JP3428573B2 - Signal reproducing device for magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] The present invention relates to a magneto-optical interaction.
Therefore, magneto-optical recording for reading information bits (magnetic domains)
The present invention relates to a medium signal reproducing apparatus. [0002] 2. Description of the Related Art Local heating by laser light irradiation
An information bit or bubble domain is formed, which is
Field by read magneto-optical recording / reproducing method by interaction
In order to increase the recording density of the magneto-optical recording,
To reduce the information domain, that is, to reduce the information domain
However, in this case, in a general magneto-optical recording / reproducing method,
In order to secure the S / N at the time of reproduction, the laser at the time of reproduction
It is restricted by the wavelength, the numerical aperture of the lens, and the like. An example
For example, at present, information bits (magnetic domains) of 0.2 μm are
It is impossible to read with a laser beam with a pot diameter of 1μm
It is. [0003] SUMMARY OF THE INVENTION The present invention provides
Solves the problem of the recording density constraint defined by the conditions at birth
In the case where the recording information bits are miniaturized,
Also has a sufficient reproduction output, and therefore has an S / N (C / N)
Aim up. [0004] According to the present invention, there are provided a
At least a laser and laser light are applied to a magneto-optical recording medium.
Pickup with objective lens for focusing
And the magneto-optical recording medium and the laser light
And a mechanism for moving it.
At least a first magnetic film and a third magnetic film for holding a recording magnetic domain.
Film and a second magnetic film disposed between the magnetic films.
Wherein the second magnetic film comprises a first magnetic film and a third magnetic film.
A first magnetic film comprising a magnetic film having a lower Curie temperature
Coercive force Hc₁Is the Curie temperature Tc of the second magnetic film_Twoof
Small enough in the vicinity, the coercive force Hc of the third magnetic film_ThreeIs room temperature
T_RTFrom the Curie temperature Tc of the second magnetic film_TwoHigher re
Raw temperature T_PBLarge enough to hold the magnetized state up to
The selected magneto-optical recording medium is used. And
At the position of the laser beam irradiation part of the magneto-optical recording medium,
Higher than the Curie temperature of the second magnetic film and the third magnetic film
Reproduction temperature T that can maintain the magnetization state of the film_PBTo give
The magnetic coupling between the first and third magnetic films is cut further, and
The magnetic domain of the recording information of the first magnetic film is expanded,
Interaction of Laser Light in Magnified Information Domain
To detect car rotation angle or Faraday rotation angle
Thus, the recorded information is read out. As described above, in the device of the present invention,
Read information by changing the magnetic domain state of the signal reproducing magnetic film
Is not restricted by the optical system.
The S / N can be increased. [0006] DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described. this
In the case, for example, as shown in FIG.
Also as a light-transmitting protective film or interference film depending on
Is formed on the dielectric film 2, and a room temperature T is formed on the dielectric film 2.
_RTMagnetically coupled with each other mainly contributes to signal reproduction
First magnetic film 11 and second magnetic film 12 serving as an intermediate film
And each of the third magnetic films 13 mainly contributing to record retention.
A stacked structure of a perpendicular magnetization film is formed, and first, second and third
The Curie temperature of each of the magnetic films 11, 12 and 13 is set to T
_C1, T_C2And T_C3And T_C2> T_RTAnd T
_C2<T_C1, T_C3And the coercive force H of the first magnetic film 11_C1
Is the Curie temperature T of the second magnetic film 12_C2Small enough near
And the coercive force H of the third magnetic film 13_C3Is room temperature T_RTFrom the second
Curie temperature T of the magnetic film 12_C2Higher required temperature T
_PBMagneto-optics larger than required magnetic field in the temperature range up to
The recording medium S is used. [0007] The reproducing apparatus according to the present invention provides
Is the Curie temperature T of the second magnetic film 12_C2Above
Required temperature T_PBAnd the recording magnetic domain of the first magnetic film 11,
Report bit and the demagnetizing field added to it, and if necessary
Magnify by external applied magnetic field and read in this state
You. The surface is protected on the third magnetic film 13 if necessary.
A film 4 is deposited. [0010] Recording on the above-mentioned magneto-optical recording medium S is not performed.
That is, the formation of the information magnetic domain is performed in the usual manner, for example, in the initial state.
The magnetization direction of the third magnetic film 13 near the recording temperature at
Laser light is applied while a reverse bias magnetic field is applied.
Focusing and irradiating, thereby forming a third magnetic film
13 is heated above its Curie temperature and laser
External magnetic field and stray magnetic field during cooling after optical scanning
By the formation of bubble domains reversed in the direction
The information of "1" is recorded. In other words, this information bubble magnet
Recording of binary information of "1" and "0" depending on the presence or absence of a ward
Do. [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
That is, 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,
Magnetic film with large Kerr rotation angle or Faraday rotation angle
If it is used, recording on the first magnetic film 11 is mainly performed.
With information, the substantial increase in the area of this information domain
Thus, a large reproduction output can be obtained, and the S / N (C
/ N) can be improved. Then, a state where the information magnetic domain is expanded,
In other words, with the read magnetic domain area substantially increased
Since the reproduction is performed, the reproduction output increases, and as a result, S
/ N can be improved. After the reproduction, that is, of the laser beam
The reading unit cools after the irradiation unit moves by scanning
If so, the first to third magnetic films 11 to 13 are kept at, for example, room temperature.
T_RTIn the process of cooling down, the third magnetic film 1 having a high coercive force
3 acts as a magnetic recording holding film, and the second magnetic film 12
Magnetized by its magnetic coupling,
The first magnetic film 11 magnetically coupled to the film 12 is magnetized.
The information bit domain in the initial recording state is formed again and recorded.
Restored to state. According to the above configuration, the magneto-optical recording medium is
The second magnetic film 12 as an intermediate layer of the body S
Magnetic coupling state between third magnetic films 11 and 13;
By taking both aspects of the disconnected state,
Is that the second magnetic film 12 of the intermediate layer is composed of the first and third magnetic films.
The magnetic coupling between the magnetic films 11 and 13 of FIG.
To expand the recorded information magnetic domain of the magnetic film 11 of FIG.
The third magnetic film 13 has a magnetic property for maintaining its magnetization state.
The first magnetic film 11 retains the function as a recording holding layer,
A read layer that expands the magnetic domain during read to improve read output
To improve recording density
Even if the magnetic domain as bit information is made finer,
Raw output can be obtained to achieve higher recording density.
Can be. Further referring to FIG. 2, first to third magnetic films 1
Magnetization state when each of 1 to 13 is a ferromagnetic film
Will be described. Now, as shown in FIG.
No. 3 in the unrecorded state, the direction of magnetization is perpendicular to one direction
Assuming that it is in the magnetized state,
By recording "1", as shown in FIG.
Information bits due to magnetization in the direction opposite to the initial state
Information Domain B_MIs formed. This information domain B_MAbout reading for
In this case, as shown in FIG. 2C,
So that information domain B_MLaser light L_BIrradiate
In a state where
Required temperature T_PBIs obtained. At this time, the second
Magnetic film 12 has its Curie temperature T_C2That is more than
As a result, the magnetism is lost and the first and third magnetic films 1
The magnetic coupling between 1 and 13 is interrupted.
In this state, the direction of the external bias magnetic field during recording,
Magnetic domain B_MDirection of the original magnetization, that is, the direction of magnetization during recording
Externally applied magnetic field H in the same direction as_exBy giving this
By the sum of the magnetic field and the demagnetizing field, the temperature T_PBWith coercive force
H_C1Domain B of the first magnetic film 11 in which_MIs
It is enlarged. As shown in FIG. 2D, the laser light L
_BIrradiation of information domain B_MWhen illuminated outside, the information
Since the temperature rise in the magnetic domain is relatively small,
Information bits, ie domain B_MIs hardly expanded. One
In the center of laser light scanning in the
Magnetic domain L_BRecording magnetic domain B existing at the center of_MAt
Only domain expansion can occur. Accordingly, in this case, for example, as shown in FIG.
Thus, the information recording magnetic domain B_MAre arranged at equal pitch
When laser beam scanning is performed on the recording medium, the output
Represents the magnetic domain B as shown in FIG. 3B._MIdeal disappearance disappeared
When the magnetic level is set to 0 level, the information magnetic domain B_MRead
Shows large level upwards in one-way view
It can be extracted as a waveform output. Incidentally, in practice, the first to third magnetic films 11 to 11
13 is a rare earth-transition metal magnetic film,
The sub-lattice magnetization and the sub-lattice magnetization of the rare earth metal are opposite to each other.
When the magnetic film has a ferrite magnetism, each magnetic film has a transition metal sublattice magnetization.
Dominant film or rare-earth sublattice magnetization dominant film
The externally applied magnetic field H given at the time of reproduction_exChoose the orientation of
There is a need. 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 of 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, for example.
Is made of, for example, a resin plate such as an acrylic plate, and is not shown.
Has a track groove for tracking servo on one side
For example, it is formed with a 1.6 μm pitch.
Ba Si_ThreeN_FourA dielectric film 2 composed of a film,
3 magnetic films 11 to 13 and a protective film 4 thereon.
Is continuous sputtering using a magnetron sputtering device, for example.
Continuously formed by ring or vapor deposition
You. As the first magnetic film 11, for example, GdC
o, GdFeCo, GdFe, and the second
The 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 by TbFeCo, DyFeCo, etc.
According to the third magnetic film 13, a magnetic film having a diameter of 0.1 μm or less is used.
District B_MCan be formed. Embodiment 1 A track pitch of 1.6 μm was used.
Si on a glass substrate with track grooves_ThreeN_FourConsist of
Dielectric film 2 and first magnetic film 1 made of GdFeCo film
1, a second magnetic film 12 made of a DyFeCo film,
a third magnetic film 13 made of a yFeCo film;_ThreeN_Four
Magnetron sputtering apparatus
Formed by continuous sputtering with light
A magnetic recording medium, that is, an optical disk S was manufactured. This place
Thickness of each magnetic film 11 to 13 as a single-layer film and
Table 1 shows the magnetic properties. [0023] [Table 1] In Table 1, FeCo-rich means room temperature
Indicates a FeCo sublattice magnetization dominant film,
The term “switch” indicates a Dy sublattice magnetization dominant film at room temperature. The magneto-optical recording medium S according to the first embodiment
Recording frequency of carrier level versus noise level (C / N)
FIG. 4 shows the measurement results of the dependence. The solid curve in FIG.
Numerical aperture N. 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), zero externally applied magnetic field during reproduction, reproduction power
3.5 mW, and the dotted line in FIG.
This is a case where the reproducing power is set to 1.5 mW. in this way
When the reproducing power is 1.5 mW, the entire magnetic film
When an optical disk is composed of a single-layer film of TbFeCo.
Shows the same result as the frequency dependence of C / N
Was. This is because at such a reproducing power, the second magnetic film 1
Curie temperature T of 2_C2The heating temperature has not reached until the record
Domain considered not deformed during regeneration
Can be In contrast, when the reproducing power is 3.5 mW,
The magnetic domain length, that is,
C / N increased remarkably when the cut length 1 <0.7 μm. Also
Even if l = 0.3 μm, C / N is low but no signal component is obtained.
Was. On the other hand, when l> 0.7 μm, the C / N decreases conversely.
However, this is due to an increase in noise N. Again
A place where the place where the raw power was reproduced with 3.5 mW is reproduced again
In both cases, the reproduction power is 1.5 CW / 3.5 mW and the C / C
It was confirmed that N was reproduced. Further, in the first embodiment described above, the reproduction
When the power of the laser light is constant, the thermal diffusion in the medium S
The temperature profile is widened and the small information bits
(Magnetic domain) reproduction resolution is reduced.
For example, corresponding to the minimum bit length to make the file steeper
Can be reproduced with pulse laser light with narrow width at frequency intervals
It will be good. Furthermore, thermal energy absorbed by the magnetic film
Good thermal conductivity so that heat is quickly dissipated
The Al heat dissipation film is formed on the third magnetic film 13 (with the second magnetic film 12).
On the side opposite to the contacting side). [0027] As described above, according to the present invention, only light
The magneto-optical effect of laser light on magnetic recording media,
Read information using the Kerr effect or Faraday effect
It does not do this,
Causes the temperature to rise, causing a change in the magnetization state,
Since the recorded information is read, the playback signal level
Therefore, S / N (C / N) is the shape and size of the recording magnetic domain.
Furthermore, the numerical aperture of the readout optical diameter, readout laser light
Laser beam spot diameter limited by the
Is not directly limited by the
By giving necessary changes, the signal level and S /
N (C / N) can be improved, and
Reducing the size of the recording magnetic domain and therefore increasing the recording density
be able to. According to the present invention, the magnetic film has first to
At room temperature as a structure in which three magnetic films 11 to 13 are laminated.
In other words, in the normal state, the three are magnetically coupled
To maintain the state, but also to heating during regeneration
In this case, the second magnetic film 12 is replaced with the first and third magnetic films 11.
To obtain the effect of breaking the magnetic coupling between
To expand the information magnetic domain of the first magnetic film 11
To improve the S / N (C / N) of the playback output.
Despite being measurable, its third magnetic film
Since the recording state of 13 can be maintained,
After the end of playback, it can be restored to the recorded state again.
Good reproduction characteristics can be obtained without impairing the reproduction
Wear. According to the present invention, as described above,
Since sufficient reproduction output can be obtained, the recorded information
Information domain B_MCan be reduced sufficiently, which in itself
The recording density can be improved, and
Track grooves are formed on the substrate for magneto-optical recording media
The information domain B_MShrink
As a result, the land can be used as usual.
Is limited to forming the recording domain only in the
No recorded magnetic domains both in the land and in the track groove
The ability to perform
The degree can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a magneto-optical recording medium used in the apparatus 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. [Description of Signs] 1 {Base, 11-13} First to Third Magnetic Films, S}
‥ Magneto-optical recording media

Claims (1)

(57) [Claims] A pickup comprising at least a laser and an objective lens for focusing the laser light on the magneto-optical recording medium, and a mechanism for relatively moving the magneto-optical recording medium and the laser light, A magnetic film having at least a first magnetic film, a third magnetic film in which a recording magnetic domain is held, and a second magnetic film disposed between the magnetic films. The first magnetic film has a lower Curie temperature than the third magnetic film, and the coercive force Hc ₁ of the first magnetic film is equal to 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 the laser is provided at the irradiation position of the laser beam on the magneto-optical recording medium. By providing a reproduction temperature _TPB higher than the Curie temperature of the second magnetic film and capable of maintaining the magnetization state of the third magnetic film,
The magnetic coupling between the magnetic films is cut to enlarge the recording information magnetic domain of the first magnetic film, and the Kerr rotation angle due to the magneto-optical interaction of the laser light in the enlarged recording information magnetic domain of the first magnetic film. Alternatively, a signal reproducing apparatus for a magneto-optical recording medium, which reads recorded information by detecting a Faraday rotation angle.