JP2001110108A - Signal reproduction device for magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sufficient reproduction output and a signal-to-noise (carrier-to- noise) ratio even when the recording information bit of a signal recording and reproducing device for a magneto-optical recording medium is microminiaturized. SOLUTION: The magneto-optical recording medium which has a first magnetic film 11, a third magnetic film 13 held with recording magnetic domains and a second magnetic film 12 arranged between these magnetic films and of which the second magnetic film 12 consists of the magnetic film having a Curie temp lower than the Curie temperatures of the first magnetic film 11 and the third magnetic film 13 is used. Further, the device has a means for applying an external magnetic field where the sum of a demagnetizing field and the external magnetic field attains a value smaller than the coercive force Hc3 of the third magnetic film. The magnetic domain state of the first magnetic film is changed by applying a reproduction temperature TpB which is higher than the Curie temperature of the second magnetic film and at which the magnetization state of the third magnetic film may be held in the position of the magneto-optical recording medium of the portion irradiated with a laser beam and the reading-out of recording information is executed by detection of the Kerr rotating angle or Faraday rotating angle of the laser beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal reproducing apparatus for a magneto-optical recording medium for reading information bits (magnetic domains) by magneto-optical interaction.

[0002]

2. Description of the Related Art In the case where information bits, that is, bubble magnetic domains are formed by local heating by laser beam irradiation and are read out by magneto-optical interaction by a magneto-optical recording / reproducing method, in order to increase the recording density of the magneto-optical recording, In this case, the bit length is reduced, that is, the information magnetic domain is miniaturized. In this case, in a general magneto-optical recording and reproducing method,
In securing the S / N at the time of reproduction, there are restrictions on the laser wavelength at the time of reproduction, 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.

[0003]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem of the restriction on the recording density defined by the conditions at the time of reproduction, and provides a sufficient reproduction output even when the recording information bits are miniaturized. Therefore, the S / N (C / N) is improved.

[0004]

According to the present invention, there is provided a pickup having at least a laser and an objective lens for focusing a laser beam on a magneto-optical recording medium. A third magnetic film in which a recording magnetic domain is held, and a second magnetic film disposed between the magnetic films, wherein the second magnetic film is composed of the first magnetic film and the third magnetic film. The first magnetic film has a coercive force Hc _{1 that} is sufficiently small near the Curie temperature Tc ₂ of the second magnetic film,
Third coercive force Hc ₃ of the magnetic layer is a magneto-optical recording comprising been selected large enough to hold the magnetization state in the range of from room temperature T _RT to a high regeneration temperature T _PB above the Curie temperature Tc ₂ of the second magnetic layer A medium is used. Further, a mechanism for relatively moving the magneto-optical recording medium and the laser beam, and a configuration for applying an external magnetic field in which the sum of the demagnetizing field and the external magnetic field is smaller than the coercive force Hc ₃ of the third magnetic film. And a first reproducing temperature T _PB higher than the Curie temperature of the second magnetic film and capable of maintaining the magnetization state of the third magnetic film at the position of the laser beam irradiation portion of the magneto-optical recording medium. The magnetic domain state of the magnetic film is changed, and the recorded information is read out by detecting the Kerr rotation angle or the Faraday rotation angle due to the magneto-optical interaction of the laser light.

As described above, in the device of the present invention,
By reading the information by changing the magnetic domain state of the signal reproducing magnetic film, the S / N can be increased without being restricted by the optical system.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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
The Curie temperature of each of the magnetic films 11, 12 and 13 is set to T
_{When C1} , T _C2 and T _C3 , T _C2 > T _RT and T
_C2 <T _C1 , T _C3, and the coercive force H _{C1 of} the first magnetic film 11
Is sufficiently small near the Curie temperature T _{C2 of} the second magnetic film 12, and the coercive force H _{C3 of} the third magnetic film 13 is _higher than the room temperature T _RT by the second
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.

[0007] Depending on the reproducing apparatus according to the present invention, the recording magnetic domain, that is, the information bit, of the first magnetic film 11 is added to the second magnetic film 12 at the above-mentioned required temperature _TPB which is _{equal to} or higher than the Curie temperature T _C2. It is expanded by a demagnetizing field and, if necessary, an externally applied magnetic field, 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 having 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, thereby heating the third magnetic film 13 to a temperature equal to or higher than its Curie temperature, and at the time of cooling after leaving the laser beam scanning, the third magnetic film 13 is reversed in the direction by the external magnetic field and the stray magnetic field. For example, information "1" is recorded by forming the bubble magnetic domain. That is, binary information of "1" and "0" is recorded depending on the presence or absence of the information bubble magnetic domain.

[0009] Such information is recorded.
Reading of information from the magneto-optical recording medium S, that is,
In the reproduction of, for example, by laser light irradiation
No Kerr rotation angle due to magneto-optical interaction with or without magnetic domain
The record is read out by the Faraday rotation angle.
In this case, the temperature of the reading section is set to a required temperature T _PB
In other words, the Curie temperature T of the second magnetic film 12_C2Over
The first and third magnetic films
The magnetic coupling between 11 and 13 is broken. Accordingly
In this state, the first magnetic film 11 becomes the third magnetic film 13.
This recording information domain
Depends on the demagnetizing field given to this and
Required magnetic field by the sum of externally applied magnetic fields etc.
Therefore, the first magnetic film 11 further has the temperature T_PBKeep
It expands due to the reduced magnetic force.

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.

Then, a state where the information magnetic 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.

[0012] Then, after the reproduction, i.e. after the irradiation portion is moved by scanning of the laser beam, if the read unit is cooled, reduced cooling in the first to third magnetic films 11 to 13, for example at room temperature T _RT In the process, the third magnetic film 1 having a high coercive force
3 functions as a magnetic recording holding film, the second magnetic film 12 is magnetized by its magnetic coupling, and the first magnetic film 11 magnetically coupled to the second magnetic film 12 is magnetized, The information bit magnetic domain in the recorded state is formed again and restored to the recorded state.

According to the above-described configuration, the second magnetic film 12 as an intermediate layer of the magneto-optical recording medium S is in the state of magnetic coupling and disconnection 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 sufficient reproducing output can be obtained even when the recording density is improved and the magnetic domain as the bit information is miniaturized. 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.

[0015] With reference 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, , The magnetic domain B _M of the first magnetic film 11 in which the coercive force H _C1 is small at this temperature T _PB is enlarged.

As shown in FIG. 2D, the laser light L
_In the state where the irradiation of _B is irradiated outside the information magnetic domain B _M , the temperature rise in the information magnetic domain is relatively small, so that the information bit, that is, the magnetic domain B _M hardly expands. That can be expanded magnetic domains cause only the information recording magnetic domain B _M existing in the center of the magnetic domain L _B in the center of the laser beam scanning in the reading state.

[0017] Therefore, in this case, for example, as shown in FIG. 3A, when the information recording magnetic domain B _M performs laser beam scanning the magnetic recording medium arranged in an equal pitch, 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
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,
Externally applied magnetic field direction H during reproduction _exOutside when recording direction
Considering the direction of the local bias magnetic field, in this case
Curie temperature T of third magnetic film 13 governing direction_C3straight
If the saturation magnetization below is the transition metal sublattice magnetization dominant film or rare
Discussing separately whether it is an earth sublattice magnetization dominant film
You. Here, the information magnetic domain B in the first magnetic film 11_MJoin
Exclude the floating magnetic field and demagnetizing field. [1] The magnetization of the third magnetic film 13 has a Curie temperature T_C3Directly below
In the case where the film is a transition metal sublattice magnetization dominant film, (1-a) Curie temperature T of the second magnetic film 12_C2In the vicinity
When the magnetization of the first magnetic film 11 is dominated by the transition metal sublattice,
The direction of the external magnetic field during reproduction is the direction of the external magnetic field during recording.
Information recording domain B by giving in the same direction as the_Mof
It can be increased. (1-b) Curie temperature T of the second magnetic film 12_C2In the vicinity
If the magnetization of the first magnetic film 11 is close to zero,
Is the Curie temperature T of the second magnetic film 12._C2From nearby
By further increasing the magnetization of the first magnetic film 11, the transition metal
Play back when the child is dominant.
Externally applied magnetic field H in the same direction_exBubble domain B below_MIncrease
We can do it. (1-c) Curie temperature T of second magnetic film 12_C2In the vicinity
When the magnetization of the first magnetic film 11 is dominated by the rare earth sublattice,
Externally applied magnetic field H when raw_exIs set in the opposite direction to that during recording.
Domain B_MCan be expanded
You. [2] The magnetization of the third magnetic film 13 has a Curie temperature T_C3
When the rare-earth sublattice is dominant immediately below: (2-a) Curie temperature T of the second magnetic film 12_C2In the vicinity
When the magnetization of the first magnetic film 11 is dominated by the transition metal sublattice,
Externally applied magnetic field H during reproduction_exIs the opposite direction to that at the time of recording
Bubble domain B_MMeasure expansion
be able to. (2-b) Curie temperature T of the second magnetic film 12_C2In the vicinity
When the magnetization of the first magnetic film 11 is close to zero, the temperature during reproduction is
Degree T_PBIs the Curie temperature T of the second magnetic film 12_C2From nearby
By further increasing the magnetization of the first magnetic film 11, the transition metal
The externally applied magnetic field H_exWhen recording
In the opposite direction to that of domain B_MExpansion
Can be measured. (2-c) Curie temperature T of the second magnetic film 12_C2In the vicinity
When the magnetization of the first magnetic film 11 is dominated by the rare earth sublattice,
External bias magnetic field H at birth_exIs the same direction as that during recording
And the bubble domain B_MTo expand
Can be.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A substrate 1 is made of a light-transmissive glass plate or a resin plate such as an acrylic plate. Although not shown, track grooves for tracking servo are formed on one surface at a pitch of 1.6 .mu.m, for example. A dielectric film 2 made of, for example, an Si ₃ N ₄ film, first to third magnetic films 11 to 13, and a protective film 4 are further formed on the dielectric film 2 by, for example, continuous sputtering using a magnetron sputtering apparatus. Alternatively, it is continuously formed by vapor deposition or the like.

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 and a first magnetic film 1 made of a GdFeCo film on a glass substrate having a track groove with a track pitch of 1.6 μm.
1, a second magnetic film 12 made of a DyFeCo film,
a third magnetic film 13 made of a yFeCo film and Si ₃ N ₄
A protective film 4 composed of a film was 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.

[0023]

[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 in the first embodiment. In FIG. 4, the solid curve represents the numerical aperture of the objective lens. A. = 0.50, laser wavelength 7
Using an 80 nm pickup, the linear velocity is 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
Since the heating temperature did not reach the Curie temperature T _C2 of No. 2 and the recorded magnetic domain was considered to have not been 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 case where the reproducing power was 1.5 mW. Even when l = 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. Further, when a place reproduced with a reproduction power of 3.5 mW is reproduced again, C / C is not required at any of the reproduction power of 1.5 mW and 3.5 mW.
It was confirmed that N was reproduced.

When the power of the laser beam at the time of reproduction is constant in the first embodiment, the temperature profile is widened due to the 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.

[0027]

According to the present invention, as described above, the information is not simply read out by using the magneto-optical effect of the laser light in the magneto-optical recording medium, that is, the Kerr effect or the Faraday effect, but this laser light is used. Irradiation causes the temperature to rise at the same time, causing a change in the magnetization state,
Since the recorded information is read out, the reproduction signal level, and thus the S / N (C / N), is limited by the shape and size of the recording magnetic domain, the numerical aperture of the reading optical diameter, and the wavelength of the reading laser light. By giving a required change to the magnetization state of the recording magnetic domain without being directly restricted by the spot diameter of light, its signal level and S /
The N (C / N) can be improved, and the recording magnetic domains can be made finer, and the recording density can be increased.

According to the present invention, the magnetic film has a structure in which the first to third magnetic films 11 to 13 are laminated so that the three members can maintain the magnetically coupled state at normal temperature, that is, in the normal state. However, during heating during reproduction, the second magnetic film 12 becomes the first and third magnetic films 11
And 13 is expanded to obtain the effect of breaking the magnetic coupling between the first and second magnetic films 11 and 13, thereby improving the S / N (C / N) of the reproduction output. Although the recording state can be maintained with respect to the third magnetic film 13 though it is possible,
After the end of the reproduction, the recording state can be restored again, 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 a device of the present invention.

FIGS. 2A to 2D are diagrams showing the magnetization state of a magneto-optical recording medium for explaining the apparatus 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.

[Explanation of symbols]

1 {base, 11-13} first to third magnetic films, S}
‥ Magneto-optical recording media

Claims (1)

[Claims] 1. A pickup comprising at least a laser and an objective lens for focusing laser light on a magneto-optical recording medium, wherein the magneto-optical recording medium has at least a first magnetic film and a recording magnetic domain. A third magnetic film, and a second magnetic film disposed between the magnetic films, wherein the second magnetic film has a Curie temperature lower than that of the first magnetic film and the third magnetic film. A coercive force Hc ₁ of the first magnetic film is lower than the Curie temperature Tc ₂ of the second magnetic film.
, The coercive force Hc ₃ of the third magnetic film.
Is the Curie temperature Tc ₂ of the second magnetic film from the room temperature T _RT.
A magneto-optical recording medium having a size that can maintain a magnetized state in a range up to a higher reproduction temperature T _PB is used, and a mechanism for relatively moving the magneto-optical recording medium and the laser light; A configuration in which an external magnetic field in which the sum of the demagnetizing field and the external magnetic field is smaller than the coercive force Hc ₃ of the third magnetic film is applied to the magneto-optical recording medium at the irradiation position of the laser beam. A reproduction temperature T _PB higher than the Curie temperature of the second magnetic film and capable of maintaining the magnetization state of the third magnetic film.
Recording information is read out by detecting the Kerr rotation angle or the Faraday rotation angle by the magneto-optical interaction of the laser light to change the magnetic domain state of the first magnetic film. Media signal playback device.