JPH0814900B2 - Writing method to magneto-optical recording medium - Google Patents

Description

The present invention relates to a writing method in which a magneto-optical recording medium such as a magneto-optical disk has a high-speed overwriting function.

(Prior Art) Conventionally, recording (writing of information) on a magneto-optical disk
Is applied to a uniformly magnetized optical recording medium (a perpendicularly magnetized thin film such as a Tb-Fe thin film) while applying a bias magnetic field below the anisotropic magnetic field in the opposite direction to the magnetization and irradiating a laser beam to control the temperature of the irradiation area. Utilizing the fact that the magnetization is reversed in the direction of the bias magnetic field in the process of cooling the medium after the temperature has been raised above the Curie temperature, and information is recorded as a series of magnetization reversals by turning the laser beam on and off. .

(Problems to be Solved by the Invention) In this method, when new information is recorded again in a region that has been once recorded, the medium is heated by irradiating a continuous laser beam in a bias magnetic field in the opposite direction so that all the magnetization is eliminated. It was necessary to align in such a direction (this is called the erasing process). That is, it is necessary to record again after erasing,
By recording another information on the pre-recorded area like the writing of information in normal magnetic recording, the previous information is not automatically erased, which is an obstacle to speeding up the access speed. Was there.

An object of the present invention is to provide a method of writing on a magneto-optical recording medium such as a magneto-optical recording medium such as a magneto-optical disk, which has an access speed equivalent to that of magnetic recording and can write new information without passing through an erasing process. To provide.

(Means for Solving Problems) In order to achieve the above object, the present invention has a perpendicular magnetization thin film (first medium) having a high Curie temperature and an anisotropic magnetic field larger than the anisotropic magnetic field of this thin film. A magneto-optical recording medium having a two-layer structure with a perpendicularly magnetized thin film (second medium) having a Curie temperature lower than that of the thin film is used, and information is recorded on the first medium as a sequence of magnetization reversal using a magnetic recording head. Then, the recording region is subsequently heated by the light beam to the Curie temperature of the second medium or higher, and the magnetization reversal information of the first medium is transferred to the second medium in the process of cooling the second medium.

(Operation) According to the present invention, it is possible to write new information at the same access speed as that of magnetic recording and without passing through the erasing process.

(Example) FIG. 1 schematically shows a magneto-optical disk used in the method of the present invention. In the figure, reference numeral 11 is a magneto-optical disk substrate, in which a 2p agent, which is an ultraviolet curable resin, is applied on a glass disk, and concentric track grooves are formed by using the photolithographic technique. 77% on this substrate 11 using the sputtering method
After forming a Fe-23% Tb thin film (second medium) 12 to a thickness of 600 Å, continue to deposit 80% Co-20% Cr thin film (first medium) 13 to a thickness of 1000 Å
The magneto-optical disk medium 10 was formed with a large thickness. That is, the first medium
13 is composed of a perpendicular magnetization thin film having a high Curie temperature, the second medium 12 has an anisotropic magnetic field larger than that of the first medium 13, and the Curie temperature is lower than that of the first medium 13. Become. Reference numeral 14 denotes an optical head, which transmits a light beam 15 of laser light through the glass substrate 11 to the optical disk medium 10.
The light is focused on the top and the tilt of the polarization due to the Kerr effect of the reflected light is detected. Reference numeral 16 is a magnetic recording head. In the present embodiment, the magnetic recording head 16 has a main magnetic pole excitation type structure for the purpose of perpendicular magnetic recording, but in principle perpendicular magnetic recording is possible with either a ring type or an auxiliary magnetic pole excitation type. Is. The width of the main pole is 300 μm, which is much larger than the groove width of the substrate (1.6 μm). However, this difference in size is not a problem in principle by using the method of the present invention. The write operation mechanism according to the present invention will be described below.

When the magneto-optical disk medium 10 is rotating in the arrow direction, information is first recorded on the Co—Cr thin film 13 by the magnetic field generated from the main magnetic pole of the head 16. This process is the same as the writing process in conventional magnetic recording. The recording magnetic field at this time is about 4000 Oe, and the coercive force (Hc =
Since it is sufficiently larger than 7000 Oe), the Co-Cr thin film 13 is completely magnetized, but since it is smaller than Hc (15 k Oe) of the Tb-Fe thin film 12, the Tb-Fe thin film 12 is not magnetized. Information recording is completed through the following steps. Subsequently, the medium 10 is moved under the optical head 14 and heated by the light beam 15. The power of the light beam 15 is 10 mW, and the maximum temperature of the irradiated portion is estimated to be 150 ° C. Since the Curie temperature of the Tb-Fe thin film 12 is about 125 ° C, it easily becomes non-magnetic, whereas the Curie temperature of the Co-Cr thin film 13 is as high as about 600 ° C, so the magnetization information remains without being destroyed. A leakage magnetic field is generated from the bit. Next, when the medium moves and the temperature of the region irradiated with the light beam 15 is lowered, the magnetization of the Tb-Fe thin film 12 is aligned in the magnetic field direction generated from the Co-Cr thin film 13, so that Co- The magnetization information written in the Cr thin film 13 is transferred to the Tb-Fe thin film 12. That is, magnetic information is recorded on the Tb-Fe thin film 12 in the track having the width of the light beam 15.

The reproduction of the written information can be read as a difference in the inclination of the polarization plane of the reflected light of the light beam 15. It is necessary to set the laser power at this time so that the medium temperature is usually sufficiently lower than the Curie temperature of the Tb-Fe thin film 12. In this embodiment, the power at the time of reading is 2 mW.
Overwriting on the medium 10 can be achieved by writing new information on the Co—Cr thin film 13 by the magnetic head 16. Co-C
r Overwriting on the thin film 13 is usually accompanied by an unerased component of about -40 dB, but it can be said that this value is extremely small. At this time, since Hc of both media 12 and 13 is Tb-Fe >> Co-Cr, the magnetic field for overwriting magnetizes only the Co-Cr thin film 13 and does not affect the Tb-Fe thin film 12. Next, a specific example will be described.

The first medium of the first rotating disk medium 10 (Co-C
10 μm bit is written to (r thin film) 13 and then the light beam (10 mW) is focused to a diameter of 1 μm to create a recording area.
When heated to 150 ° C., the recording bit of the Co—Cr thin film 13 was transferred to the second medium (Tb—Fe thin film) 12. The SN ratio of the reproduced signal of this recorded bit was 55 dB. Next, a magnetic head 16 was used to write a bit with a bit length of 15 μm in the same area, and after that, the signal was reproduced by heating with a light beam 15 to transfer magnetic information, and an SN ratio of 45 dB was obtained. It was

That is, according to the present invention, the recorded information can be continuously written on the Co—Cr thin film 13, so that overwriting can be performed without the erasing process. In addition, Co-Cr by the magnetic head 16
Since the writing process on the thin film 13 does not go through a low speed mechanism such as heat diffusion, in principle, high speed writing (several + MHz) equivalent to magnetic recording can be realized. On the other hand, compared with magnetic recording, since a light beam is used in the magnetic transfer process and the reading process, there is an advantage that narrow track recording of the μm order and its servo can be realized. The track servo of the write magnetic head is not particularly necessary, and there is also an advantage that writing can be performed with a head having a wide width. Since recorded information is detected by irradiating light from the glass substrate side, there is also an advantage that dust and defects on the medium are less affected.

The first and second media in this example are examples of perpendicular films having a high Curie temperature and a low Curie temperature and a high anisotropic magnetic field, respectively. In addition to this, the first medium is a perpendicular magnetic recording medium. Barium ferrite film under consideration, Co
The second medium is a Mn-Bi alloy film, a YIG film, a Co film, which is a medium for magneto-optical recording, such as a film obtained by adding various additive elements to a -Cr alloy.
It is considered that a ferrite film or the like can be applied.

(Effects of the Invention) As described above, according to the present invention, as a magneto-optical recording medium capable of overwriting, Tb-on a perpendicularly magnetized thin film such as a Co--Cr alloy.
The magnetic recording head writes information on the Co-Cr thin film by laminating films with large magneto-optical effect such as Fe thin film, heating the Tb-Fe thin film with a laser beam, and magnetizing the Co-Cr thin film. Since information is transferred to the Tb-Fe thin film, high-speed overwriting can be achieved. That is, since the drive frequency of the magnetic recording head sufficiently follows up to several tens of MHz,
Upper limit of writing speed recorded by light beam (several MH
Compared with z), there is an advantage that the writing speed does not need to be servoed at the time of writing to the Co-Cr thin film, while at the same time, the speed can be remarkably increased. The track width of the magneto-optical recording disk is 1 to 2 μm, while the track servo error of the current magnetic recording head is about 1 μm. Therefore, it is necessary to simply write a signal to the magneto-optical recording medium using the magnetic recording head. In that case, the problem of the track servo becomes a very serious hindrance factor, but the present invention has a remarkable effect that there is no such technical difficulty.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a method of writing on a magneto-optical disk according to the present invention. In the figure, 11 is a magneto-optical disk substrate, 12
Is the second medium (80% Fe-20% Tb thin film), 13 is the first medium (80% Fe-20% Tb thin film)
% Co-20% Cr thin film), 14 is an optical head, 15 is a light beam, 16
Is a magnetic recording head.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Iwahata Hatakeyama, No. 162 Shirahane, Shirahata, Tokai-mura, Naka-gun, Ibaraki Prefecture, Ibaraki Prefectural Telecom Research Institute (72) Inventor, Tetsuo Iijima Tokai-mura, Oita, Shirokata, Shirone 162, Nippon Telegraph and Telephone Corporation, Ibaraki Research Institute of Telecommunications (56) References JP-A-58-57645 (JP, A) JP-A-58-50639 (JP, A)

Claims (2)

[Claims] 1. A perpendicular magnetization thin film (first medium) having a high Curie temperature and an anisotropic magnetic field larger than the anisotropic magnetic field of the thin film and having a Curie temperature lower than the thin film (second medium). ) And a magneto-optical recording medium having a two-layered structure, the information is recorded on the first medium as a sequence of magnetization reversal using a magnetic recording head, and the recording area is subsequently curried on the second medium with a light beam. A method for writing on a magneto-optical recording medium, characterized in that the magnetization reversal information of the first medium is transferred to the second medium in the process of heating the medium to a temperature or higher and cooling the second medium. 2. A Co—Cr alloy thin film as the first medium,
A rare earth / transition metal alloy thin film (rare earth element includes at least one of Tb, Gd, Nd, and Dy, and a transition metal includes at least one of Fe, Co, and Ni) as the second medium. The method for writing on a magneto-optical recording medium according to claim 1, which is used.