JP2910082B2 - Magneto-optical recording / reproducing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magneto-optical recording / reproducing method for reading recorded information (magnetic domains) by magneto-optical interaction, that is, the Kerr effect.

[Summary of the Invention]

The present invention uses a magneto-optical recording medium in which a recording-holding magnetic layer and a reproducing magnetic layer that are magnetostatically coupled are stacked, and prior to the reproduction, the reproducing magnetic layer is magnetized in one direction with an external magnetic field and initialized. Thereafter, in a specific temperature rising region based on the temperature distribution in the reproducing light irradiation spot during reproduction, the recording magnetization information of the recording holding magnetic layer is transferred to the reproducing magnetic layer by a static magnetic field due to the recording magnetization of the recording holding magnetic layer. The magnetic information transferred onto the reproducing magnetic layer is read out by magneto-optical interaction. By doing so, ultra-high density recording, that is, linear density (recording on a recording track) is achieved. Density) along with improving the track width direction density and the S / N of reproduction.

[Conventional technology]

When an information bit, i.e., a magnetic domain is formed by local heating by laser light irradiation, and this is read out by magneto-optical interaction, that is, the Kerr effect, the recording density of the magneto-optical recording is increased by using the bit. In order to shorten the length, that is, to miniaturize the information magnetic domain, in this case, the laser wavelength and the numerical aperture of the lens at the time of reproduction are generally used to secure the S / N at the time of reproduction in a general magneto-optical recording and reproduction method. Is constrained by

In order to solve the problem of the recording density defined from the conditions at the time of reproduction, there is a signal reproduction method for a recording medium disclosed in Japanese Patent Application Laid-Open No. 1-143041. In this reproducing method, a magnetic domain on a magneto-optical recording medium is expanded by utilizing a temperature rise caused by irradiation of a laser beam during reproduction, thereby enabling reproduction of a signal having a higher density than the above-mentioned restriction of the recording density. It is.

Although such a reproducing method can improve the linear density, there is a problem in improving the track width direction, that is, the track density. In particular, if the information bit and the recording information magnetic domain interval, that is, the bit interval is longer than the optical cut period depending on the code data, crosstalk with the recording magnetic domain on another track adjacent to the track becomes a problem.

[Problems to be solved by the invention]

An object of the present invention is to solve the above-mentioned problem of crosstalk, to improve the linear density and the track width density, and to improve the S / N of reproduction.

[Means for solving the problem]

The present invention provides a magneto-optical recording medium (3) in which a reproducing magnetic layer (1) and a recording and holding magnetic layer (2) magnetostatically coupled thereto are laminated as shown in a schematic enlarged sectional view of FIG. Prepare The reproduction mode of the magneto-optical recording medium (3) is, for example, as shown in FIG. 2, as shown schematically in FIG. 2, as indicated by arrows in each of the magnetic layers (1) and (2). By applying the external magnetic field Hini, the magnetization state of the reproduction magnetic layer (1) is first magnetized in one direction as shown by a region I to initialize it, and heating information during reproduction, that is, reproduction light, for example, semiconductor laser light The recording magnetization information of the record holding magnetic layer (2) is transferred to the reproducing magnetic layer (1) by the magnetostatic magnetic field due to the recording magnetization as shown in a region II in a heating state by irradiation with L, as shown in a region II. The magnetic information transferred above is read out by the magneto-optical interaction, that is, the Kerr effect.

Here, the transfer of the recording magnetization on the record holding magnetic layer (2) to the reproducing magnetic layer (1) is relatively weak as shown in FIG. 2, that is, the transfer is such that transfer cannot be caused by itself. an auxiliary magnetic field H _R, the initialization external magnetic field Hini as given in the irradiation of reproducing light L in the opposite direction, the transfer to the recording holding magnetic layer (2) on the recording magnetization by reproducing magnetic layer (1) A magnetostatic magnetic field may be assisted to ensure that the transfer occurs.

[Action]

According to the present invention, upon reproduction, the reproduction magnetic layer (1)
Is initialized once to transfer the information magnetization recorded in the record holding magnetic layer (2) in the specific portion of the reading section irradiated with the reproduction light L and read out the same, thereby reproducing the reproduction light. The readout portion is specified by selecting the temperature distribution on the magnetic recording medium (3) and the magnetic properties and temperature properties of each of the recording holding magnetic layer (2) and the reproducing magnetic layer (1) of the magnetic recording medium (3). Since information can be read out by using the transferred magnetization only in the portion, a state in which no transfer magnetization occurs in the reproduction magnetic layer (1) can be formed in the adjacent track at this time. By performing the reproduction in such a state, crosstalk between tracks can be effectively avoided, and thereby, ultra-high-density recording and S / N can be improved.

〔Example〕

First, an example of the magneto-optical recording medium (3) used in the method of the present invention will be described with reference to FIG. In this example, a highly transparent substrate (4) having a high transmittance for light having a wavelength for performing magneto-optical recording and reproduction, for example, a semiconductor laser beam, such as a glass substrate, polycarbonate, or resin such as acrylic for a magneto-optical disk The read magnetic layer (1), that is, the first perpendicular magnetic film, and the read magnetic layer (1) are formed on the substrate via a dielectric layer (5) made of, for example, SiN and having a Kerr rotation enhancement effect or a function as a protective film. )
A recording / holding magnetic layer (2), that is, a second perpendicular magnetization film, formed through a nonmagnetic thin film (6) such as SiO ₂ so as to be magnetostatically coupled without being exchange-coupled with the recording medium; A protective layer (7) made of an ultraviolet-curable resin or the like is sequentially formed thereon.

Then, the migration course of the magneto-optical recording medium (3), as shown in FIG. 2, the magnetic field generating means for generating the respective opposite directions in the thickness direction of the external magnetic field Hini, and H _R medium (3) ( 11) and (12) are provided. Specifically, during the transition of the portion where reproduction of the magneto-optical recording medium (3) is to be performed toward the reproducing light irradiation section, the initialization external magnetic field Hini by the first magnetic field generating means (11) is applied to the medium (3). In one direction of the thickness direction,
Given over pointing to comprise eg both sides a track that the track wishing to make a play, then the second magnetic field generating means (12) by transferring auxiliary magnetic field H _R is made as provided in the opposite direction with reproducing light irradiation unit You. That is, when the magneto-optical recording medium (3) is a magneto-optical disk, as shown in the schematic diagram of FIG. 3, a reproduction laser beam is applied to a portion including a track to be reproduced in the rotation direction indicated by the arrow a. The first magnetic field generation means (1
1) is provided to provide a further initialization external magnetic field Hini, and a transfer assisting magnetic field H _R opposite to the magnetic field Hini from the second magnetic field generating means (12) is opposed to the irradiated portion of the reproduction light L. Is given.

For recording information on the magneto-optical recording medium (3), an ordinary method is applied. For example, a magnetization, that is, a magnetic domain is formed on the record holding magnetic layer (2) based on the recorded information by a usual method. That is, for example, a semiconductor laser beam is irradiated in accordance with recording information in a state where a required external bias magnetic field is applied, thereby locally causing magnetization reversal, and performing the recording, or performing the magnetic field modulation recording method.

In the reproduction, first, the first magnetic field generating means (11) is made to pass through the readout portion so that its magnetization direction is aligned in one direction in the thickness direction, for example, in the upward direction indicated by the region I in FIG. Perform the conversion.

In this case, when the coercive force of the reproducing magnetic layer (1) is H _C1 and the coercive force of the recording and holding magnetic layer (2) is H _C2 , H _C1 <Hini <H _C2 ‥‥‥ (1) at room temperature. when the temperature of the magnetic recording medium (3) rises is, and by irradiation of reproducing light L is, at the predetermined temperature _{T th, H R + H S2} + H d1 = H C1 ‥‥‥ (2) the temperature T is, in T> T _th, when H _S2 is in the same direction as H _R, when the _{H R + H S2 + H d1} > H C1 ‥‥ (3a) _{opposite, H R + H d1 <H} C1 + H S2 ‥‥‥ (3b) Set so that Here, H _S2 is the reproducing magnetic layer (1)
Is a stray magnetic field based on magnetization from the recording and holding magnetic layer (2), that is, a static magnetic field applied to the reproducing magnetic layer (1), and H _d1 is a demagnetizing field of the reproducing magnetic layer (1).

FIG. 4 shows the manner of magnetization of the adjacent _first , _second and _third tracks t ₁ , t ₂ and t ₃ of such a magnetic recording medium (3). Circle indicated by reference numeral b represents the portion irradiated with reproducing light L, now looking at the case of reproducing with respect to the center of the track t _2, the magnetic recording medium (3) is an arrow in the Figure 4 In a state where the magnetic recording medium (3) shifts in the direction indicated by a, that is, from left to right in the figure, first, the first magnetic field generating means (11) applies the magnetic field Hini to satisfy the condition of the above equation (1). Based on this, the magnetization of the reproducing magnetic layer (1) is initialized as shown by a region I in FIG. And
Thereafter, the light enters the irradiation part b of the reproduction light L. At this time, the local temperature of the magnetic recording medium (3) rises due to the irradiation of the reproducing light L, for example, the semiconductor laser light. When the temperature rises to T _th or more, the temperature increases depending on the recording magnetization direction of the recording holding magnetic layer (2). by (3a) formula or (3b) equation, that is, in the recording magnetization magnetization state of the second external magnetic field H _R in the same direction of the recording holding magnetic layer (2), wherein (3a)
Second recording holding magnetic layer also by equation (2) when the recording magnetization orientation is H _R and the direction opposite to the manner in the region II and the region III shown in Figure 2, respectively, by the relationship of the (3b) Formula In the reproducing magnetic layer (1), the magnetization of the record holding magnetic layer (2) is transferred. That is, as shown by diagonal lines in FIG. 4, a transfer magnetic domain d in which the information magnetization of the record holding magnetic layer (2) is transferred to a predetermined portion offset behind the reproduction light L on the magnetic recording medium (3). Occurs.

The information is read out by detecting the magneto-optical interaction in the reproducing magnetic layer (1), that is, the Kerr rotation angle of the irradiated light L, and reading out the information.

In this case, FIG. 5 shows a temperature distribution diagram of the medium by the laser beam irradiation. Fifth horizontal axis figure shows taking the position x of this than the track width direction as the origin the center of the reproducing track t ₂ of interest, the boundary position between adjacent tracks for example t ₁ or t ₃ of the track t ₂ by setting so that the temperature T _th of the foregoing is available at the center side of the track t ₁ from the position shown the temperature T _S at the boundary position X _S when the X _S, FIG. 4 inside than the position X _S A transfer magnetic domain d, which is schematically shown by hatching, occurs.

In the above-mentioned magnetic recording medium (3), the reproduction is performed such that only the information transferred to the reproduction magnetic layer (1), that is, the magnetic domain, is read. In the reproduction, the recording holding magnetic layer (2) is used. The reproducing magnetic layer (1) is selected to have a large absorption of the reproducing light L and a film thickness of a certain degree or more so as not to reproduce the signal in the above. For example, when an amorphous rare earth-transition metal magnetic film is used as the reproducing magnetic layer (1), when a semiconductor laser having a wavelength of 780 nm is used as reproducing light, its thickness is selected to be 300 mm or more.

On the other hand, the record holding the magnetic layer (2), wherein (3a) and Formula (3b) it is intended that is desired H _S2 is larger in terms of satisfying the equation, in practice the H _S2 i.e. the hold magnetic layer Since the magnitude of the stray magnetic field from (2) is restricted, the coercive force H _C1 of the reproducing magnetic layer (1) is preferably small to satisfy the expression (3b). Further, in order to improve the reproduction S / N, the reproduction magnetic layer (1) is preferably made of a material having a high Curie point and a large Kerr rotation angle.
Therefore, the Curie point T _C1 of the reproducing magnetic layer (1) is 250
℃, coercive force H _C1 is 500 (Oe) or less, for example GdFeCo
It is desirable to be constituted by. However, in practice, when the coercive force H _C1 with respect to the temperature T is flat in this kind of magnetic material, for example, as shown in FIG. 7, it is difficult to control the above-mentioned predetermined temperature T _th . Therefore, it is desirable to use a material having a relatively large H _C1 near room temperature and a sharp decrease in H _C1 near T _th. However, since it is practically difficult to select such a material, this reproducing magnetic layer (1 )
For example, as shown in FIG. 6, the temperature characteristic of the coercive force is represented by T _{th as} shown by a broken line (61).
A first reproducing magnetic layer having a Curie point in the vicinity and having a relatively large coercive force at room temperature; and a second reproducing characteristic indicated by a broken line (62) having a large Kerr rotation angle but a flat characteristic as in, for example, GdFeCo. These layers are laminated so as to be exchange-coupled with each other, and their overall characteristics show a high coercive force at room temperature and a low coercive force near T _th as shown by the solid curve (63) in FIG. A reproduction magnetic layer (1) having characteristics can be constituted. In this case, a second reproducing magnetic layer having a large Kerr rotation angle is arranged on the substrate (4) side in FIG.

Further, the coercive force H _{C2 of} the recording holding magnetic layer (2) is large so that its magnetization does not change at room temperature due to the first external magnetic field Hini, and deformation does not occur near T _{th of the} reproducing temperature. It can be formed of a material having a relatively high Curie point, for example, a TbFeCo magnetic thin film magnetic layer having a Curie point of 200 ° C. or higher. In this case, since it is desired that H _S2 is as large as possible at the time of reproduction, it is desirable that the FeCo-dominant, that is, the transition metal sublattice magnetization-dominant film configuration be formed at room temperature.

〔The invention's effect〕

According to the above-described method of the present invention, the recording, that is, the magnetization according to the information is performed in the recording holding magnetic layer (2), and the reading is performed by the Kerr effect in the reproducing magnetic layer (1). In the reproduction, the reproduction magnetic layer (1) is initialized by the initialization magnetic field Hini, and limited only in that state, that is, in a portion where the temperature has been increased by a predetermined amount by the irradiation of the reproduction light in a state of being magnetized in one direction. The information is generated by transferring the magnetization based on the magnetization of the record holding magnetic layer (2), and reading is performed by this. Therefore, not only the longitudinal direction of the track, that is, the linear density is improved, but also the track width direction is improved. In addition, it is possible to effectively avoid the occurrence of crosstalk due to information between adjacent tracks, and to improve the recording density and S / N. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged cross-sectional view of an example of a magneto-optical recording medium for carrying out the method of the present invention, FIG. 2 is a schematic diagram for explaining a reproducing mode thereof, and FIG. 3 is an explanatory diagram of a magneto-optical recording / reproducing method. , Fourth
The figure shows the appearance of the transfer magnetization during the reproduction,
FIG. 5 is a temperature distribution diagram of the medium by laser light irradiation, FIG. 6 is a temperature characteristic diagram of the coercive force of the reproducing magnetic layer, and FIG. 7 is a temperature characteristic diagram of the coercive force of the comparative example. (1) is a reproducing magnetic layer, (2) is a recording holding magnetic layer, (3)
The magneto-optical recording medium, (6) a non-magnetic thin film (11) is the initial magnetization external magnetic field generating means Hini, (12) the magnetic field generating means of the transfer auxiliary magnetic field H _R.

Claims (1)

(57) [Claims] A magneto-optical recording medium in which a reproducing magnetic layer and a recording holding layer, which are magnetostatically coupled to each other, is stacked and magnetized in one direction prior to reproduction to initialize the reproducing magnetic layer. Sometimes, by irradiating the reproducing magnetic layer with a laser beam, the temperature of the reproducing layer is raised, and a signal recorded in the recording holding layer is partially irradiated in the reproducing spot according to the temperature distribution of the reproducing layer due to the temperature rise. A magneto-optical recording / reproducing method characterized in that reading is performed by magneto-optical interaction while transferring data only in a magnetic disk.