Magneto-optical recording medium having a transfer control layer

A magneto-optical recording medium, including a recording layer, a transfer control layer magnetically coupled to the recording layer, and a reproduction layer. The recording layer includes a recording magnetic domain in which information is recorded by a magnetization direction vertical to the surface of the film. The reproduction layer includes a reproduction magnetic domain in which information in the recording layer is transferred and formed as a magnetization direction by magnetic coupling. The direction of magnetization of the recording magnetic domain of the recording layer and the direction of magnetization of the transfer control layer corresponding to the recording magnetic domain are in opposite directions in at least part of the range of temperatures less than a transfer temperature where the reproduction magnetic domain is transferred to the reproduction layer. The Curie point temperature of the transfer control layer is higher than this transfer temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magneto-optical recording medium and reproducing method thereof to carry out recording and reproducing information by using a laser light by applying a magneto-optical effect, more specifically relates to the magneto-optical recording medium and reproducing method thereof to make a high density recording signal possible.

2. Related Art of the Invention

In magneto-optical recording being a high density, writable, recording and reproducing method, a part of layered magnetic films (a recording film structure) of a magneto-optical recording medium is locally heated to a Curie temperature or a temperature above a compensation temperature by radiating laser light, and an information signal is recorded in a predetermined part of the magnetic film contained in the recording film structure by forming a recordable magnetic domain in an external magnetic field, and this information is read by using a magneto-optical effect.

One of such magneto-optical recording system for the magneto-optical recording medium is the magnetic field modulation recording system. In this system, thermal magnetic recording is performed in a predetermined part by using an external magnetic field of which direction has been modulated according to a recording signal after raising entirely the temperature of a recording magnetic film by radiating a laser light of a certain strength using a semiconductor laser or the like. The other of the recording system is the light intensity modulation recording system. In this system, thermal magnetic recording is performed in the direction of the external magnetic field by raising the temperature of the recording magnetic film of a predetermined part by radiating the laser light which has been modulated according to the strength of the recording signal, applying the external magnetic field of a certain strength.

At the time of reproducing the recorded signal, when the laser light (reproducing light) of which polarization direction is arranged to be identical, is condensed on the magneto-optical recording medium, the direction of magnetization of recording magnetic domain is detected as the rotation of the polarization direction of the reflected light or transmitted light by a magneto-optical effect caused by the magneto-optical recording medium. By this effect, the information signal recorded is reproduced.

However, in the conventional magneto-optical recording medium, when the size of the recording magnetic domain becomes smaller than that of the light spot (reproducing-light spot) of a reproducing light on the magneto-optical recording medium, not only the recording magnetic domain to be reproduced, but also the recording magnetic domain located in front and back of the position becomes contained in the reproducing-light spot, i.e., a detection range. Therefore, some problems occur exemplified as follows: the reproducing signal becomes small to lower an S/N ratio or the reproducing signal is not outputted, because of an interference by those recording magnetic domains.

To solve these problems, a magnetic field modulation recording system using magnetically induced super resolution has been proposed to read the reproducing signal from a part of domain of the reproducing-light spot.

(I) The following is a description of a magneto-optical record reproducing system by using the magnetically induced super resolution named a double mask system which is a system of the magnetically induced super resolution.

FIG. 12shows a configuration in reproducing by the double mask system.FIG. 12(A)is a plane view of showing a part of track of the magneto-optical recording medium60in the conventional double mask system.12(B) is a sectional view showing the configuration (particularly the direction of magnetization) of a recording film structure of the magneto-optical recording medium60.

As shown in the sectional view ofFIG. 12(B), the recording film structure of the magneto-optical recording medium60is configured by including a reproduction layer63, a reproduction supporting layer64, a middle layer65, and a recording layer66, which are layered on a substrate (not illustrated) in order. An arrow160shown in theFIG. 12(B)is a movement direction along with the track of the magneto-optical recording medium60. Arrows illustrated in respective layers63to66are show directions of magnetization in respective positions.

This conventional magneto-optical recording medium60requires reproducing magnetic field generating means61applied to the domain of the reproducing-light spot67, initialized magnetic field generation means62located in the frontal position of the reproduction magnetic field generating means61in the movement direction160. Hereafter, reference numerals61and62are used for a description of a reproducing operation of generated magnetic field generated by the reproducing magnetic field generating means61and an initialized magnetic field generated by the initialized magnetic field generation means62, respectively. The following is the magneto-optical recording medium60of the double mask system configured by such manner.

First, a signal (information) is previously recorded by thermal magnetization as the recording magnetic domain69in the recording layer66. Before the laser light is radiated in reproducing, the direction of magnetization of the reproduction layer63is arranged in the direction of the initialized magnetic field62. At the time of reproducing, as shown in theFIG. 12(A), the reproducing laser light is radiated to the rotating magneto-optical recording medium60to make the reproducing-light spot67and raise a temperature of the recording film structure. According to this step, the distribution of temperatures as shown in theFIG. 12(A)occurs on the magneto-optical recording medium60to form a low temperature region71, a high temperature region72, and a intermediate temperature region70.

The direction of magnetization of the reproduction layer63in the low temperature region71near a room temperature is arranged in the direction of the initialized magnetic field62by blocking of a exchange coupling between the reproduction layer63and the recording layer66by the middle layer65. In the intermediate temperature region70, the exchange coupling between the reproduction layer63and the recording layer66becomes dominant by decrease in coercive force of the reproduction layer63according to temperature rise caused by radiation of the reproducing laser light and also by transition of the middle layer65from a in-plane magnetized film having in-plane magnetic anisotropy to a perpendicular magnetized film having perpendicular magnetic anisotropy. Therefore, The direction of magnetization of the reproduction layer63is arranged in the direction of magnetization of the recording layer66.

In the high temperature region72of the reproduction supporting layer64becoming a Curie temperature Tc, the exchange coupling between the reproduction layer63, the middle layer65, and the recording layer66is blocked by extinction of magnetization of the reproduction supporting layer64to arrange the direction of magnetization of the reproduction layer63, of which coercive force is small, to the direction of the reproducing magnetic field61. Therefore, a recording magnetic domain69is masked by both the low temperature region71and the high temperature region72inside the reproducing-light spot67and information can be read as a reproducing signal through the reflected light from only the recording magnetic domain69presented in the intermediate temperature region70.

The direction of the reproducing magnetic field61is an opposite direction to the initialized magnetic field62. After the reproducing-light spot67passed, the temperature of the recording layer66dropped again and the recording layer66and the reproduction layer63are blocked again by the middle layer65.

According to such magneto-optical recording medium60, even in a smaller recording magnetic domain69than the reproducing-light spot67, recorded information can be reproduced with a high density without occurrence of interference by frontal and back recording magnetic domain69.

However, the above described magneto-optical recording medium60has a defect in that the initialized magnetic field62or the reproducing magnetic field61are required to arrange the magnetization direction of the reproduction layer63to an identical direction.

Thus, a reproducing method has been proposed by using a magnetically induced super resolution to solve the above described defect.

As a method unnecessary of the initialized magnetic field or the reproducing magnetic field, a method proposed in Japanese Patent Laid-Open No. 5-81717 will be described below with reference to drawings13(A) and13(B). TheFIG. 13(A)is the planeview showing a part of the track of the magneto-optical recording medium80disclosed in the above described publication and13(B) is a sectional view showing the configuration of the recording film structure (particularly of the direction of magnetization) of the magneto-optical recording medium80.

As shown in the sectional view of theFIG. 13(B), the magneto-optical recording medium80has the recording film structure containing a reproduction layer83and recording layer85formed on the substrate (not illustrated). A middle layer84is put between the reproduction layer83and the recording layer85. The arrow180shown in theFIG. 13(A)shows the movement direction along with the track of the magneto-optical recording medium80. Arrows illustrated in respective layers83and85of theFIG. 13(B)show the magnetization direction in respective positions. In the magneto-optical recording medium80, differing from the magneto-optical recording medium60previously described, the magnetic film having in-plane magnetic anisotropy is used as the reproduction layer83at room temperature.

As same as the magneto-optical recording medium60, the reproducing-light spot87is formed by radiating the reproducing laser light in reproducing information of the magneto-optical recording medium80. When the reproducing laser light is radiated to the magneto-optical recording medium80during rotation, the temperature distribution of the recording film structure containing a reproduction layer83and recording layer85does not form rotation symmetry to the center of the circle of the reproducing-light spot87. A radiated part of the reproducing-light spot87and the right-hand end of the back of the reproducing-light spot87become the high temperature region90. The external part, included in the reproducing-light spot87, of the high temperature region90becomes the low temperature region91.

Followings are description of reproducing operation of the magneto-optical recording medium80configured as described above.

The recorded information is previously recorded in the recording layer85as a recording magnetic domain89smaller than the reproducing-light spot87by the thermal magnetic recording. The reproduction layer83is the in-plane magnetized film at room temperature and is the magnetic film having characteristic of becoming the perpendicular magnetized film only in the part of the high temperature region90inside the reproducing-light spot87. The high temperature region90and the low temperature region91are formed by temperature rise caused by radiation of the reproducing laser light. In the high temperature region90, the reproduction layer83changes to the perpendicular magnetized film and is arranged to the magnetization direction of the recording layer85by magnetic coupling through the intermediate layer84. The reproduction layer83changes again to the in-plane magnetized film by drop of temperature caused by movement of the magneto-optical recording medium80. Therefore, the reproduction layer83(the in-plane magnetized film) in the low temperature region91inside the reproducing-light spot87works as a mask and the recording magnetic domain89of the recording layer85is transferred only from the high temperature region90of the reproducing-light spot87. Thus, the signal of a recording mark (the recording magnetic domain89) smaller than the reproducing-light spot87can be detected.

According to the steps described above, in the magneto-optical recording medium80, information of the recording magnetic domain89smaller than the reproducing-light spot87can be reproduced without the use of the initialized magnetic field and the reproduction magnetic field.

In the above described magneto-optical recording medium80by using the in-plane magnetized film in the reproduction layer83, there is an effect of capability of making the initialized magnetic field and the reproducing magnetic field unnecessary, however, there is the following defect.

First, the direction of magnetization of the reproduction layer83is attracted to the direction of the magnetization of the recording layer85by magnetic interaction between the reproduction layer83and the recording layer85even in the low temperature region91masked. Therefore, an ideal surface magnetizing direction is not maintained resulting in having a vertical component of magnetization. Resultingly, transfer occurs in a domain unnecessary of transfer of the recording magnetic domain89to cause a deficiency of resolution and a noise in reproducing.

Second, variation of the power of the reproducing laser light (a reproducing power) changes a region, to which the recording magnetic domain89is transferred, to deteriorate reproducing characteristic by the wave form interference of a transfer domain, because a critical temperature, in which the reproduction layer83changes from the in-plane magnetized film to the perpendicular magnetized film, is constant.

In addition, change of an ambient temperature such as the temperature in a drive and the like requires change of setting of reproducing power. However, in the case where particularly the ambient temperature rises, requires reducing the reproducing power to decrease in temperature difference between the critical temperature and the room temperature capable of transfer of the signal of the recording layer85. As the result, the region (the low temperature region91) masked by the reproduction layer83, that has become the in-plane magnetized film, reduces. Therefore, there are problems in which the reproducing signal is deteriorated by decrease in resolution and the signal transfer in the recording layer85becomes insufficient.

In other words, the high temperature region varies according to variation of the above described variation of reproducing power and the above described variation of ambient temperature.

(II) On the other hand, in the magneto-optical recording medium by using the above described magnetically induced super resolution system, a rare earth-transition metal alloy is mainly used for the magnetic layer.

FIG. 27shows the vertical component of a magnetic moment of the sub-lattice of the transition metal in the magneto-optical recording medium by using the magnetically induced super resolution system based on the conventional art. Arrows1300and1400in a first magnetic layer1100and a second magnetic layer1200represent the vertical components of the magnetic moments of the sub-lattices of the transition metals of the first magnetic layer1100and the second magnetic layer1200, respectively.

The first magnetic layer1100is the in-plane magnetized film at room temperature and changes from the in-plane magnetized film to the perpendicular magnetized film according to temperature rise. The second magnetic layer1200is a film consisting of such as TbFeCo and DyFeCo and having a large perpendicular magnetic anisotropy at room temperature. Recorded information is kept depending on upward or downward direction of the magnetizing domain of this second magnetic layer1200toward the surface of the film.

When a light beam is radiated from the substrate side to the magneto-optical recording medium with the above described configuration, a temperature gradient occurs in a beam spot1700to present a region of a high temperature and a region of a low temperature. In this condition, the first magnetic layer1100does not contribute to pole Kerr effect to the utmost because it becomes the in-plane magnetized film and the recorded information stored in this second magnetic layer1200is masked to disappear, in the region of the low temperature in the beam spot1700.

On the other hand, in the region of the high temperature in the beam spot1700, the magnetically induced super resolution is realized by that the first magnetic layer1100becomes the perpendicular magnetized film to cause a magnetostatic coupling with the second magnetic layer1200. Therefore, Information stored in recorded in the second magnetic layer1200is transferred to the first magnetic layer1100.

As a whole of the beam spot1700, the magnetically induced super resolution is realized by that recorded information in the second magnetic layer1200is transferred to a smaller region in comparison with the size of the beam spot1700, because of a part masked by the first magnetic layer1100.

The magneto-optical recording medium by using such magnetically induced super resolution system can satisfy requirement of high density by a narrowed track. In the above described configuration, a transition region occurs as an intermediate condition to change from the in-plane magnetized film to the perpendicular magnetized film in the beam spot1700. Namely, a whole film does not change abruptly from the in-plane magnetized film to the perpendicular magnetized film in a predetermined temperature, but a certain range of temperature becomes transition region.

In the transition region, the first magnetic layer has not become a perfect in-plane magnetized film and perfect masking of the recorded information kept by the second magnetic layer is impossible. On the contrary, the first magnetic layer is not a perfect perpendicular magnetized film in the transition region and a magnetostatic coupling force with the second magnetic layer is small to be difficult to yield a large signal.

Therefore, the first magnetic layer in the transition region cannot mask sufficiently the recorded information kept by the second magnetic layer to increase cross talk from an adjacent track. In addition, the first magnetic layer in the transition region has a weak magnetostatic coupling force with the second magnetic layer to make sufficient transfer of the recorded information from the second magnetic layer impossible.

Furthermore, the first magnetic layer is frequently prepared by using a material, a rare earth metal generally expensive. This makes the cost of material high in the case where the magnetic layer is prepared thick and productivity is worsen. Thus, a cheap magneto-optical recording medium is difficult to be provided.

SUMMARY OF THE INVENTION

(I) The present invention was created in consideration of the problem in that the high temperature region varies according to the variation of the above described reproducing power and the variation of the above described ambient temperature. The objects thereof were (1) to provide a magneto-optical recording medium having reproducing characteristics of high resolution and high performance, in which two incompatible characteristics, the stable magnetically induced super resolution masking characteristic and the transfer performance of a recording signal to a reproduction layer, can be simultaneously improved, even when the ambient temperature varies, and (2) to provide a reproducing method of the magneto-optical recording medium suitable for a high density recording by using the above described magneto-optical recording medium.

A magneto-optical recording medium according to one aspect of the present invention comprises:

a recording layer having a recording magnetic domain in which information is recorded according to a magnetization direction vertical to a surface of a film;

a reproduction layer in which information recorded in said recording layer is transferred and formed as a reproduction magnetic domain of the magnetization direction vertical to the surface of the film by magnetic coupling; and

a transfer control layer magnetically coupled to said recording layer,

wherein a direction of magnetization of said recording layer and the direction of magnetization of said transfer control layer corresponding to said recording layer are in opposite direction in a part of temperature range less than a temperature in which said reproduction magnetic domain is transferred to said reproduction layer, and

said transfer control layer becomes a Curie point or higher in at least a part of temperature range higher than said transfer temperature.

A magneto-optical recording medium according to the another aspect of the present invention comprises:

a recording layer having a recording magnetic domain in which information is recorded according to a magnetization direction vertical to a surface of a film;

a reproduction layer in which information recorded in said recording layer is transferred and formed as a reproduction magnetic domain of the magnetization direction vertical to the surface of the film by magnetic coupling; and

a transfer control layer magnetically coupled to said recording layer,

wherein a direction of magnetization of said recording layer and the direction of magnetization of said transfer control layer corresponding to said recording layer are opposite directions in a part of temperature range less than a temperature in which said reproduction magnetic domain is transferred to said reproduction layer, and

the direction of magnetization of said recording layer and the direction of magnetization of said transfer control layer corresponding to said recording layer are coincide in at least a part of temperature range higher than said transfer temperature.

The magneto-optical recording medium according to still another aspect of the above present invention is characterized in that

the direction of magnetization of said recording layer and the direction of magnetization of said transfer control layer corresponding to said recording layer are in opposite directions in the temperature range less than said transfer temperature.

The magneto-optical recording medium according to any one of the above present invention is characterized in that a domain enlarged layer having a shrinking function is formed on said reproduction layer.

Particularly, according to this configuration, even the magneto-optical recording medium including an reproducing expansion layer of the magnetic domain having a characteristic of performing a magnetic wall movement in an area near a transfer temperature at a shrinking action or a reproducing operation of the reproduction magnetic domain (transfer domain), can perform smoothly transfer of the reproducing signal and form the reproduction magnetic domain (transfer domain) enlarged than the recording magnetic domain of the recording layer to transfer and read.

The Curie temperature of the above described transfer control layer may be at least lower than the Curie temperature of either the above described recording layer or the above described reproduction layer. According to this, the magnitude of the magnetostatic field can be abruptly increased for transferring the signal of the recording layer to the reproduction layer.

Alternatively, the Curie temperature of the above described transfer control layer may be lower than the compensation temperature of the above described reproduction layer. Further, the compensation temperature of the above described transfer control layer may be lower than the compensation temperature of the above described reproduction layer. By this, the reproduction magnetic domain transferred to the reproduction layer can be stably detected.

Alternatively, the above described transfer control layer may be put far from a light incident surface in comparison with the above described recording layer.

Alternatively, an intermediate layer made of a nonmagnetic material may be further put between the above described reproduction layer and the above described recording layer.

Alternatively, a layer made of an dielectric material may be further put as the intermediate layer made of the above described nonmagnetic material. By this, the recording magnetic domain can be effectively transferred and read by the magnetostatic field from the recording layer to the reproduction layer.

Alternatively, the intermediate layer made of a magnetic material and having the Curie temperature lower than both the Curie temperature of the above described reproduction layer and the Curie temperature of the above described recording layer may be put between the above described reproduction layer and the above described recording layer. By this, the masking effect of the reproduction layer or the transfer characteristic of the recording magnetic domain can be improved by using the magnetic exchange coupling force between the recording layer and the reproduction layer.

Alternatively, the above described recording layer may have the compensation temperature between the room temperature and the transfer temperature.

Alternatively, an heat sink layer made of a metal may be further formed. By this, temperature distribution for the recording film can be controlled to yield a transferred and reproduced signal of the higher signal quality.

A magneto-optical recording medium according to yet another aspect of the present invention comprises:

a recording layer having a recording magnetic domain in which information is recorded according to a magnetization direction vertical to a surface of a film;

a reproduction layer in which information recorded in said recording layer is transferred as a reproduction magnetic domain of the magnetization direction vertical to the surface of the film; and

a transfer control layer magnetically coupled to said recording layer,

wherein the magneto-optical recording medium is configured to have a region which becomes a critical temperature in which magnetization of said recording layer and magnetization of said transfer control layer corresponding to said recording layer are opposite in direction each other in a light spot of a reproducing light radiated at the time of reproduction of said information recorded, and coincide in magnitude.

Preferably, the magnitude of an added magnetization yielded by adding the magnetization of the above described recording layer and the magnetization of the above described transfer control layer is 100 emu/cc or less in a temperature region above the room temperature and under the above described critical temperature. By this, the reproduction layer, which yields the masking effect as the magnetic film having magnetic anisotropy in the direction to inside of the film surface, can have a satisfactory masking characteristic in the reproducing-light spot.

Further, the present invention according to still yet another aspect is a reproducing method for the magneto-optical recording medium comprising at least a recording layer having a recording magnetic domain in which information is recorded in a magnetization direction vertical to a surface of a film, a reproduction layer in which information recorded in the above described recording layer is transferred in a magnetization direction vertical to a surface of a film as a reproduction magnetic domain, and a transfer control layer coupled magnetically with the above described recording layer, wherein

a reproducing-light spot is formed by radiating a reproducing light to the above described magneto-optical recording medium in reproducing information recorded in the above described magneto-optical recording medium, a domain becoming a critical temperature, in which magnetization of the above described recording layer and magnetization of the above described transfer control layer corresponding to the above described recording layer are opposite in directions and consistent in magnitude, is formed in the above described reproducing-light spot, and

a signal of the transfer domain formed on the above described reproduction layer in a region of temperature higher than the above described critical temperature is reproduced.

(II) Furthermore, a still further aspect of the present invention is created in consideration of a problem of increase in cross talk from the above described adjacent track to provide the magneto-optical recording medium and a reproducing method thereof with a purpose of realizing a high density by narrowing the track.

In order to achieve the above described purpose, the present invention is the magneto-optical recording medium comprising a first magnetic layer that becomes a in-plane magnetized film at least in a room temperature and becomes a perpendicular magnetized film in a predetermined temperature higher than the above described room temperature and a second magnetic layer having perpendicular magnetic anisotropy, wherein

the above described first magnetic layer has a thickness allowing passing a light beam, the above described second magnetic layer is arranged allowing magnetic coupling with the above described first magnetic layer, and when the incident light beam for reproducing reaches from the above described first magnetic layer side, rotation of polarized plane of the light beam reflected off the above described first magnetic layer and rotation of polarized plane of the light beam passed through the above described first magnetic layer and reflected off the above described second magnetic layer compensate each other to cancel them.

Furthermore, the present invention is the reproducing method of the magneto-optical recording medium carrying out reproducing information recorded in the above described second magnetic layer by coupling magnetically the above described first magnetic layer and the above described second magnetic layer by radiation of the light beam to the magneto-optical recording medium, wherein

the reproducing method of the magneto-optical recording medium comprises

a step, in a high temperature region in the above described beam spot, of transferring information recorded in the above described second magnetic layer to the above described first magnetic layer by making the above described first magnetic layer to the perpendicular magnetized film and by coupling magnetically the above described first magnetic layer and the above described second magnetic layer and

a step, in a low temperature region in the above described beam spot, performing reproducing the above described information by that the rotation of polarized plane of the light beam reflected off the above described first magnetic layer and the rotation of polarized plane of the light beam passed through the above described first magnetic layer and reflected off the above described second magnetic layer compensate each other to cancel them.

According to a yet further aspect of the present invention, in the magneto-optical recording medium using the magnetically induced super resolution system, making the film thickness of the first magnetic layer thinner allows canceling the rotation angles of the polarization surfaces in the transition region from the in-plane magnetized film to the perpendicular magnetized film, masking sufficiently the recorded information of the second magnetic layer in temperatures from the room temperature to a high temperature region in the beam spot, and reproducing sufficiently the recorded information in the high temperature region in the beam spot.

DESCRIPTION OF SYMBOLS

1Substrate2Dielectric material layer3Reproduction layer4Intermediate layer5Recording layer6Transfer control layer7Protecting layer8Overcoat layer9Reproducing-light spot10High temperature region11,12Low temperature region13Recording magnetic domain21Substrate22Dielectric material layer23Enlarged layer of magnetic domain24Reproduction layer25Intermediate layer26Recording layer27Transfer control layer28Dielectric material layer29Heat sink layer30Overcoat layer31Low temperature region32High temperature region33Middle temperature region34Recording magnetic domain344Enlarged recording magnetic domain35Reproducing-light spot101First magnetic layer102Second magnetic layer103Vertical component of a magnetic moment of the sub-lattice of the transition metal of the first magnetic layer104Vertical component of a magnetic moment of the sub-lattice of the transition metal of the second magnetic layer105Reproductive track106Abutting track107Beam spot108Substrate109First dielectric material layer110Second dielectric material layer111Third dielectric material layer112Overcoat layer113Heat releasing layer

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described below with specific preferred embodiments in detail. The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The following embodiment is therefore to be considered in all respects as illustrative and not restrictive.

Herewith, a first preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1is a sectional view showing diagrammatically the configuration of the magneto-optical recording medium100of the first embodiment of the present invention.

In theFIG. 1, reference numeral1denotes a poly-carbonate-made optical disk substrate having a guide groove for tracking guide of the light spot. On the top of the optical disk substrate1, a dielectric layer2made of SiN is formed for enhancing and a GdFeCo reproduction layer3, an SiN intermediate layer4, a TbFeCd recording layer5, a TbFe transfer control layer6are further sequentially layered thereon to make a four layer structure of the recording film structure. Furthermore, a SiN protecting layer7and an overcoat layer8epoxy acrylate are put on this structure.

The recording film structure composed of respective 3 to 6 layers is for realizing a recording and reproducing method to increase a record density by using the magnetically induced super resolution system (hereafter, CAD system) named CAD (Center Aperture Detection) to detect the recorded information from only the high temperature region of the reproducing-light spot and has a multilayer structure with a magnetic coupling to increase reproducing signal magnitude in case of reproduction of high density record with the diameter of the domain equal to or below 0.5 μm at the time of reproduction.

In forming the magneto-optical recording medium100having the structure of theFIG. 1, first, a Si target is subjected to reactive sputtering in an atmosphere of a mixture of argon gas and nitrogen gas using a direct current magnetron sputtering machine to form an SiN film2of 80 nm, which is, on a poly-carbonate substrate1having a pre groove which is a guide groove for tracking guide of the light spot. Further, a 20 mm GdFeCo film3is formed in argon gas using a GdFeCo target followed by forming a 15 nm SiN film4by reactive sputtering. Furthermore, 35 nm TbFeCo recording layer5and 35 nm TbFe transfer control layer6using respective targets of TbFeCo and TbFe are layered, respectively. In addition, a 50 nm SiN protecting layer7is formed and subsequently, a 6 μm UV curing resin of epoxyacrylate is coated by spin coating to receive ultraviolet light radiation to harden to make an overcoat layer8and finally, yield the magneto-optical recording medium100of the first embodiment of the present invention.

FIG. 2shows a configuration at the time of reproduction of the magneto-optical recording medium100by the CAD system in the present embodiment; (a) is a plan view showing a part of a track of the magneto-optical recording medium100, and (b) is a sectional view showing the structure of (particularly direction of magnetization) a recording film of the magneto-optical recording medium100.

The principle of reproduction by the CAD system is briefly described below.

As shown in theFIG. 2(B), the structure of the recording film of the magneto-optical recording medium100is composed of reproduction layer3, intermediate layer4, recording layer5, and transfer control layer6. In theFIG. 2(A), reference numeral9denotes the reproducing-light spot,12denotes a mask region, and10denotes a reproduction region. The arrow110shown inFIG. 2(A)is the direction of movement along with the track of the magneto-optical recording medium100and arrows illustrated in respective layers3,5, and6of theFIG. 2(B)show the direction of magnetization in respective points.

FIGS. 3(A) to 3(C)show the results of measurements of a Kerr hysteresis loop, which is a magnetic property in a single layer condition of the GdFeCo reproduction layer3used in the magneto-optical recording medium100of the present invention, by changing the strength of the reproducing laser light. Specifically,FIG. 3(A)toFIG. 3(C)are the results of measurements of temperature around the room temperature (strength of the laser light is 0.8 mW) 100° C. (strength of the laser light is 1.4 mW) and 170° C. (strength of the laser light is 2.2 mW) respectively.

As shown in theFIG. 3(A)toFIG. 3(C), magnetic anisotropy in the direction vertical to the film surface of the reproduction layer3increases according to temperature rise. In other words, in comparing theFIG. 3(A)toFIG. 3(C), the reproduction layer3is the magnetic film having magnetic anisotropy in the direction of the film surface in the low temperature around the room temperature shown in theFIG. 3(A), however, as shown in (B) and (C), magnetic anisotropy in the direction vertical to the film surface is induced according to temperature rise in accordance with increase in the reproducing power particularly to make the perpendicular magnetized film at a certain temperature or more as shown in (C).

When the reproduction layer3becomes the perpendicular magnetized film by temperature rise, as shown in theFIG. 2(B), the recording magnetic domain13of the recording layer5is transferred to the reproduction layer3to read through the intermediate layer4by magnetic interaction from the side of the recording layer5. The reproduction layer3becomes the in-plane magnetized film in the range from the room temperature up to a temperature region11lower than a reproduction temperature in which the magnetic domain of the recording layer5is transferred, because the magnetic anisotropy in the surface direction of the film surface is large. Thus, information recorded in the recording layer5as vertically magnetizing characteristic is not transferred to the reproduction layer3resultingly to realize masking action.

Repeatedly, when the magneto-optical recording medium100rotates in the direction of the arrow110to pass the recording layer5through the reproducing laser light spot9, the temperature of the recording layer5gradually rises. In the low temperature region12around the front of the reproducing laser light spot9, the reproduction layer3acts as a mask as the in-plane magnetized film. In the high temperature region10above a temperature in which the reproduction layer3becomes the in-plane magnetized film, the reproduction magnetic domain13is transferred and formed according to the direction of magnetization of the recording layer5. Subsequently, after the reproducing laser light spot9passed, the temperature of the recording film structure drops again, the recording magnetic domain of the recording layer6is not transferred, and the reproduction layer3returns to the condition of the in-plane magnetized film.

In the magneto-optical recording medium100, based on such principle of reproduction, of the present embodiment, the front temperature region11of the reproducing laser light spot9and adjacent temperature region12act as masks without use of a bias field at the time of reproduction, as described with reference toFIGS. 2(A) and 2(B). Transfer and reproduction can be carried out using the signal of recording magnetization of the recording layer5by the action of magnetic coupling force with the recording layer5in the temperature, in which the magnetic anisotropy in the surface vertical direction of the reproduction layer3increased.

In other words, information recorded in the recording layer5can be read only from the high temperature region10.

Therefore, in the magneto-optical recording medium100having the structure of the present embodiment, the signal from a region smaller than the reproducing-light spot9can be reproduced. Specifically, recording and reproducing in the domain length of 0.4 μm become possible. In addition, in this reproducing method, reproduction is carried out by a laser power of a 2.5 mW that is higher than normal one, because a difference in temperature between the low temperature regions11and12in which the reproduction layer3is the in-plane magnetized film and functions as a mask (surface masking) and the high temperature region10in which the signal is transferred.

For the first magnetic layer101, the magneto-optical recording medium of the present invention, the rare-earth elements-transition metal alloy, in which composition is dominant in the sub-lattice magnetic moment of rare-earth elements, was used. The first magnetic layer101has magnetic characteristics, shown in theFIGS. 16(A),16(B), and16(C), according to the temperature, respectively.

FIG. 16(A)is a view showing a relationship between a Kerr rotation angle and an external magnetic field at room temperature. The first magnetic layer101is the in-plane magnetized film at room temperature. Therefore, magnetization is not easily directed to the vertical direction in the external magnetic field in a small magnetic direction. For directing the magnetization to the vertical direction, very large external magnetic field is required.

FIG. 16(B)is a view showing a relationship between the Kerr rotation angle and the external magnetic field in a temperature in which the surface direction of magnetization changes to the vertical direction of magnetization. In this temperature range, applying a certain magnitude of the external magnetic field directs magnetization of all films to the vertical direction, however, acts as the in-plane magnetized film to the small external magnetic field to make the Kerr rotation angle small.

FIG. 16(C)is a view showing a relationship between the Kerr rotation angle of the external magnetic field in a high temperature. In the high temperature, change to the perpendicular magnetized film occurs, saturation occurs in the small external magnetic field, and a large Kerr rotation angle is yielded. For the first magnetic layer101, the film, which is the in-plane magnetized film at room temperature and changes to the perpendicular magnetized film according to rising to the high temperature, was used as shown in FIGS. (A), (B), and (C).

In the first magnetic layer101, the temperature range, in which the in-plane magnetized film changes to the perpendicular magnetized film, can be set by changing proportion of respective elements composing the first magnetic layer. As a rule, increasing the proportion of rare-earth elements raises the temperature region in which the in-plane magnetized film changes to the perpendicular magnetized film. In contrast, decreasing the temperature region, in which the in-plane magnetized film changes to the perpendicular magnetized film, can be achieved by reducing the proportion of rare-earth elements.

FIG. 17is a view showing a relationship of a perpendicular magnetic anisotropy energy Ku and an demagnetizing field energy 2πMs2of the first magnetic layer101, which is the in-plane magnetized film in the above described room temperature and changes to the perpendicular magnetized film in the high temperature, with temperatures. As a rule, in case of the above described magnetic layer, the following formula is held if the perpendicular magnetic anisotropy energy and saturation magnetization are assumed as Ku and Ms, respectively.
Ku<2πMs2[Equation 1]
Where, 2πMs2is demagnetizing field energy. If it is assumed that Ku is smaller than 2πMs2, the magnetic layer becomes the in-plane magnetized film. If it is assumed that the temperature in which Ku and 2πMs2coincide is Tm, the low temperature region less than Tm becomes the in-plane magnetized film in such first magnetic layer101. As shown in theFIG. 17, when the temperature of magnetic layer is increasing, the magnitude of Ku and 2πMs2come close and if it becomes higher than Tm, the next formula is held.
Ku>2πMs2[Equation 2]

The magnetic layer becomes the vertical magnetized film, if the formula is held.

The first magnetic layer101is the layer contributing to reproducing of information recorded in the second magnetic layer102and therefore, a larger Kerr rotation angle is better.FIG. 18is a view showing a relationship between the Kerr rotation angle and the Curie point. As shown in theFIG. 18, a higher Curie temperature increases the Kerr rotation angle.

In the recording film structure in the magneto-optical recording medium100having the structure of the present embodiment, The GdFeCo reproduction layer3has a composition rich in rare-earth elements at room temperature and a 300° C. of the Curie point, and the compensation temperature of 270° C. The intermediate layer is the SiN film and then, the interaction works between it and the recording layer5by the static magnetic field. The TbFeCo recording layer5has the composition rich in transition metals at room temperature and the Curie point of 280° C. The transfer control layer6made of TbFe has the composition rich in rare-earth elements at room temperature and the Curie point of 160° C., and a configuration with exchange coupling to the recording layer5.

FIG. 4shows temperature dependency of magnetization of such recording layer5and transfer control layer6. In theFIG. 4, a broken line shows temperature dependency of magnetization of the recording layer5and a dotted line shows temperature dependency of magnetization of the transfer control layer6. Besides, a solid line shows temperature dependency of magnitude of magnetization, i.e., the magnetic field for transfer (transferred magnetic field,) yielded by adding magnetization of both the recording layer5and the transfer control layer6in a layered condition.

By this, it is known that the magnitude of transferred magnetic field, i.e., the magnitude of the added magnetization of the recording layer5and the transfer control layer6which have been layered, abruptly increases at around 80° C. Therefore, in the case where the recording magnetic domain13of the recording layer5is transferred to the reproduction layer3by the static magnetic field, the magnitude of the static magnetic field abruptly changes according to the temperature to make detection of the reproducing signal easy.

FIG. 5shows characteristics of the carrier level of a signal in contrast to the reproducing power at room temperature of 25° C. This signal is actually read from the signal recorded by the laser pulsed magnetic field modulation recording with a 30% pulse width of the radiation laser, applying a magnetic field of the recording modulation magnetic field of 300 Oe to the magneto-optical recording medium100of the present embodiment. In this experiment, NA of an objective lens of an optical head was 0.55 and a wavelength of a laser light source was 680 nm. A linear velocity of the rotating magneto-optical recording medium was 3.5 m/s, recording power was 8 to 9 mW, and a modulation frequency of the recording magnetic field is set to adjust a mark length to 0.47 μm for recording. For comparison,FIG. 5shows characteristics of the reproducing signal of the magneto-optical recording medium, which uses the conventional magnetically induced super resolution without use of the transfer control layer6of the present invention, against the reproducing power (the condition of measurement is the same as the above described.).

In the magneto-optical recording medium of conventional configuration, the magnitude of magnetization of the recording layer increases moderately according to the temperature and the reproduction layer changes moderately from the in-plane magnetized film to the perpendicular magnetized film. Therefore, as shown in theFIG. 5as a comparative example (the dotted line) the signal of −30 dB or stronger was transferred according to the maximum value of the carrier level even by a 1.0 mW reproducing power. The carrier level to be transferred gradually increases according to the temperature rise in accordance with increase in the reproducing power. As the result, in the conventional configuration, a critical temperature between the region to be masked by the reproduction layer and the region to be transferred in the magnetic domain of the recording layer is unclear and the change of the ambient temperature causes that the temperature range of the region to be subjected to the surface masking may become narrow and even a small laser power may transfer the recording magnetic domain of the recording layer. Therefore, the conventional configuration lacking the transfer control layer like the present invention causes that magnetically induced super resolution action becomes unstable and the reproduced signal deteriorates.

In contrast to this, concerning the change of the carrier level according to the reproducing power of the magneto-optical recording medium100of the present embodiment, the signal of almost recording magnetic domain of recording layer5is not transferred until 1.1 mW of the reproducing power and the carrier level abruptly increased starting around 1.2 mW of the carrier level. This is because of the following reasons.

In the magneto-optical recording medium100of the present embodiment, as shown in theFIG. 4, the recording magnetic domain of the recording layer5at low temperature is not transferred in case of a low reproducing power. Because the recording layer5and the transfer control layer6, which have different direction of magnetization, are combined. However, in the high temperature region where the recording magnetic domain of the recording layer3is transferred, the transfer control layer6reaches the Curie point or higher and thus, transfer and reproduction is carried out by magnetization from only the recording layer3side. Particularly, around the critical temperature where the signal is transferred to the reproduction layer3, the abrupt change of magnetization is yielded by extinction of the magnetization of the transfer control layer6and increase in the magnetization of the recording layer5. Thus, detection of the transferring signal becomes possible without any effect of the ambient temperature.

As described above, use of the magneto-optical recording medium100of the present embodiment allows abrupt change of characteristics of magnetization transferred by the magnetostatic field according to the reproducing power in case of magnetically induced super resolution using reproduction layer3of the in-plane magnetized film. Thus, the magneto-optical recording medium having a large reproducing power margin in comparison with the change of the ambient temperature can be realized. In addition, the reproduced signal deteriorated by cross talk in the mask region of magnetically induced super resolution was reduced. On these advantages, the magneto-optical recording medium capable of excellent high density recording and reproducing and a good information reproducing method can be provided.

According to the configuration of the magneto-optical recording medium100of the present embodiment, the configuration, in which the transfer control layer6has magnetic characteristics opposite to the direction of the recording layer5, allows decreasing the effect of a floating magnetic field due to the recording layer5at a peripheral part of the record mark in recording in the recording layer by the magnetic characteristics of opposite direction. By this, the recording magnetic field characteristics can be improved.

The magneto-optical recording medium of the present embodiment has the same configuration as that of theFIG. 1shown in the first embodiment and specifically, has the recording film structure in which the dielectric layer2for enhancing is formed on an optical disk substrate1made from a plastic material and the reproduction layer3, intermediate layer4, recording layer5, and transfer control layer6are sequentially layered. Further, protecting layer7and overcoat layer8are formed thereon. In addition, a heat controlling and absorbing layer such as Al and Cu having a large heat conductivity may be added to the top on the transfer control layer6through the dielectric layer.

The recording film structure composed of respective layers3to6realizes the recording and reproducing method to increase recording density by using the CAD system as same as that of the first embodiment, and has the multilayer structure magnetically coupled to increase the reproducing signal magnitude in case of reproduction of the high density record with the diameter of the domain equal to or below 0.5 μm at the time of reproduction. In addition, the present embodiment has a configuration using the GdDyFe magnetic film as the intermediate film4, forms a surface mask in the low temperature region by exchange coupling between the reproduction layer3and the intermediate layer4, and transfers and reproduces the recording magnetic domain13of the recording layer5only in the case where the intermediate layer4becomes a high temperature, that is the Curie temperature or higher. The characteristic of the reproduction layer3and the principle of operation at the time of reproduction is almost same as that of the first embodiment and detailed description will be omitted herewith.

The magneto-optical recording medium of the present embodiment will be described below with reference to theFIG. 1. The optical disk substrate1consisting of a poly-olefin and having a pre-pit serpentined for the tracking guide of the light spot is used, and thereon, A ZnS film with 80 nm thickness is formed by RF sputtering as the dielectric layer2for enhancing. The recording film structure thereon has a form made by DC sputtering of the 30 nm GdFeCo reproduction layer3, 25 nm GdDyFe intermediate layer4, 50 nm TbFeCoCr recording layer5, and 35 nm DyFeCo transfer control layer6, respectively sequentially. Further thereon, a ZnS-SiO2protecting layer7is formed to make a thickness of 10 nm by RF sputtering and an AlTi heat sink layer with a thickness of 40 nm is formed by DC sputtering. Besides, thereto, an epoxy-based ultraviolet light-hardening resin is applied by spin coat to harden finally resulting in the overcoat layer8.

In the recording film of the present embodiment, the GdFeCo reproduction layer3has the composition rich in rare-earth elements at room temperature, the Curie point of 310° C., and the compensation temperature of 280° C. The GdDyFe intermediate layer4has the composition rich in transition metals having the magnetic anisotropy in the direction of film surface and the Curie point of 140° C. Furthermore, the TbFeCoCr recording layer5put through the intermediate layer4has the composition rich in transition metals at room temperature and the Curie point of 270° C. The transfer control layer6consisting of DyFeCo has the composition rich in rare-earth elements at room temperature, the Curie point of 200° C., the compensation temperature of 110° C., and configuration by the exchange coupling to the recording layer5.

FIG. 6shows temperature dependency of magnetization of such the recording layer5and the transfer control layer6. In theFIG. 6, the broken line shows temperature dependency of magnetization of the recording layer5and the dotted line shows temperature dependency of magnetization of the transfer control layer6. Besides, the solid line shows temperature dependency of magnitude of magnetization, i.e., the magnetic field for transfer (transferred magnetic field,) yielded by adding magnetization of both the recording layer5and the transfer control layer6in a layered condition.

As shown in the figure, magnetization of the recording layer5and magnetization of the transfer control layer6are opposite each other in the direction of magnetization in a temperature up to about 110° C., a compensation temperature, of the transfer control layer6and therefore, both the layers cancel each other out. However, in a temperature above the compensation temperature, the transfer control layer6has the composition rich in rare-earth elements, the direction of magnetization thereof coincides with the direction of magnetization of the recording layer5, and the transferred magnetic field abruptly increases, because magnetization of the transfer control layer6is added to magnetization of the recording layer5.

At the moment, if the intermediate layer4has been set to the Curie point or higher, extinction of magnetism occurs to make stable transfer possible.

In addition, the intermediate layer4is the surface magnetizing film below the Curie point to support a surface magnetization component of magnetization of the reproduction layer3and thus, the masking characteristic is improved. As a result, the reproduced signal can be detected with a short mark (recording magnetic domain).

Resultingly, concerning the change of carrier level according to the reproducing power of the magneto-optical recording medium of the present embodiment, as same as that of the first embodiment, the signal of the recording magnetic domain of the recording layer5is not almost transferred until the recording power of 1.2 mW and the carrier level abruptly increases starting from about 1.4 mW of the recording power.

In the present embodiment, the configuration using the transfer control layer6allows decreasing the transferred magnetic field in the low temperature. In a temperature range 80° C. and lower which includes the temperature (in other words, critical temperature) in which magnetization of the recording layer5and magnetization of the transfer control layer6show opposite direction and coincide their magnitude each other, the magnitude of magnetization (transferred magnetic field) yielded by addition of the recording layer5and magnetization of the transfer control layer6that have been layered is 100 emu/cc (refer to theFIG. 6.) Therefore, the transferred magnetic field is almost canceled around the critical temperature.

In the present embodiment, the temperature is around the room temperature the added magnetization (transferred magnetic field) has relatively increased in an opposite direction. However, in the temperature range around the room temperature near there, the in-plane magnetic anisotropy of the reproduction layer increases to have a sufficient masking characteristic and thus, the characteristic of the opposite direction of the added magnetization is not a problem.

Consequently, according to the configuration of the present embodiment, in the low temperature region, the recording magnetic domain of the recording layer5is not transferred and therefore, the surface masking characteristic of the reproduction layer3is improved. On the other hand, in the high temperature region in which the recording magnetic domain of the recording layer5is transferred, the transfer control layer6becomes the compensation temperature or higher and therefore, transfer is stably carried out by magnetization from the side of the recording layer3and thus reproduction is performed. Resultingly, in the magneto-optical recording medium of the present embodiment, recording and reproducing with domain length of 0.4 μm is possible.

As described above, in the present embodiment, the excellent magneto-optical recording medium, in which the information signal of 0.5 μm or smaller is stably recorded and reproduced, can be realized according to the configuration, in which the recording layer and the transfer control layer are layered, in the CAD system using the magnetically induced super resolution.

FIG. 7is a sectional view showing diagrammatically the configuration of the magneto-optical recording medium300of the present embodiment.

In this embodiment a reproduction magnetic domain enlarged layer which enlarges reproduction signals at a reproduction layer is called as “domain enlarged layer”.

In theFIG. 7, a dielectric layer22for enhancing, consisting of SiN, is formed on the optical disk substrate21consisting of a poly-carbonate and having a guide groove for the tracking guide of the light spot. Thereon, the recording film structure with five layer structure is made by layering sequentially the GdFeCo domain enlarged layer23, GdFeCoCr reproduction layer24, AIN intermediate layer25, TbFeCo recording layer26, and DyTbFeCo transfer control layer27. On such recording film structure, an AlCrN heat shield layer28, an AlCr heat sink layer29, and an epoxy-based ultraviolet light-hardening resin overcoat layer30are formed.

As forming method for the magneto-optical recording medium300of the present embodiment, first, a Si target is subjected to reactive sputtering in an atmosphere of a mixture of argon gas and nitrogen gas using a direct current magnetron sputtering machine to form an SiN film22of 80 nm, which is, on a poly-carbonate substrate21having the configuration which can record in a land part and a groove part for tracking guide of the light spot. Further, a 20 mm GdFeCo film23is formed by sputtering in argon gas using a GdFeCo target followed by forming a 15 nm GdFeCoCr film24by sputtering in argon gas by using a GdFeCoCr target. Furthermore, a 25 nm AIN film is formed by the DC sputtering of the Al target in the mixture of argon gas and nitrogen gas. Thereon, 35 nm TbFeCo recording layer26and 30 nm DyTbFeCo transfer control layer27are layered by using respective targets of TbFeCo and DyTbFeCo, respectively. AlCrN heat shield layer28is formed to make a thickness of 20 nm by reactive sputtering in the atmosphere of the mixture of argon gas and nitrogen gas by using AlCr target, and the AlCr target is subjected to the DC sputtering in argon gas to form 50 nm heat sink layer29. In addition, thereon, a 6 μm epoxy-based UV resin is coated by spin coating to receive ultraviolet light radiation to harden to make an overcoat layer30and finally, yield the magneto-optical recording medium300of the present embodiment.

The recording film structure of the magneto-optical recording medium300, composed of respective layers23to27, of the present embodiment, allows achieving a method for increasing the recording density through the multilayer film structure by using magnetic domain enlargement using the magnetic domain enlarged layer23of a shrink type, and has the multilayer film structure magnetically coupled to amplify the reproducing signal magnitude in case of the high density recording and reproducing of the domain diameter of 0.4 μm or smaller at the time of reproduction.

FIG. 8shows a configuration figure in the reproducing operation of the magneto-optical recording medium300using the magnetic domain enlarged layer23of the shrink type, which is a system of the magnetic domain enlargement of the present embodiment; (a) is a plan view showing a part of a track of the magneto-optical recording medium300, and (b) is a sectional view showing the structure of (particularly direction of magnetization) a recording film of the magneto-optical recording medium300. The arrow310shown in theFIG. 8(A)is a movement direction along with the track of the magneto-optical recording medium300. Arrows illustrated in respective layers23,24,26, and27of theFIG. 8(B)show directions of magnetization in respective positions.

The principle of reproduction according to the present embodiment will be briefly described below with reference to theFIG. 8.

As shown in theFIG. 8(B), the structure of recording film according to the magneto-optical recording medium300of the present embodiment is the five layer structure composed of the domain enlarged layer23, reproduction layer24, intermediate layer25, recording layer26, and transfer control layer27. In theFIG. 8(A),35is a reproducing laser light spot,31and32are masking regions (specifically,31is a low temperature region and32is a high temperature region) and33is a reproducible temperature region. The recording magnetic domain34is recorded in the recording layer26. Where, the following relationships are necessary: the recording layer26and the transfer control layer27have opposite magnetization at room temperature, the reproducible temperature region33is in a temperature of the Curie point or higher of the transfer control layer27, and the Curie point of the recording layer26is higher than the temperature of the reproducible temperature region33.

In the structure of recording film according to the magneto-optical recording medium300of the present embodiment, GdFeCo domain enlarged layer23has a composition rich in rare-earth elements at room temperature, the Curie point of 310° C., and the compensation temperature of 100° C. The reproduction layer24has the composition rich in transition metals of the in-plane magnetized film at room temperature and is made from GdFeCoCr with the Curie point of 190° C. The AIN intermediate layer25is a film to block the exchange coupling, and TbFeCo recording layer26, which is layered through the intermediate layer25, has the composition rich in rare-earth elements at room temperature, the Curie point of 300° C., and the compensation temperature of 110° C. The transfer control layer27made of DyTbFeCo has the composition rich in transition metals at room temperature, the Curie point of 140° C., and a configuration with exchange coupling to the recording layer26.

FIGS. 10(A) to 10(C)are figures showing the magnetic property (the Kerr hysteresis loop and direction of magnetization) of a single layer condition of the domain-enlarged layer23in the magneto-optical recording medium300of the present embodiment in different temperatures. Specifically,FIG. 10(A)is a graph in 50° C., (B) is in 110° C., and (C) is in 160° C., respectively.

In the Kerr hysteresis loop of theFIG. 10(A)as an example, when the magnetic field H is applied to the domain enlarged layer23from a positive side to a negative side, the magnetizing condition of A in the figure changes to the opposite magnetizing condition of B in magnetic field of about −180 Oe. In addition, when the magnetic field H is applied to the domain enlarged layer23from the magnetizing condition of B toward the positive side, the domain enlarged layer23returns to the magnetizing condition of A around about −70 Oe, which is the magnetic field in the negative side than zero. As described above, in the Kerr hysteresis loop of the domain enlarged layer23contained in the magneto-optical recording medium300of the present embodiment, as shown in theFIGS. 10(A) to 10(C), the magnetic field applied is shifted to the negative direction. Particularly, in case of the low temperature shown inFIG. 10(A)orFIG. 10(B), a characteristic, in which the direction of magnetization is arranged to one direction, is observed in case of no external magnetic field to result in masking by the shrinking action through magnetization in one direction.

The functions of the reproduction layer24are same as those of the first and second embodiment.

Therefore, in the low temperature region31in the recording light spot35, the reproduction layer24has magnetic anisotropy in the direction of the surface of the film and thus, the recording magnetic domain34of the recording layer26is not transferred to the domain enlarged layer23to be masked by the shrinking action of the above described domain enlarged layer23.

In the high temperature region32in the recording light spot35, the reproduction layer24reaches a temperature equal to or higher than the Curie point and therefore, the recording magnetic domain34of the recording layer26is merely slightly transferred to the domain enlarged layer23.

By this reason, the recording magnetic domain34is transferred, from only the middle temperature region33in the recording light spot35, to and formed in the domain enlarged layer23through the reproduction layer24. Then, the reproduction layer24reaches a temperature equal to or higher than the Curie point and therefore, a domain wall of the domain enlarged layer23is easy to move to the direction of the high temperature region32and a region344larger than the recording magnetic domain34is transferred and formed in the domain enlarged layer23.

In other words, the part S of the domain enlarged layer23formed in the part (hatched part) in which magnetization extinguished in the reproduction layer24is largely influenced by the part P of the domain enlarged layer23formed in the part which is vertically magnetized by the middle temperature of the reproduction layer24in comparison with the influence by the recording layer26. Thus, the domain enlarges toward the direction thereof.

As the result, the transfer signal of the recording magnetic domain34is reproduced as the reproduced region344enlarged by domain wall movement. In the reproducing method of the shrink type of the present embodiment, reproduction is carried out by the laser power of 2.5 mW larger than a normal one to satisfy the above described reproducing operation.

FIG. 9shows temperature dependency of magnetization of the recording layer26and the transfer control layer27contained in such magneto-optical recording medium300of the present embodiment. In theFIG. 9, the broken line shows temperature dependency of magnetization of the recording layer26and the dotted line shows temperature dependency of magnetization of the transfer control layer27. Besides, the solid line shows temperature dependency of magnitude of magnetization, i.e., the magnetic field for transfer (transferred magnetic field) yielded by adding magnetization of both the recording layer26and the transfer control layer27in the layered condition.

In the structure of recording film of the present embodiment, TbFeCo recording layer26has the composition rich in rare-earth elements at room temperature, the Curie point of 300° C., and the compensation temperature of 110° C. The transfer control layer27made of DyTbFeCo has the composition rich in transition metals at room temperature, the Curie point of 140° C., and a configuration with exchange coupling to the recording layer26. Concerning the magnitude of magnetization (transferred magnetic field) yielded by addition of the recording layer26and the transfer control layer27which are layered, in a temperature range 100° C. or lower, magnetization of the recording layer and magnetization of the transfer control layer show opposite direction each other and therefore magnetization of both layers cancels each other. On the other hand, in a temperature over about 100° C., the direction of magnetization of both layers coincide and therefore, the magnitude of magnetization (transferred magnetic field) yielded by addition abruptly increases. Therefore, when transfer to the domain enlarged layer23is carried out by using magnetic coupling through the intermediate layer25, the magnitude of magnetic interaction abruptly changes according to the temperature in the condition in which the reproduction layer24, the recording layer26, and the transfer control layer27are layered, and the recording magnetic domain34is easily formed by transfer in the middle temperature region33in the recording light spot35. In the domain enlarged layer23, the recording magnetic domain is formed by transfer in the enlarged status (refer to a reference numeral344in theFIG. 8).

Actually, concerning the carrier level, which changes according to the reproducing power, of the signal generated by reproducing the signal, with a 0.27 μm mark length, which was recorded by the laser pulsed magnetic field modulation recording with a 40% pulse width, applying a magnetic field of the recording magnetic field of 3000 e to the magneto-optical recording medium300of the present embodiment, the carrier level increases abruptly by the reproducing power of 1.0 mW or larger, as same as that of the first embodiment. Besides, in the magneto-optical recording medium300of the present embodiment, as shown in the graph of characteristic for a signal amplitude of the reproduced signal according to the mark length (the size of recording magnetic domain) of theFIG. 11, deduction of the signal amplitude is small even in case that the mark length becomes small.

FIG. 11is a view made by plotting a normalized signal amplification (a normalized signal) which is standardized with amplitude in the mark length of 3 μm, to the mark length. Thus, in the configuration of the present embodiment, the amplitude above 50% of the amplitude level in the mark length of 3 μm can be obtained even below the mark length of 0.3 μm. Therefore, according to the present embodiment, even in a short recording magnetic domain34, it is observed that the recording magnetic domain34is reproduced by forming as the domain344enlarged in transfer. For comparison, theFIG. 11shows data also obtained from the magneto-optical recording medium of the conventional art and the magneto-optical recording medium of the first embodiment of the present invention.

As described above, using the magneto-optical recording medium300of the present embodiment allows abrupt change of the transfer characteristics according to the reproducing power even in case of use of the magnetic domain enlarged layer23of the shrink type, and the magneto-optical recording medium providing a large recording power margin according to the change of the ambient temperature can be achieved.

In addition, it is possible to reduce cross talk on the basis of enlargement of transfer magnetic domain and the mask properties, and it becomes possible to provide the magneto-optical recording medium allowing excellent recording and reproducing and a good information reproducing method even in case of recording with the high density below the mark length of 0.3 μm.

In the recording and reproducing method for the magneto-optical recording medium of the respective embodiments of the present invention, the signal (record signal) is detected by using a magneto-optic record reproducing device by a configuration allowing reproducing by the reproducing power higher than the normal one for the magneto-optical recording medium of the present invention as described above.

In the magneto-optic record reproducing device of such magneto-optical recording medium, recording, reproducing, and deleting of information is executed by the laser light. In reproducing the signal in a part of regions in the reproducing laser light spot radiated to the magneto-optical recording medium, the magnitude of magnetization of the recording layer and the magnitude of magnetization of the transfer control layer in the opposite direction coincide each other (becoming the temperature, i.e., becoming the critical temperature to cause the coincidence.) In the region having the temperature higher than the critical temperature in which the magnitudes of magnetization coincides each other, the recording magnetic domain of the recording layers are transferred to and reproduced from the reproduction layer having a characteristic to change from the surface direction to the magnetic film in the vertical direction. Thus, the signal from the region smaller than the reproducing-light spot can be reproduced. As a result, the magneto-optic recording and reproducing device and the reproducing method of the excellent magneto-optical recording medium in which controlling the transfer region is easy and the reproducing margin for the change of the ambient temperature due to abrupt change from a low temperature masking region to a high temperature transfer region can be increased.

According to other aspects of the present invention, in the reproducible temperature range near the temperature in which saturation magnetization with addition of the magnetization of the recording layer and the magnetization of the transfer control layer, which have been layered, becomes maximum, the signal (recorded signal) is reproduced by transferring the domain recorded in the recording layer to the reproduction layer, as the configuration in which a magnetic coupling force of the recording layer, the intermediate layer, and the reproduction layer through the reproducing supporting layer increases further than a constricting force of the domain wall of the reproduction layer. At this time, at least a part of the light spot of the magneto-optical recording medium of which temperature rises by the laser light radiated at the time of reproducing the signal carries out the rising process of the temperature to reach the critical temperature being the temperature in which magnetization of the recording layer and magnetization of the transfer control layer are opposite in direction each other but coincide in magnitude. According to this, the signal recorded is transferred only from the temperature range which is possible of signal transfer by magnetic coupling force between the recording layer and reproduction layer in the region in the reproducing-light spot and other than near the critical temperature range as described above, in order to detect as the reproduced signal. Or, when the signal recorded is transferred from only the temperature range which is possible of signal transfer by magnetic coupling force between the recording layer and reproduction layer in the region in a part of the reproducing-light spot and other than near the critical temperature range in which, magnetization of the recording layer and opposite magnetization of the transfer control layer coincide in magnitude each other, the domain transferred may be enlarged (i.e., using the domain transferred) to detect the signal.

As described above, use of the magneto-optical recording medium and reproducing method of the present invention can provide the magneto-optical recording medium capable of excellent high density recording and reproducing and a good information reproducing method, which can achieve the magneto-optical recording medium of which reproducing power margin is large and the transfer characteristics are excellent according to the change of ambient temperature in case of using magnetically induced super resolution using the in-plane magnetized film and also achieve that the reproduced signal deteriorated by cross talk in the mask region of magnetically induced super resolution are reduced.

(II) Next, other respective embodiments of the present invention will be described below with reference to drawings.

FIG. 15is a sectional view of the magneto-optical recording medium according to the fourth embodiment of the present invention. The substrate108is a substrate made of poly-carbonate. The substrate made of poly-carbonate is easy to mold and therefore frequently used for the substrate of the magneto-optical recording medium. The substrate108has a configuration by the land-groove with the track width of 0.6 μm.

The magneto-optical recording medium according to the present embodiment is configured by forming sequentially the first dielectric layer109, the first magnetic layer101, the second dielectric layer110, the second magnetic layer102, the third dielectric layer111, and the overcoat layer112on the substrate108.

Next, the method for preparing the magneto-optical recording medium shown in theFIG. 15.

A thin film on the substrate108was formed using a sputtering machine. In the sputtering machine, TbfeCo alloy target, GdFeCo alloy target, and Si target are fitted to separate cathodes, respectively. The substrate108made of poly-carbonate is fitted to a substrate holder in the sputtering machine. After the substrate108is fitted, inside of the chamber of the sputtering machine was vacuum exhausted with a cryopump up to a high vacuum of 2×10−7Torr or lower.

After exhaust to the high vacuum, Ar gas of 2×10−3Torr and N2gas of 4×10−3Torr was introduced into the chamber, an electric power of 1 kW was applied, and SiN film, which is the first dielectric layer109, was formed on the substrate108by using the DC sputtering. In the present embodiment, the thickness of the SiN film, which was the first dielectric layer109, was made 80 nm.

Next, again, the vacuum pressure in the chamber was adjusted to 2×10−7Torr or lower to introduce Ar gas of 5×10−3Torr in the chamber. After introducing Ar gas, a GdFeCo film, which is the first magnetic layer101, was formed on the first dielectric layer109. The sputtering was the DC sputtering as same as the first dielectric layer109.

The film thickness of the first magnetic layer101was configured to be thinner to allow passing the light beam. In the present embodiment, the GdFeCo film, which is the first magnetic layer101, was made 20 nm.

In the present embodiment, the composition of the GdFeCo film, which is the first magnetic layer101, was Gd30.6Fe61.1 Co8.3 (atomic percentage). The first magnetic layer101of the present embodiment was the GdFeCo film having the Curie point of 320° C., changing from the in-plane magnetized film to perpendicular magnetized film in the temperature range near 150° C., and having a composition rich in rare-earth elements.

After forming the first magnetic layer101, vacuum exhaust was carried out up to 2×10−7Torr again to from the second dielectric layer110on the first magnetic layer101. For the second dielectric layer110, the SiN film was used as same as the first dielectric layer109, film forming condition was same as the first dielectric layer109, Ar gas of 2×10−3Torr and N2 gas of 4×10−3Torr were introduced to inside the chamber, and electric power of 1 kV was applied to form the film.

The thickness of the second dielectric layer110considerably influences to magnetostatic coupling of the first magnetic layer101with the second magnetic layer102. A thinner thickness of the second dielectric layer110makes a distance between the first magnetic layer101with the second magnetic layer102short to increase magnetostatic coupling force. Therefore, the thickness of the second dielectric layer110is preferably made 100 nm or thinner, and more preferably 30 nm. However, if the thickness of the second dielectric layer110is made very thin, the exchange coupling force between the first magnetic layer101with the second magnetic layer102becomes larger than magnetostatic coupling force. Therefore, it is necessary to make the thickness of the second dielectric layer1102 nm or thicker. In the present embodiment, the thickness of the second dielectric layer110was made 10 nm. The upper limit of the thickness of the second dielectric layer110is preferably 100 nm or thinner and a thickness over this makes magnetostatic coupling force between the first magnetic layer101and the second magnetic layer102small.

Subsequently, after vacuum exhaust up to 2×10−7Torr again, Ar gas of 5×10−3Torr was introduced in the chamber, a TbFeCo film, which is the second magnetic layer102, was formed to make 50 nm thickness on the second dielectric layer110.

In the present embodiment, the composition of the TbFeCo film was Tb22.1Fe71.2Co6.7 (atomic percentage) The TbFeCo film, which was the second magnetic layer102of the present embodiment, had the Curie pint of 240° C. and was rich in transition metals.

Next, vacuum exhaust up to 2×10−7Torr was again carried out. After vacuum exhaust, Ar gas of 2×10−3Torr and N2 gas of 4×10−3Torr was introduced into the chamber as same as the first dielectric layer109. After the introduction, an electric power of 1 kW was applied to the second magnetic layer102as same as the first dielectric layer109and the second dielectric layer110to form the SiN film, which is the third dielectric layer111.

The thickness of the third dielectric layer111should protect the second magnetic layer102to such corrosion as oxidization and is preferably 50 nm or thicker. In the present embodiment, the thickness of the third dielectric layer111was 80 nm.

The overcoat layer112was formed by picking up the magneto-optical recording medium of which respective thin films were formed on the substrate108under the above described condition, from the chamber; applying the ultraviolet hardening resin to the surface of the film side of the magneto-optical recording medium by spin coat, and radiation of ultraviolet light. In the present embodiment, the film thickness of the overcoat layer112is made 10 μm by viscosity of the ultraviolet hardening resin and controlling rotation of a spin coater.

The reproduction layer of this embodiment has same or similar characteristic to the reproduction layer used in the first embodiment.

On the basis of the above described, a material and a composition, which increase the Curie point, are suitable for the first magnetic layer101. In the present embodiment, the Curie point of the GdFeCo film being the first magnetic layer101is 320° C.

FIG. 19is a view showing a relationship between a saturation magnetization Ms and the temperature of the second magnetic layer102used in the present embodiment. Magnetostatic coupling force has strong correlation with a magnetic moment and a larger magnetic moment increases magnetostatic coupling force. Magnetic moment proportions to a product of multiplying saturation magnetization by a film thickness and thus, saturation magnetization largely influences on magnetostatic coupling force. The second magnetic layer102used in the present embodiment is the TbFeCo film having a transition metal rich composition in which the composition is Tb22.1Fe71.2Co6.7 (atomic percentage) and the Curie point is 240° C.

When the compensation temperature of the second magnetic layer102is in near the room temperature, difference between saturation magnetization at room temperature and saturation magnetization in a transfer temperature becomes large to change saturation magnetization according to temperature abruptly. The perpendicular magnetic anisotropy is large and coercivity is also large at room temperature and therefore, the recorded information can be stably kept. The saturation magnetization of the second magnetic layer102used at room temperature in the present embodiment is approximately zero. According to temperature rise, the saturation magnetization of the second magnetic layer102gradually increases and shows a value of the saturation magnetization capable of satisfactory transfer of information recorded in the second magnetic layer102to the first magnetic layer101by the signal in a predetermined temperature, i.e., the temperature in transferring the recorded information to the first magnetic layer101.

The film thickness of the second magnetic layer102is preferably 20 nm or thicker to increase the magnetic moment of the second magnetic layer102in order to transfer the signal to the first magnetic layer101. On the other hand, too thick film of the second magnetic layer102increases the power of the light beam necessary for temperature rise to cause lowering of recording sensitivity. Therefore, the film thickness of the second magnetic layer102is preferably 20 nm or less. In the present embodiment, the film thickness of the second magnetic layer102was 50 nm.

Next, the recording and reproducing performance of the magneto-optical recording medium prepared in the present embodiment were tested.

A semiconductor laser of 650 nm wavelength and an objective lens of 0.6 NA were used for the reproducing method according to the present invention. The linear velocity of the medium was 3.5 m/s.

For recording the signal in the magneto-optical recording medium, the laser pulsed magnetic field modulation recording system was applied. A recording power was 9 mW, duty was 50%, the light beam was radiated to the magneto-optical recording medium, and the temperature of the second magnetic layer102was raised to the Curie temperature or higher. The signal was recorded by putting a magnetic head in a position close to an opposite surface of the light beam followed by modulating the direction of a magnetic flux generated by the magnetic head in the recording magnetic field of 3500 e.

For reproducing information recorded in the second magnetic layer102, first, the light beam is radiated to the magneto-optical recording medium to make the region of vertical magnetized film by raising the temperature of the first magnetic layer101in a beam spot107and then, the temperature of the second magnetic layer102is raised to increase the magnetic moment of the second magnetic layer102in the beam spot107.

Subsequently, the signal of the second magnetic layer102is transferred to the first magnetic layer101by magnetostatic coupling of the first magnetic layer101with the second magnetic layer102.

Finally, the signal is detected from the light beam reflected off the magneto-optical recording medium by magneto-optical effect.

FIG. 20is a view showing a relationship between a signal magnitude and the reproducing power in the magneto-optical recording medium according to the present embodiment andFIG. 21is a view showing a relationship between a cross talk magnitude and the reproducing power in the magneto-optical recording medium according to the present embodiment. Quantity of the signal is the magnitude of 1.88 μm signal. The cross talk magnitude is expressed by the ratio of the signal quantity leaked from an abutting track106on a reproductive track105to the signal quantity yielded by reproducing the 1.88 μm signal in the reproductive track105, after recording the 1.88 μm signal in the abutting track106of one side.

In a small reproducing power, almost part of the beam spot107is the low temperature region and the first magnetic layer101is the in-plane magnetized film. Therefore, the rotation of the polarized surface of the light beam reflected off the first magnetic layer101is not large, passes through the first magnetic layer101, and canceled by the rotation of the polarized surface of the light beam reflected off the second magnetic layer102. Thus, as shown in theFIG. 20, only a small quantity of signal is detected.

Changing the reproducing power to somewhat large the first magnetic layer101around the center of the beam spot107from the in-plane magnetized film changes slightly to the perpendicular magnetized film. The signal can be detected from the region where the first magnetic layer101changed to the perpendicular magnetized film. However, a part, where the first magnetic layer101changed to the perpendicular magnetized film, in the beam spot107is a narrow region and therefore, has very small signal quantity. In a region far from the center in the beam spot107, the first magnetic layer101is a temperature region where the in-plane magnetized film changes to the perpendicular magnetized film and therefore, rotation of polarized plane of the light beam reflected off the first magnetic layer101and rotation of polarized plane of the light beam passed through the first magnetic layer and reflected off the second magnetic layer102cancel each other.

Increasing the reproducing power further larger makes a wide region from the center in the beam spot107to the high temperature region and changes the first magnetic layer101from the in-plane magnetized film changes to the perpendicular magnetized film. In the wide region in the beam spot107, the first magnetic layer101changes to the perpendicular magnetized film.

In the high temperature region in the beam spot107, the first magnetic layer101changes to the perpendicular magnetized film and therefore, rotation of polarized plane of the light beam reflected off the first magnetic layer101becomes larger than rotation of polarized plane of the light beam reflected off the first magnetic layer101in the temperature region during process of change of the first magnetic layer101from the in-plane magnetized film to the perpendicular magnetized film by a small reproducing power. Rotation of polarized plane of the light beam reflected off the first magnetic layer101in the beam spot107becomes larger than rotation of polarized plane of the light beam reflected off the second magnetic layer102to give a higher priority to the rotation of polarized plane of the light beam reflected off the first magnetic layer101and therefore, a large signal can be detected.

Larger reproducing power widens the high temperature region in the beam spot107. Then, the first magnetic layer101changes from the in-plane magnetized film to the perpendicular magnetized film resulting in a larger signal in the wider region in the beam spot107.

As shown in properties of cross talk magnitude, which leaks in from the abutting track106ofFIG. 21, according to the reproducing power, when the reproducing power is small, namely, when the temperature of inside of the beam spot107is near the room temperature, the signal magnitude is small and cross talk magnitude is relatively large. Increase in reproducing power increases the cross talk magnitude. It is known that in a range of the reproducing power (a range of 1.2 to 2.0 mW in the figure,) cross talk from the abutting track106has reduced.

In the region, as shown in theFIGS. 20 and 21, of reproducing power where the signal magnitude is large and the cross talk magnitude decreases, the first magnetic layer101in the region near the center of the beam spot107is vertically magnetized film and the first magnetic layer101in the region far from the center of the beam spot107is the temperature region during changing from the in-plane magnetized film to the perpendicular magnetized film.

As shown in theFIG. 14, in the region far from the center of the beam spot107, the vertical component103of the sub-lattice magnetic moment of transition metal elements of the first magnetic layer becomes smaller than that of the central region. Therefore, the light beam reflected off the first magnetic layer101and the light beam passed through the first magnetic layer101and reflected off the second magnetic layer102are opposite in the rotation direction of polarized plane and approximately equal in magnitude. The abutting track106is a region far from the center in the beam spot107and relatively low in temperature and therefore, the light beam reflected off the first magnetic layer101and the light beam passed through the first magnetic layer101and reflected off the second magnetic layer102are opposite in the rotation direction of polarized plane and approximately equal in magnitude. Consequently, cross talk from the abutting track106greatly reduces.

On the contrary, the region around the center of the beam spot107, that is, the reproductive track105is the high temperature region and the first magnetic layer101changes from the in-plane magnetized film to the perpendicular magnetized film, and therefore the large signal can be yielded.

The following is explanation of saturation magnetization of the second magnetic layer102in this status.FIG. 19shows relation between saturation magnetization of the second magnetic layer102and temperature. Saturation magnetization at room temperature is very small. Increase in temperature from the room temperature by radiation of the light beam causes increase in saturation magnetization up to a certain temperature.

Radiating the light beam with the reproducing power allowing the large signal magnitude makes saturation magnetization around the center of the beam spot107maximum. In the region far from the center of the beam spot107, the temperature is low than the region around the center and then, saturation magnetization is small than saturation magnetization around the center of the beam spot107.

As shown inFIGS. 20 and 21, the large signal magnitude yields in the wide range of the reproducing power and the cross talk magnitude becomes −20 dB or smaller. The cross talk magnitude is the signal magnitude from the abutting track106and thus, the region far from the center of the beam spot107and the low temperature region in the beam spot107. Then, the signal magnitude according to the cross talk magnitude becomes 1/10 or smaller to the signal magnitude of the high temperature region in the beam spot107and does not cause deterioration of the reproducing signal.

Reproducing method for the magneto-optical recording medium used in the present embodiment will be described below in detail.

The light beam is radiated from the substrate108side of the magneto-optical recording medium. In the present embodiment, the wavelength of the light beam is 650 nm and the numerical aperture NA of the objective lens is 0.6.

FIG. 14shows the first magnetic layer101, the second magnetic layer102, and the vertical component103of the sub-lattice magnetic moment of transition metal elements of the first magnetic layer and the vertical component104of the sub-lattice magnetic moment of transition metal elements of the second magnetic layer, in radiating the light beam with the reproducing power capable of sufficient yield of the signal magnitude. In the configuration of the present embodiment, the first magnetic layer101is thin to allow passing light and therefore, a part of light beam radiated from the substrate108side passes through the first magnetic layer101and reaches the second magnetic layer102.

As shown in theFIG. 14, in the configuration of the present embodiment, the first magnetic layer101is in the process of changing from the in-plane magnetized film to the perpendicular magnetized film in the region far from the center of the beam spot107. Thus, the vertical component103of the sub-lattice magnetic moment of transition metal elements of the first magnetic layer is smaller than that of the central region. When the track width becomes small to detect signal within a beam spot107of 1.0 μm range, according to the configuration of a light pick-up, the light beam passes through the first magnetic layer101in the abutting track106and a part of signals from the second magnetic layer102is detected to result in deterioration of the reproduced signal.

However, in the present embodiment, the light beam reflected off the first magnetic layer101and the light beam passed through the first magnetic layer101and reflected off the second magnetic layer102are opposite in the rotation direction of polarized plane and approximately equal in magnitude. The abutting track106is a region far from the center in the beam spot107and relatively low in temperature and therefore, the light beam reflected off the first magnetic layer101and the light beam passed through the first magnetic layer101and reflected off the second magnetic layer102are opposite in the rotation direction of polarized plane and approximately equal in magnitude. Consequently, cross talk from the abutting track106greatly reduces.

On the contrary, the reproductive track105around the center of the beam spot107is the high temperature region and the first magnetic layer101changes from the in-plane magnetized film to the perpendicular magnetized film.

Therefore, the rotation of polarized plane of the light beam reflected off the first magnetic layer101becomes larger than the rotation of polarized plane of the light beam reflected off the second magnetic layer102and the rotation of polarized plane of the light beam reflected off the first magnetic layer101is given a priority. The light beam reflected off the first magnetic layer101and the second magnetic layer102is detected by a detector, converted to an electric signal, and passed through a signal processing system to read information.

A fifth embodiment will be described below.FIG. 22is a sectional view showing the magneto-optical recording medium according to the present embodiment. In the present embodiment, the magneto-optical recording medium was prepared to have the 30 nm thickness of GdFeCo film corresponding to the first magnetic layer101of the embodiment 4. Specifically, in the configuration thereof, the first dielectric layer109, the first magnetic layer101, second dielectric layer110, the second magnetic layer102, the third dielectric layer111, the heat releasing layer113, and the overcoat layer112are sequentially formed on the substrate108, the GdFeCo film being the first magnetic layer101is made 30 nm, and a heat releasing layer113is put between the SiN film being the third dielectric layer111and the overcoat layer112. The substrate108is a substrate made of poly-carbonate with the track width of 0.6 μm.

The AlTi film, the heat releasing layer113, was formed by fitting an AlTi alloy target to one of the cathode of the sputtering machine used in the present embodiment and carrying out vacuum exhaust up to 2×10−7Torr for inside of the chamber. After vacuum exhaust, Ar gas of 1.5×10−3Torr was introduced in the chamber. After introducing Ar gas, electric power of 600 W was applied and the DC sputtering was applied to forming the AlTi film. Other films were formed by the DC sputtering under the same film forming condition as that of the magneto-optical recording medium according to the present embodiment 4 using the same sputtering machine as that of the magneto-optical recording medium according to the present embodiment 4.

In the present embodiment, the recording and reproducing of the signal in and from the magneto-optical recording medium were performed by the same method as the present embodiment 4.FIG. 23is a view showing a relationship between the signal magnitude and the reproducing power in the magneto-optical recording medium according to the present embodiment andFIG. 24is a view showing a relationship between the cross talk magnitude and the reproducing power in the magneto-optical recording medium according to the present embodiment.

Also in the abutting tracks106in the present embodiment, the light beam reflected off the first magnetic layer101and the light beam passed through the first magnetic layer101and reflected off the second magnetic layer102cancel each other in opposite directions of the rotation directions of polarized planes. Therefore, an effect of reducing cross talk yielded around the reproducing power as same as that of the present embodiment 4.

A sixth embodiment will be described below. The present embodiment is configured by that the first dielectric layer109, the first magnetic layer101, a second dielectric layer110, the second magnetic layer102, the third dielectric layer111, the heat releasing layer113, and the overcoat layer112are sequentially formed on the substrate108, the thickness of the GdFeCo film being the first magnetic layer101is made 40 nm, and the thickness of the SiN film being the second dielectric layer110is made 5 nm.

In the present embodiment, as same as the embodiment 5, the heat releasing layer113with a 35 nm thickness is put between the SiN film being the third dielectric layer111and the overcoat layer112. The substrate108is a substrate, for sample servo system, made of poly-carbonate with the track width of 0.6 μm. Concerning film forming method and film forming conditions, films were formed by the DC sputtering under the same film forming condition as that of the magneto-optical recording medium according to the present embodiment 5 using the same sputtering machine as that of the magneto-optical recording medium according to the present embodiment 5.

In the present embodiment, the recording and reproducing of the signal in and from the magneto-optical recording medium were performed by the same method as the present embodiment 4.FIG. 25is a view showing a relationship between the signal magnitude and the reproducing power in the magneto-optical recording medium according to the present embodiment andFIG. 26is a view showing a relationship between the cross talk magnitude and the reproducing power in the magneto-optical recording medium according to the present embodiment.

Also in the abutting tracks106in the present embodiment, the light beam reflected off the first magnetic layer101and the light beam passed through the first magnetic layer101and reflected off the second magnetic layer102cancel each other in opposite directions of the rotation directions of polarized planes. Therefore, the effect of reducing cross talk yielded around the reproducing power as same as those of the present embodiment 4 and the present embodiment 5.

An embodiment 7 will be described below. The present embodiment is configured by that the first dielectric layer109, the first magnetic layer101, a second dielectric layer110, the second magnetic layer102, the third dielectric layer111, the heat releasing layer113, and the overcoat layer112are sequentially formed on the substrate108and the magneto-optical recording medium was prepared changing the composition of GdFeCo film being the first magnetic layer101.

In the present embodiment, the composition of the first magnetic layer101was made in a proportion of Gd25.0Fe66.7 Co8.3 (atomic percentage) and with a film thickness of 30 nm. The thickness of the SiN film being the second dielectric layer110was made 10 nm. As same as the embodiment 5, the heat releasing layer113with a 35 nm thickness is put between the SiN film being the third dielectric layer111and the overcoat layer112. The substrate108is a substrate made of poly-carbonate with the track width of 0.8 μm. Concerning film forming method and film forming conditions, films were formed by the DC sputtering under the same film forming condition as that of the magneto-optical recording medium according to the present embodiment 5 using the same sputtering machine as that of the magneto-optical recording medium according to the present embodiment 5.

Comparison of the case where the composition of the first magnetic layer101was Gd25.0Fe66.7Co8.3 (atomic percentage) with the case where the composition was that of the embodiment 5 showed a lower temperature region of change from the in-plane magnetized film to the perpendicular magnetized film in the present embodiment. However, setting the reproducing power low allows magnetically induced super resolution action and achievement of recording and reproducing with the high density in the composition of the present embodiment.

In the present embodiment, recording and reproducing of the signal in the magneto-optical recording medium were performed by the same method as the present embodiment 4.

Also in the present embodiment in which the composition of the first magnetic layer101was Gd25.0Fe66.7Co8.3 (atomic percentage) in the abutting tracks106, the light beam reflected off the first magnetic layer101and the light beam passed through the first magnetic layer101and reflected off the second magnetic layer102cancel each other in opposite directions of the rotation directions of polarized planes. Therefore, the following effect as same as that of the present embodiment 5 yielded: cross talk magnitude showed −20 dB or smaller in a wide range of the reproducing power, particularly, cross talk magnitude showed −25 dB or smaller in the reproducing power ranging 1.2 mW and 2.2 mW.

The present embodiment has same configuration as that of the embodiment 7 and is the magneto-optical recording medium prepared by increasing the proportion of rare-earth elements in the composition of the first magnetic layer101as Gd35.4Fe 56.3Co 8.3 (atomic percentage,) in contrast to the embodiment7. The configuration was made by sequential forming of the first dielectric layer109, the first magnetic layer101, a second dielectric layer110, the second magnetic layer102, the third dielectric layer111, the heat releasing layer113, and the overcoat layer112on the substrate108. The thickness of the first magnetic layer101was 30 nm. As same as that of the embodiment 7, the thickness of the SiN film being the second dielectric layer110was made 10 nm. As same as those of the embodiment 5 and the embodiment 7, the heat releasing layer113with the 35 nm thickness was put between the SiN film being the third dielectric layer111and the overcoat layer112. The substrate108is a substrate made of poly-carbonate with the track width of 0.7 μm. Concerning film forming methods and film forming conditions, films were formed by the DC sputtering under the same film forming condition as that of the magneto-optical recording medium according to the present embodiment 5 using the same sputtering machine as that of the magneto-optical recording medium according to the present embodiment 5.

Comparison of the case where the composition of the first magnetic layer101was Gd35.4Fe56.3Co8.3 (atomic percentage) with the case where the composition was that of the embodiment 5 showed a higher temperature region for change from the in-plane magnetized film to the perpendicular magnetized film in the present embodiment. However, setting the reproducing power high allows magnetically induced super resolution action and achievement of recording and reproducing with the high density in the composition of the present embodiment. In this case, increasing the Curie point of the second magnetic layer102yields a higher effect.

In the present embodiment, recording and reproducing of the signal in the magneto-optical recording medium were performed by the same method as the present embodiment 4.

Also in the present embodiment in which the composition of the first magnetic layer101was Gd35.4Fe56.3Co8.3 (atomic percentage) in the abutting tracks106, the light beam reflected off the first magnetic layer101and the light beam passed through the first magnetic layer101and reflected off the second magnetic layer102cancel each other in opposite directions of the rotation directions of polarized planes. Therefore, the following effect as same as that of the present embodiment 5 yielded: cross talk magnitude showed −20 dB or smaller in a wide range of the reproducing power, particularly, cross talk magnitude showed −25 dB or smaller in the reproducing power ranging 2.0 mW and 3.0 mW.

According to the above described respective embodiments, the magneto-optical recording medium having the configuration using the disk substrate made of poly-carbonate or poly-olefin and comprising a spiral or annular guide groove or the serpentined pit for tracking guide of the light spot has been mentioned. However, the disk substrate of the configuration having a serpentined spiral guide groove having an address information or the pre-pit for tracking guide of sample surbo system, on the disk substrate may be used.

In the embodiment of the present invention, the substrate used was of the track width of 0.6 μm to 0.8 μm. However, the substrate having 1 μm or narrower shows same or similar effect as above.

The configuration is that, in the abutting tracks106through which the light beam passes, the light beam reflected off the first magnetic layer101and the light beam passed through the first magnetic layer101and reflected off the second magnetic layer102cancel each other in opposite directions of the rotation directions of polarized planes. Thus, the thickness of the first magnetic layer101is preferably 40 nm or thinner in consideration of the relationship between the thickness of the first magnetic layer101and the normalized signal shown in theFIG. 28, more preferably, 30 nm or thinner to yield the higher effect. However, the thickness less than 5 nm does not yield a satisfactory reproducing signal and therefore, a thickness of 5 nm or thicker, more preferably 8 nm or thicker.

For the first magnetic layer101of the embodiment of the present invention, GdFeCo with the composition allowing becoming in-plane magnetized film and the perpendicular magnetized film at room temperature and the high temperature, respectively, was used. Even if the composition of the first magnetic layer101is that other than the above described embodiment, the composition yields the same effect, if having the characteristics allowing becoming in-plane magnetized film and the perpendicular magnetized film at room temperature and the high temperature, respectively.

Even if the composition of the first magnetic layer101is that made of the rare-earth elements-transition metal alloy, such as GdTbFeCo, GdDyFeCo, and DyFeCo, other than the GdFeCo alloy, the composition yields the same effect if having the characteristics allowing becoming in-plane magnetized film and the perpendicular magnetized film at room temperature and the high temperature, respectively.

Even if the composition of the first magnetic layer101is made by adding such metals as Cr or Al to the rare-earth elements-transition metal alloy, the composition yields the same effect if having the characteristics allowing becoming in-plane magnetized film and the perpendicular magnetized film at room temperature and the high temperature, respectively.

In the embodiment of the present invention, TbFeCo alloy with the composition consisting of Tb22.1Fe71.2 Co6.7 (atomic percentage) was used for the second magnetic layer102. Even the composition other than the above described composition yields the same effect, if the composition has a large coercivity at room temperature, is the perpendicular magnetized film at room temperature, and keeps the recorded information.

As the recording film structure, the magneto-optical recording medium having the configuration by layering a plurality of the magnetic films such as TbFeCo, TbFe, and GdFeCo has been mentioned. However, a film made of rare-earth transition metal amorphous alloy such as TbCo, GdCo, GdTbFe, GdTbFeCo, and DyFeCo, or MnBi, PtMnSn, an magneto-optic material using a polycrystal material, or garnet, platinum group-transition metal alloy such as PtCo, and PdCo, a gold and platinum group-transition metal periodical structure alloy may be used. Or, the recording film structure containing them and configured by a plurality of the magnetic films different in materials or compositions may be used. On the other hand, an element such as Cr, Al, Ti, Pt, and Nb may be added to the above described magnetic film to improve reliability.

Concerning the recording layer and the transfer control layer which are layered on the reproduction layer and the intermediate layer, the configuration having the recording layer of a thickness ranging from 30 nm to 50 nm, and the transfer control layer of a thickness ranging from 30 nm to 35 nm has been mentioned above. The thickness is not restricted to those described above and may be a film thickness configuration satisfying a sufficient magnetic coupling force between the recording layer and the reproduction layer to satisfy the characteristics of the present invention. More preferably, the thickness of both the recording layer and the reproduction layer are in the range from 10 nm to 200 nm to yield an equal effect.

The configuration in which the transfer control layer is arranged in a side far from the recording layer in view from a side of light incidence has been mentioned above. However, when a configuration allows an abrupt change of the magnetic field transferred to the reproduction layer, the configuration in which the recording layer is arranged in a side far from the transfer control layer in view from a side of light incidence may be employed.

Magneto-optical recording medium and reproducing method thereof or the enlarging and reproducing method of the reproduction magnetic domain by shrinking action in the case of applying the magnetically induced super resolution reproducing of the CAD system by using the recording film structure of the multilayer configuration has been described so far. Applying such recording and reproducing methods to achieve a high signal quality and high recording density as other FAD system, RAD system, or other magnetically induced super resolution system or the domain enlarging and reproducing method by the domain wall moving type, or the reproducing method of the reproducing magnetic field alternation type, use of a configuration having the transfer control layer yields an equal or a better result at the time of reproducing and transferring the recording magnetic domain.

On the other hand, using the configuration of the present invention for magneto-optical recording medium having the recording film configuration applying the magnetostatic coupling for the direct overwrite system of the light modulation yields the magneto-optical recording medium and recording and reproducing method thereof excellent for abrupt transfer property.

In the third embodiment of the present invention, the configuration using the reproduction layer has been so far described. As the other configuration, a recording assist layer or the like may be added.

In case of using a nonmagnetic blocking layer as the intermediate layer, a dielectric film or a nonmagnetic alloy film may be appropriate. Besides, in case of the above described nonmagnetic alloy film, using a configuration having a reflecting layer of a nonmagnetic alloy further containing at least Al, Cu, Ag, Au can improve characteristics. The intermediate layer composed of the reflecting layer and the dielectric layer may be put on.

In the embodiment of the present invention, SiN was used for the first dielectric layer109, the second dielectric layer110, and the third dielectric layer111. The same effect is yielded by using a dielectric layer such as a nitride such as AlN and SiAlN films, an oxide such as SiO and AlO, a chalcogen compound such as ZnS and ZnTe, or a nonmagnetic material other than dielectric layer material.

In case of using the magnetic film as the intermediate layer, the intermediate layer of which domain wall energy is smaller than these layers may be put between the recording layer and the reproduction layer (or the domain enlarging layer.)

The configuration in which the heat sink layer made from a metal is put on the transfer control layer through the dielectric layer has been described so far, the configuration may be that having the heat sink layer, made from a metal, which is arranged directly on the transfer control layer or the recording layer.

The configuration may be that in which the metal made reflecting layer is further put in.

The same effect can be yielded by using a metal film such as AlTi, AlCr, Cu, Au, and Ag or a film having large heat conductivity and containing at least one species thereof, replacing to the heat releasing layer.

According to the configuration of the embodiment of the present invention as described above, the film thickness of the first magnetic layer can be decreased to 40 nm or thinner. Therefore, reduction of cost for material is possible and time for preparing a film can be shorten to improve productivity greatly.

In addition, preparing a thin film is possible. Thus, heat dispersion and heat absorbency are improved. Temperature distribution inside the magnetic layer in the region on which the beam spot is radiated can be made abrupt to improve resolution in the magnetically induced super resolution system.

According to the present invention as described above, making the thickness of the first magnetic layer thinner provides a narrowed track and a distinct effect of high density recording by that the light beam reflected off the first magnetic layer and the light beam reflected off the second magnetic layer cancel each other, the recorded information in the second magnetic layer is sufficiently masked in a temperature from the room temperature to the high temperature, and reproducing the recorded information is sufficiently made possible in the high temperature region in the beam spot, in the region changing from the in-plane magnetized film to the perpendicular magnetized film in the beam spot at the time of reproduction.