JPH05258372A - Magneto-optical disk and recording and reproducing method for the magneto-optical disk - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a double-layer transfer type high-density magneto-optical disk capable of transferring information of the recording layer to the reproducing layer even in the initialization magnetic field, and capable of 2-beam verification using this magneto-optical disk. To provide various recording / playback methods. [Structure] It is composed of two layers, a recording layer for recording and holding information and a reproducing layer for irradiating a laser to read out information, and the magnetization of the reproducing layer is preliminarily aligned in one direction. In a magneto-optical disk of the type in which the temperature of the recording layer is increased by the temperature rise, the magnetization of the recording layer is transferred to the reproducing layer, and only the transferred information in the irradiation spot is read out, the coercive force of the reproducing layer is Hc at room temperature and Hc at the reproducing temperature. ', The coercive force and the exchange coupling force are Hc'<Hex', coercive force, exchange when the exchange coupling force that the reproducing layer receives from the recording layer is Hex at room temperature, Hex at the reproducing temperature, and the externally applied magnetic field is Hb. The binding force and the externally applied magnetic field are -Hc '+ Hex'<Hb<H
The configuration is such that the condition of c + Hex is satisfied, and the magnetization is transferred to the reproducing layer even when an external magnetic field is applied, so that high density reproduction can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-layered magneto-optical disk capable of high-density recording and reproduction, and a recording and reproducing method for the magneto-optical disk. Regarding playback method.

[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 the beam diameter.
As a method for 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 Application Laid-Open No. 3-93058, this system uses an initializing magnet to align the magnetization of the reproducing layer in one direction before reproducing, so that the temperature distribution generated in the beam irradiation spot during reproducing can be controlled. It is used to transfer the magnetization of the recording layer only in the temperature rising portion above a certain value to the reproducing layer. That is, the reproducing layer has a uniform magnetization direction regardless of the recording layer before reproduction, and the temperature of the rear part of the beam irradiation portion rises most during reproduction, 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. Can be read.

On the other hand, recently, high-speed transfer of data is required. Therefore, in order to perform high-speed transfer at the time of recording, a two-beam verify function is used in which two beams are used to confirm and reproduce a recording signal immediately after recording. .. With this method, 1 after recording
The transfer speed is about twice that of the conventional method of verifying after rotation. The interval between the two beams is usually several μm to several tens μm, and two optical systems are formed in one pickup.

[0005]

By the way, in the conventional two-layer transfer type high-density magneto-optical technique, it is necessary to align the magnetization of the reproducing layer in one direction before reproducing, so that an external magnetic field for initialization is used. Was there. However, since the initialization magnetic field is not taken into consideration, the conventional two-layer transfer type high-density magneto-optical disk cannot use the two-beam verify function of one pickup.

That is, in the double-layer transfer type high-density magneto-optical disk, the magnetization of the reproducing layer is not initialized in a uniform direction immediately after recording, and high-density information cannot be reproduced unless it is initialized before reproduction. There is a problem that you can not. Therefore, in the conventional method, initialization is performed using a permanent magnet for initialization.
A reproducing magnetic field is used to assist the magnetization reversal of the reproducing layer during reproduction, and this magnetic field has a direction opposite to the initializing magnetic field. Therefore, when the influence of the initializing magnetic field extends to the reproducing beam, there is a problem that reading cannot be performed in the conventional example. Further, in the verification using two beams, the distance between the recording beam and the reproducing beam for verifying is only about several tens of μm, and when initialization is performed between the recording beam and the verifying beam by using a permanent magnet as in the conventional case. It was unavoidable that the initialization magnetic field would affect the reproduction beam.

The present invention has been made in view of the above-mentioned circumstances of the prior art, and a first object thereof is a double-layer transfer type high density light capable of transferring information of a recording layer to a reproducing layer even in an initializing magnetic field. To provide a magnetic disk. A second object is to provide a recording / reproducing method capable of 2-beam verification using this magneto-optical disk.

[0008]

The above object is composed of two layers, a recording layer for recording and holding information and a reproducing layer for reading information by irradiating a laser, and the magnetization of the reproducing layer is previously aligned in one direction. During playback, part of the laser irradiation spot rises in temperature due to temperature rise, and the magnetization of the recording layer is transferred to the playback layer.
In a magneto-optical disk of the type that reads out only the information transferred in the irradiation spot, the coercive force of the reproducing layer is Hc at room temperature, Hc 'at the reproducing temperature, and the exchange coupling force received by the reproducing layer from the recording layer is Hex at room temperature. When the reproduction temperature is Hex 'and the external magnetic field is Hb, the coercive force and exchange coupling force are Hc'.
<Hex ', and the coercive force, the exchange coupling force, and the externally applied magnetic field are -Hc' + Hex '<Hb <Hc + Hex.
It is achieved by setting the relationship to satisfy.

In this case, it is preferable that the reproducing layer is composed of a magnetic film having a compensation temperature, and the temperature at the time of reproduction is set near the compensation temperature. The externally applied magnetic field Hb is recorded on this magneto-optical disk. It is necessary to apply the voltage from the beam irradiation position to at least a point at which the temperature of the medium drops to about room temperature, at least between the irradiation of the recording beam and the irradiation of the verifying reproducing beam after irradiation of the recording beam.

[0010]

The recording layer functions as a layer for recording information, and the reproducing layer functions as an information reading layer depending on the Kerr rotation angle during reproduction. Information is always recorded in the recording layer, but the reproducing layer is initialized immediately after recording / reproducing and becomes uniform magnetization. During reproduction, the information of the recording layer is transferred to the reproduction layer and reproduced only in the high temperature portion of the reproduction beam.

In order to explain the principle of this operation, the state of the magneto-optical disk is divided into three types, that is, a room temperature state, a reproducing temperature state, and a recording temperature state, and each state will be described using a change in coercive force with temperature and a magnetization curve. For this description, a transition metal (TM) rich magnetic film was used for both the recording and reproducing layers.

FIG. 5 shows the change in coercive force with temperature. As shown in the figure, the coercive forces of the recording and reproducing layers at room temperature are Hc1 and Hc2, respectively, and the Curie temperatures are Tc1 and Tc1, respectively.
Tc2. Exchange coupling forces act between the layers, and the exchange coupling forces received by each layer are Hex1 and Hex2. FIG. 6 is a magnetization curve. The state at room temperature draws a two-step loop as seen in the magnetization curve. The loop having a large coercive force is the recording layer, and the small one is the reproducing layer. An explanation of the magnetization state model diagram in the figure is shown in FIG. The upper part shows the reproducing layer, the lower part shows the recording layer, the white arrow shows the magnetization, the solid line shows the TM moment, and the broken line shows the RE moment. The magnetization curve shown in FIG. 5 is the TM-rich layer in both the recording and reproducing layers, and therefore the TM moment of the solid line largely coincides with the magnetization direction. The exchange coupling force indicates the force that the moments of TM or RE try to move in the same direction.

In the magnetization curve of FIG. 6, the reproducing layer receives the exchange coupling force from the recording layer and the loop shifts. Therefore, when the original coercive force is Hc1, the apparent coercive force is given by Hc1 + Hex1. This Hex1 indicates the exchange coupling force that the reproducing layer receives from the recording layer.

Since the reproducing layer needs to be initialized before reproduction, the initializing magnetic field Hini must be applied under the condition of Hini> Hc1 + Hex1.

Next, consider the recording state. Considering the case of recording information on the erased disc, the erasing is performed in the negative direction (downward) in this example. At the time of recording, since the temperature has risen to the Curie temperature of the recording layer or higher, the magnetization curve is only in the reproducing layer. The recording magnetic field Hrec is applied in the positive direction (upward) in this example, and its magnitude is set to be larger than Hrec> Hc1 ″ and the coercive force Hc1 ″ of the reproducing layer at the recording temperature. Therefore, in the recorded state, the magnetic moment of the reproducing layer follows the direction of the recording magnetic field, and the magnetization of the recording layer follows the direction of the recording magnetic field when the temperature drops. When writing information, the previous information has been erased beforehand,
The erasing direction is opposite to the direction of the recording magnetic field. Therefore, by modulating the laser light intensity, information is recorded at high power (upward magnetization, 1), but not at low power (downward magnetization, 0).

Next, the reproduction state will be considered. The reproduction power has a two-step magnetization curve as shown by the magnetization curve. Particularly, when the magnetization curve of the reproducing layer draws a minor loop, the loop is drawn completely in a magnetic field in a constant direction. That is, the magnetization of the reproducing layer in the zero magnetic field is the same as that of the recording layer, and is always in a fixed direction. Therefore, in this temperature state, the reproducing layer always has the same magnetization direction as the recording layer, and the information of the recording layer can be read by the reproducing layer.

It can be seen that even if a magnetic field is applied, this state can be maintained up to a certain magnetic field. Its size is
At this time, the coercive force and the exchange coupling force are respectively Hc
Assuming 1 ′ and Hex1 ′, this limiting magnetic field Hl is Hl <−Hc1 ′ + Hex1 ′.

At this time, if the bias magnetic field Hb is -Hc1 '+ Hex1'>Hb> Hc1 + Hex1 Hb> Hc '', it is understood that the same magnetic field is satisfied for all recording, reproduction and initialization. Then, by applying this bias magnetic field onto the two beams, the two-beam verification of the high density disk becomes possible.

That is, in this means, the exchange coupling force is controlled so that even if the initializing magnetic field is applied, it can be inverted by the exchange coupling force in the direction opposite to the applied magnetic field, whereby information can be obtained. After the recording, the reproducing layer is reversed by the recording magnetic field, and then the verifying beam is used for verifying. As a result, it is not necessary to apply a weak magnetic field, which is the opposite of the initializing magnetic field, as a reproduction auxiliary magnetic field, and initialization and verification can be performed immediately after recording.

[0020]

EXAMPLE FIG. 1 shows an example of the present invention. FIG. 1 is an explanatory diagram showing a schematic structure of a magneto-optical disk and a magneto-optical disk according to this embodiment when recording and reproducing.

The magneto-optical disk 10 uses a recording film composed of two layers, a recording layer 11 and a reproducing layer 12. The recording / reproducing apparatus has a two-pickup structure including a recording pickup 1 and a reproducing pickup 2, and a bias magnetic field generating magnet 3 for generating a recording and initializing magnetic field is sandwiched between the recording films of the magneto-optical disk 10 to pick up the pickups 1 and 2. It is provided at a position opposite to.

FIG. 2 shows a detailed structure of the magneto-optical disk 10 according to the present invention. The magneto-optical disk 10 is composed of a substrate 13, an interference film 14, a recording film and a protective film 15, and the recording film is composed of two layers of the recording layer 11 and the reproducing layer 12 as described above.
The substrate 13 is made of polycarbonate (PC) and is provided with a tracking groove as in the conventional magneto-optical disk. The interference film 14 and the protective film 15 are formed of a silicon nitride film (Si ₃ N ₄ ). These interference films 1
4 and the protective film 15 are formed by reactive sputtering in a nitrogen atmosphere using a silicon target. The protective film 15 is further coated with an ultraviolet curable resin.

The recording film is composed of two layers, the recording layer 11 for recording and holding information as described above and the reproducing layer 12 for reading out a signal during reproduction. FIG. 3 shows the temperature change of the coercive force of the recording film. The recording layer 11 needs to have a large coercive force at room temperature and a low Curie temperature. In this example, an amorphous alloy (Tb-Fe-Co) film made of terbium (Tb), iron (Fe), cobalt (Co) was used. This film has a transition metal (TM) rich composition at room temperature, a coercive force (Hc) of 10 kOe and a Curie temperature (Tc) of 190 ° C. at room temperature. On the other hand, the reproducing layer requires a material having a small coercive force and a high Curie temperature, and in this embodiment, gadolinium (Gd), iron, and a cobalt amorphous alloy (Gd-Fe-).
Co) film was used. This film is a rare earth metal (RE) at room temperature.
The composition is rich and the compensation point is at about 130 ° C. The coercive force at room temperature is 700 Oe and the Curie temperature is 300 ° C. or higher. The recording film was prepared by magnetron sputtering. An alloy target is used as the target,
A recording / reproducing two-layer film was continuously produced in the same chamber.

The magnetization curve of the recording film is shown in FIG. The magnetization curve at room temperature is a combination of the magnetization curves of the recording layer 11 and the reproducing layer 12, and draws a two-step loop. The magnetization curve of the reproducing layer 12 having a small coercive force slightly shifts due to the exchange coupling force. The shift direction at this time is a direction in which the recording layer 11 is TM-rich and the reproduction layer 12 is RE-rich, so that the respective coercive forces are weakened. Therefore, the apparent coercive force is given by Hc1-Hex1. However, since the minor loop of the reproducing layer 12 is shown by the broken line in the figure, an initializing magnetic field of Hc1 + Hex1 is required for initializing, as in the case where the reproducing layer 12 has a TM-rich composition. In this embodiment, the bias magnetic field (Hb) is set to a value of Hb> Hc1 + Hex1 as shown in the figure, and initialization can be performed immediately after recording.

Next, consider the recording state. In the recorded state, the temperature of the recording layer rises above the Curie temperature, so that the magnetization curve of the recording film is only that of the reproducing layer 12. At this time, since the bias magnetic field Hb corresponding to the recording magnetic field is Hb> Hc1 ″ with respect to the coercive force Hc1 ″ of the reproducing layer 12 at this temperature, information is written in this bias magnetic field direction.

When writing information, the previous information is erased in advance, and the erasing direction is opposite to the direction of the recording magnetic field. Therefore, by modulating the laser light intensity, information is recorded at high power (upward magnetization, 1),
It will not be done at low power (downward magnetization, 0).

Next, the reproduction state will be considered. The magnetization curve in the temperature state irradiated with the reproducing light is a two-step loop, which is the same as the room temperature state, but the magnetization curve of the reproducing layer in the reproducing state is completely unidirectional as seen in the minor loop. Pictured in a magnetic field. That is, the magnetic moment of the reproducing layer in the zero magnetic field is always in a fixed direction following the recording layer. In this state, assuming that the coercive force at this temperature is Hc1 ′ and the exchange coupling force is Hex1 ′, there is a relationship of −Hc1 ′ + Hex1 ′ <0. Further, the bias magnetic field Hb becomes Hb <−Hc1 ′ + Hex1 ′. Since it is set, the magnetization of the reproducing layer follows the magnetic moment of the recording layer even in this magnetic field.

In this embodiment, the reproducing layer 12 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 increases near the compensation temperature. Since the exchange coupling force is represented by Hex = σw / (2Ms × t), the exchange force is infinite at the compensation temperature in calculation. Therefore, Hex1 <Hex1 ', and the magnetization curve and temperature characteristics of this embodiment are obtained.

In the recording film having the above temperature characteristics,
Immediately after the recording state, both the recording layer 11 and the reproducing layer 12 are oriented in the recording magnetic field direction, but in the erased state, only the magnetization of the reproducing layer 12 is inverted by the bias magnetic field and oriented in the recording magnetic field direction. That is, immediately before the verifying reproduction beam, the recording state is on two points a and b on the magnetization curve. Therefore, the magnetization of the reproducing layer 12 is always upward regardless of the state of the recording layer 11. When reproduction is performed from this state, there are two points a'and b'at the reproduction temperature, and the respective information can be obtained by the magnetization of the recording layer 11. At this time, a temperature distribution is generated on the beam spot, only a part of the beam spot is inverted, and high density reproduction can be performed.

According to this embodiment, by controlling the exchange coupling force, the reproducing layer 12 can be formed even in a magnetic field in the same direction as the initialization direction.
Information can be transferred to. As a result, the two-layer transfer type high-density magneto-optical disk can be subjected to two-beam verification.

Further, at this time, in the application range of the bias magnetic field Hb, a temperature drop occurs between the irradiation point of the recording beam and at least after the irradiation of the recording beam and before the irradiation of the reproducing beam for verification, the medium temperature is lowered to about room temperature. It is necessary to go up to the point. As a result, it acts as a recording magnetic field at the recording point and as an initializing magnetic field at the temperature drop point. In the present embodiment shown in FIG. 1, since the verify method uses two beams with one big up, application is performed beyond the reproduction beam position. By applying over the reproducing beam position as in the present embodiment, after the reproduction, the recording is initialized again by the bias magnetic field, so that the recording and initialization magnetic fields can be covered by one magnetic field.

[0032]

As is apparent from the above description, the present invention has the following effects.

That is, the coercive force of the reproducing layer is Hc at room temperature,
When Hc 'is the reproducing temperature, the exchange coupling force the reproducing layer receives from the recording layer is Hex at room temperature, Hex' is the reproducing temperature, and the externally applied magnetic field is Hb, the coercive force and the exchange coupling force are Hc '<H.
According to the invention of claim 1, wherein the coercive force, the exchange coupling force and the externally applied magnetic field are in the relationship of ex ', and the externally applied magnetic field is in the relationship of -Hc' + Hex '<Hb <Hc + Hex. Since it is set to be smaller than the sum of coercive force and exchange coupling force and larger than the upper limit of the limit magnetic field, it is possible to perform recording, reproduction, and initialization in the same magnetic field, and even in the initialization magnetic field, the recording layer Information can be transferred to the reproduction layer.

According to the invention as set forth in claim 2, wherein the reproducing layer is composed of a magnetic film having a compensation temperature and the temperature at the time of reproducing is set near the compensation temperature, the magnetization of the reproducing layer is always independent of the state of the recording layer. Since it can be held constant, the magnetization of the recording layer makes it possible to obtain information from both the recording layer and the reproducing layer.

With respect to the magneto-optical disk according to claim 1 or 2, the temperature drop occurs between the recording beam irradiation position of the externally applied magnetic field and at least after the recording beam irradiation until the verification reproducing beam is irradiated, and the medium temperature. According to the invention as set forth in claim 3, the information is transferred to the reproducing layer even when an external magnetic field is applied, so that the two beams are close to each other. Even if it exists, it can be used and 2-beam verification is possible.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a magneto-optical disk according to an embodiment of the present invention and a schematic configuration when recording / reproducing is performed on the magneto-optical disk.

FIG. 2 is a sectional view showing a structure of a magneto-optical disk according to an example.

FIG. 3 is a characteristic diagram of a recording film used in the magneto-optical disk according to the example.

FIG. 4 is a magnetization curve of a recording film used in the magneto-optical disk according to the example.

FIG. 5 is a characteristic diagram of a recording film for explaining the operation of the magneto-optical disk according to the present invention.

FIG. 6 is a magnetization curve of a recording film for explaining the operation of the magneto-optical disk according to the present invention.

7 is an explanatory diagram of a magnetization model used in FIGS. 4 and 6. FIG.

[Explanation of symbols]

 1 recording pickup 2 reproducing pickup 3 bias magnetic field generating magnet 10 magneto-optical disk 11 recording layer 12 reproducing layer 13 substrate 14 interference film 15 protective film

Claims (3)

[Claims] 1. A two-layer structure comprising a recording layer for recording and holding information and a reproducing layer for irradiating laser to read information, wherein the magnetization of the reproducing layer is preliminarily aligned in one direction. In the magneto-optical disk of the type in which the temperature of the recording layer rises due to the temperature rise, the magnetization of the recording layer is transferred to the reproducing layer, and only the transferred information in this irradiation spot is read out, the coercive force of the reproducing layer is Hc at room temperature, and the reproducing temperature is , Hc ', the exchange coupling force of the reproducing layer from the recording layer is Hex at room temperature, the reproducing temperature is Hex', and the externally applied magnetic field is Hb, the coercive force and the exchange coupling force have a relationship of Hc '<Hex'. And a coercive force, an exchange coupling force, and an externally applied magnetic field have a relationship of −Hc ′ + Hex ′ <Hb <Hc + Hex. 2. The magneto-optical disk according to claim 1, wherein the reproduction layer is made of a magnetic film having a compensation temperature, and the temperature at the time of reproduction is set near the compensation temperature. 3. A magneto-optical disk recording / reproducing method according to claim 1, wherein the magneto-optical disk has a verify function for confirming recorded information immediately after recording by using two beams. On the other hand, the externally applied magnetic field Hb is applied from the irradiation position of the recording beam to at least a point where the temperature of the medium drops to about room temperature at least between the irradiation of the recording beam and the irradiation of the verify reproducing beam. A recording / reproducing method for a magneto-optical disk characterized by the above.