JPH0417140A - Method of magneto-optical recording/reproducing, magneto-optical recording/reproducing device and recording medium to be used therefor - Google Patents

Abstract

PURPOSE:To enable overwriting with high sensitivity without a danger of erasing the recorded information with reproducing light by applying a bias magnetic field on the magneto-optical recording medium in a different direction or with different intensity from the bias magnetic field used on recording when the recorded information is to be reproduced. CONSTITUTION:Magnetization of the first magnetic layer 3 of the medium is transferred to the second magnetic layer 4 with reproducing bias magnetic field on overwriting, and thereby, the first magnetic layer 3 and the second magnetic layer 4 have the same magnetization direction. In this state, a light beam for reproducing is made to irradiate the medium. The magnetization of the first magnetic layer 3 and second magnetic layer 4 is oriented to give exchange coupling to each other, and this state is stable and can not be changed even when the reproducing light has same intensity as the low level of light for recording. Thereby, breaking of the recorded information is avoided even when irradiated by reproducing light of large intensity, and high-sensitive overwriting can be performed.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a magneto-optical recording and reproducing method, a magneto-optical recording and reproducing apparatus and a recording medium used therein, and more specifically, a method for recording information by irradiating a magnetic thin film with a light beam to change the direction of magnetization of the thin film. A method of reproducing information by irradiating a light beam onto a thin film on which information has been recorded, using the Kerr effect, which is the interaction between light and magnetism. In particular, during recording, recording new information on top of old information ( The present invention relates to a magneto-optical recording and reproducing method and apparatus capable of overwriting. [Prior art] As a magneto-optical recording and reproducing technology that allows overwriting, the second
A magneto-optical recording medium having an exchange-coupled magneto-optical double layer as shown in the figure is known (for example, Japanese Patent Publication No. 175948/1982; or the literature "Solid State Physics, Vol. 23, No. 67 (1988), pp. 494-50
0 pages). As shown in FIG. 2(a), the magneto-optical recording medium includes a transparent substrate 1, a dielectric layer 2 such as silicon nitride, and a TbFe layer 2.
First magnetic layer (memory M) 3, T
b Second magnetic layer (auxiliary layer) such as D y Fe Co
4. Protective layers 5 made of silicon nitride or the like are laminated in order. The first magnetic layer and the second magnetic layer constitute an exchange-coupled magneto-optical two-layer film, and the Curie temperature (Tc1) of the first magnetic layer 3 is lower than the Curie temperature (Tc2) of the second magnetic layer 4, and is room temperature. In this case, the coercive force of the second magnetic layer 4 is smaller than the coercive force of the first magnetic layer 3. The first magnetic layer 3 has a thickness that does not allow light to pass through. Therefore, the light does not reach the second magnetic layer 4, and the light does not reach the first magnetic layer 3.
The plane of polarization is rotated by reflecting only the magnetization state of . The protection M5 serves to protect the first magnetic layer 3 and the second magnetic layer 4 from corrosion such as oxidation. The second magnetic layer 4 is magnetically exchange-coupled with the first magnetic layer N3, and overwriting is performed as follows. (b) As shown in the figure, during recording, first, by applying an initializing magnetic field HINI using a permanent magnet or the like, the magnetization of only the second magnetic layer 4 with a small coercive force is changed to the initializing magnetic field Hr+u.
Align in the direction (bl, b2). At this time, the magnetization of the first magnetic layer 3 does not change because the coercive force is greater than the initialization magnetic field HINI. After such initialization, a laser beam is irradiated while applying a weak bias magnetic field HBR in the opposite direction to the magnetic field HINI. When the intensity of the laser beam is relatively low, the temperature of the first magnetic layer 3 exceeds the Curie point Tcm (b3), so the magnetization of the first magnetic layer 3 aligns with the direction of magnetization of the second magnetic layer 4 during subsequent cooling. (b4). Furthermore, when the intensity of the laser beam is relatively large, the temperature of the second magnetic layer 4 also exceeds its Curie temperature TC2 (b5), so that during subsequent cooling, the second magnetic layer 4
The direction of magnetization of is aligned with the direction of the bias magnetic field HBR (b6
), and as the cooling progresses further, the magnetization of the first magnetic layer 3 aligns with the direction of magnetization of the second magnetic layer 4 (bl). Therefore, as shown in figure (C), by modulating the intensity of the laser beam according to the binary information to be recorded,
The value information is recorded as the direction of magnetization of the second magnetic layer 4. As described above, new information can be directly written on a recording medium on which information is recorded without erasing it, that is, overwriting can be performed. In order to reproduce the overwritten information on the magneto-optical recording medium, in order not to destroy the recorded information, (c)
As shown as the reproduction light level PR in the figure, the magneto-optical recording medium is irradiated with light with an even lower intensity than the light with a low intensity (low level PL) used during recording, and the reflected light is affected by the magneto-optic effect. This takes advantage of the fact that the polarization state changes. At this time, since the recorded information is on the first magnetic layer 3, light for this reproduction is also irradiated from the first magnetic layer 3 side. The dielectric layer 2 has the function of multiple-reflecting the laser light incident from the substrate 1 side, thereby increasing the rotation (Kerr rotation) of the plane of polarization caused by the first magnetic M3. [Problems to be Solved by the Invention] As described above, in the conventional magneto-optical recording and reproducing method that performs overwriting, the temperature of the magneto-optical recording medium increases due to the reproducing light on the first magnetic layer 3 during reproduction. In order to reduce the risk of erasing recorded information, the intensity of the reproducing light is lowered or the recording sensitivity of the magnetic layer is lowered to increase the temperature at which information is erased. However, if the intensity of the reproduction light is lowered, the signal intensity becomes smaller, so a sufficient C/N ratio cannot be obtained. Further, when the recording sensitivity is lowered, a laser beam with a high intensity is required, but it is not easy to obtain a laser light source that generates a laser beam with such a high intensity, and it is not desirable as a recording/reproducing device. In addition, in conventional technology, the temperature of the recording medium increases within a predetermined range when irradiated with three types of light: a low-intensity laser beam, a high-intensity laser beam, and a reproduction beam. Because it was necessary to avoid overlapping each other, the temperature of the recording medium when irradiated with high-intensity laser light increased, and the range of environmental temperatures in which this recording medium could be used was extremely narrow. Ta. For this reason, the recording medium is exposed to extremely high temperatures during recording, and when overwriting is performed many times, the characteristics of the recording medium deteriorate, resulting in problems such as signal amplitude becoming small and overwriting becoming impossible. - Also, when reproducing recorded information by irradiating the first magnetic layer 3 with reproduction light, if the first magnetic layer 3 is thin, the light may reach the second magnetic layer 4, which is magnetized in a negative direction. This causes a problem in that the magneto-optic effect becomes smaller, resulting in a reduction in signal output. Furthermore, two laser beams are irradiated using the same lens, and the recorded information is immediately read out and confirmed.
When adopting the so-called direct read afterwrite method, the magnetization state of the first magnetic layer 3 and the second magnetic layer 4 during direct read afterwrite immediately after recording is different from the magnetization state during normal reproduction. However, there was a problem in that lead-after-write reliability could not be obtained. This is because before normal reproduction, the direction of magnetization of the second magnetic M4 is uniformly aligned, but during read-after writing,
This is because the second magnetic layer 4 is magnetized in a direction aligned by exchange coupling with the first magnetic layer 3. The main purpose of the present invention is to solve the above-mentioned problems, and to provide a magneto-optical recording and reproducing method and a magneto-optical recording device that are highly sensitive and capable of overwriting without the risk of erasing the information recorded by the reproducing light. It is about providing. Another object of the present invention is to provide a magneto-optical recording and reproducing method and a magneto-optical recording device that allow highly reliable overwriting without deteriorating the characteristics of a recording medium even when overwriting is repeated many times. It is in. Still another object of the present invention is to provide an overwritable magneto-optical recording and reproducing method and a magneto-optical recording device that provide good signal quality and a high C/N ratio. A further object of the present invention is to provide an overwritable magneto-optical recording and reproducing method and a magneto-optical recording device that can perform direct read-after-write with high reliability.

[Means to solve the problem]

In order to achieve the above object, the present invention uses the following means. When using a magneto-optical recording medium formed by laminating at least a first magnetic layer 3 and a second magnetic layer 4 on a substrate, when the magneto-optical recording medium is irradiated with recording light of a first intensity and When reproducing recorded information in a magneto-optical recording and reproducing method that performs overwriting by utilizing the fact that the magnetization information recorded is different when irradiating recording light with a second intensity weaker than the recording light with a second intensity, A bias magnetic field having a direction or intensity different from the bias magnetic field during recording is applied to the magneto-optical recording medium. That is, before or during reproduction of recorded information, a means or step is provided for transferring magnetization information of the first magnetic layer to the second magnetic layer. By applying a predetermined bias magnetic field before or during reproduction, the intensity of the reproduction light irradiated to reproduce the information recorded on the magneto-optical recording medium can be changed to the above-mentioned low-intensity recording. It was made to be as large as light or larger. In one preferred embodiment, the thickness of the magnetic layer on the side to which the reproduction light is irradiated, of the first magnetic layer and the second magnetic layer, is set to a thickness through which the reproduction light is transmitted. The thickness of such a magnetic layer is approximately 40 nm or less. especially,
The effect that the magneto-optic effect strengthens between the two magnetic layers is 1
This is noticeable in the film thickness range of 5 nm to 30 nm. In another preferred embodiment, a magnetic layer is provided on the side opposite to the side on which the reproduction light is irradiated to the first magnetic layer and the second magnetic layer, compared to the first magnetic layer and the second magnetic layer. A thermal diffusion layer 17 with high thermal conductivity was provided. As a result, the heat generated in the first magnetic layer and the second magnetic layer due to the irradiation of the recording light and the reproduction light is diffused toward the heat diffusion layer having high thermal conductivity, so that the temperature of the magneto-optical recording medium increases. Therefore, even if overwriting is repeated many times, the characteristics of the magneto-optical recording medium will not deteriorate. moreover,
Since the response of the magneto-optical recording medium to heat becomes faster, the shape of the recording magnetic domain is stabilized and signal quality is improved. In order to make the above-mentioned magneto-optical recording and reproducing method even more effective, confirmation of recorded information performed when recording information on a magneto-optical recording medium (
After recording the information (read-after-write), the recorded information was checked before aligning the direction of magnetization of the second magnetic layer in one direction. As a means for irradiating light for checking the recorded information, it was decided to irradiate the recording light through the same lens as the lens that condenses the recording light. This makes it possible to check the recorded information immediately after recording, thereby further reducing time. Further, the reproducing light was made the same as the light for confirming the recorded information. In this case, it was decided to irradiate the above-mentioned reproduction light and light for confirming the recorded information through a lens different from that for the recording light. Furthermore, the wavelengths of the reproduction light and the light for confirming the recorded information (read-after-light light) were made shorter than the wavelength of the light used for recording information. As another embodiment of the present invention, before reproducing recorded information,
While applying a bias magnetic field with a different intensity or direction from that used when recording information, light for recording information is irradiated, and a second
The direction of magnetization of the magnetic layer 4 is aligned to the direction of exchange coupling with the first magnetic layer 3. In this case, the direction of magnetization of the first magnetic layer 3 is not changed. One embodiment of the recording medium according to the present invention is such that the direction of magnetization of the second magnetic layer 4 is always aligned in the direction of exchange coupling with the magnetization of the first magnetic layer 3 when no magnetic field is applied at room temperature. was configured. [Function] The overwritable magneto-optical recording and reproducing method and apparatus according to the present invention performs reproduction by transferring the magnetization of the first magnetic layer of the overwritten recording medium to the second magnetic layer, such as a bias magnetic field for reproduction. Sometimes the first magnetic layer and the second magnetic layer of the recording medium
The magnetic layers are irradiated with a reproduction light beam (hereinafter referred to as reproduction light) while being magnetized in the same direction. In this state, the magnetization directions of the first magnetic layer and the second magnetic layer are already aligned in the direction of exchange coupling, so it is stable, and the reproduction light level PR irradiates light with the same intensity as the low level PL during recording. Because it doesn't change even if you do. Recorded information is not destroyed even if the intensity of the reproducing light is increased compared to the conventional one. Therefore, the degree of latitude in setting the recording light intensity increases. Also, at this time, since the magnetization directions of the first magnetic layer and the second magnetic layer are aligned, the magneto-optical effect (Kerr effect) produced by both layers is added, and as a result, the signal output increases. do. Furthermore, since the magnetization directions of the first magnetic layer and the second magnetic layer are aligned, the reproduction light may be irradiated from either side of the layer. Therefore, it is possible to make the layer on the side to which the reproduction light is irradiated a layer with a high Curie temperature. Generally, a layer with a high Curie temperature has a large magneto-optic effect, so a large signal output can be obtained. That is, as shown in FIG. 3, the C/N ratio improves as the Curie temperature increases. Furthermore, since the magnetization directions of the two magnetic layers are aligned, even if the magnetic layer is made thin enough to allow light to pass through, the magneto-optic effects of the transmitted light are added together, and the signal output does not decrease. FIG. 4 shows the Kerr rotation angle when the thickness of the first magnetic layer 3 is changed. Here, the solid line is the first
The broken line represents the Kerr rotation angle when the magnetizations of the magnetic layer and the second magnetic layer are aligned in the direction of exchange coupling, and the broken line represents the Kerr rotation angle when the magnetization of the first and second magnetic layers is in the opposite direction to the direction of exchange coupling. It represents the rotation angle. That is, the Kerr rotation angle when the magnetization directions of the two layers are aligned does not decrease even if the thickness of the first M layer is made thinner. In this case, since the total film thickness of the two layers is thin, a heat diffusion layer with high thermal conductivity is provided on the opposite side from where the reproduction light is irradiated, so that the two magnetic layers are not exposed to extremely high temperatures. There is no need to worry about deterioration of the characteristics of the magneto-optical recording medium even if overwriting is repeated many times. This effect appears only when the magnetic layer is thin, as shown in FIG. At this time, if the heat diffusion layer is used as a reflective layer, the C/N ratio is further improved. Furthermore, when implementing the door-after-write method in which recorded information is checked immediately after recording, the time required for the check is shortened and the reliability of the check is improved for the following reasons. After recording information on the magneto-optical recording medium and before aligning the direction of magnetization of the second magnetic layer in one direction, the recorded information can be confirmed. The time required is shortened, and there is no need to worry about the recorded information being destroyed by the light irradiated onto the recording medium to confirm the information. Also, at this time, since the magnetization of the first magnetic layer is oriented in the direction of exchange coupling with the magnetization of the second magnetic layer, the magneto-optical effects of the two layers mentioned above are added together, resulting in Improved signal output. Furthermore, since the magnetization state of the recording medium at this time matches the magnetization state during reproduction, the reliability of recording confirmation is improved. If the light for checking the recorded information is irradiated through the same lens as the lens that condenses the recording light, it becomes possible to check the recorded information immediately after that, which further reduces the time. If the reproducing light is made the same as the light for confirming the recorded information, the conditions during reproduction and during recording confirmation will be the same, thereby improving the reliability of recording confirmation. By making the wavelength of the reproduction light and the light used to confirm recorded information shorter than the wavelength of the light used to record information, it becomes possible to reliably read out information even when small magnetic domains are recorded. High-density recording can be achieved. In this case, the intensity of the reproduction destination and read-after-light light does not need to be very strong. If the reproducing light and the light for confirming recorded information are irradiated through a lens separate from that for the recording light, it becomes easy to irradiate bias magnetic fields with different intensities or directions at the positions of the recording light and the reproducing light. In this case, since there is no need to reverse the strength or direction of the magnetic field, it is possible to use a fixed permanent magnet or the like as the means for generating the bias magnetic field. [Example] Examples of the present invention will be described in detail below. (Embodiment 1) FIG. 1 shows the configuration of an embodiment of a magneto-optical recording and reproducing apparatus according to the present invention. The disc-shaped recording medium 6 is rotationally driven by a rotational drive means 9. The initializing magnetic field applying means 11 is for magnetizing the second magnetic layer (auxiliary layer) of the recording medium 6 in the same direction as the initializing magnetic field HINT when recording information, and is preferably a permanent magnet. Initialization magnetic field application means 11
may be removed during playback. The bias magnetic field applying means 12 is an electromagnet that applies a recording bias magnetic field HBR during recording and a reproducing bias magnetic field I (0) during reproduction, and a predetermined current is applied from the bias power supply 10. A light beam 1 of a level corresponding to the content of the information to be recorded at the position where the information of 6 is to be recorded or the position to be reproduced.
Generates 4. The level of the light beam 14 is intensity-modulated by a laser drive circuit 29 using a binary signal of information to be recorded. The light beam 14 is focused by the lens 13 and irradiated onto a predetermined position on the recording medium 6. The scanning control means 8 is a means for performing tracking control, and the light source 7 and bias magnetic field application means 12 are connected to a disk-shaped recording medium 6
move in the radial direction. The information reproducing circuit 28 detects a change in the polarization state of the reflected light of the optical beam 14, which is the reproducing light, on the recording medium 6 during reproduction, converts it into an electrical signal, and reads out the recorded information. Note that although the embodiment shown in FIG.
All you have to do is remove the parts of the diagram that are necessary only for recording. FIG. 6 shows a partial cross-sectional view of one embodiment of a recording medium according to the invention. The layer structure is the same as in FIG. 2, but the difference is that the first magnetic layer is thinner. The transparent substrate 1 was loaded into a high-frequency magnetron sputtering device, and after evacuation to below 0.1 m-Pa, a mixed gas of Ar and N2 was introduced to 1.3P.
At a gas pressure of a, reactive sputtering is performed using Si as a target, and SiNx is deposited to a thickness of 70 nm as the dielectric layer 2. After that, sputtering was performed using a T b Fe C, o alloy target at an Ar gas pressure of 0.7 Pa, and the first
As the magnetic layer 3, a 40 nm thick Tb2□Fe74C05 amorphous alloy thin film is laminated. Next, a TbDyFeCo alloy target was sputtered at the same Ar gas pressure of <0.7 Pa,
The second magnetic layer 4 is Tb□. Dy□6Fe66Co, l
1100n of amorphous alloy thin films are laminated. The first magnetic layer 3 and second magnetic layer 4 stacked in this manner are magnetically exchange-coupled with each other. Next, after evacuation to 0.1 mPa or less again, a mixed gas of Ar gas and N2 gas was introduced, and reactive sputtering was performed using Si as a target at a gas pressure of 1.3 Pa.
n laminated. In this example, the first magnetic layer 3 is rich in transition metals and has a Curie temperature (Tc) of 230°C. , the second magnetic layer 4 is rich in transition metals and has a Curie temperature (Tc2
) is 250°C. Further, at room temperature, the coercive force (3 kOe) of the second magnetic layer 4 is equal to the coercive force (10 kOe) of the first magnetic layer 3.
It is smaller than e). The exchange coupling force is also not very large. FIG. 7(b)) shows a characteristic diagram showing the relationship between temperature and holding force of the above embodiment of the recording medium. In addition, since the first magnetic layer 3 and the second magnetic layer 4 used in this example are rare earth transition metal amorphous alloy films, the direction of magnetization of each layer is the moment and transition of the rare earth elements coupled in opposite directions. The direction changes depending on which metal has more moment. Therefore, materials with a large amount of rare earth moments are called rare earth-rich, and materials with a large amount of transition metal are called transition metal-rich. In general, rare earth-rich materials often change to transition metal-rich materials at high temperatures. A method of recording and reproducing using the magneto-optical recording/reproducing apparatus shown in FIG. 1 and the recording medium having the layer structure shown in FIG. 6 will be described. Recording is the same as before. By simply applying an initializing magnetic field (H!N) at room temperature by the initializing magnetic field applying means 11, the magnetization of only the second magnetic layer 4 is aligned in one direction.At this time, since the first magnetic layer 3 has a large coercive force Hcm, , the previously recorded magnetization state (information) is preserved as is, and there is an upwardly magnetized part and a downwardly magnetized part. Immediately after recording, when irradiated with a high-intensity laser beam (Po), the first magnetic state The magnetization of N3 and the second magnetic layer 4 is aligned with the direction of the bias magnetic field HB during recording, and the direction of magnetization is upward.On the other hand, when irradiated with a laser beam (PL) of low intensity, the magnetization of the first magnetic layer 3 is aligned with the direction of the bias magnetic field HB during recording. It is aligned downward by exchange coupling with the second magnetic layer 4. Since the recording medium 6 is rotating, the initialization magnetic field HTNI
Initialized by That is, the direction of magnetization of the second magnetic layer 4 is aligned in the direction of the initialization magnetic field HINI. During reproduction, while applying the bias magnetic field H8,
The reproduction light 14 is irradiated. At this time, the bias magnetic field H8 during reproduction is applied with a stronger intensity than the bias magnetic field HBR during recording. Then, part of the magnetization of the second magnetic layer 4 becomes
Exchange coupling force with the first magnetic layer 3 and bias magnetic field H during reproduction
It is reversed under the influence of both o. At this time, in the part where the magnetization of the first magnetic layer 3 faces downward, it is already aligned in the direction of exchange coupling with the second magnetic layer, so it is stable, no reversal occurs, and the first magnetic layer 3 Only the magnetization of the portion of the second magnetic layer 4 where the magnetization of the second magnetic layer 4 faces upward is reversed. Therefore, as a result, the magnetization state of the first magnetic layer 3 is transferred to the second magnetic layer 4. In this state, the magnetization directions of the first magnetic layer 3 and the second magnetic layer 4 are already aligned in the direction of exchange coupling, so the recording light (PH
) does not change even if it is irradiated with light of the same intensity. Recorded information is not destroyed even if the intensity of the reproduction light is increased. FIG. 8 shows recording by high intensity recording light (PH) and low intensity recording light (PL) in the recording medium of this embodiment.
) and the transfer of the magnetization of the first magnetic layer 3 to the second magnetic layer 4 by the reproduction light are realized by the bias magnetic field and the applied laser beam. This shows the relationship of strength. When the applied laser beam is strengthened when the bias magnetic field is strong, the magnetization of the first magnetic layer 3 is transferred to the second magnetic layer 4 24
It can be seen that when the irradiation of the laser beam is strengthened when the bias magnetic field is relatively weak, the magnetization of the second magnetic layer 4 is first transferred to the first magnetic layer 3 . Also,
This shows that regardless of the bias magnetic field, recording is performed when recording light (Po) of sufficiently high intensity is irradiated. Among these, the transfer 23 and recording of the magnetization of the second magnetic layer 4 to the first magnetic layer 3 indicates that the information recorded in the first magnetic layer 3 is destroyed or erased. on the other hand,
Once the transfer 24 of the magnetization of the first magnetic layer 3 to the second magnetic layer M4 has occurred, the transfer 23 of the magnetization of the second magnetic layer 4 to the first magnetic layer 3 does not occur until it is initialized again. Therefore, even if the reproduction light intensity (PR) is increased, the recorded information will not be destroyed. That is, as shown in FIG. 9, the intensity of the reproduction light (PR
) can be made stronger than the low-intensity recording light (P+, ) during recording. Here, the solid line in FIG. 9 shows the C/N when the output of the continuously irradiated laser beam is increased from the pre-recorded state while applying the bias magnetic field HBR during recording. The point at which the eC/N ratio becomes O is the point at which the initial recorded signal is completely erased, i.e.,
Since the magnetization of the first magnetic layer 3 shows the intensity of the laser beam aligned to the second magnetic layer 4, which is magnetized uniformly, it can be seen that the recording light (PL) with a small intensity should be larger than this. . On the other hand, the broken line in the figure is the bias magnetic field H during reproduction. It shows the change in C/N when the output of the laser beam to be irradiated was increased while applying . As shown in FIG. 9, the bias magnetic field H during reproduction. It can be seen that the laser beam intensity, which causes destruction of recorded information, increases significantly when . Here, the dashed-dotted line in the figure shows the recording characteristics due to high-intensity laser light. As described above, by using the method of this embodiment, the intensity of the reproduction light can be increased, so as shown by the dashed line in FIG. 10, the C/N ratio is improved compared to the conventional method (solid line). I understand that. Recording and reproducing characteristics were investigated using the magneto-optical recording medium of this example. When this recording medium 6 was rotated at a rotation speed of 360 rpm and recording was performed with a recording mark length of 5 μm at a position with a radius of 60 mm, a C/N ratio of 62 dB was obtained. At this time, the laser light output of the reproduction light, the low-intensity recording light (PL), and the high-intensity recording light (PH) was 3.5 mW, respectively.
, 3mW, and 9mW. (Example 2) The transparent glass substrate 1 was loaded into a high-frequency magnetron sputtering device, and after evacuation to a high vacuum of 0.1 mPa or less, a mixed gas of Ar gas and N2 gas was introduced, and 1.3P
Reactive sputtering is performed using Sj-Tat at a gas pressure of a, and 80 nm of SiNx is laminated as the dielectric M2. After that, using a TbFeCO alloy target,
Sputtering was performed at an Ar gas pressure of 0.7 Pa, and a 30% Tb2Fe72Co6 amorphous alloy thin film was formed as the first magnetic layer 3.
Stack layers. Next, a TbDyFeCo alloy target was sputtered at the same Ar gas pressure of <0.7 Pa,
The second magnetic layer 4 is T bxsD Vx7F e5t. A 60 nm thick CO□1 amorphous alloy thin film is laminated. The first magnetic layer 3 and second magnetic layer 4 stacked in this manner are magnetically exchange-coupled with each other. Next, 0.1 mPa again
After evacuation, a mixed gas of Ar gas and N2 gas was introduced and reactive sputtering was performed using Si as a target at a gas pressure of 1.3 Pa.
A layer of 100n was laminated. In this embodiment, the Curie temperature (T
C) is 220°C, and the Curie temperature (Te3) of the second magnetic layer 4 is 250°C. Further, at room temperature, the coercive force (3 kOe) of the second magnetic layer 4 is smaller than the coercive force (12 kOe) of the first magnetic layer 3. As shown in FIG. 7(a), its magnetic properties were such that the first magnetic layer 3 had a transition metal-rich composition and the second magnetic layer had a rare earth-rich composition. 21i
Since the exchange bonding force between 1 is not so large, at room temperature,
The magnetizations of the first magnetic layer 3 and the second magnetic layer 4 are independently reversed. This film could also be overwritten in the same manner as in Example 1. Furthermore, during reproduction, the magnetization of the first magnetic layer 3 can be transferred to the second magnetic layer 4 by irradiating the recording medium 6 with a bias magnetic field H8 (approximately 5000 e) and reproduction light in the opposite direction to that during recording. Ta. FIG. 11 shows recording by high-intensity recording light (PH) and low-intensity recording light (P) in the recording medium of this example.
L) transfers the magnetization of the second magnetic layer 4 to the first magnetic layer M3 and transfers the magnetization of the first magnetic layer 3 to the second magnetic layer 4 by the reproducing light.Bias magnetic field H8 and irradiated laser light This shows the power relationship between From this, if the applied laser beam is strengthened while applying a bias magnetic field in the opposite direction to that during recording, the magnetization of the first magnetic layer 3 is
Transfer 24 to the magnetic layer 4 takes place. On the other hand, it can be seen that when the intensity of the laser beam is increased while applying a bias magnetic field in the same direction as during recording, the transfer 23 of the magnetization of the second magnetic layer 4 to the first magnetic layer 3 occurs first. In addition, if the recording light (PI()22) of sufficiently high intensity is irradiated at that time,
Indicates that recording will occur. Of these, the transfer 23 and recording of the magnetization of the second magnetic layer 4 to the first magnetic layer 3 is performed in the first magnetic layer 3.
This indicates that the information recorded on the magnetic layer 3 will be destroyed or erased. On the other hand, once the transfer 24 of the magnetization of the first magnetic layer 3 to the second magnetic layer 4 occurs, the transfer 23 of the magnetization of the second magnetic layer 4 to the first magnetic layer 3 does not occur until it is initialized again. do not have. Therefore, even if the reproduction light intensity (PR) is increased, the recorded information will not be destroyed. As described above, in the method of this embodiment, the magnetization of the first magnetic layer 3 is transferred to the second magnetic layer 4 by irradiating reproduction light while applying a bias magnetic field in the opposite direction to that during recording. be able to. This allows the intensity of the reproduction light to be increased, so
C/N ratio improves. In addition, since the thickness of the first magnetic layer 3 is made thinner and the overall recording film thickness is made thinner, the recording sensitivity is 5 inches in radius and the rotation speed is 36 inches.
At the outermost periphery of 00 rpm, it is significantly improved to 8 mW. (Example 3) FIG. 12 shows a laminated structure of another example of the recording medium according to the present invention. As in Example 2, the radius is 5.
A 25-inch transparent glass substrate 1 was loaded into a high-frequency magnetron sputtering device, and after evacuation to 0.1 mPa or less, a mixed gas of Ar gas and N2 gas was introduced, and a 1.3P
Reactive sputtering is performed using Si as a target at a gas pressure of
Stack. After that, using a TbFeCo alloy target,
The first magnetic layer 3 is formed by sputtering at an Ar gas pressure of 0.7 Pa.
As a result, a 12 nm thick T bz□Fe, oCo, and amorphous alloy thin film is laminated. Next, a TbDyFeCo alloy target is sputtered at the same Ar gas pressure of <0.7 Pa to form the second magnetic layer 4 with Tb2oD y, □F e, , CO
A 25 nm thick amorphous alloy thin film is laminated. The first magnetic layer 3 and second magnetic layer 4 stacked in this manner are magnetically exchange-coupled with each other. Next, after evacuation to Q and 1 mPa or less, a mixed gas of Ar gas and N2 gas was introduced, and reactive sputtering was performed using Si as a target at a gas pressure of 1.3 Pa. SiNx
are laminated to a thickness of 20 nm. Further, using an AlTi alloy target, sputtering was performed at an Ar gas pressure of 0.7 Pa to deposit 60 nm of AI Ti x as a thermal diffusion layer 17. This heat diffusion layer 17 functions as a heat diffusion layer to prevent the recording film from being exposed to extremely high temperatures and improves the number of rewrites, and as a reflection layer to increase the Kerr rotation angle through optical interference effects. have In this embodiment, the Curie temperature (T
c1) is 220°C, and the Curie temperature (Te3) of the second magnetic layer 4 is 270°C. Furthermore, at room temperature, the coercive force (4 kOe) of the second magnetic layer 4 is equal to the coercive force (4 kOe) of the first magnetic layer 3.
12 kOe). As shown in FIG. 7(a), the first magnetism N3 has a transition metal rich composition, and the second magnetism J!
4 is a rare earth rich composition. In this embodiment as well, overwriting is possible, as in the above two embodiments. In this example, a C/N ratio of 64 dB was obtained at a recording mark length of 5 μm, which was even better than in Example 1. This is because during reproduction, the magnetization of the first magnetic layer 3 is transferred to the second magnetic layer 4, so the Kerr rotation angles of both layers are added together, and the Faraday effect of light transmitted through both layers is also added. This is because the effective Kerr rotation angle increases. Furthermore, in this example, the recording and reproducing characteristics (C/N) do not deteriorate even if overwriting is repeated as shown in FIG. This is because, as shown in FIG. 14, the temperature distribution on the first magnetic layer 3 and the second magnetic layer 4 becomes smooth, and they are no longer exposed to extremely high temperatures. This effect is remarkable when the thickness of the magnetic layer is thin as shown in FIG. 5, but in the method of the present invention for transferring the magnetization of the first magnetic layer 3 to the second magnetic layer 4, This is very effective because the C/N ratio does not decrease even if the thickness of the magnetic layer is made sufficiently thin (to the extent that light can pass through it). (Embodiment 4) FIG. 15 shows the laminated structure of another embodiment of the magneto-optical recording medium according to the present invention. First, a transparent glass substrate 1 with a radius of 5.25 inches was loaded into a high-frequency magnetron sputtering device, and after the vacuum was evacuated to a high vacuum of 1 mPa or less, a mixed gas of Ar gas and N2 gas was introduced, and the Reactive sputtering is performed using a Si target under gas pressure, and 80 nm of SiNx is laminated as the dielectric layer 2. Then TbDyFeC. An alloy target was sputtered at the same Ar gas pressure of <0.7 Pa, and Tb, GDy1□Fe5 was formed as the second magnetic layer 4.
A 60 nm thick 6Co11 amorphous alloy thin film is laminated. Then T
b Using Fe Co alloy target, 0°7Pa
Sputtering is performed at an Ar gas pressure of
A 30 nm thick Tb2□Fe7□Co6 amorphous alloy thin film is laminated. The first magnetic layer 3 and second magnetic layer 4 stacked in this manner are magnetically exchange-coupled with each other. Next 0.
After evacuation to 1 mPa or less, a mixed gas of Ar gas and N2 gas was introduced and reactive sputtering was performed using Si as a target at a gas pressure of 1.3 Pa.
1100n of Nx was laminated. The magnetic properties of the two magnetic layers 3.4 in the present invention are the same as in Example 2 above. Therefore, similar to the second embodiment, overwriting is possible, and the magnetization of the first magnetic layer 3 is changed to the second magnetic layer during reproduction.
It can be transferred to the magnetic layer 4. In the configuration of the recording medium 6 of this embodiment, the second magnetic layer 4 side (
The reproduction light is irradiated from the substrate side). However, during reproduction, the information recorded in the first magnetic layer 3 is transferred to the second magnetic layer 4. Recorded information can be reproduced accurately. In this case, the Curie temperature (Tc
x) is higher than the first magnetic layer 3, so the Kerr rotation angle is large. In particular, since a large Kerr rotation angle is maintained even when the temperature of the recording medium increases, the Kerr rotation angle does not decrease even when high intensity reproduction light is irradiated, and a large C/N ratio can be obtained. This result is shown by the broken line in FIG. As shown in FIG. 3, the C/N ratio is particularly large in areas where the intensity of the reproduction light is greater than in other areas. In this embodiment, the reproduction light is irradiated from the second magnetic layer 4 side, but as shown in FIG. A similar effect can be obtained by irradiating the (Example 5) Using the magneto-optical recording medium 6 described in Example 2, as shown in FIG. The same lens 13 is used to irradiate a light beam for reading data without being applied. In this case, the magneto-optical recording device has the same structure as the embodiment shown in FIG. That is, the area irradiated with the recording light 20 and the read-after-write light 21 is provided with a bias magnetic field applying means 12 such as an electromagnet.
This makes it possible to apply a bias magnetic field HBR during recording and a bias magnetic field H8 during reproduction. During recording, recording is performed by modulating the intensity of the recording light 20 according to the recording information while applying a recording bias magnetic field HBR. At that time, the information recorded by the recording light 20 is
It is immediately read out by the read-after light 21,
Check the recorded information. During such read-after-write immediately after recording, the magnetization of the first magnetic layer 3 and the second magnetic layer 4 are aligned in the direction of exchange coupling with each other as described above, so the read-after-write is stable and has a high intensity. Even if the light 21 is irradiated, the recorded information will not be destroyed. During reproduction, read-after-write light 21 is irradiated while applying a bias magnetic field H0 for reproduction, which is in the opposite direction to that for recording. That is, the lead afterlight light 21
is used as the reproduction light. Although the recording light 20 may be used as reproduction light, it is better to perform reproduction under the same conditions as during read-after-write - the reliability of door-after-write is improved. Furthermore, during reproduction, low-intensity recording light 20 is simultaneously irradiated. As a result, the magnetization of the first magnetic layer 3 is transferred to the second magnetic layer 4 before the recorded information is reproduced by the read-after-write light 21. Therefore, compared to the transfer using the read-after-write light 21, it is very advantageous in that the generation of noise due to reversal of magnetization and the generation of noise due to incomplete transfer can be suppressed. In this embodiment, since the light used for recording and transfer and the light used for reproduction and read-after-write are completely separated, the wavelengths of recording light 20 and read-after-write light 21 are different. can be taken as a thing. That is, a high-output semiconductor laser is used to generate the recording light 20 that requires high intensity, and the read-after-write light 21 (reproduction light) that requires high resolution has a short wavelength. In this embodiment, as the recording light 20, 5
A hybrid SH with a wavelength of 530 nm is used as the read afterlight light (reproduction light) 21 using a 0 mW semiconductor laser.
A G semiconductor laser was used. As a result, the recording and reproducing characteristics at high frequencies are the best compared to conventional ones.
As shown in Figure 8, there was a significant improvement. (Embodiment 6) FIG. 19 shows the main part configuration of another embodiment of the magneto-optical recording/reproducing apparatus according to the present invention. In the recording medium 6, a recording layer 18 consisting of a first and second magnetic layer having the same structure as in the third embodiment is laminated on a disk-shaped substrate 1. The recording medium 6 is configured to pass under the initializing magnetic field applying means 11, the bias magnetic field applying means 12, and the transfer magnetic field applying means 27 in order as it rotates. First, an initializing magnetic field HINI is applied to the recording medium 6 by the initializing magnetic field applying means 11, and the magnetization of the second magnetic layer 4 in the recording layer 18 is aligned in one direction. Thereafter, while a bias magnetic field HBR during recording is applied by the bias magnetic field applying means 12, information is recorded by the recording light 20 whose intensity is modulated according to the information. As mentioned above, in the state where information is recorded, the first magnetic layer 3
The magnetization directions of the second magnetic layer 4 and the second magnetic layer 4 are stable because they are aligned in the direction of exchange coupling with each other. Therefore, even if the recording medium moves and passes under the transfer magnetic field HT generated by the transfer magnetic field applying means 27, its magnetization state does not change. Therefore, the transfer magnetic field HT does not affect the read-after write by the read-after write light 21. When reproducing information next, the direction of magnetization of the second magnetic layer 4 is aligned in advance by the initialization magnetic field HINI. After that, a bias magnetic field I (BR) is applied during recording, but during reproduction, the intensity of the recording light is sufficiently small so that the recorded information is not destroyed.After that,
Information is transferred by the transfer magnetic field HT. That is, in areas where the magnetizations of the second magnetic layer 4 and the first magnetic layer M3 are not aligned in the direction of exchange coupling, the magnetization of the second magnetic layer M4 is likely to be reversed, and the magnetization can be reversed by the transfer magnetic field HT of an appropriate magnitude. Can be reversed. On the other hand, since the magnetization of the second magnetic layer 4 is difficult to reverse in a portion where both layers have the same magnetization, reversal does not occur. In this way, the transferred state is exactly the same as the magnetization state immediately after recording, so that the recorded information can be accurately reproduced by the linear aphthalite light 21. Also,
The reproduction signal beam is exactly the same as that at the time of door afterlight. In this embodiment, the initialization magnetic field application means 11, the bias magnetic field application means 12, and the transfer magnetic field application means 27 are all composed of permanent magnets, and each has a magnetic field strength of 4 kOe,
They are 0.5 kOe and 1 kOe. In this example, as in Example 6, the wavelength of the read-after-write light 21 is 530 nm, and the wavelength of the recording light 20 is 780 nm.
Since the resolution during reproduction is improved, the recording and reproduction characteristics at high frequencies as shown in FIG. 19 are improved. In this embodiment, since the lens 13 for condensing the recording light 20 and the lens 13 for condensing the read-after-light beam 21 are separate, the optical systems for different wavelengths can be completely separated, and the configuration can be simplified. Further, since no reversal of the magnetic field is required, the device can be made smaller. Example 3 shows that the number of repeated recordings and the C7N ratio are improved.
It is similar to In the configuration of this embodiment, it is also possible to make the magnitude of the transfer magnetic field HT zero by adjusting the magnetic characteristics of the recording medium 6. In this case, the initialization magnetic field application means 11 and the bias magnetic field application means 12 are used in common, and the intensity thereof is made different between the recording light position and the initialization position. Furthermore, since the transfer magnetic field applying means 27 is not required, the device configuration is further simplified. [Effects of the Invention] In the magneto-optical recording and reproducing method of the present invention, there is no fear that recorded information will be destroyed even if high-intensity reproducing light is irradiated, and a highly sensitive overwritable magneto-optical recording and reproducing method and apparatus are realized. Ru. Furthermore, it is possible to provide an overwritable magneto-optical recording medium that is free from deterioration of the characteristics of the recording medium even if overwriting is repeated many times. Furthermore, it is possible to obtain an overwritable high C/N magneto-optical recording medium that can obtain a large Kerr rotation angle without reducing sensitivity. Furthermore, it is also possible to perform a highly reliable aphthalite.

[Brief explanation of drawings]

Fig. 1 is a block diagram of one embodiment of magneto-optical recording and reproducing according to the present invention, Fig. 2 is a diagram for explaining conventional magneto-optical recording and reproducing, Figs. 3, 5, 9, and 10. Figure, Figure 13, 1st
4 and 18 are characteristic diagrams for explaining the effects of the embodiments of the present invention, FIG. 4 is a diagram showing the relationship between the film thickness of the magnetic layer and the Kerr rotation angle, and FIGS. 6 and 12. and FIG. 15 is a partial cross-sectional structural diagram of an embodiment of the magneto-optical recording medium according to the present invention,
7 and 16 are diagrams showing the magnetic characteristics of the first magnetic layer and the second magnetic layer in an example of the magneto-optical recording medium according to the present invention, and FIGS. 8 and 11 are diagrams showing the bias magnetic field and laser intensity. 17 and 19 are diagrams illustrating changes in the magnetic material of the magneto-optical recording medium in relation to the relationship between the magneto-optical recording medium and the magneto-optical recording/reproducing apparatus according to the present invention. Explanation of symbols 1... Transparent substrate, 2... Dielectric layer, 3... First magnetic layer, 4... Second magnetic layer, 5... Protective layer, 6... Recording medium, 7...・Laser light source, 8...Scanning control means, 9.
...Rotation immediate action means, 10...Bias power supply, 11...
- Initialization magnetic field applying means, 12... Electromagnet, 13... Lens, 14... Light beam, 15... First dielectric layer,
16... Second dielectric layer, 17... Heat diffusion layer, 18.
... Recording layer, 2o... Recording light, 21... Read-after-write light, 22... Minimum value of PH, 23... Transfer of magnetization of second magnetic layer to first magnetic layer, 24. ... Transfer of magnetization of the first magnetic layer to the second magnetic layer, 25 - Coercive force of the first magnetic layer, 26... Coercive force of the second magnetic layer, ... Information reproducing circuit, transfer magnetic field applying means,・Laser drive circuit.

Claims (1)

[Claims] 1. A magneto-optical recording medium having at least a first magnetic layer and a second magnetic layer laminated on a substrate is used, and the magneto-optical recording medium is irradiated with recording light of a first intensity. In a magneto-optical recording and reproducing method that performs overwriting by utilizing the difference in magnetization information recorded when irradiating recording light with a second intensity smaller than the first intensity, the recorded information is A magneto-optical recording and reproducing method characterized by applying a bias magnetic field having a direction or intensity different from the bias magnetic field during recording during reproduction. 2. When using a magneto-optical recording medium formed by laminating at least a first magnetic layer and a second magnetic layer on a substrate, when the magneto-optical recording medium is irradiated with recording light of a first intensity; In a magneto-optical recording and reproducing method that performs overwriting by utilizing the fact that the magnetization information recorded is different depending on the irradiation of recording light with a second intensity smaller than that of the recording light, the recording light is used before or during the reproduction of the recorded information. . A magneto-optical recording and reproducing method comprising the step of transferring magnetization information of a first magnetic layer to a second magnetic layer. 3. The magneto-optical recording and reproducing method according to claim 1 or 2, wherein a pretreatment is performed to align the magnetization direction of the second magnetic layer in one direction before recording information. How to play. 4. In the magneto-optical recording and reproducing method according to claim 1, 2 or 3, the intensity of the reproduction light irradiated for reproducing the information recorded on the magneto-optical recording medium is equal to the second intensity. A magneto-optical recording and reproducing method characterized in that the intensity is equal to or higher than that of recording light. 5. In the magneto-optical recording and reproducing method according to any one of claims 3 to 5, after recording information on the magneto-optical recording medium and before aligning the direction of magnetization of the second magnetic layer in one direction, A magneto-optical recording and reproducing method characterized by reading the recorded information for confirmation. 6. A magneto-optical recording medium used in the magneto-optical recording and reproducing method according to any one of claims 1 to 5, wherein one of the first magnetic layer and the second magnetic layer is irradiated with the reproducing light. 1. A magneto-optical recording medium, wherein one layer is composed of a magnetic layer whose Curie temperature is higher than the Curie temperature of the other layer. 7. In a magneto-optical recording medium having a laminated first magnetic layer and a second magnetic layer, the thickness of the magnetic layer on the side to which the reproduction light is irradiated among the first magnetic layer and the second magnetic layer is determined by the reproduction light. What is claimed is: 1. A magneto-optical recording medium characterized in that the film thickness is such that the film is transparent. 8. In claim 6 or 7, the magnetic layer has a thermal conductivity higher than that of the first magnetic layer and the second magnetic layer on the side opposite to the side of the magnetic layer to which the reproduction light is irradiated. A magneto-optical recording medium characterized by being provided with a heat diffusion layer. 9. A method for recording information on a magneto-optical recording medium according to any one of claims 1 to 8, wherein the recorded information is confirmed immediately after irradiating the magneto-optical recording medium with recording light modulated according to the information. A magneto-optical recording method characterized by irradiating light for. 10. When using a magneto-optical recording medium formed by laminating at least a first magnetic layer and a second magnetic layer on a substrate, when the magneto-optical recording medium is irradiated with recording light of a first intensity; An apparatus for reproducing recorded information on an overwritable magneto-optical recording medium that utilizes the fact that magnetization information recorded is different when irradiated with recording light of a second intensity lower than the first magnetic field. a light source for irradiating reproduction light to at least one of the magnetic layer and the second magnetic layer; a magnetic field applying means for applying a bias magnetic field to a portion of the magneto-optical recording medium irradiated with the reproduction light or the vicinity thereof; A magneto-optical recording and reproducing device comprising: signal processing means for detecting recorded information from the reproducing light that is reflected by at least one of the first magnetic layer and the second magnetic layer. 11. The magneto-optical recording and reproducing apparatus according to claim 10, wherein the intensity of the reproducing light is greater than or equal to the intensity of the recording light having the second intensity. 12. When using a magneto-optical recording medium formed by laminating at least a first magnetic layer and a second magnetic layer on a substrate, when the magneto-optical recording medium is irradiated with recording light of a first intensity; an overwritable magneto-optical recording section that utilizes the fact that magnetization information recorded is different when irradiated with recording light of a second intensity smaller than the recording light intensity; and a reproducing section that reproduces recorded information on the magneto-optical recording medium. The magneto-optical recording section has means for irradiating the magneto-optical recording medium with a light beam for confirming recorded information immediately after recording, and the reproducing section has a means for irradiating the magneto-optical recording medium with a light beam for confirming recorded information immediately after recording, and the reproducing section has a means for irradiating the magneto-optical recording medium with a light beam for confirming recorded information immediately after recording, and a light source for irradiating reproduction light to at least one of the layers; a magnetic field applying means for applying a bias magnetic field to a portion of the magneto-optical recording medium to which the reproduction light is irradiated or a vicinity thereof; 1. A magneto-optical recording and reproducing device comprising: signal processing means for detecting recorded information from the reproducing light reflected by at least one of the magnetic layer and the second magnetic layer. 13. Claim 12, wherein the means for irradiating the magneto-optical recording medium with a light beam for confirming recorded information immediately after recording is configured to irradiate the recording light through a lens. A magneto-optical recording and reproducing device characterized by: 14. Claim 12, wherein the means for irradiating the magneto-optical recording medium with a light beam for confirming recorded information immediately after recording is performed through a lens different from a lens for irradiating the recording light. A magneto-optical recording and reproducing device characterized by being configured as follows. 15. In claim 12, 13 or 14,
A magneto-optical recording and reproducing apparatus characterized in that the wavelengths of the reproducing light and the light beam for confirming the recorded information are shorter than the wavelength of the light used for recording information. 16. A magneto-optical recording medium having a layer in which a first magnetic layer and a second magnetic layer are laminated, and when the direction of magnetization of the second magnetic layer is at room temperature and no magnetic field is applied, the magnetization of the first magnetic layer is the same as that of the first magnetic layer. An overwritable magneto-optical recording medium characterized by being magnetized in the direction of exchange coupling with the magneto-optical recording medium.