JP3164058B2 - Method and apparatus for reproducing signal from magneto-optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for reading information bits (magnetic domains) by magneto-optical interaction, a signal reproducing method for the magneto-optical recording medium, and a signal. It relates to a playback device. 2. Description of the Related Art In the case where information bits, ie, bubble magnetic domains are formed by local heating by laser beam irradiation and read out by magneto-optical interaction, and the magneto-optical recording / reproducing method is adopted, the recording density of the magneto-optical recording is reduced. To increase the bit length, the bit length must be shortened, that is, the information domain must be miniaturized. In this case, in a general magneto-optical recording / reproducing method, in order to secure the S / N at the time of reproduction, it is necessary to increase the reproduction time. Are limited by the laser wavelength, the numerical aperture of the lens, and the like. For example, at present, it is impossible to read out information bits (magnetic domains) of 0.2 μm with a laser beam having a spot diameter of 1 μm. SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem of the limitation of the recording density defined by the conditions at the time of reproduction, and is sufficiently applicable even when the recording information bits are miniaturized. Reproduction output, and therefore, S / N (C / N) is improved. A signal reproducing method for a magneto-optical recording medium according to the present invention comprises irradiating a magnetic film of a magneto-optical recording medium with a laser beam, and applying a laser beam to a magnetic domain of the magnetic film. A signal reproducing method for a magneto-optical recording medium for reading recorded information by magneto-optical interaction, wherein the magneto-optical recording medium comprises: a first magnetic film from which recorded information is read by at least magneto-optical interaction; A medium including a third magnetic film for retaining magnetic domains and a second magnetic film disposed between the magnetic films is used. Then, by changing the size of the magnetic domain of the first magnetic film, the recording magnetic domain of the third magnetic film can be retained, and a laser beam having a power capable of giving a temperature equal to or higher than the Curie temperature of the second magnetic film is irradiated. A process of reading recorded information from the first magnetic film by magneto-optical interaction, and a state in which irradiation of power laser light is completed;
And returning the magnetic domains of the first magnetic film to the magnetic domains before the change in the size of the magnetic domains. Further, a signal reproducing apparatus according to the present invention is an apparatus for performing the above-described signal reproducing method for a magneto-optical recording medium according to the present invention, and includes a pickup having at least the laser for obtaining the laser light and an objective lens, and a magneto-optical recording medium. A mechanism for relatively moving the laser light from the pickup for irradiating the laser beam and the magneto-optical recording medium, and a means for detecting the magneto-optical interaction of the laser light and reading the recorded information. The magneto-optical recording medium includes a first magnetic film from which recorded information is read out by at least magneto-optical interaction, a third magnetic film holding recording magnetic domains, and a second magnetic film disposed between the magnetic films. The magnetic domain of the first magnetic film can be changed, the recording magnetic domain of the third magnetic film can be held, and the power that can provide a temperature equal to or higher than the Curie temperature of the second magnetic film can be obtained. A step of irradiating a laser beam to read recorded information from the first magnetic film by magneto-optical interaction, and, in a state where the laser beam irradiation of the power is completed, the above magnetic domain of the first magnetic film becomes the magnetic domain of the magnetic domain. It has a configuration for implementing a signal reproducing method by a process of returning to the magnetic domain before the size change. [0005] One embodiment of the present invention will be described. In this case, for example, as shown in FIG. 1, a dielectric film 2 as a light-transmitting protective film or an interference film is similarly formed on the light-transmitting substrate 1 as necessary, and Room temperature T
_A first magnetic film 11 magnetically coupled to each other at _RT and mainly contributing to signal reproduction, and a second magnetic film 12 serving as an intermediate film
To form a laminated structure of each perpendicular magnetization film of the third magnetic film 13 which mainly contributes to recording retention, and the first, second, and third
When the respective Curie temperatures of the respective magnetic films 11, 12 and 13 are T _C1 , T _C2 and T _C3 , T _C2 > T _RT and T _C2 <T _C1 and T _C3, and the first magnetic film 11 coercive force H
_C1 is sufficiently small in the vicinity of the Curie point T _{C2 of} the second magnetic film 12, and the coercive force H _{C3 of} the third magnetic film 13 is _lower than the room temperature T _RT by the second value.
Required temperature T higher than the Curie temperature T _C2 of the magnetic film 12 of FIG.
_A magneto-optical recording medium S that is sufficiently larger than a required magnetic field in a temperature range up to _PB is used. At the time of the reproduction, the recording magnetic domain, that is, the information bit, of the first magnetic film 11 at the above-mentioned required temperature _TPB which is _{equal to} or higher than the Curie temperature T _{C2 of} the second magnetic film 12 is converted into a demagnetizing field applied thereto. It is expanded by an externally applied magnetic field given as necessary and read out in this state. A surface protection film 4 is formed on the third magnetic film 13 as needed. In the recording on the magneto-optical recording medium S, that is, the formation of the information magnetic domain, a bias magnetic field in a direction opposite to the magnetization direction near the recording temperature of the third magnetic film 13 in the initial state is applied as usual. In this state, the laser beam is focused and irradiated, and thereby the third magnetic film 13 is irradiated.
Is heated above its Curie temperature, and the information of, for example, "1" is recorded by forming a bubble magnetic domain which is inverted in the direction by the external magnetic field and the stray magnetic field at the time of cooling after the laser beam scanning is completed. That is, binary information of "1" and "0" is recorded depending on the presence or absence of the information bubble magnetic domain. In reading information from the magneto-optical recording medium S on which such information has been recorded, that is, in reproducing the information, for example, a Kerr rotation angle or a Kerr rotation angle due to magneto-optical interaction due to the presence or absence of the magnetic domain is irradiated by laser light irradiation. When reading the record by the Faraday rotation angle, the temperature of the reading unit is set to a required temperature T _PB ,
That is, by setting the temperature to exceed the Curie point T _C2 of the second magnetic film 12, the magnetic coupling between the first and third magnetic films 11 and 13 is broken. Therefore, in this state, the first magnetic film 11 is not subjected to the magnetic restriction by the third magnetic film 13, and the recorded information magnetic domain is provided with the demagnetizing field given thereto and, if necessary, at this time. The first magnetic film 11 further expands due to a reduction in coercive force at this temperature _TPB due to a required magnetic field based on the sum of the externally applied magnetic field and the like. Therefore, as the first magnetic film 11,
If a magnetic film having a large Kerr rotation angle or a Faraday rotation angle is used, a large reproduction output can be obtained mainly by the recorded information in the first magnetic film 11 due to a substantial increase in the information magnetic domain. S / N (C
/ N) can be improved. [0010] Then, this information domain is expanded,
That is, since the reproduction is performed in a state where the read magnetic domain area is substantially increased, the reproduction output is increased.
/ N can be improved. After the reproduction, that is, after the irradiation part is moved by the scanning of the laser beam, if the reading part is cooled, the first to third magnetic films 11 to 13 are kept at, for example, the room temperature T _RT.
During the cooling process, the third magnetic film 13 having a high coercive force acts as a magnetic recording holding film, the second magnetic film 12 is magnetized by its magnetic coupling, and the second magnetic film 1
The first magnetic film 11, which is magnetically coupled to the magnetic recording medium 2, is magnetized, and the information bit magnetic domain in the initial recording state is formed again to restore the recording state. According to the above-described method, the second magnetic film 12 as an intermediate layer of the magneto-optical recording medium S has a magnetically coupled state and a disconnected state between the first and third magnetic films 11 and 13. By adopting both aspects, at the time of reproduction, the second magnetic film 12 of the intermediate layer becomes the first and third magnetic films.
The magnetic coupling between the magnetic films 11 and 13 of FIG.
The third magnetic film 13 has a function as a magnetic recording holding layer for holding its magnetization state, and the first magnetic film 11 has a function of reproducing. Sometimes, the magnetic domain is enlarged to have a function as a reproducing layer for improving the reproducing output, so that even if the magnetic domain as the bit information is reduced by improving the recording density, a sufficient reproducing output can be obtained. Higher recording density can be achieved. Further referring to FIG. 2, first to third magnetic films 1
The magnetization state when 1 to 13 are ferromagnetic films, respectively, will be described. Now, as shown in FIG.
Assuming that the direction of magnetization is in a perpendicular magnetization state in one direction in the unrecorded state, the information "1" is now recorded and the initial state as shown in FIG. , An information bit, that is, an information magnetic domain B _M is formed by the reverse magnetization. [0014] Referring to read for the information magnetic domain B _M, in this case, in a state irradiated with the laser beam L _B for the information domain B _M as shown in FIG. 2C, as described above, in the example, the center portion The above-mentioned required temperature T _PB is obtained. At this time, the second
The magnetic film 12 loses its magnetism when its Curie temperature T _C2 or higher, and the first and third magnetic films 1
The magnetic coupling between 1 and 13 is interrupted. In this state, by applying an externally applied magnetic field _Hex in the same direction as the direction of the external bias magnetic field at the time of recording, that is, the original magnetization direction of the magnetic domain B _M , that is, the direction of the magnetization at the time of recording, At this temperature T _PB , the coercive force H
The magnetic domain B _M of the first magnetic film 11 in which _C1 is small is enlarged. As shown in FIG. 2D, the laser light L
In a state where the irradiation is irradiated to the outside of the information magnetic domain B _M of _B, the temperature rises in the information magnetic domain, since relatively small, the expansion of the information bits or domains B _M hardly occurs. That can cause enlargement of the magnetic domain only in the information recording magnetic domain B _M existing in the center of the magnetic domain B _M in the center of the laser beam scanning in the reading state. [0016] Therefore, in this case, for example, as shown in FIG. 3A, when performing laser beam scanning the magnetic recording medium by the information recording magnetic domain B _M are arranged at equal pitches, the output, as shown in FIG. 3B when an ideal demagnetization level domain B _M is lost and 0 level, it is possible to take out the waveform output indicating the great level upward in one direction view by reading the information magnetic domain B _M. Incidentally, in practice, the first to third magnetic films 11 to 11 are formed.
13 is a rare earth-transition metal magnetic film, and when the sublattice magnetization of the transition metal and the sublattice magnetization of the rare earth metal have ferrimagnetism in opposite directions, each magnetic film is a transition metal sublattice magnetization dominant film. It is necessary to select the direction of the externally applied magnetic field _Hex given at the time of reproduction depending on whether the film is a rare earth sublattice magnetization dominant film. To explain this, now, in this case, the direction of the externally applied magnetic field _Hex at the time of reproduction is considered with reference to the direction of the external bias magnetic field at the time of recording. In this case, the third magnetic film which controls the direction of recording It is separately considered whether the saturation magnetization immediately below the Curie point T _{C3 of} 13 is a transition metal sublattice magnetization dominant film or a rare earth sublattice magnetization dominant film. Here information in stray field and demagnetizing field applied to the information magnetic domain B _M of the first magnetic film 11 is considered excluded. [1] When the magnetization of the third magnetic film 13 is a transition metal sublattice magnetization dominant film immediately below the Curie point T _C3 , (1-a) the first magnetic film near the Curie point T _{C2 of} the second magnetic film 12 when the magnetization of the magnetic film 11 is dominant transition metal sublattice, the external magnetic field direction during reproduction it is possible to increase of the information recording magnetic domain B _M by applying the external magnetic field in the same direction during recording . (1-b) is close to the magnetization is zero in the second first at the Curie point T _C2 vicinity of the magnetic film 12 of the magnetic film 11, the Curie point T _C2 of the temperature at the time of reproduction the second magnetic film 12 magnetization of the first magnetic film 11 is reproduced in a state in which the dominant transition metal sublattice further increased from the vicinity of, in this case the increase in bubble magnetic domains B _M externally applied magnetic field H _ex of a recording time of the same direction Can be measured. (1-c) When the magnetization of the first magnetic film 11 is dominated by the rare earth sublattice near the Curie point T _{C2 of} the second magnetic film 12, the externally applied magnetic field _Hex during reproduction is in the opposite direction to that during recording. , The magnetic domain B _M can be expanded. [2] When the magnetization of the third magnetic film 13 is dominated by the rare-earth sublattice immediately below its Curie point T _C3 , (2-a) the first magnetic film near the Curie point T _{C2 of} the second magnetic film 12 if the magnetization 11 is dominant transition metal sublattice, the external applied magnetic field H _ex of reproduction, from that at the time of recording can be achieved expansion of the bubble magnetic domain B _M by selecting the reverse direction. (2-b) When the magnetization of the first magnetic film 11 is close to zero near the Curie point T _C2 of the second magnetic film 12, the temperature _TPB during reproduction is set to the Curie point T _C of the second magnetic film 12. measure the expansion of the magnetic domain B _{M by C2} further raised from near the magnetization of the first magnetic film 11 is in the opposite direction from that during recording the external magnetic field H _ex as state becomes dominant transition metal sublattice be able to. (2-c) When the magnetization of the first magnetic film 11 is dominated by the rare-earth sublattice near the Curie point T _{C2 of} the second magnetic film 12, the external bias magnetic field _Hex during reproduction is in the same direction as that during recording. it is possible to measure the expansion of the bubble magnetic domain B _M by. The substrate 1 is made of a light-transmitting material such as a glass plate or a resin plate such as an acrylic plate. Although not shown, one surface has track grooves for tracking servo at a pitch of 1.6 μm, for example. A dielectric film 2 made of, for example, a Si ₃ N ₄ film, first to third magnetic films 11 to 13, and a protective film 4 thereon are further formed, for example, by a magnetron sputtering apparatus. Is continuously formed by continuous sputtering or evaporation. As the first magnetic film 11, for example, GdC
o, GdFeCo, GdFe, and the second magnetic film 12 is made of, for example, DyFe, DyFeCo, TbF.
e, and the third magnetic film 13 is made of TbFe,
It can be formed of TbFeCo, DyFeCo, or the like. According to the third magnetic film 13, a magnetic domain B _M having a diameter of 0.1 μm or less can be formed. Example 1 A dielectric film 2 made of Si ₃ N ₄ was formed on a glass substrate having a track groove having a track pitch of 1.6 μm, and GdFeC.
a first magnetic film 11 made of an O film, a second magnetic film 12 made of a DyFeCo film, and a third magnetic film 12 made of a DyFeCo film.
The magnetic film 13 and the protective film 4 made of a Si ₃ N ₄ film were sequentially formed by continuous sputtering using a magnetron sputtering apparatus, thereby producing a magneto-optical recording medium, that is, an optical disk S. Table 1 shows the thickness and magnetic characteristics of each magnetic film 11 to 13 as a single layer film in this case. [Table 1] In Table 1 above, FeCo-rich indicates a FeCo sublattice magnetization dominant film at room temperature, and Dy-rich indicates a Dy sublattice magnetization dominant film at room temperature. FIG. 4 shows the measurement results of the recording frequency dependence of the carrier level versus the noise level (C / N) of the magneto-optical recording medium S according to the first embodiment. In FIG. 4, the solid curve represents the numerical aperture of the objective lens. A. = 0.50, laser wavelength 78
A linear velocity of 7.5 m /
sec, recording power 7.0 mW, recording external magnetic field 500
(0e), the externally applied magnetic field during reproduction is zero, and the reproduction power is 3.5 mW. The dotted line in FIG. 4 is the case where the reproduction power is 1.5 mW. When the reproducing power was 1.5 mW, a result equivalent to the frequency dependency of C / N in the optical disk when the entire magnetic film was constituted by a single layer film of TbFeCo was shown. This is because at such a reproducing power, the second magnetic film 1
It is considered that the heated magnetic domain did not reach the Curie point T _{C2 of} 2 and the recorded magnetic domain was not deformed during reproduction. On the other hand, when the reproducing power was 3.5 mW, the C / N was remarkably increased at the magnetic domain length, that is, the bit length l <0.7 μm, as compared with the reproducing power of 1.5 mW. And l =
Even at 0.3 μm, a signal component was obtained although the C / N was low. Conversely, when l> 0.7 μm, the C / N decreases, but this is due to the increase in noise N. Also, when a place reproduced with a reproducing power of 3.5 mW is reproduced again,
It was confirmed that C / N was reproduced at any of the reproduction powers of 1.5 mW and 3.5 mW. In the first embodiment, when the power of the laser beam at the time of reproduction is kept constant, the temperature profile is widened due to thermal diffusion in the medium S, and the reproduction resolution of minute information bits (magnetic domains) is reduced. However, in order to sharpen the temperature profile, it is sufficient to perform reproduction with a pulse laser beam having a narrow width at a frequency interval corresponding to, for example, the minimum bit length. Further, for example, an Al heat radiating film having good thermal conductivity is placed on the third magnetic film 13 (on the side opposite to the side in contact with the second magnetic film 12) so that the heat energy absorbed by the magnetic film is quickly radiated. Can be adhered to. As described above, according to the present invention, the information is not simply read out by using the magneto-optical effect of the laser beam in the magneto-optical recording medium, that is, the Kerr effect or the Faraday effect. In this reading, the irradiation of the laser beam simultaneously raises the temperature to cause a change in the magnetization state, thereby reading the recorded information. Therefore, the read signal level, and hence the S / N (C / N)
However, without being directly restricted by the shape and size of the recording magnetic domain, the numerical aperture of the readout optical system, and the spot diameter of the laser light limited by the wavelength of the readout laser light,
By giving a required change to the magnetization state of the recording magnetic domain, the signal level and S / N (C / N) can be improved, so that the recording magnetic domain can be made finer, and thus the recording density can be increased. Can be measured. In the above-described reproducing method, the magnetic film has a structure in which the first to third magnetic films 11 to 13 are laminated, and at room temperature, that is, in the normal state, the three magnetically maintain the magnetically coupled normal state. However, the first magnetic film 11 is heated so that the second magnetic film 12 has the effect of cutting off the magnetic coupling between the first and third magnetic films 11 and 13 during heating during reproduction. S / N (C / N) of reproduction output by expanding information domain
The third, despite being able to improve
Since the recording state of the magnetic film 13 can be maintained, the recording state can be restored again after the reproduction is completed, and good reproduction characteristics can be obtained without impairing the repeated reproduction. According to the present invention as described above,
Since a sufficient reproduction output can be obtained, the recording information magnetic domain B _M can be sufficiently reduced, and the recording density can be improved by itself, and further, as the magneto-optical recording medium, Even in the case where the track groove is formed in the structure, since the information magnetic domain B _M can be sufficiently reduced, the formation of the recording magnetic domain only in the land portion as usual is not limited. Since the recording magnetic domain can be formed both in the land portion and in the track groove, the recording density of information can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a magneto-optical recording medium used in the method of the present invention. FIGS. 2A to 2D are diagrams showing magnetization states for explaining the method of the present invention. FIG. 3 is a diagram illustrating a reproduction output waveform together with a magnetization state. FIG. 4 is a diagram showing a reproduction characteristic curve with respect to a recording frequency. [Description of Signs] 1 {base, 11-13} first to third magnetic films, S}
‥ Magneto-optical recording media

Claims (1)

(57) [Claims] A signal reproducing method for a magneto-optical recording medium, comprising irradiating a magneto-optical recording medium with laser light and reading recorded information by magneto-optical interaction between the laser light and magnetic domains of the magnetic film, Comprises at least a first magnetic film from which recorded information is read out by the magneto-optical interaction, a third magnetic film holding recording magnetic domains, and a second magnetic film disposed between these magnetic films. The Curie temperature Tc ₂ of the _second magnetic film is lower than the Curie temperatures Tc ₁ and Tc _{3 of} the first magnetic film and the third magnetic film, respectively. The coercive force Hc ₁ is sufficiently small near the Curie temperature Tc ₂ of the _second magnetic film, and the coercive force Hc ₃ of the third magnetic film is _calculated from the room temperature _TRT to the Curie temperature of the second magnetic film. Regeneration temperature T higher than Tc _2
The size is selected so that the magnetization state can be maintained in the range up to _PB .
By irradiating a laser beam having a power capable of holding a recording magnetic domain of the magnetic film of the second magnetic film and giving a temperature equal to or higher than the Curie temperature of the second magnetic film, recording information is output from the first magnetic film by the magneto-optical interaction. A signal reproducing method for a magneto-optical recording medium, comprising: a step of reading; and a step of returning the first magnetic film to a state before the expansion of the magnetic domain after the irradiation of the laser beam with the power is completed. 2. A signal reproducing apparatus for a magneto-optical recording medium for irradiating a magneto-optical recording medium with a laser beam and reading recorded information, comprising: a laser for obtaining the laser beam; a pickup having an objective lens; and the magneto-optical recording medium A mechanism for relatively moving the laser light from the pickup and the magneto-optical recording medium for irradiating the laser light, and a means for reading the recording information by detecting return light of the laser light from the magneto-optical recording medium 2. A signal reproducing apparatus for a magneto-optical recording medium used in carrying out the method for reproducing a signal on a magneto-optical recording medium according to claim 1, wherein the signal reproducing apparatus has at least: