JP3484184B1 - Magneto-optical recording medium and reproducing method thereof - Google Patents

Abstract

A magneto-optical recording medium capable of preventing generation of a ghost signal and performing magnetic domain expansion reproduction without applying a reproduction magnetic field, and a recording / reproducing apparatus therefor. SOLUTION: The magneto-optical recording medium comprises a recording layer 5, an intermediate layer 4
And a reproduction layer 3. The reproducing layer 3 is formed of a rare earth transition metal alloy in which the rare earth metal is superior, and the intermediate layer 4 and the recording layer 5
Is formed from a transition metal dominant rare earth transition metal alloy.
Since the intermediate layer 4 shows in-plane magnetization at 140 ° C. or higher, the exchange coupling force between the recording layer 5 and the reproducing layer 3 is cut off during reproduction. Middle layer 4
And the magnetostatic repulsive force of the reproducing layer causes the magnetic domain 3A transferred to the reproducing layer 3 to expand to the size of the minimum magnetic domain diameter. Generation of a ghost signal can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium and a recording / reproducing apparatus therefor, and more particularly to a magneto-optical recording medium capable of reliably reproducing information recorded at high density with sufficient reproduction signal strength. The present invention relates to the recording / reproducing apparatus.

[0002]

2. Description of the Related Art With the progress of information society, the recording density of an external storage device for storing enormous amount of information has been remarkably improved. The same is true for magneto-optical disks with exchangeable media, and studies on high density by reducing the light spot size by a blue laser and a high NA lens are being actively conducted. However, since it is difficult to supply a large amount of blue laser at low cost at present, it is desired to increase the capacity with another technique while using the red laser. Since such a technique can be applied even when a large amount of blue lasers can be supplied in the future, it is considered that further large capacity recording will be possible. From such a background, in magneto-optical recording, there has been proposed a large-capacity technology utilizing the characteristics of heat and magnetism. As such a capacity increasing technique, for example, a magnetic super-resolution technique disclosed in JP-A-3-93056, a domain wall displacement reproducing technique disclosed in JP-A-6-290496, and JP-A-8-182 are disclosed.
The magnetic domain expansion reproduction technology disclosed in Japanese Patent No. 901 and the central aperture rear expansion detection technology disclosed in Japanese Patent Laid-Open No. 11-162030 are available.

When the wavelength of the light used for recording / reproducing is λ and the numerical aperture of the objective lens is NA, the diffraction limit of the focused light spot is represented by λ / NA, and half of this size can be reproduced. The minimum mark size. Since the wavelength of the blue laser is smaller than that of the red laser, the light spot size of the blue laser is smaller than that of the red laser. Therefore, by using the blue laser, it becomes possible to detect the reproduction signal from a narrower area than the conventional one. This means that it is possible to reproduce minute magnetic domains recorded at high density.

However, it is possible to effectively narrow the signal reproducing area without reducing the spot diameter of the laser beam. Magnetic super-resolution reproduction technology (Magnetic Sup
er Resolution: MSR), the effective light spot diameter is reduced by utilizing the magnetization characteristics of the recording film with respect to temperature.
The magneto-optical recording medium used in the magnetic super-resolution reproducing technique is provided with an intermediate layer having a low Curie temperature and a reproducing layer on a recording film. All of these three layers are formed by using a transition metal-dominant rare earth transition metal alloy.

The magnetic characteristics of the magneto-optical recording medium using the magnetic super-resolution reproducing technique are described in detail in, for example, Japanese Patent Laid-Open No. 3-93056 and Trikeps ultra-high density magneto-optical recording technique, page 54. The principle of magnetic super-resolution reproduction described in JP-A-3-93056 will be briefly described with reference to FIG. FIG. 49 shows the magnetization states of the magnetic domains of the recording layer, the intermediate layer and the reproducing layer of the magneto-optical recording medium for magnetic super-resolution reproduction at low temperatures. Since these three layers are exchange-coupled, the magnetic domain of the recording layer is sequentially transferred as it is to the intermediate layer and the reproducing layer. Further, as conceptually shown in FIG. 49, the magnetic layers of the three layers are attracted to each other and are also magnetostatically stabilized. Here, when the magneto-optical recording medium is irradiated with reproducing light having a large reproducing power and the intermediate layer is heated to the Curie temperature or higher, magnetization disappears in a region (high temperature region) in which the Curie temperature of the intermediate layer is exceeded. (Becomes non-magnetic), and the exchange coupling between the magnetic sections of the reproducing layer and the recording layer located above and below that area is broken. When a reproducing magnetic field (reproducing magnetic field for mask formation) is applied thereto, the magnetization of the region of the reproducing layer where the exchange coupling force is disrupted is aligned in the direction of the reproducing magnetic field to form a magnetic mask. As a result, the recording mark of the recording layer can be reproduced only in a region having a temperature lower than the Curie temperature of the intermediate layer, that is, through a narrow region which is not masked. In this magneto-optical recording medium,
If a magnetic film with a small coercive force is used for the reproducing layer, the intermediate layer that has reached the Curie temperature when the external magnetic field is applied when the reproducing light is irradiated and the optical spot center temperature is set to the Curie temperature of the intermediate layer or higher The recording magnetic domain left in the reproducing layer adjacent to the non-magnetic portion can be easily erased by the external magnetic field. Therefore, the high temperature part of the regeneration layer is
The information of the recording magnetic domain is not transferred, and it functions as a magnetic mask. When the linear velocity is increased, the temperature distribution on the recording film due to light irradiation flows in the opposite direction to the light spot traveling direction, and the recording magnetic domain can be reproduced in front of the light spot, but the information is reproduced by the mask above the center of the light spot. Not done. Since this type of magnetic super-resolution reproduction uses the front part of the light spot as the opening, the front aperture detection (Front Ap
erture detection) or FAD. However, in FAD, the resolution is increased (the mask is enlarged).
The smaller the area where the reproduced signal can be enjoyed becomes, the more the absolute signal amount decreases. This has been a problem when the density of the magneto-optical recording medium is increased, and has been a cause of limiting the improvement of recording density. Types such as center aperture detection (Rear Aperture Detection) and rear aperture detection (Rear Aperture Detection) are known for magnetic super-resolution reproduction, but any type of magnetic super-resolution reproduction has similar problems. There is.

Therefore, in order to solve this reduction of the reproduction signal, the inventors of the present invention, in Japanese Patent Laid-Open No. 182901/1996, transfer a minute recording magnetic domain recorded in the recording layer to the reproducing layer and simultaneously reproduce the reproducing magnetic field. Magnetic Amplifying MO that increases the reproduced signal by expanding with
System), or MAMMOS. However, the MAMMOS has a problem that the device configuration is complicated because the reproducing magnetic field is used for expanding the magnetic domains.

On the other hand, although the absolute signal amount does not increase so much, a domain wall moving reproducing technique is disclosed in Japanese Patent Laid-Open No. 6-2904 as a technique for ensuring a necessary minimum signal intensity and reproducing with high resolution.
No. 96 publication. The structure of the magneto-optical recording medium used in the domain wall motion reproducing technique is composed of a recording layer intermediate layer and a reproducing layer as in the FAD. In the domain wall motion reproducing technology, the domain wall in front of the magnetic domain transferred from the recording layer to the reproducing layer is disconnected from the recording layer in the region where the intermediate layer is heated and demagnetized, and this domain wall exists in the light spot. Move to the center of heat (maximum temperature reached). As a result, the magnetic domain transferred to the reproducing layer is enlarged, that is, the area of the minute magnetic domain is effectively increased, thereby slightly increasing the reproduced signal. This is because domain wall displacement type detection (Domain Wall Displacement Detection)
It is also called DWDD. Since this technique uses the force of the domain wall to move to a position where the domain wall energy is low, the inventors of the present invention can make this method feasible by the inventors' monthly publication 1998 Optical Alliance July issue page 19 As described in the left column, lines 6 to 11, it is necessary to reduce the saturation magnetization of each layer as much as possible so as not to hinder the domain wall motion. Therefore, DW
The recording layer, the intermediate layer, and the reproducing layer in the DD are all made of a magnetic material whose compensation temperature is lower than the Curie temperature. This is also described in the Institute of Electrical Engineers of Japan 1998 Study Group Material MAG98-189, page 43, right column, lower row, third line to page 44, left column, upper column, fifth line.

According to DWDD, it is possible to reproduce a minute magnetic domain, but there is a problem that the reproduction signal is small and the signal size is only the minimum level that can be accurately reproduced. Also, since it is based on the above principle, it is good to expand the magnetic domain in front of the non-magnetized region of the intermediate layer, but since the magnetic domain also expands in the rear of the non-magnetized region, the reproduced signal becomes complicated, which poses a practical problem. Became. The magnetic domain expansion from the rear appeared as an extra expansion signal on the reproduction signal and was called a ghost signal. The generation of the ghost signal is caused by devoting only the domain wall energy to the operation of domain expansion.

In order to solve the ghost signal of DWDD, it was slightly improved by providing an intermediate layer having a slightly higher Curie temperature and a smaller saturation magnetization. However, the magnitude of the reproduced signal is still insufficient.

In DWDD, in order to allow the domain wall of the reproducing layer to move smoothly, only the groove of the land groove substrate is annealed at a high temperature with high laser power to lower the domain wall energy, or the groove of the land groove substrate is reduced. It is essential to make the depth extremely deep so that the recording film practically adheres only slightly to the wall portion of the groove. However, these techniques have the following inconveniences. That is, it is difficult to fabricate a deep groove molded substrate with a high density track pitch for high density.
As Kaneko et al. Announced at NTERMAG2000, it is very difficult to accurately record the minute magnetic domains.

Further, a technique for increasing the amount of movement of the domain wall of the DWDD is disclosed in JP-A-11-162030. According to this publication, an intermediate layer of the in-plane magnetized film and a reproducing layer which changes from the in-plane magnetized film to the perpendicular magnetized film near the reproducing temperature are used. Therefore, when the reproducing layer is a predetermined temperature or lower, it becomes an in-plane magnetized film to form a mask, and the domain wall can be moved only in the central portion of the light spot having a predetermined temperature or higher. With such a configuration, the coercive force of the reproducing layer is lowered and the domain wall moves more smoothly, so that the amount of movement of the domain wall becomes larger than that of the DWDD described above. Since this is a domain wall movement detection with only the central part of the light spot as the opening, it is possible to use CARED (Center Aperture Rear
Expansion Detection) is called.

However, since a ghost signal is produced in CARE as in DWDD, another magnetic layer is added as an additional intermediate layer to prevent the ghost signal. However, when an additional intermediate layer is added, it is possible to prevent ghosts for short magnetic marks, but it is possible to prevent ghost signals for long magnetic marks in the case of CARED as well as DWDD. There wasn't. Therefore, in the recording / reproducing apparatus, only a signal processing system with a limited length can be used.

The present invention is based on the above-mentioned MSR, MAMMOS,
The present invention has been achieved in order to eliminate the inconvenience of DWDD and CARED, and its first object is to provide a magneto-optical recording medium, a reproducing method and a reproducing apparatus therefor capable of obtaining a reproduced signal of a sufficiently large size. is there.

A second object of the present invention is to provide a magneto-optical recording medium in which a ghost signal does not occur regardless of the mark length of a recording mark, a magnetic domain expansion reproducing method and apparatus thereof.

A third object of the present invention is to provide a magneto-optical recording medium capable of executing magnetic domain expansion reproduction of a magneto-optical recording medium without applying a reproducing magnetic field, and a reproducing method and apparatus thereof. .

According to a first aspect of the present invention, a magneto-optical recording medium, a recording layer formed of a magnetic material; a reproducing layer formed of a magnetic material and exhibiting perpendicular magnetization;
An intermediate layer formed of a magnetic material and existing between the recording layer and the reproducing layer; and a compensation temperature T comp of the reproducing layer.
1. Compensation temperature T comp 2 of the intermediate layer and compensation of the recording layer
償温degree T comp 3 is a compound represented by the following formula (1) and (2): T comp 2 < 120 ℃ <T comp 1 ··· (1) T comp 3 <120 ℃ <T comp 2 ··· (2) If either one of the above is satisfied, the recording layer, the intermediate layer and the reproducing layer are magnetically exchange-coupled to each other in the state where the magneto-optical recording medium is not irradiated with light, and the magneto-optical recording medium is irradiated with light to be irradiated with light. Temperature T at which the exchange coupling force between the recording layer and the reproducing layer is cut off
A magneto-optical recording medium in which the magnetic domain transferred from the recording layer to the reproducing layer is expanded by heating to r, and information is reproduced from the expanded magnetic domain. The change rate of the exchange coupling magnetic field is 100 O at the above temperature Tr.
There is provided a magneto-optical recording medium characterized by being e / ° C. to 270 Oe / ° C.

In the magneto-optical recording medium according to the first aspect of the present invention, it is preferable that the reproducing layer is made of a rare earth-transition metal alloy mainly containing GdFe.

In the magneto-optical recording medium according to the first aspect of the present invention, the compensation temperature of the reproducing layer is preferably Curie temperature or higher.

In the magneto-optical recording medium according to the first aspect of the present invention, the reproducing layer preferably has a film thickness of 15 nm to 30 nm.

According to a second aspect of the present invention, there is provided a magneto-optical recording medium, which is a recording layer formed of a magnetic material; formed of a rare earth transition metal alloy containing GdFe as a main component, and exhibits perpendicular magnetization. A reproducing layer; formed of a magnetic material, present between the recording layer and the reproducing layer, and having a perpendicular magnetic anisotropy energy at room temperature of 0.4 × 10 ⁶ erg /
cm ³ to 1 × 10 6 erg / cm 3 of an intermediate layer; and a compensation temperature T comp 1 of the reproduction layer and a compensation of the intermediate layer.
The temperature T comp 2 and the compensation temperature T comp 3 of the recording layer are below
Serial formula (1) and (2): T comp 2 < 120 ℃ <T comp 1 ··· (1) T comp 3 <120 ℃ satisfies one of <T comp 2 ··· (2) , The recording layer, the intermediate layer and the reproducing layer are magnetically exchange-coupled to each other when the magneto-optical recording medium is not irradiated with light, and the recording layer and the reproducing layer are exchanged by irradiating the magneto-optical recording medium with light. Temperature T at which binding force is cut off
A magneto-optical recording medium in which the magnetic domain transferred from the recording layer to the reproducing layer is expanded by heating to r or more, and information is reproduced from the expanded magnetic domain. Of the exchange coupling magnetic field of 10 at the above temperature Tr.
Provided is a magneto-optical recording medium having a temperature of 0 Oe / ° C to 270 Oe / ° C.

In the magneto-optical recording medium according to the second aspect of the present invention, it is preferable that the intermediate layer is made of a rare earth-transition metal alloy mainly containing TbFe.

In the magneto-optical recording medium according to the second aspect of the present invention, the intermediate layer preferably has a film thickness of 5 nm to 15 nm.

According to a third aspect of the present invention, there is provided a magneto-optical recording medium, a recording layer formed of a magnetic material; a rare-earth transition metal alloy containing GdFe as a main component and exhibiting perpendicular magnetization A reproducing layer; formed of a rare earth transition metal alloy mainly containing TbFe, present between the recording layer and the reproducing layer, and having a perpendicular magnetic anisotropy energy at room temperature of 0.4 × 10 ⁶ erg / cm ³ ~ 1 x 106er
an intermediate layer of g / cm @ 3; comprising a compensation temperature of the reproduction layer
T comp 1, compensation temperature T comp 2 of the above intermediate layer and the above record
The compensation temperature T comp 3 of the layer is expressed by the following equations (1) and (2): T comp 2 <120 ° C. <T comp 1 (1) T comp 3 <120 ° C. <T comp 2 (2) ) Is satisfied, the recording layer, the intermediate layer and the reproducing layer are magnetically exchange-coupled to each other in the state where the magneto-optical recording medium is not irradiated with light, and the magneto-optical recording medium is irradiated with light. Temperature T at which the exchange coupling force between the recording layer and the reproducing layer is cut off
A magneto-optical recording medium in which the magnetic domain transferred from the recording layer to the reproducing layer is expanded by heating to r or more, and information is reproduced from the expanded magnetic domain. Of the exchange coupling magnetic field of 10 at the above temperature Tr.
Provided is a magneto-optical recording medium having a temperature of 0 Oe / ° C to 270 Oe / ° C.

According to a fourth aspect of the present invention, the magneto-optical recording medium according to any one of the first to third aspects of the present invention is irradiated with reproducing light to interrupt the exchange coupling force between the recording layer and the reproducing layer. There is provided a reproducing method of a magneto-optical recording medium, which is characterized in that information is reproduced from the magneto-optical recording medium by heating it to a temperature Tr or higher.

In the reproducing method of the magneto-optical recording medium of the present invention,
By enlarging the magnetic domain transferred from the recording layer to the reproducing layer, it is preferable to detect the recording magnetic domain before the recording magnetic domain to be reproduced reaches the center of the reproducing light.

According to a fifth aspect of the present invention, there is provided a reproducing apparatus for reproducing recorded information from the magneto-optical recording medium according to any one of the first to third aspects of the present invention, wherein There is provided a reproducing device including a magnetic field applying unit, a signal processing unit that detects and processes a signal, and a disk drive unit.

In the magneto-optical recording medium of the present invention, an external magnetic field is applied to a magnetic domain transferred from a recording layer (hereinafter also referred to as an information recording layer) to a reproducing layer (hereinafter also referred to as an expanding reproducing layer) via an intermediate layer. It is possible to detect by enlarging by irradiating the reproducing light without doing so. In the present invention, such magnetic domain expansion is enabled by 1) the presence of the minimum magnetic domain diameter of the expanded reproducing layer, 2) generation of repulsive force between the intermediate layer and the recording layer or between the intermediate layer and the reproducing layer, and 3) expansion. It is based on factors such as controlling the exchange coupling force between the reproducing layer and the recording layer. First, those factors will be described, and then the magnifying and reproducing principles of three types of magneto-optical recording media that realize the magneto-optical recording media of the present invention will be described.

[Magnetic domain expansion factor] 1) Magnetic domain expansion principle due to existence of minimum magnetic domain diameter In order to expand the magnetic domain of the reproducing layer without requiring an external magnetic field, the minimum (stable) state that can exist stably in the reproducing layer. It is necessary to consider the size of the magnetic domain. If the magnetic domain diameter of the minimum magnetic domain in the magnetic layer having a uniform temperature is d, the energy of the domain wall of the expansion reproducing layer is σw, the saturation magnetization is Ms, and the coercive force is Hc, the minimum magnetic domain diameter d is d = σw / (Ms · It can be written as Hc).
In general, d is large when Ms is relatively small, and d is small when Ms is large.

In the present invention, as shown in FIG. 1A, as the material of the expansion reproducing layer 3, the minimum diameter of the magnetic domain SM1 which can exist magnetically stably in the expansion reproducing layer 3 (hereinafter referred to as "minimum magnetic domain"). Material with a relatively large diameter, eg Gd
Fe is used. That is, in the expansion reproducing layer 3, magnetic domains smaller than the magnetic domain SM1 cannot exist magnetically stably. On the other hand, the information recording layer 5 is shown in FIG.
Since a magnetic material such as TbFeCo which reduces the minimum magnetic domain diameter of the magnetic domain SM2 as shown in (4) is used, it is possible to record small recording magnetic domains in the information recording layer 5 at high density. Here, when the magnifying reproducing layer 3 and the information recording layer 5 are connected by a strong exchange coupling force, the magnetic domain SM2 recorded in the information recording layer 5 is magnified and reproduced as shown in FIG. 1 (c). The magnetic domain S is magnetically transferred to the layer 3
M3 occurs. However, the magnetic domain SM3 magnetically transferred to the expansion reproducing layer 3 is unstable because it is smaller than the minimum magnetic domain diameter in the expansion reproducing layer 3. Therefore, if the magnifying reproducing layer 3 is separated from the information recording layer 5 as shown in FIG. 1D, the minute magnetic domains transferred to the magnifying reproducing layer 3 are magnified and shown in FIG. 1A. Return to a stable magnetic domain SM1 having such a minimum magnetic domain diameter. In the present invention, FIG.
The process transitioning to (d) is executed by controlling the magnitude of the exchange coupling force between the enlargement reproducing layer 3 and the information recording layer 5 using various intermediate layers (enlargement trigger layer) described later.

2) Repulsive Force and Exchange Coupling Force of Magnetic Layer For the magnetic material of the recording layer, the intermediate layer and the reproducing layer, for example, a rare earth transition metal alloy can be used. Heavy rare earth is used as the rare earth, and in this case, the magnetic spins of the rare earth metal and the transition metal face in opposite directions to each other, so that the magnetic layer exhibits ferrimagnetism. If the magnetic spins of the rare earth metal and the transition metal are of the same magnitude, the magnetization directions are opposite to each other, that is, the magnetizations cancel each other, so the overall magnetization (sum of magnetic spins)
Is zero. This state is called a compensation state, and the temperature at which it is in a compensation state is called the compensation temperature. The composition of the magnetic layer that is in the compensation state is called the compensation composition. When the magnetic spin of the transition metal is larger than that of the rare earth metal, the transition metal rich (TM)
Rare earth metal (Rare) metal magnetic spin is greater than the transition metal magnetic spin (Rare earth rich (Rare)
Earth rich: called RE rich). In the present invention,
Compensation temperature Tcomp1 of the reproducing layer, compensation temperature Tcomp2 of the intermediate layer
And the compensation temperature Tcomp3 of the recording layer satisfies one of the following equations (1) and (2). Tcomp2 <120 ° C <Tcomp1 (1) Tcomp3 <120 ° C <Tcomp2 (2)

Expressions (1) and (2) represent the condition that there is a repulsive force that is a trigger for the expansion of magnetic domains in the present invention. In the case of Formula (1), the compensation temperature of the intermediate | middle layer 4 exists in the temperature lower than 120 degreeC, and the compensation temperature of the reproduction | regeneration layer exists in the temperature higher than 120 degreeC. For example, when the reproducing layer 3 and the intermediate layer 4 are each made of a ferrimagnetic rare earth transition metal, the intermediate layer 4 is TM rich at 120 ° C. and the reproducing layer 3 is RE as shown in FIG. 2A. Become rich. Therefore, the magnetic spins (sub-network magnetization) of the transition metal in the intermediate layer 4 and the reproducing layer 3 are oriented in the same direction, and the magnetizations (overall magnetization) are in mutually opposite directions, and a repulsive force is generated. In the present invention, generation of such a repulsive force is a requirement for magnetic domain expansion in the reproducing layer 3. Here, assuming that the recording layer 5 is composed of a TM-rich rare earth transition metal like the intermediate layer 4, the magnetic spins of the transition metals are connected between the reproducing layer 3, the intermediate layer 4 and the recording layer 5, and reproduction is performed. An exchange coupling force acts between the layer 3 and the recording layer 5 via the intermediate layer 4. Here, since the exchange coupling force has temperature dependence, 1
When the temperature rises from 20 ° C., the repulsive force exceeds the exchange coupling force and the magnetic domains of the reproducing layer 3 are likely to be reversed. This domain reversal causes domain expansion.

In the case of the formula (2), the compensation temperature of the recording layer 5 exists at a temperature lower than 120 ° C., and the compensation temperature of the intermediate layer 4 exists at a temperature higher than 120 ° C. For example, when the recording layer 5 and the intermediate layer 4 are each made of a ferrimagnetic rare earth transition metal, as shown in FIG.
At 0 ° C., the recording layer 5 is TM rich and the intermediate layer 4 is RE.
Become rich. Therefore, the magnetization of the recording layer 5 and the magnetization of the intermediate layer 4 are in opposite directions, and a repulsive force is generated. Here, assuming that the reproducing layer 3 is made of a RE-rich rare earth transition metal like the intermediate layer 4, the exchange coupling force acts on the reproducing layer 3 and the recording layer 5 via the intermediate layer 4. Since the exchange coupling force has temperature dependency, when the temperature rises from 120 ° C., the repulsive force between the magnetization of the reproducing layer 3 and the intermediate layer 4 and the magnetization of the recording layer 5 causes the exchange coupling between the recording layer 5 and the reproducing layer 3. Surpass the power,
The magnetic domains of the intermediate layer 4 and the reproducing layer 3 are easily reversed. The domain reversal of the reproducing layer 3 causes the domain expansion. If either of the above equations (1) and (2) is satisfied, a repulsive force that triggers the expansion of magnetic domains will be generated in the present invention. In the following description of the reproduction principle of each type of magneto-optical recording medium, description will be made mainly using the condition of the expression (1).

As described above, in the present invention, the relationship between the repulsive force and the exchange coupling force controls the magnetic domain expansion. It should be noted that the temperature of 120 ° C. is assumed to be the temperature of the region where the magnetic domain expansion will start to occur due to the irradiation of the reproducing light. That is, in the present invention, the region where the magnetic domain expansion begins is not the central portion, that is, the high temperature portion (heat center), but the peripheral portion, that is, the low temperature portion, in the region that is heated by being irradiated with the reproducing light. On the other hand, in the high temperature portion, the exchange coupling force between the recording layer and the magnifying and reproducing layer is cut off, as will be described later. This high temperature region is 140 ° C. in the present invention.
It is assumed that the temperature exceeds.

3) Control of Exchange Coupling Force In the magneto-optical recording medium of the present invention, the intermediate layer has the exchange coupling force and the repulsive force acting between the recording layer and the expansion reproducing layer in any type of magneto-optical recording medium. By controlling the size, the magnetic domain expansion in the expansion reproducing layer is optimized and the generation of a ghost signal is prevented. Particularly, at the time of information reproduction, the intermediate layer blocks the exchange coupling force acting between the recording layer and the expansion reproducing layer in the high temperature region within the region irradiated with the reproduction light, and the magnetic domain of the expansion reproducing layer in the low temperature region is blocked. Expands to high temperature regions. The temperature at which this exchange coupling force is cut off is called the exchange coupling force cutoff temperature. The exchange coupling force cutoff temperature can be obtained from the temperature dependence of the exchange coupling force (exchange coupling magnetic field). The exchange coupling force can be determined from the magnetic field dependence of the magneto-optical Kerr rotation angle from the expansion reproducing layer side. FIG. 25 shows an example of measurement of the hysteresis curve of the magneto-optical Kerr rotation angle (θ) of the magneto-optical recording medium of the present invention at room temperature. An exchange coupling force (exchange coupling magnetic field) acts as a bias magnetic field from the information recording layer having a large coercive force on the expansion reproducing layer. Therefore, the hysteresis curve is shifted to the left by the magnetic field, and this shift amount is the exchange coupling force. An example of the temperature dependence of this exchange coupling force is shown in FIG. The exchange coupling force cutoff temperature corresponds to the temperature at which this exchange coupling force becomes almost zero.

[First Type Magneto-Optical Recording Medium] In order to control the magnitude of the exchange coupling force between the magnifying reproducing layer and the information recording layer, the first type magneto-optical recording medium has a high temperature, for example, 140 ° C. The above shows in-plane magnetization, and at low temperature, for example, 120 ° C.
Below, an intermediate layer that exhibits perpendicular magnetization is used. A perpendicularly magnetized magnetic layer can be used for the recording layer and the reproducing layer. in this case,
When the intermediate layer exhibits perpendicular magnetization, the exchange coupling force between the expansion reproducing layer and the information recording layer is strong, but when the intermediate layer exhibits in-plane magnetization at high temperature, the exchange coupling force between the expansion reproducing layer and the information recording layer. Is weakened by being cut or blocked by the intermediate layer. In order to increase the exchange coupling force between the expansion reproducing layer and the information recording layer at a low temperature, the Curie temperature Tc2 of the intermediate layer may be set higher than the Curie temperature Tc1 of the expansion reproducing layer. However, in order to avoid the adverse effect of recording on the information recording layer,
Tc2 needs to be lower than the Curie temperature Tc3 of the information recording layer. Therefore, in the magneto-optical recording medium of the first type, the Curie temperatures of those magnetic layers can have a relationship of Tc1 <Tc2 <Tc3.

Here, as shown in FIG. 3, an intermediate layer between the information recording layer 5 and the expansion reproducing layer 3, which exhibits in-plane magnetization at high temperature and perpendicular magnetization at low temperature, such as an expansion trigger layer. Consider a magneto-optical recording medium in which 4'is present. It is assumed that minute magnetic domains are recorded in the recording layer 5 at a high density. When the laser beam is not irradiated, the magnetic domain 5A recorded in the information recording layer 5 is expanded by the large exchange coupling force between the expansion reproducing layer 3 and the information recording layer 5 via the expansion trigger layer 4 '. Magnetically transferred to form magnetic domains 3A.
As shown in FIG. 4, when the magneto-optical recording medium is irradiated with laser light while advancing in the direction of arrow DD, the temperature of the region within the laser spot of the magneto-optical recording medium rises. Of the region where the temperature has risen at this time, a particularly high temperature portion (for example, 140 ° C.)
In the above), since the magnetic anisotropy of the expansion trigger layer 4'abruptly decreases, the easy axis of magnetization of the expansion trigger layer 4'is directed from the vertical direction to the film surface direction. At this time, since the perpendicular magnetization component of the expansion trigger layer 4'is reduced, the exchange coupling force between the expansion reproducing layer 3 and the information recording layer 5 is sharply reduced and cut off. If the temperature at which this exchange coupling force is cut off is Tr,
As shown in FIG. 5, in the temperature region exceeding Tr, the expansion reproducing layer 3 and the information recording layer 5 are magnetically independent. Tr is, for example, 120 ° C to 180 ° C, preferably 140 ° C to 180 ° C.

Further, the magneto-optical recording medium advances in the direction DD, and as shown in FIG.
When approaching the region of> Tr, the combined magnetization of the magnetization of the magnetic domain 5A of the information recording layer 5 and the magnetization of the magnetic domain 4'A of the expansion trigger layer 4'and the magnetization of the transfer magnetic domain 3A of the expansion reproduction layer 3 The magnetostatic repulsive force exceeds the exchange coupling force between the magnetic domain 3A of the expansion reproducing layer 3 and the magnetic domain 5A of the information recording layer 5 through the expansion trigger layer 4 '. In particular, the magnetic domain 3 of the expansion reproducing layer 3
B is a magnetic domain transferred from the magnetic domain 5B of the recording layer 5 by the exchange coupling force. However, since it is in the laser spot, the repulsive force with the magnetic domain 4'B of the expansion trigger layer is stronger than the exchange coupling force. ing. Further, as described above, the expansion reproducing layer 3
Since the diameter of the stable magnetic domain is large, the magnetic domain 3A has a force to return to its original size. Therefore, magnetic domain 3A and magnetic domain 3B
Magnetic pressure acts on the domain wall (3AF) between
As shown in FIG. 7, when the magnetic domain 3B is inverted, the magnetic domain 3A
Expands. Then, the enlarged magnetic domain 3A spreads in the vicinity of the region where the exchange coupling force is weakened, as shown in FIG. The enlarged region can be considered to have a size corresponding to the stable magnetic domain diameter of the enlarged reproducing layer 3. As described above, the expansion trigger layer 4 ′ causes the magnetic domain of the expansion reproducing layer 3 to expand due to the temperature change.

What is important here is that when the magnetic domain 3A expands, even if the front edge 3AF (see FIG. 6) of the magnetic domain 3A expands toward the spot center, the rear edge 3AR does not move. This is because if the rear edge 3AR also moves toward the spot center in conjunction with the expansion of the front edge 3AF, the area of the magnetic domain 3A does not increase. Therefore, the important point of the magnetic domain expansion layer 3 is that the front edge 3AF is easy to expand, the rear edge 3AR having a temperature slightly lower than the front edge 3AF does not move, and the magnetic domain of the recording layer 5 remains transferred. Is that you are saving. To achieve this, a material that has a steep temperature gradient of the exchange coupling force in the vicinity of Tr may be used. Experimentally, this temperature gradient is −10 near 130 ° C. which is considered to be near Tr.
It is preferably 0 (Oe / ° C.) or more. Further, if the thickness of the expansion reproducing layer 3 is large, it tends to be difficult to expand, and it is preferably 15 to 30 nm.

FIG. 9 shows a state in which the magneto-optical recording medium moves with respect to the light spot and the magnetic domain 5C adjacent to the magnetic domain 5A is enlarged and reproduced according to the principle of the present invention. Figure 1
0 shows that the magneto-optical recording medium further moves with respect to the light spot and the magnetic domain 5D adjacent to the magnetic domain 5C reproduced in FIG. 9 is enlarged and reproduced. As can be seen from FIG. 10, the information recording layer 5 in the temperature region exceeding Tr
The magnetic domain 5A of FIG. 3B emits a leakage magnetic field toward the expansion reproducing layer 3, but the leakage magnetic field is blocked because the magnetic domain of the expansion trigger layer 4 ′ located thereabove shows in-plane magnetization. Therefore, regardless of the direction of the magnetic domain of the recording layer 5 located in the region where the enlargement is occurring, the enlargement operation of the enlargement reproducing layer 3 is not affected.

Now, as shown in FIG. 11, the recording magnetic domain 5A which has been enlarged and reproduced and reproduction is completed is cooled when it escapes from the light spot. In the cooled region, the perpendicular magnetic anisotropy of the magnetic domain 4'A of the expanded trigger layer 4'is restored,
Exchange coupling between the magnetic domain 3A of the expansion reproducing layer 3 and the magnetic domain 5A of the recording layer 5 will be restored. However, since the magnetostatic repulsive force is stronger than the exchange coupling force, the magnetic domain 5A is not transferred to the expansion reproducing layer 3. Further, in FIG. 12 where the magnetic domain 3A is away from the spot, the exchange coupling force is large, but as explained in FIG. Requires a lot of energy. Therefore, even in this state, the magnetic domain 5A of the recording layer is not yet transferred to the expansion reproducing layer 3. Therefore, in the present invention, the ghost signal due to the retransfer of the magnetic domain 5A of the recording layer in which the reproduction of the information is completed to the expansion reproducing layer 3 does not appear.

[Second Type Magneto-Optical Recording Medium] The operation principle of the second type magneto-optical recording medium will be described below with reference to the drawings. The recording layer, the intermediate layer, and the reproducing layer of this type of magneto-optical recording medium are all made of a rare earth transition metal alloy exhibiting perpendicular magnetization. 16 middle layers
It has a Curie temperature of 0 ° C. or lower and a compensation temperature of room temperature or lower. Therefore, when the magneto-optical recording medium is heated by being irradiated with the reproducing light, the magnetization disappears in the high temperature region (160 ° C. or higher) of the intermediate layer. FIG. 13 shows the states of the magnetic domains of the recording layer 5, the intermediate layer 4 and the reproducing layer 3 of the magneto-optical recording medium before being irradiated with the reproducing light. The sizes of the magnetic domains in each layer are all the same in the disc traveling direction. In FIG. 13, the thick arrow (white arrow) is
The thin arrows inside the thick arrows indicate the total (synthetic) magnetization of each layer, and transition metals (Fe and Co)
Shows the magnetic spin of. In this type of magneto-optical recording medium, when reproducing light is irradiated and heated to near the reproducing temperature (for example, 120 ° C. to 200 ° C.), the reproducing layer 3 is RE rich as shown in FIG. And whether the intermediate layer 4 and the recording layer 5 are TM-rich (Equation (1) above)
Alternatively, the reproducing layer 3 and the intermediate layer 4 are RE rich, and the recording layer 5 is TM rich (satisfying the above formula (2)).

Since the respective transition metals of the recording layer 5, the intermediate layer 4 and the reproducing layer 3 are bonded to each other with a strong bonding force of several tens kOe or more at room temperature, as shown in FIG. In the magnetic domains in the same column of the transition metals of the intermediate layer 4 and the reproducing layer 3, all the thin arrows indicating the magnetic spins point in the same direction. Since the intermediate layer 4 and the recording layer 5 are TM-rich, their overall magnetizations are oriented in the same direction as the spin of the transition metal in the same column magnetic domain. On the other hand, since the reproducing layer 3 is RE-rich, the overall magnetization is in the direction opposite to the spin of the transition metal. That is, the overall magnetization of the magnetic domains in the reproducing layer 3 is opposite to the overall magnetization of the magnetic layers of the intermediate layer 4 and the recording layer 5 thereunder,
The magnetic domains of the recording layer 5 are transferred to the reproducing layer 3 in the opposite direction.
Here, if the respective magnetic domains of the reproducing layer 3 and the intermediate layer 4 are conceptually regarded as the magnets 3a and 4b as shown in the right side of FIG. The opposite state is the same as the state in which the same poles of the magnets 3a and 4a are close to each other, and is a state that is extremely unstable magnetostatically. That is, the magnetostatic energy repulsive force acting between the intermediate layer 4 and the reproducing layer 3 causes an unstable state. However, since the exchange coupling force between spins of the transition metals of the reproducing layer 3 and the intermediate layer 4 is stronger than the repulsive force of magnetostatic energy, the reproducing layer 3 and the intermediate layer 4 as shown in FIG. The state in which the overall magnetization is opposite to each other is maintained.

In order to reproduce information, as shown in FIG. 14A, a reproducing laser beam is focused on a magneto-optical recording medium by an objective lens and irradiated to form a light spot S on the reproducing layer 3. A temperature distribution is generated in the light spot S according to the light intensity distribution of the laser light, and the temperature near the center of the light spot S becomes high. At this time, the region 11 heated below the Curie temperature of the intermediate layer 4 (hereinafter referred to as the regeneration temperature region)
Then, the magnetization disappears, and the magnetic coupling (exchange coupling) between the magnetic domain 15 of the recording layer 5 and the magnetic domain 13 of the reproducing layer 3 located above and below the reproducing temperature region 11 of the intermediate layer is lost. In this way, the intermediate layer 4 blocks the exchange coupling force between the recording layer 5 and the reproducing layer 3 by heating by irradiation with laser light, and thus the intermediate layer can also be called an exchange coupling force blocking layer.

Here, as shown in FIG. 14A, the reproducing temperature region 1 of the intermediate layer 4 is heated by the irradiation of the reproducing laser beam.
Consider the magnetic domain 23 of the reproducing layer 3 and the magnetic domain 25 of the intermediate layer 4 below that which are adjacent to the part where the magnetization of No. 1 disappears. In this situation, the magnetic domain 13 existing in the reproducing temperature region of the reproducing layer 3 also loses the exchange coupling force with the recording magnetic domain 15 of the recording layer 5. At this time, the transfer magnetic domain 23 in the light spot of the reproducing layer 3 is considered to be either enlarged as shown in FIG. 14B or contracted as shown in FIG. 14C.

Here, as shown in FIG. 15A, it is assumed that the magnetic domain wall 26 of the magnetic domain 23 of the reproducing layer 3 does not move when irradiated with the reproducing laser beam and remains in the same state. At that time, the relationship between the magnetostatic energy repulsive force acting on the lower surface of the reproducing layer 3 and the exchange energy attractive force (exchange coupling force) is shown in FIG. As shown in FIG. 15A, in the right part of the reproduction light spot, the temperature of the reproduction layer 3 is still low, and a large exchange energy attractive force and a relatively large magnetostatic energy repulsion force are exerted on the reproduction layer 3. The exchange energy attractive force is an attractive force generated based on the exchange coupling energy between the transition metal of the reproducing layer 3 and the transition metal of the intermediate layer 4. Since the transition metals exhibit strong binding force, they are extremely large in the low temperature region. It shows the value and exceeds the repulsive force of magnetostatic energy. Then, the exchange energy attractive force sharply decreases from the low temperature region to the regeneration temperature region,
It becomes zero in the regeneration temperature range. This is because the magnetization of the intermediate layer 4 disappears in the reproduction temperature region and the exchange coupling force disappears. On the other hand, the magnetostatic energy repulsive force is a repulsive force based on magnetostatic energy that acts between the entire magnetization of the intermediate layer and the overall magnetization of the reproducing layer, which are opposite to each other.
In the region 4A of the mid layer 4, the magnetostatic repulsive force exceeds the exchange coupling force. As shown in FIG. 15B, the repulsive force of the magnetostatic energy decreases because the magnetization of the intermediate layer 4 decreases as the temperature approaches the reproduction temperature range from the low temperature range. However, the magnetostatic energy repulsive force does not become zero even in the reproduction temperature region and has a predetermined value. That is, the magnetostatic energy repulsive force acts on the magnetic domain 27 of the reproducing layer in the reproducing temperature region. This is because, as shown in FIG. 15A, the magnetization of the magnetic domain 27 of the reproducing layer in the reproducing temperature region is opposite to the magnetization of the magnetic domain 28 of the recording layer in the reproducing temperature region, and the repulsive force is generated between the magnetic domains. Because it is working. In this case, first, as shown in FIG.
In the magnetic domain 23 'on the left side of 3, the repulsive force of magnetostatic energy exceeds the exchange energy attractive force, so that the magnetic domain 23' is reversed. The minimum magnetic domain diameter of the magnified reproducing layer is larger than the minimum magnetic domain diameter of the recording magnetic domain, and the magnetic characteristics are adjusted so as to be approximately the same as the light spot diameter (80 μemu / cm ² <saturation magnetization of reproducing layer × film thickness <220 μemu / cm ² ), the magnetic domain of the expansion reproducing layer expands to almost the light spot diameter like the magnetic domain 23A of FIG. 16B. At this time, FIG.
As shown in (b), the magnetization of the enlarged magnetic domain 23A of the reproducing layer is oriented in the same direction as the magnetization of the magnetic domain 28 of the recording layer, so that the repulsive force of magnetostatic energy is further reduced. That is, FIG.
The transfer magnetic domain 23 in the reproducing temperature region within the light spot of the expanding reproducing layer 3 shown in FIG. 14A is expanded as shown in FIG. 14B. This is due to the magnetic property that the small magnetic domain cannot be maintained due to the size of the minimum magnetic domain diameter when the magnetization of the expansion reproducing layer 3 is relatively small. When such magnetic domain expansion is used, a large reproduction signal can be detected from the reproduction layer. FIG. 19 shows a case where the disk further advances in the direction of the arrow and the recording magnetic domain 25 in FIG. 16B moves to a high temperature portion in the light spot. In this case, the leakage magnetic field extends from the recording magnetic domain 25 to the expansion reproducing layer 3, but since the expansion reproducing layer 3 has the minimum transferable magnetic domain diameter as described above, a magnetic domain smaller than this can be transferred. Can not. That is, the state of the recording layer 5 (recording magnetic domain 25) in the high temperature portion is not transferred to the expansion reproducing layer 3.

As shown in FIG. 14 (c), when the transfer magnetic domain of the reproducing layer is contracted, the magnetostatic energy in the reproducing layer rises, resulting in an unstable energy state. Therefore, it is considered that the magnetic domain 23 does not shrink as shown in FIG.

In order to better expand the magnetic domain in such a reproducing layer, it is preferable that the intermediate layer has a large perpendicular magnetic anisotropy energy (Ku) and is a perpendicular magnetic film up to around the Curie temperature. . Here, an example in which Ku of the intermediate layer is small is shown in FIGS. 17 (a) and 17 (b). Middle layer 4
When Ku is small, the magnetic domain 59 near the Curie temperature of the intermediate layer 4 is oriented in the in-plane direction due to the repulsive force of the magnetostatic energy from the reproducing layer 3. Therefore, the magnetic domain expansion of the reproducing layer 3 occurs in the reproducing layer region 23B immediately above the non-magnetic region ((Tc ≦ T)) of the Curie temperature of the intermediate layer 4 as shown in FIG. Is small.
Further, in this case, the place where the reproduction layer and the intermediate layer are disconnected becomes ambiguous, which may increase the amount of jitter. therefore,
The intermediate layer 4 preferably has large perpendicular magnetic anisotropy. However, when an experiment was performed using a TbFe alloy having a maximum Ku near the Curie temperature of 150 degrees for the intermediate layer, the temperature gradient of the exchange energy attractive force became too steep, and therefore the static energy shown in FIG. In some cases, the buds of magnetic domain expansion due to magnetic energy repulsive force became even. From the experimental results, the Ku of the intermediate layer is 0.4er.
It was found that g / cm ^{3 to 1} erg / cm ³ is preferable. From the experimental results, in order to reduce the error rate in particular, the optimum intermediate layer was the case where the TbGdFe alloy was used and the atomic ratio of Gd to Tb was 1/5 or less. A relatively good recording / reproducing result can also be obtained by adding a non-magnetic metal or the like to the TbFeCo alloy to reduce Ku and keep the value of Ku within the above range.

Here, when magnetic domain expansion reproduction is performed in the second type magneto-optical recording medium, DWDD and CARE D
The reason why the ghost signal generated in 1 is prevented will be described below with reference to the drawings.

In FIG. 18A, when the medium is scanned with the light spot, the recording magnetic domain 25 of the recording layer 5 existing in the light spot is cooled to the Curie temperature or lower and regained the magnetization. 4 shows the state in which the retransferred magnetic domain 31 is generated by being transferred to No. 4 of FIG. At this time, since the magnetostatic energy repulsion is strong in the high temperature side of the retransfer magnetic domain 31 of the intermediate layer, that is, in the right region 31A, the retransfer magnetic domain 31 of the intermediate layer and the magnetic domain of the reproducing layer cannot be exchange-coupled. In addition, retransfer magnetic domain 3
In the region 31B on the left side of 1, the retransfer magnetic domain 31 and the magnetic domain of the reproducing layer can be exchange-coupled, but the transfer magnetic domain size is too small to transfer. Therefore, since the transfer magnetic domain does not appear, the ghost signal does not appear. Further, FIG. 18 (b)
As shown in FIG. 18, when the disc is further rotationally moved from the state shown in FIG. 18A (when the recording magnetic domain 25 is separated from the light spot), the area of the portion to be exchange-coupled on the left side of the retransfer magnetic domain 31. Therefore, the transfer magnetic domain 23 appears in the reproducing layer. However, the magnetic domain 55 on the right side of the transfer magnetic domain 23 of the reproducing layer (the magnetic domain on the light spot side) cannot be reversed because the magnetostatic energy repulsive force is predominant at the interface 31A with the intermediate layer 4, and therefore, No ghost signal is generated.

In the DWDD, the magnetizations of the reproducing layer, the intermediate layer and the recording layer are designed to be extremely small, so that the magnetostatic energy repulsive force between the reproducing layer and the intermediate layer does not act as in the present invention, and the reproducing layer can be easily formed. The magnetic domain is retransferred to. Therefore, the high temperature side domain wall of the retransfer magnetic domain moves along the temperature gradient to generate a ghost signal. In CARE, as a result of the optimization of the intermediate layer at the 2000 Academic Lecture Meeting of the Japan Society for Applied Magnetics, GdFeCr with a small Ku was good for the intermediate layer, and Tb
It has been reported that the characteristics are not improved in FeCoSi. However, in the present invention, the result that the ghost signal does not appear by using TbGdFe for the intermediate layer was obtained. This means that when the non-magnetic region of the intermediate layer is restored from the high temperature portion to the low temperature portion, the Ku of GdFeCr is only 2 × 1.
Since it is only about 0 ⁵ erg / cm ³ , the force is reduced in the in-plane direction so as not to repel the magnetostatic energy repulsive force and exchange energy attractive force of the reproducing layer.
Therefore, the magnetic domains of the recording layer are easily transferred to the reproducing layer by the exchange energy attractive force, and a ghost signal is generated. However, the TbG used in Example 8 described later
Since Ku of dFe is as large as 7 × 10 ⁵ erg / cm ^3, it is considered that no ghost signal appears because retransfer from the intermediate layer to the reproducing layer is not easily allowed. Further, when the magneto-optical Kerr effect is examined by making light incident on the magneto-optical disk from the film surface side, in the case of the magneto-optical disk using GdFeCr for the intermediate layer, the Kerr hysteresis loop shifts to the left or right, Moreover, it does not show the abrupt transition peculiar to the perpendicular magnetization film. However, in the case of the magneto-optical disk using TbGdFe for the intermediate layer, a steep transition is shown in the portion shifted with respect to the external magnetic field. Therefore, the above method can be used as a method for investigating the influence of Ku in the intermediate layer.

In the second type of magneto-optical recording medium,
An example in which the TM-rich rare earth transition metal is used for the intermediate layer 4 has been described according to the above-described formula (1). However, the magnetostatic repulsive force may be established between the expansion reproducing layer 3 and the recording layer 5, that is, the intermediate layer is RE
It may be rich. In FIG. 47, near the regeneration temperature (1
The intermediate layer showed a RE-rich state at 20 ° C to 160 ° C. In this case, the spins of the transition metals of the expansion reproducing layer 3, the intermediate layer 4 and the recording layer 5 are oriented in the same direction (upward) due to the exchange coupling force when the recording magnetic domain 5A is close to the light spot. It can be seen that a magnetostatic repulsive force is generated between the magnetic domain 4A and the magnetic domain 5A of the recording layer 5. When the disk further rotates and approaches the light spot, as shown in FIG. 48, in the magnetic domain 4B adjacent to the magnetic domain 4A, the exchange coupling force with the magnetic domain 5B immediately below the magnetic domain 4B is weakened, and the magnetostatic force in those magnetic domains is increased. Since the repulsive force is stronger than the exchange coupling force, the magnetic domain 4B of the intermediate layer is reversed. As a result of this, the magnetic domain 3B of the magnified reproducing layer, which was transferred by the exchange coupling force with the magnetic domain 4B, is also inverted. Inversion of magnetic domain 3B
Corresponds to the start of expansion. After that, the magnetic domain 3A further expands to the minimum magnetic domain diameter. As described above, even when the magnetostatic repulsive force exists between the magnifying and reproducing layer 3 and the recording layer 5, that is, even when the above-mentioned formula (2) is satisfied, the effect of the magnetic domain magnifying and reproducing of the present invention is obtained. Is obtained. The above equation (2) is applicable to the above-mentioned first type magneto-optical recording medium and the third type magneto-optical recording medium described later.

[Third Type Magneto-Optical Recording Medium] In the third type magneto-optical recording medium, the substance forming the intermediate layer at the interface between the intermediate layer and the recording layer or at the interface between the intermediate layer and the expansion reproducing layer is It has different substances in between. This material reduces the Curie temperature of the intermediate layers at their interface,
Alternatively, the Curie temperature of the substance itself is lower than the Curie temperature of the intermediate layer. By having such a substance on the surface of the intermediate layer or at the interface between the intermediate layer and the recording layer or the expanding reproducing layer, the exchange coupling force between the recording layer and the expanding reproducing layer is blocked at the reproducing temperature. In order to introduce such a substance, the intermediate layer or its interface may be subjected to sputtering, ion etching or heat treatment. Alternatively, a layer having a low Curie temperature, for example, a rare earth element or nickel may be deposited on the interface between the recording layer and the intermediate layer or the interface between the expansion reproducing layer and the intermediate layer by a vapor phase method or the like.

In the third type of magneto-optical recording medium, the intermediate layer 4 may remain magnetized at the reproducing temperature or higher. That is, the Curie temperature of the material of the intermediate layer 4 may be the regeneration temperature, particularly 160 ° C. or higher. Therefore, in the third type magneto-optical recording medium, the Curie temperature of the intermediate layer may be set higher than the Curie temperature of the expansion reproducing layer, as in the first type magneto-optical recording medium.

In the first to third types of magneto-optical recording media, in order to more easily expand the magnetic domain transferred to the reproducing layer, it is desirable to reduce the magnetization of the reproducing layer to some extent. The saturation magnetization of the layer is preferably 80 emu / cm ³ or less at a temperature of 120 ° C.
Further, in order to prevent generation of a ghost signal, the saturation magnetization of the reproducing layer is preferably 40 emu / cm ³ or more at around 120 ° C.

In the magneto-optical recording media of the first to third types, the exchange energy attractive force (exchange coupling force) as shown in FIG. 15B is sharply reduced at the boundary between the reproducing temperature region and the low temperature region. It is preferable to design As a result, the domain wall on the light spot center side of the minute magnetic domain transferred to the reproducing layer moves toward the light spot center side, so that even if the minute magnetic domain transferred to the reproducing layer expands, it is opposite to the light spot center of the minute magnetic domain. The domain wall on the side is fixed without moving (Fig. 6).
(See front edge 3AF and rear edge 3AR) of
More stable expansion playback is possible. In order to make the inclination of the exchange energy attractive force curve shown in FIG. 15B steep at the boundary between the reproduction temperature region and the low temperature region, for example, the perpendicular magnetic anisotropy energy at room temperature of the intermediate layer is 0.4 × 10
^It may be ⁶ erg / cm ³ or more.

In the present invention, particularly in the second type magneto-optical recording medium, the magnetization of the intermediate layer is preferably large to some extent, and the saturation magnetization near 100 ° C. is 50 em.
It is preferably u / cm ³ or more. As a result, an appropriate magnetostatic energy repulsive force for easily enlarging the transfer magnetic domain of the reproducing layer can be obtained, and the DWDD and CARED can be obtained.
It is possible to prevent the occurrence of such a ghost signal.
As a material having such characteristics, for example, TbGd containing Gd at a ratio of 1/5 or less with respect to Tb is used.
Fe alloys are preferred. A non-magnetic metal may be added instead of some Gd. In the second type magneto-optical recording medium, if the Curie temperature of the intermediate layer is too high, the magnetic domain expansion signal from the reproducing layer may be small when information is reproduced. Is 160 ° C
The following are preferred.

Further, as shown in FIG. 15B, in order to obtain an appropriate repulsive force of magnetostatic energy, the saturation magnetization of the recording layer is 50 emu / cm ^{3 in} the temperature range of 150 ° C. to 200 ° C.
The above is preferable.

The magneto-optical recording medium of the present invention has a reproducing layer of 20.
Since it is a perpendicular magnetization film in the temperature range from ℃ to near the Curie temperature, it effectively prevents the magnetic domain of the recording layer from being retransferred to the reproducing layer and generating a ghost signal. A GdFe alloy such as GdFe or GdFeCo is most suitable for such a reproducing layer.

The recording layer of the magneto-optical recording medium of the present invention is preferably formed with a gas pressure of 0.4 Pa or more using a sputtering gas mainly containing argon. 0.4 Pa
In the recording layer formed by the above gas pressure, since the magnetic particles are made finer, fine reversal magnetic domains can exist in the recording layer, and it becomes possible to surely form minute magnetic domains.

In order to form a minute magnetic domain in the recording layer,
At the time of information recording, it is preferable to reduce the influence of a leakage magnetic field from a magnetic layer other than the recording layer. To do this, for example,
The Curie temperature of the reproducing layer may be lower than the Curie temperature of the recording layer by 30 ° C. or more. As a result, the magnetization of the reproducing layer disappears or becomes smaller due to the heating due to the irradiation of the recording laser beam at the time of recording information, so that the leakage magnetic field is prevented or reduced from being applied to the recording layer. Further, in order to be able to form a minute magnetic domain in the recording layer, the recording layer is made of a metal mainly composed of a noble metal such as Pt, Pd, Au, Ag or a dielectric such as SiO _2. Clusters having a particle size of 20 nm or less may be mixed at a concentration of 30% or less. The concentration of the substance mixed in the recording layer is 30%
If it exceeds, the magnetization or perpendicular magnetic anisotropy energy may decrease and the recording performance may deteriorate. Therefore, the content is preferably 30% or less. Such a recording layer has a magnetic domain diameter of 50 nm or less and 100 nm when demagnetized by AC at around 150 ° C.
Recording of the following magnetic domains becomes easy.

Further, in order to record a finer minute magnetic domain in the recording layer, a part or the whole of the recording layer, for example, Co
Of 0.4 nm or less mainly composed of Pd or 1.2 nm or less, preferably 0.8 n or less mainly composed of Pd or Pt
It is preferable to use a magnetic multilayer film in which 5 or more and 40 or less metal layers having a thickness of m or less are alternately laminated. Such a magnetic multilayer film has a perpendicular magnetic anisotropy energy which is more than twice as large as that of the TbFeCo single layer. The recording layer having a large perpendicular magnetic anisotropy energy can stably store the formed fine magnetic domain for a long period of time. Further, the large perpendicular magnetic anisotropy energy of the magnetic multilayer film varies depending on the state of the underlayer of the magnetic multilayer film. When a magnetic multilayer film is used as the recording layer, Pt, Pd, Au, A
It is preferable that clusters having a particle size of 20 nm or less, which are composed of a metal mainly composed of g or other noble metal or a dielectric such as SiO _2, be mixed and have a particle size of 20 nm or less. In order to record fine minute magnetic domains in the recording layer, part or all of the recording layer may be formed of a local compound alloy containing Co and Pd or Pt as a main component. Alternatively, Pt, Pd, Au, on the side opposite to the magnetic domain expansion reproducing layer in contact with the information recording layer,
A metal layer mainly composed of a noble metal such as Ag or SiO
May form a _{layer 2} or the like dielectric particle size 50nm following clusters are mixed with 10% or more atomic weight ratio in a thickness of 20nm or more.

When high-resolution recording / reproduction is performed using the magneto-optical recording medium of the present invention, the reproduced waveform has the following characteristics. For example, when the wavelength of the laser light is λ, the numerical aperture of the objective lens is NA, and the length of λ / NA is twice the period L, the maximum length of 0.2 (or 0.1) × L is obtained. At the reproducing power (Pr) where the largest signal-to-noise ratio (C / N) can be obtained in the dense recording magnetic domain, an isolated magnetic domain having a length of 0.2 (or 0.1) × L with a period L is recorded. Compared to the signal strength A and half width B of the reproduced waveform, this isolated magnetic domain is P
The signal strength of the reproduced waveform reproduced with the reproduction power of 1/2 of r is 1/2 or less of A, and the half width is 2 or more times of B. When such a condition is satisfied, it is possible to achieve high-density recording / reproduction in both resolution and reproduction signal strength.

Although the above description is a very effective method for improving the density in the linear density direction, the following method is effective for reducing the density in the track direction. For example, when both the land portion and the groove portion are used as the recording areas as the substrate, it is advantageous to make the half-value width of the groove wider than the half-value width of the land. This is because the groove width is effectively narrowed by the film formation. As a result, it is possible to eliminate the difference in recording / reproducing characteristics between the land portion and the groove portion.
Alternatively, the information may be recorded on either the land or the groove. In this case, one area for recording information can be made smaller than the other area.

Further, the magneto-optical recording medium of the present invention is a DWD
Unlike the D medium, it is not necessary to use a deep groove land groove substrate, and an existing substrate can be used.

When the magneto-optical recording medium of the present invention is used for recording / reproducing by making light incident from the substrate side, the substrate used has a land index of n when its refractive index is n. Sidewall height (or groove depth) is λ /
It is preferably (16n) to λ / (5n). When recording / reproducing is performed by making light incident from the side opposite to the substrate of the magneto-optical recording medium, the height (or groove depth) of the side wall of the land is preferably λ / 16 to λ / 5.

In the present invention, as shown in FIG.
The full width at half maximum G of the groove formed on the substrate of the magneto-optical recording medium (referred to as the groove width at a depth of half the groove depth D) is the half width at half maximum of the land L (half the groove depth D). (Which means the land width at the depth of 1), and the recording / reproducing power sensitivity can be improved by recording information in the groove portion. According to the inventor's experiment,
It was found that the recording and reproducing power sensitivities are different between the land recording system medium and the groove recording system medium. Due to the shape of the substrate, the behavior of the heat flow at the time of recording / reproducing is different between the land portion and the groove portion, and in particular, heat is likely to escape at the land portion, which may reduce the power sensitivity. In the present invention, the ratio (G / L) of the groove half width (G) and the land half width (L) of the magneto-optical recording medium is 1.3 ≦ (G / L) ≦
It is preferably 4.0. By maintaining G / L within this range, it is possible to reduce the bit error rate and obtain good C / N. In addition, it is possible to secure a sufficient push-pull signal required for tracking.

In the case of the above G / L ratio, the groove
Substrate groove depth in the area where the land is formed (D)
Is preferably 30 nm to 80 nm. When the reproduction groove depth is within this range, a push-pull signal sufficient for stable tracking can be secured, and a layer such as a recording layer can be formed on the groove with a required thickness. .

The inclination angle (θ) of the land side wall surface is 40 ° to
It is preferably 75 °. By setting the tilt angle (θ) in this range, it is possible to prevent the reproduction signal from being deteriorated due to the influence of adjacent tracks, and to form a recording layer or the like on the groove with a required thickness.

According to the present invention, the magneto-optical recording medium of the present invention is irradiated with reproducing light to heat the magneto-optical recording medium at a temperature higher than the temperature at which the exchange coupling force between the recording layer and the reproducing layer is cut off to reproduce information from the magneto-optical recording medium. A reproducing method for a magneto-optical recording medium is provided. By using this method, the magnetic domain transferred to the reproducing layer can be surely expanded and detected without generating a ghost signal, so that a large reproduced signal can be obtained at high C / N. With this method, it is possible to detect the recording magnetic domain before the recording magnetic domain reaches the center of the reproducing light for reproduction. Further, in this method, it is not necessary to apply an external magnetic field to the magneto-optical recording medium when reproducing information.

According to the present invention, there is provided a magneto-optical recording / reproducing apparatus for performing magnetic field modulation recording on the magneto-optical recording medium of the present invention.

The magneto-optical recording / reproducing apparatus of the present invention can record information on the magneto-optical recording medium of the present invention by a magnetic field modulation recording method which is overwritable and excellent in high linear density recording. The recording / reproducing apparatus can record information on a magneto-optical recording medium by the optical pulse magnetic field modulation recording method. In case of optical pulse magnetic field modulation recording, pulse duty is 25%
Good magnetic domain recording can be achieved at 45%. This is because a fast thermal response is required. The magneto-optical recording medium of the present invention has a relatively large fluctuation in the DC component of the reproduced signal. The recording / reproducing apparatus of the present invention may be provided with a signal processing apparatus for cutting low-frequency signals using differential detection, differential detection, or a low-frequency removal filter of 100 kHz or less in order to compensate for fluctuations in the DC component. Furthermore, in order to realize stable magnetic domain expansion reproduction, a trigger that actively induces magnetic domain expansion is required. This can be realized by modulating the reproduction light power instead of a constant value and irradiating it. It is more preferable to use a device in which a reference clock is embedded in advance on a substrate and a PLL circuit is used to produce a precise clock to improve the recording / reproducing synchronization accuracy. As another method of generating a trigger, it is effective to apply a reproducing magnetic field or modulate the reproducing magnetic field instead of a constant value and apply the reproducing magnetic field. Also in this case, it is preferable to perform accurate synchronous reproduction of recording and reproduction by the clock pits embedded in the substrate.

[0072]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a magneto-optical recording medium, a reproducing method therefor and a recording / reproducing apparatus according to the present invention will be specifically described below, but the present invention is not limited thereto.

[0073]

Example 1 In this example, a magneto-optical disk 300 having the structure shown in FIG. 20 is manufactured. The magneto-optical disk 300 corresponds to the magneto-optical recording medium of the first type of the present invention. The magneto-optical disk 300 includes a dielectric layer 2, an expansion reproducing layer (magnetic domain expansion reproducing layer) 3, an expansion trigger layer 4 ′, a recording layer 5, a protective layer 7, a heat sink layer 8 and a protective coat layer 9 on a substrate 1. Prepare The magneto-optical recording medium 300 is
It was manufactured as follows using a high frequency sputtering device.

As the substrate 1, a polycarbonate substrate having a shape as shown in FIG. 21 was used. The substrate 1 has a track pitch TP = 700 nm, a land half width L = 200 nm,
Groove half width G = 500 nm, groove depth D = 60
nm and a thickness of 0.6 mm. Note that the groove depth D is D for the land half width L and the groove half width G, respectively.
It means the width of the land and the groove at the depth position of / 2. The inclination angle θ of the land side wall (or the inclination angle of the groove) was about 65 °. The substrate 1 was mounted on a substrate holder in a film forming chamber of a high frequency sputtering apparatus, the film forming chamber was evacuated to an ultimate vacuum of 1.0 × 10 ⁻⁵ Pa, and then SiN as a dielectric layer 2 of 60 nm was formed on the substrate 1. The film was formed with a film thickness of.

Next, a rare earth-rich GdFeCo amorphous alloy was formed in a thickness of 20 nm as an expansion reproducing layer 3 on the dielectric layer 2. This GdFeCo amorphous alloy has a Curie temperature of about 230 ° C. and a compensation temperature of the Curie temperature or higher. Saturation magnetization at 160 ℃ is about 30
It was emu / cm ³ . The sputtering gas pressure when forming the enlarged reproduction layer 3 was adjusted to 0.3 Pa. Next, a transition metal-rich TbGdFeCo amorphous alloy layer having a film thickness of 10 is formed on the expansion reproducing layer 3 as an expansion trigger layer 4 '.
nm. This TbGdFeCo amorphous alloy has a Curie temperature of about 240 ° C. and a compensation temperature below room temperature. This expanded trigger layer 4'is from room temperature to about 120
It exhibits perpendicular magnetization up to ° C, the in-plane magnetization component increases from about 140 ° C, and exhibits in-plane magnetization up to the Curie temperature.

Then, the recording layer 5 is formed on the expansion trigger layer 4 '.
As a TbFeCo amorphous alloy, a film thickness of 60 nm was formed. The amount of Co in the recording layer 5 is the Co in the expansion trigger layer.
More than quantity. This TbFeCo amorphous alloy has a Curie temperature of about 270 ° C. and a compensation temperature of 80 ° C.
The sputtering gas pressure during film formation of the recording layer 5 was 1 Pa. In this way, the reason for making the sputtering gas pressure at the time of forming the recording layer to be at least twice as high as that at the time of forming the expanding reproducing layer is to increase the sputtering gas to facilitate the formation of fine magnetic domains and increase the recording density. is there. The sputtering gas pressure during the recording layer deposition is
0.4 Pa or more is preferable. On the other hand, in the enlarged reproducing layer, it is better not to increase the sputtering gas pressure so much in order to increase the minimum magnetic domain diameter.

Then, as the protective layer 7, S is formed on the recording layer 5.
iN was deposited to a thickness of 20 nm, and Al was deposited to a thickness of 30 nm as a heat sink layer 8 on the protective layer 7. Then, this disk was taken out from the sputtering apparatus, and an ultraviolet curable resin was spin-coated to a thickness of about 5 μm, and was irradiated with ultraviolet rays to be cured. Thus, the magneto-optical disk 300 having the laminated structure shown in FIG. 20 was obtained.

The performance of the magneto-optical disk 300 thus obtained was evaluated as follows. For evaluation, wavelength 65
A commercially available tester equipped with an optical head having an objective lens numerical aperture NA = 0.60 of 0 nm was used. The light spot diameter on the magneto-optical disk of the light beam emitted from the optical head was about 1 μm. Disk linear velocity is 3.5-5.0m
The disc was rotated so that it would be / sec. First, a magnetic domain having a diameter of 0.2 μm, which corresponds to one fifth of the light spot diameter, was formed in the recording layer by optical pulse magnetic field modulation recording. On this occasion,
The recording clock period is 40 nsec and the optical pulse width is 1
The recording laser power was 8 nsec, and the recording surface was about 10 mW. While irradiating the magneto-optical disk with this optical pulse, a recording magnetic field of +3 with a pulse width of 40 nsec is obtained.
Positive magnetic field of 00 Oe and -30 with pulse width of 360 nsec
A negative magnetic field of 0 Oe was combined and applied repeatedly. Therefore, if the positive magnetic field is the recording direction (black magnetic domain formation) and the negative direction is the erasing direction (white magnetic domain), the recording magnetic domain length is 200 nm for the black magnetic domain and 1800 nm for the white magnetic domain. Was done.

The repetitive recording pattern thus formed on the magneto-optical disk was irradiated with reproduction light to be reproduced. The reproduction light was continuous light. When the reproducing light power Pw = 1.5 mW, this repetitive recording pattern could be observed as a waveform as shown in FIG. 22, although the signal intensity was slight. The light spot diameter was about 1 μm, so 0.2
The length of the skirt of the reproduction signal waveform of the recording magnetic domain of μm is 1 μm +
It can be seen that it is 0.2 μm, that is, 1.2 μm. The full width at half maximum was about 0.6 μm. Next, when the reproducing light power was changed to 3.0 mW and the above repeated recording pattern was reproduced, a reproduced waveform as shown in FIG. 22 was obtained. As can be seen from FIG. 22, the full width at half maximum is 0.2 μm, which is the same as the length of the recording magnetic domain, and this full width at half maximum is as narrow as about one-third when the reproducing light power is 1.5 mW. On the other hand, the reproduction signal strength is 1.
It is more than doubled compared to the case of 5 mW. FIG. 22
From the reproduction signal waveform of, the reproduction light power is 3.0 mW.
In the case of, it can be seen that the recording magnetic domain is transferred to the reproducing layer, enlarged, and reproduced. On the other hand, the reproduction light power is 1.
In the case of 5 mW, the expansion did not occur, and it is considered that the recording magnetic domain transferred to the reproducing layer was reproduced as it was.

Further, by comparing the waveforms of FIG. 22, the following important facts can be seen. The peak center when the reproducing light power is 3.0 mW appears earlier in time than the peak center when the reproducing light power is 1.5 mW. That is, when expansion of the magnetic domain transferred to the reproducing layer occurs, this magnetic domain can be detected before the transferred magnetic domain reaches the center of the light spot. This can be understood from the theoretical explanation that, as shown in FIG. 5, the recording magnetic domain 5A approaching the light spot is transferred to the expansion reproducing layer 3 and expanded in the light spot. Thus, detecting the recording magnetic domain by advancing in time from the center of the light spot is a major feature of the reproducing method using the magneto-optical recording medium of the present invention.

Next, an NRZI random pattern having a shortest mark length of 0.12 μm, which corresponds to about 1/10 of the light spot diameter, was recorded, and this pattern was reproduced with various reproduction light powers. The reproduction power dependence of the error rate from the reproduction signal was measured, and the result is shown in FIG. When 5000 data is recorded, if there is one error, the error rate is 5 × 10 ⁻⁴ , and data correction is practically possible. From FIG. 23, the reproduction power margin satisfying the error rate of 5 × 10 ⁻⁴ or less is 20.5%, which is ± 10.
You can see that it has achieved more than%. Therefore, it can be said that the magneto-optical disk of the present invention is a practically practical medium with respect to the reproduction power margin. Next, the recording power was changed to record the NRZI random pattern with the shortest mark length of 0.12 μm, and the error rate when the recorded information was reproduced was obtained. The change in the error rate with respect to the recording power is shown in FIG. 5 × even if the recording power changes ± 10% or more (22.5% or more) as well as the reproducing power
It was found that an error rate of 10 ⁻⁴ or less can be secured. Therefore, the magneto-optical disk of the present invention also satisfies the recording power margin. Furthermore, when the decrease of the effective laser power with respect to the tilt of the magneto-optical disk was observed, it was found that the practical target of ± 0.6 ° was satisfied.

[0082]

[Embodiment 2] The magnifying reproducing layer 3 of the magneto-optical disk is provided with 10 to 5 layers.
A plurality of magneto-optical disk samples were manufactured in the same manner as in Example 1 except that the film thickness was changed to various values of 0 nm. The bit error rate (BER) of these magneto-optical disks was measured in the same manner as in Example 1. Enlarged playback layer 3
The relationship between the various film thicknesses t and the measured bit error rate is shown in FIG. From FIG. 31, the thickness t of the enlarged reproduction layer 3 is 1
It can be seen that the bit error rate of 1 × 10 ⁻⁴ is achieved in the range of 5 to 30 nm. This is the enlarged reproduction layer 3
If the film thickness is smaller than this, the recording magnetic domains of the expansion trigger layer and the recording layer can be seen through the reproducing layer, which makes accurate signal reproduction difficult. Further, when the thickness of the expansion reproducing layer 3 is thicker than 30 nm, it becomes difficult to magnetically transfer the minute recording magnetic domain.
This is because it is considered that the expansion of the minute magnetic domain is unlikely to occur.
Therefore, the thickness of the expansion reproducing layer 3 is 15 to 30 nm.
Is desirable.

[0083]

[Embodiment 3] In this embodiment, a method of determining the magnitude of an exchange coupling magnetic field (exchange coupling force) acting between the magnifying reproducing layer and the recording layer of the magneto-optical disk manufactured in Embodiment 1 will be described. The exchange coupling force is from the magnifying reproducing layer side to the magneto-optical car (Ke
It can be determined by measuring the magnetic field dependence of the rr) effect. FIG. 25 shows a hysteresis curve of the magneto-optical disk of Example 1 at room temperature. The hysteresis curve was obtained by measuring the magnetic field dependence of the polar magneto-optical Kerr rotation angle with the measurement light incident from the magnifying and reproducing layer side. The exchange coupling magnetic field acts on the expansion reproducing layer from the information recording layer having a large coercive force, and the hysteresis curve is shifted to the left (minus magnetic field side) accordingly. This shift amount corresponds to the exchange coupling magnetic field.

The temperature dependence of the exchange coupling magnetic field (Hexc) is shown in FIG.
26. To maintain the magnetic domains transferred to the magnified reproducing layer
As the magnitude of the exchange coupling magnetic field required for, for example, 3 kO
At a temperature of about e, the exchange coupling magnetic field (exchange coupling
Force) temperature gradient is -350 to -185 Oe /
It was ℃. This exchange coupling magnetic field is
It becomes larger as it becomes thinner, and the saturation magnetization of the magnified reproducing layer becomes smaller.
I know it will grow. So expand
Various magneto-optical devices with varying thickness and saturation magnetization of the reproducing layer
Disk to determine the temperature dependence of these exchange coupling magnetic fields.
Measure the temperature at an exchange coupling magnetic field of about 3 kOe.
The temperature gradient was calculated. Note that the saturation magnetization in the expansion reproducing layer
The composition of Gd was changed and adjusted. These magneto-optical disks
Bit error at the shortest mark length of 0.12 μm
(BER) is measured and the temperature gradient and bit error rate are measured.
I investigated the relationship between the two. NRZI is used for the recording pattern
It was This shortest mark length is about 1/8 of the light spot diameter.
, Which is far beyond the resolution of light. Display in absolute value
FIG. 45 shows changes in the bit error rate with respect to the temperature gradient.
It was shown to. Generally, a good bit error rate is 1x1
0^-4Or 5 × 10 ^-4The following are practical places
5 × 10^-4Looking at it, this temperature gradient is -10
If the gradient is 0 Oe / ° C or more, good bit error
I found out that I could get a booth.

[0085]

Example 4 The saturation magnetization (saturation magnetization at room temperature) was changed by changing the film thickness of the expanding reproducing layer of the magneto-optical disk manufactured in Example 1 from 10 nm to 40 nm and changing the composition of the expanding reproducing layer. A magneto-optical disk having an enlarged reproducing layer which was changed to various values was prepared. The bit error rate (BER) of these magneto-optical disks was measured in the same manner as in Example 1. The shortest mark length is 0.13 μm
And The relationship between the product of the film thickness and the saturation magnetization and the bit error rate is shown in FIG. Film thickness t of the reproducing layer and saturation magnetization M
The product of s corresponds to the magnetic energy that causes domain expansion. Looking at the range satisfying the bit error rate of 5 × 10 ⁻⁴ , the product of the film thickness and the saturation magnetization is 80 μemu.
It can be seen from FIG. 27 that a relatively good bit error rate can be obtained if / cm ^{2 to} 220 μemu / cm ² .

The Ms × t of the magnified reproducing layer can also be measured from the manufactured magneto-optical disk. FIG. 46 shows the results of magnetization measurement per unit area (cm ² ) of the disk of the present invention at around 120 ° C. Since the magnifying and reproducing magnetic layer has a small coercive force, it can be reversed by a relatively small magnetic field. However, the information recording layer has a large coercive force and does not easily cause magnetization reversal. Therefore, it is considered that the falling portion of the hysteresis curve appearing on the negative low magnetic field side in FIG. 46, that is, the magnetization change (A in the drawing) at the external magnetic field of about 7 kOe corresponds to the magnetization reversal of the reproducing layer. Further, when the applied magnetic field is further increased, the information recording layer has an external magnetic field of 12 kOe.
You can see that it begins to flip around. In this way, the magnetization per unit area of the expansion reproducing layer can be measured from the falling portion of the hysteresis curve on the low magnetic field side of the magnetization curve. However,
Since the magneto-optical disk also includes the intermediate layer, the magnetization that can be read from the hysteresis loop also includes the magnetization of the intermediate layer.

[0087]

Example 5 A magneto-optical disk was manufactured in the same manner as in Example 1 except that the groove depth of the substrate was changed to various depths. The bit error rate of each manufactured magneto-optical disk was measured in the same manner as in Example 1. Bit error rate (BE
FIG. 28 shows the dependency of R). From FIG. 28, it is understood that when the groove depth is 27 nm to 82 nm, a bit error rate of 5 × 10 ⁻⁴ or less can be obtained. Since the groove depth is generally determined as a function of the wavelength of light based on the reflectance of light, the optimum groove depth is λ, where λ is the wavelength of light and n is the refractive index of the light incident side substrate or the protective layer. /
16n to λ / 5n.

[0088]

[Sixth Embodiment] Groove half width G relative to land half width L
A magneto-optical disk was manufactured in the same manner as in Example 1 except that the substrates in which the ratio G / L was changed to various values were used. The bit error rates of these magneto-optical disks were measured in the same manner as in Example 1 when the shortest mark length was 0.13 μm (NRZI). FIG. 29 shows the change in bit error rate with respect to G / L. G / L is 1.2-4.
It can be seen that within the range of 5, a bit error rate of 5 × 10 ⁻⁴ or less is obtained.

[0089]

[Embodiment 7] A magneto-optical disk was manufactured in the same manner as in Embodiment 1 except that a substrate in which the inclination angle θ of the land side wall was changed to various values was used. Bit error rates of these magneto-optical disks were measured in the same manner as in Example 1. However, the shortest mark length in the recorded NRZI random pattern was 0.13 μm. The measurement result is shown in FIG. From FIG. 30, the inclination angle θ of the land side wall is 35 ° to 77 °.
It is understood that an error rate of 5 × 10 ⁻⁴ or less can be obtained within the range of.

[0090]

Embodiment 8 FIG. 32 shows a schematic structure of a magneto-optical recording medium according to the present invention. The magneto-optical recording medium 100 comprises a substrate 1, a dielectric layer 2, an expansion reproducing layer 3, an intermediate layer 4, a recording layer 5,
The auxiliary magnetic layer 6, the protective layer 7, and the heat sink layer 8 are provided. The magneto-optical recording medium 100 was formed as follows by using a high frequency sputtering device.

The substrate 1 has a land width of 0.6 .mu.m, a .0.
A groove width of 6 μm, a groove depth of 60 nm and a thickness of 0.
A 6 mm polycarbonate substrate was used. The substrate 1 is mounted in the film forming chamber of the sputtering apparatus, and the vacuum degree reaching the film forming chamber is 8 × 1.
0 ^-5 was evacuated to Pa, and 5 hours in vacuum baking the substrate at 80 ° C., on such substrate 1, SiN as the dielectric layer 2
Was formed into a film having a thickness of 60 nm.

Then, a rare earth-transition metal alloy GdFe was formed into a film having a thickness of 20 nm as an expansion reproducing layer 3 on the dielectric layer 2. GdFe has a Curie temperature of about 240 ° C. and a compensation temperature of the Curie temperature or higher. The saturation magnetization at 160 ° C. was about 55 emu / cm ³ . Next, a rare earth-transition metal alloy TbGdFe having a compensation temperature at room temperature or lower was formed as a middle layer 4 on the expansion reproducing layer 3 to have a film thickness of 10 nm. The Curie temperature is about 150 ° C. Tb and Gd
Was 14%. Then, a rare earth transition metal alloy TbFeCo having a Curie temperature of 280 ° C. and a compensation temperature of about room temperature is formed as a recording layer 5 on the intermediate layer 4 in a thickness of 60 nm.
It was formed into a film. Expansion reproduction layer 3, intermediate layer 4, and recording layer 5
All the magnetic layers were perpendicular magnetic films from room temperature to the Curie temperature.

Next, in order to enable accurate recording on the recording layer 5 with a small recording magnetic field, a rare earth transition metal alloy GdFeCo having a Curie temperature of 290 ° C. at a compensation temperature of room temperature or less is used as the auxiliary magnetic layer 6. The film thickness is 10 nm
Was deposited. Then, SiN was deposited to a thickness of 20 nm as the protective layer 7 on the auxiliary magnetic layer 6, and Al was deposited to a thickness of 30 nm as the heat sink layer 8 on the protective layer 7. Thus, the magneto-optical recording medium 100 having the laminated structure shown in FIG. 32 was manufactured.

Next, the magneto-optical recording medium was mounted on an evaluation machine and a recording / reproducing test was conducted. In the recording / reproducing test, a laser beam having a wavelength of 650 nm and an objective lens having a numerical aperture NA of 0.60 were used. The linear velocity is 5 m / sec. First, in order to confirm the magnetic domain expansion phenomenon in the magnetic recording / reproducing layer, an optical pulse magnetic field modulation recording method was used for a magneto-optical recording medium, the recording power of laser light was 10 mW, the recording magnetic field was ± 200 Oe, and the length was 0. 20 μm isolated magnetic domains were recorded. The pulse duty of light was set to 30%. The recording cycle was 2.0 μm. This value is the light spot diameter λ /
It is about twice as long as NA (about 1 μm). On the other hand, the recorded length of the isolated domain is about 1/5 of the light spot diameter λ / NA.
Equivalent to the length of.

The magneto-optical recording medium having such isolated magnetic domains formed was reproduced by using two kinds of reproducing powers of reproducing power of 1.5 mW and 3.0 mW. FIG. 33 shows that reproduction power 1.
The isolated magnetic domain reproduction signal when reproduced at 5 mW and when reproduced at reproduction power of 3.0 mW is shown. Here, 3.
It was confirmed by preliminary experiments that the reproduction power of 0 mW was the optimum reproduction power that maximized the signal-to-noise ratio (C / N). When the reproducing power is 1.5 mW, the half width of the reproduced signal waveform is 0.66 μm and the width of the skirt is 1.34 μm.
m, the signal amplitude is about 54 mV. On the other hand, when the reproduction power is 3.0 mW, the full width at half maximum of the reproduction signal waveform is 0.2
0 μm, skirt width 0.64 μm, signal amplitude about 126
mV. From this result, it can be seen that the width of the reproduced signal waveform is narrowed, the resolution is improved, the signal amplitude is also increased, and the magnetic domain expansion reproduction is successful by adjusting the reproduction power to 3.0 mW.

Generally, the signal amplitude increases as the reproduction power increases. However, when the reproducing power becomes high, the temperature of the reproducing layer rises and the magneto-optical effect is reduced. In fact, at high temperatures the magneto-optical effect is significantly reduced. Therefore, for reference, the expansion rate of the magnetic domain in the expansion reproducing layer was calculated. The expansion ratio was estimated by normalizing the signal amplitude with the reproduction power. The standardized signal amplitude at a reproducing power of 1.5 mW is 36 mV / mW, 3.0 m
It can be seen that the standardized signal amplitude when W is 42 mV / mW, which is expanded by at least 16% or more.

Next, the dependence of the signal-to-noise ratio (C / N) on the mark length of the magneto-optical recording medium of this example was examined. FIG. 34
The results are shown in. In FIG. 34, for comparison, DWD
D report example (T. Shiratori: J. Magn.Soc. Jpn., Vol.22
Also shown is the mark length dependence of the signal-to-noise ratio (C / N) of the magneto-optical recording medium of Supplement No. 2 (1998) p50 Fig. 10) and the conventional magneto-optical recording medium. From the graph of FIG. 34, for example, the above C / N of 0.20 μm is 45.4 in the present invention.
It shows an extremely large value of dB, but it is 4 in DWDD.
It is as low as about 1 dB. Further, in DWDD, a long mark cannot be measured because it is a ghost signal, but in the present invention, a reproduction signal exceeding 45 dB is obtained even when the mark length is 1.0 μm.

FIG. 35 shows the shortest mark length of 0.1 according to the present invention.
3 shows a reproduced waveform of a 2 μm NRZI random pattern.
Since the magneto-optical recording medium of the present invention does not generate a ghost signal, there is no need to limit the length of the recording mark, and a good eye pattern was obtained regardless of the mark length. When the center of the signal of FIG. 35 was simply sliced and the bit error rate was measured, it was 4.7 × 10 ⁻⁵ . It has cleared 1 × 10 ^-4, which is a practical guideline.

[0099]

[Embodiment 9] FIG. 36 shows a structure of a recording / reproducing apparatus most suitable for recording / reproducing of a magneto-optical recording medium of the present invention. The recording / reproducing apparatus 71 shown in FIG. 36 is controlled by the magneto-optical disk 100 at the time of recording / reproducing, and a laser light irradiating section for irradiating the magneto-optical disk 100 with light pulsed at a constant cycle in synchronization with code data. Magnetic field applying section for applying a magnetic field,
It mainly comprises a signal processing system for detecting and processing a signal from the magneto-optical disk 100. In the laser light irradiation unit, the laser 72 is connected to a laser driving circuit 73 and a recording pulse width / phase adjusting circuit 74 (RC-PPA), and the laser driving circuit 73 receives a signal from the recording pulse width phase adjusting circuit 74 and is a laser. The laser pulse width and phase of 72 are controlled. The recording pulse width / phase adjusting circuit 74 receives a clock signal described later from the PLL circuit 75 and generates a first synchronizing signal for adjusting the phase and pulse width of the recording light.

In the magnetic field applying section, the magnetic coil 76 for applying a magnetic field is a magnetic coil drive circuit (M-DRIVE) 7
7, the magnetic coil drive circuit 77 is connected to the encoder 7 through which the data is input from the encoder 70 to which the data is input.
A) It receives the input data through 78 and controls the magnetic coil 76. On the other hand, at the time of reproduction, a clock signal described later is received from the PLL circuit 75 and a second synchronization signal for adjusting the phase and the pulse width is generated through the reproduction pulse width / phase adjustment circuit (RP-PPA) 79 to generate the second synchronization signal. The magnetic coil 76 is controlled based on the signal. A recording / reproducing switch (RC / RPSW) 80 is connected to the magnetic coil driving circuit 77 in order to switch the signal input to the magnetic coil driving circuit 77 between recording and reproducing.

In the signal processing system, the first polarizing prism 81 is arranged between the laser 72 and the magneto-optical disk 100, and the second polarizing prism 82 and the detectors 83 and 84 are arranged beside it. . The detectors 83 and 84 are both connected to the subtractor 87 and the adder 88 via the I / V converters 85 and 86, respectively. The adder 88 is connected to the PLL circuit 75 via a clock extraction circuit (SCC) 89. A subtractor 87 is a sample hold (S / H) circuit 90 that holds a signal in synchronization with a clock, and an A / D that similarly performs analog-digital conversion in synchronization with a clock.
It is connected to a decoder 93 via a conversion circuit 91 and a binary signal processing circuit (BSC) 92.

The signal processing system, as shown in FIG.
A signal processing device 190 that cuts a low frequency signal is provided between the H circuit 90 and the A / D conversion circuit 91. After the sample and hold, the signal processing device 190 compresses the low frequency noise by equalizing the waveform in the equalizing circuit and forming the modulated signal in the A / D circuit.

In the above device configuration, the light emitted from the laser 72 is collimated by the collimator lens 94, passes through the polarization prism 81, and is condensed on the magneto-optical disk 100 by the objective lens 95. The reflected light from the disk is directed by the polarizing prism 81 toward the polarizing prism 82, transmitted through the half-wave plate 96, and then split into two directions by the polarizing prism 82. The divided lights are condensed by the detection lens 97 and guided to the photodetectors 83 and 84. Here, pits for generating the tracking error signal and the clock signal may be formed in advance on the magneto-optical disk 100. A signal indicating the reflected light from the clock signal generation pit is detected by the detectors 83 and 84 and then extracted by the clock extraction circuit 89. Then, the PLL circuit 75 connected to the clock extraction circuit 89 generates a data channel clock.

At the time of data recording, the laser 72 modulates the laser 72 at a constant frequency so as to be synchronized with the data channel clock, emits continuous narrow pulsed light, and rotates the data of the magneto-optical disk 100. The recording area is locally heated at equal intervals. Further, the data channel clock controls the encoder 70 of the magnetic field application unit to generate the data signal of the reference clock period. The data signal passes through the phase adjusting circuit 78 and the magnetic coil driving device 7
Send to 7. The magnetic coil drive device 77 includes a magnetic field coil 76.
Is controlled to apply a magnetic field having a polarity corresponding to the data signal to the heated portion of the data recording area of the magneto-optical disk 100.

The optical pulse magnetic field modulation method is used as the recording method. This method irradiates the laser light in pulses when the applied recording magnetic field reaches a sufficient level, so recording in the area where the external magnetic field switches can be omitted, and as a result, minute magnetic domains can be reduced. It is a technology that can record with noise.

For reproducing information, it is not necessary to apply a reproducing magnetic field to the magneto-optical recording medium, and reproducing light is irradiated onto the magneto-optical recording medium to reproduce the magneto-optical recording medium of the above-mentioned first to third types. Based on the principle, the minute magnetic domains of the recording layer are transferred to the reproducing layer and enlarged. Information is reproduced by detecting the return light from the magneto-optical recording medium with a photodetector. Continuous light or pulsed light can be used as the reproduction light. It is also possible to use reproduction light whose reproduction power is modulated.

When reproducing the magneto-optical recording medium, a modulated reproducing magnetic field may be applied in order to facilitate the expansion of the magnetic domain of the reproducing layer based on the above-mentioned principle.

[0108]

Example 10 Another magneto-optical recording medium according to the present invention will be described with reference to FIGS. As shown in FIG. 37, the magneto-optical disk 200 includes a dielectric layer 2, an expansion reproducing layer 3, an expansion trigger layer 4 ′, a recording layer 5, a recording auxiliary layer 6 ′, a protective layer 7 and a heat sink on a substrate 1. The layer 8 is provided. In the magneto-optical disk 200, the above layers were formed by using a high frequency sputtering device (not shown) as follows.

The substrate 1 has a diameter of 120 mm and a thickness of 0.6 m.
m is a transparent polycarbonate. As shown in FIG. 21, the land 1L is formed on the surface of the substrate 1 by injection molding.
And a groove 1G defined between the lands 1L is formed. As shown in FIG. 21, when the inclination angle of the land side wall LW is θ, the height of the land 1L, that is, the land 1L at a height position half (D / 2) the depth D of the groove 1G.
Is defined as the land half width L. Further, the width of the groove at a height position half the depth D of the groove 1G is defined as the groove half-value width G. The groove half width is the distance between the midpoint in the height direction of the land side wall LW of a certain land and the midpoint in the height direction of the land side wall LW of the adjacent land.
In this case, the track pitch TP is represented by TP = G + L.

In this example, substrates having various shapes and dimensions as shown in Table 1 were prepared.

[0111]

[Table 1]

The surface of the above-mentioned substrate was irradiated with ultraviolet rays having a peak wavelength λ of 185 + 254 nm by using an ultraviolet lamp. The lamp was placed 70 mm above the surface of the substrate 1 and the substrate 1 was rotated at a speed of 2 rpm to smooth the surface roughness to 0.3 nm.

Then, on the land / groove forming surface of the substrate 1, Si was used as a target material, and a dielectric layer 2 was formed to a thickness of 60 nm in an Ar + N ₂ atmosphere. The dielectric layer 2 is a layer for causing multiple interference of the reproduction light beam in the layer and substantially increasing the detected Kerr rotation angle.

Then, Gd and F are formed on the surface of the dielectric layer 2.
The single target of e was sputtered at the same time to form the enlarged reproduction layer 3 so as to have a film thickness of 20 nm. As a result, the GdFe expansion reproducing layer 3 thus formed was a perpendicular magnetization film, the Curie temperature was about 240 ° C., and the compensation temperature was the Curie temperature or higher. The expansion reproducing layer 3 is a layer in which the magnetic domain transferred from the recording auxiliary layer 6'is expanded.

Then, a single target of Tb, Gd and Fe was simultaneously sputtered on the enlarged reproducing layer 3 to form an enlarged trigger layer 4'having a film thickness of 10 nm. At this time, the TbGdFe expansion trigger layer 4 ′ was a perpendicular magnetization film, and the Curie temperature was 140 ° C. and the compensation temperature was room temperature or lower. The expansion trigger layer 4'is magnetically exchange-coupled to the expansion reproduction layer 3 and the recording layer 5, respectively.

Then, on the expansion trigger layer 4 ', Tb,
The TbFeCo recording layer 5 was formed to a film thickness of 75 nm by simultaneously sputtering a single target of Fe and Co. The Curie temperature of the recording layer 5 was 250 ° C., and the compensation temperature was about 25 ° C. The recording layer 5 is a layer in which information is recorded as magnetization.

Then, Gd, Fe and C are formed on the recording layer 5.
By sputtering the single target of o at the same time,
The GdFeCo recording auxiliary layer 6'was formed with a film thickness of 10 nm. The Curie temperature of the recording auxiliary layer 6 ′ was 270 ° C., and the compensation temperature was room temperature or lower. The recording auxiliary layer 6 ′ is a layer that exchange-couples with the recording layer 5 and enables recording on the recording layer 5 with a smaller modulation magnetic field.

Then, Ar + N _{2 is formed} on the recording auxiliary layer 6 '.
The protective layer 7 was formed to a thickness of 20 nm by performing sputtering using Si as a target material in the atmosphere. The protective layer 7 includes layers 2 to 6 laminated on the substrate 1.
Is a layer for protecting the.

A heat sink layer 8 having a thickness of 30 nm was formed on the protective layer 7 by using an AlTi alloy as a target. The heat sink layer 8 is a layer for radiating heat generated in the magneto-optical disk during recording to the outside. Further, an acrylic ultraviolet curable resin was applied onto the heat sink layer 8 and then irradiated with ultraviolet rays to be cured to form a protective coat layer 9 with a film thickness of 10 μm.

Next, the magneto-optical disk 200 manufactured in this example was subjected to an information recording / reproducing test by using a magneto-optical recording / reproducing apparatus (not shown). The magneto-optical recording / reproducing apparatus includes an optical head having a laser beam having a wavelength of 640 nm and an objective lens having a numerical aperture (NA) of 0.6. As the recording method, an optical pulse magnetic field modulation method was used, in which a laser beam was applied in a pulse shape and an external magnetic field was applied while being modulated according to the recording information. The linear velocity during recording was 3.5 m / sec, and the recording magnetic field was modulated to ± 200 Oe. The duty of the pulsed light during recording was set to 30%, and the recording power of the laser light was optimized. After recording a random pattern with the shortest mark length of 0.12 μm in the groove portion, the bit error rate (BER) was measured using the reproduction light of the optimized reproduction power. The bit error rates of the magneto-optical disks having various G / L ratios shown in Table 1 were measured, and the graph of FIG. 38 shows changes in the bit error rate with respect to G / L. The threshold value (upper limit) of the bit error rate was set to 5 × 10 ⁻⁴ . Figure 3
It can be seen from the graph of 8 that a good bit error rate is exhibited when G / L is 1.3 ≦ G / L ≦ 4.0.

In this embodiment, an example in which the magneto-optical disk has eight layers (excluding the protective coating layer 9) has been shown, but the basic layer structure is a recording layer for holding information on the substrate and its holding. It has been found that the above range of G / L is effective in the case of a magneto-optical disk having a magnified reproduction layer in which the reproduced information is transferred during reproduction. Further, in the present embodiment, the ultraviolet irradiation method was used as the method for smoothing the substrate surface, but a substrate heating method, a plasma etching method or the like may be used.

[0122]

[Embodiment 11] A magneto-optical disk was prepared in the same manner as in Embodiment 10 except that the dimensions of the grooves and lands of the substrate 1 were prepared as shown in Table 2.

[0123]

[Table 2]

In this example, a plurality of magneto-optical disks were manufactured by changing only the groove depth D. In the same manner as in Example 10, a random pattern was recorded / reproduced using a magneto-optical recording / reproducing device (not shown). The change of the bit error rate with respect to the groove depth D was examined for each magneto-optical disk. The result is shown in FIG. 39. When the threshold of the bit error rate is 1 × 10 ⁻⁴ , from FIG. 39, when the value of D is 30 nm to 80 nm,
It can be seen that a good bit error rate is achieved.

As a modification, as the expansion trigger layer, T
bGdFeCo is formed with a film thickness of 10 nm, and the groove depth of the substrate is 70 nm, 65 nm, 60 nm, 55 nm, 5
Various magneto-optical disks were prepared in the same manner as in this example except that the thickness was 0 nm, 45 nm, 40 nm, 35 nm and 30 nm. This expansion trigger layer is made of Tb, Gd, F
A single target of e and Co was simultaneously sputtered, and the film composition was adjusted so that a perpendicular magnetization film having a compensation temperature of room temperature or less was obtained. The expansion trigger layer 4 is a reproducing layer 3 and a recording layer 5 at 140 ° C.
Acts to block the exchange coupling force of. The bit error rates of these magneto-optical disks were measured in the same manner as in Example 11, and changes in the bit error rates with respect to the groove depth D were examined. The result is shown in FIG. 39 as a modified example. The shortest mark length is 0.13 μm. It can be seen that when the value of D is 35 nm to 65 nm, a good bit error rate is achieved.

When the groove depth of the substrate is deeper than 70 nm, it is considered that the edge of the groove is hard to be heated and the expansion / reproduction of the recording mark is hindered, so that the error rate is lowered. On the other hand, when the depth of the substrate is 30 nm or less, the tracking signal becomes small and the groove cannot be traced. Therefore, the groove depth is 30-7
It can be seen that 0, particularly 35 nm to 65 nm, is optimum for the magneto-optical disk in this example.

In this embodiment, as an example, the wavelength is 650 nm.
However, the phase difference between the incident light entering the substrate and the reflected light from the substrate is uniquely determined by the wavelength of the reproducing laser light, the refractive index of the substrate, and the groove depth of the substrate. Therefore, from this example, the groove depth is λ /
It can be seen that a magneto-optical disk having a substrate of 12n to λ / 7n is desirable.

[0128]

Example 12 A magneto-optical disk was produced in the same manner as in Example 10 except that the groove and land of the substrate 1 were formed as shown in Table 3.

[0129]

[Table 3]

In this example, a plurality of magneto-optical disks were manufactured using the substrates shown in Table 3 by changing only the inclination angle θ of the land side wall surface (wall surface defining the groove) of the substrate. In the same manner as in Example 10, a random pattern was recorded / reproduced using a magneto-optical recording / reproducing device (not shown). For each magneto-optical disk, the change in bit error rate with respect to the inclination angle θ of the land side wall surface was examined. The results are shown in Fig. 40. When the threshold value (upper limit) of the bit error rate is 5 × 10 ⁻⁴ , the value of θ is preferably 35 ° to 77 ° from FIG. 40, and when the threshold value of the bit error rate is 1 × 10 ⁻⁴ , θ of θ is obtained. Values of 40 ° to 75 ° are preferred.

[0131]

[Comparative Example (Land recording)] The groove and land of the substrate 1 were set to have a track pitch (TP) of 0.70 μm, a land half width (L) of 0.50 μm, and a groove half width (G) of 0.20.
A magneto-optical disk was produced in the same manner as in Example 10, except that the groove was formed so that the groove depth (D) was 60 nm, and the land sidewall inclination angle (θ) was 65 °. Then, on this magneto-optical disk, in the same manner as in Example 10,
A random pattern was recorded and reproduced using a magneto-optical recording and reproducing device. However, changing the recording power of the laser light,
A random pattern having a shortest mark length of 0.13 μm was recorded on the land portion. Each recording pattern was reproduced to examine the recording power dependence of the bit error rate. FIG. 41 is a graph showing the recording power dependence of the bit error rate. Next, the reproduction power dependence of the bit error rate when the reproduction power was varied while the recording power was kept constant was determined. FIG. 42 is a graph showing the reproduction power dependence of the bit error rate. In each case, the upper limit of the threshold value was set to 1 × 10 ⁻⁴ .

[0132]

[Reference Example (Groove Recording)] The groove and land of the substrate 1 have a track pitch (TP) of 0.70 μm, a land half width (L) of 0.20 μm, and a groove half width (G) of 0.5.
A magneto-optical disk was produced in the same manner as in the comparative example except that it was formed to have a groove depth (D) of 0 μm, a sidewall sidewall surface inclination angle (θ) of 65 °. However, in this magneto-optical disk, a random pattern was recorded in the groove as in the comparative example. The dependence of the bit error rate on the recording power and the reproduction power was investigated. The result is
41 and 42 for comparison with the land recording.

From FIGS. 41 and 42, it can be seen that the recording and reproducing power sensitivity with respect to the bit error rate can be increased more when the information is recorded in the groove portion than when the information is recorded in the land portion. . As a result, it is possible to reduce the power consumption of the drive of the magneto-optical recording / reproducing apparatus, and by extension, the magneto-optical recording / reproducing apparatus itself.

[0134]

Example 13 In this example, a magneto-optical disk 400 having a structure as shown in FIG. 43 is manufactured. Magneto-optical disk 400
Is the same as the magneto-optical disk manufactured in Example 1 except for the magnifying and reproducing layer 3, the intermediate layer 4 and the recording layer 5. A rare earth transition metal alloy GdF is formed on the dielectric layer 2 as an expansion reproducing layer 3.
e was formed into a film having a thickness of 20 nm. The GdFe film had a Curie temperature of about 200 ° C. and a compensation temperature of the Curie temperature or higher. The saturation magnetization of the expansion reproducing layer 3 at 130 ° C. was about 50 emu / cm ³ .

On the expanded reproducing layer 3, as the intermediate layer 4, a rare earth transition metal alloy TbGdFe having a compensation temperature of room temperature or lower is used.
Co was deposited to a film thickness of 10 nm. This TbGdFeCo
The Curie temperature of the film was about 220 ° C. higher than the Curie temperature of the expanded reproducing layer. T in TbGdFeCo film
The ratio of b and Gd (Tb / Gd) was 20%, and the ratio of Fe and Co (Fe / Co) was 15%. Middle layer 4
After film formation, the surface of the intermediate layer is slightly nitrided or oxidized.

As a processing method, after the formation of the intermediate layer 4, Ar gas mixed with nitrogen or oxygen may be introduced into the vacuum chamber of the sputtering apparatus, and sputter etching may be performed on the laminated intermediate layer. By this treatment, a thin nitride layer or oxide layer of, for example, one atom to several atoms is formed on the surface of the intermediate layer 4. Alternatively, this treatment mixes oxygen atoms or nitrogen atoms into the surface of TbGdFeCo forming the intermediate layer 4. Therefore, the middle layer 4
The Curie temperature of the surface part of is decreased. If the lowered Curie temperature is lower than the reproducing temperature, the magnetization of this surface portion is lost by irradiation of reproducing light, and the exchange coupling force between the recording layer and the expanding reproducing layer is shielded or blocked. Therefore, it becomes possible to control the exchange coupling force between the recording layer and the expansion reproducing layer and the temperature change thereof independently of the temperature change of the magnetization of the intermediate layer. Then, the magnetization of the intermediate layer coupled to the expansion reproducing layer does not disappear, and in the expansion reproducing layer, the exchange coupling force with the recording layer is critically released at a temperature during reproduction, and the magnetic domain begins to expand sharply, Expand to the smallest domain size. A large reproduced signal can be obtained from this enlarged magnetic domain.

The degree of surface treatment of the intermediate layer depends on the partial pressure ratio of nitrogen and oxygen as the sputtering gas to the Ar gas, the total gas pressure, the input power, the sputter etching time, and the like, and can be appropriately adjusted. What is important is that the temperature at which the exchange coupling force is shielded or blocked at the interface between the intermediate layer 4 and the enlarged reproduction layer 3 is set to the temperature (high temperature) generated near the central portion of the reproduction light spot. Generally, this temperature is considered to be 160-180 ° C. The temperature change of the exchange coupling force of the reproducing layer and the recording layer can be measured from the temperature change of the minor loop of the Kerr hysteresis curve as described above.

In this example, as a surface treatment condition, Ar gas mixed with 5% of nitrogen was introduced into the chamber at a pressure of 0.3 Pa, and RF power of 50 W was applied to carry out sputter etching for 3 seconds. . As a result, the temperature at which the exchange coupling force was cut off was 160 ° C. This exchange coupling force cutoff temperature becomes lower than the Curie temperature (about 220 ° C.) of the intermediate layer due to the surface treatment of the intermediate layer. Therefore, the middle layer 4
The Curie temperature of can be set independently of the Curie temperature of the expanded reproducing layer 3. Generally, the surface treatment of the intermediate layer 4 lowers the exchange-coupling-force blocking temperature below the Curie temperature of the intermediate layer, so it is more effective to set the Curie temperature of the intermediate layer 4 higher than the Curie temperature of the expansion reproducing layer 3. .

On the intermediate layer 4 surface-treated as described above,
As the recording layer 5, a rare earth transition metal alloy TbFeCo having a Curie temperature of 260 ° C. and a compensation temperature of about room temperature is formed to a film thickness of 4
The film was formed at 0 nm. All the three layers of the expansion reproducing layer 3, the intermediate layer 4 and the recording layer 5 were perpendicular magnetization films from room temperature to the Curie temperature.

In the magneto-optical disk constructed as described above, the Curie temperature of the intermediate layer is higher than that of the expansion reproducing layer, but the temperature at which the exchange coupling force at the interface between the intermediate layer and the recording layer is cut off is 160 ° C. Since the magnetic domains were expanded at the same temperature as in Example 8 where the Curie temperature of the layer was 150 ° C., the recording and reproducing characteristics of both were almost the same.

In this example, after forming the intermediate layer, the surface of the intermediate layer was treated, but the surface of the expanding reproduction layer may be treated in the same manner as described above after forming the expanding reproduction layer. The surface on the intermediate layer side may be treated. Alternatively, a substance that lowers the Curie temperature in the vicinity of the interface between the intermediate layer and the recording layer or the interface between the intermediate layer and the magnifying and reproducing layer may be distributed in an island shape, or may be deposited in a thickness of 1 to several atomic layers. Good. A rare earth element or nickel may be used as the substance that lowers the Curie temperature. Alternatively, the surface treatment as described above may be performed during the deposition of the intermediate layer.

[0142]

By using the magneto-optical recording medium of the present invention, a sufficiently large reproduced signal can be obtained even if, for example, a circular magnetic domain having a diameter of 0.3 μm is recorded in the recording layer 5. Therefore, in the present invention, the land portion or the groove portion is laser-annealed so that the magnetic domain can be smoothly expanded, and the recording film attached to the boundary portion between the land portion and the groove portion is thinned by using a special film forming method. No complicated processing is required, and it is possible to obtain an amplified reproduced signal from the minute magnetic domain even if a normal substrate is used.

In the magneto-optical recording medium of the present invention, the minute magnetic domains recorded in the recording layer can be transferred to the reproducing layer with the opposite magnetization and expanded in the reproducing layer without applying the reproducing magnetic field. Also, unlike DWDD and CARED, it does not generate a ghost signal in spite of the three-layer structure and the small number of layers, and is therefore extremely effective as a next-generation large-capacity magneto-optical recording medium.

The substrate groove shape of a magneto-optical recording medium, in particular, a magneto-optical recording medium utilizing a MAMMOS of a type which does not apply a reproducing magnetic field is designed to have a value within the above range, and
In particular, by adopting the method of recording information in the groove, the recording / reproducing power sensitivity can be increased. That is, it is possible to significantly improve the characteristics in recording / reproducing on / from the magneto-optical recording medium as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a principle of expanding a magnetic domain of a reproducing layer ((a) to (d)).

FIG. 2 is a diagram illustrating an exchange coupling force and a repulsive force generated between an information recording layer and an expansion reproducing layer.

FIG. 3 is a diagram illustrating a reproducing principle of a first type magneto-optical recording medium.

FIG. 4 is a diagram for explaining the reproducing principle of the first type magneto-optical recording medium.

FIG. 5 is a diagram illustrating a reproduction principle of a first type magneto-optical recording medium.

FIG. 6 is a diagram illustrating a reproducing principle of the first type magneto-optical recording medium.

FIG. 7 is a diagram for explaining the reproducing principle of the first type magneto-optical recording medium.

FIG. 8 is a diagram for explaining the reproducing principle of the first type magneto-optical recording medium.

FIG. 9 is a diagram illustrating a reproducing principle of the first type magneto-optical recording medium.

FIG. 10 is a diagram for explaining the reproducing principle of the first type magneto-optical recording medium.

FIG. 11 is a diagram for explaining the reproducing principle of the first type magneto-optical recording medium.

FIG. 12 is a diagram for explaining the reproducing principle of the first type magneto-optical recording medium.

FIG. 13 is a diagram for explaining the reproducing principle of the second type magneto-optical recording medium, which is a reproducing layer before being irradiated with reproducing light;
The magnetization state of the intermediate layer and the recording layer is shown.

FIG. 14 is a diagram for explaining the principle of magnetic domain expansion in the second type magneto-optical recording medium.
FIG. 14A shows a state in which reproduction light is irradiated.
FIG. 14B shows a state where the magnetic domain of the reproducing layer expands from the state of FIG. 14A, and FIG. 14C shows a state where the magnetic domain of the reproducing layer contracts from the state of FIG.

15 (a) and 15 (b) are diagrams showing a relationship between magnetostatic energy repulsive force and exchange energy attractive force when the magnetic domain of the reproducing layer is not expanded.

16 (a) and 16 (b) are diagrams for explaining how the magnetic domain of the reproducing layer of the second type magneto-optical recording medium expands.

17 (a) and 17 (b) are diagrams for explaining the magnetic domain expansion of the reproducing layer when the perpendicular magnetic anisotropy of the intermediate layer of the second type magneto-optical recording medium is small. .

18A and 18B are views for explaining the reason why a ghost signal does not occur in the second type magneto-optical recording medium.

FIG. 19 is a diagram illustrating that the region of the magnified reproduction layer in which the magnetic domain is enlarged is not affected by the leakage magnetic field from the recording magnetic domain.

20 is a schematic cross-sectional view of the magneto-optical recording medium manufactured in Example 1. FIG.

FIG. 21 is a diagram schematically showing cross-sectional shapes of lands and grooves of magneto-optical recording media produced in Examples 1, 10 to 13, Comparative Examples and Reference Examples.

FIG. 22 is a graph showing a reproduction signal waveform when the magneto-optical disk manufactured in Example 1 is reproduced with different reproduction light powers.

FIG. 23 is a graph showing the reproduction light power dependency of the bit error rate when reproducing the magneto-optical disk manufactured in Example 1.

FIG. 24 is a graph showing the recording light power dependence of the bit error rate when the magneto-optical disk manufactured in Example 1 was recorded with various recording light powers.

FIG. 25 is a graph showing a hysteresis loop for obtaining the exchange coupling force of the magneto-optical disk manufactured in Example 1.

26 is a graph showing temperature dependence of exchange coupling force of the magneto-optical disk manufactured in Example 1. FIG.

FIG. 27 is a graph showing the relationship of the bit error rate to the thickness t of the magnified reproduction layer of the magneto-optical disk manufactured in Example 1 × the saturation magnetization Ms.

28 is a graph showing the relationship between the bit error rate and the groove depth D of the substrate of the magneto-optical disk manufactured in Example 1. FIG.

FIG. 29 is a graph showing the relationship between the G / L ratio of the substrate of the magneto-optical disk manufactured in Example 1 and the bit error rate.

FIG. 30 is a graph showing the relationship between the bit error rate and the inclination angle θ of the land side wall of the substrate of the magneto-optical disk manufactured in Example 1.

FIG. 31 is a graph showing the relationship between the bit error rate of the magneto-optical disc manufactured in Example 2 and the thickness t of the magnifying reproducing layer.

FIG. 32 is a schematic cross-sectional view of the magneto-optical recording medium manufactured in Example 8.

FIG. 33 shows a reproduced waveform when an isolated magnetic domain having a mark length of 0.2 μm recorded in the magneto-optical recording medium of Example 8 was reproduced at reproducing powers of 1.5 mW and 3.0 mW.

FIG. 34 is a graph showing the mark length dependence of C / N of the magneto-optical recording medium of Example 8.

FIG. 35 is an eye pattern at the time of recording an NRZI random signal having a shortest mark length of 0.12 μm.

FIG. 36 is a schematic configuration diagram of a recording / reproducing apparatus according to the present invention.

FIG. 37 is a schematic cross-sectional view of magneto-optical recording media manufactured in Examples 10 to 12, Comparative Examples and Reference Examples.

38 is a graph showing the relationship between the bit error rate and the ratio G / L of the groove half width G and the land half width L in Example 10. FIG.

FIG. 39 is a graph showing the relationship between the bit error rate and the groove depth D in Example 11.

FIG. 40 is a graph showing the relationship between the bit error rate and the land side wall surface inclination angle θ in Example 12.

FIG. 41 is a graph showing the relationship between the bit error rate and the recording power in the comparative example and the reference example.

FIG. 42 is a graph showing the relationship between the bit error rate and the reproduction power in the comparative example and the reference example.

43 is a schematic sectional view showing the structure of the magneto-optical disk of Example 13. FIG.

FIG. 44 is a graph showing exchange coupling force cutoff temperature.

FIG. 45 is a graph showing a relationship between a temperature gradient of exchange coupling force and a bit error rate.

FIG. 46 shows a hysteresis curve of the magneto-optical disk of the present invention near 120 ° C.

FIG. 47 is a conceptual diagram illustrating the reproducing principle of the second type magneto-optical recording medium satisfying the expression (2).

FIG. 48 is a diagram showing a state in which the magneto-optical disk has further moved with respect to the light spot from the state shown in FIG.

FIG. 49 is a diagram for explaining the principle of FAD magnetic super-resolution.

[Explanation of symbols]

1 substrate 2 Dielectric layer 3 playback layers 4 Middle class 4'Expansion trigger layer 5 recording layers 6 Auxiliary magnetic layer 6'recording auxiliary layer 7 protective layer 8 Heat sink layer 9 Protective coating layer 71 recording / reproducing apparatus 100, 200 Magneto-optical recording medium

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI G11B 11/105 586 G11B 11/105 586M (72) Inventor Shosuke Shimazaki 1-88, Torora, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd. In-house (72) Inventor Sho Imai 1-88, Torora, Ibaraki-shi, Osaka Prefecture Hitachi Maxell Co., Ltd. (72) Inventor, Kazuko Inoue 1-88, Torora, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd. (72 ) Inventor Yoshikazu Suzuki, 1-88, Torora, Ibaraki-shi, Osaka, Hitachi Maxell Co., Ltd. (72) Inventor: Yasuhiko Kokuda, 1-88, Torora, Ibaraki-shi, Osaka (72) Inventor, Hitachi Maxell Osamu Ishizaki 1-88 1-88, Tora, Ibaraki-shi, Osaka Within Hitachi Maxell Co., Ltd. (56) References JP 2000-173117 (JP, A) (58) (Int.Cl. ^7, DB name) G11B 11/00 - 13/08

Claims (11)

(57) [Claims] 1. A magneto-optical recording medium, comprising: a recording layer formed of a magnetic material; a reproducing layer formed of a magnetic material and exhibiting perpendicular magnetization; and a recording layer and a reproducing layer formed of a magnetic material. And an intermediate layer existing between the reproducing layer and the intermediate layer, and the compensating temperature T comp 1 of the reproducing layer and the compensating temperature of the intermediate layer.
T comp 2 and the compensation temperature T comp 3 of the recording layer are expressed by the following formula.
(1) and (2): T comp 2 < 120 ℃ satisfies one of <T comp 1 ··· (1) T comp 3 <120 ℃ <T comp 2 ··· (2), the recording The layers, the intermediate layer, and the reproducing layer are magnetically exchange-coupled to each other when the magneto-optical recording medium is not irradiated with light, and the exchange coupling force between the recording layer and the reproducing layer is irradiated by irradiating the magneto-optical recording medium with light. By heating to a temperature Tr that shuts off
A magneto-optical recording medium in which a magnetic domain transferred from the recording layer to the reproducing layer is expanded, and information is reproduced from the expanded magnetic domain, wherein a change rate of an exchange coupling magnetic field between the recording layer and the reproducing layer is increased. 100Oe / ℃ ~270Oe / ℃ in the above temperature T r
A magneto-optical recording medium characterized by: 2. The magneto-optical recording medium according to claim 1, wherein the reproducing layer is formed of a rare earth transition metal alloy mainly containing GdFe. 3. The magneto-optical recording medium according to claim 1, wherein the compensation temperature of the reproducing layer is not lower than the Curie temperature. 4. The magneto-optical recording medium according to claim 1, wherein the reproducing layer has a film thickness of 15 nm to 30 nm. 5. A magneto-optical recording medium comprising: a recording layer formed of a magnetic material; a reproducing layer formed of a rare earth transition metal alloy mainly containing GdFe and exhibiting perpendicular magnetization; formed of a magnetic material. , Which exists between the recording layer and the reproducing layer and has a perpendicular magnetic anisotropy energy of 0.
4 × 10 ⁶ erg / cm ³ to 1 × 10 ⁶ erg / cm 3
Compensating temperature T comp 1 of the reproducing layer, compensating temperature of the intermediate layer
T comp 2 and the compensation temperature T comp 3 of the recording layer are expressed by the following formula.
(1) and (2): T comp 2 < 120 ℃ satisfies one of <T comp 1 ··· (1) T comp 3 <120 ℃ <T comp 2 ··· (2), the recording The layers, the intermediate layer, and the reproducing layer are magnetically exchange-coupled to each other when the magneto-optical recording medium is not irradiated with light, and the exchange coupling force between the recording layer and the reproducing layer is irradiated by irradiating the magneto-optical recording medium with light. A magneto-optical recording medium in which the magnetic domain transferred from the recording layer to the reproducing layer is expanded by heating to a temperature Tr or higher at which the magnetic field is cut off, and information is reproduced from the expanded magnetic domain. The rate of change of the exchange coupling magnetic field between the layer and the reproducing layer is 100 Oe / ° C. to 270 Oe /
A magneto-optical recording medium having a temperature of ° C. 6. The magneto-optical recording medium according to claim 5, wherein the intermediate layer is made of a rare earth transition metal alloy mainly containing TbFe. 7. The magneto-optical recording medium according to claim 5, wherein the intermediate layer has a film thickness of 5 nm to 15 nm. 8. A magneto-optical recording medium, comprising: a recording layer formed of a magnetic material; a reproducing layer formed of a rare earth transition metal alloy containing GdFe as a main component and exhibiting perpendicular magnetization; and mainly containing TbFe. It is formed of a rare earth transition metal alloy, is present between the recording layer and the reproducing layer, and has a perpendicular magnetic anisotropy energy of 0.4 × 10 ⁶ erg / room temperature at room temperature.
cm ³ to 1 × 10 6 erg / cm 3 of an intermediate layer; and a compensation temperature T comp 1 of the reproduction layer and a compensation temperature of the intermediate layer.
T comp 2 and the compensation temperature T comp 3 of the recording layer are expressed by the following formula.
(1) and (2): T comp 2 < 120 ℃ satisfies one of <T comp 1 ··· (1) T comp 3 <120 ℃ <T comp 2 ··· (2), the recording The layers, the intermediate layer, and the reproducing layer are magnetically exchange-coupled to each other when the magneto-optical recording medium is not irradiated with light, and the exchange coupling force between the recording layer and the reproducing layer is irradiated by irradiating the magneto-optical recording medium with light. A magneto-optical recording medium in which the magnetic domain transferred from the recording layer to the reproducing layer is expanded by heating to a temperature Tr or higher at which the magnetic field is cut off, and information is reproduced from the expanded magnetic domain. The rate of change of the exchange coupling magnetic field between the layer and the reproducing layer is 100 Oe / ° C. to 270 Oe /
A magneto-optical recording medium having a temperature of ° C. 9. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is irradiated with reproduction light to heat the magneto-optical recording medium to a temperature Tr or higher at which the exchange coupling force between the recording layer and the reproduction layer is cut off. A reproducing method of a magneto-optical recording medium, characterized in that information is reproduced from the magnetic recording medium. 10. The magnetic domain transferred from the recording layer to the reproducing layer is enlarged to detect the recording magnetic domain before the recording magnetic domain to be reproduced reaches the center of the reproducing light. A method for reproducing the magneto-optical recording medium according to 1. 11. A reproducing apparatus for reproducing recorded information from the magneto-optical recording medium according to claim 1, comprising a laser beam irradiating section, a magnetic field applying section, and a signal detecting section. And a reproduction device including a signal processing unit for processing and a disk drive unit.