JP2808597B2 - Magnetic field applying electromagnet for magneto-optical disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic field applying electromagnet for a magneto-optical disk.

(Prior Art) When erasing recorded information in conventional magneto-optical recording, an external magnetic field is applied with a polarity opposite to that during recording, and a laser beam is uniformly applied to the recording medium at the same intensity as during recording. Irradiation, so-called batch erasure, is performed. That is, the magnetization state of the recording medium is returned to the initial state before recording by applying an external magnetic field.

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

(Problems to be Solved by the Invention) In the above-described magnetic field applying means, an applied magnetic field of several hundred Oersted or more is usually required at the time of recording and erasing.
Accordingly, the switching speed of the magnetic field is reduced, and a required applied magnetic field cannot be obtained unless the distance between the recording medium and the coil is sufficiently reduced. Also, when an electromagnet is used, the size of the magnetic field applying means is increased and the inductance of the coil is large, so that the magnetic field switching speed is slow. Further, when a permanent magnet is used, a complicated mechanism is required for switching the magnetic field using a mechanical driving means, and the magnetic field switching speed is also slow in this case. As described above, since the magnetic field switching speed is slow by any of the conventional external magnetic field applying means, the above-described batch erasing method is used for erasing, and when recording, the laser power is rapidly modulated during application of a constant magnetic field. Is used. That is, the conventional apparatus has a problem that it is difficult to provide a so-called overwrite function for overwriting already recorded information with new information at a high speed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new external magnetic field applying unit that solves the conventional problems and enables high-speed switching of a large magnetic field.

(Means for Solving the Problems) A magnetic field applying electromagnet for a magneto-optical disk according to the present invention is folded back at the end surface of the magneto-optical disk into a U-shape, and the two linear portions of the U-shape are formed on both sides of the magneto-optical disk. A high-permeability magnetic body facing each other, and a first parallel coil group provided on a part of the high-permeability magnetic body and having n coils connected in parallel to generate a magnetic field in the same direction. A second parallel coil group having one end connected to the first parallel coil group and connected in parallel so as to generate a magnetic field in a direction opposite to a magnetic field generated by the first parallel coil group. And the above-described n-parallel three-terminal coil.

Here, as the high magnetic permeability magnetic material, ferrite (MnZn, NiZn, etc.), permalloy (NiFe), sendust, amorphous (CoZr, CoZr, FeCoZr, CoNb, CoTa, CoHf, etc.), iron core, and the like can be considered.

The concentric hollow portion of the U-shaped high magnetic permeability magnetic material is set between the laser condensing lens and the magneto-optical medium, and the inner diameter of the hollow portion allows a laser beam to pass therethrough and is tracked by tracking. The size is set so that the lens can be moved. The first and second n coils are electrically connected in parallel, respectively, and the first and second coil groups are connected to one terminal to form a three-terminal electromagnet as a whole. The inductance of the coil is greatly reduced due to the parallel connection. Therefore, since the rise time of the recording current is reduced due to the small inductance, the switching speed of the magnetic field can be greatly increased.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of one embodiment of the present invention. In the figure, the magnetic field applying electromagnet for the magneto-optical disk is a magneto-optical disk 5
A high-permeability magnetic body 1 which is opposed to both sides of the optical disk and is folded at the end surface of the optical disk to form a U-shape; a first magnetic-permeability magnetic body 1 provided in the middle of the high-permeability magnetic body 1 and electrically connected in parallel; , And one terminal is connected to the first parallel coil group 2 and the second parallel coil group 3. A recording current is supplied from the electromagnet drive circuit 4 to the first parallel coil and the second parallel coil alternately.

FIG. 2 is a circuit diagram of FIG. 1, in which a first parallel coil group 2 and a second parallel coil group 3 each made of n insulated conductors, and an electromagnet drive circuit for driving these parallel coil groups 4 is shown.

By applying an electric current alternately to the first and second parallel coil groups 2 and 3 by the electromagnet drive circuit 4, an applied magnetic field in the vertical direction of the recording medium is given. In addition, high permeability magnetic material 1
A 3 mm thick film having a length of about 20 cm was used, and a first and second parallel coil group having a wire diameter of 150 μm was used. A current value of several hundred mA to 1.0 A is appropriate.
In the magnetic field applying means configured in this manner, since the coil is electrically connected in parallel, it is easy to reduce the inductance L of the coil to 1 μH or less. At a distance of mm, a magnetic field of several hundred Oersteds can be easily switched at a high speed of several MHz.

FIG. 3 is a block diagram of a magneto-optical recording / reproducing apparatus in which a peripheral system is added to the embodiment of FIG. 1, and recording / reproducing / erasing on the magneto-optical disk 5 is performed by this apparatus. In FIG. 3, the output current of the electromagnet drive circuit 4 is the first parallel coil group 2 and the second parallel coil group 2.
, And upward and downward magnetic fields are alternately applied to the recording medium constituted by the magnetic thin film 6 of the magneto-optical disk 5.

The magneto-optical recording head 31 is equivalent to a conventional one, and has the following configuration. Reference numeral 32 denotes a linearly polarized laser light source, for example, a semiconductor laser. 33, 34 and 35 are beam splitters. The laser beam focusing lens 36 is supported by an actuator 37. The focus error and tracking error signals are input to the servo control circuits 40 and 41 by the focus error signal detecting light receiving element 38 and the tracking error signal detecting light receiving element 39, respectively, and are fed back to the actuator 37 as servo signals. After passing through the polarization filter 42, the reproduction signal is detected by the light-receiving element 43 for reproduction signal and amplified by the reproduction signal amplifier circuit 44. A Gram-Thompson prism is used as the polarization filter
Used a PIN photodiode. Laser light source 32
The laser light source modulation circuit 45 is used for the modulation of
The power of the laser beam is modulated at the time of erasure and reproduction.

TbFeCo on SiN formed by sputtering on a 120 mm diameter plastic substrate as a magneto-optical disk
A disk having a thickness of 800 Å and a SiN layer formed on the TbFeCo film was used. The substrate used was a so-called pre-group substrate in which a groove having a track pitch of 1.6 μm and a depth of 700 Å was formed in advance.

4A to 4C are operation mode diagrams of recording.
While irradiating the recording medium with a laser beam of a constant intensity capable of raising the temperature above the Curie temperature, a first
By applying a modulation current as shown in FIG. 4 (b) to the parallel coil groups 2 and 3 of the second and the third, an external magnetic field corresponding to the recording pattern is applied, and the cooling process accompanying the running of the recording medium is performed. Thus, a recording magnetization state as shown in FIG. 4 (c) is realized corresponding to the direction of the applied magnetic field. First, while irradiating a constant-intensity laser beam of 10 mW on the disk surface at a linear velocity of 9 m / sec, a modulation current of 800 mA was passed at 1 MHz to the parallel coils 2 and 3 of the external magnetic field applying means, and good recording was possible. Was. When a recording magnetic field was newly applied to this recording track under the same conditions at 0.5 MHz, recording corresponding to this recording magnetic field was performed, and the previously recorded signal remained unerased.

FIGS. 5 and 6 are a configuration diagram and a circuit diagram, respectively, of another embodiment of the present invention. In this embodiment, the first, second and third parallel three-terminal coils 7, 8 and 9 are arranged in parallel with the three-terminal parallel coil group of the first embodiment on the high-permeability magnetic body 1.
The first, second and third electromagnet drive circuits 10, 11 and 12 are connected to the respective coils, and these three electromagnet drive circuits are driven by the same recording clock. Thereafter, the overwrite characteristics were measured using an optical head having the same configuration as that of the first embodiment. As a result, overwrite characteristics equivalent to those of the first embodiment were obtained.

(Effects of the Invention) As described above, according to the present invention, a U-shaped high magnetic permeability magnetic material facing both sides of a magneto-optical disk is used, and n
Since the coils are electrically connected in parallel, the inductance can be reduced, so that a high-speed switching of a large magnetic field is possible, and a magnetic field applying electromagnet for a magneto-optical disk with high magnetic flux utilization efficiency can be provided. Therefore, the magneto-optical recording / reproducing method has an effect that an overwrite performance capable of directly performing a desired recording can be realized without requiring the conventional batch erasing.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a circuit diagram of FIG. 1, FIG. 3 is a block diagram of a case where the embodiment of FIG. 1 is applied to a magneto-optical disk drive, FIG. FIG. 3 is a diagram showing a recording operation mode in FIG. 3, FIG. 5 is a block diagram showing another embodiment of the present invention, and FIG.
The figure is the circuit diagram of FIG. 1. High magnetic permeability magnetic body 2. First parallel coil group 3,
... A second parallel coil group, 4... An electromagnet drive circuit, 5.
... optical disk, 6 ... optical disk magnetic medium, 7,8,9 ...
First, second, third parallel three-terminal coils, 10, 11, 12, ... first, first
2, a third electromagnet drive circuit, 13 ... flip-flop, 21
… Hollow part, 31… Head for magneto-optical recording, 32… Laser light source, 33, 34, 35… Beam splitter, 36… Laser beam focusing lens, 37… Actuator, 38… Focus error Light receiving element for signal detection, 39 ... Light receiving element for tracking error signal detection, 40, 41 ... Servo control circuit, 42 ... Polarizing filter, 43 ... Light receiving element for reproduction signal detection, 44 ... Amplifier circuit, 45 ... ... Laser light source modulation circuit.

Claims (1)

(57) [Claims] 1. A high-permeability magnetic material which is folded at an end surface of a magneto-optical disk to form a U-shape, wherein two straight portions of the U-shape face each of both surfaces of the magneto-optical disk, and the high-permeability magnetic material. A first parallel coil group provided on a part of the body, wherein n coils are connected in parallel so as to generate a magnetic field in the same direction; one end connected to the first parallel coil group; A second parallel coil group connected in parallel so as to generate a magnetic field in a direction opposite to a magnetic field generated by the first parallel coil group, and the n-parallel three-terminal coil. A magnetic field applying electromagnet for a magneto-optical disk.