JPH0440761B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for moving a photothermal magnetic track, and more particularly to a method for moving a photothermal magnetic track on which bit information recorded photothermally and magnetically is arranged is moved by irradiating light. This technology relates to extremely useful technology that enables various operations such as erasing information, selective reading, and rewriting information.

All conventional photothermal magnetic recording utilizes a large coercive force to retain and stabilize bit information, so it has been impossible to move the bit information once written due to the large coercive force.

However, as a result of the inventor's discovery that bit information can be stably retained in a magnetic thin film made using a magnetic material with sufficiently small coercive force, it has been found that bit information can be stably retained using conventional techniques. A method for selectively moving tracks of bit information has been completed.

Accordingly, the present invention provides a method for selectively moving tracks on which photothermomagnetically recorded bit information is lined up by irradiating light.

The magnetic material that can be used in the present invention has a domain wall coercive force that is sufficiently smaller than the bias magnetic field applied when recording bit information, and has strong uniaxial magnetic anisotropy in the direction perpendicular to the film surface of the magnetic thin film. It is a soft magnetic material having an easy axis of magnetization on its film surface, and can form a so-called soft magnetic film with easy magnetization perpendicular to its film surface. Furthermore, even at the temperature of the soft magnetism, when this soft magnetic easily magnetized film perpendicular to the surface of the film is applied as a magnetic recording medium, the diameter of the bit written thereon is determined essentially only by the applied bias magnetic field. It is preferable that the amount is within a certain range. Therefore, the coercive force of the magnetic material used is preferably about 3 Oe or less, more preferably about 1 Oe or less. Such magnetic thin films are formed by growing crystals such as YSmCaFeGe based garnet on a crystal substrate of rare earth gallium garnet such as soft magnetic gallium carnet (GGG) by liquid phase epitaxial method (LPE). is preferable.

By applying a bias magnetic field of a predetermined intensity to the soft magnetic easily magnetized film perpendicular to the film surface obtained as described above, the magnetic field is easily magnetized over the entire surface of the film in the direction perpendicular to the film surface. A single magnetic domain having magnetization in the same direction as the magnetization direction of the applied bias magnetic field is formed. When this single magnetic domain is irradiated with a light pulse, a bit is formed as a cylindrical magnetic domain having magnetization in the direction opposite to the applied bias magnetic field and perpendicular to the film surface. The bias magnetic field applied when forming this bit is the runout magnetic field.
H ₂ and the collapse field H ₀ . Naturally, this range varies somewhat depending on the magnetic material used, but for example, one type of YSmCaFeGe garnet mentioned above (YSmCa) ₃ (FeGe) ₅ O ₁₂ LPE
In membranes it is between 57 Oe and 73 Oe.

To move a desired bit from the track of bits formed as described above, a substantially continuous beam of light is moved from the track while applying a bias field within the range of the runout and collapse fields. Irradiation is performed at a predetermined distance, and the bits accompanying the continuous light repel the bits that are to be moved, which are approaching due to the temperature gradient formed by the incident light, to the outside of the track due to the repulsive force. It is done by flying.

Substantially continuous light used in the present invention should be understood to include not only normal continuous light but also intermittent light to the extent that no record is left even if the light is incident. Any pulse repetition rate of the beam may be used as long as it is sufficiently faster than the relative speed between the magnetic thin film and the beam. This essentially continuous light requires one bit to be accompanied at all times, and its intensity is such that it repels rather than entrains the bit to be moved, which is attracted by the temperature gradient formed by its incidence. It is preferable that the force be such that it can be thrown a predetermined distance. Note that even if the substantial intensity of the continuous light is high, it can be adjusted to generate a repulsive force between the bits by adjusting the distance of light incidence from the moving track.

In the present invention, the bias magnetic field during track movement continues to be applied without changing the direction of application of the bias magnetic field during recording of bit information.
The bits resulting from the incidence of the substantially continuous light have the same magnetization direction as the recorded bits. Therefore, since both bits have the same magnetization direction, when they get close to a certain distance, if the repulsive force is greater than the force that absorbs the attracted bit, the bit being moved can be repelled. . This repulsive force increases as the bit diameter increases, and the bit diameter increases as the bias magnetic field decreases. Therefore,
It is preferable that the light incident for moving bit information be performed by applying a bias magnetic field as small as possible within the range of the runout magnetic field and the collapse magnetic field. For example, (Y _1.92 Sm _6.1 Ca _0.98 ) (Fe _4.02
Ge _0.98 ) O ₁₂ Garnet case 48Oe and 56Oe
This is possible by applying a bias magnetic field within the range of .

On the other hand, the force by which the bit is attracted by the temperature gradient caused by the substantially continuous light irradiated to cause track movement can be expressed by the following equation.

8/π Hc/4πMs+2｜Vd｜/μ _w 4πMs=C _M △Ms/Ms−
C〓△σ _w /σ _w μ _w : Mobility C _M , C〓: Positive integer determined by physical constants Vd: Bit moving speed Ms: Magnetization σ _w : Domain wall energy △ Ms: Magnetization Ms at both ends of the bit diameter Gradient △σ _w : Gradient of domain wall energy at both ends of the bit diameter Here, the temperature coefficient of σ _w is generally negative and its absolute value is larger than the temperature coefficient of Ms, so the direction of movement of the bit can be calculated using the above equation. is dominated by the second term on the right-hand side of , and is the direction where σ _w is smaller, that is, the direction where the temperature is higher. Furthermore, as can be seen from the above equation, the coercive force (Hc) must be sufficiently small to make the bit follow the light beam.

Therefore, as mentioned above, by adjusting the repulsive force between the bits to be greater than the force that attracts the bits due to the temperature gradient caused by the thermomagnetic effect accompanying light incidence, the desired mode can be achieved. It enables the movement of tracks of bit information.

By the method according to the present invention, desired bit information can be selectively moved from the track, and it is possible to read out only the necessary predetermined bit information, or to use it in combination with other bit information. It is possible. Furthermore, depending on the incident position of the continuous light, desired bit information can be selectively moved to either the right or left side of the track, and this movement operation is possible even during the operation, making it extremely practical in practice. It's convenient. For example, if you first make continuous light enter a predetermined position on the left side of the track and move the bit information to the right of the track, then move the continuous light to a predetermined position on the right side of that track and continue to make the bit information enter the track. Information can be moved to the left of the track. Additionally, if there is bit information in the same track that does not need to be moved, the bit information can be selectively moved by moving the continuous light farther away and moving it to a position where it is not affected by the temperature gradient. You can also do it. Furthermore, according to the method of the present invention, similarly,
It is also possible to return the bit information to its original position on the track by injecting continuous light on the outside of the moved bit information.

Note that if the incident position and the amount of incident light of the incident continuous light are made constant, the amount of movement of the bit can be made constant. In this case, if a method called tracking servo is used, any bit can be accurately moved in any direction.
The track of bit information that has been moved by a certain amount of movement in this way forms a new track, and it is possible to read out the necessary information using only this track. Therefore, both the new track moved in this way and the original track can be used for readout, and along either track, the 488 nm
If the wavelength is , reading can be performed by inputting weak light that does not affect the bits or long wavelength light with weak absorption. In this case, the bit information that was not moved will be erased in the new track created by moving, and the bit information that was moved will be erased in the original track. Further, by selectively combining and performing the operations described above, it is possible to select information and rewrite the information. Furthermore, since new bit information can be recorded in the trace of the moved bit information, it is extremely useful to be able to record a variety of information on one track.

As described above, the photothermal magnetic track moving method according to the present invention enables a wide variety of operations such as erasing bit information, selective reading, and rewriting information.

Hereinafter, the present invention will be explained with reference to Examples.

Example 1 As a sample, (Y _1.92 Sm _0.1 Ca _0.98 ) (Fe _4.02 Ge _0.98 ) O ₁₂ garnet was grown by liquid phase epitaxial method (LPE) on a 0.5 mm thick Gd ₃ Ga ₅ O ₁₂ substrate. A thin film with a thickness of 4.6 μm was used. Saturation magnetization of this thin film 4πMs = 142G, domain wall coercive force Hc = 0.5Oe,
The collapse magnetic field H ₀ was 62.7 Oe.

Using this thin film, a thermomagnetic optical recording/reading device 1 as shown in FIG. 1 was formed. This device is
A non-reflective coating layer 1c is formed on a thin film obtained by growing a magnetic thin film 1a such as the aforementioned (YSmCa) ₃ (FeGe) ₅ O ₁₂ garnet on a rare earth gallium garnet crystal substrate 1b by a liquid phase epitaxial method. On the opposite side of the substrate from which the magnetic thin film is provided, a reflective film 1d made of, for example, a 0.3 μm thick aluminum vapor-deposited film, and on the outside thereof a protective film 1e made of silicon dioxide, for example, 0.5 μm thick. . As shown in FIG. 2, the thermomagnetic recording readout device 1 having such a configuration is fixed, for example, removably attached to a bias magnetic field generating device 2 such as a permanent magnet, and a bias magnetic field is constantly applied thereto. Place it like this. This thermomagnetic optical recording/reading device can be configured to be movable by a motor 3 or the like. Further, an auxiliary bias coil 4 may be placed around the device to increase the bias magnetic field as required.

In the apparatus 1 having such a configuration, an argon laser with a wavelength of 488 nm, for example, generated from the light generator 5 is introduced into the optical modulator 6 and extracted as pulsed light, and the pulsed light is transmitted to the polarizer 7 and the half mirror. The beam was incident on lens 9 through lens 9 to form a bit. In this case, the incident light amount P was 15 mW, the pulse width was 50 μs, the repetition frequency was 1 Hz, and the bias magnetic field was 51 Oe. While irradiating pulsed light under the conditions described above, the device 1
By moving the bits in one direction at a constant speed, a track was formed in which bits were lined up in a straight line with an interval of about 27 μm.

Next, light was irradiated at a repetition rate of 100 Hz without changing the intensity and width of the light, and without changing the bias magnetic field, at a distance of about half the bit diameter from the track in the opposite direction to the direction of movement of the device during writing. As a result, it was found that the bit moved to a position approximately the diameter of the bit on the opposite side to which the 100 Hz pulsed light was irradiated, forming a new track.

The substantial continuous light irradiation position in the present invention is
The tracking movement is determined by a rotation detection mechanism 11 attached to the motor 3, and the position of the motor is moved by a movable chassis 13 by a drive gear 12 provided in conjunction with the rotation detection mechanism 11. You can do it by leaning.

Reading of bit information recorded in this thermomagneto-optical recording/reading device 1 is performed using a reflective film 1d of this device.
The polarized reflected light may be introduced into the detector 15, sent to the photomultiplier tube 16, and its output may be observed with an oscilloscope 17 or the like. In addition, when recording and reading is performed using transmitted light, the reflective film 1d is removed from the reading device 1, and the bias magnetic field generating device 2 is placed not at the bottom of the device but at the periphery, so that the light is linearly polarized due to the Faraday effect. Reading may be performed using transmitted light.

Example 2 A bit track recorded using the same sample and under the same conditions as in Example 1 was moved in the same manner as in Example 1. In this case, the sample moving speed v was set to 29μ without changing the incident amount and bias magnetic field.
The track movement state was investigated at m/sec using a 20x aperture objective lens. The results are shown in FIG. In the figure, in the area to the right of curve A, the approaching bit is absorbed by the light and disappears, and in the area below curve B, the bit does not follow the light beam and is left behind and cannot move.
Therefore, the areas in which the bit information track can be moved are the area to the left of curve A and the area above curve B.

Example 3 A bit track recorded using the same sample and under the same conditions as in Example 1 was moved in the same manner as in Example 1. In addition, the incident light intensity of the light used for track movement was 11.3 mm, and the pulse width was
50μs, and the bias magnetic field is 56Oe, the critical light pulse frequency ν (Hz) at which the bit follows the light beam is determined by the specimen moving speed v (μ
m/sec). The results are shown in FIG. From FIG. 4, it has been found that the critical light pulse frequency ν and the sample moving speed v are proportional. This result shows that when v/ν, that is, the amount of bit movement between light pulses, exceeds a certain value (9.5 μm in FIG. 4), the bits cannot keep up with the light beam. In FIG. 4, the area above the straight line is the area where the track can be moved.

Example 4 Tracking was performed using the same samples and conditions as used in Example 3. The light used for track movement has a pulse width of 50 μs, the sample is moved at 29 μm/s with a bias magnetic field of 56 Oe, and the critical light pulse frequency ν is changed to adjust the incident light intensity P.
Sample movement between light pulses v/ν (μm) as a function of
I asked for The results are shown in FIG. In FIG. 5, the area above the curve is the area where the track can be moved.

As shown in the first embodiment, in the area where the track can be moved in FIGS. 3 to 5, the following necessary conditions are simultaneously satisfied in order for the track to move. That is,
The repulsive force generated between the bit accompanying the incident light beam for track movement and other approaching bits is caused by the temperature gradient formed by the incident light beam. It is stronger than the force that attracts the bits, and the light beam always accompanies one bit even where no other bits are present, and the position of the repeated light beam used for track movement and its bit interval are Even if the bit is separated during the break, the next pulse can attract other bits again.

In addition, in Figures 3 to 5, although track movement is theoretically possible even in the areas on the edge of the boundaries indicated by the curves and straight lines, other bits may come close to the incident light beam for track movement. When the light beam is repelled by the bits in the light beam, the bits accompanying the light beam are also repelled and thrown out by the reaction, so when moving the track, it is necessary to It is practically preferable not to use a light beam, and it is desirable to take measures such as allowing some leeway in conditions such as the amount of incident light. Furthermore, under such conditions on the edge of the boundary line, malfunctions may occur if the physical properties of the sample are non-uniform, so it is preferable to avoid such conditions.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a thermomagneto-optical recording/reading device used in the present invention, FIG. 2 is a block diagram schematically showing an example of a device for carrying out the present invention, and FIGS. 3 to 5 is a graph showing the characteristics of track movement. In addition, in the symbols used in the drawings, 1...
...Magneto-optical recording and reading device, 1a...Magnetic thin film,
1b...Crystal substrate, 2...Bias magnetic field generator, 11...Rotation detection mechanism, 13...Moving chassis.

Claims (1)

[Claims] 1 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, The direction of the bias magnetic field is not changed and the strength of the bias magnetic field is between the runout magnetic field and the collapse magnetic field, and substantially continuous light is irradiated at a predetermined distance from the track of the bit information. A method for moving a photothermal magnetic track, characterized in that the track is moved from the track by a repulsive force with an accompanying bit.