JPS6383938A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To execute the overwrite of information by providing the magnetic layer of the high magnetic permeability having a vertical anisotropy, on a protective film. CONSTITUTION:A magnetic layer 5 consists of a high magnetic permeability material, and constituted by bringing it to perpendicular magnetization against the film surface by controlling a film forming condition and the thickness of a film. When an external magnetic field does not exist, the magnetization of a magnetic domain 8 of a recording layer 3 becomes a reflux structure, and a magnetic pole is not generated in the outside, but when the external magnetic field 9 of magnitude for distributing the magnetizing direction to a prescribed direction is applied, the magnetic domain 8 is oriented and a polarization is generated on the upper and lower faces, and when a magnetic domain 10 therein is taken notice of, a loop-shaped magnetic flux distribution 11 as indicated with a short dash line is generated, and as a result, the horizontal component of a magnetic flux of the external magnetic field 9 and the horizontal component of a magnetic flux generated from the magnetic domain 10 are offset mutually, and on the other hand, the vertical components intensity each other, and as a result, the vertical component of the magnetic field applied to the recording layer 3 is increased. In such a manner, since a high frequency magnetic field such as a ring head can be used, overwrite can be executed.

Description

[Detailed Description of the Invention] [Summary] In order to enable overwriting on a magneto-optical disk, a base film, a recording layer, and a protective film are formed on a transparent substrate. A magneto-optical disk with a high permeability magnetic layer magnetized perpendicular to the surface.

[Industrial application field]

The present invention relates to the structure of a magneto-optical disk that enables overwriting by efficiently using a high-frequency magnetic field.

A magneto-optical disk is a memory that uses laser light to record high-density information along with an optical disk, and has excellent features such as a large storage capacity, non-contact recording and playback, and being unaffected by dust. have.

In other words, the laser beam can be narrowed down to a small spot with a diameter of about 1 μm by a lens, and therefore 1 μm in diameter.
The area required for recording bit information is approximately 1 μm2.

In addition, since the distance to the focal plane of the laser beam narrowed down by the lens can be 1 to 21 cm, non-contact is possible, and the diameter of the light beam is approximately 111 mm at the substrate surface, so even if the laser beam is Even if there is dust with a size of several tens of micrometers, it can be done with almost no effect on recording and reproduction.

Here, an optical disk is a read-only memory that uses a low-melting point metal as a recording medium and records and reproduces information using the presence or absence of holes (pits).
) On the other hand, magneto-optical disks are being developed as rewritable memories (Erasable Memory), and the recording medium consists of a perpendicularly magnetized magnetic film. Magnetization reversal is used to record and erase information, and reproduction is performed by utilizing the fact that the rotation of the polarization plane of light reflected or transmitted from a magnetic film differs depending on the direction of magnetization.

The present invention relates to improvements in such magneto-optical disks.

[Conventional technology]

Magneto-optical disks have a perpendicular magnetic film made of an amorphous rare earth-transition metal alloy as a recording layer, and the dominant materials for this are terbium, iron, and cobalt (
Tb Fe Co), gadolinium cobalt (Gd
Co), terbium iron (Tb Fe), and gadolinium terbium iron (Gd Tb Fe).

FIG. 6 is a sectional view illustrating the structure of a magneto-optical disk, which is a stamper made by heating and melting a resin such as polymethyl methacrylate (PMMA) or polycarbonate (PC), and forming a large number of guide grooves in advance. A disk-shaped substrate 1 with a thickness of about 1.2*n is made by molding using a metal mold called .

Then, on top of this, a base film 2. Recording layer 3. An optical disc is produced by forming a layer with the protective film 4.

Here, the base film 2 prevents deterioration of the recording layer 3 due to oxidation due to the intrusion of moisture through the substrate 1 and the migration of gases or monomers adsorbed by the substrate, and is made of silicon nitride (SiJ*
), aluminum nitride (AIN), and other thin films are used.

The protective film 4 is provided to prevent the recording N3 from being oxidized from above, and is made of a dielectric thin film or a metal thin film as described above.

Additionally, glass with guide grooves formed by photoetching may be used as the substrate 1, but in this case, there is less deterioration due to moisture permeation and adsorbed gas, so the formation of the base film 2 can be omitted. - Magneto-optical disk In this way, a recording layer 3 is formed on a transparent substrate 1 with an oxidation-resistant structure.In order to record information on a magneto-optical disk, a magnetic field is applied perpendicularly, and a lens is passed through the substrate 1. The recording layer 3 is irradiated with a laser beam focused at , and the temperature of the irradiated area rises to near the Curie temperature, causing the coercive force to decrease and the direction of magnetization of the perpendicularly magnetized film to change due to the external magnetic field. This is done by utilizing the reversal in the direction of.

Furthermore, information is erased by heating the material by irradiating it with laser light without applying a magnetic field in the direction opposite to the direction of magnetization at the recording position, thereby reversing the magnetization to its original direction.

However, in order to erase the information that has already been recorded and record other information at this location, overwriting (such as with magnetic disks) is required.
0νer-write) is impossible, and it takes only one revolution of the magneto-optical disk to erase information.

It takes one rotation to reverse the magnetic field and one rotation to record information.

The reason why overwriting is not possible unlike with magnetic disks is that the magnetic head cannot get close to the recording layer.In order to record information, a large high-frequency wave that can reverse the magnetization of the perpendicularly magnetized film according to the signal is used. It is necessary to apply a magnetic field, and the inductance of the coil is too large for this purpose, making it impossible to quickly reverse the magnetic field.

[Problem that the invention seeks to solve]

As mentioned above, magneto-optical disks cannot be overwritten and require at least one rotation to erase conventional information, one rotation to reverse the magnetic field, and one rotation to record new information, which makes high-speed processing impossible. That's a problem.

[Means for solving problems]

The above problem occurs in a magneto-optical disk in which a base film, a recording layer, and a protective film are sequentially formed on a transparent substrate equipped with a guide groove. This problem can be solved by providing a means to increase the perpendicular component of the magnetic field line distribution of the external magnetic field applied to the recording layer, so that magnetization reversal can occur in a high-frequency magnetic field such as a ring head even at a distance.

[Effect]

FIGS. 1A and 1B are principle diagrams explaining the present invention, in which a base film 2 is placed on a transparent substrate 1. Recording layer 3. A magnetic layer 5 is formed on the magneto-optical disk formed with a protective film 4.
If the magnetic layer 5 is a horizontally magnetized film as shown in FIG. The magnetic field lines 7 passing through the layer 3 contain a significant horizontal component.

On the other hand, when the magnetic layer 5 is formed of a perpendicularly magnetized film as shown in FIG. 2A, the lines of magnetic force 7 do not spread, and therefore the lines of force 7 perpendicularly enter the recording layer 3, increasing the magnetic flux density.

In the present invention, the magnetic layer 5 made of a perpendicularly magnetized film is provided in this way, and by focusing the magnetic lines of force of the electromagnet, it is possible to reverse the magnetization of the recording N3 even in a weak magnetic field. This enabled the use of high-frequency magnetic fields such as

Here, the magnetic layer 5 according to the present invention is made of iron (Fe).

It is made of a high magnetic permeability material such as nickel (Ni), cobalt (CO), or an alloy thereof, such as Fe Co or Fe Ni, and is magnetized perpendicular to the film surface by controlling the film formation conditions and film thickness.

That is, the perpendicularly magnetized film is formed by slowing down the film formation rate, such as the evaporation rate or sputtering rate, and by forming the film to be relatively thick.

2 and 3 are cross-sectional views of such magnetic N5, and FIG. 2 shows the magnetic domain structure of the recording layer 3 made of a perpendicularly magnetized film in the absence of an external magnetic field, as shown in the figure. The magnetization of the magnetic domain (Domain) 8 has a circular current structure, and no magnetic poles are generated on the outside.

However, if an external magnetic field 9 of a magnitude that can orient the magnetization direction of the magnetic domain in a certain direction (downward in this example) is applied,
The magnetic domains 8 constituting the recording layer 3 are oriented as shown in FIG. 3, and polarization occurs on the upper and lower surfaces. Focusing on the magnetic domains 10 among them, a loop-shaped magnetic flux distribution 11 as shown by the dotted line is generated. , as a result, the horizontal component of the magnetic flux of the external magnetic field 9 and the magnetic domain 1
The horizontal components of the magnetic flux generated from 0 cancel each other out, while
As shown in the figure, the vertical components strengthen each other, resulting in Figure 1 (A)
As shown in FIG. 2, the perpendicular component of the magnetic field applied to the recording layer 2 increases, thereby making it possible to use a high frequency magnetic field such as a ring head.

〔Example〕

Example 1: Using a sputtering method on a substrate 1 made of PMMA with a thickness of 1.2+n, 5iJ4 was deposited as the base film 2, Tb Pe Co as the recording layer 3, and Si3Nm as the protective film 4 with a thickness of 1000 μm each. It was formed.

Next, using a sputtering method on the protective film 4, a composition ratio of 80
: Magnetic layer 5 made of 20 Fe Ni alloy
A magneto-optical disk according to the present invention was fabricated by forming the film to a thickness of 5000 mm at a film formation rate of S.

Here, the magnetic layer 5 formed under these conditions exhibits a magnetization curve as shown in FIG. 4, indicating that it has perpendicular anisotropy.

Next, recording, reproducing, and erasing experiments were conducted using the magneto-optical disk 12 using a composite head in which a ring head 13 and an optical head 14 were combined as shown in FIG.

First, a 0.2 MHz signal is given with the ring head 13,
4. When a signal was recorded with a laser power of 0.81 and reproduced with a power of 0.81, the C/N (Carrier-1ev
A value of el/No1se-Level) = 50 dB was obtained.

Next, when a 0.5 MHz signal was applied, the signal was overwritten with a 4.0 m laser power, and the signal was reproduced with a 0.8 mW power, the C/N of the 0.5 MHz signal was 49 to 50 dB.
, and there was no change in quality or noise level.

Example 2: Substrate 1. Base film 2. Recording layer 3. After the protective film 4 was formed in the same manner as the actual side 1, the magnetic layer 5 was formed using the sputtering method, and FeN1 (Fe, .Niz.) was deposited at a deposition rate of 10 persons/s for 2000 persons in the same manner as in Example 1. It was formed to a thick film.

It was confirmed from the magnetization curve that the magnetic film formed under these conditions was an in-plane magnetized film.

When the same test as in Example 1 was conducted using this magneto-optical disk, it was found that 0.2 MH
An unerased z component of about 10 dB was observed.

〔Effect of the invention〕

According to the present invention, information can be overwritten by providing a high permeability magnetic layer with perpendicular anisotropy on a conventional magneto-optical disk.

[Brief explanation of the drawing]

Figure 1 is a principle diagram explaining the present invention, Figure 2 is a diagram of the magnetic domain structure in the absence of an external magnetic field, Figure 3 is a diagram of the magnetic domain structure in the presence of an external magnetic field, and Figure 4 is the F of this embodiment.
e The magnetization curve of the Ni magnetic layer, FIG. 5 is a perspective view illustrating recording, reproducing, and erasing according to the present invention, and FIG. 6 is a sectional view showing the structure of a magneto-optical disk. In the figure, 1 is the substrate, 2 is the base film, 3 is the recording layer,
4 is a protective film, 5 is a magnetic layer,
7 is a magnetic field line, 9 is an external magnetic field, 11 is a magnetic flux distribution, 13 is a ring head, and 14 is an optical head. Leather 2 times $38 i j 14#: always to ndone 6 figure

Claims (1)

[Claims] A magneto-optical disk in which a base film, a recording layer, and a protective film are sequentially formed on a transparent substrate provided with a guide groove, in which a highly transparent magnet magnetized perpendicularly to the substrate surface is provided on the protective film. A magneto-optical disk characterized by being provided with a magnetic layer having a high magnetic flux.