JPH06325418A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide a magneto-optical recording medium capable of increasing a recording bias magnetic field and having stable domains. CONSTITUTION:This magneto-optical recording medium has a memory layer 3 performing thermomagnetic recording and magneto-optical readout, a writing layer 5 formed so as to enable overwriting by exchange coupling force to the memory layer 3 and an intermediate layer 4 interposed between the layers 3, 5, controlling the exchange coupling force, also utilizable as a reflecting layer at the time of readout and having an axis of easy magnetization in the surface. A rare earth metal-transition metal alloy having no compensation temp. and such a compsn. as to give predominance to the sub-lattice magnetization of the rare earth metal is used for the writing layer 5 and a noble metal- transition metal alloy as a ferromagnetic material is used for the intermediate layer 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording medium, and more particularly to improvement of its overwriting characteristics.

[0002]

2. Description of the Related Art In a conventional medium of this type, the domain wall energy between the memory layer (M layer) and the write layer (W layer) is disclosed, for example, in Japanese Patent Laid-Open No. 63-117354. The description that an intermediate layer is provided to adjust the temperature is above.

[0003]

However, since the bias magnetic field for recording and the magnetostatic energy of the intermediate layer are not taken into consideration, there is a drawback that the bias magnetic field interferes during erasing.

An object of the present invention is to solve the drawback that the recording bias magnetic field which the above-mentioned conventional products have has a hindrance to erasure, whereby the recording bias magnetic field can be increased, the domain becomes stable, and the CNR is also improved. Another object of the present invention is to provide a magneto-optical recording medium.

[0005]

In a magneto-optical recording medium using an optical modulation overwrite system, the exchange coupling force between the M layer and the W layer is controlled to reduce the magnitude of the initializing magnetic field, and In order to stabilize the interface domain wall that exists when the transition metal moments of the layer and the W layer are coupled antiparallel,
An intermediate layer (I layer) having an easy axis of magnetization in the in-plane direction is required.

At the present time, when performing magneto-optical reading, the M layer and the W layer are optically blocked, and the light transmitted through the M layer is reflected to increase the reproduction signal intensity. It is advantageous to use expensive materials.

As a material having a high reflectance in the in-plane magnetized film, there is a noble metal / transition metal alloy, which is ferromagnetic. However, when the I layer of the ferro-magnetic material is combined with the W layer of the ferri-magnetic material having the conventional compensation temperature and the recording is performed at the compensation temperature or higher, that is, in the temperature region where the sublattice magnetization of the transition metal is dominant, At that time, the direction of the necessary bias magnetic field is opposite to the direction that the I layer should have when transferring the magnetization direction from the W layer to the M layer in the erasing process,
Erase becomes difficult.

There are two possible means for solving this problem. One is to use a ferrimagnetic material for the I layer and a ferrimagnetic material having a compensation temperature for the W layer. However, in this combination, a precious metal / transition metal alloy having a high reflectance cannot be used for the I layer.

The other is to use a ferromagnetic material for the I layer and a ferrimagnetic material for which the sublattice magnetization of the rare earth metal having no compensation temperature is dominant for the W layer.

[0010]

In this case, the sublattice magnetization of the rare earth metal is dominant even at the recording temperature, and the direction of the bias magnetic field required there is
When the magnetization direction is transferred from the W layer to the M layer in the erasing process, I
The bias field will support erasure for the I layer, as it would be in the direction that the layer must face. Therefore, the bias magnetic field that can be applied is increased, and the stability of the recording domain is also improved.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is an enlarged cross-sectional view of a main part of a magneto-optical recording medium according to an embodiment of the present invention, FIG. 2 is a cross-sectional view when applied to an air-sand Germany type disk, and FIG. 3 is a case where it is applied to a close-bonding type disk. FIG.

In these figures, 1 is a substrate made of glass or transparent synthetic resin, 2 is an enhancement layer, and 3 is M.
A layer, 4 is an I layer, 5 is a W layer, 6 is a protective layer, 7 is an inner peripheral spacer, 8 is an outer peripheral spacer, 9 is a hub, and 10 is an adhesive layer.

Next, a specific example will be described.

Example 1 A glass nitride plate was pre-grooved and pre-formed with a UV curable resin, and 800 Å of an enhancement layer of a silicon nitride dielectric film and M layer of a Tb _22.5 Fe ₆₇ Co _10.5 amorphous alloy film were formed on the substrate. 200 Å, 50 I of Pt _79.5 Co _20.5 alloy film, and 5 W of Tb ₃₀ Fe ₅₈ Co ₁₂ amorphous alloy film.
A magneto-optical disk was prepared by sequentially laminating a protective layer of 00Å and a protective layer of a silicon nitride dielectric film of 1000Å, and adhering the protective layer with an air-sintered structure.

When the initializing magnetic field is 2KOe, 4.93M
The track recorded at Hz was overwritten with light having a 3.7 MHz signal modulated with a bias magnetic field of 600 Oe with a high power of 12 mW and a low power of 5 mW. afterwards,
When reproduced at 1.5 mW, the signal at 4.93 MHz was completely erased and the CNR at 3.7 MHz was 55 dB.

From this result, it was found that the disk of the present embodiment could be overwritten even with a large bias magnetic field and had a sufficient CNR.

Example 2 On a polycarbonate substrate, 800 Å of an enhancement layer of silicon nitride dielectric film, 150 Å of M layer of Tb _23.5 Fe _66.5 Co ₁₀ amorphous alloy film, and 2 I layers of Pt ₈₄ Co ₁₆ alloy film were formed.
0 Å, Gd ₁₀ Tb ₂₀ Fe ₆₀ Co ₁₀ amorphous alloy film W layer 400 Å, silicon nitride dielectric film protective layer 150 Å, aluminum titanium amorphous alloy film thermal diffusion layer 300 Å,
A magneto-optical disk was produced by sequentially stacking and closely bonding.

With an initializing magnetic field of 2.5 KOe, 4.9
3.7MHz on the track recorded at 3MHz
Was overwritten with a bias magnetic field of 450 Oe with a high power of 13 mW and a low power of 5.5 mW. Then 1.
When reproduced at 5 mW, the 4.93 MHz signal was completely erased and the 3.7 MHz CNR was 52 dB. From this result, it was found that the disk of this example could be overwritten even with a large bias magnetic field, and the CNR could be sufficiently obtained.

FIG. 4 is a characteristic diagram showing temperature dependence of magnetic properties of the M layer and W layer, FIG. 5 is a characteristic diagram showing temperature dependence of magnetic properties of the I layer, and FIG. 6 is laser power at carrier noise level. It is a characteristic view which shows dependence.

[0020]

As described above, in the present invention, a rare earth / transition metal alloy having a composition in which the sublattice magnetization of the rare earth metal is predominant in the W layer and has no compensation temperature is used.
Since the I layer between the W layer and the W layer is made of a noble metal / transition metal alloy that is ferromagnetic and has an easy axis of magnetization in the film surface and high reflectivity, the bias magnetic field can be increased and stable. The domain could be formed and the CNR was also improved.

[Brief description of drawings]

FIG. 1 is an enlarged view of a main part of a magneto-optical recording medium according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an Air Sun Germany type magneto-optical recording medium according to an example of the present invention.

FIG. 3 is a cross-sectional view of a contact-bonding type magneto-optical recording medium according to an example of the present invention.

FIG. 4 is a characteristic diagram showing temperature dependence of magnetic characteristics of the M layer and the W layer.

FIG. 5 is a characteristic diagram showing temperature dependence of magnetic characteristics of the I layer.

FIG. 6 is a characteristic diagram showing laser power dependence of carrier noise level.

[Explanation of symbols]

 1 Substrate 2 Enhance Layer 3 M Layer 4 I Layer 5 W Layer 6 Protective Layer

Claims (3)

[Claims] 1. A memory layer for thermomagnetic recording and magneto-optical reading, a write layer provided to enable overwriting by the exchange coupling force with the memory layer, and the memory layer and the write layer. In a magneto-optical recording medium having an intermediate layer having an easy axis of magnetization in the film surface, which controls the exchange coupling force and can also be used as a reflective layer at the time of reading, the write layer has no compensation temperature. A magneto-optical recording medium characterized by using a rare earth transition metal alloy having a composition in which a sublattice magnetization of a rare earth metal is predominant, and using a noble metal transition metal alloy which is a ferromagnetic material in the intermediate layer. 2. The magneto-optical recording medium according to claim 1, wherein a platinum cobalt alloy or a palladium cobalt alloy is used for the intermediate layer. 3. The magneto-optical recording medium according to claim 1, wherein the thickness t of the intermediate layer is 0 <t ≦ 100Å.