JPH06139644A - Magneto-optical recording method - Google Patents

Abstract

PURPOSE:To surely eliminate an existing domain and to improve reliability in overwrite by converging a light beam so that the irradiation intensity of the beam in the radial direction of a disk changes gradually and heating an exchange coupling magnetic layer. CONSTITUTION:When the exchange coupling magnetic layer 12 is heated by the high power light beam converged so that the irradiation intensity in the radial direction of the disk displaces gradually, the circumference of the domain is initialized covering a wide range simultaneously the domain is formed separately from initialization by the beam with low power. Then, the occurrence of an erasure omission area is prevented at the time of the overwrite replacing a minimum domain Dmin with a maximum domain Dmax and forming by converging the beam so that the range Wi becomes larger than the width WDmax of the maximum domain always.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulation type magneto-optical recording method for overwriting by an exchange coupling magnetic layer.

The magneto-optical disk device has a larger storage capacity per magneto-optical disk as a recording medium than the magnetic disk device, and moreover, the medium can be freely exchanged like the flexible disk. It is rapidly becoming popular as a storage device. Along with this, it is desired to improve the reliability of overwrite that enables high-speed data transfer.

[0003]

2. Description of the Related Art A magneto-optical disk device is a random access memory device capable of recording and reproducing. In recording in which a domain (also referred to as a mark) that is a magnetic domain region corresponding to recorded information is formed, the magnetic layer in the recording track is locally heated by light irradiation to weaken its coercive force, and in parallel with this, This is done by applying a magnetic field and specifying the direction of magnetization. The reading (reproduction) of the domain is performed by irradiating a light beam having a lower power than that at the time of recording and detecting the state of rotation of the polarization plane due to the magnetic Kerr effect.

Generally, one optical head is commonly used for such recording and reproduction. At the time of recording and reproducing, focusing is performed to position the objective lens of the optical head in the disc rotation axis direction in order to make the light irradiation range constant.

In the magneto-optical disk device, as shown in FIG. 6, so-called pit edge recording is performed in which the edge portion of the domain (that is, the magnetization reversal portion in the recording track direction) is associated with the recording information. According to the pit edge recording, in principle, the linear recording density can be doubled as compared with the case of performing the pit position recording in which the central portion of the domain is associated with the recording information.

In FIG. 6, the record information is an original bit string input from a computer or the like, between 1 and 2
It is converted into a bit string suitable for magnetic recording by a 2-7 modulation method in which seven 0s are arranged. The domain is formed so that its edge is associated with 1 in the bit string. In FIG. 6, the shortest domain Dmi, which is the domain having the shortest dimension (length) in the recording track direction, is indicated.
n and the longest domain, the longest domain Dmax, are shown.

On the other hand, there is known a magneto-optical disk device which realizes an overwrite for rewriting recorded information with one access to a recording track by utilizing the temperature characteristic of an exchange coupling magnetic layer.

The principle of overwriting of this type of magneto-optical disk device will be briefly described below with reference to FIG. Memory layer 12A and auxiliary layer 1 forming the exchange coupling magnetic layer 12
The coercive force of 2B changes according to the temperature as shown in FIG. The memory layer 12A is made of TbFe or the like, and the auxiliary layer 12B is made of TbFeCo or the like.

At room temperature Ts, the coercive force of the auxiliary layer 12B is smaller than that of the memory layer 12A. Therefore, the magnetization direction of the auxiliary layer 12B is initialized by applying the initialization magnetic field Hini prior to the heating by the light irradiation.

At the light irradiation position, a magnetic field Hb weaker than the initialization magnetic field Hini and in the opposite direction is always applied.
If the light irradiation has high power, the memory layer 13 and the auxiliary layer 1
2 of 4 is the domain formation temperature (high temperature process start temperature) Th
The temperature rises to a temperature in excess of that of the magnetic field Hb
Aligned by At this time, the region where the directions of magnetization are aligned becomes a domain. On the other hand, when the light irradiation has low power, the temperatures of the memory layer 13 and the auxiliary layer 14 exceed the magnetic initialization temperature (low temperature process start temperature) Ti but do not reach the domain formation temperature Th. In this case, the magnetization reversal of the auxiliary layer 12B does not occur, and the magnetization direction of the memory layer 12A becomes the same as the magnetization direction of the auxiliary layer 12B due to magnetic exchange coupling. That is, the magnetization direction of the memory layer 13 is also initialized, and the existing domain formed during the previous recording is erased.

[0011]

When a domain is formed by light modulation as described above, the planar shape of the domain is a tear with the rear end side spreading in the disk radial direction due to thermal diffusion in the traveling direction of the light spot. It becomes a drop shape. The extent of expansion in the disk radial direction increases as the domain lengthens. That is, the long domain has a larger dimension (width) in the disk radial direction than the short domain.

However, conventionally, during recording, focusing is performed in the same manner as during reproduction, and a light beam focused so as to form the same minimum light spot as during reproduction, that is, from the center to the end of the light spot. The exchange-coupling magnetic layer 12 was heated by irradiating a light beam having a steep intensity distribution in which the irradiation intensity rapidly changes.

Therefore, as shown in FIG. 8, particularly, the longest domain Dmax (shown by a broken line) is set to the shortest domain Dmin.
When overwrite is performed by replacing with, the part of the longest domain Dmax remains on the both sides of the shortest domain Dmin as the erasure leakage area Derror, which causes a problem in reproduction.

It is an object of the present invention to surely erase an existing domain and improve the reliability of overwriting regardless of the size relationship between the existing domain and a newly formed domain.

[0015]

In order to solve the above-mentioned problems, the method according to the invention of claim 1 has a magneto-optical disk 1 having an exchange coupling magnetic layer 12 as shown in FIGS. 1 and 2.
0 is used as an overwrite recording medium, and is a magneto-optical recording method in which a domain having a length corresponding to recording information is replaced with an existing domain by power modulation of a light beam irradiated as a heat source. By heating the exchange-coupling magnetic layer 12 by condensing it so that the irradiation intensity in the radial direction of the disk gradually changes, the width Wi of the region heated to the magnetic initialization temperature Ti is set to be smaller than the width WDmax of the longest domain. Enlarge.

According to a second aspect of the present invention, the irradiation spot shape of the light beam is an ellipse elongated in the disk radial direction.

[0017]

When the exchange-coupling magnetic layer 12 is irradiated with a condensed light beam, the irradiation intensity distribution in the irradiation spot and the temperature distribution of the exchange-coupling magnetic layer 12 depending on the irradiation intensity distribution are normal distributions having a peak in the central portion. Is almost equal to. The change in irradiation intensity and temperature becomes gentler as the irradiation spot diameter increases.

Referring to FIG. 2, when the exchange coupling magnetic layer 12 is heated by a high-power light beam focused so that the irradiation intensity in the disc radial direction changes gradually, the irradiation intensity changes rapidly. Compared with the case of heating with a condensed light beam, the difference between the range Wi that rises to the magnetic initialization temperature Ti and the range WDmin that rises to the domain formation temperature Th at the center thereof becomes larger. That is, apart from the initialization by the low power light beam, the domain periphery is initialized over a wide area simultaneously with the formation of the domain.

Therefore, the shortest domain Dmin is set to the longest domain D by focusing the light beam so that the range Wi is always larger than the width WDmax of the longest domain.
It is possible to prevent the occurrence of an erase-miss region when overwriting by replacing max.

[0020]

FIG. 1 is a schematic diagram showing the construction of the main part of a magneto-optical disk device 1 according to the present invention, and FIG. 2 is a relationship between irradiation spots corresponding to FIG. 1 and temperature distribution in the disk radial direction and domains. FIG.

In FIG. 1, the magneto-optical disk device 1 is
It has a magneto-optical disk 10 which is an overwrite recording medium, and an optical head 20 for performing pit edge recording and reproduction of bit information using a laser beam.

The magneto-optical disk 10 is composed of a substrate 11 made of, for example, polycarbonate, an exchange coupling magnetic layer 12 having a multi-layer structure, a protective layer 13 and the like, and has a pre-groove 15 for tracking on the inner surface side of the substrate 11. is doing. The pre-grooves 15 are provided in a spiral shape in plan view at a pitch of 1.6 μm. The magneto-optical disk 10
Then, the portion between the pre-grooves 15 becomes the recording track 16.

On the other hand, the optical head 20 comprises the semiconductor laser 2
1, collimator lens 22, beam shaping lens 23, beam splitter 25, objective lens 26, half-wave plate 2
7, a condensing lens 28, a polarization beam splitter 29, a cylindrical lens 30, photodetectors 40 and 41, and an actuator 50 for finely moving the objective lens 26 in two directions to perform tracking and focusing. There is.

At the time of reproduction, the rotation amount of the polarization plane of the detection light is determined by separating the detection light by using the ½ wavelength plate 27 and the polarization beam splitter 29, and detecting the difference between the respective light amounts, that is, S / N. It is converted into the data signal RF by a so-called differential detection method which is advantageous in terms of ratio. for that reason,
The photoelectric conversion signals of the photodetectors 40 and 41 are applied to the differential amplifier 45 as its differential input.

The photodetector 40 is a two-divided photodetector having two light receiving surfaces, and the photoelectric conversion signal corresponding to each light receiving surface is also used to generate a track error signal by the push-pull method. The photodetector 41 is a four-division photodetector having four light receiving surfaces, and the photoelectric conversion signal corresponding to each light receiving surface is also used to generate a focus error signal by the astigmatism method.

The drive current of the semiconductor laser 21 is increased / decreased by a control circuit (not shown) and emits a laser beam having a power suitable for each of recording and reproduction. The power of the laser beam is constant at the time of reproduction, but at the time of recording, it is binary-modulated according to the recorded information by the 2-7 modulation method, for example.

The laser beam emitted from the semiconductor laser 21 passes through the collimator lens 22 and the beam shaping lens 23 to become a parallel and circular beam, and irradiates the exchange coupling magnetic layer 12 through the beam splitter 25 and the objective lens 26.

At the time of reproduction, the laser beam is an irradiation spot SP having a diameter of, for example, about 1 μm, which is shown by a broken line in FIG.
It is focused by the objective lens 26 so as to form r. On the other hand, during recording, the laser beam
It is condensed by the objective lens 26 arranged at a position slightly different from that at the time of reproduction so as to form an irradiation spot SPw having a diameter larger than that of the irradiation spot SPr.

As the irradiation spot diameter increases, the irradiation intensity distribution becomes a mountain-shaped distribution with a gentle gradient, and the temperature distribution of the exchange coupling magnetic layer 12 (shown by the solid line in FIG. 2) is also the same. Distribution. Therefore, as is clear from comparison with the temperature distribution shown by the one-dot chain line in FIG. 2 (distribution when a high-power laser beam is focused in the same way as during reproduction), the magnetic initialization temperature Ti (see FIG. 7) Range Wi for increasing temperature and range WDmin for increasing temperature to domain forming temperature Th
The difference between and becomes relatively large, and the periphery of the domain is initialized over a wide area.

In the present embodiment, the range Wi when forming the shortest domain Dmin is the width WD of the longest domain.
The diameter of the irradiation spot SPw (that is, the degree of focusing) is selected so as to be larger than max.

As a result, when overwriting is performed by replacing the shortest domain Dmin with the longest domain Dmax that is wide by the difference w in thermal diffusion distance, the existing longest domain Dmax can be completely erased.

FIG. 3 is a block diagram showing an example of the structure of the focus control unit 60 for switching the light collecting state.
The focus control unit 60 has a differential amplifier 61 and a phase compensation filter 62, and is configured to drive the actuator 50 according to the focus error signal Sf and maintain the just focus state as a basic operation.

However, at the time of recording, the write gate signal S
The input of the selector 63 is switched in response to w, and a constant amount of offset current is applied to the actuator 50.
Thereby, the irradiation spots SPr, S having different diameters from each other
Pw can be obtained.

FIG. 4 is a schematic diagram showing the structure of the main part of a magneto-optical disk device 1b according to another embodiment, and FIG. 5 shows the relationship between the irradiation spot, the temperature distribution in the disk radial direction, and the domain corresponding to FIG. FIG. In these figures, the constituent elements corresponding to those in FIGS. 1 and 2 are designated by the same reference numerals, and the description thereof will be omitted.

The difference between the magneto-optical disk device 1b and the above-mentioned magneto-optical disk device 1 is that the beam shaping lens 2 is used.
This is a point that recording / reproducing is performed by the optical head 20b in which the number 3 is omitted.

The laser beam radially emitted from the semiconductor laser 21 is converted into a parallel beam by the collimator lens 22, and then the objective lens 2 remains as an elliptical laser beam.
It is incident on 6 and is condensed. However, since the semiconductor laser 21 has an astigmatic difference, and therefore the laser beam after focusing also has astigmatism, if the position of the objective lens 26 is appropriately set, a substantially circular irradiation spot is formed. can do.

Therefore, during reproduction, focusing is performed to keep the irradiation spot SPrb having a substantially circular shape as shown in FIG. On the other hand, at the time of recording, by applying an offset current to the actuator 50 as described above,
By arranging the objective lens 26 intentionally at the non-focus position, the irradiation spot SP that is long in the disk radial direction
form wb.

Also in this case, in the radial direction of the disk, the temperature distribution of the exchange-coupling magnetic layer 12 has a gentle distribution, so that upon overwriting, regardless of the size relationship between the existing domain and the new domain, the existing domain can be used. The domain of can be completely erased to achieve reliable playback.

According to the above-described embodiment, since the minimum circular irradiation spots SPr and SPrb are formed during reproduction, crosstalk between recording tracks can be suppressed.

According to the embodiment shown in FIG. 5, as compared with the embodiment shown in FIG. 2, mutual thermal interference between domains formed at predetermined intervals according to recorded information is reduced, and edge shift of the domains is suppressed. You can

In the embodiment of FIG. 5, an elliptical irradiation spot SPw similar to that used for recording a laser beam during reproduction is used.
The light may be condensed to form b.

[0042]

According to the present invention, when pit edge recording is performed in which domains having different lengths are formed according to the recorded information, the existing domain is irrespective of the size relationship between the existing domain and the newly formed domain. The domain of can be surely erased to improve the reliability of overwrite.

According to the second aspect of the present invention, it is possible to reduce the thermal interference between the domains and suppress the edge shift of the domains.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a main part of a magneto-optical disk device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between irradiation spots, temperature distribution in the disc radial direction, and domains corresponding to FIG.

FIG. 3 is a block diagram showing an example of a configuration of a focus control unit for switching a light collecting state.

FIG. 4 is a schematic diagram showing a configuration of a main part of a magneto-optical disk device according to another embodiment.

5 is a diagram showing a relationship between irradiation spots, temperature distribution in a disc radial direction, and domains corresponding to FIG. 4;

FIG. 6 is a diagram showing an example of pit edge recording.

FIG. 7 is a diagram showing the principle of overwrite using an exchange coupling magnetic layer.

FIG. 8 is a plan view showing an example of overwriting erasure failure.

[Explanation of reference numerals] 12 exchange coupling magnetic layer 10 magneto-optical disk Ti magnetic initialization temperature Wi range WDmax longest domain width

Claims (2)

[Claims] 1. A magneto-optical disk (10) having an exchange-coupling magnetic layer (12) is used as an overwrite recording medium, and a domain having a length corresponding to recorded information is formed by power modulation of a light beam irradiated as a heat source. A magneto-optical recording method, which is formed by replacing an existing domain, wherein the light beam is condensed so that the irradiation intensity in the radial direction of the disk gradually changes, and the exchange coupling magnetic layer (12).
The width (Wi) of the region heated to the magnetic initialization temperature (Ti) is set to the width of the longest domain (WDma).
x) The magneto-optical recording method is characterized in that it is made larger than that. 2. The irradiation spot shape of the light beam is an ellipse elongated in the radial direction of the disk.
The described magneto-optical recording method.