrate side 15, a silicon nitride dielectric enhancement layer 5 having a thickness of about 850 ° and a terbium-iron-cobalt having a thickness of about 250 ° are provided. A recording layer 6 made of an amorphous alloy, an intermediate layer 7 made of a non-stoichiometric cobalt oxide having a thickness of about 150 °, and an auxiliary layer made of a gadolinium-terbium-iron-cobalt amorphous alloy having a thickness of about 1200 ° 8
And a protective layer 9 made of a silicon nitride dielectric having a thickness of about 1000 ° are sequentially laminated to produce a single disk 16 shown in FIG.

Finally, the two disk single plates 16 manufactured as described above are bonded concentrically with the layers 5 to 9 inside, and the magneto-optical disk 17 having the close bonding structure shown in FIG. Produced. In this figure, reference numeral 18 denotes an adhesive layer for adhering the individual discs 16.

The coercive force-temperature characteristics and the saturation magnetization-temperature characteristics of the recording layer and the auxiliary layer formed on each of the magneto-optical disks of the first and second embodiments were examined. I found out. That is, the recording layer 6 has a higher coercive force at room temperature than the auxiliary layer 8,
With a lower Curie point. The recording layer 6 has a lower saturation magnetization at room temperature than the auxiliary layer 8.

The L-level laser power required for erasing the recording magnetic domain and the H-level laser power required for recording information were examined for each of the magneto-optical disks of the first and second embodiments. Also, as shown in FIG.
By applying an L level laser power of mW or less, a previously recorded signal can be reproduced, and about 14 m
It was found that information could be recorded by applying an H level laser power of W or more.

Further, while changing the magnitude of the initialization magnetic field in various manners, the signal of 1.85 [MHz] is overwritten on the track on which the signal of 4.93 [MHz] is recorded, and the signal of 4.93 [MHz] is overwritten. MHz] signal is completely erased.
The magnitude of the initialization magnetic field at which the signal of 85 [MHz] was overwritten was examined. As shown in FIG. 7, each of the magneto-optical disks of the first and second embodiments has about 1 [KO].
e) just by applying the initializing magnetic field of 4.9 recorded earlier.
Conventionally, a signal of 3 [MHz] is completely erased, and a signal of 1.85 [MHz] recorded later has reached a saturation level, and an initialization magnetic field of 5 to 6 [KOe] must be applied. It has been found that the initialization magnet can be much smaller than the technology.

However, for the magneto-optical disk of the first embodiment, a signal of 1.85 [MHz] is transmitted at an L level of 6 [m].
W] and H levels are intensity-modulated to 14 [mW] and overwritten, and for the magneto-optical disk of the second embodiment,
The L level of a 1.85 [MHz] signal is 5.5 [m].
W] and H levels were intensity-modulated to 12 [mW], overwritten and overwritten. The power of the reproducing laser beam was 1.5 [mW].

The same effects as described above were confirmed not only for the magneto-optical disks of the first and second embodiments but also for the magneto-optical recording medium of the present invention.

[0032]

As described above, according to the present invention,
Since an intermediate layer is provided between the recording layer and the auxiliary layer to reduce the exchange coupling force acting between the two layers, the size of the initialization magnet for initializing the auxiliary layer can be reduced, and the size of the device can be reduced. And the dynamic characteristics of the head can be improved. In addition, even when there is no external magnetic field, the interface domain wall can be stabilized, so that the recording magnetic domains are hardly lost and stable recording characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a film structure of a medium according to a first embodiment.

FIG. 2 is a cross-sectional view showing a structure for bonding media according to the first embodiment.

FIG. 3 is a sectional view showing a film structure of a medium according to a second embodiment.

FIG. 4 is a cross-sectional view illustrating a medium bonding structure according to a second embodiment.

FIG. 5 is a graph showing coercive force-temperature characteristics and saturation magnetization-temperature characteristics of a recording layer and an auxiliary layer.

FIG. 6 is a graph showing the magnitude of laser power required for overwriting information.

FIG. 7 is a graph showing the magnitude of an initialization magnetic field required for overwriting information.

FIG. 8 is a cross-sectional view showing a film structure of a magneto-optical recording medium according to a conventional technique.

FIG. 9 is a coercive force-temperature characteristic diagram of a magneto-optical recording medium according to a conventional technique.

FIG. 10 is an explanatory diagram of a drive that performs overwrite of the light intensity modulation method.

FIG. 11 is an explanatory diagram illustrating the principle of light intensity modulation method overwriting.

[Explanation of symbols]

 Reference Signs List 4 transparent substrate 5 enhance layer 6 recording layer 7 intermediate layer 8 auxiliary layer

Continuation of the front page (56) References JP-A-2-24801 (JP, A) JP-A-4-38637 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 11 / 105

Claims (3)

(57) [Claims] 1. A magneto-optical recording medium comprising a recording layer and an auxiliary layer on a substrate, wherein the recording layer has a coercive force at room temperature.
Is higher than the coercive force of the auxiliary layer at room temperature, and
Compare the Curie point of the recording layer with the Curie point of the auxiliary layer.
A magneto-optical recording medium, wherein an intermediate layer made of a magnetic oxide having an easy axis of magnetization in a film surface direction is provided between the recording layer and the auxiliary layer. 2. The magneto-optical recording medium according to claim 1, wherein the magnetic oxide constituting the intermediate layer is at least one element selected from the group consisting of [iron, cobalt, chromium, manganese, nickel]. A magneto-optical recording medium characterized by using a magnetic oxide whose main component is the above-mentioned oxide. 3. A magneto-optical recording medium according to claim 1, wherein said intermediate layer has a thickness of 1000 ° or less. "