JPH0363950A - Magneto-optical recording system - Google Patents

Abstract

PURPOSE:To increase the erasing ratio of old signals at the time of overwriting and to decrease imperfect erasing by presetting the magnetization state of a recording layer in such a manner as to attain the same recording magnetization state as the recording magnetization state obtd. when irradiated with a laser beam of a low-intensity level. CONSTITUTION:The magnetization of the respective magnetic films 11, 12 of the recording layer is so set as to be the same in the magnetization direction shown when recording is executed by the laser beam of the low-intensity level 2. Since the magnetization direction of the respective magnetic layers is the same as the initial magnetization direction of the magneto-optical recording medium 14, recoding magnetic domains 11, 12 are not formed. The magnetization direction of the respective magnetic layers 11, 12 of the recording layer exhibited when the recording is executed by irradiation of the laser beam of the high-intensity level 3 is different from the initial magnetization direction of the magneto-optical recording medium 14 and, therefore, the recording magnetic domains 11, 12 are formed. The recording magnetic domains are, therefore, eventually formed only by the laser beam of the high-intensity level on the magneto-optical recording medium 14. Namely, the probability that the imperfect erasing arises is only in the case in which the laser beam of the high-intensity level is cast. The imperfect erasing is prevented in this way and the erasing ratio is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to magneto-optical recording, and particularly to a magneto-optical recording system that allows overwriting.

[Conventional technology]

Magneto-optical recording media are capable of recording, reproducing, and erasing information. In recent years, a new magneto-optical recording method has been proposed using this magneto-optical recording medium to enable overwriting. Magneto-optical recording systems that allow overwriting are broadly divided into two types: magnetic field modulation and optical intensity modulation. Examples of the former are JP-A-61-188758 and 63-204532.
An example of the latter is JP-A-62-175948,
63-156752, etc.

When comparing the two methods, the latter method is more advantageous because it is capable of high-speed modulation and high-speed recording, and can have a structure in which two magneto-optical recording media are bonded together. .

[Problem to be solved by the invention]

However, the above-mentioned conventional technology does not take into consideration the overwrite characteristic, that is, when a new signal is overwritten on an old signal, the old signal is sufficiently erased. ) occurred.

The present invention prevents unerased areas and increases the erasure ratio (suppression ratio of old signals).
The aim is to improve

[Means to solve the problem]

In order to achieve the above object, the present invention comprises two or three or more magnetic layers having perpendicular magnetic anisotropy and comprising a rare earth element and a transition metal as the S layer of the magneto-optical recording medium. , a magnetic coupling force is generated between adjacent layers due to exchange coupling.

The magnetic layer made of rare earth and transition metal is T b
-F'e, Tb-F, e-Go,
G d -T b -F e , G d -F e
-Co, N d -'l' b -F e -Go
, or a small amount of A flooding, Ni, Nb.

A material to which Rh, Pt, Cr, etc. are added is used.

A magneto-optical recording medium is constructed by providing such a magnetic layer and a protective layer on a substrate to prevent corrosion of the magnetic layer and improve the Kerr rotation angle. Here, the protective layer is S
in, SiN, AQN.

Dielectric films such as A Q x Oa, Aft, Ta, T
i.

A metal film such as Au or Ag is used.

Recording or overwriting is performed by irradiating such a magneto-optical recording medium with an intensity-modulated laser beam. As shown in FIG. 4, the intensity-modulated laser beam takes a binary state of a low intensity level and a high intensity level during recording. However, the intensity level of the reproduction light is set even lower than the low intensity level during recording. Further, if necessary, other intensity levels may be provided at the rise and fall of the low intensity level and the high intensity level.

The ratio of the irradiation time of the low-intensity level laser light and the high-intensity level laser light is usually set to be larger.

That is, at a low intensity level, information is erased, and at a high intensity level, information is recorded. When overwriting, the 6-magneto-optical recording medium rewrites the old signal by making recording at a low intensity level correspond to, for example, "017" recording, and making recording at a high intensity level correspond to "1". After fabrication, first, the magnetization of each magnetic layer of the recording M is directed in a desired direction. For this purpose, an electromagnet or a permanent magnet may be used, or a drive device for a magneto-optical recording medium may be used. At this time, the magnetization of each magnetic film of the recording layer is set to be the same as the magnetization direction shown when writing (or erasing or overwriting) with a low-intensity laser beam.

[Effect]

The direction of magnetization of each magnetic layer in the recording layer when recording (or erasing, or overwriting) by irradiating low-intensity laser light is the same as the initial magnetization direction of the magneto-optical recording medium, so recording is not possible. No magnetic domains are formed. The magnetization direction of each magnetic layer of the recording layer when recording is then performed by irradiation with a high-intensity laser beam is different from the initial magnetization direction of the magneto-optical recording medium, so that recording magnetic domains are formed. Therefore, in the magneto-optical recording medium, recording magnetic domains are formed only by laser light at a high intensity level. That is, there is a possibility that unerased portions will occur only when laser light of a high intensity level is irradiated.

The above reason will be further explained below.

After producing a magneto-optical recording medium, an unsaturated magnetized region exists in the state as it is, so it is necessary to magnetize it. At this time, the direction of magnetization of the magneto-optical recording medium after magnetization is as shown in Table 1: ■ Direction of magnetization shown when recording is performed by irradiation with laser light at a low intensity level, ■ Direction of magnetization shown when recording is performed by irradiation with laser light at a high intensity level There are three magnetization directions: (1), (2), and (3) magnetization directions shown when recorded by irradiation.

Now, as shown in FIG. 4, the intensity-modulated laser beam 4 has a reproduction light intensity level of 1. It has a low intensity level of 2° and a high intensity level of 3.

Table 1 When this laser beam 4 is irradiated onto magneto-optical recording media (1), (2), and (2) having the respective magnetization directions shown in Table 1, the results are shown in Table 1. That is, in the case of ■, an inverted magnetic domain with a magnetization direction different from the magnetization direction is formed when irradiated with a laser beam at a high intensity level, and conversely, in the case of ■, an inverted magnetic domain is formed when irradiated with a laser beam at a low intensity level. Ru. Moreover, in the case of (2), an inverted magnetic domain is formed when laser light of any intensity level is irradiated.

Such situations are shown in FIGS. 1 to 3.

FIG. 1 shows the case (2) above. The magnetic domain 5 formed by laser beam irradiation at a high intensity level has one surrounding unrecorded area 7.
The direction of magnetization is different from that of . Figure 2 shows the case of ■. The magnetic domain 6 formed by laser beam irradiation at a low intensity level is different from the magnetization direction of the unrecorded area 7 . In this case, reflecting the temperature distribution of the magneto-optical recording medium during laser beam irradiation, magnetic domains 5 formed by low-intensity laser beam irradiation are formed around the magnetic domains 5 formed by high-intensity laser beam irradiation. A magnetic domain 6 exists, and the width of the magnetic domain becomes wide in that part. Therefore, this part remains after overwriting. A similar phenomenon also occurs in the case of (2) shown in FIG. In the case of ■ shown in FIG. 1, since the magnetic domain 6 formed by low-intensity laser light irradiation does not exist in the first place, there is no remaining area after overwriting.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 5, on a glass substrate 8 with a diameter of 130 m, an ultraviolet curing resin 9 having a guide groove of 1.6 μm is placed about 3 times.
0pm was set. On top of this, a silicon nitride film 10 of 85 OA is applied.
, Tb-Fe-Co magnetic film 11 of 600λ, Tb-Dy
-Fe-Go magnetic earthwork by 21,500 people, silicon nitride film 13 by 1,000λ.

Manufactured by sputtering. Silicon nitride film 10.
A silicon target was used for manufacturing No. 13, and the film was formed in a mixed gas atmosphere of argon gas and nitrogen gas. Tb-
Fa-Co magnetic film 11 and "l'b'-D y -F e
-Co magnetic film 12 is produced by using a composite target in which a Tb chip and a CO chip, or a 1゛b chip, a lay chip, and a CO chip are pasted on an Fe disk.
The film was formed in an argon gas atmosphere.

When the temperature change of the coercive force Hc of each magnetic film was measured, Tb
- Compensation temperature T c o m on the Fe-Go film at 160°C
p and Curie temperature T c at 190°C, '1' b -D y -F e -Co
At magnetic film 12. It was found that it had 'rc o m p at 180°C and Tc at 290°C. Therefore, in both magnetic films, the magnetic moment of the rare earth element is at room temperature (20°C).
is dominant.

A magnetic field of 20 KOe is applied to this magneto-optical recording medium 4,
Each magnetic film was magnetized at room temperature so that the magnetization was directed toward the figurine or the substrate.

After this, as shown in FIG. 6, the magneto-optical recording medium 14 is attached to the spindle 23, and the motor 20
Rotated at rpm. On the other hand, the laser beam 16 emitted from the semiconductor laser 15 is made into parallel light by a collimating lens 17, focused by a focusing lens 18, and irradiated onto the magneto-optical recording medium 14. At this time, the laser beam 16 is made to enter from the glass substrate 8 side. Furthermore, a permanent magnet 19 for generating a bias magnetic field is installed near the medium irradiated with the laser beam 16, and the side facing the magneto-optical recording medium 4 is set as the north pole. Further, at one end of the yoke 21, T b -
A permanent magnet 22 for an initialization magnetic field for aligning the magnetization of the D y -F e -Co film in one direction.

The side facing the magneto-optical recording medium 14 was set as the north pole.

When the semiconductor laser 5 was driven to irradiate pulsed light with an intensity as shown in FIG. 4 and a 1.4 MHz signal was recorded, a C/N (carrier-to-noise ratio) of 45 dB was obtained. After this, when the 2 MHz signal was overwritten, a C/N of 44 dB was obtained, and the 1,4 MHz signal was
The old signal of z was OdB.

That is, the cancellation ratio was 45 dB.

On the other hand, when the direction of magnetization of the magneto-optical recording medium 14 is set to various other states and a 1.4 MHz signal is recorded and then a 2 MHz signal is overwritten, the C
/N and the erasure ratio are shown in FIG.

As is clear from these results, the maximum erasure ratio is obtained in the case (2), that is, when the magnet is magnetized from the clay figurine toward the substrate side. The magnetization direction at this time matches the direction of magnetization of each magnetic film caused by irradiation with the low intensity level 2 laser light. In addition, in the case of ■ and ■ in Figure 1, the magnetization direction does not match the direction of magnetization of each magnetic layer (direction of ■) caused by irradiation with low intensity level 2 laser light, and the erasure ratio is small. It has become.

h-', the optimum magnetization direction is not limited to the above-mentioned direction. That is, the polarity of the permanent magnet 19 for bias magnetic field generation and the polarity of the permanent magnet 22 for initialization magnetic field are
When the side facing the magneto-optical recording medium 14 is the S pole,
Optical magnetism tc! @The direction of magnetization of the medium may be such that the magnetization is directed from the substrate side toward the figurine. This direction is the direction of magnetization of each magnetic film caused by irradiation with the low intensity level 2 laser beam.

〔Effect of the invention〕

As explained in detail above, according to the present invention, in the magneto-optical recording method in which information is recorded or overwritten by irradiation with a laser beam whose intensity is modulated in two stages: a low intensity level and a high intensity level, By setting the magnetization state of the recording layer of the magneto-optical recording medium in advance to be the same as the recording magnetization state obtained by irradiating the magneto-optical recording medium with a low-intensity laser beam, the old signal can be removed during overwriting. It is possible to increase the erasure ratio and significantly reduce the amount of unerased material.

[Brief explanation of drawings]

Figure 1 is a model diagram of the recording state in the magneto-optical recording system of the present invention, Figures 2 and 3 are model diagrams of the recording state in other magneto-optical recording systems, and Figure 4 is the intensity of the laser beam. FIG. 5 is a cross-sectional view of a magneto-optical recording medium, FIG. 6 is a front view of a magneto-optical recording device according to an embodiment of the present invention, and FIG. 7 is a signal waveform diagram showing modulation.
The figure is a diagram showing the relationship between the magnetization direction and the erasure ratio. l...Reproducing light level, 2...Low intensity level, 3...
- High intensity level, 5...Magnetic domain formed by laser light irradiation at a high intensity level, 6...Magnetic domain formed by laser light irradiation at a low intensity level, 7...Unrecorded area, 8...・Substrate, 11.12... Magnetic film, 15...
Semiconductor laser, 19.22...Permanent magnet, 20...
motor. Figure 81 Figure 2 Figure 4 Figure 5 Figure 81 Exclusion/112 Jlt Sex Warm 350-

Claims (1)

[Claims] 1. A substrate, a recording layer formed on the substrate in which two or three or more magnetic layers having perpendicular magnetic anisotropy and made of rare earth and transition metal are laminated, and a protection made of dielectric or metal. Information can be recorded or overwritten by using a magneto-optical recording medium having a layer and by irradiating the magneto-optical recording medium with laser light whose intensity is modulated in two stages: a low intensity level and a high intensity level. In the magneto-optical recording method, the magnetization state of the recording layer of the magneto-optical recording medium is set in advance to be the same as the magnetization state obtained by irradiating the magneto-optical recording medium with a low-intensity laser beam. A magneto-optical recording method characterized by: