JP2604700B2 - Magneto-optical recording / reproduction / erasing method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magneto-optical recording / reproducing / erasing system for recording / reproducing / erasing information by using a laser beam and an apparatus therefor.

(Prior art and its problems) The optical recording method, especially the optical disk memory method,
In recent years, it has attracted attention as one of large-capacity file memories because it can perform large-capacity recording and can also perform non-contact and high-speed access. Among them, MnB as a recording medium
crystalline magnetic thin films such as i, MnCuBi, MnTiBi, MnAlGe or
Magneto-optical disk memory using an amorphous magnetic thin film made by combining rare earth metals such as Tb, Gd, Dy, Ho and transition metals such as Fe, Co, Ni, etc. Due to its advantages, it is being actively studied in various places.

Conventionally, in the known magneto-optical recording / reproducing / erasing method, the following operations are performed for recording / reproducing / erasing information. The recording medium is preliminarily magnetized in one direction by an external magnetic field greater than the coercive force of the medium.

For recording, heat generated by a laser beam is used. The laser light beam is narrowed down to a minute spot of 1 to 2 μmφ and irradiated on the recording medium to raise the medium temperature. When performing Curie temperature recording, the recording medium is raised to a Curie temperature or higher, and a reversal 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 to around room temperature, raise the temperature to a certain temperature by irradiating a laser light beam, and form a reversal magnetic domain by an externally applied magnetic field using the decrease in the coercive force of the medium. . 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 performed using a magneto-optical effect (Kerr effect or Faraday effect). That is, information is read from the recording medium by utilizing the fact that the polarization plane of reflected light or transmitted light from the medium is rotated according to the presence or absence of the reversal 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 transmitted light.

When erasing recorded information, an external magnetic field is applied with a polarity opposite to that during recording, and the recording medium is uniformly irradiated with a laser beam at 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.

Here, the known external magnetic field applying means is, for example, a method using an air core coil, a method using an electromagnet, or a method using a permanent magnet.

However, there is a difference in applied magnetic field of 300 Oe or more between recording and erasing.Therefore, when using an air-core coil, the coil becomes large and the required applied magnetic field cannot be obtained unless the distance between the recording medium and the coil is sufficiently close. There is a disadvantage that it cannot be done. Also, when an electromagnet is used, there is a disadvantage that the magnetic field applying means becomes large and the magnetic field switching is slow. When a permanent magnet is used, the magnetic field is switched using mechanical driving means, and thus has a disadvantage that a complicated mechanism is required.

In any of the conventional systems, the recording mode and the erasing operation mode are as shown in FIGS. 4 (a), (b), (c) and (d) during recording (FIGS. 4 (a) and (d)). b)) Applied magnetic field Hw
And erasing (Fig. 4 (c), (d)) is not eliminated disadvantage large difference of the applied magnetic field H _E of.

(Object of the Invention) An object of the present invention is to eliminate such a conventional drawback, and to use a small and easy magnetic field applying means, and to provide a novel magneto-optical recording / reproducing apparatus capable of easily performing recording / reproducing / erasing. An erasing method and apparatus are provided.

(Constitution of the Invention) According to the present invention, in a magneto-optical recording / reproducing / erasing method for recording / reproducing / erasing information on a recording medium including a magnetic thin film having perpendicular magnetic anisotropy with a laser beam, the magnetization direction of the magnetic thin film The recording process of forming a magnetic domain in the magnetic thin film by applying a constant magnetic field and irradiating a laser beam modulated by information with a random demagnetized state as an initial state within the spot size of the reproducing laser light, A magneto-optical recording / reproducing / erasing method comprising a reproducing process of reproducing information from the polarization rotation of the laser reflected light corresponding to the presence / absence and an erasing process of returning the magnetization state of the recording thin film to a demagnetized state by applying a magnetic field and irradiating a laser beam is obtained. A magneto-optical recording / reproducing / erasing apparatus for recording / reproducing / erasing information on a recording medium including a magnetic thin film having perpendicular magnetic anisotropy by using a laser beam A recording medium comprising a magnetic thin film whose magnetization direction is initially set to a random demagnetized state within a spot size of a reproducing laser beam; a magnetic field generating means for applying a magnetic field to the recording medium; A magneto-optical recording head for irradiating a laser beam, and a current supply source for changing a current supplied to a magnetic field generating means for recording and erasing. The irradiation is performed by forming magnetic domains in the magnetic thin film whose magnetization direction is upward or downward with respect to the medium surface by irradiation, and reproduction is performed by extracting the polarization plane rotation of laser reflected light corresponding to the presence or absence of the magnetic domains of the recording thin film as a signal. And erasing is performed by returning the magnetization state of the recording thin film to a demagnetized state by applying a magnetic field and irradiating a laser beam. Recording and playback erasing device can be obtained.

(Detailed Description of Configuration) The present invention has solved the problems of the conventional technology by adopting the above configuration. FIG. 1 shows a recording / erasing operation mode diagram of the magneto-optical recording / reproducing / erasing method according to the present invention. The magnetization state of the magnetic thin film used for the recording medium is set to a demagnetized state, and this is set to an initial state. Here, the demagnetized state refers to a state in which the magnetization state of the magnetic thin film is as follows. When the magnetization state of the magnetic thin film is in a random state within the spot size of the reproducing laser beam, that is, when a perpendicular magnetization film is used, the upward and downward magnetizations with respect to the thickness direction of the recording film. This is a state in which the image is divided into small portions that are sufficiently smaller than the spot size and are mixed. Recording is performed by forming magnetic domains in the magnetic thin film in the demagnetized state (FIG. 1A). The magnetization direction of the magnetic domain may be upward or downward with respect to the medium surface. In FIG. 1B, it corresponds to the applied magnetic fields Hw and Hw '. Whereas conventional recording performs recording by forming a reversal magnetic domain in a magnetic thin film magnetized in one direction, in the recording according to the present invention, it is sufficient to form a magnetic domain in a demagnetized magnetic thin film. ,
The applied magnetic field required for recording may be smaller than in conventional recording. In the reproduction, as in the conventional reproduction, the polarization plane rotation of the laser light reflected from the magnetic thin film is extracted as a signal. Clearly, the rotation of the polarization plane due to the Kerr effect is different between a region having a magnetic domain and a demagnetized region, so that a sufficient reproduction signal can be obtained. When reproducing the demagnetized area, it is difficult to determine the individual magnetization in the vertical direction, and the reproduction signal from the recording medium is composed of the reproduction signal from the upper magnetization and the reproduction signal from the lower magnetization. Intermediate level. Figure 1 is an erase (c), the external magnetic field H _E is applied, the magnetization state initial state after erasing the predetermined value and the laser beam P _E of constant intensity in a region requiring the erase as shown in (d) of It becomes the same demagnetized state.

Hereinafter, details of the present invention will be described with reference to the drawings.
FIG. 2 shows an example of the configuration of a magneto-optical recording / reproducing / erasing apparatus according to the present invention.

A magneto-optical recording head 3 is provided above a magneto-optical disk 1 using a magnetic thin film 2 having perpendicular magnetic anisotropy as a recording medium, and a magnetic field applying means is provided between the magneto-optical disk 1 and the magneto-optical recording head 3. This is a configuration in which an air core coil 4 is provided.
The magnetic thin film 2 is a crystalline or amorphous magnetic thin film, for example, a crystalline magnetic thin film such as MnBi, MnCuBi, MnTiBi, MnAlGe, or a rare earth metal such as Sm, Tb, Gd, Dy, Ho and F.
An amorphous magnetic thin film formed by a combination with a transition metal such as e, Co, and Ni. The magneto-optical disk 1 is rotated at a predetermined speed by a disk drive motor 5. The magneto-optical recording head 3 includes an optical system for magneto-optical recording / reproducing and erasing and a light detecting mechanism. The magneto-optical recording head 3 itself is a magneto-optical disk 1 as indicated by an arrow in the figure.
At a predetermined speed in the radial direction.

In the magneto-optical recording head 3, reference numeral 6 denotes a linearly polarized laser light source, for example, a semiconductor laser. 7, 8, and 9 are beam splitters. The laser light beam focusing lens 10 is supported by an actuator 11.

The focus error and tracking error signals are respectively detected by the focus error detecting light receiving element 12 and the tracking error detecting light receiving element 13 and input to the servo control circuits 14 and 15 to become servo signals, which are fed back to the actuator 11. The reproduction signal is detected by the reproduction signal detecting light receiving element 17 after passing through the polarization filter 16 and is amplified by the reproduction signal amplifier circuit 18. As the polarizing filter 16, for example, a Glan-Thompson prism is used. As the reproduction signal detecting light receiving element 17, for example, a PIN photodiode or an avalanche photodiode is used. A laser light source modulation circuit 19 is used to modulate the laser light source 6, and modulates the power of the laser light source 6 at the time of recording, erasing, and reproducing.

The air-core coil 4 is integrated with the magneto-optical recording head 3 and supplied with a current for obtaining a desired applied magnetic field from a current supply source 20. Since the applied magnetic field required for recording / erasing may be smaller than in the conventional example, the air-core coil 4 may be smaller than in the conventional example.

(Example 1) Using the magneto-optical recording / reproducing / erasing apparatus shown in FIG. 2, information was recorded, reproduced, and erased on the magneto-optical disk.
As the magneto-optical disk, a disk in which a TbFe film was formed to a thickness of 800 mm by a sputtering method on a 120 mmφ plastic substrate was used. As the substrate, a so-called pre-group substrate in which a groove having a width of 0.8 μm and a pitch of 2.5 μm and a depth of 700 ° was formed in advance was used.

First, after the magnetized magneto-optical disk was initially magnetized in one direction, a bias magnetic field of 140 Oe was applied to the magneto-optical disk in the initial magnetized direction, and a constant intensity laser beam of 4 mW was irradiated on the disk surface at a linear velocity of 9 m / sec. . As a result of observing the magnetization state of the irradiated disk track with a polarizing microscope, it was confirmed that the disk track was uniformly demagnetized.

Next, a 1 MHz signal was recorded on the demagnetized magneto-optical disk while changing the applied magnetic field at a power of 4 mW.
The reproduction C / N was saturated in the range of 0 Oe or more in the magnetization reversal direction and 270 Oe or more in the initial magnetization direction as shown in FIG. 3, and good recording was possible.

The erasure was performed by applying a magnetic field of 140 Oe in the initial magnetization direction and using a laser beam having a constant intensity of 4 mW. No disappearance of the recorded signal was observed.

(Example 2) Using the magneto-optical recording / reproducing / erasing apparatus shown in Example 1 and a magneto-optical disk, recording / erasing of a 1 MHz signal was repeated.

Recording power 4mW, recording applied magnetic field 0Oe, erase power 4m
W, the applied magnetic field at the time of erasing was 140 Oe (initial magnetization direction). 10 ⁵
No change was observed in the recording / erasing characteristics even after the repetition.

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

Since the demagnetized state of the magnetic thin film is set to the initial state, the amount of change in magnetic field required for recording / reproducing / erasing may be 1/2 or less as compared with the conventional recording / reproducing / erasing method.

Since the amount of change in the magnetic field required for recording / reproducing / erasing is smaller than that of the conventional method, the magnetic field generating means can be reduced in size, and accordingly, the magneto-optical recording / reproducing / erasing device can be reduced in weight and size.

Due to the miniaturization of the magnetic field generating means, the magnetic field switching speed can be increased, and recording / erasing not only in tracks but also in sector units becomes easy.

Further, the present invention has been described in the embodiment as a magneto-optical disk.
The present invention is not limited to the TbFe film but can be widely applied to a crystalline thin film for magneto-optical recording or an amorphous magnetic thin film.

[Brief description of the drawings]

1 is an operation mode diagram of the magneto-optical recording / reproducing / erasing method according to the present invention, FIG. 2 is a configuration diagram of a magneto-optical recording / reproducing / erasing apparatus to which the present invention is applied, and FIG. 3 is used in an embodiment of the present invention. FIG. 4 is a diagram showing the recording characteristics of the magneto-optical disk obtained, and FIG. 4 is an operation mode diagram of a conventional magneto-optical recording / reproducing / erasing method. In the figure, 1 ... magneto-optical disk, 2 ... magnetic thin film, 3 ...
Magneto-optical recording head, 4 air-core coil, 5 disk drive motor, 6 laser light source, 7, 8, 9 beam splitter, 10 laser beam focusing lens, 11
… Actuator, 12, 13 …… Light receiving element for error detection, 1
4,15 ... servo control circuit, 16 ... polarizing filter, 17 ...
A light receiving element for detecting a reproduction signal, 18 an amplifier circuit, 19 a laser light source modulation circuit, and 20 a current supply source.

Claims (2)

(57) [Claims] 1. A magneto-optical recording / reproducing / erasing method for recording / reproducing / erasing information on a recording medium including a magnetic thin film having perpendicular magnetic anisotropy by using a laser beam, wherein the magnetization direction of the magnetic thin film is the same as that of the reproducing laser beam. A recording process of forming a magnetic domain in the magnetic thin film by applying a constant magnetic field and irradiating a laser beam modulated by information with a random demagnetized state as an initial state within the spot size, and a laser reflection corresponding to the presence or absence of a magnetic domain in the recording thin film A magneto-optical recording / reproducing / erasing method comprising: a reproducing process of reproducing information from a polarization rotation of light; and an erasing process of returning a magnetization state of the recording thin film to a demagnetized state by applying a magnetic field and irradiating a laser beam. 2. A magneto-optical recording / reproducing / erasing apparatus for recording / reproducing / erasing information on a recording medium including a magnetic thin film having perpendicular magnetic anisotropy by using a laser beam, wherein the magnetization direction is within the spot size of the reproducing laser beam. A recording medium comprising a magnetic thin film having a random demagnetized state as an initial state; a magnetic field generating means for applying a magnetic field to the recording medium; a magneto-optical recording head for irradiating the recording medium with laser light; And a current supply source capable of changing a current supplied to the magnetic field generating means. The recording is performed by applying a constant magnetic field and irradiating a laser beam modulated by information so that the magnetization direction of the magnetic thin film is directed upward with respect to the medium surface. Alternatively, the reproduction is performed by forming a downward magnetic domain, and the reproduction is performed by extracting the polarization plane rotation of the laser reflected light corresponding to the presence or absence of the magnetic domain of the recording thin film as a signal. Ri performed, erasing, magneto-optical recording and reproducing erasing apparatus which is characterized in that by returning the magnetization state of the recording thin film by a magnetic field applied and laser light irradiation demagnetized.