JPH0673201B2 - Magneto-optical recording / reproducing method and device - Google Patents

Description

The present invention relates to a magneto-optical recording / reproducing / erasing method and apparatus for recording / reproducing / erasing information by 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,
The magneto-optical disk memory using an amorphous magnetic thin film made 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.

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

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 laser beam irradiation, and use the reduction of the coercive force of the medium to form an inverted magnetic domain by an externally applied magnetic field. . By the means, 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 Faradey 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 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.

When erasing recorded information, so-called collective erasing is performed in which an external magnetic field is applied with a polarity opposite to that used during recording, and a laser light beam is uniformly applied to the recording medium 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 or a method using a permanent magnet. However, since an applied magnetic field of several hundred nirsted or more is usually required at the time of recording and erasing,
When an air-core coil is used, the size of the coil becomes large, and accordingly, the magnetic field switching speed becomes slow, and the required applied magnetic field cannot be obtained unless the distance between the recording medium and the coil is sufficiently short. Further, even when an electromagnet is used, the magnetic field applying means becomes large in size and the magnetic field switching speed is slow, which is a drawback. Furthermore, when a permanent magnet is used, a complicated mechanism is required to switch the magnetic field by using a mechanical driving means, and in this case as well, the magnetic field switching speed becomes slow.

As described above, since the magnetic field switching speed is slow in any of the conventional methods, the batch erasing method described above is used for erasing, and a method for high-speed modulation of laser power during constant magnetic field application is used for recording. Was used. This method has a drawback that the difference between the applied magnetic field during recording and the applied magnetic field during erasing is large. Further, in the conventional apparatus, it is impossible to have so-called overwrite performance, in which new information is overwritten on already recorded information at high speed.

(Object of the Invention) The object of the present invention was made in order to eliminate such drawbacks of the prior art, using a small and simple magnetic field applying means,
You can easily record / playback / delete,
It is an object of the present invention to provide a novel magneto-optical recording / reproducing / erasing method and apparatus having overwrite performance.

According to the present invention, in a magneto-optical recording / reproducing / erasing method in which a magnetic thin film having perpendicular magnetic anisotropy is used as a recording medium and information is recorded / reproduced / erased by a laser beam and an externally applied magnetic field, The magnet and one of the magnetic poles of the permanent magnet are in contact with each other at a right angle to the permanent magnet, and one end of the right-angled opposing portion is in contact with the other end of the permanent magnet. As described above, the core portion of the high-permeability magnetic body composed of parallel facing portions configured to face the permanent magnets in parallel and a winding wound around the parallel facing portions are provided, and a current flows through the windings. A magnetic field applying device that applies a magnetic field to the recording medium during heating, and does not apply a magnetic field to the recording medium when no current is flowing through the winding, with a predetermined interval on one side of the recording medium. Fixed The recording medium is irradiated with a predetermined laser beam, and different levels of current are applied to the windings of the magnetic field applying device during recording and erasing so that different levels of magnetic field can be applied to the recording medium. A magneto-optical recording / reproducing / erasing method is obtained which is characterized by

Further, in the magneto-optical recording / reproducing / erasing apparatus according to the present invention, in the magneto-optical recording / reproducing / erasing apparatus including an optical head and a magnetic field applying means for the recording medium, the magnetic field applying means is installed on one side of the recording medium, A permanent magnet and a right-angled facing portion configured to contact one of the magnetic poles of the permanent magnet so as to face the permanent magnet at a right angle, and one end of the right-angled facing portion contacts the right-angled facing portion and the other end approaches the other magnetic pole of the permanent magnet. A magnetic field is applied to the recording medium when a current flows and a core portion of a high-permeability magnetic body composed of parallel facing portions configured to face each other in parallel with the permanent magnet, Windings wound around the parallel facing portions so as not to apply a magnetic field to the recording medium when no current is flowing, and further, a current source is connected to the windings. .

(Detailed Description of Configuration) Next, the configuration of the present invention will be described in detail with reference to the drawings. FIGS. 1 (a) and 1 (b) show a recording / erasing operation mode diagram of a first magneto-optical recording / reproducing / erasing method according to the present invention. The magnetized state of the magnetic thin film used for the recording medium is set to the demagnetized state, which is the initial state. Demagnetized state, a medium region other than at least a recording track, the applied magnetic field H _W 'and after magnetized in the same direction, the recording track H _W' in the same direction of the erasing magnetic field H _E
This can be achieved by applying erase power P _E while applying. Recording is performed by forming magnetic domains in the demagnetized magnetic thin film as shown in FIGS. The magnetization direction of the magnetic domain corresponds to the applied magnetic field H _W or H _W ′,
It may be upward or downward with respect to the medium surface. In contrast to conventional recording in which a reversed magnetic domain is formed in a magnetic thin film magnetized in one direction to perform recording, in the recording according to the present invention,
Since the magnetic domains may be formed in the demagnetized magnetic thin film, the applied magnetic field required for recording may be smaller than that 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. Since the rotation of the deflecting surface due to the Kerr effect is obviously different between the region having magnetic domains and the demagnetized region, a sufficient reproduction signal can be obtained. At the time of erasure, as shown in FIGS. 1 (c) and (d),
By applying a constant intensity laser light P _E and a constant external magnetic field H _E to the region requiring erasing, the same demagnetization state as the initial state is achieved.

FIG. 2 shows the configuration of a magneto-optical recording / reproducing / erasing apparatus according to the present invention. According to this, a magneto-optical disk 1 using a magnetic thin film 2 having perpendicular magnetic anisotropy as a recording medium.
A magneto-optical recording head 3 is provided above, and an external magnetic field applying unit 4 is provided below the magneto-optical recording head 3. Here, the magneto-optical recording head 3 is equivalent to a conventional one having an optical system for recording / reproducing / erasing and a photodetection mechanism, but the external magnetic field applying means is different from the conventional one.

FIG. 3 is a view showing the structure of the external magnetic field applying means, which has a plate-shaped permanent magnet 22, a portion of the permanent magnet that faces the magnetic pole on the side facing the recording medium, and a winding 24. And a core portion 23 made of a high-permeability magnetic material. The winding 24 is connected to the current source 20, and the application and shielding of the magnetic field to the recording medium is selected depending on the presence / absence of current in the winding 24, as shown in FIG. Ie winding
When no current is flowing in 24, the core portion 23 causes the magnetic flux generated from the magnetic poles of the permanent magnets 22, as shown in FIG.
In order to form a magnetic path that leads efficiently to the other magnetic pole,
A magnetic field is hardly applied to the recording medium side. On the other hand, the fourth
As shown in FIG. 2B, when a current I flows through the winding wire 24, the magnetic flux leaks from the magnetic pole of the permanent magnet 22 to the outside by the amount of the magnetic flux generated in the core portion 23 by the current I, and the magnetic flux is transferred to the recording medium. A vertical bias magnetic field is applied.

FIG. 4 (c) shows the current I flowing in the winding and the bias magnetic field.
The relationship with H _B is shown. The bias magnetic field H _B increases with the increase of the current I, and as the magnetization of the core portion 23 approaches saturation, the bias magnetic field H _B also tends to saturate. , At a current value I _S or more, a bias magnetic field equivalent to that of the conventional permanent magnet bias can be obtained. In FIG. 2,
Such an external magnetic field applying means is arranged below the recording medium so that the magnetic pole N of the permanent magnet faces the medium. Therefore, while the winding is energized, an upward bias magnetic field is applied to the recording medium. Further, the magnitude of the bias magnetic field can be controlled by the magnitude of the current flowing through the winding.

As the permanent magnet 22, a samarium-cobalt magnet, an alnico magnet, or a ferrite magnet having a thickness of several millimeters and a width and a length of several millimeters to several tens of millimeters is used, and the core portion 23 has a thickness of several millimeters and a magnetic path length. And a width of several millimeters to several tens of millimeters of NiFe alloy, or soft ferrite such as NiZn ferrite or MnZn ferrite is used, and as the winding wire 24, a copper wire having a wire diameter of several tens of microns to several hundreds of microns is used. The line is dozens of turns. Further, the current value I _S is preferably several tens to several hundreds of milliamperes.

In the external magnetic field applying means thus configured, it is easy to set the inductance L of the winding to 1 μH or less,
High-speed switching can be easily realized even from a position several millimeters away from the recording medium with a magnetic field of several hundred oersteds of several megahertz order.

The magneto-optical recording head 3 is the same as the conventional one as described above and has the following configuration. Reference numeral 6 is a linearly polarized laser light source, and for example, a semiconductor laser is used. 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 detected by the focus error detection light receiving element 12 and the tracking error detection light receiving element 13, respectively, and the servo control circuit is detected.
The signals are input to 14, 15 and serve as servo signals, which are fed back to the actuator 11. After passing through the polarization filter 16, the reproduction signal is detected by the reproduction signal detecting light receiving element 17 and amplified by the reproduction signal amplifying circuit 18. As the polarization filter 16, for example, a Gram Thomson prism is used. As the light receiving element 17 for detecting the reproduction signal, for example, a PLN photodiode or an avalanche photodiode is used. A laser light source modulation circuit is used to modulate the laser light source 6, and the power of the laser light is modulated at the time of recording, erasing, and reproducing.

5 to 9 are diagrams showing other configuration examples of the external magnetic field applying means.

In FIG. 5, the core portion 27 is characterized in that the width of the portion provided with the winding wire 28 is smaller than the portion facing the magnetic pole of the permanent magnet 22.

In FIG. 6, the core portion 29 is characterized in that the portion where the winding wire 30 is applied is thinner than the portion facing the magnetic pole of the permanent magnet 22.

In FIG. 7, the core portion 31 is characterized in that the width and thickness of the portion to which the winding 32 is applied are smaller than the portion facing the magnetic pole of the permanent magnet 22.

Compared with the first configuration example shown in FIG. 3, in each of these configuration examples, the magnetization of the winding portion is saturated at a lower current value by reducing the cross-sectional area of the winding core. As a result, high speed switching of the applied magnetic field is facilitated.

In FIG. 8, since the core portion 37 has a U shape, the magnetic flux generated from the magnetic pole of the permanent magnet can be guided to the other magnetic pole more efficiently than in the first configuration example. 36
It is possible to more completely shield the applied magnetic field when no current is applied to the.

In FIG. 9, a concentric cylindrical permanent magnet 39 is attached to a core portion 40 provided with a hole 42 of the same size as the inner diameter, with the hole position and the inner diameter aligned. In this case, since the hole 42 can be used as a passage for the light beam, it is suitable when the external magnetic field applying means is arranged on the same side as the optical head with respect to the recording medium.

Next, a second recording / reproducing / erasing method according to the present invention will be described. FIGS. 10 (a) and 10 (b) show operation mode diagrams in the case where the same device as that in FIG. 2 is used. Also in this case, the demagnetized state should be applied magnetic field at least in the medium area other than the recording track.
After magnetizing in the same direction as H _W ′ (from bottom to top in FIG. 2),
This can be achieved by applying the erasing power P _E while applying the erasing magnetic field H _E in the same direction as H _W ′ to the recording track. Here, the winding current required to generate the erase magnetic field H _E is I _E. In this method, at the time of recording, while applying the same constant power as the above erasing power, the externally applied magnetic field H _E
And the recording magnetic field H _W ′ are sequentially applied. In the cooling process accompanying the strike of the recording medium, a recording magnetization state is realized in the demagnetized state portion 43 as shown in FIG. In the conventional recording, the reversed magnetic domain is formed in the magnetic thin film magnetized in one direction to perform the recording, whereas in the recording according to the present invention, the recording magnetization state is determined corresponding to the current value flowing in the winding. It Therefore, the present method has the overwrite performance capable of realizing desired recording without the need for the batch erasing process. In reproduction, as in conventional reproduction, the polarization plane rotation of the laser light reflected from the magnetic thin film is taken out as a signal.

Example 1 Using the magneto-optical recording / reproducing / erasing apparatus shown in FIG. 2, information recording / reproducing / erasing was performed on a magneto-optical disk. As the external magnetic field applying means, the one shown in FIG. 7 was used.
As the permanent magnet, an Alnico magnet with a thickness of 2 mm and a width of 30 mm and a height of 30 mm is used.For the core part, the part facing the magnetic pole of MnZn ferrite is 2 mm thick, 35 mm wide, and the winding part is 1 mm thick. It is made by molding a product with a height of 10 mm and bonding both with an adhesive. The winding consists of a copper wire with a diameter of 100 μm wound 50 turns. As a magneto-optical disk, a disk in which a TbFe film was formed to a thickness of 800 Å on a 120 mmφ plastic substrate by a sputtering method was used. As the substrate, a so-called pre-groove substrate in which a groove having a width of 0.8 μm, a pitch of 2.5 μm and a depth of 700 Å was previously formed was used.

First, the magneto-optical disk was initially magnetized in one direction, and then a bias magnetic field of 1400e was applied in the initial magnetization direction to obtain a linear velocity of 9 m / se.
At c, a constant intensity laser beam of 4 mW was irradiated on the disk surface.
As a result of observing the magnetized state of the irradiated disk track with a polarization microscope, it was confirmed that the magnet was uniformly demagnetized. Next, a 1 MHz signal was recorded on the demagnetized magneto-optical disk by changing the applied magnetic field with a power of 4 mW. As shown in FIG. 11, 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, and good recording was possible. The erasing 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. The rest of the recorded signal was not seen.

(Embodiment 2) Using the magneto-optical recording / reproducing / erasing apparatus and the magneto-optical disk shown in Embodiment 1, the recording power is kept constant at 4 mW, and the demagnetizing field H _E 140Oe is applied in the initial magnetization direction as the recording magnetic field. When the magnetic domain forming magnetic field H _W '300 Oe was alternately applied at 1 MHz, good recording was achieved as in Example 1. On this recording track,
When a recording magnetic field was newly applied at 0.5 MHz under the same conditions,
Recording was possible corresponding to the recording magnetic field. No erasure of the previously recorded signal was seen.

(Effects of the Invention) As described above, the present invention has the following effects 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 external magnetic field generating means can switch the magnetic field at a higher speed than the conventional one, it is possible to provide a recording / reproducing / erasing apparatus and method having overwrite performance.

[Brief description of drawings]

1 and 10 (a) to 10 (d) are operation mode diagrams of the magneto-optical recording / reproducing / erasing method according to the present invention, and FIGS. 2, 3 and 5-9 are outside of the present invention. The figure which shows the structural example of magnetic field application means, 4 (a), (b) and (c) are the operation | movement explanatory drawings of an external magnetic field application means, FIG. 11 is the light used by the Example of this invention. It is a figure which shows the recording characteristic of a magnetic disc. In the figure, 1 ... magneto-optical disk, 2 ... magnetic thin film,
3 ... Magneto-optical recording head, 4, 26, 33, 34, 35, 38 ... External magnetic field applying means, 5 ... Recording medium strike direction, 6 ... Laser light source, 7, 8, 9 ... Beam splitter , 10 ...... Laser beam focusing lens, 11 ...... Actuator, 12, 13 ...... Error detection light receiving element, 14, 15 ...... Servo control circuit, 16 ...
... Polarizing filter, 17 ... Receiving signal detection light receiving element, 18 ...
… Amplifier circuit, 19 …… Laser light source modulation circuit, 20 …… Current source, 21 …… Relationship between winding current and applied magnetic field, 22,39 …… Permanent magnet, 23,27,29,31,37,40 ...... Cores made of high-permeability magnetic material, 24, 28, 30, 32 ... windings, 42 ... holes. 43 ……
Degaussed state part

Claims (2)

[Claims] 1. A magneto-optical recording / reproducing / erasing method in which a magnetic thin film having perpendicular magnetic anisotropy is used as a recording medium to record / reproduce / erase information by a laser beam and an externally applied magnetic field.
A permanent magnet and a right-angled facing portion configured to contact one of the magnetic poles of the permanent magnet so as to face the permanent magnet at a right angle, and one end of the right-angled facing portion contacts the right-angled facing portion and the other end approaches the other magnetic pole of the permanent magnet. As described above, the core portion of the high-permeability magnetic body composed of parallel facing portions configured to face the permanent magnets in parallel and a winding wound around the parallel facing portions are provided, and a current flows through the windings. A magnetic field applying device that applies a magnetic field to the recording medium when the recording medium is flowing and does not apply a magnetic field to the recording medium when no current is flowing to the winding is provided on one side of the recording medium with a predetermined interval. The recording medium is fixedly installed, and different levels of current are applied to the windings of the magnetic field applying device to apply different magnetic fields to the recording medium during recording and erasing while irradiating the storage medium with a predetermined laser beam. I can do it Magneto-optical recording and reproducing erasing method being characterized in that the. 2. A magneto-optical recording / reproducing / erasing apparatus comprising an optical head and a magnetic field applying means for a recording medium, wherein the magnetic field applying means is installed on one side of the recording medium, and a permanent magnet and one of the permanent magnets are provided. A right-angled facing portion configured to contact the magnetic pole of the permanent magnet and to face the permanent magnet at a right angle, and one end of the right-angled facing portion is brought into contact with the other end of the right-angled facing portion so as to approach the other magnetic pole of the permanent magnet. A core portion of a high-permeability magnetic body composed of parallel facing portions configured to face each other, and a magnetic field is applied to the recording medium when a current is flowing, and the recording is performed when a current is not flowing in the winding. A magneto-optical recording / reproducing / erasing apparatus comprising: a winding wound around the parallel facing portions so as not to apply a magnetic field to the medium; and a current source connected to the winding.