JP2796602B2 - Magneto-optical recording method - Google Patents

Description

The present invention relates to an overwritable magneto-optical recording method.

[Problems to be solved by conventional technology and invention]

In recent years, as a rewritable magneto-optical medium, a magneto-optical recording medium utilizing a magneto-optical effect has been vigorously researched and developed.
Some have been put to practical use. This magneto-optical recording medium has advantages such as large-capacity, high-density recording, non-contact recording / reproducing, easy access, and overwriting (overwriting). It is expected to be used for memories and the like. There are several technical issues in using a magneto-optical recording medium as a recording medium having performance equal to or higher than that of a magnetic disk, and one of the major ones is an overwrite technique. Currently proposed overwrite technologies are roughly classified into a magnetic field modulation system and a light modulation system (multi-beam system, two-layer film system, etc.) according to a recording method.

The magnetic field modulation method is a method of performing recording by inverting the polarity of an applied magnetic field according to recording information. In this method, the magnetic field must be reversed at a high speed, so that it is necessary to use a floating type magnetic head, and it is difficult to exchange the medium.

On the other hand, the light modulation method is a method of performing recording by turning on / off or modulating the intensity of an irradiation laser beam according to recording information. Of these methods, the multi-beam method is a pseudo overwrite method in which recording / erasing is performed for each track by using two or three laser beams and inverting the direction of the magnetic field for each rotation, but the device configuration is complicated. Disadvantages such as cost increase. In the two-layer film system, the recording layer of the magneto-optical recording medium is formed as a two-layer film to achieve overwriting, and is disclosed in, for example, JP-A-62-175948. The method described in the publication is, for example, a two-layered structure of a memory layer made of TbFe and an auxiliary layer made of TbFeCo.
After initialization is performed using a magneto-optical recording medium having a layered recording layer, overwriting is attempted by applying an external magnetic field and irradiating a laser beam having a different power. That is, in this method, prior to recording, the magnetization of the auxiliary layer is aligned in one direction by an initialization magnetic field in advance, and a medium laser is irradiated with a high-power laser beam to raise the medium temperature T to T> T _C2 (T _C2 is the Curie temperature of the auxiliary layer. ), The temperature of the auxiliary layer is reversed by applying a recording magnetic field (in the direction opposite to the initialization magnetic field), and the magnetization is transferred to the memory layer when the medium is cooled. Then, the medium temperature is increased by irradiating a low-power laser beam to a temperature where T _C1 <T <T _C2 (T _C1 is the Curie temperature of the memory layer), and the magnetization direction of the auxiliary layer is transferred to the memory layer. Is erased.
For this reason, this method requires two external magnetic fields, a recording magnetic field and an initialization magnetic field, which makes it difficult to reduce the size of the drive device. Further, the recording layer of the magneto-optical recording medium used is a two-layer film. Therefore, there were problems such as difficulty in media design.

The present invention solves the above-mentioned drawbacks of the prior art, and provides a magneto-optical recording method that enables overwriting with a single laser beam and a single magnetic field using a single-layer magneto-optical recording medium. With the goal.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, a magneto-optical recording medium having a recording layer of a magnetic material having a compensation temperature of room temperature or higher is used. A magneto-optical recording method for performing magneto-optical recording by irradiating the magnetic recording medium, wherein the magneto-optical recording medium has two points at which the external magnetic field and the coercive force of the recording layer are equal to each other at room temperature or higher. Tcom the compensation temperature of the layer
p, Curie temperature as Tc, temperatures at which the external magnetic field equals the coercive force of the recording layer, T _B1 and T _B2 (T _B1 <T _B2 ), and room temperature as Troom
And the medium temperature T is T in a normal medium driving state.
_A laser beam is continuously irradiated so that _B1 <T <Tcomp is maintained, a high-power laser beam is irradiated so that the medium temperature T becomes T> T _B2 during recording, and the medium temperature T is TroomT <T during erasing. There is provided a magneto-optical recording method characterized by performing overwritable magneto-optical recording by stopping laser beam irradiation or irradiating a low-power laser beam so as to achieve _B1 .

 Hereinafter, the present invention will be described in detail with reference to the drawings.

The magneto-optical recording medium used in the method of the present invention has a single-layer recording layer, and the recording layer is made of a ferrimagnetic material having a compensation temperature of room temperature or higher. FIG. 1 shows a configuration example of such a magneto-optical recording medium. This recording medium is made of Si on a transparent support 1 made of glass, plastic, ceramics or the like.
₃ N ₄ , SiO, SiO ₂ Protective film 2 (film thickness 100Å to 500
0Å), and a magnetic film 3 made of a ferrimagnetic material is provided thereon.
(Thickness: 100Å to 5000 設 け), and then Si ₃ N ₄ ,
SiO, protective film 4 made of SiO ₂ (thickness 100A～5000A)
Is provided. Each film can be formed by a sputtering method, an evaporation method, an ion plating method, or the like. The magnetic film 3 is made of, for example, Tb-Fe, Gd-Fe, Dy-Fe, Tb-Fe-Co, Gd-.
It can be composed of a rare earth-transition metal based amorphous film such as Fe-Co, Gd-Tb-Fe-Co or a polycrystalline film such as Co spinel ferrite, and its coercive force H _C and temperature characteristics of saturation magnetization Ms are as follows. The characteristics must be as shown in FIG. That is, the magnetic film 3 has its compensation temperature
Tcomp is equal to or higher than the room temperature Troom, and the temperature at which the coercive force H _C is equal to the external magnetic field Hex applied during recording and erasing is the room temperature T room temperature.
There are two points (T _B1 , T _B2 ; T _B1 <T _B2 ) above the room. Generally, such a tendency is observed when the compensation temperature Tcomp is closer to the room temperature Troom.

The layer configuration of the magneto-optical recording medium used in the present invention is not limited to that shown in FIG.
For example, a reflective film may be provided on the protective film 4 or the protective films 2 and 4 may be appropriately removed.

In the present invention, as shown in FIG. 1, a single laser beam is applied while applying an external magnetic field Hex in the same direction at the time of recording and erasing using the above-described magneto-optical recording medium having a single-layer recording film. Performs magneto-optical recording. At this time, the initialization magnetic field is not used, and the power of the laser beam to be irradiated is changed in the normal driving state of the medium (the driving state when recording and erasing are not performed), and during recording and erasing. Hereinafter, each mode will be described.

First, in the normal driving state of the medium, a laser beam having a medium level power is continuously irradiated so as not to be affected by the external magnetic field Hex (FIG. 3), and the medium temperature T is set to T _B1 <T <Tcomp. It is assumed that the magnetic force H _C is large. If T <T _B1 , H _C
<Hex (FIG. 2), and the magnetization becomes unstable, which is not preferable. Also, in this state, since the reproduction is also performed at the same time, if the medium temperature T is excessively increased, the saturation magnetization Ms is reduced, and the reproduction characteristics are deteriorated. Therefore, it is more preferable to set the temperature close to T _B1 .

Recording was performed by irradiating a high-power laser beam (third
FIG. 1 shows that the medium temperature T is set to T> T _B2 , and an external magnetic field Hex in the same direction (upward) as the direction of the saturation magnetization Ms is applied as shown in FIG. The magnetization that was upward at room temperature Troom is T> T
_{In B2} , the magnetization is downward (small), but the external magnetic field He
It is inverted by x and turned upward. Then, during cooling, when the temperature exceeds the compensation temperature Tcomp during cooling, the magnetization changes in the opposite direction (downward) and is maintained.

When erasing, lower the laser power or stop the laser irradiation (FIG. 3) and raise the medium temperature T to TroomT <T _B1
And an external magnetic field Hex is applied in the same direction as during recording. Since the external magnetic field Hex in the medium temperature T is greater than the coercive force H _C, the magnetization is aligned in a direction of the external magnetic field Hex, the erase is performed.

Thus, in the present invention, as shown in FIG. 3, the medium is continuously irradiated with a constant power during normal driving, the laser power is increased when recording is performed, and the laser power is decreased or laser irradiation is stopped when erasing. Do it. An external magnetic field Hex in the same direction is applied during recording and erasing. Thus, overwriting can be performed with a single laser beam and a single magnetic field without using a magnetic field for initialization.

〔Example〕

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the examples illustrated here.

The following films were sequentially laminated in vacuum on a grooved polycarbonate substrate (130 mm in diameter) by rf binary magnetron sputtering to obtain a recording medium.

Protective film: Si ₃ N ₄ film (1000 Å) magnetic _{film: Tb 0 · 25 (Fe 0.85} Co 0 · 15) 0.75 layer (800 Å) protective film: Si ₃ N ₄ film (1000 Å) Curie temperature T _C and the magnetic film The compensation temperature Tcomp was as follows.

Tcomp = 120 ° C T _C = 230 ° _C Medium temperature at which H _C is 1 kOe (external magnetic field and magnitude)
T _B1 and T _B2 were 50 ° C. and 180 ° C., respectively.

The recording medium obtained as described above was applied with an external magnetic field of 1 kOe in the same direction during recording and erasing at a linear velocity of 10 m / sec in recording and erasing. A 1 MHz signal was recorded and reproduced by changing the power, and the recording / reproducing characteristics were evaluated.

Laser power during recording: 7.2 mW Laser power during normal drive of the medium: 3.4 mW (continuous irradiation) Laser power during erasing: 0 mW (off) As a result, the C / N ratio was 48 dB. Furthermore, when overwriting was performed on the recording medium under the same conditions at a recording frequency of 2 MHz, a good value was exhibited at a C / N ratio of 47 dB. In addition,
During recording, normal temperature of the medium and the temperature rise of the medium by laser beam irradiation during erasing are 220 ° C, 70 ° C, and 30 ° C, respectively.
Met.

〔The invention's effect〕

According to the present invention, the above configuration enables overwriting with a single laser beam and a single magnetic field using a single-layered recording medium. Therefore, the structure of the drive device can be simplified and the drive device can be downsized.
In addition, there is an advantage that the cost can be reduced because the medium design becomes easy.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the method of the present invention, and FIG. 2 is a coercive force H _C and saturation magnetization of a magnetic film of a magneto-optical recording medium used in the present invention.
FIG. 3 is a diagram showing temperature characteristics of Ms, and FIG. 3 is a diagram showing an example of laser power levels during recording, in a normal drive state of the medium, and during erasing. 1 ... Support 2,4 ... Protective film 3 ... Magnetic film

Claims (1)

(57) [Claims] 1. A magneto-optical recording medium having a recording layer made of a magnetic material whose compensation temperature is equal to or higher than room temperature. The magneto-optical recording is performed by applying an external magnetic field in the same direction during recording and erasing and irradiating a laser beam. A magneto-optical recording method, wherein the magneto-optical recording medium has two temperatures at which the external magnetic field and the coercive force of the recording layer are equal to or higher than room temperature, and the compensation temperature of the recording layer is Tcomp and Curie. Temperature Tc,
The temperatures at which the external magnetic field and the coercive force of the recording layer are equal are defined as T _B1 and T _B1 .
_B2 (T _B1 <T _B2 ), when the room temperature is Troom, the laser beam is continuously irradiated so that the medium temperature T is maintained at T _B1 <T <Tcomp in a normal medium driving state. By irradiating a high-power laser beam so that T becomes T> T _B2 , by erasing the laser beam or irradiating a low-power laser beam so that the medium temperature T becomes Troom T <T _B1 during erasing. A magneto-optical recording method comprising performing over-writeable magneto-optical recording.