JP2591729B2 - Magneto-optical recording / reproduction / erasing method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magneto-optical recording / reproducing and erasing system for performing magneto-optical recording / reproducing / erasing using a laser beam, and an apparatus therefor.

(Prior art and its problems) The optical recording method, especially the optical disk
In recent years, it has attracted attention as one of large-capacity file memories because it can perform large-capacity recording and can also perform non-contact and high-speed access. Among them, MnB as a recording medium
crystalline magnetic thin films such as i, MnCuBi, MnTiBi, MnAlGe or
Magneto-optical disk memory uses an amorphous magnetic thin film made of a combination of rare earth metals such as Tb, Gd, Dy, and Ho and transition metals such as Fe, Co, and Ni. Due to its advantages, it is being actively studied in various places.

2. Description of the Related Art Conventionally, in a known magneto-optical recording / reproducing / erasing method and apparatus, the following operations are performed for recording, reproducing, and erasing information.

For recording, heat generated by a laser beam is used. The laser light beam is narrowed down to a minute spot of 1 to 2 μmψ and irradiated on the recording medium to increase the medium temperature. When performing Curie temperature recording, the recording medium is raised to a Curie temperature or higher, and a reversal 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 to around room temperature, raise the temperature to a certain temperature by irradiating a laser light beam, and form a reversal magnetic domain by an externally applied magnetic field using the decrease in the coercive force of the medium. . By the means described above, the recording binary signals "1" and "0" can be recorded in a form corresponding to the presence or absence of the reversal magnetic domain of the recording medium.

Reproduction is performed using a magneto-optical effect (Kerr effect or Faraday effect). That is, information is read from the recording medium by utilizing the fact that the polarization plane of reflected light or transmitted light from the medium is rotated according to the presence or absence of the reversal 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 transmitted light.

Here, the intensity level of the laser beam used for reproduction is set to a level that does not change the magnetization state of the recording medium.

When erasing recorded information, an external magnetic field is applied with a polarity opposite to that during recording, and the recording medium is uniformly irradiated with a laser beam 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.

In the above-described conventional magneto-optical recording / reproduction / erasing method and apparatus, rewriting of recorded information is performed by first erasing recorded information according to the erasing operation, and then recording new recorded information according to the recording operation. Perform the step operations. At this time, since the direction of the external magnetic field applied to the recording medium during erasing and during recording is opposite, during erasing,
At the time of recording, means for switching the direction of the externally applied magnetic field must be provided.

For example, when applying an external magnetic field with a coil,
As shown in FIG. 4, recording is performed on the magneto-optical disc 1,
In order to perform erasing, a method is known in which the direction of the current flowing through the coil 21 is switched by the coil current polarity switching means 22 in synchronization with the recording operation and the erasing operation of the laser beam from the optical head 5.

When an external magnetic field is applied by the permanent magnet 23 as shown in FIG. 5, a system and a device using a magnet drive mechanism are known (Japanese Patent Laid-Open Nos. 57-24046 and 57-2404).
7). 6 (a),
The application direction of the external magnetic field is reversed as shown in the operation mode diagram of FIG. Each of the systems and apparatuses has a disadvantage that the apparatus configuration is complicated.

(Object of the Invention) An object of the present invention is to solve the drawbacks of the conventional magneto-optical recording / reproducing and erasing method and apparatus, and to rewrite recorded information by a simple apparatus configuration without switching the application direction of an external magnetic field. An object of the present invention is to provide a novel magneto-optical recording / reproducing and erasing method and apparatus which are possible.

(Constitution of the Invention) According to the present invention, there is provided a magneto-optical recording / reproducing / erasing method in which a magnetic thin film having perpendicular magnetic anisotropy is used as a recording medium, and recording / reproducing / erasing is performed by a laser beam. Recording information by changing the intensity of the laser light, reproducing the recording information by irradiating the recording medium with laser light of a constant intensity, and recording by irradiating the laser light of a constant intensity. In an optical recording / reproducing / erasing method in which a constant magnetic field is applied to a recording medium from the outside through an erasing process for erasing information, the magnetic thin film of the recording medium is a rare earth-transition metal alloy thin film, and the reproducing laser power in the reproducing process is as described above. It is set to a level that does not change the magnetization state of the magnetic thin film of the recording medium, and the erasing laser power in the erasing process causes the magnetic thin film of the recording medium to be higher than the Curie temperature of the magnetic thin film. And the magnetization state of the erasing portion of the magnetic thin film of the recording medium formed by the erasing process becomes an aggregate of small magnetic domains smaller than the beam spot diameter of the irradiation laser light. A level at which the recording laser power in the recording process raises the temperature of the magnetic thin film of the recording medium above the Curie temperature of the magnetic thin film, and a magnetization state of the magnetic thin film of the recording medium formed by the recording process. Is a level that is an aggregate of minute magnetic domains different from the magnetization state of the erased portion, and the magneto-optical rotation angle when the information recording portion formed by the recording process is observed with the reproduction laser beam is the erased portion. At a level different from the magneto-optical rotation angle when observing with the reproduction laser light. The effective applied magnetic field at the time of erasing, which is the direction opposite to the demagnetizing field applied to the recorded recording film and is the sum of the externally applied magnetic field strength and the demagnetizing field at the time of erasing, changes the magnetization state in the erasing process to the initial erasing portion magnetization. A magneto-optical recording / reproducing / erasing method characterized by being set to the same level as the state is obtained, further comprising: a recording medium; a magnetic field generating means for applying a constant magnetic field to the recording medium; An optical head for irradiating a laser beam; and a laser light source modulation circuit for changing an oscillation laser light intensity of a laser light source in response to recording, reproducing, and erasing, wherein a reproducing laser power level during the reproducing is the recording medium. And the erasing laser power level at the time of erasing is constant, and the temperature of the magnetic thin film of the recording medium rises above the Curie temperature of the magnetic thin film. A bell,
The recording laser power level at the time of recording is constant, and is pulse-modulated in accordance with recording information, and is a level at which the magnetic thin film of the recording medium is heated to a temperature higher than the Curie temperature of the magnetic thin film. The externally applied magnetic field strength in the process is in the opposite direction to the demagnetizing field applied to the laser-irradiated recording film, and the effective applied magnetic field at the time of erasing is the sum of the externally applied magnetic field strength and the demagnetizing field at the time of erasing. A magneto-optical recording / reproducing / erasing apparatus characterized in that the magnetization state in the process is set to the same level as the initial magnetization state of the erasure portion.

(Detailed Description of Configuration) The present invention has solved the problems of the prior art by adopting the above configuration.

Hereinafter, details of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration example of a magneto-optical recording / reproducing / erasing apparatus to which the present invention is applied. In FIG. 1, a magneto-optical disk 1 has a magnetic thin film 3 having an easy axis of magnetization in a direction perpendicular to the substrate surface formed on one or both surfaces of a disk 2 made of an organic resin substrate, a glass substrate, or a metal substrate.

The magnetic thin film 3 is a crystalline or amorphous magnetic thin film, for example, a crystalline magnetic thin film such as MnBi, MnCuBi, MnTiBi, MnAlGe, or a rare earth metal such as Sm, Tb, Gd, Dy, Ho and Fe, An amorphous magnetic thin film formed by a combination with a transition metal such as Co or Ni. The magneto-optical disk 1
Is rotated at a predetermined speed by a disk drive motor 4. The optical head 5 has an optical system for magneto-optical recording / reproduction and erasing, and a light detecting mechanism. The optical head 5 itself is movable at a predetermined speed in the radial direction of the magneto-optical disc 1 as indicated by an arrow in the figure.

In the optical head 5, reference numeral 6 denotes a linearly polarized laser light source, for example, a semiconductor laser. 7, 8, and 9 are beam splitters.

The laser light beam focusing lens 10 is supported by an actuator 11. The magnetic field generating means 12 is provided on the opposite side or the same side as the laser light beam focusing lens via the magneto-optical disk, and uses a permanent magnet or a combination of a coil and a DC power supply. The focus error and tracking error signals are received by the light receiving element 13 for detecting the focus error and the light receiving element 14 for detecting the tracking error, respectively.
Is detected and input to the servo control circuits 15 and 16 to become a servo signal, which is fed back to the actuator 11. After passing through the polarization filter 17, the reproduction signal is detected by the reproduction signal detecting light-receiving element 18 and amplified by the reproduction signal amplifier circuit 19. For example, a Glan-Thompson prism is used as the polarizing filter. For example, a PIN photodiode or an avalanche photodiode is used as the light-receiving element for detecting a reproduction signal. A laser light source modulation circuit 20 is used to modulate the laser light source 6, and modulates the power of the laser light source 6 at the time of recording, erasing, and reproducing.

Next, the operation method of the magneto-optical recording / reproducing / erasing apparatus having the above configuration,
In particular, an erasing method different from the conventional method will be described with reference to FIG.

The binary signal information shown in FIG. 2A is already recorded on the magneto-optical disk 1 along the disk track. At this time, the magnetization state of the magnetic thin film 3 of the magneto-optical disk 1 is indicated by hatching in FIG. 2 (b), and the magnetization direction is inverted with respect to the surroundings in response to the "1" signal.

If the next want to erase the recorded information, for adjusting the power level of the laser light irradiated on the magnetic thin film 3 at a constant power level P _E as in the second diagram (c). This can be adjusted by the laser light source modulation circuit 20.

_PE is the laser beam power whose magnetization direction returns to the initial state (“0” signal level) regardless of the magnetization state of the recorded portion (that is, whether or not there is magnetization reversal). The magnetization of the magnetic thin film 3 is brought into the state shown in FIG. 2D by the irradiation of the laser beam power shown in FIG. 2C, and the recorded information is erased.

Subsequently, when recording new binary signal information, for example, signal information as shown in FIG.
The laser light source modulation circuit 20 is adjusted so that the laser light power absorbed by the laser light source reaches the level shown in FIG. In FIG. 2 (f), the laser light power level Pw indicates a laser light power sufficient to form a magnetization reversal portion ("1" signal).

P _R denotes the laser beam power required to detect a focus error, tracking error at the time of recording.
P _R is the laser light power at the same level at the time of reproduction.

When recording is performed with the laser beam power shown in FIG. 2 (f), the magnetization state of the magnetic thin film 3 is changed to FIG. 2 (g).

As described above, in a series of erasing and recording processes, _a constant magnetic field Ha is applied to the magnetic thin film 3 by the magnetic field generating means 12 composed of a magnetic field applying coil or a permanent magnet, and does not need to be changed through recording / reproducing / erasing. . That is, the recorded information can be erased by changing the laser beam power without changing the applied magnetic field, and new information can be recorded.

In magneto-optical recording, at the time of recording, a magnetic field is applied in the magnetization direction of a recording mark, and a laser beam is irradiated. At this time, in addition to an externally applied magnetic field, a magnetic field from a magnetization component of the magnetic thin film, that is, a so-called “demagnetizing field” is applied to the recording mark portion of the magnetic thin film. This demagnetizing field component varies substantially depending on the magnitude of the magnetization of the magnetic thin film. When the magnetization of the magnetic thin film is large, the "diamagnetic field" also increases. Therefore, when the demagnetizing field is large, a recording mark may be formed even if the externally applied magnetic field is small or the direction of the applied magnetic field is opposite to the magnetization direction of the recording mark. Also,
When the demagnetizing field is small, it is necessary to apply an external magnetic field to some extent along the magnetization direction of the recording mark.

In the present invention, if the level of the externally applied magnetic field is properly selected, a recording mark can be formed by pulse-like recording power irradiation while the externally applied magnetic field is kept constant, and erasing can be performed by irradiating a fixed level of erasing power. It is. As a result of detailed analysis of this new phenomenon, the following became clear. At the time of erasing, the irradiation of the erasing laser changes the magnetization state of the magnetic thin film into a magnetization state having a magnetic domain of submicron or less, which is much smaller than the spot size of the laser beam. This occurs when the external magnetic field component (demagnetizing field + applied magnetic field) received by the laser heating region during cooling is small. In this case, in the region immediately after the passage of the laser beam, the temperature of the thin film itself is still higher than the Curie temperature, and no magnetization has appeared. Therefore, there is no demagnetizing field component from this region, and the external magnetic field applied to the laser-irradiated portion is reduced accordingly. At this time,
Bits before the erase operation are completely erased. The small magnetic domain formed here is not detected as a signal because it is smaller than the laser spot diameter.

Next, when recording is performed from this state, the external magnetic field received by the laser heating area is the sum of the externally applied magnetic field and the demagnetizing field from all around the laser irradiation part. Therefore, the external magnetic field at this time contributes to the magnetization reversal more than the external magnetic field at the time of erasing described above. Therefore, in this case, a recording mark can be formed by appropriately setting the applied magnetic field.

In a commonly used magneto-optical recording medium, the magnetization state of the recording film after laser recording changes according to the applied magnetic field strength.
As shown in FIG. 7, when recording is performed by applying a magnetic field of a certain level or more downward from above the recording film, the magnetization state of the recording portion is aligned downward in the entire surface. When the applied magnetic field strength at the time of recording approached zero, the magnetization state after recording gradually increased in the upwardly magnetized microdomain region, and at zero applied magnetic field strength, the upper and lower magnetization states were arranged uniformly. It becomes demagnetized. Thereafter, when the direction of the applied magnetic field is reversed and the applied magnetic field is increased in the upward direction, the fine magnetic domain region magnetized in the upward direction further increases, and finally, the magnetized state is all aligned in the upward direction.

Next, the recording operation and the erasing operation according to the present invention will be described in the eighth.
This will be described with reference to the drawings after the figure.

FIG. 8A shows an initial state before recording and erasing. The recording film is not in a state in which the magnetizations are aligned in one direction, but in a state having minute magnetic domains.

When erasing the recording film in this state, a laser beam set to a constant power is irradiated. At this time, on the recording film, the temperature rising region extends behind the laser irradiation portion, so that the magnetization disappearing region extends horizontally. That is, since the region after passing the laser is also in a heated state, as shown in FIG. 8 (b), the horizontally elongated region extending slightly backward is heated by the laser irradiation and the magnetization disappears.

On the other hand, since the laser power is radiated in a pulsed manner during recording, the temperature rising region during the laser irradiation becomes a circular shape substantially similar to the shape of the laser beam, and the magnetization in this region disappears.

FIG. 9 schematically shows the demagnetizing field component applied to the recording film at the time of recording and erasing according to the present invention.
Here, the region indicated by oblique lines is a region where the temperature has been raised by laser irradiation and the magnetization has disappeared.

FIG. 9 (a) shows the demagnetizing component at the time of erasing.
Assuming that the region 5 is a region irradiated with the laser, the region 4 is a region after passing the laser. However, since the laser is irradiated with a constant power, the amount of temperature rise is still large and the magnetization is lost. Therefore, the demagnetizing field Hde acting on the region 5 at this time is equal to the regions 1, 2, 3, 6, 7, 8, 9 surrounding the region 5.
And Hde = Hde1 + Hde2 + Hde3 + Hde6 + Hde7 + Hde8 + Hde9. Here, Hdei is a demagnetizing field from the region i to the region 6.

Similarly, FIG. 9 (b) shows the demagnetizing component at the time of recording, and it is assumed that the region 5 is a region irradiated with the laser. In this case, the region 4 is a region after passing the laser, but the magnetization is not lost because the laser irradiation is pulse-like. Therefore, at this point, the demagnetizing field Hdw acting on the region 5
Is the sum of the demagnetizing fields from the areas 1, 2, 3, 4, 6, 7, 8, 9 surrounding the area 5, and Hdw = Hdw1 + Hdw2 + Hdw3 + Hdw4 + Hdw6 + Hdw7 + Hdw8 + Hdw9. Here, Hdwi is a demagnetizing field from the region i to the region 5.

FIG. 10 summarizes the relationship between the demagnetizing field Hd at the time of recording and erasing according to the present invention, the effective applied magnetic field Haf to the laser irradiation part, and the magnetization state when the effective applied magnetic field Haf is applied to the recording film. It is. Demagnetizing field component at erasing (Hde)
As described with reference to FIG. 9, since the demagnetizing field from the region 4 in FIG. 9A disappears, the absolute value becomes smaller than the demagnetizing field (Hdw) at the time of recording. That is, the relationship | Hdw |> | Hde | holds. However, when Hdw = 0, Hde = 0.

The horizontal axis in FIG. 10 is the effective applied magnetic field Haf formed by combining the externally applied magnetic field Ha and the demagnetizing field Hd. When Haf = 0, the recording film is demagnetized in the course of laser heating and cooling. Haf is H
When it is larger than a +, the recording film becomes a uniform magnetized state in the process of laser heating and cooling. When Haf is smaller than Ha−, the recording film is in a uniform magnetization state in the direction opposite to the case where Haf is larger than Ha + during laser heating and cooling.

In the present invention, the magnetization state after erasing is the same as the initial magnetization state. In FIG. 11, the initial magnetization state is A
When a point is selected, the demagnetizing field Hdw at the time of recording is HdwA, and the demagnetizing field Hde at the time of erasing is HdeA. Therefore, in order to return the magnetization state to point A through the erasing process, a magnetic field having a magnitude larger than HaA shown in FIG. 11 should be applied as the externally applied magnetic field Ha. At this time, the magnetization state of the recording mark is point B, and has a different magnetization state from point A. FIG. 11A shows a case where the demagnetizing field is relatively small because the saturation magnetization of the recording film is small. At this time, the point B is closer to the demagnetized state than the point A. FIG. 11B shows a case where the demagnetizing field is relatively large because the saturation magnetization of the recording film is relatively large. At this time, the points B and A have different magnetization states with the demagnetization state therebetween. Become.

Example 1 Using the magneto-optical recording / reproducing / erasing apparatus shown in FIG. 1, information was recorded, reproduced, and erased on the magneto-optical disk.
As the magneto-optical disk, a disk having a TbFe film formed to a thickness of 700 mm on a 120 mmφ polycarbonate resin substrate by a sputtering method was used. The substrate is 0.8 μm wide in advance,
A so-called pre-group substrate having a pitch of 2.5 μm and a depth of 700 ° was formed.

As a protective film on the TbFe film SiO ₂ is by vacuum evaporation 12
00Å is formed.

FIG. 3 shows the measurement results of the erasing characteristics. After applying a constant magnetic field of 175 Oe to the magneto-optical disk in the same direction as the magnetization of TbFe by a coil placed behind the disk, and recording a 1 MHz signal at a laser beam power Pw at a linear velocity of 9 m / sec, it is the result when irradiated with predetermined laser beam power P _E for erasing the recorded tracks. In the area A, the recorded signal, that is, the 1 MHz signal is completely erased. Meanwhile complete the erasing laser power P _E is in the region of B Shonama was not.
The area C is an area where signal recording cannot be performed because Pw is equal to or smaller than the recording threshold. The reproducing power is a power that does not change the magnetization state of the recording film, and it is sufficient that the reproducing power is sufficiently lower than the temperature Curie temperature on the disk. Linear speed 5-20m / s
In the range, 1 to 1.5 mW is usually used.

The recording power and the erasing power are set higher than the reproducing power because the temperature of the recording film needs to be higher than the Curie temperature. In the present invention, the recording threshold power is set higher than the known recording threshold power in magneto-optical recording. In this embodiment, the recording threshold power is 3 mW. As shown in FIG. 3 of the present invention, the relationship between the recording power and the erasing power can be arbitrarily set, for example, 6 mW and 5 mW, or 7 mW and 7 mW as long as complete erasure can be realized. is there.

The externally applied magnetic field strength at which the present invention is realized differs depending on the recording film used, but in the present embodiment, it is realized with an applied magnetic field of 175 Oe in the same direction as the magnetization. The externally applied magnetic field range is an applied magnetic field between a "recording threshold magnetic field" which is an applied magnetic field at which recording in normal magneto-optical recording starts and a "saturated recording magnetic field" at which a signal level at the time of recording is saturated. ,
It can be set to any magnetic field strength.

The relationship with the characteristics of the magnetic thin film of the recording medium cannot be uniquely determined because the above-described parameters (recording power, erasing power, reproducing power, applied magnetic field) vary depending on the characteristics of the magnetic thin film. Any magneto-optical recording medium, that is, a rare earth-transition metal alloy thin film, can be used as a magnetic thin film that is an object of the present invention. Note that the magnetization characteristics of the TbFe recording film shown in the examples of the present invention have a coercive force of 2.9 KO.
e, Curie temperature is 130 ° C.

(Example 2) using a magneto-optical recording and reproducing erasing device and the magneto-optical disc shown in Example ^{1, Pw = 9.5 mW, P} E = 9.5 mW P R = 1.0 mW, linear velocity
Recording and erasing of a 1 MHz signal were repeated under the condition that a magnetic field of 9 m / sec and 175 Oe were applied in the same direction as the magnetization of TbFe. Change the recording and erasing to the recording and erasing characteristics be repeated 10 ⁵ times was observed.

(Effects of the Invention) As described above, according to the present invention, the following effects are obtained as compared with the conventional example.

That is, recording and erasing can be achieved in a constant external magnetic field application state without switching the application direction of the external magnetic field, so that the configuration of the magneto-optical recording / reproducing / erasing apparatus can be simplified. The present invention is not limited to the TbFe film shown in the embodiment as a magneto-optical disk, but can be widely applied to a crystalline magnetic thin film for magneto-optical recording and an amorphous magnetic thin film.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a magneto-optical recording / reproducing / erasing apparatus to which the present invention is applied, and FIGS. 2 (a) to 2 (g) are schematic diagrams showing operation modes and recording states of respective parts during erasing and recording. It is. FIG. 3 is a view showing a measurement result of one embodiment of the present invention. FIGS. 4 and 5 are configuration diagrams of a conventional magneto-optical recording / reproducing / erasing apparatus, and FIGS. 6 (a) and 6 (b) are schematic diagrams showing operation modes of respective parts of a conventional magneto-optical recording / reproducing / erasing system. . FIG. 7 is a diagram showing the relationship between the applied magnetic field intensity and the magnetization state of the recording film, FIG. 8 is a diagram showing the magnetization state of the recording film for performing recording and erasing, and the temperature rising state during laser beam irradiation. FIG. 10 is a diagram schematically showing a demagnetizing field component applied to a recording film at the time of recording and erasing according to the present invention, and FIG. 10 is a diagram showing a demagnetizing field Hd and a laser irradiating unit at the time of recording and erasing according to the present invention. FIG. 11 summarizes the relationship between the effective applied magnetic field Haf and the magnetization state when the effective applied magnetic field Haf is applied to the recording film, and FIG. 11 shows the demagnetizing field and the effective applied magnetic field and the recording film during recording and erasing operations. FIG. 4 is a diagram showing the relationship between the magnetization states of FIG. In the figure, 1 is a magneto-optical disk, 2 is a disk, 3 is a magnetic thin film, 4 is a disk drive motor, 5 is an optical head, 6 is a laser light source, 7, 8, and 9 are beam splitters, and 10 is a laser light beam. Focusing beam focusing lens, 11 is actuator,
12 is a magnetic field generating means, 13 is a light receiving element for focus error detection, 14 is a light receiving element for tracking error detection, 15 and 16 are servo control circuits, 17 is a polarization filter, 18 is a light receiving element for detecting a reproduction signal, and 19 is a reproduction signal. An amplification circuit, 20 is a laser light source modulation circuit, 21 is a coil, 22 is a coil power supply and coil current polarity switching means, and 23 is a magnetic field generating means using a permanent magnet.

Claims (2)

(57) [Claims] 1. A magneto-optical recording / reproducing / erasing method for recording / reproducing / erasing information by a laser beam using a magnetic thin film having perpendicular magnetic anisotropy as a recording medium, the intensity of the laser beam applied to the recording medium. Changing the information, recording the information, irradiating the recording medium with a constant intensity laser beam to reproduce the recorded information, and irradiating the constant intensity laser beam to erase the recorded information. A magneto-optical recording / reproducing / erasing method for applying a constant magnetic field to a recording medium from outside through a process, wherein the magnetic thin film of the recording medium is a rare earth-transition metal alloy thin film, and the reproducing laser power in the reproducing process is a magnetic thin film of the recording medium. The erasing laser power in the erasing process raises the temperature of the magnetic thin film of the recording medium to a temperature higher than the Curie temperature of the magnetic thin film. And the level of magnetization of the erased portion of the magnetic thin film of the recording medium formed by the erasing process is a level at which small magnetic domains are aggregated compared to the beam spot diameter of the irradiation laser light. The recording laser power in the recording process is at a level where the magnetic thin film of the recording medium is heated to a temperature higher than the Curie temperature of the magnetic thin film, and the magnetization state of the magnetic thin film of the recording medium formed in the recording process is This is a level that forms an aggregate of small magnetic domains different from the magnetization state of the erased portion, and the magneto-optical rotation angle when the information recording portion formed by the recording process is observed with the reproduction laser beam, The level is different from the magneto-optical rotation angle when observed with a laser beam. The effective applied magnetic field at the time of erasing, which is the direction opposite to the demagnetizing field applied to the recording film and is the sum of the externally applied magnetic field strength and the demagnetizing field at the time of erasing, changes the magnetization state in the erasing process to the initial erasing part magnetization state. A magneto-optical recording / reproducing / erasing method set to the same level as that of the above. 2. A recording medium, a magnetic field generating means for applying a constant magnetic field to the recording medium, an optical head for irradiating the recording medium with laser light, and a laser light source corresponding to recording, reproduction and erasing. A laser light source modulation circuit for changing the intensity of the oscillating laser light, wherein the reproducing laser power level during the reproduction is a constant level that does not change the magnetization state of the magnetic thin film of the recording medium, and the erasing laser during the erasing. The power level is constant, and is a level at which the magnetic thin film of the recording medium is heated to a temperature higher than the Curie temperature of the magnetic thin film. The recording laser power level at the time of recording is constant, and pulse modulation is performed in accordance with recording information. And a temperature at which the magnetic thin film of the recording medium is heated to a temperature higher than the Curie temperature of the magnetic thin film. The effective applied magnetic field at the time of erasing, which is the direction opposite to the demagnetizing field applied to the irradiated recording film and is the sum of the externally applied magnetic field strength and the demagnetizing field at the time of erasing, changes the magnetization state in the erasing process to the initial erasing portion. A magneto-optical recording / reproducing / erasing apparatus, wherein the level is set to be the same as the magnetization state.