JP2000215533A - Magneto-optical recording medium, magneto-optical recording and reproducing method using the same, and magneto-optical recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To close up a mark pitch and a track pitch with a simple layer structure by successively laminating a reproducing magnetic layer, a recording layer, a photoconductive layer and a magnet layer from the light beam incidence side. SOLUTION: A GdFe film having 30 nm thickness, a TbFeCo film having 60 nm thickness, a CuO film having 100 nm thickness, a GdTbFeCo film having 50 nm thickness are used as a reproducing layer 11, a recording layer 12, a photoconductive layer 13 and a magnet layer 14, respectively. The magnetization of the recording layer 12 is aligned upward, when a large quantity of conductive electrons are formed in the photoconductive film in a part rich in number of photons near the central part of a spot during irradiation with recording light, an exchange magnetic field in the part exceeds the coercive force of the recording layer, the exchange magnetic field is dominant and the sum of vectors of the magnetic field is upward. The size of recording marks is decided by a part in which the photoconductivity of the photoconductive film increases, marks having a size smaller than that of the total half-width of a laser spot can be formed and high density recording is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magneto-optical recording / reproducing technique for recording / reproducing information by irradiating a light beam.

[0002]

2. Description of the Related Art A magnetic film having an axis of easy magnetization in a direction perpendicular to the film surface is irradiated with a light beam and heated to reduce the coercive force of a heating portion and to apply a magnetic field to a portion where the coercive force is reduced. The magneto-optical recording / reproducing method of recording and erasing information by applying the magnetization direction to the direction of the applied magnetic field and reproducing the information using Kerr rotation according to the direction of the magnetization is a music miniature. It has been put to practical use for disks, backup files for personal computers, etc., and is expected to have a larger capacity and a higher transfer rate as the amount of information increases. The storage capacity of magneto-optical recording, that is, the recording density, is mainly determined by the wavelength of the light source and the NA of the focusing lens, and the size of the recording mark (the mark length corresponding to the shortest bit length or the mark width corresponding to the track pitch) depends on the focal position. Is about the full width at half maximum (FWHM) of the laser spot. Basically, the FWHM defines the shortest mark length, the shortest space (between marks) length, and the track pitch. Therefore, if the wavelength and NA are determined, the recording density is almost determined. Techniques for overcoming this wavelength limit include recording of marks and spaces shorter than FWHM by magnetic field modulation recording, low inter-code interference reproduction of narrow pitch mark arrays by magnetic super-resolution reproduction (MSR), and magnetic domain expansion reproduction (MAMMOS)
Has been proposed for high C / N reproduction of fine marks. The magnetic field modulation recording modulates information of an external magnetic field and irradiates a recording beam in a DC manner or in a pulse at a single frequency. If the recording light spot is at a certain position on the recording track, for example, if a magnetic field having a magnitude equal to or larger than the recording saturation magnetic field is applied downward, the magnetization of the recording layer in the range equivalent to the FWHM of the spot is magnetized downward at that moment. I do. If a magnetic field having a magnitude equal to or larger than the recording saturation magnetic field is applied upward when the spot moves half of the FWHM with respect to the medium, for example, the magnetization of the recording layer corresponding to the FWHM of the spot is magnetized upward at that moment. FWH magnetized downward before
Half of the magnetization corresponding to M is magnetized upward, resulting in FW
The advantage of magnetic field modulation recording is that marks and spaces shorter than HM can be recorded. FW by magnetic field modulation recording
A mark can be recorded at a narrower pitch than the length corresponding to the HM, but this is simply performed with a Gaussian spot (the same spot as that used for normal recording is used) in which the e-2 diameter spans about twice the area of the FWHM. Reproduction causes large intersymbol interference and makes it difficult to obtain a practical C / N. So, for example, Joint-
MORIS / ISOM97 Technical Digest p. 70, p. 78, p. 80, p. 174, p. 25
4 or the like, or for example, Jo
int-MORIS / ISOM97 Technical Digest p. 36, p. 42, p. 262 or H10 IEEJ National Convention S.S. MAM disclosed in 10-6
MOS regeneration technology has been proposed. MSR, MAMMO
S is also classified into various methods if it is finely classified. Basically, the MSR uses an exchange interaction or a magnetostatic interaction between a plurality of magnetic layers (in the simplest case, a recording layer and a reproducing layer). Transfer only a part of the magnetization of the recording layer to the reproducing layer,
The area other than the transfer area is a technique for increasing the reproduction resolution by using a mask, and MAMMOS also utilizes an exchange interaction or a magnetostatic interaction between a plurality of magnetic layers (most simply, a recording layer and a reproduction layer). In this technique, only a part of the magnetization of the recording layer is transferred to the reproducing layer, and the transferred magnetic domain is enlarged by using the domain wall moving force or the nucleation force to improve the reproducing C / N.

According to the above-mentioned prior art, the mark pitch can be made shorter than the FWHM length of the spot, so that high-density recording / reproduction exceeding the wavelength limit is possible. Since the external magnetic field must be provided at a position close to the recording film by several microns, basically, a bonded disk cannot be used, and the capacity of the disk is not so much improved. There are also problems such as power consumption of the magnetic field source and contact between the magnetic field source and the disk during disk tilt. Although the mark length and the space length can be shortened, the mark width is equivalent to FWHM, so that there is no effect of reducing the track pitch.

[0004] Even in the simplest configuration, the MSR and MAMMOS require a reproducing magnetic layer in addition to the recording magnetic layer. This method can be implemented with a simple configuration, but when applying to optical modulation recording that requires a multi-layered recording magnetic layer (that can be overwritten), Joint-MORI
S / ISOM97 Technical Digest p. 174
As disclosed in 6, the number of magnetic layers alone, the interference layer,
The combination of the reflective layers requires a complicated medium configuration of ten layers, which is not practical.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is intended to solve the above-mentioned problems by magnetic field modulation recording and MS.
With a simple layer structure equivalent to the combination of R and MAMMOS reproduction, it is possible to narrow the mark pitch as well as the magnetic field modulation recording and also the track pitch. It is an object of the present invention to provide a magneto-optical recording medium, a recording / reproducing method and a recording / reproducing apparatus using the same.

[0006]

According to the present invention, as a means for realizing the above object, a reproducing magnetic layer, a recording magnetic layer, a photoconductive layer, and a magnet layer are laminated in this order from the light beam incident side. A magneto-optical recording medium, wherein the conductive layer is provided on at least one interface selected from between the recording magnetic layer and the photoconductive layer, between the photoconductive layer and the magnet layer. Wherein the magneto-optical recording medium and the magnetic layer are uniformly magnetized in the same direction in a direction perpendicular to the film surface at the memory holding temperature. At the holding temperature, the above-mentioned magneto-optical recording medium characterized in that it is magnetized in the plane, and the above-mentioned medium is irradiated with a light beam at a recording power level, and the irradiated part of the photoconductive layer is switched to conductive. And the recording magnetic layer and the magnet layer through conduction electrons In the exchange-coupled state, recording is performed with the magnetization direction of the recording magnetic layer aligned with the magnetization direction of the magnet layer, and a light beam at the reproducing power level is irradiated to change the magnetization of the recording magnetic layer of the irradiated part to the reproducing magnetic layer. Magneto-optical recording / reproducing method, characterized in that the magnetic domain transferred to the reproducing magnetic layer is reproduced by enlarging the magnetic domain transferred to the reproducing magnetic layer. Irradiating a beam to the recording magnetic layer, by applying a magnetic field in a direction opposite to the direction of the exchange magnetic field applied at the time of recording, and performing the erasing operation, the magneto-optical recording and reproducing method, and Irradiating the magneto-optical recording medium with a light beam at a recording power level,
Switching the photoconductive layer of the irradiated part to conductive, making the recording magnetic layer and the magnet layer exchange-coupled via conduction electrons, and performing recording with the magnetization direction of the recording magnetic layer aligned with the magnetization direction of the magnet layer Another object of the present invention is to provide a magneto-optical recording / reproducing apparatus characterized in that a reproducing power level light beam is irradiated to transfer the magnetization of the recording magnetic layer of the irradiated portion to the reproducing magnetic layer to perform reproduction.

[0007] The recording principle of the magneto-optical recording medium of the present invention is essentially different from that of the prior art. Conventionally, the recording magnetic layer is heated by irradiating the recording light → the coercive force of the recording layer is reduced → the recording of the coercive force reduced portion According to a series of heat mode processes of aligning the direction of magnetization of the layer with the direction of the applied magnetic field, the present invention provides recording light irradiation → conduction by photoexcitation of the photoconductive film in the center of the spot → conduction electrons. A recording principle according to a series of photon mode processes is used in which exchange coupling between the recording magnetic layer and the magnet layer → the magnetization direction of the recording layer is aligned with that of the magnet layer. Since the part where the coercive force of the recording layer of the recording light irradiating part is brought down in the heat mode is the heat mode, it can be accurately described as a photon mode / heat mode hybrid process.

[0008] The magnet layer itself does not undergo magnetization reversal during the recording process, but merely supplies an exchange magnetic field to the recording layer. For example, when a mark position recording method in which the position of a mark to be recorded is determined is adopted, the magnetization direction of the magnet layer is only the position where the mark is to be recorded, and the initial magnetization of the recording layer (the initial direction is set to the erasing direction). In the case of performing mark edge recording with a higher recording density, the recording mark position cannot be specified, so the magnet layer is set at the memory holding temperature (generally room temperature). (In the vicinity), it is preferable to have the same magnetization perpendicular to the film surface.

As an initial state, for example, the direction of magnetization of the recording magnetic layer is made opposite to that of the magnet layer. In such an initial state, if the room temperature coercive force of the recording layer and the magnet layer are different,
For example, after applying a magnetic field equal to or greater than the coercive force of the layer with the larger coercive force at room temperature and aligning the magnetization directions of both layers to the same direction, the coercive force of less than the coercive force of the layer with the larger coercive force is small. A magnetic field greater than the coercive force of the other layer may be applied in a direction opposite to the first direction. When the coercive force at room temperature of both layers is tight, irradiate a light beam at the recording power level in a DC manner, and apply a magnetic field greater than the exchange force between the recording layer and the magnet layer from the outside in the opposite direction to the exchange magnetic field. Or a leakage magnetic field applied from a magnet layer described later to the recording layer may be used.

In the recording process, light having a power level enough to generate conduction electrons in the photoconductive film at the center of the spot is irradiated. The portion of the recording layer where the conduction electrons are sufficiently generated and the exchange force exceeds the coercive force of the recording layer has the same magnetization as that of the magnet layer. The magnitude of the exchange force depends not only on the photoconductive properties of the photoconductive film but also on the interface domain wall energy that can be controlled by the choice of the two magnetic layers and the magnetization and thickness of the recording layer. Since it depends on the thermomagnetic characteristics of the recording layer, if the setting is properly made including the selection of the recording power level, a mark finer than the FWHM of the spot can be recorded. Moreover, the mark size is in principle equivalent to the location where a sufficient number of conduction electrons are generated in the photoconductive film at the center of the spot.
Not only can the space length be reduced, but also the mark width can be reduced, so that the track pitch can be reduced.

The reproduction of a fine mark is performed by MSR or MAM.
Reproduction is possible by MOS technology. The MSR reproduction method may be any method as long as it has a magnetic optical aperture in a part of the reproduction spot.
-Aperture-Detection), FAD
(Front-Aperture-Detection
n), CAD (Central-Aperture-D)
(Election) can be applied, and the recording magnetic layer and the reproducing magnetic layer may be exchange-coupled or may be merely magnetostatically coupled. MAMM
OS regeneration was also submitted to the H10 IEEJ National Convention. Various schemes disclosed in 10-6 are applicable. The minimum number of magnetic layers required for implementing the present invention is three, which is a much simpler configuration than, for example, a conventional MSR medium capable of overwriting with light modulation.

The recording magnetic layer material which can be used in the present invention is a rare earth element (RE: RE) used in conventional magneto-optical recording.
Gd, Tb, Dy, Nd, etc.)-Transition metal (TM: Fe,
(Co etc.) alloy thin film, multilayer artificial lattice based thin film such as Co / Pt, Co / Pd, Whistler alloy thin film represented by PtMnSb, oxide magnetic material represented by Ba ferrite, etc. And typically T
A bFeCo thin film or the like is selected. As the photoconductive layer, any material may be used as long as the material has an optical gap narrower than the operating laser energy. Si, Ge, InGaP, CdSe,
ZnTe, GaN, GaAs, ZnSe, ZnO, Al
It can be freely selected from As, AlSb, Si-C and the like.
In the case where conduction electrons are generated by excitation to an impurity level in the optical gap or multiphoton excitation through the impurity level, the optical gap may be higher than the operating laser energy. Typically, amorphous Si or the like is selected. As the magnet layer, any magnetic layer having a higher Curie point than the recording layer may be used. For supplying a large leakage magnetic field to the recording layer in light modulation overwrite recording described later, a film material having a large temperature change in magnetization is preferable. . Specifically, in addition to the RE-TM thin film having a higher Curie point than the recording layer, a multilayer artificial lattice, a Whistler alloy, a Co-Pt alloy film, a Co-Cr thin film used for magnetic recording may be used. I can do it. The reproducing magnetic layer has the MSR effect or MA
Any material may be used as long as it has an MMOS effect, but a RE-TM film having a perpendicular magnetic anisotropy smaller than that of the recording magnetic layer, for example, a Gd-FeCo film is preferable. In order to simplify the light modulation overwrite operation described later, in-plane magnetization at room temperature,
It is preferable to arrange a gate layer having a relatively low Curie point between the reproducing layer and the recording layer by using a film having perpendicular magnetization at the reproducing temperature and perpendicular magnetization even near the recording temperature.

Although the recording magnetic layer and the photoconductive layer or the photoconductive layer and the magnet layer may be directly laminated,
In general, a semiconductor film, particularly an Si or Ge system, and a magnetic film react with each other to form an interface layer such as silicide, which may impair exchange coupling of the recording layer and the magnet layer via conduction electrons.
Preferably, a conductive barrier layer is provided at the interface between the recording layer and the photoconductive layer and at the interface between the photoconductive layer and the magnet layer. The barrier layer material may be any conductive material that does not easily react with a magnetic substance and a semiconductor, but it is preferable to use a compound conductive film such as TiN or ITO. The conductive barrier layer need not be provided particularly when an oxide magnetic material is used as the magnetic layer or when an oxide is used as the photoconductive layer.

The magneto-optical recording / reproducing method of the present invention using the magneto-optical recording medium outlined above basically involves irradiating a light beam at the recording power level to make the irradiated portion of the photoconductive layer conductive. The recording magnetic layer and the magnet layer are exchange-coupled via conduction electrons, and the recording is performed with the magnetization direction of the recording magnetic layer aligned with the magnetization direction of the magnet layer. Then, the magnetization of the recording magnetic layer of the irradiated portion is transferred to the reproducing magnetic layer to perform the MSR or MAMMOS reproduction. However, the MAMMOS reproduction for enlarging and reproducing the magnetic domain transferred to the reproducing magnetic layer is high even with a finer mark. C
/ N, and more preferably, irradiating a light beam of an erasing power level to the recording magnetic layer.
It is preferable to perform an optical modulation overwrite operation in which an erasing operation is performed by applying a magnetic field opposite to the direction of the exchange magnetic field applied during recording. There are several methods for applying a magnetic field in the direction opposite to the direction of the exchange magnetic field during recording to the recording layer by irradiating light at the erasing power level. The simplest is the application of a DC external magnetic field, and utilizes the fact that the magnitude of the exchange magnetic field differs at different power levels. That is, a power having an exchange magnetic field smaller than that at the time of recording power level irradiation is selected as the erasing power level, and a magnetic field having a direction opposite to the exchange magnetic field and smaller than the exchange magnetic field at the time of recording and larger than the exchange magnetic field at the time of erasure is selected as the external magnetic field. You can use it.

When a leakage magnetic field from each magnetic layer constituting the medium is used in addition to the external magnetic field, light modulation overwriting is easily performed. Although it depends on how to select the thermomagnetic properties of the magnet layer,
If the magnitude of the magnetization of the magnet layer is selected so as to decrease from room temperature to the high temperature side, the leakage magnetic field applied from the magnet layer to the recording layer is opposite to the direction of the magnetization of the magnet layer, that is, the erasing direction. It becomes easier to write. If a RE-TM film is selected as the magnet layer, the direction of the magnetization of the net can be reversed above the compensation point while maintaining the direction of the sublattice magnetization of the RE and TM, so that a larger leakage magnetic field can be generated. The magnitude of the leakage magnetic field can be adjusted by the thickness of the magnet layer.

In addition to the leakage magnetic field of the magnet layer, as described above,
It is also possible to use a leakage magnetic field generated from the reproducing magnetic layer.
For example, a film having in-plane magnetization at room temperature and perpendicular magnetization upon heating is selected for the reproducing layer, a gate layer having a relatively low Curie point is inserted between the reproducing layer and the recording layer, and the layers are exchange-coupled. At the time of reproduction, assuming that the gate layer is below the Curie point, the magnetization of the gate layer is first aligned in the direction of magnetization of the recording layer, and this is transferred to the reproduction layer to realize MSR reproduction or MAMMOS reproduction. At the time of erasing, a power level higher than that of reproducing is selected, and the gate layer is heated to the Curie point or higher. No exchange force acts between the reproducing layer and the recording layer in a portion where the gate layer is heated above the Curie point. If a relatively small external magnetic field is applied from the outside in an erasing direction, the direction of magnetization of the reproducing layer is oriented in the erasing direction at the time of erasing regardless of the direction of magnetization of the recording layer. Due to the spatial distribution of the magnetization, a leakage magnetic field in the erasing direction is applied to the recording layer to facilitate light modulation overwrite recording. If the recording power level is higher than the erasing power level, the reproducing layer can be heated above the Curie point during recording.
Although a leakage magnetic field suitable for erasing is generated at the time of erasing, a device can be devised such that recording is not performed at the same time and recording is facilitated at the same time.

The magneto-optical recording medium of the present invention preferably employs the above-described optical modulation overwrite operation, but it is also possible to apply the magnetic field modulation overwrite operation. In the ordinary magnetic field modulation recording, the external magnetic field is oscillated in plus or minus around the zero level, but when applying the magnetic field modulation recording to the present invention, the recording direction magnetic field is merely an exchange magnetic field between the recording layer and the magnet layer. It is not necessary to apply an external magnetic field in the recording direction (although the external magnetic field may be applied supplementarily, the main component of the recording magnetic field is an exchange magnetic field). It is preferable to adopt a method of setting the erasing direction magnetic field to be opposite to the exchange magnetic field and larger than the exchange magnetic field.

A magneto-optical recording / reproducing apparatus according to the present invention is an apparatus which mounts the above-described magneto-optical recording medium according to the present invention and realizes the above-described magneto-optical recording / reproducing method. It is preferable that the device is an optical modulation recording device. At least in the case of not overwriting recording (when the external magnetic field is different between recording and erasing), the external magnet during erasing is an exchange magnetic field between the recording layer and the magnet layer. Is applied in a direction opposite to the direction of It is preferable that the overwrite recording device has at least three different power levels of recording, erasing, and reproduction, but in this case, the direction of the external magnetic field depends on the magnitude and direction of the leakage magnetic field inside the medium. And the size are determined. An external magnetic field may not be provided, but even if it is present, the distance from the medium is set at a distance of about several millimeters, thereby enabling the use of a bonded disc. The magnitude relationship between the recording power level and the erasing power level is determined by the magnitude of the exchange magnetic field acting between the recording layer and the magnet layer and the temperature characteristics of the leakage magnetic field of each layer. The present invention mainly uses a high-speed photon mode process in principle of recording, and uses high-speed magnetic transfer or magnetic expansion for reproduction. Therefore, it is better that the disk rotation speed is high.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings. [Embodiment 1] FIG. 1 is a sectional view showing an embodiment of a magneto-optical recording medium according to the present invention, and corresponds to a basic structure. In FIG. 1, 11 is a reproducing magnetic layer, 12 is a recording magnetic layer, 13 is a photoconductive layer, 14 is a magnet layer, 15 is a substrate, 16 is a first interference layer,
17 is an intermediate layer and 18 is a protective layer. Playback layer, recording layer,
The materials that can be used for the photoconductive layer and the magnet layer are as described above. In Example 1, a GdFe film having a thickness of 30 nm was used as the reproducing layer, and a TbFeCo film having a thickness of 60 nm was used as the recording layer.
Film, a 100 nm thick CuO film (optical gap: 2 eV) as a photoconductive layer, and a 50 nm thick GdT as a magnet layer
Each of the bFeCo films was used. As the substrate, a polycarbonate substrate provided with a groove (a groove for tracking guide) generally used as an optical disk was used.
The track pitch was changed between 0.2 μm and 0.5 μm in order to examine characteristics such as crosstalk and cross erase. In addition, a quartz substrate for measuring thermomagnetic properties, photoconductivity and the like was appropriately used. The interference layer, the intermediate layer, and the protective layer are not necessarily provided in the practice of the present invention. However, the interference layer is provided for controlling the magnetic interaction between the layers and the reproducing layer and the recording layer for enhancing the reproduction signal. In order to control the temperature difference, the protective layer has a function for preventing the medium from being oxidized, as the name implies. In the first embodiment, the thickness of the interference layer is 100 n
m, a 15 nm-thick SiN film as an intermediate layer,
A 100 nm-thick SiN film was used as each protective layer. The medium shown in FIG. 1 can be created, for example, by the following procedure.

After a master is prepared by a normal mastering process, a stamper is formed by a Ni electroforming process, and a polycarbonate substrate can be obtained by an injection molding process. The track pitch was adjusted by adjusting the laser power and the wavelength in the mastering process. The substrate was set in a holder of a multi-chamber sputtering apparatus, and after evacuation, the layers were sequentially formed. Each magnetic layer can be obtained by DC magnetron sputtering of a magnetic alloy target in Ar gas, and the photoconductive layer in this embodiment is obtained by RF magnetron sputtering of a CuO target in an Ar-O2 mixed gas. For the SiN film, a B-doped Si target is Ar
It can be obtained by DC reactive sputtering in -N2 gas. After the film formation, a UV curable resin was applied as an adhesive layer on the protective film, and a counter substrate (a dummy substrate without a film was used in the embodiment of the present invention) for preventing tilt was attached. Thereafter, the initial magnetization direction was set using an electromagnet. The coercive force of each layer can be controlled by selecting the element and composition. As described later, in this embodiment, the in-plane magnetization of the reproducing layer, the perpendicular magnetization of 8 kOe of the coercive force of the recording layer, and the coercive force of the magnet layer at around room temperature in this embodiment. Since the magnetization was set to 4 kOe perpendicular magnetization, first, a magnetic field of 12 kOe was applied perpendicularly to the film surface and downward in FIG. 1 to direct the magnetization of both the recording layer and the magnet layer downward, and then upwardly perpendicular to the film surface. Then, a magnetic field of 6 kOe was applied to adjust the magnetization direction of the magnet layer upward. Since the reproducing layer is magnetized in the plane near room temperature, the direction of the magnetization after being extracted from the electromagnet is random in the plane. The direction of the initial magnetization of each magnetic layer is schematically shown in FIG.

The magneto-optical recording medium of the present invention prepared as described above and shown in FIG. 1 was evaluated according to the following procedure. First, CuO on a quartz substrate prepared in advance under the same conditions as those for forming FIG.
The photoconductive film is patterned into an electrode shape, and the wavelength is 488 nm.
(2.54 eV) was irradiated with an Ar ion laser to examine the photoconductive characteristics. The photocurrent was examined while applying a voltage to the CuO electrode pattern to change the light irradiation power (the number of photons: Np), and the photoconductivity (σ) was derived. A wavelength of 488 was applied to a sample in which a recording layer, a photoconductive layer, and a magnet layer separately formed were laminated.
Heating was performed while irradiating an Ar ion laser of nm (2.54 eV), the magnetization curve was examined using a VSM, and the exchange magnetic field (Hexg) between the recording layer and the magnet layer and the coercive force of the recording layer were examined. The relationship between the irradiation power and the medium film temperature was converted by thermal analysis under the condition that the Ar ion laser was condensed and irradiated to the same degree as the disk operation described later. These results are summarized in FIG. The photoconductivity σ increases as the number of photons Np increases,
Thermal analysis showed a high constant value near the Curie point (Tcw) of the recording layer. Under such σ-T (analytical film temperature), the exchange magnetic field Hexg and the coercive force Hcw of the recording layer derived from the thermomagnetic characteristics of the VSM are shown in FIG.
Was found to behave. Although not shown in the figure to avoid complication, Hexg was zero over the entire temperature range without light irradiation. This is because when the photoconductive film is off and there are no conduction electrons, the photoconductive film simply acts as a non-magnetic intermediate layer, so that no exchange interaction works between the recording layer and the magnet layer. Hexg shown in FIG. 3 was obtained when light having the same power as that when σ was examined was irradiated. When σ is small (corresponding to the case where the converted temperature in thermal analysis is low), H
exg does not act, but Hexg increases with an increase in σ, and Hexg exceeds Hcw near Tcw, and Tcw
In this case, both Hexg and Hcw become zero. Here, Hexg is the exchange energy (equivalent to the interface domain wall energy when the recording layer and the magnet layer are directly laminated without a photoconductive film), Ew is the magnetization of the recording layer, Msw is the film thickness of the recording layer. To d
If w, Hexg = Ew / (Msw × dw). For reference, H obtained from VSM temperature measurement of a comparative sample in which a recording layer without a photoconductive film and a magnet layer were directly laminated was used.
exg is also shown in FIG. It can be seen that the behavior of Hexg in a power region where σ reaches a large constant value is similar to Hexg, and that Hexg shows a smaller value than Hexg in a region where σ shows a small value. It has been proved from the characteristics of FIG. 3 that the recording principle of the present invention basically holds.

FIG. 4 is a diagram showing the thermomagnetic characteristics of the reproducing layer, the recording layer, and the magnet layer used in the medium of FIG. 1. FIG. 4A shows the temperature characteristics of the magnetization (Ms), and FIG. Is the coercive force (Hc)
Is the temperature characteristic. The magnetization means the magnetization in the perpendicular direction, and the in-plane magnetization is shown as zero. In FIG. 4, R represents a reproducing layer, W represents a recording layer, and P represents a magnet layer, Tcomp represents a compensation point, Tc represents a Curie point, and the suffixes of the respective symbols correspond to the reproducing layer, the recording layer, and the magnet layer. I have. The magnetic layers selected in this embodiment are all RE-TM films, but the RE-TM film is a ferrimagnetic film in which the sub-lattice magnetization of RE and the sub-lattice magnetization of TM are in opposite directions. At a low temperature, the sublattice magnetization of the RE is dominant, and the magnetization (Ms) of the net is aligned in the same direction as the RE magnetization, and the magnitude is the magnitude obtained by subtracting the TM magnetization from the RE magnetization. At the compensation point, the magnitudes of the RE magnetization and the TM magnetization match, and apparently Ms is zero. At a temperature higher than the compensation point, the TM magnetization becomes dominant, Ms is aligned in the same direction as the TM magnetization, and the magnitude thereof is obtained by subtracting the RE magnetization from the TM magnetization. At the Curie point, both RE magnetization and TM magnetization disappear. The compensation point and the Curie point can be controlled by the selection of the RE element and the TM element. The higher the RE composition ratio, the higher the compensation point. There is also a composition range up to the point. Curie point is RE
In the relationship of Gd>Tb> Dy, in TM, Co> F
e. Hc has a relationship of Tb>Dy> Gd in the RE. If the Gd is large, the perpendicular magnetic anisotropy is small (Hc is small), and the film is magnetized in-plane by the influence of the demagnetizing field except in the temperature range where Ms near the compensation point is small. That is why the characteristics of the reproducing layer are shown only in the vicinity of the compensation point in FIG. 3 (the transition region from the in-plane magnetization to the perpendicular magnetization is shown by a fine broken line).

The recording / reproducing method of the present invention will be described with reference to FIGS. The recording process is mainly in the photon mode as described above. That is, during irradiation of the recording light, a large amount of conduction electrons are generated in the photoconductive film in the portion having a large number of photons near the center of the spot, and the exchange magnetic field Hexg in that portion reduces the coercive force Hcw of the recording layer as shown in FIG. There is a leakage magnetic field applied from another layer to the recording layer in addition to Hexg, and an external magnetic field applied as necessary. Hexg is dominant, and the vector sum (effective magnetic field) of the magnetic field is large in the upward direction in FIG. When is equal to or higher than Hcw, the magnetization of the recording layer is aligned upward.
Since the recording mark size is determined in principle by the portion where σ of the photoconductive film increases during recording, it is determined by the Hexg characteristic and Hcw characteristic caused by σ, and a mark smaller than the FWHM of the laser spot can be formed. As a result, high density recording is realized.

The erasing process is simple in a non-overwrite embodiment in which an external magnetic field is changed between recording and erasing. In erasing, a larger external magnetic field is simply applied downward than during recording, and the recording layer is moved near the Curie point. What is necessary is just to make the effective magnetic field applied to the area heated in the downward direction downward. In the non-overwrite type, the reproducing layer, the recording layer, and the magnet layer have a high degree of freedom in their thermomagnetic properties. In performing the light modulation overwrite using the same external magnetic field during recording and erasing, it is necessary to control the effective magnetic field with power. In this case, in particular, a leakage magnetic field applied to the recording layer from another layer is used, so it is necessary to design the thermomagnetic characteristics of the other magnetic layer according to the characteristics of the recording layer. In the characteristic of FIG. 4, a leakage magnetic field mainly generated from the magnet layer can be used. At room temperature, the direction of magnetization of the magnet layer is uniform and does not supply a leakage magnetic field to the outside of the film. However, if a spatial distribution of magnetization is formed by heating, a leakage magnetic field is generated outside the film. When the magnet layer magnetized upward as shown in FIG. 1 is locally heated by the laser beam, the magnetization Msp of the heating portion is lower than the surroundings from the characteristics of FIG. 4, and apparently reverses at Tcompp or more. It should be noted here that the direction of Msp is apparently reversed,
Since the directions of the magnetizations of E and TM are not changed, the direction of the exchange magnetic field remains upward before and after the compensation point. This Ms
A leakage magnetic field is generated downward from the magnet layer according to the spatial distribution of p and is applied to the recording layer. There are various variations in the setting of the erasing power level. For example, when power modulation of the effective magnetic field is performed by using the temperature difference of each layer,
There is an embodiment in which the erasing power is set higher than the recording power. The recording layer is closer to the light beam incident side than the magnet layer, and the photoconductive layer between the recording layer and the magnet layer thermally acts as a temperature difference forming layer. Sometimes, the temperature of the recording layer is set higher than the temperature of the magnet layer, and in the cooling process, the temperatures of the recording layer and the magnet layer can be made almost the same due to thermal diffusion between the layers. Therefore, if the recording power is set lower than the erasing power, during recording, when the recording layer is near Tcw, the magnet layer is at a temperature lower than Tcw and the leakage magnetic field is small, and the exchange magnetic field is more dominant than the leakage magnetic field. The recording layer is magnetized upward, and when erasing,
When the recording layer is near Tcw (when cooled from a higher temperature), the magnet layer is at a temperature where the leakage magnetic field is larger than during recording near Tcw, and the recording layer is dominant in the leakage magnetic field rather than the exchange magnetic field. It can be magnetized downward. In addition to utilizing the temperature difference, the fact that the recording layer has a finite time for the magnetization reversal of the recording layer makes use of the fact that there is a difference in the time that the recording layer passes through the magnetization reversal temperature zone near the Curie point between recording and erasing. However, light modulation overwriting can be achieved.

Next, the reproducing process of the present invention will be described with reference to FIGS. The reproducing layer may or may not be a film having an in-plane magnetization near room temperature as in the present embodiment. The reproducing layer is vertically magnetized in a temperature range where the MsR near the compensation point TcompR is small, and is aligned with the magnetization of the recording layer. When the recording layer and the reproducing layer are directly laminated, an exchange force acts between the kilo-layer and the reproducing layer. Therefore, in the temperature range where the reproducing layer is perpendicularly magnetized, the magnetization of the reproducing layer is exchanged from the recording layer. When the magnetization direction of the recording layer is aligned by the magnetic field, and a non-magnetic layer is interposed between the reproducing layer and the recording layer as shown in FIG. 1, a leakage magnetic field corresponding to the magnetization distribution of the recording layer acts on the reproducing layer. Then, the magnetization of the reproducing layer is also aligned with the magnetization of the recording layer due to the leakage magnetic field. In any case, since the portion not irradiated with light does not contribute to magneto-optical reproduction based on the Kerr effect due to in-plane magnetization, the magnetization of the recording layer is transferred only to the reproduction light irradiated portion. Although the size of the transfer area depends on the thermomagnetic characteristics of the reproducing layer and the exchange magnetic field or the leakage magnetic field from the recording layer, the transfer area can be made smaller than the laser spot size. High resolution playback (MSR playback). Also, the domain wall energy as the reproducing layer is smaller than the demagnetizing field energy,
Further, when a film material having a high domain wall moving speed is used, a minute mark transferred from the recording layer to the reproducing layer is enlarged in the reproducing layer and has a high C value.
/ N reproduction.

The above-mentioned recording / reproducing process was verified by a disk operation, and for the purpose of clarifying the effect of the present invention, the disk of the first embodiment was installed in a prototype experimental drive to perform a recording / reproducing operation. The experimental drive is an experimental device for optical modulation recording using an AOM modulator having an Ar ion laser as a light source. The spot size on the medium surface is:
The FWHM related to recording is 0.38 μm, and the e-2 diameter related to reproduction is 0.68 μm.

In a recording apparatus having this spot size, in a normal magneto-optical recording medium having only an RE-TM recording layer as a magnetic layer, a recording mark length at which a value of 45 dB or more is obtained as a reproduction C / N is 0.35 μm. As described above, when the track pitch is 0.46 μm or more, recording of a mark smaller than this is unstable without a power margin, and when the mark pitch is narrowed from the above value at a recording power capable of obtaining a stable mark size. The influence of intersymbol interference and crosstalk was large, and C / N was significantly degraded. Naturally, when using a conventional magneto-optical recording medium, optical modulation overwriting was not possible, and it was necessary to apply an external magnetic field in the opposite direction to the recording to erase the data at the time of erasing. . Furthermore, since the recording data transfer speed is limited by the thermal response of the medium, increasing the linear velocity to about 15 m / s or more causes a decrease in recording sensitivity and a deterioration in C / N due to the influence of thermal interference.

On the other hand, in the magneto-optical recording medium of the present invention, even when the GdFe-MSR film of Example 1 is employed as the reproducing layer, the recording mark length at which a value of 45 dB is obtained as the reproducing C / N is 0.25 μm. , Track pitch 0.2
It could be reduced to 5 μm. If the composition ratio of the reproduction layer is adjusted to enable enlarged reproduction (MAMMOS) after transfer, the mark length and track pitch indicating C / N: 45 dB can both be further reduced to 0.2 μm. . These numerical values are values obtained by linear velocity: 15 m / s and light modulation overwriting. Further, the recording principle of the present invention is that, because the high-speed photon mode process is dominant, good recording sensitivity and high C / N were obtained even when the linear velocity was increased to 30 m / s. Here, the recording / erasing / reproducing power is optimized based on the C / N, the erasing rate, etc.
At m / s, they were 12/6/2 mW, respectively. As a result of optimizing the DC external magnetic field, it was necessary to apply a magnetic field of about 200 Oe downward in FIG. [Embodiment 2] In the above embodiment, CuO having photoconductivity at a relatively short wavelength was selected as a photoconductive film, and ArO having a wavelength of 488 nm was selected.
An example in which the effect of the present invention was verified using an experimental machine using an ion laser was described. In this embodiment, a red LD having a wavelength of 650 nm is used.
Tried a practical operation in. FIG. 2 shows the configuration of the magneto-optical recording medium used in the second embodiment. In FIG. 2, 21 is a reproducing layer, 22 is a recording layer, 23 is a photoconductive layer, 24 is a magnet layer, 25 is a substrate, 26 is an interference layer, 27 is a gate layer, 28
A protective layer, 29 is a lower barrier layer, and 210 is an upper barrier layer. The structural difference from the first embodiment is that the nonmagnetic intermediate layer 17
Instead of using a gate layer 27 having an in-plane magnetization, the recording layer and the reproducing layer were exchange-coupled through the gate layer, and a barrier layer was used at two interfaces between the photoconductive layer, the recording layer, and the magnet layer. Is a point. In Example 2, the thickness of the reproducing layer was 25 nm.
GdDyFeCo film, 60 nm thick T as a recording layer
bFeCo film, 100 nm-thick amorphous Si film (optical gap: 1.2 eV) as a photoconductive layer, 50 nm-thick GdTbFeCo film as a magnet layer, 10 nm-thick GdDyFe film as a gate layer, upper and lower barrier layers Used are TiN films each having a thickness of 10 nm.

In this embodiment, since a long-wavelength-sensitive amorphous Si is used as the photoconductive film, if there is no barrier layer, an Fe silicide layer is formed at the interface between Si and the magnetic layer.
The exchange magnetic field acting between the recording layer and the magnet layer was reduced (compared to a sample in which the recording layer and the magnet layer were directly laminated). When the barrier layer was provided, no decrease in the exchange magnetic field was observed. As the barrier layer, any conductive material may be used,
Those having low reactivity to the semiconductor and the magnetic material are preferable, and ITO other than TiN used in this embodiment is preferable. When ITO is used, since the ITO transmits light, the photoconductive characteristics of the photoconductive film are not impaired even if the lower barrier layer is thickened.

As the substrate, a polycarbonate substrate provided with the same groove (groove for tracking guide) as in Example 1 was used. The interference layer and the protective layer were the same as those in Example 1, and the disk samples were formed by the magnetron sputtering method as in Example 1. The relationship between the photoconductivity measured by irradiating a light beam with a wavelength of 650 nm, the exchange magnetic field acting between the recording layer and the magnet layer during photoconduction, and the coercive force of the recording layer is the same as that shown in FIG. showed that.

FIG. 5 shows the thermomagnetic characteristics of the reproducing layer and the gate layer. The recording layer and the magnet layer exhibited the same characteristics as in Example 1.
FIG. 5A shows the temperature characteristic of the magnetization Ms in the vertical direction.
[B] is the temperature characteristic of the coercive force Hc. Both the reproducing layer and the gate layer used in the present embodiment are magnetized in-plane near room temperature Ta, and the magnetization decreases with heating, the perpendicular magnetic anisotropy is developed, and the state shifts to the perpendicular magnetization state. The reproducing layer used in Example 1 had perpendicular magnetization only near the compensation point, but the reproducing layer and the gate layer used in Example 2 maintained perpendicular magnetization between the compensation point and the Curie point. The difference between these characteristics is that the reproducing layer is made of the material of Example 1 and the reproducing layer is made of Dy, G
This was obtained due to the addition of d. The Curie point TcR of the reproducing layer was set to a value close to that of the recording layer Tcw, and the Curie point of the gate layer was set to a value lower than Tcw.

Since the details of the recording / reproducing process have been described in the first embodiment, only the parts different from the first embodiment will be described here. In the first embodiment, in the erasing operation, only the magnet layer applies the leakage magnetic field in the erasing direction to the recording layer. Therefore, it is necessary to apply an external magnetic field of 200 Oe to the erasing side in order to obtain a sufficient erasing ratio. Was. Since the external magnetic field in the erasing direction is continuously applied even during recording in the light modulation overwrite operation, the external magnetic field has an effect of reducing the effective recording magnetic field. In the second embodiment, the film for applying the leakage magnetic field in the erasing direction to the recording layer includes a reproducing layer in addition to the magnet layer. Basically, the reproducing layer is heated to a relatively low temperature of Hc before and after the compensation point at the reproducing power level, and the heating section exchange-couples with the recording layer via the gate layer to form the minute recording magnetic domain in the recording layer. It has the function of transferring and expanding and reproducing. An additional effect of the reproducing layer is the above-described generation of a stray magnetic field to the recording layer. When the recording layer is in the temperature range where the magnetization can be reversed near the Curie point at the time of irradiating light at the erasing power level, the reproducing layer still has a perpendicular magnetization orientation near the Curie point for most of the heated region. On the other hand, since the heating portion of the gate layer is heated above the Curie point, no exchange magnetic field acts between the recording layer and the reproducing layer. Therefore, the magnetization of the heating portion of the reproducing layer is aligned with the direction of the leakage magnetic field from the magnet layer or the relatively small downward external magnetic field applied as necessary. The spatial distribution of the magnetization of the reproducing layer is such that the cooling portion is in-plane in the cooling portion and the heating portion is in the downward direction. Therefore, a downward or erasing-oriented leakage magnetic field is applied to the recording layer to assist the erasing process. Since the power of the recording process is different from that of the erasing process, the difference in the temperature difference between each layer between the heating process and the cooling process, and the difference in the time during which the recording layer passes through the temperature zone where the magnetization can be reversed can be used. In the recording process, the erasing magnetic field applied from the reproducing layer to the recording layer is set smaller than in the erasing process. The same can be said for the leakage magnetic field from the magnet layer as described in Example 1.

The above-described recording / reproducing process was verified by disk operation, and for the purpose of clarifying the effect of the present invention, the disk of Example 2 was installed in an experimental magneto-optical drive in the optical modulation overwrite mode to perform the recording / reproducing operation. went. Light source is wavelength 6
With a 50 nm LD, the spot size on the medium surface is 0.5 μm for FWHM related to recording, and e
-2 diameter is 0.9 μm.

In a recording apparatus having this spot size, in a normal magneto-optical recording medium having only a RE-TM recording layer as a magnetic layer, a recording mark length at which a value of 45 dB or more is obtained as a reproduction C / N is 0.42 μm. As described above, when the track pitch is 0.6 μm or more, recording of a mark smaller than this is unstable without a power margin, and when the mark pitch is narrowed from the above value at the recording power at which a stable mark size is obtained. The influence of intersymbol interference and crosstalk was large, and C / N was significantly degraded. Naturally, when using a conventional magneto-optical recording medium, optical modulation overwriting was not possible, and it was necessary to apply an external magnetic field in the opposite direction to the recording to erase the data at the time of erasing. . Furthermore, since the recording data transfer speed is limited by the thermal response of the medium, increasing the linear velocity to about 15 m / s or more causes a decrease in recording sensitivity and a deterioration in C / N due to the influence of thermal interference.

On the other hand, in the magneto-optical recording medium of the present invention, the recording mark length at which a value of 45 dB was obtained as the reproduction C / N was reduced to 0.27 μm, and the track pitch was reduced to 0.27 μm. This is the wavelength of 488 nm used in Example 1.
In other words, it can be said that the medium of the second embodiment can substantially perform higher-density recording than the medium of the first embodiment. The above value is the linear velocity: 15m /
s is a value obtained by light modulation overwriting. Further, the recording principle of the present invention is that, because the high-speed photon mode process is dominant, good recording sensitivity and high C / N were obtained even when the linear velocity was increased to 30 m / s. here,
The recording / erasing / reproducing power was optimized on the basis of C / N, erasing rate, etc., and was 12/6/2 mW at a linear velocity of 15 m / s. As a result of optimizing the DC external magnetic field, in order to obtain a sufficient erasing ratio, 50-1 in the downward direction in FIG.
It is sufficient to apply a magnetic field of about 00 Oe. In Example 2, it was proved that a leakage magnetic field for erasing was applied from the reproducing layer to the recording layer in the erasing process.

In Embodiments 1 and 2 described above, an example was described in which a film having in-plane magnetization at room temperature was used as a reproducing layer. However, the reproducing layer may have perpendicular magnetization at room temperature. As shown in the above, a magnetic multilayer structure may be formed. The material of the magnetic film, the material of the photoconductive film, the material of the barrier film, the material of the interference film, and the material of the protective film can be widely selected without departing from the gist of the present invention. The present invention is basically based on conduction electrons generated in a photoconductive layer by irradiation of recording light, so that at least two magnetic films above and below a photoconductive film exert an exchange interaction and a recording mark smaller than a spot size is formed. A magneto-optical recording medium, a magneto-optical recording / reproducing method, a magneto-optical recording / reproducing method, which reproduces the small recording mark with high resolution and high C / N by magnetizing transcription from the recording layer to the reproducing layer or by magnetizing transcription and magnetic domain expansion. A recording / reproducing apparatus is provided, and a number of modified examples other than the embodiment can be given.

[0037]

According to the present invention, a record mark array smaller than the light spot size can be recorded at a high speed.
Since a fine recording mark array can be reproduced with a high resolution and a high C / N, a remarkable improvement in the recording surface density and storage capacity of the magneto-optical recording system and an increase in the data transfer speed can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional configuration view of a first embodiment of a magneto-optical recording medium according to the present invention.

FIG. 2 is a sectional configuration diagram of a second embodiment of the magneto-optical recording medium of the present invention.

FIG. 3 is a diagram illustrating a recording process of the present invention.

FIG. 4 shows an example of thermomagnetic characteristics of each layer used in the first embodiment of the magneto-optical recording medium of the present invention.

FIG. 5 is an example of the thermomagnetic characteristics of each layer used in the second embodiment of the magneto-optical recording medium of the present invention.

[Explanation of symbols]

 11: reproducing layer, 12: recording layer, 13: photoconductive layer, 14: magnet layer, 15: substrate, 16: interference layer, 17: non-magnetic intermediate layer, 18: protective layer, 21: reproducing layer, 22: recording Layer, 23: photoconductive layer, 24: magnet layer, 25: substrate, 26: interference layer, 27: gate layer, 28: protective layer, 29: lower barrier layer, 210: upper barrier layer

Claims (8)

[Claims] 1. A magneto-optical recording medium comprising a reproducing magnetic layer, a recording magnetic layer, a photoconductive layer, and a magnet layer laminated in this order from the light beam incident side. 2. The method according to claim 1, wherein a conductive layer is provided on at least one interface selected between the recording magnetic layer and the photoconductive layer and between the photoconductive layer and the magnet layer. 3. The magneto-optical recording medium according to claim 1. 3. The light according to claim 1, wherein the magnet layer is uniformly magnetized in the same direction perpendicular to the film surface at the memory holding temperature. Magnetic recording medium. 4. The reproducing magnetic layer has a memory holding temperature,
3. The method according to claim 1, wherein the surface is magnetized.
The magneto-optical recording medium according to any one of [2] and [3]. 5. Claims [1], [2], [3] and [4]
Irradiates the magneto-optical recording medium described in any of the above with a light beam of a recording power level, switches the photoconductive layer of the irradiated portion to conductive, and exchanges the recording magnetic layer and the magnet layer through conduction electrons. Then, recording is performed by aligning the direction of magnetization of the recording magnetic layer with the direction of magnetization of the magnet layer, and irradiating the magneto-optical recording medium with a light beam having a reproduction power level, thereby changing the magnetization of the recording magnetic layer of the irradiated portion. A magneto-optical recording / reproducing method, wherein reproduction is performed by transferring the data to a reproducing magnetic layer. 6. The magneto-optical recording / reproducing method according to claim 5, wherein the magnetic domain transferred to the reproducing magnetic layer is reproduced while being enlarged. 7. The erasing operation is performed by irradiating a light beam having an erasing power level and applying a magnetic field in a direction opposite to a direction of an exchange magnetic field applied at the time of recording to the recording magnetic layer. The magneto-optical recording / reproducing method according to any one of claims [5] and [6]. 8. Claims [1], [2], [3], [4]
Irradiates the magneto-optical recording medium described in any of the above with a light beam of a recording power level, switches the photoconductive layer of the irradiated portion to conductive, and exchanges the recording magnetic layer and the magnet layer through conduction electrons. Then, recording is performed by aligning the direction of magnetization of the recording magnetic layer with the direction of magnetization of the magnet layer, and irradiating the magneto-optical recording medium with a light beam having a reproduction power level, thereby changing the magnetization of the recording magnetic layer of the irradiated portion. A magneto-optical recording / reproducing apparatus characterized in that reproduction is performed by transferring to a reproducing magnetic layer.