JPS5814304A - Optical thermomagnetic erasing and recording method - Google Patents

Abstract

PURPOSE:To simplify operations of erasing and recording of bit information, by making a practical continuous light incident without changing the direction of an applied bias magnetic field when bit information is recorded on a recording medium. CONSTITUTION:A thermomagnetic optical recording reader 1 is fixed freely attachably and detachably to a bias magnetic field generating device 2 such as a permanent magnet by adhesion and is so arranged that a bias magnetic field is always applied to the device 1. The argon laser having, for example, wavelength 488mm. generated from a light generating device 5 is led to an optical modulator 6 and passes through a polarizer 7 and a half mirror 8 to record bits on the reader 1. In case that recorded bit information is erased, the incident light is irradiated so as to be superposed slightly onto bits to be erased while being moved in the direction opposite to the direction for write. Thus, operations of erasing and recording of bit information are simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photothermal magnetic recording and erasing method. More specifically, the present invention relates to a photothermal magnetic recording and erasing method. This invention relates to a method of recording bit information.

There are two methods for erasing bit information that has been conventionally recorded photothermally and magnetically. , Apra4)', :t
Boutiques (ppl ied Opt 1cm),
Vol. 16 (@ No. 4), pp. 770-777) and a 1 (e.g. Japanese Journal of Applied Physics)
18 (1979) Supplement 18-1, pp. 231-234).

However, in the method of erasing bit information by applying a bias magnetic field larger than the coercive force, if a magnetic material with a large coercive force is used, such as an MnB1 film, for example, 10tt
It is necessary to apply a bias magnetic field as strong as 7oooe with an incident light amount of sW. Since the application of a strong bias magnetic field is also required for erasing, the device must be made by Osaka Securities Co., Ltd., which is not practical. Moreover, it is inconvenient that the recorded bit information cannot be selectively erased.

In addition, in the conventional erasing method, where bit information is erased by applying a bias magnetic field in the opposite direction to that during recording,
For example, when using a GdCo film, writing and erasing are performed under the application of a fairly low bias magnetic field of 900°. Erasing using this method requires that the optical pulse for erasing be applied to the recorded bits so as to completely overlap them, and requires tracking and strict signal synchronization between the bits. If this signal synchronization goes out even slightly, the recorded bits will only be partially erased, and the remaining bits will remain, which may not only cause a decrease in contrast, but also cause new Even if bit information is recorded, the previous recording may remain, which is not desirable in practice.

With the conventional technology as described above, it is impossible to record new bit information at the same time as erasing bit information.

The present invention is capable of selectively erasing recorded bit information by injecting substantially continuous light without changing the direction of the bias magnetic field applied when recording bit information on a recording medium. , provides a method for recording new bit information by intermittent continuous light.

Erasing in the method according to the invention is carried out by irradiating the placement medium with substantially continuous light to erase bit information within the range of the temperature gradient that has been formed.

In the present invention, the substantially continuous light used for erasing bit information includes not only normal continuous light but also intermittent light to the extent that no record remains even if the light is incident. It should be understood that In some cases, such intermittent light encompassed by substantially continuous light in the present invention may include, for example, repetitive light pulses of 50 Hg@degrees.

In the erasing method of the present invention, if we consider the focus shift when a temperature gradient is formed by irradiating substantially continuous light, when a gradient is created in magnetization M and domain wall energy ~ due to the temperature gradient, the bit will be It moves according to the speed Vd given by Eq.

~: Mobility CM% C#: A positive integer bit determined by a physical constant moves toward the side where the magnetization M is larger or the domain wall energy ~ is smaller. Generally, the temperature coefficients of -MS and g are negative, and their absolute values are larger for ~, so the bit has a tendency to move to the high temperature side. Therefore, the part heated by the light beam has a force that pulls the cloudy bit within the range of its temperature gradient, so if this force overcomes the coercive force term in the above equation and the repulsive force between the bits, then
It is considered that the bit to be erased is inserted into the light beam IN+/) and erased. Since such a light beam erases bits within the range of the temperature gradient formed, there is no need for strict signal synchronization as in the prior art, and even if the light beam is aligned with the bit to be erased, Of course, the bit can be erased not only when the bits overlap, but also when the bit is located at a certain distance, that is, within the range of the formed temperature gradient, and generally, the bit is separated from the bit track by about the diameter of the bit.

In the recording method according to the present invention, when continuous light is irradiated intermittently in order to erase bit information recorded on a disk, the direction of magnetization is opposite to that of the applied noisy magnetic field. A new cylindrical magnetic domain will be formed. Subsequently, by further irradiating continuous light, the bit information can be erased all at once. Therefore, by repeating the continuous light irradiation a and the interruption of the continuous light, erasing and writing can be repeatedly performed. It is extremely advantageous that part of the blurred bit information recorded in the eyeglass T can be left in the form of a Chinese translation without being erased, and can be arbitrarily combined with newly formed focus information. In the case of this recording, the operation is extremely simple, as it is only necessary to intermittent the substantially continuous light irradiated for erasing.

Note that the method according to the present invention is a method for recording bits recorded as cylindrical magnetic domains having a magnetization direction opposite to the direction of the bias magnetic field in a magnetic thin film made of a magnetic material whose domain wall coercive force is sufficiently smaller than the applied bias magnetic field. It can be applied to simultaneously erase information and record new bit information using such cylindrical magnetic domains. What can be used as such a magnetic material is, for example, a soft magnetic material that has strong one-strand magnetic anisotropy in the direction perpendicular to its film surface and has an easy-to-moderate axis in its film surface, (Y8mCa)g(F@G
e) Examples include YSmCaFeGe garnets such as i and On. The above-mentioned magnetic material can form a so-called soft magnetic film with easy magnetization perpendicular to the film surface, and the degree of soft magnetism is such that when this is applied to a magnetic recording material, the actual bit diameter to be written is determined. It is preferable that the coercive force is 11&, which is determined only by the upper bias magnetic field, and the coercive force is about 30e or less, preferably about 10e or less. Such a magnetized thin film is produced by growing a crystal such as Y8mCaFIGe-based garnet on a substrate crystal such as rare earth gallium garnet such as this soft magnetic gallium garnet (GGG) by liquid phase epitaxial method (LPFi).
It is preferable to form the same. When a bias magnetic field of a predetermined intensity is applied to the soft magnetic film 11fi easily magnetized film thus obtained, a single magnetic domain exists over the entire surface of the film, and the magnetization is oriented perpendicular to the film surface. become a state. It is obvious that the strength of the bias magnetic field to be applied varies somewhat depending on the type of the soft magnetic film surface-perpendicular easily magnetized film used, and it is between the runout magnetic field H1 and the collapse magnetic field Ho, for example, as mentioned above ( Y8mCa)1(F@Ge)g
In the case of 012LPg film, it is between 57ρ- and 730e. Bit information is written by applying a bias magnetic field to the entire surface, and by injecting a light pulse into a soft magnetic film with easy magnetization perpendicular to the surface of the film, where the bias magnetic field is a single domain with the magnetization direction perpendicular to the film surface. This can be done by forming a cylindrical magnetic domain with a predetermined diameter η whose magnetization direction is opposite to the applied bias magnetic field.

Erasing the bit information written in this way is performed while applying a bias magnetic field within the range of the runout magnetic field and the collapse magnetic field, but the bias magnetic field is This is extremely advantageous since it can be carried out in the same state without having to change anything. Of course, it is amazing that even if the strength δ of the bias magnetic field is changed within the above-mentioned magnetic field range to be different from the recording range within the above-mentioned magnetic field range, the same erasure can be achieved.The method according to the present invention The magnetic material to which this can be applied is one in which bit information can be written and recorded and the recorded bit information can be erased while applying a bias magnetic field within the same range, that is, between the runout magnetic field and the collapse magnetic field.

Therefore, within the range of the bias magnetic field, the magnetic material has an area where bit information can be written, the so-called write area, and an area where the written bit information can be erased, the so-called erase area. It must have a part. It is possible to erase bit information by irradiating continuous light while applying a complementary bias magnetic field to this overlapping portion, and record new bit information by cutting off the continuous light.

As described above, since the photothermal magnetic erasing and recording method according to the present invention uses a material with a small domain wall coercive force, it is only necessary to apply a relatively small bias magnetic field, and it is possible to perform write recording, erasure, and new write recording. It is extremely advantageous because there is no need to change the bias magnetic field at this time, which simplifies the operation. Use virtually continuous light to create a temperature gradient.

Since the bit information within the range of temperature gradient can be drawn in and erased, there is no need for partial loss of bit information, and there is no need for strict signal synchronization as in conventional methods, which is extremely advantageous during operation. Hereinafter, the present invention will be explained in more detail with reference to Examples. II! As a koji example convention 1, Gd1o11,01. with a thickness of 0.51. (Y 10M 8 mg, I Cm O,N) (P
A thin film of 012 garnet with a thickness of 4.6 plI4 was used. Saturation magnetization of this thin film 4πMm = 142G, domain wall coercive force Hc = 0-50
The collapse magnetic field Ho = 62.70e.

Using this thin film, a thermomagneto-optical recording gun extraction device (1) as shown in FIG. 1 was formed. This device was previously described (
A non-reflective coating layer (1C) is applied to the thin layer obtained by growing a magnetic thin film (11) such as Y8mC 8012 garnet on a rare earth gallium garnet crystal substrate (1b) by liquid phase epitaxial method. On the opposite side of the crystal substrate where the magnetic thin film was provided, there is a reflection 1@(1d) made of an aluminum vapor deposited film with a thickness of, for example, 0.3 #I, and on the outside thereof there is a reflection layer 1@ (1d) with a thickness of, for example, 0.5 #I. It has a structure in which a protective film (1C) made of silicon dioxide of m is deposited. As shown in FIG. 2, the thermomagneto-optical recording/reading device (1) having such a configuration is attached and fixed to a bias magnetic field generating device (21) such as a permanent magnet, for example, in a removable manner so as to maintain constant bias. Arranged so that a magnetic field is applied.This thermomagneto-optical recording/reading device can be configured to be movable by a motor (3), etc.In addition, an auxiliary bias coil (4) is installed around the device. If necessary, the bias magnetic field can be increased by arranging a
By introducing 1 argon laser into the optical modulator (6) and extracting it as a light pulse, the light pulse is focused by a condenser lens (9) via a polarizer (7) and a half mirror (8). The bit was recorded. In this case, the incident light amount Pn is 15 mW, the optical pulse width is 50 M, and the device can be moved at a constant speed in one direction under the conditions of a repetition rate of 2 Hz and a bias magnetic field of 600 mm, and the bit interval is approximately 25 mm. The bits were formed to become #FFl. To read the bit information recorded in this device (1), the polarized light reflected by the reflective film (1d) of this device is introduced into the analyzer Ql, and the light is passed through the photomultiplier tube αυ.
You may also send it to a computer and observe its output with an oscilloscope. When reading records using transmitted light, the reflective film (1) is connected to the readout device (1).
Except for d), the bias magnetic field generator (2) may be placed at the periphery of the device rather than at the bottom, and reading may be performed using transmitted light that is linearly polarized by the Faraday effect.

To erase the recorded bit information as in the previous case,
When the incident light is continuous light with an incident light intensity of 15 mW and the sample with bit information written is moved in the opposite direction to the writing direction, the bit is erased when it is irradiated so as to slightly overlap the bit to be erased. It was observed that

Furthermore, when the continuous light was interrupted, a new bit was formed at that location.

Example 2 Using the sample and apparatus used in Example 1, writing and erasing were performed while changing the amount of incident light and the bias magnetic field. The results are shown in FIG. In FIG. 3, the curved line is critical for writing, and writing is possible in the upper region of this curve. Curve B shows the critical line for erasure, and the region to the right of this curve is the erasable region. Therefore, the area to which the method according to the present invention can be applied is an area where the write area and the erasable area overlap.

[Brief explanation of drawings]

FIG. 111 is a sectional view showing a thermomagnetic optical recursive readout device that can be used in the present invention, FIG. 11112 is a block diagram of a bit observation device, and FIG. 3 is a graph showing write areas and erase areas. In addition, considering the symbols used in the drawings, (1)・・・・・・・・・・・・Thermomagnetic record reading device (1a)・・・・・・・・・・・・Magnetic thin film (1b)...Crystal substrate (2)...
......It is a bias magnetic field generator. Agent Katsu I Doyo Osamu Matsuzai

Claims (1)

[Claims] Bit information recorded as a cylindrical magnetic domain with a magnetization direction opposite to the direction of the applied bias magnetic field in a magnetic thin film made of a magnetic material whose domain wall coercive force is sufficiently smaller than the applied bias magnetic field is By keeping the direction of the magnetic field unchanged and setting the magnitude of the bias magnetic field between the runout magnetic field and the collapse magnetic field, the bit information can be erased by the thermal magnetization effect accompanying light incidence by substantially continuous light. Photothermal magnetic erasure and recording of bit information by discontinuing substantially continuous light and forming new cylindrical magnetic domains whose magnetization direction is opposite to the bias magnetic field. Recording method.