JPH0536147A - Magneto-optical recording method - Google Patents

Abstract

PURPOSE:To attain overwriting of high reliability with a single laser beam and single bias magnetic field or without the bias magnetic field. CONSTITUTION:The magneto-optical recording medium constituted by providing a recording layer 3 consisting of a ferromagnetic film which has a compensation temp. between room temp. and Curie temp. and exhibits perpendicular magnetic anisotropy on a base 1 and further, providing a layer 4 consisting of a high permeability material adjacent to this recording layer 3 is used. Recording and erasing are executed by changing only the irradiation conditions (spot diameter, pulse width, laser power, single pulse or continuous pulses, etc.) of the light with which the magneto-optical recording medium is irradiated, by which the overwriting is attained.

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 method.

[0002]

2. Description of the Related Art In recent years,
As a rewritable optical recording medium, a magneto-optical recording medium utilizing the magneto-optical effect has been energetically researched and developed, and some have come to practical use. This magneto-optical recording medium has the advantages of large-capacity and high-density recording, non-contact recording / playback, easy access, and overwriting (overwriting), so that it can be used for document information files, video / still image files, and computers. It is expected to be used for memory etc. In order to make a magneto-optical recording medium a recording medium having a performance equal to or higher than that of a magnetic disk, there are some technical problems, and one of the main ones is an overwrite technique. The currently proposed overwrite technology is roughly classified into a magnetic field modulation method and an optical modulation method (multi-beam method, two-layer film method, etc.) depending on the recording method.

The magnetic field modulation method is a method in which the polarity of an applied magnetic field is reversed according to recording information to perform recording. In this method, since the reversal of the magnetic field must be performed at high speed, it is necessary to use a flying type magnetic head, and it is difficult to exchange the medium.

On the other hand, the optical modulation system is a system for recording by irradiating the irradiation laser beam on / off or by modulating the intensity according to the recording information. Of these methods, the multi-beam method is a pseudo-overwrite method in which the direction of the magnetic field is reversed for each rotation and recording / erasing is performed for each track by using two or three laser beams, but the device configuration is complicated. However, there is a drawback that the cost is increased. Further, the two-layer film system is one in which the recording layer of the magneto-optical recording medium is a two-layer film in order to achieve overwrite.
It is disclosed in Japanese Patent No. 175948. The system described in the publication uses a magneto-optical recording medium having a two-layer recording layer including a memory layer made of TbFe and an auxiliary layer made of TbFeCo, for example. It is intended to realize overwriting by irradiating laser beams having different powers and applied powers. That is,
In this system, prior to recording, the magnetization of the auxiliary layer is aligned in one direction with an initializing magnetic field in advance, and the medium temperature T is T> Tc ₂ (Tc ₂ is the Curie temperature of the auxiliary layer) by irradiation with a high-power laser beam. Recording is performed by raising the temperature to a temperature, applying a recording magnetic field (direction opposite to the initialization magnetic field) to reverse the magnetization of the auxiliary layer, and transferring the magnetization to the memory layer when the medium is cooled. Further, the medium temperature is raised to a temperature of Tc ₁ <T <Tc ₂ (Tc ₁ is the Curie temperature of the memory layer) by irradiating a low-power laser beam, and the magnetization direction of the auxiliary layer is transferred to the memory layer. To erase. Therefore, this method requires an initialization magnet.
Since temperatures near c ₁ and Tc ₂ are used for recording and erasing, there is a problem that recording sensitivity is deteriorated.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a magneto-optical recording method capable of reliably overwriting with a single laser beam.

[0006]

In order to achieve the above object, according to the present invention, a recording layer made of a ferromagnetic film having a compensation temperature between room temperature and Curie temperature and exhibiting perpendicular magnetic anisotropy is provided. It is possible to perform overwritable magneto-optical recording by using a magneto-optical recording medium in which a layer made of a high magnetic permeability material is provided adjacent to the magneto-optical recording medium and changing only the irradiation condition of the light with which the magneto-optical recording medium is irradiated. A featured magneto-optical recording method is provided.

The present invention will be described in detail below with reference to the drawings. First, a magneto-optical recording medium used in the method of the present invention will be described. Basically, a magnetic layer made of a high magnetic permeability material is adjacent to a recording layer made of a ferromagnetic film having a large coercive force and exhibiting perpendicular magnetic anisotropy. It is configured by stacking. FIG. 1 shows an example of the structure of such a magneto-optical recording medium.

This recording medium is made of glass, plastic,
SiO ₂ on the transparent support 1 made of ceramics,
Protective film 2 made of SiO, Si ₃ N _4, etc. (film thickness 100-
5000 Å) is provided, on which room temperature and Curie temperature Tc
A recording layer 3 made of a ferromagnetic film having a compensation temperature Tcomp and exhibiting perpendicular magnetic anisotropy is provided between the two. The recording layer 3 is Tb-F
e, Gd-Fe, Gd-Tb-Fe, Tb-Dy-F
e, Gd-Dy-Fe, Tb-Fe-Co, Gd-Fe
-Co, Dy-Fe-Co, Tb-Dy-Fe-Co,
Rare earth-transition metal based amorphous films such as Gd-Tb-Fe-Co and Gd-Dy-Fe-Co, Co-Pt, C
The film is made of a polycrystalline film such as o-Cr and has a film thickness of 100Å to 5000Å. A magnetic layer made of a high magnetic permeability material (hereinafter referred to as a high magnetic permeability layer) is provided on the recording layer 3. The high magnetic permeability layer 4 is made of a film of permalloy, Mo permalloy, supermalloy, Mn-Zn ferrite, Ni-Zn ferrite, Cu-Zn ferrite, etc., and has a film thickness of 1
It should be between 00Å and 10000Å. S on the high magnetic permeability layer 4
A protective film 5 (film thickness 100Å to 5000Å) made of i ₃ N ₄ , SiO ₂ , SiO or the like is provided. Each film is sputtered,
It can be formed by a vapor deposition method, an ion plating method, or the like.

The layer structure of the magneto-optical recording medium used in the present invention is not limited to that shown in FIG. 1, and various modifications and changes can be made. For example, a reflective film is provided on the protective film 5. Alternatively, the protective films 2 and 5 may be appropriately removed.

Next, the magneto-optical recording method of the present invention will be described. The magneto-optical recording method of the present invention realizes overwriting by changing only the irradiation condition of irradiation light using the above-mentioned magneto-optical recording medium. As the external magnetic field, a small bias magnetic field of about several Oe to 300 Oe may be applied during recording or erasing, or may not be applied depending on the case. The irradiation conditions to be changed include the spot diameter of the irradiation light, the pulse width, the irradiation power, single pulse or continuous pulse, and the like. These may be changed alone, or two or more kinds may be changed.

Here, a specific example of the method of changing the irradiation condition will be described, but of course, the present invention is not limited to the example. First, as a first example, the direction of the magnetic domain of the portion to be recorded is changed from upward to downward, or
When switching from downward to upward, there is a method of changing the pulse width of irradiation light from other times. The recording and erasing operations using this method will be described below.

FIG. 2 shows the results of experiments conducted by the present inventors. The pulse width was changed to a rare earth-transition metal type amorphous magnetic film having a compensation temperature Tcomp of room temperature or higher (laser irradiation energy was kept constant). It shows the change of the radius of the reversed magnetic domain (when the temperature is returned to room temperature) and the radius of the area heated to the Curie temperature Tc or higher when laser irradiation is performed. Thus, it can be seen that the size of the written magnetic domain differs by changing the laser irradiation conditions. Further, it can be seen that there are irradiation conditions that cannot be written. Therefore, in this example, the magneto-optical recording medium having the above-described configuration is used, and a small bias magnetic field Hex is applied (need not be added) in the saturation direction of the magnetization of the recording layer, and the irradiation condition A in FIG. Is recorded and erased by combining the condition B) (the condition that the reversed magnetic domain is small) with B. The principle is shown in FIG. In FIG. 3, the case where a domain wall is formed is represented as “1”, and the case where a new domain wall is not formed by extending the previous magnetic domain is represented as “0”. First, as shown in (a), laser light is first irradiated under the A irradiation condition to form a large inverted magnetic domain, and "1" is recorded. After that, when recording "0", as shown in (b) and (c), the laser beam is irradiated under the B irradiation condition such that a part of the previous magnetic domain overlaps the irradiation spot. At that time, a reverse magnetic domain having a small magnetic domain before the magnetic domain is formed in the central portion, and the magnetic domain extends to the small magnetic domain so that "0" recording can be performed.
When this is repeated and laser light is continuously irradiated under the B irradiation condition, the previous magnetic domain is expanded more and more. Then, when it is desired to cut the magnetic domain, that is, to make a new magnetic domain wall and perform "1" recording, irradiation is performed under the A irradiation condition so that a part of the previous magnetic domain overlaps as shown in (d). Then, since a reversed magnetic domain having a large previous magnetic domain is formed, the previous magnetic domain cannot be extended and stops there, and "1" recording can be performed.

In the above, when the direction of the magnetic domain of the portion to be recorded is switched, the pulse width of the irradiation light is changed from that at other times. In this case, the irradiation condition is changed when the direction of the magnetic domain is switched. Some examples of the method of changing are shown in FIG. In the figure, (a) recording information signal, (b)-
(K) is an example of each irradiation method.

FIG. 5 shows another method (3) for changing the irradiation condition.
It is an explanatory view of (value overwrite). In this method, in addition to the irradiation conditions of A and B of the first example, the irradiation condition of A ', which completely erases the reversed magnetic domain, is used to perform recording under the irradiation conditions of A and B. Erasing is performed under the irradiation condition of B.

FIG. 6 is an explanatory view of another method (binary overwrite) for changing the irradiation condition. In this method, the conditions A and A'in the method of FIG. 5, that is, the irradiation condition A for forming the reversed magnetic domain and the irradiation condition A'for erasing the reversed magnetic domain are used,
Recording is performed under the A irradiation condition and erasing is performed under the A ′ irradiation condition.

In the method of the present invention, overwriting can also be realized by changing the pulse width and irradiation power, combining a single pulse and a continuous pulse, or combining DC and a pulse.

In the method of the present invention, since the magneto-optical recording medium having the above-mentioned structure is used, the demagnetizing field from the surrounding magnetization acting on the portion irradiated with the laser as shown in FIG. 1 is reluctance via the high magnetic permeability layer. Since it effectively works by reducing (magnetic resistance), it is possible to widen the margin of irradiation conditions for recording and erasing and improve the reliability of overwriting.

[0018]

EXAMPLES The present invention will now be described in more detail by way of examples, which should not be construed as limiting the invention thereto. Polycarbonate substrate with groove (diameter 13
The following films were sequentially laminated in a vacuum on the substrate (0 mm) by an rf magnetron sputtering method to obtain a recording medium. Protective film: Si ₃ N ₄ (1000Å) recording _{film:. Tb 0 23 (..} Fe 0 9 Co 0 1) 0 77 (1000Å) high permeability _{film:... Fe 0 22 Ni} 0 78 (2000Å) Protection Membrane: Si ₃ N ₄ (1000Å)

The compensation temperature Tcomp and the Curie temperature Tc of the recording layer were as follows. Tcomp = 100 ℃ Tc = 200 ℃

The recording medium obtained as described above was used at a linear velocity of 10
Driving at m / sec, applying an external magnetic field Hex = 100 Oe, and changing the laser irradiation conditions during recording, erasing and reproducing as described below to record / reproduce a signal of 1 MHz, An evaluation was made. Laser power during recording: 8 mW Pulse width during recording: 100 ns Laser power during erasing: 14 mW Pulse width during erasing: 50 ns Laser power during reproducing: 1 mW As a result, the C / N ratio was 48 dB. Further, as a result of overwriting on the same recording medium under the same conditions at a recording frequency of 2 MHz, the C / N was 48 dB, which was 2 dB better than when the high magnetic permeability layer was not provided.

[0019]

According to the present invention, since the magneto-optical recording medium provided with the high magnetic permeability layer adjacent to the recording layer is used and the overwriting is performed only by changing the irradiation condition of the irradiation light, the overwriting is performed. It is possible to improve the reliability of writing and expand the margin of the irradiation condition for recording and erasing.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a layer structure of a magneto-optical recording medium according to the present invention.

FIG. 2 is a diagram showing a change in radius of an inverted magnetic domain and a radius of an area heated to a Curie temperature Tc or higher when laser irradiation is performed with a pulse width changed on a magnetic film having specific magnetic characteristics. ..

FIG. 3 is a diagram illustrating the principle of recording and erasing in an example recording method according to the present invention.

FIG. 4 is a diagram showing an example of a method of changing an irradiation condition when switching the direction of a magnetic domain from other times.

FIG. 5 is an explanatory diagram of another example in which irradiation conditions of irradiation light are changed.

FIG. 6 is an explanatory diagram of yet another example in which the irradiation conditions of irradiation light are changed.

[Explanation of symbols]

 1 Support 2, 5 Protective Layer 3 Recording Layer 4 High Permeability Layer

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Ms. Kurosawa 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (1)

Claim: What is claimed is: 1. A layer made of a high magnetic permeability material is provided adjacent to a recording layer made of a ferromagnetic film having a compensation temperature between room temperature and Curie temperature and exhibiting perpendicular magnetic anisotropy. A magneto-optical recording method in which overwritable magneto-optical recording is performed by using the provided magneto-optical recording medium and changing only the irradiation condition of the light with which the magneto-optical recording medium is irradiated.