JPH05314566A - Magneto-optical recording method - Google Patents

Abstract

PURPOSE:To obtain a recording bit of the desired length and to secure the high signal quality in a reproduced state by modulating the laser light power to a high or low level according to the information and irradiating the laser light on a magneto-optical memory element having a vertically magnetized film. CONSTITUTION:In an over-light system of an optical modulation system, the information is recorded with a certain irradiating period of time of the laser light of a high level PH and with the variable irradiating period of time of the laser light of a low level PL respectively. Under such conditions, the laser power light is varied in response to the irradiating period of time of the laser light of level PL. Then the laser light power is increased as the length of the recording bit corresponding to the level PL is increased. Therefore the laser power is equivalent to the irradiating period of time of level PH and is not dependent on the irradiating period of time of level PL in a domain where the temperature of an auxiliary layer exceeds the Curie point. Thus a recording bit having the length corresponding to the irradiating period of time of level PH is formed on a memory layer. As a result, the high signal quality is secured in a reproduced state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording method for overwriting a magneto-optical memory device such as a magneto-optical disk by an optical modulation method.

[0002]

2. Description of the Related Art In recent years, a magneto-optical memory device such as a magneto-optical disk has attracted attention as a high-density and large-capacity memory device capable of rewriting information. In particular, the need for a magneto-optical memory element capable of overwriting by an optical modulation method that does not require erasure of information when rewriting information, can support double-sided recording, and is easy to multi-beam is increasing year by year. ..

This type of magneto-optical memory device is described in Jpn.
As described in J. Appl. Phys., Vol. 26 (1987) Suppl. Pp155-159, it has a memory layer and an auxiliary layer made of a perpendicular magnetization film. The memory layer has a high coercive force and a low Curie point for holding and reading information, and the auxiliary layer has a higher coercive force than the above memory layer for transferring information to the memory layer for overwriting. Also has a low coercive force and a high Curie point. Information recording or erasing is performed by utilizing the exchange coupling force acting between the memory layer and the auxiliary layer. In addition, prior to the recording of information,
Initialization of the auxiliary layer is required. Therefore, the magnetization direction of the auxiliary layer is aligned in one direction by applying the initialization magnetic field.

J. Appl. Phys., Vol.67, No. 9,1 May 1990, pp
4415-4416 describes a magneto-optical memory element which does not require the above-mentioned initialization magnetic field by providing an initialization layer in the magneto-optical memory element. This magneto-optical memory element has an exchange-coupling four-layer film including a memory layer, an auxiliary layer, a control layer, and an initialization layer. Then, the control layer turns on / off the exchange coupling between the auxiliary layer and the initialization layer, thereby transferring the magnetization from the initialization layer to the auxiliary layer as necessary, and aligning the magnetization direction of the auxiliary layer. ..

Therefore, in this method, if the magnetic field perpendicular to the film surface of the initialization layer is applied only once before using the magneto-optical memory element, and the magnetization of the initialization layer is aligned in one direction, After that, there is no need to perform initialization.

[0006] In the magneto-optical memory device having a magneto-optical memory device and initializing layer using the initialization magnetic field, as shown in FIG. 10 (a), according to the information, a high level of power of the laser light P _H or Overwriting is performed while switching to the low level P _L.

That is, when a high-level P _H laser beam is irradiated, the temperature of the irradiated portion rises to near the Curie point of the auxiliary layer, and the magnetization direction of the auxiliary layer in that portion is reversed by the recording magnetic field. When the laser light moves along the track of the magneto-optical memory element and the temperature of the above part cools to near the Curie point of the memory layer, the exchange force acting on the interface between the memory layer and the auxiliary layer causes the magnetization of the memory layer. The direction of is the same as the direction of magnetization of the auxiliary layer.
As a result, the recording bit having the magnetization in the direction parallel to the recording magnetic field is formed in the memory layer.

On the other hand, when the laser beam of low level P _L is irradiated, the temperature rises only up to near the Curie point of the memory layer, and the magnetization direction of the auxiliary layer is not reversed by the recording magnetic field. However, the magnetization direction of the memory layer is reversed so as to match the magnetization direction of the auxiliary layer.

Further, at the time of reproduction, laser light of a level lower than the laser light of low level P _L is applied to the memory layer, and information is reproduced by utilizing the magneto-optical effect.

[0010]

By the way, in the above-mentioned conventional structure, at the time of recording, the high level P _H or the low level P _{H is set.}
There is a problem in that the desired recording bit length cannot be obtained because the rising temperatures of the memory layer and the auxiliary layer differ depending on the length of time of the _L laser beam irradiation.

For example, as shown in FIG. 10A, when recording is performed while the irradiation time of the high-level P _H laser beam is constant and the length of the low-level P _L laser beam irradiation time is changed, The region where the temperature of the layer rises above the Curie point T _C becomes smaller as the irradiation time of the laser light of low level P _L becomes longer, as shown in FIG. For this reason, the length of the recording bit formed in the memory layer becomes shorter than the length corresponding to the irradiation time of the high-level P _H laser beam, as shown in FIG.

On the contrary, as shown in FIG. 11A, recording is performed while the irradiation time of the low-level P _L laser beam is kept constant and the irradiation time of the high-level P _H laser beam is changed. When this is done, the region where the temperature of the auxiliary layer rises above the Curie point T _C is at the high level P, as shown in FIG.
_It increases as the irradiation time of _H laser light increases. For this reason, the length of the recording bit formed in the memory layer becomes longer than the length corresponding to the irradiation time of the laser beam of high level P _H , as shown in FIG.

As described above, since the length of the recording bit is affected by the duration of the high-level P _H or low-level P _L laser beam, the desired recording bit length cannot be obtained. ing.

[0014]

In order to solve the above-mentioned problems, a magneto-optical recording method according to the present invention modulates the power of laser light to a high level or a low level according to information, and a perpendicular magnetization film is formed. In a magneto-optical recording method for forming a recording bit having upward or downward magnetization by irradiating a magneto-optical memory element such as a magneto-optical disk having the recording bit, the recording bit corresponding to a low level is formed. The higher the low level power, the higher the correction level, or when forming the recording bit corresponding to the high level, the longer the recording bit, the lower the high level power is corrected. The feature is that the power of one of the laser beams is corrected.

[0015]

With the above structure, the power of the laser beam is modulated to a high level or a low level according to the information, and the magneto-optical memory device such as a magneto-optical disk having a perpendicular magnetization film is irradiated with the laser beam so that the laser beam is directed upward or downward. In a magneto-optical recording method for forming a recording bit having magnetization, when a recording bit corresponding to a low level is formed, the longer the recording bit is, the higher the correction of the low level power is made, or the high level is corrected. When forming the corresponding recording bit, the longer the recording bit, the higher the level of the power is corrected to a lower level, and the power of at least one of the laser beams is corrected. It is almost constant regardless of the bit length. As a result, it is possible to form a recording bit having a desired length. Therefore, good signal quality can be obtained during reproduction.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment of the present invention will be described below with reference to FIGS.

A magneto-optical disk as a magneto-optical memory element used in this embodiment comprises a disc-shaped substrate having light transparency and a magneto-optical recording medium layer formed on the substrate.

On the above-mentioned substrate, for tracking,
A spiral or concentric guide groove is formed.
As the substrate material, glass or plastic such as polycarbonate is used.

The magneto-optical recording medium layer has a memory layer and an auxiliary layer made of a perpendicularly magnetized film whose magnetization is oriented perpendicularly to the substrate surface. As the perpendicular magnetization film, for example, a rare earth-transition metal amorphous alloy such as DyFeCo is used. The memory layer and the auxiliary layer form an exchange-coupling bilayer film that is exchangeably coupled to each other. For this reason, it is necessary to apply an initializing magnetic field prior to recording information to align the magnetization direction of the auxiliary layer in one direction, so-called initialization of the auxiliary layer.

In the above-mentioned magneto-optical disk, dielectric layers may be arranged on both sides of the exchange coupling two-layer film in order to improve reliability and performance during reproduction. Further, by providing a reflecting layer made of a metal such as Al on the surface of the magneto-optical recording medium layer which is not the substrate side, it may be used as a reflection type magneto-optical disk. A protective layer made of an ultraviolet effect resin or the like is usually formed on the magneto-optical recording medium layer or the reflective layer in order to improve reliability.

In the light modulation type overwrite method of the present embodiment, as shown in FIG. 1A, the length of the irradiation time of the laser light of high level P _H is kept constant and low level P _{L is set.}
If recording is performed while changing the length of the irradiation time of the laser light, depending on the length of the irradiation time of the laser beam of low level P _L, and varying the power of the low level P _L.

That is, as shown in the correction curve of FIG.
According irradiation time of the laser beam of low level P _L becomes longer, which increases the power of the low level P _L.
In other words, the power of the low level P _L is increased as the length of the recording bit corresponding to the low level P _L becomes longer. As a result, the region where the temperature of the auxiliary layer rises above the Curie point T _C has a size corresponding to the length of irradiation time of the high-level P _H laser light, as shown in FIG. 1B. , The low-level P _L laser light does not depend on the length of irradiation time. Therefore, FIG.
As shown in, a recording bit having a length corresponding to the irradiation time of the high-level P _H laser beam can be formed in the memory layer. Therefore, good signal quality can be obtained during reproduction.

[0023] Incidentally, the power of the laser beam of low level P _L, as shown in FIG. 3, according to the length of the recording bits corresponding to the low level P _L, may be discretely corrected ..

The second embodiment of the present invention will be described below with reference to FIGS. 4 to 6. In addition,
For convenience of explanation, the structure of the magneto-optical disk as the magneto-optical memory element is the same as that of the above-mentioned embodiment, and therefore its explanation is omitted.

In the light modulation type overwrite method of the present embodiment, as shown in FIG. 4A, the length of the irradiation time of the laser light of the low level P _L is made constant and the high level P _{H is set.}
When performing recording while changing the length of the irradiation time of the laser light, depending on the length of the irradiation time of the laser beam of high level P _H, and varying the power of the high level P _H.

That is, as shown in the correction curve of FIG.
According irradiation time of the laser beam of high level P _H becomes longer, which reduces the power of the high level P _H.
In other words, the power of the high level P _H is reduced as the length of the recording bit corresponding to the high level P _H becomes longer. As a result, the region where the temperature of the auxiliary layer rises above the Curie point T _C has a size corresponding to the length of irradiation time of the high-level P _H laser light, as shown in FIG. 4B. , And does not depend on the length of irradiation time of the high-level P _H laser light. Therefore, FIG.
As shown in, a recording bit having a length corresponding to the irradiation time of the high-level P _H laser beam can be formed in the memory layer. Therefore, good signal quality can be obtained during reproduction.

[0027] Incidentally, the power of the laser beam of high level P _H, as shown in FIG. 6, according to the length of the recording bits corresponding to the high level P _H, may be discretely corrected ..

The third embodiment of the present invention will be described below with reference to FIG. Incidentally, for convenience of explanation, the structure of the magneto-optical disk as the magneto-optical memory element is the same as that of the above-mentioned embodiment, and therefore its explanation is omitted.

In the light modulation type overwrite method of the present embodiment, as shown in FIG. 7, when recording is performed while changing the irradiation time of both the high-level P _H and low-level P _L laser beams, depending on the length of the irradiation time of the laser beam of high level P _H, with which by changing the power of the high level P _H, depending on the length of the irradiation time of the laser beam of low level P _L, the low level P Changing the power of _L.

[0030] That is, the as in the first embodiment, in accordance with the irradiation time of the laser beam of low level P _L becomes longer, with which to increase the power of the low level P _L, the second embodiment Similarly, following the irradiation time of the laser beam of high level P _H becomes longer, which reduces the power of the high level P _H and.

The correction of the low level P _L and the high level P _H is performed continuously or discretely as in the above-mentioned embodiment.

In this embodiment, since both the low level P _L and the high level P _H are corrected, it is possible to form a recording bit of a more accurate length than that of the above-mentioned embodiments. Therefore, better signal quality can be obtained during reproduction.

The fourth embodiment of the present invention will be described below with reference to FIGS. 8 and 9. In addition,
For convenience of explanation, the structure of the magneto-optical disk as the magneto-optical memory element is the same as that of the above-mentioned embodiment, and therefore its explanation is omitted.

As shown in FIG. 8, the optical modulation type overwrite method of the present embodiment continuously changes the high level P _H and the low level P _L (sawtooth) within the irradiation time for recording one recording bit. It is different from the third embodiment in that it is changed in a wavy manner.

In this embodiment, since the difference between the temperature gradient when the temperature rises and the temperature gradient when the temperature falls is small, it is possible to form a recording bit of a more accurate length than that of the above-mentioned embodiment. Therefore, better signal quality can be obtained during reproduction.

As shown in FIG. 9, the high level P _H and the low level P _L may be changed discretely (in a pulse form) within the irradiation time for recording one recording bit.

In the above embodiments, the magneto-optical disk having the exchange coupling double-layer film including the auxiliary layer and the memory layer has been described as an example. However, the exchange coupling force between the auxiliary layer and the memory layer is reduced. In the case of using a magneto-optical disk having an exchange-coupling three-layer film having an intermediate layer inserted therein, an initial layer exchange-coupling with an auxiliary layer, and having an exchange-coupling four-layer film or an exchange-coupling two-layer film that does not require an initializing magnetic field Also, the present invention can be applied.

As the magneto-optical memory element, it is possible to use a magneto-optical card, a magneto-optical tape or the like other than the magneto-optical disk.

[0039]

As described above, in the magneto-optical recording method according to the present invention, when the recording bit corresponding to the low level is formed, the longer the recording bit, the higher the low level power is corrected. Alternatively, when forming a recording bit corresponding to a high level, the longer the recording bit, the lower the high level power is corrected, and at least one of the laser light power corrections is performed. The temperature rise of the perpendicular magnetization film is almost constant regardless of the length of the recording bit. As a result, it is possible to form a recording bit having a desired length. Therefore, there is an effect that good signal quality can be obtained at the time of reproduction.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a magneto-optical recording method according to a first embodiment of the present invention, in which (a) is a change in laser light intensity and (b) is a diagram.
Shows the temperature change of the auxiliary layer of the magneto-optical disk, and (c) shows the recording bit corresponding to the high level.

2 is a graph showing a correction curve of the power of low-level laser light with respect to the recording bit length in the magneto-optical recording method of FIG.

FIG. 3 is a graph showing another example of a correction curve of the power of low-level laser light with respect to the recording bit length in the magneto-optical recording method of FIG.

FIG. 4 is an explanatory diagram showing a magneto-optical recording method of a second embodiment of the present invention, in which (a) is a change in laser light intensity and (b) is a diagram.
Shows the temperature change of the auxiliary layer of the magneto-optical disk, and (c) shows the recording bit corresponding to the high level.

5 is a graph showing a correction curve of the power of low-level laser light with respect to the recording bit length in the magneto-optical recording method of FIG.

6 is a graph showing another example of a correction curve of the power of low-level laser light with respect to the recording bit length in the magneto-optical recording method of FIG.

FIG. 7 is an explanatory diagram showing changes in the intensity of laser light in the magneto-optical recording method of the third embodiment of the present invention.

FIG. 8 is an explanatory diagram showing changes in laser light intensity in a magneto-optical recording method according to a fourth embodiment of the present invention.

FIG. 9 is an explanatory diagram showing another example of the intensity change of laser light in the magneto-optical recording method of the fourth embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a conventional magneto-optical recording method,
(A) shows the intensity change of laser light, (b) shows the temperature change of the auxiliary layer of the magneto-optical disk, and (c) shows the recording bit corresponding to the high level.

11A and 11B are explanatory views showing another conventional magneto-optical recording method, in which FIG. 11A is a laser light intensity change, FIG. 11B is a temperature change of an auxiliary layer of a magneto-optical disk, and FIG. The corresponding recording bits are shown.

[Explanation of symbols]

P _H High level laser power P _L Low level laser power T _C Curie temperature of auxiliary layer

Claims (1)

[Claims] According to information, the power of a laser beam is modulated to a high level or a low level, and a magneto-optical memory device such as a magneto-optical disk having a perpendicular magnetization film is irradiated with the laser beam to have an upward or downward magnetization. In a magneto-optical recording method of forming a recording bit, when forming a recording bit corresponding to a low level, the longer the recording bit is, the higher the correction of the low level power is made, or the recording corresponding to the high level is performed. A magneto-optical recording method, characterized in that, when forming a bit, the power of at least one of the laser beams is corrected so that the higher level power is corrected to a lower level as the recording bit is longer.