JPH0721893B2 - Magneto-optical recording method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magneto-optical recording system for performing magneto-optical recording using laser light.

(Prior art and its problems) The optical recording method, particularly the optical disk memory method, has recently attracted attention as one of large-capacity file memories because it enables high-density and large-capacity recording and also enables non-contact and high-speed access. Are gathering. Among them, MnBi, M as a recording medium
nCuBi, MnTiBi, MnAlGe or other crystalline magnetic thin film or Tb,
A magneto-optical disk memory using an amorphous magnetic thin film created by combining rare earth metals such as Gd, Dy, Ho and transition metals such as Fe, Co, Ni is said to be able to rewrite recorded information. Because of its advantages, it is being actively researched in various places.

In the conventional known magneto-optical recording method,
The following operations are performed for reproduction and deletion, respectively.

The heat generated by the laser light is used for recording. The laser light beam is focused on a minute spot of 1 to 2 μmφ and irradiated on the recording medium to raise the medium temperature. When Curie temperature recording is performed, the recording medium is heated to a temperature above the Curie temperature and an inverted magnetic domain is formed by an externally applied magnetic field or a demagnetizing field of the recording medium. When performing compensation temperature recording, set the compensation temperature of the recording medium near room temperature, raise it to a certain temperature by irradiating the beam of laser light, and use the reduction of the coercive force of the medium to form a reversed magnetic domain by an externally applied magnetic field. By the means described above, the recording binary signals "1" and "0" can be recorded in a form corresponding to the presence or absence of the reversed magnetic domain of the recording medium.

Reproduction is magneto-optical effect (Kerr effect or Faraday effect)
Is performed using. That is, information is read from the recording medium by utilizing the fact that the polarization plane of the reflected light or the transmitted light from the medium rotates depending on the presence or absence of the reversed magnetic domain of the recording medium. The recording medium is irradiated with a laser beam having a lower power level than during recording, and a signal is reproduced from the reflected light or the transmitted light.

Here, the intensity level of the laser beam used for reproduction is set to a level that does not change the magnetization state of the recording medium.

In the case of erasing recorded information, an external magnetic field is applied with a polarity opposite to that at the time of recording, and a laser light beam is uniformly irradiated onto the recording medium with the same intensity as during recording. By applying an external magnetic field, the magnetization state of the recording medium returns to the initial state before recording.

In the conventional magneto-optical recording method, in order to rewrite recorded information, first, existing recorded information is erased according to the erasing operation, and then new recording information is recorded according to the recording operation. Do it. At this time, since the direction of the external magnetic field applied to the recording medium is opposite between the erasing time and the recording time, means for switching the direction of the externally applied magnetic field during the erasing time and the recording time must be provided.

For example, when an external magnetic field is applied by a coil, as shown in FIG. 4, in order to perform recording and erasing on the magneto-optical disk 2, the recording operation and the erasing operation of the laser light from the magneto-optical head 1 are synchronized. Then, a method is known in which the direction of the current flowing through the coil 6 is switched by the coil current polarity switching means 12.

Further, as shown in FIG. 5, when an external magnetic field is applied by the permanent magnet 13, a method using a magnet driving mechanism is known (Japanese Patent Laid-Open Nos. 57-24046 and 57-24047). In both of the above-mentioned systems and devices, the direction of application of the external magnetic field is reversed as shown in the operation mode diagrams of FIGS.

In either method, the erasing operation is indispensable, and there is a drawback that the two-step operation of erasing / recording is inevitable for new recording.

(Object of the Invention) An object of the present invention is to solve the drawbacks of the conventional magneto-optical recording method, and to rewrite recorded information with a simple device configuration without switching the application direction of an external magnetic field. To provide magneto-optical recording.

(Structure of the Invention) According to the present invention, a magnetic thin film having perpendicular magnetic anisotropy is used as a recording medium, and when recording "1" of a recording binary signal, a recording laser light pulse synchronized with a clock signal is recorded on the recording medium. A recording laser synchronized with the clock signal is applied while applying an external magnetic field sufficient for forming a magnetization reversal bit to the recording medium in synchronization with the clock signal and recording "0" of the recording binary signal. A recording laser light pulse that is an optical pulse and is longer than the laser light pulse width at the time of "1" recording of the recording binary signal is applied to the recording medium, and the magnetization of the recording medium is irrespective of the presence or absence of a magnetization reversal bit. An external magnetic field sufficient to initialize the state is applied to the recording medium in synchronization with the clock signal to form a magnetization reversal bit of a shape corresponding to the recording binary signal. A magneto-optical recording method is provided which is characterized by recording information.

(Detailed Description of Configuration) The present invention has solved the problems of the prior art by adopting the above configuration. Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a recording operation mode of the magneto-optical recording system of the present invention. It is assumed that the recording medium for recording information, that is, the magnetized state of the tracks of the magneto-optical disk has already been magnetized in one direction as shown in FIG. When the recording information (recording binary signal) shown in FIG. 1 (b) is recorded on the magneto-optical disk track, as shown in FIG. 1 (d) in synchronization with the clock signal shown in FIG. 1 (c). At the same time as irradiating the magneto-optical disk track with pulse-modulated laser power (P _W ), an external magnetic field tuned to the clock signal and modulated by the recording binary signal as shown in FIG. Supply to. In FIG. 1 (d), the pulse-modulated laser power (P _W ) has a pulse width of t _{P 1} when a magnetization reversal bit corresponding to “1” of a binary signal is formed. When the magnetization reversal bit is not formed corresponding to "0" of the signal, the pulse width is t
It is set to be _{P 0} . Here, the pulse width is selected so that t _{P 1} <t _{P 0} . Sufficient external magnetic field to the external magnetic field H _W in FIG. 1 (e) to form a magnetization reversal bit, H _E is sufficient to initialize the magnetization state of the magneto-optical disk track or without magnetization inversion bit External magnetic field. When the recording operation of FIG. 1 (b) to (e) is executed, the disc track is shown in FIG. 1 (f).
A magnetization reversal bit having a shape corresponding to the recorded binary signal is formed as shown in FIG.

Next, the rewriting operation mode using the magneto-optical recording method of the present invention will be described. It is assumed that the magnetization reversal bit is already formed on the track of the magneto-optical disk as shown in FIG. When the new recording information (recording binary signal) shown in FIG. 2 (b) is recorded on this track, it is synchronized with the clock signal shown in FIG. 2 (c) and shown in FIG. 2 (d).
As shown in FIG. 2 (e), the external magnetic field synchronized with the clock signal and modulated by the recording binary signal is irradiated with the pulse-modulated laser power (P _W ) as shown in FIG. Supply to magnetic disk track. Here, the clock signal shown in FIG. 2 (c) is synchronized with the recorded bits.

In FIG. 2 as well, similar to FIG. 1 (d), the pulse-modulated laser power (P _W ) has a pulse width t _{p 1} when forming the magnetization reversal bit corresponding to “1” of the binary signal.
And when the magnetization reversal bit is not formed corresponding to “0” of the binary signal, the pulse width is t _{P 0} (> t _P
1 ) is set. The external magnetic field H _W is sufficient external magnetic field to form a magnetization reversal bit, H _E is a sufficient external magnetic field to initialize the magnetization state of the magneto-optical disk track or without magnetization inversion bit. Thus the pulse-modulated laser power (P _W) is irradiated on the recorded bits, if the magnetization reversal bit is not formed because the external magnetic field H _E is applied to the case of recording the "0" signal at the timing Further, when recording the "1" signal, the external magnetic field H _W is applied, so that the magnetization reversal bit is formed.

The laser pulse width during recording and rewriting is shown in Fig. 1 (d).
As shown in FIG. 2 (d), the pulse width t _{P 0} corresponding to the binary signal “0” is more than the pulse width t _{P 1} corresponding to the binary signal “1”. Is also set to be long. The pulse width t _{P 0} is set longer than t _{P 1} for the following reason. At the time of “0” recording of a binary signal, the magnetized state of the laser irradiation area must be aligned with the initial magnetization direction regardless of the magnetized state of the magneto-optical disk track irradiated by the laser at that timing. When the magnetization reversal bit is formed in the irradiation area, if the laser pulse width is made longer than the laser pulse width at the time of "1" recording, and thereby the temperature rising area of the disk track is widened, a part of the magnetization reversal bit is left. This is because the magnetization reversal bit can be erased and "0" recording can be achieved without doing so (FIG. 2 (f)).

An example of the configuration of the magneto-optical recording device to which the present invention is applied is as shown in FIG. The magneto-optical head 1 is composed of a semiconductor laser serving as a light source, a beam splitter, a condenser lens with an actuator, a laser beam shaping lens and prism, and a signal detection photodiode. The laser light from the magneto-optical head 1 is applied to the magneto-optical disk 2. A clock signal for driving the semiconductor laser and the external magnetic field is generated in the clock signal generating circuit 3 by a reproduction signal or a reproduction signal from a synchronization pit in each track of the magneto-optical disk.

The generated clock signal is supplied to the external magnetic field generating current source 4 and the laser pulse current source 5. The external magnetic field generating current is modulated by the clock signal and the recording binary signal and supplied to the air-core coil 6.

The pulse width of the laser pulse current is modulated by the clock signal and the recording binary signal, and the pulse width becomes long corresponding to “0” of the recording binary signal. The laser pulse current is supplied to the semiconductor laser. Further, the focus error signal and the tracking error signal are obtained by an error detection photodiode in the magneto-optical head 1, and the focus error servo amplifier 7 and the tracking error servo amplifier 8 are provided, respectively.
A servo signal is generated by and is supplied to the actuator that drives the condenser lens of the magneto-optical head 1. The reproduction signal is detected by the signal reproduction photodiode in the magneto-optical head 1 and taken out through the reproduction amplifier 9.

An electromagnet 10 placed behind the magneto-optical disk 2 is for generating an auxiliary magnetic field. 11 is a motor.

(Example) Information recording and rewriting were performed on a magneto-optical disk according to the magneto-optical recording method shown in FIGS. 1 and 2. As the magneto-optical disk, a disk in which a TbFe film was formed to a thickness of 800 Å on a 120 mmφ resin substrate by a sputtering method was used. The board has a width of 0.8 μm, a pitch of 2.5 μm, and a depth of 700
A pregroup substrate in which a groove of Å is formed was used. Tb
On the Fe film, 1200 Å of SiO ₂ was formed as a protective film.

The magneto-optical recording device having the structure shown in FIG. 3 was used. A semiconductor laser having λ = 30 nm was used, and the NA of the condenser lens was 0.55.

First, rotate the magneto-optical disk at a linear velocity of 10 m / sec.
A 1MHz clock signal was generated using the reproduced signal from the synchronization pit of each tonk sector. Next, the recording laser pulse power is 8 mW, and the pulse width during "1" recording is 100 nsec.
The pulse width at the time of “0” recording is set to 200 nsec., And the external magnetic fields H _W and H _E are set to 20 Oe in the magnetization reversal direction and 270 Oe in the initial magnetization direction, respectively, and the binary signal is output. Recorded. Recording under this condition was good, and a sufficient reproduction signal was obtained with a reproduction laser beam of 1 mW.

Subsequently, rewriting was performed on the already-recorded track under the same conditions as the recording. At this time, the clock signal was generated from the reproduction signal of the synchronization bit of each track sector. It was confirmed that rewriting is possible by this method.

(Effects of the Invention) As described above, according to the present invention, the following effects are obtained as compared with the conventional example.

Since there is no mode equivalent to the conventional "erase",
Information can be rewritten in a so-called “overwrite” form.

Since the clock signal is synchronized with the recorded binary signal, the rotational speed jitter of the disk does not affect the "recording mode" and "rewriting mode".

Since the laser pulse width at the time of recording is longer than the laser pulse width at the time of "1" recording, no erasure remains when rewriting. Also. Even if there is some synchronization deviation of the clock signal, it does not affect the rewriting characteristics.

Since the laser power (P _W ), the laser pulse width (t _{P 0} , t _{P 1} ), and the external magnetic field (H _W ) (H _E ) at the time of recording can be independently varied, the present invention is not limited to the embodiment of the present invention. The present invention can be applied to a magneto-optical disk using the magnetic thin film of.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the operation mode and recording state of each part during recording of the magneto-optical recording method according to the present invention, and FIG. 2 is the operation mode of each part during rewriting of the magneto-optical recording method according to the present invention and It is a schematic diagram which shows a recording state. Also, the third
The figure is a block diagram of a magneto-optical recording apparatus to which the present invention is applied. 4 and 5 are configuration diagrams of a magneto-optical recording apparatus based on the conventional magneto-optical recording method, and FIG. 6 is a diagram showing operation modes of the conventional magneto-optical recording method. In the figure, 1 ... Magneto-optical head, 2 ... Magneto-optical disk, 3
...... Clock signal generation circuit, 4 …… Current source for external magnetic field generation, 5 …… Laser pulse current source, 6 …… Air core coil, 7
...... Focus error servo amplifier, 8 ...... Tracking error servo amplifier, 9 ...... Playback amplifier, 10 …… Electromagnet, 11 …… Motor, 12 …… Coil current polarity switching means,
13 ... Permanent magnet.

Claims (1)

[Claims] 1. A magnetic thin film having perpendicular magnetic anisotropy is used as a recording medium, and at the time of recording "1" of a recording binary signal, a recording laser light pulse synchronized with a clock signal is applied to the recording medium and magnetization is performed. An external magnetic field sufficient to form an inversion bit is applied to the recording medium in synchronization with the clock signal, and at the time of recording “0” of the recording binary signal, it is a recording laser light pulse synchronized with the clock signal. A recording laser light pulse longer than the laser light pulse width at the time of "1" recording of the recording binary signal is applied to the recording medium, and the magnetization state of the recording medium is initialized regardless of the presence or absence of a magnetization reversal bit. In order to record information, a sufficient external magnetic field is applied to the recording medium in synchronization with the clock signal to form a magnetization reversal bit having a shape corresponding to the recording binary signal. Magneto-optical recording method, comprising and.