JPH0456362B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a magneto-optical disk device, and more particularly to a mechanism of the device that applies a bias magnetic field necessary for recording, reproducing, and erasing to a magneto-optical disk.

(b) Background of the Technology As electronic computers become faster and have larger capacities, storage devices, which are the main part of computers, are also required to have higher density and larger capacity. Currently, magnetic storage devices such as magnetic disks, which are easy to record and read, are the mainstream, but optical disks that record and read information optically can theoretically achieve a recording density one order of magnitude higher than current magnetic disks. It has begun to be used particularly for recording and reproducing image information. Furthermore, due to the nature of the recording medium, magneto-optical disks, which allow users to erase and repeatedly record and reproduce information, have a much higher recording density than magnetic disks as large-capacity storage media that require frequent rewriting. It is attracting attention as a recording medium that has the potential to provide comparable access times and low bit costs comparable to magnetic tape.

(c) Prior Art and Problems The magneto-optical recording method currently being developed is a so-called heat mode recording method using a laser beam as a heat source, also called a thermomagnetic recording method. As shown in the characteristic diagram of the coercive force Hc and the Curie temperature Tc of the magneto-optical recording medium shown in Figure 1, writing in magneto-optical recording is performed at the Curie temperature Tc of the magneto-optical disk medium
This is done by taking advantage of the sudden drop in coercive force Hc in the vicinity.

That is, when the magneto-optical medium layer 2 on the substrate 1 is magnetized in the direction of the upward arrow as shown in FIG. When a laser beam 3 is focused by a lens 4 and a spot image 5 is irradiated onto the magnetic medium layer 2, the temperature of the irradiated surface increases, and the coercive force Hc of the area increases due to the recording magnetic field (bias magnetic field and demagnetizing field). When the value decreases below (the sum of
A cylindrical magnetic domain is recorded as shown in . This process is a magnetic state transition and does not require any thermal energy, so it has the advantage of high recording sensitivity.

It is obvious that information can be erased by reversing the direction of the bias magnetic field H and irradiating the recording area of the magneto-optical recording medium with a laser beam.

To reproduce information recorded, the Faraday effect is used when the laser beam is transmitted through the magneto-optical medium layer 2, and the Kerr effect is used when the laser beam is reflected.
This method uses a polarizer to detect the rotation of the polarization plane of the projected laser beam 1 due to magnetization to read information. Since this rotation angle is a delicate one of about 0.4°, efforts are being made to improve the signal-to-noise ratio.

FIG. 3 is a block diagram showing the structure of a magneto-optical disk device as an optical information recording/reproducing device.

In the figure, a laser beam 3 emitted from a semiconductor laser 6 passes through a collimating lens 7 and a circular correction prism 8 to become a parallel laser beam 9 having a circular cross section, which is linearly polarized by a polarizer 10.
The beam passes through a beam splitter 11 and a reflecting mirror 12, enters an objective lens 13, and is projected onto a magneto-optical disk 14 to form a minute spot image 5. At this time, information is recorded by the bias magnetic field H applied by the magnetic application device (not shown) as described above.

During reproduction, the beam splitter 11 separates the light reflected by the magneto-optical disk 14 from the laser light beam 9 incident through the same optical path as described above from the incident light, and the separated reflected light 15 is split into a second beam. A beam splitter 16 separates the signal for information reproduction and for servo signals. That is, the laser light beam 15a transmitted through the beam splitter 16 is split by a reflecting mirror 17 which also serves as a mask, and after entering the condensing lens 18, two
It is projected onto a segmented detector 20 and a focus error signal is obtained from the difference of the detector 20.

On the other hand, it is reflected by the reflecting mirror 17 and passes through the condensing lens 19.
The incident laser beam 15a is also projected onto a two-split detector 21, and a tracking signal is obtained as a difference.

The signal reproducing laser beam 15b reflected by the beam splitter 16 passes through an analyzer 22 for detecting changes in the optical polarization plane, and then passes through a condenser lens 23.
The light is focused and incident on the photodetector 24, where the optical signal is photoelectrically converted into an electrical signal.

Here, information is read out as the rotation of the plane of polarization by the reversed magnetization portion of the magneto-optical medium layer 2 of the magneto-optical disk 14.

In the above configuration, let us consider the aforementioned bias magnetic field application device essential for recording, reproducing, and erasing information.

There are methods using permanent magnets and electromagnets as bias magnetic field applying devices, but both have drawbacks as described below.

When using permanent magnets, in order to switch the direction of the applied magnetic field, there are methods such as reversing the magnet itself or using two magnets and mechanically switching them alternately, but both require a long switching time and require a lot of space inside the device. There are drawbacks such as the need for extra space. In particular, the long switching time is a fatal drawback when used for electronic computer files.

When using an electromagnet, a large current must be continuously passed through the excitation coil to maintain a predetermined bias magnetic field during recording or erasing operations, resulting in a significant temperature rise in the electromagnet and the need to switch the magnetic field. Because the rise and fall of the time-reversed magnetic field is delayed, special cooling means are required.

As described above, the emergence of a high-performance bias magnetic field applying device that eliminates the drawbacks peculiar to conventional bias magnetic field applying devices for magneto-optical disk devices has been long awaited.

(d) Purpose of the Invention The present invention has been made in view of the above-mentioned points, and is intended for use as a bias magnetic field in a magneto-optical disk device, by electrically reversing the direction of an applied magnetic field at high speed, and by reducing the amount of heat generated by the magnetic field applying device itself. The present invention is intended to provide a bias magnetic field applying device that does not require a bias magnetic field.

(e) Structure of the Invention The object of the above invention is to record or record information by condensing a light beam from a light source such as a semiconductor laser using an optical lens and projecting the light spot onto a magneto-optical disk to which a bias magnetic field is applied. In the optical information recording/reproducing device, the bias magnetic field applying means is made of a semi-hard magnetic material and has a magnetic core having a sufficient distance between the north pole and the south pole, and excitation capable of reversing the polarity of the magnetic pole. This can be easily achieved by employing a magneto-optical disk bias magnetic field applying device characterized by comprising a coil and a pulse excitation current power supply.

(f) Embodiment of the Invention Before describing an embodiment of the present invention, the magnetic material of the magnetic core of the magnet will be described below.

As is well known, magnetic materials are broadly classified into soft magnetic materials and hard magnetic materials depending on their magnetic properties. Semi-hard magnetic materials have characteristic values between soft and hard magnetism, and coercive force Hc
This term is especially used when a magnet of about 10 to 100 Oe is used to reverse the magnetization or change the magnetic flux using a magnetizing coil, and the point is that the residual magnetic flux after the magnetic field is removed is used. It is the same as hard magnetic material.

Using a semi-hard magnetic material as the magnetic core material of an electromagnet has the following advantages. That is, (1) since the coercive force Hc is about 100 Oe, the magnetization direction can be easily reversed electrically.

(2) It has strong magnetic anisotropy and excellent squareness, so once it is magnetized, the direction of magnetization will not reverse unless an external magnetic field with a coercive force Hc or higher is applied. Therefore, it is sufficient to flow a pulsed magnetization reversal current only when switching between recording and erasing information.

(3) The residual magnetic flux density of semi-hard magnetic materials is usually
It can be more than 10,000G, and if Fe-Co alloy is used,
Since it reaches 15,000 to 20,000 G, it is possible to generate a magnetic field with approximately the same strength as that obtained with an electromagnet whose core is made of permanent magnet materials such as Alnico magnetic material, R-Cos magnetic material, or pure iron.

(4) Unlike hard magnetic materials, semi-hard magnetic materials are generally soft and have good mechanical workability, and can be easily processed into any shape required for magneto-optical disk devices.

etc.

The present invention makes full use of the characteristics of the semi-hard magnetic material described above. An example of this is shown in the fourth section.
It is conceptually shown in the perspective view of the figure.

As shown in the figure, a magnetic core 30 having an elongated magnetic pole face M is placed over the entire length of the data area in the radial direction of the magneto-optical disk 14 (length D as shown). Place and fix with a gap of . The semi-hard magnetic material of the magnetic core 30 has strong magnetic anisotropy, and the direction of the anisotropy is aligned perpendicular to the magneto-optical disk 14.

The magnetic pole surface M of the magnetic core 30 is elongated as described above, and the magnetic core 30 is somewhat thin, but the portion indicated by B in the opposite figure is relatively thick and narrow. An excitation coil 31 is wound around this B portion, and is connected to a pulse excitation power source (not shown) through a terminal T. The pulse excitation power source is controlled in conjunction with the write/read/erase control circuit of the magneto-optical disk device.

On the other hand, using a conventional optical system, the laser beam 9 is projected onto the magneto-optical disk 14 from the side opposite to the magnetic pole surface M of the magnetic core 30 for the bias magnetic field of the magneto-optical disk 14, as shown in the figure. Recording, reproduction, and erasing are performed by forming a spot image 5 (see FIG. 3) and heating the magneto-optical medium layer 2 (see FIG. 2) at that point.

Since the leakage magnetic field from the electromagnet for driving the movable parts of these optical systems, especially the focusing of the optical head, is 30 to 50 Oe, a semi-hard magnetic material baicaloy (Fe-Co-V) with a coercive force Hc of about 80 Oe is suitable. be.

Note that 32 shown in FIG. 4 is a yoke, which is preferably made of a semi-hard magnetic material, but may also be made of pure iron. Further, it is not necessarily necessary to arrange it at a position close to the opposite side of the magnetic pole M.

FIG. 5 is a time chart of the polarity reversal of the magnetic core 30 described above, and the horizontal axis is the time axis. FIG. 5a is a time chart of the erasing operation, and E indicates the erasing operation. FIG. 5b is a recording (writing) time chart, and R indicates the recording operation. At this time, the bias magnetic field of the magneto-optical disk device must be reversed, as shown in Fig. 5c.
Pulsed excitation currents of P+P and P- are passed through the excitation coil as shown in the time chart. Since the power of this excitation current is extremely small, it does not generate any heat that requires cooling, and therefore the pulse excitation current has a steep rise and fall, making it ideal for high-speed information processing. Another advantage is that no extra cooling device is required.

(g) Effects of the invention As is clear from the above description, a semi-hard magnetic material is used for the magnetic core of a magnetic field device that applies a bias magnetic field to a magneto-optical disk device based on the present invention, and recording on a magneto-optical disk is achieved. By applying a pulsed excitation coil current in response to erasure and reversing the polarity of the magnetic field, it is possible to reverse the bias magnetic field at high speed with less power, and there is no need for a cooling device for the excitation coil. Since information can be recorded and reproduced, it has the effect of further improving the performance of magneto-optical disks as large-capacity, high-speed recording media.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the temperature characteristics of the coercive force Hc of a magneto-optical medium, Fig. 2 is an explanatory diagram showing the principle of information recording on a magneto-optical disk, and Fig. 3 is a configuration diagram of a conventional magneto-optical disk device. FIG. 4 is a perspective view showing one embodiment of a bias magnetic field applying device based on the present invention;
The figure is a time chart showing the mutual relationship between the recording and erasing operations of the magneto-optical disk and the excitation coil current of the bias magnetic field applying device interlocked with the recording and erasing operations. In the figure, 1 is the substrate of the magneto-optical disk, 2 is the magneto-optical medium layer, 3 is the laser beam, 4 is the lens, and 5 is the magneto-optical disk.
is a light spot image, 6 is a semiconductor laser, 7 is a collimating lens, 8 is a perfect circle correction prism, 9,
15 and 15b are laser beams, 10 is a polarizer,
11 and 16 are beam splitters, 12 is a reflecting mirror,
13 is an objective lens, 14 is a magneto-optical disk, 17
18, 19, 23 are condenser lenses, 20, 21 are two-split detectors, 22 is an analyzer, 24 is a photodetector, 30 is a magnetic core, 31 is an excitation coil, 32 is a reflecting mirror that also serves as a mask, 32 is a Each yoke is shown.

Claims (1)

[Claims] 1. In an optical information recording/reproducing device that records or erases information by condensing a light beam from a light source such as a semiconductor laser using an optical lens and projecting the light spot onto a magneto-optical disk to which a bias magnetic field is applied. , the bias magnetic field applying means is composed of a magnetic core made of a semi-hard magnetic material and having a sufficient distance between the north and south poles, an excitation coil capable of reversing the polarity of the magnetic poles, and a pulsed excitation current power supply. Features: Bias magnetic field application device for magneto-optical disks.