JPH05120753A - Magneto-optical recording method - Google Patents

Abstract

PURPOSE:To simplify system configuration by reducing the control of the intensity of a laser from a ternary to a binary, and also to rapidly rise the temperature of a recording medium, to improve the uniformity of a recording pit and to improve signal quality, as well by irradiating with a laser beam similar intensity to a high level time even at a low level time, as well. CONSTITUTION:In the case of over-writing by optical modulation to a magneto- optical memory element, the binary level power of high level power PH reproducing level power PR is used and also, by using plural short pulses with the level power equal to the high level PH and with shorter time width than the high level PH, the low level power is generated and information is rewrited.

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 been attracting attention as a high-density and large-capacity memory device capable of rewriting information. Above all, the need for a magneto-optical memory element capable of optical modulation overwriting, which does not require erasing of information when rewriting information, and facilitates multi-beam formation and double-sided recording, is increasing year by year.

In the above optical modulation overwrite, Jpn. J.
As described in Appl. Phys., Vol. 26 (1987) Suppl. 26-4 p155-159, a magneto-optical memory device having a memory layer made of a perpendicular magnetization film and an auxiliary layer is used. The memory layer has a high coercive force and a low Curie point for retaining and reading information, and the auxiliary layer has a lower coercive force and a higher Curie point than the memory layer, and the information in the memory layer is high. Is transferred to perform overwriting. Information is recorded or erased by utilizing the exchange coupling force acting between the memory layer and the auxiliary layer. In this case, prior to the recording of information, it is necessary to align the magnetization direction of the auxiliary layer in one direction with an initialization magnetic field to initialize the auxiliary layer.

Also, J. Appl. Phys. Vol.67, No.9, 1 M
ay 1990 p4415-4416 describes an optical modulation overwrite method that does not require an initialization magnetic field by providing an initialization layer in a magneto-optical memory element. That is, the magneto-optical memory device used in this system 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 controls the exchange coupling between the auxiliary layer and the initialization layer to be turned on and off, thereby transferring the magnetization from the initialization layer to the auxiliary layer and aligning the magnetization direction of the auxiliary layer as necessary. , The auxiliary layer is initialized. Therefore, in this method, before using the magneto-optical memory element, a magnetic field is applied once perpendicularly to the film surface to align the magnetization of the initialization layer in one direction, and thereafter, initialization is performed. No need.

In the optical modulation overwrite by the method using the initialization magnetic field and the method using the initialization layer, for example, as shown in FIG. 9, at a recording frequency of 1 MHz, 50
Information is rewritten by overwriting while switching the intensity of the laser beam between the high level power P _H and the low level power P _L every 0 ns.

That is, by irradiating the laser beam of high level power P _H , the temperature of the magneto-optical memory element rises to near the Curie point of the auxiliary layer and the magnetization direction of the auxiliary layer is reversed by the recording magnetic field. When the laser spot is removed and the memory layer is cooled to near the Curie point, the magnetization direction of the memory layer matches the magnetization direction of the auxiliary layer due to the exchange force acting on the interface between the memory layer and the auxiliary layer.

On the other hand, when the laser light of low level power P _L is irradiated, the temperature of the magneto-optical memory element rises only up to near the Curie point of the memory layer, and the magnetization direction of the auxiliary layer is recorded. Although it is not reversed due to the influence of the magnetic field, if the magnetization direction of the memory layer does not match the magnetization direction of the auxiliary layer, the magnetization direction of the memory layer is adjusted so that it matches the magnetization direction of the auxiliary layer. The magnetization is reversed.

Further, at the time of reproduction, laser light having a lower intensity (reproduction level power P _R ) than that at the time of recording is irradiated so that the information recorded in the magneto-optical memory element is reproduced by utilizing the magneto-optical effect. It has become.

[0009]

However, the conventional magneto-optical recording method described above has problems that the system configuration is complicated and the signal quality is deteriorated.

That is, in the optical modulation recording, a high level for raising the temperature rise level of the magneto-optical memory element by irradiation of laser light to near the Curie point of the auxiliary layer, a low level for raising to near the Curie point of the memory layer, and the above Although it is necessary to set the reproduction level to three values lower than the high level and the low level, in the conventional magneto-optical recording method, the setting of each level is generated by changing the intensity of the laser beam.

Therefore, in addition to the reproduction level power P _R , the three-level laser power of the high level power P _H and the low level power P _L at the time of overwriting recording is required, and the three levels of laser power are controlled. In addition, the system configuration becomes complicated. In addition, since the laser light of low level power P _L is used at the time of low level overwrite recording, it takes time to raise the temperature of the magneto-optical memory element, and the recording bits become non-uniform, resulting in deterioration of signal quality. ..

[0012]

In order to solve the above-mentioned problems, the magneto-optical recording method of the present invention irradiates a low-level or high-level laser beam according to the information to be recorded,
In the magneto-optical recording method for recording information in the magneto-optical memory element, the magneto-optical memory element having a perpendicular magnetization film is heated to different temperatures at a temperature higher than a reproducing level at the time of reproducing, and the low level is recorded. Is generated by using a short pulse having a level power substantially equal to that of the high level and having a time width shorter than that of the laser pulse of the high level.

[0013]

According to the above structure, the low level at the time of recording is generated by using a short pulse having a level power substantially equal to that of the high level and a time width shorter than that of the high level laser pulse. Therefore, the control of the laser power has two values, the high level at the time of recording and the reproduction level at the time of reproducing, and the system configuration is simplified as compared with the case of the conventional three values. Further, since the magneto-optical memory element is irradiated with the laser beam at the same intensity as that at the high level even at the low level, the temperature of the magneto-optical memory element is rapidly raised, and the uniformity of the recording bit is improved. improves.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

A magneto-optical disk as a magneto-optical memory element used in this embodiment is a magneto-optical recording medium layer formed on a disc-shaped substrate having a light transmitting property such as polycarbonate. This 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 surface of the magneto-optical disk. 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 are coupled to each other by exchange force. As described above, when the exchange coupling two-layer film is used as the magneto-optical recording medium layer, the magnetization direction of the auxiliary layer is aligned in one direction by using the initialization magnetic field prior to the recording of information.
It is necessary to initialize the auxiliary layer.

A magneto-optical disk having a magneto-optical recording medium layer having a structure in which the perpendicularly magnetized film is sandwiched between dielectric films is also used. Furthermore, a reflective layer made of a metal such as Al may be provided on the magneto-optical recording medium layer of such a transmissive magneto-optical disk to use as a reflective magneto-optical disk. still,
On the magneto-optical recording medium layer or the reflective layer, a protective layer made of an ultraviolet curable resin or the like is usually provided in order to improve reliability. In addition, a spiral or concentric guide groove is formed in advance on the substrate for tracking.

In the magneto-optical recording method of this embodiment, a laser drive signal waveform generating circuit as shown in FIG. 2 is used.

The circuit described above inputs an oscillator 3 for generating a signal of a predetermined frequency, a first frequency divider 2 and a second frequency divider 4 for frequency-dividing the signal of the oscillator 3, and recording data as information. A digital modulator 1 and a duty compensation circuit 5 and a phase delay circuit 6 for respectively correcting the duty and the phase of the output signal from the second frequency divider 4.
And an OR gate 7 which outputs a laser drive signal d based on the outputs of the digital modulator 1 and the phase delay circuit 6.
And a laser driver 8 that drives a laser diode 9 based on the laser drive signal d.

In the above structure, first, the signal of the predetermined frequency output from the oscillator 3 is input to the first frequency divider 2 and the second frequency divider 4, respectively. The first frequency divider 2 frequency-divides the output of the oscillator 3 with a predetermined frequency division ratio and outputs it to the digital modulator 1. Recording data is input to the digital modulator 1, and the digital modulator 1
Based on the output of the frequency divider 2 and the recording data, for example, when the recording frequency is 1 MHz, a data signal a (see FIG. 3A) that switches between the high level and the low level is output every 500 ns.

The frequency division ratios of the first frequency divider 2 and the second frequency divider 4 are set to 1:10, and the frequency is divided by the same oscillator 3 so that the second frequency divider 4 is divided. From, the frequency is 10 times the data signal a, and the length is 1/10,
That is, the high level and the low level are switched every 50 ns at the frequency of 10 MHz, and the first level synchronized with the data signal a is generated.
A short pulse signal b (see FIG. 3B) is generated.

The first short pulse signal b is further sent to the duty compensation circuit 5 and the phase delay circuit 6, and the duty and the phase are corrected to obtain the second short pulse signal c. In the present embodiment, for example, the second short pulse signal c whose duty is 60% and whose phase is delayed by 20 ns is used.
Was generated (see FIG. 3 (c)).

Then, by connecting the data signal a and the second short pulse signal c at the OR gate 7,
A pulse-modulated laser drive signal d is obtained. When the laser drive signal d is input to the laser driver 8, the laser diode 9 is driven.

As a result, the intensity of the laser light emitted from the laser diode 9 has a level power (P _H ) equal to the high level and the bottom level is the reproduction level power P _R as shown in FIG. 60% duty
Thus, it has a plurality of short pulses whose phases are delayed by 20 ns.

First, when the magneto-optical disk rotates and passes the initializing magnetic field, the magnetization of the auxiliary layer is aligned in one direction by the downward magnetic field. After that, at the time of high-level overwriting recording, when the laser beam of high level power P _H is irradiated, the magneto-optical recording medium layer rises above the Curie point of the auxiliary layer and responds to the upward recording magnetic field. The magnetization of the auxiliary layer is reversed. Then, when the laser beam deviates from the spot of the laser light and drops to the vicinity of the Curie point of the memory layer, exchange coupling between the auxiliary layer and the memory layer causes the magnetization of the memory layer to coincide with the magnetization direction of the auxiliary layer. Furthermore even magnetization when the temperature is lowered to room temperature is stable, even if the magnetization overwriting previous memory layer is above or below, by laser irradiation of the high-level power P _H, the magnetization of the memory layer becomes upward Recording is done.

On the other hand, at the time of low level overwrite recording, when the laser light is irradiated using a plurality of short pulses, the temperature of the medium rises up to near the Curie point of the memory layer but reaches the Curie point of the auxiliary layer. Does not rise. Therefore, the magnetization of the auxiliary layer does not reverse upward due to the recording magnetic field, and only when the magnetization of the memory layer does not match the magnetization direction of the auxiliary layer, the magnetization of the auxiliary layer reverses downward. Then, the previously recorded information is erased.

That is, at the time of conventional overwrite recording, the temperature of the magneto-optical recording medium layer, which is almost the same as when the laser beam of low level power P _L is irradiated, can be obtained by using a plurality of short pulses. ..

Further, at the time of reproduction, laser light having a lower intensity (reproduction level power P _R ) than that at the time of recording is irradiated, and the information recorded in the magneto-optical memory element is read by utilizing the magneto-optical effect.

The duty of the short pulse is determined according to the temperature rise of the recording medium. FIG. 4 shows a laser including a plurality of short pulses when the duty is 50% and the phase is delayed by 25 ns. It shows a change in power.

Next, using the calculation model shown in FIG. 8, the time change of the temperature of the recording medium at the time of recording is calculated by the calculation when the recording power P _H , the period y, and the duty are set as shown in Table 1. I asked. 5 to FIG.
It shows the time change of the temperature of the magneto-optical recording medium layer under each of the above conditions.

The temperature was calculated by linear velocity 5.65 m / s, wavelength 830 nm, beam diameter 0.7 μm, recording bottom power P.
_b was performed at 0 mW. In addition, the duty is the time during which the laser light is irradiated at the level of the recording power P _H.
Then, it is represented by x / y × 100 (%).

[0031]

[Table 1]

In FIG. 5, A (indicated by the solid line in the figure) is
In the magneto-optical recording method of the present invention, this corresponds to the case where the temperature of the recording medium is raised by using a short pulse (low level). On the other hand, B (indicated by a dashed line in the figure) corresponds to a high level during conventional overwrite recording, and C (indicated by a dotted line in the figure) corresponds to a conventional low level.

As can be seen from FIG. 5, the temperature rising rate of A is almost the same as the temperature rising rate of B. Therefore, it is understood that the recording power similar to that of the conventional low level can be obtained by shortening the pulse of the high level.

Further, D to F in FIG. 6 are the above A to C.
, The cycle and the duty are changed. That is, D (indicated by a solid line in the figure) corresponds to a case where the recording medium temperature is raised by using a short pulse in the magneto-optical recording method of the present invention, that is, a low level overwrite recording, and E (in the figure). (Indicated by the chain line)
Indicates a high level during conventional overwrite recording, and F (indicated by a dotted line in the figure) corresponds to a conventional low level.

As is apparent from FIG. 6, the heating rate of D is almost the same as the heating rate of E. Therefore, it is understood that the recording power similar to that of the conventional low level can be obtained by shortening the pulse of the high level.

Further, G to I in FIG. 7 are obtained by changing the duty of the short pulse to 30%, 40% and 50%, respectively. As is clear from FIG. 7, by changing the duty, it is possible to adjust the low level according to the Curie point of the memory layer.

As described above, by using a plurality of short pulses having the level power equal to the high level and the bottom level equal to the reproduction level power, the recording level corresponding to the conventional low level power is generated, so that the laser The power control can be made into two values, a reproduction level power and a high level power at the time of recording. Therefore, in comparison with the conventional three-valued laser power control,
The system is simplified and, by using the digital circuit, the size is reduced as compared with the case of the conventional analog circuit.

Further, by using the short pulse, it is possible to raise the temperature of the recording medium more quickly than in the case of using the low level power, so that the recording bits are made uniform and the signal quality is improved.

In this embodiment, the magneto-optical disk having the exchange coupling two-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 large. Exchange-coupled three-layer membrane with an intermediate layer inserted to reduce
The present invention can also be applied to the case of using a magneto-optical disk that has an initialization layer that exchange-couples with an auxiliary layer and that does not require an initialization magnetic field and has an exchange-coupling four-layer film or an exchange-coupling two-layer film. Further, as the magneto-optical memory device, a magneto-optical card, a magneto-optical tape, or the like can be used instead of the magneto-optical disk.

[0040]

As described above, the magneto-optical recording method of the present invention generates a low level by using a short pulse having a level power substantially equal to that of the high level and having a time width shorter than that of the high level laser pulse. It is what makes them.

Therefore, the control of the laser intensity is
There are two values, a high level and a reproduction level at the time of recording, which simplifies the system configuration, improves the uniformity of recorded bits, and improves the signal quality.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a change in intensity of laser light in a magneto-optical recording method of the present invention.

FIG. 2 is a block diagram showing a circuit for generating the laser light.

FIG. 3 is an explanatory diagram of each signal generated in the generation circuit.

FIG. 4 is an explanatory diagram showing a change in laser light intensity when the duty is changed in FIG. 1;

FIG. 5 is a graph showing the time change of the recording medium temperature in the magneto-optical recording method of the present invention and the conventional magneto-optical recording method.

FIG. 6 is a graph showing the time change of the recording medium temperature when the cycle and duty are changed in FIG.

FIG. 7 is a graph showing a time change of the recording medium temperature when only the duty is changed in the magneto-optical recording method of the present invention.

FIG. 8 is an explanatory diagram of a calculation model used for producing the graphs of FIGS. 5 to 7 described above.

FIG. 9 is an explanatory diagram showing a change in intensity of laser light in a conventional magneto-optical recording method.

[Explanation of symbols]

 1 Digital Modulator 2 1st Divider 3 Oscillator 4 2nd Divider 5 Duty Compensation Circuit 6 Phase Delay Circuit 7 OR Gate 8 Laser Driver 9 Laser Diode a Data Signal b First Short Pulse Signal c Second Short Pulse Signal d Laser drive signal

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Junji Hirokane 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Kenji Ota 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Within the corporation

Claims (1)

[Claims] 1. A magneto-optical memory element having a perpendicularly magnetized film is irradiated with a low-level or high-level laser beam in accordance with information to be recorded, and the magneto-optical memory element is heated to a temperature higher than a reproducing level at the time of reproducing and has different temperatures. In the magneto-optical recording method of recording information in the magneto-optical memory element by raising the temperature, the low level is a short pulse having a level power substantially equal to that of the high level and a time width shorter than that of the high level laser pulse. A magneto-optical recording method, characterized in that