JPH06119671A - Magneto-optical disk and recording / reproducing method thereof - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a magneto-optical disk and a recording / reproducing method, which can be overwritten by one beam and has a double-layer structure, and which corresponds to a high density. [Structure] A double-layer transfer type high-density magneto-optical disk comprises a reproducing layer and a recording layer exchange-coupled. The coercive force and the exchange coupling force are controlled so that the magnetization of the recording layer is transferred to the reproducing layer during reproduction and the magnetization of the reproducing layer is transferred to the recording layer during recording and erasing. [Effect] 1 in the optical modulation type capable of high density reproduction using a double layer transfer type high density magneto-optical disk and modulating the laser intensity.
Beam overwriting becomes possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing mechanism for a magneto-optical disk capable of high density recording / reproducing, and more particularly to a high density magneto-optical disk capable of overwriting.

[0002]

2. Description of the Related Art The beam diameter of an optical disk on a disk is given by about λ / NA, where λ is the wavelength of laser light and NA is the numerical aperture of an objective lens. At this time, the shortest reproducible pit length is λ / 2NA which is 1/2 of the beam diameter. As a method of reading pits smaller than this value for high-density recording, there is a double-layer transfer type high-density magneto-optical disk that uses exchange-coupling recording and reproducing double-layer films.

As disclosed in Japanese Patent Laid-Open No. 3-93058, this system uses an initializing magnet to align the magnetization of the reproducing layer in one direction before reproducing, and utilizes the temperature distribution generated in the beam irradiation spot during reproducing. However, the magnetization of the recording layer only in the temperature rising portion of a certain value or more is transferred to the reproducing layer. That is, the reproducing layer has a uniform magnetization direction regardless of the recording layer before reproduction. During reproduction, the temperature rises most at the rear part of the beam irradiation part, and the magnetization of the recording layer is transferred only in this part. . Therefore, the transfer of the magnetization does not occur in the entire beam spot but in a part of the spot. At this time, the magnetization which is not transferred is aligned in one direction in advance, so that the pit information of 1/2 or less of the spot diameter is also included. It is readable.

[0004]

On the other hand, recently, high-speed transfer of data is required, and therefore, in order to perform high-speed transfer at the time of recording, an overwrite technique with one beam is indispensable. In particular, there is a demand for an optical modulation type overwrite system capable of modulating a laser intensity, which enables a high data transfer rate.

The conventional two-layer transfer type high-density magneto-optical technique records information on the recording layer and performs high-density reproduction by the mask effect of the reproducing layer according to temperature conditions. Since the information in this case is recorded as the magnetization direction of the recording layer, it is necessary to erase the magnetization of the recording layer in advance in order to rewrite the data. Therefore, two processes of erasing and recording are required at the time of recording, and there is a problem that one beam overwriting cannot be performed in the light modulation type for modulating the laser intensity.

[0006]

In order to solve the above-mentioned problems and achieve the object, the magnetization of the reproducing layer is utilized in that it is aligned in one direction after recording for high density reproduction, and this state is erased. It is achieved by transferring the state to the recording layer.

That is, at the time of reproduction, as in the conventional case, part of the initialized reproduction layer transfers the magnetization of the recording layer due to a temperature rise to read information.

On the other hand, at the time of recording, the laser power is modulated into a binary value which is different from the erasing power and the recording power, and at the erasing power, the magnetization of the reproducing layer, that is, the magnetization oriented in one direction is transferred to the recording layer, contrary to the reproducing operation. I shall.

[0009]

[Operation] The recording layer functions as a layer for recording and holding information,
The reproducing layer functions as an information reading layer according to the Kerr rotation angle during reproduction and as a transfer layer in the erasing direction in the erasing process. Information is always recorded on the recording layer, but the reproducing layer is initialized immediately after recording and reproducing to have uniform magnetization.

At the time of reproduction, only the high temperature portion in the reproduction spot,
Information on the recording layer is transferred to the reproducing layer. The transferred magnetization is reproduced. At this time, the other part functions as a mask. Transfer to the reproducing layer is performed by controlling the exchange coupling force.

At the time of erasing, the exchange coupling force is optimized so that the magnetization of the recording layer is aligned with the magnetization of the reproducing layer oriented in one direction, which is the reverse of the reproduction. At the time of recording, an appropriate recording magnetic field is applied where the Curie temperature of the recording layer is exceeded and recording is performed.

At least the external magnetic field is applied as a recording magnetic field at the time of recording / erasing. Therefore, in the erasing process, it is necessary to control the exchange coupling force so that the magnetization of the recording layer is aligned with the magnetization of the reproducing layer even when a magnetic field is applied. The relationship between the external magnetic field and the exchange coupling force is Hw for the recording external magnetic field, Hc 'for the coercive force of the reproducing layer during irradiation of the reproducing beam and Hex' for the exchange coupling force, and the recording layer during the irradiation of the erasing beam. Of the coercive force of Hc "and exchange coupling force of He
x "

[0013]

## EQU00002 ## -Hc '+ Hex' <Hw <-Hc "+ Hex".

Through the above steps, it becomes possible to perform overwriting with a light modulation type in which the laser intensity is modulated by using a two-layer transfer type high density magneto-optical disk.

[0015]

EXAMPLE FIG. 1 shows an example of the present invention. FIG. 1 shows the temperature characteristics of the magneto-optical disk according to the present invention.
The magneto-optical disk uses a recording film composed of two layers, a recording layer 11 and a reproducing layer 12. The recording / reproducing apparatus includes a pickup 1,
It consists of an initialization magnet 2 and a bias magnetic field.

FIG. 1A shows the magnetization state during reproduction. The arrow indicates the magnetization direction. The magnetization of the reproducing layer 12 is aligned in one direction after initialization. At this time, the magnetization of the recording layer is not affected. In the temperature rising portion 4 after laser irradiation, the magnetization of the reproducing layer is in the same direction as the magnetization of the recording layer due to the exchange coupling force and the reproducing magnetic field 31. High density reproduction is performed in this portion.

(B) shows the magnetization state during recording. At the time of recording, the laser beam is modulated into a binary value for recording and erasing, and 1-beam overwrite is performed. The recording magnetic field 32 is in the opposite direction to the reproducing magnetic field. In the temperature rising portion 5, the magnetization of the recording layer is in the reproducing direction during erasing, and is in the recording magnetic field during recording.

FIG. 2 shows the detailed structure of the magneto-optical disk according to the present invention. The disk comprises a substrate 13, an interference film 14, a recording film and a protective film 15, and the recording film is a recording layer 11,
The reproduction layer 12 is composed of two layers. The substrate is polycarbonate (PC), and has a tracking groove as in the conventional magneto-optical disk. The interference film and the protective film are formed of a silicon nitride film (Si ₃ N ₄ ).
As a forming method, sputtering is used, and a silicon target is used for reactive sputtering in a nitrogen atmosphere. The protective film is further coated with an ultraviolet curable resin.

The recording film is composed of two layers, a recording layer for recording and holding information and a reproducing layer for reading out a signal during reproduction. FIG. 3 shows the temperature change of the coercive force of the recording film. The recording layer must have a large coercive force at room temperature and a low Curie temperature. In this embodiment, terbium (Tb), iron (F
e), an amorphous alloy composed of cobalt (Co) (Tb-F)
e-Co) film was used. This film is a transition metal (T
M) It has a rich composition and has a coercive force (Hc) of 10 at room temperature.
kOe and Curie temperature (Tc) are 190 degreeC. On the other hand, the reproducing layer requires a material having a small coercive force and a high Curie temperature. In this embodiment, gadolinium (Gd), iron,
A cobalt amorphous alloy (Gd-Fe-Co) film was used.
This film has a rare earth metal (RE) rich composition at room temperature,
The compensation point is at about 130 ° C. The coercive force at room temperature is 700
Oe and Curie temperature are 300 degreeC or more. The recording film was manufactured by magnetron sputtering. An alloy target was used as a target, and a recording / reproducing two-layer film was continuously produced in the same chamber.

Magnetization curves of the recording film are shown in FIGS. 4 to 7.
Further, FIG. 8 shows an explanatory diagram of the magnetization model. In the magnetization model, the upper stage shows the reproducing layer and the lower stage shows the recording layer. The white arrow indicates the magnetization direction, and the solid line indicates the transition (TM) metal moment.
The dashed line indicates the rare earth (RE) metal moment. Since the recording layer has a TM rich composition, the solid line has a large TM moment, and the magnetization direction is also the same direction. R in the playback layer
The RE moment is large due to the E-rich composition.

FIG. 4 shows the magnetization curve at room temperature. The magnetization curve of the reproducing layer having a small coercive force slightly shifts due to the exchange coupling force. At this time, the recording layer is TM rich in the shift direction,
Since the reproducing layer is RE-rich, the coercive force of each layer is weakened. Therefore, the apparent coercive force is

[0022]

## EQU00003 ## Given by Hcr1-Hexr1. However, since the minor loop of the playback layer is shown by the broken line in the figure, in order to initialize it

[0023]

## EQU00004 ## An initialization magnetic field of Hcr1 + Hexr1 is required. In this embodiment, a bias magnetic field (Hb) is applied as shown in the figure.

[0024]

## EQU5 ## The size is set to Hini> Hcr1 + Hexr1.

In this state, the magnetization state does not change even if the reproducing magnetic field Hread is applied.

Next, consider the reproduction state shown in FIG.
The magnetization curve in the temperature state irradiated with the reproducing light has the same two-step loop as in the room temperature state, but in the reproducing state, the reproducing magnetic field Hr
In the state in which the ead is applied, the magnetization state is A, A'in the figure.
Take two states. That is, the magnetization of the reproducing layer is aligned with the recording layer due to the exchange coupling force. As a result, the recorded information is transferred to the reproducing layer and can be reproduced. In this state, the coercive force at this temperature is Hcr2 and the exchange coupling force is Hcr.
exr2

[0027]

## EQU6 ## It is necessary that the bias magnetic field Hread is set in a state of -Hread <-Hcr2 + Hexr2.

Since the magnetic field is applied to the periphery of the beam, it is necessary to satisfy the condition that the magnetization of the reproducing layer is not reversed in the room temperature state FIG. that is

[0029]

[Expression 7] -Hread> -Hcr1 + Hexr1.

Next, consider the erased state shown in FIG.

In the erased state, the magnetization of the recording layer has the characteristic of being aligned with the magnetization of the reproducing layer, contrary to the conventional case. This is because the coercive force of the reproducing layer becomes large, and the magnetization reversal of the recording layer occurs first rather than the magnetization reversal of the reproducing layer. In this state,

[0032]

When a recording magnetic field Hwrite satisfying −Hwrite <−Hcw3 + Hexw3 is applied,
The recording layer is always aligned with the magnetization state of the reproducing layer. In this case, the magnetization state can take two states of B and B ′ in the figure, but since the reproducing layer is aligned in one direction by the initializing magnet, in this case, upward, the magnetization of the recording layer is all upward. It is always in the B'state and can be erased.

However, even in the erasing process, since the reproduction temperature profile is passed, the reproduction process, that is, the process in which the magnetization of the reproduction layer is aligned with the magnetization of the recording layer must be avoided in this process. As a condition for this, from FIG.

[0034]

[Expression 9] Hwrite> −Hcr2 + Hexr2 needs to be satisfied.

Next, consider the recording state shown in FIG.
In the recorded state, the temperature of the recording layer rises above the Curie temperature, so the magnetization curve of the recording film is only that of the reproducing layer. At this time, the recording magnetic field Hwrite is against the coercive force Hcr4 of the reproducing layer at this temperature.

[0036]

Since Hwrite> Hcr4, information is written in this bias magnetic field direction. In the recorded state, the reproducing layer is also near the Curie temperature, and T
It is M rich. For this reason, the magnetization is upward during recording, but below the compensation temperature near the reproduction temperature, R
Since it is E-rich, the magnetization direction is downward. This shows the state of B in FIG. 6, and therefore the recording state opposite to the erased state B ′ is established.

In this embodiment, the reproducing layer is a magnetic film having a RE-rich composition at room temperature. In such a film, the saturation magnetization (Ms) of the magnetic film becomes zero at the compensation temperature, so that the exchange coupling force becomes large near the compensation temperature. This has an exchange coupling force

[0038]

Since it is represented by Hex = σw / (2Ms × t), the exchange force becomes infinite at the compensation temperature in the calculation. By setting the compensation temperature near the erasing temperature, specifically, near the Curie temperature of the recording layer, the magnetization curve of the present embodiment,
It becomes a temperature characteristic.

In the recording film having the above temperature characteristics,
During reproduction, a temperature distribution is generated on the beam spot and only a part of the beam spot is inverted, so that high density reproduction can be performed. Further, by modulating the laser light in two stages, it is possible to perform one-beam overwrite, that is, erasing at a low level and recording at a high level.

In the present embodiment, a material having a compensation temperature was used, but it is not always necessary to achieve this characteristic by setting the compensation temperature, and even if it is achieved by a combination of film characteristics, 1
Beam overwrite and high density reproduction are achieved.

According to this embodiment, by controlling the exchange coupling force, a two-layer transfer type high density magneto-optical disk is used.
Beam overwriting can be enabled.

[0042]

According to the present invention, by controlling the coercive force, the exchange coupling force and the bias magnetic field, the magnetization of the recording layer is transferred to the reproducing layer at the time of reproducing for high density reproducing, and at the time of erasing recording, the recording layer is recorded. Recording and erasing are possible by aligning the magnetization of the same as the magnetization of the reproducing layer. As a result, a 1-beam overwrite can be performed, and a magneto-optical disk capable of high density reproduction and a recording / reproducing method can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a recording / reproducing method for a magneto-optical disk according to an embodiment of the present invention.

FIG. 2 is a diagram showing a magneto-optical disk according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram of a recording film used in the magneto-optical disk of the present invention.

FIG. 4 is a magnetization curve diagram of a recording film used in the magneto-optical disk of the present invention at room temperature.

FIG. 5 is a magnetization curve diagram at a reproducing temperature of a recording film used in the magneto-optical disk of the present invention.

FIG. 6 is a magnetization curve diagram of a recording film used in the magneto-optical disk of the present invention at an erasing temperature.

FIG. 7 is a magnetization curve diagram at a recording temperature of a recording film used in the magneto-optical disk of the present invention.

FIG. 8 is an explanatory diagram of a magnetization model used in FIGS. 4 to 7.

[Explanation of symbols]

1 ... Pickup, 2 ... Initialization magnet, 3 ... Bias magnetic field, 31 ... Reproducing magnetic field, 32 ... Recording magnetic field, 4 ... Reproducing temperature part, 5 ... Recording temperature part, 11 ... Recording layer, 12 ... Reproducing layer, 1
3 ... Substrate, 14 ... Interference film, 15 ... Protective film.

Claims (4)

[Claims] 1. A recording layer for recording and holding information and a reproducing layer for reading information by irradiating a laser are formed on a substrate, and magnetization of the reproducing layer is preliminarily aligned in one direction by an initializing magnetic field. At the time of reproduction, a part of the laser irradiation spot becomes higher in temperature due to the temperature rise, the magnetization of the recording layer is transferred to the reproduction layer, and in the magneto-optical disk of the method of reading only the transferred information in this irradiation spot, The external magnetic field for recording is Hw, the coercive force of the reproducing layer during irradiation of the reproducing beam is Hc ', and the exchange coupling force is Hex'.
When the coercive force of the recording layer is Hc ″ and the exchange coupling force is Hex ″ when the erasing beam is irradiated, the following equation is given: −Hc ′ + Hex ′ <Hw <−Hc ″ + Hex ″ . 2. The magneto-optical disk according to claim 1,
A magneto-optical disk characterized in that a transition-rare earth alloy magnetic film having a compensation temperature is used for a reproducing layer, and the compensation temperature is set near the Curie temperature of the recording layer. 3. Recording and erasing by applying a recording magnetic field to the magneto-optical disk according to claim 1 or 2 in the same direction as the initializing magnetic field and modulating the laser beam intensity at the time of recording into high and low binary values. A recording / reproducing method for a magneto-optical disk, which is characterized by carrying out simultaneously. 4. A recording / reproducing method for a magneto-optical disk according to claim 3, wherein a reproducing magnetic field is applied at the time of reproducing, and a magnetic field having substantially the same magnitude as the reproducing magnetic field but different polarity is used as the recording magnetic field. The recording / reproducing method for a magneto-optical disk according to claim 1.