JP2616058B2 - Magneto-optical disk - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk, and more particularly to a magneto-optical disk for recording / reproducing information with a laser beam using a magneto-optical effect.

2. Description of the Related Art A conventional magneto-optical disk has been proposed in which a plurality of magnetic layers are used as recording layers of a magneto-optical disk for the purpose of improving recording and reproducing characteristics.

A typical example is a stack of a write layer having a low Curie temperature and exhibiting a high coercive force with good recording characteristics and a read layer having a high Curie temperature and exhibiting a low coercive force having a good readout characteristic, and the write layer is formed with less energy. The recording mark written on the recording layer is transferred to a reading layer having a large magneto-optical effect by exchange coupling, and is read from the reading layer side (for example, Japanese Patent Laid-Open No. 57-78652).
issue).

Next, a conventional example will be described in detail with reference to the drawings.

 FIG. 2 is a schematic sectional view showing an example of the prior art.

In the magneto-optical disk shown in FIG. 2, a transparent dielectric layer 2 is formed on a substrate 1, and a readout layer 3 having a high Curie point which is perpendicularly magnetizable and has a low coercive force is formed thereon. Magnetizable write layer with low Curie point and high coercivity
21 are sequentially laminated, and the protective layer 5 is formed thereon.

The substrate 1 is provided with a center hole 11 for rotating the disk.

The magneto-optical disk shown in FIG. 2 can write on the write layer 21 with a small recording energy and transfers it to the read layer 3 having a large magneto-optical effect by exchange coupling. Although a magneto-optical disk can be obtained, recording and reproduction are usually performed by rotating the disk at a constant angular velocity. Therefore, the linear velocity differs between the inner peripheral side and the outer peripheral side of the disk, and the linear velocity increases as the outer periphery increases. The recording sensitivity decreases.

[Problems to be solved by the invention]

However, such a conventional magneto-optical disk described above has a constant recording speed at a constant linear velocity because the thickness of the write layer is constant.
There is a disadvantage that the sensitivity is reduced on the outer peripheral side, and high sensitivity and high C / N are not obtained over the entire recording area.

[Means for solving the problem]

The magneto-optical disk of the present invention is obtained by sequentially laminating a perpendicular magnetically magnetizable read layer having a high Curie point and a low coercive force on a disk substrate and a perpendicular magnetically magnetizable write layer having a low Curie point and a high coercive force. In a magneto-optical disk in which a read layer and a write layer are exchange-coupled, the thickness of the write layer is gradually reduced from the inner peripheral side toward the outer peripheral side.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

 FIG. 1 is a schematic sectional view showing one embodiment of the present invention.

The magneto-optical disk shown in FIG. 1 has a substrate 1 having a center hole 11 for rotating the disk, a transparent dielectric layer 2, and a read layer 3 which is vertically magnetizable and has a high Curie point and a low coercive force.
A write layer 4 having a low Curie point and a high coercive force with a thin film thickness from the inner peripheral side to the outer peripheral side, having a low Curie point, a protective layer 5, and an adhesion reinforcing layer 6. You.

 Note that the adhesion reinforcing layer 6 does not necessarily need to be provided.

As the substrate 1, a synthetic resin such as an epoxy resin, a polycarbonate resin, an acrylic resin, or a polyolefin resin, glass, or the like can be used.

Further, as the transparent dielectric layer 2, silicon nitride, aluminum nitride, silicon nitride oxide, aluminum nitride oxide, silicon nitride aluminum oxide, silicon oxide,
Tantalum oxide, zinc sulfide, zinc selenide, tin oxide, and the like can be used.

As the readout layer 3, an amorphous alloy of gadolinium / iron / cobalt / titanium is most preferable, but gadolinium / iron / titanium alloy, gadolinium / iron / cobalt alloy, gadolinium / iron / cobalt / chromium alloy, gadolinium / iron
Iron, cobalt, and aluminum alloys can also be used.

The thickness of the writing layer 4 is gradually reduced from the inner peripheral side to the outer peripheral side. When the light beam is irradiated, the temperature rise in the film becomes larger as the film thickness becomes smaller, so that when recording at a constant linear velocity, the recording sensitivity is improved from the inner peripheral side to the outer peripheral side. On the other hand, when recording at a constant angular velocity, the linear velocity increases from the inner peripheral side to the outer peripheral side, so that recording can be performed with almost constant recording sensitivity almost independent of the radial position.

The writing layer 4 is most preferably an amorphous alloy of terbium / iron / titanium, but terbium / dysprosium / titanium.
Iron / titanium alloy, dysprosium / iron / titanium alloy, terbium / iron alloy, terbium / dysprosium / iron alloy, dysprosium / iron alloy, terbium, iron / chromium alloy, terbium / iron / aluminum alloy, terbium / dysprosium / iron / chrome Alloy, terbium, dysprosium, iron, aluminum alloy, dysprosium
Iron-chromium alloy, dysprosium-iron-aluminum alloy, etc. can also be used.

As the protective layer 5, silicon nitride, aluminum nitride, silicon nitride oxide, aluminum nitride oxide, silicon aluminum nitride oxide, silicon oxide, tantalum oxide, tin oxide, zinc sulfide, zinc selenide, aluminum oxide, or the like can be used.

In the magneto-optical disk shown in FIG. 1, only the write layer 4 has a recording sensitivity from the inner peripheral side to the outer peripheral side only when recording at a constant linear velocity in order to reduce the film thickness from the inner peripheral side to the outer peripheral side. Therefore, in a normal use state in which the angular velocity is constant, recording can be performed with almost constant recording sensitivity almost independent of the radial position.

On the other hand, the thickness of the readout layer 3 is made constant from the inner circumference to the outer circumference, and the reproduction characteristics are made uniform regardless of the radial position.

Therefore, a magneto-optical disk having high sensitivity and high C / N over the entire recording area on the disk can be obtained.

Hereinafter, a specific example of the embodiment shown in FIG. 1 will be described.

After reverse-sputtering an epoxy resin disk-shaped substrate 1 having a diameter of 200 mm and a thickness of 1.2 mm on which a track guide groove made of an acrylic resin is formed, a tantalum oxide film is uniformly 300 mm thick by reactive sputtering. Was formed as an adhesion strengthening layer 6.

Next, a silicon nitride film was formed as a dielectric layer 2 having a thickness of 500 mm uniformly over the entire surface of the disk by reactive sputtering.

Next, a gadolinium / iron / cobalt / titanium film of 23.0 to 58.4 to 14.6 to 4.0 in atomic% is uniformly applied to the entire surface of the disk for 200 times.
形成 Formed as a thick readout layer 3, followed by 20.2 atomic%.
The terbium / iron / titanium film with a ratio of 75.8: 4.0 to the innermost 100
A write layer 4 having a thickness gradually changing from 0 mm to the outermost 500 mm is formed as a write layer 4, and finally, a silicon nitride film is formed as a 800 mm thick protective layer 5 uniformly on the entire surface of the disk by reactive sputtering. As shown in FIG.

The method of gradually changing the film thickness from the inner peripheral side to the outer peripheral side is based on the shape of a film thickness distribution correcting plate (to be provided between the substrate 1 and the sputter target substrate 1) when the substrate 1 is sputtered while rotating around its own axis. Is obtained by adjusting.

A magneto-optical disk was manufactured by bonding the two disks manufactured as described above with a hot melt so that the film was on the inside.

This magneto-optical disk was rotated at 3600 rpm, and a semiconductor laser having a wavelength of 820 nm was irradiated through the substrate 1 to obtain a recording power of 7 mW and
When the recording / reproducing was performed over the entire area of the disk at a constant reproduction power of 2 mW, the C / N coverage was 55 dB or more over the entire area, and it was confirmed that high-sensitivity recording was possible over the entire area of the disk.

As a comparative example, the thickness of the writing layer 4 is constant at 1000 °,
Otherwise, a magneto-optical disk having exactly the same configuration as that of the above-described embodiment was manufactured, and a similar test was performed. As a result, good recording could not be performed at the outer peripheral portion of the disk due to insufficient recording power.

〔The invention's effect〕

The magneto-optical disk of the present invention can supply an appropriate recording power even in the outer peripheral portion of the disk by reducing the thickness of the write layer only from the inner peripheral side to the outer peripheral side. This has the effect of achieving a high C / N.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an embodiment of the present invention, and FIG. 2 is a schematic sectional view showing an example of the conventional art. 1 ... substrate, 2 ... dielectric layer, 3 ... readout layer, 4,21 ...
Writing layer, 5: protective layer, 6: adhesion reinforcing layer, 11: central hole.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-78652 (JP, A) JP-A-61-211854 (JP, A) JP-A-61-273761 (JP, A) JP-A-61-273761 268755 (JP, A) JP-A-63-42053 (JP, A)

Claims (1)

(57) [Claims] 1. A disk-shaped substrate, formed on the substrate and capable of being perpendicularly magnetized, having a high Curie point, having a low coercive force, and having a thickness from the inner peripheral side toward the outer peripheral side. An identical readout layer, and a write layer laminated on the readout layer, having perpendicular magnetization and having a low Curie point, exchange-coupled to the readout layer, and having a thickness reduced from an inner peripheral side toward an outer peripheral side. And a magneto-optical disc comprising: