JPH11144339A - Magneto-optical recording medium and its reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium which embodies good magnetic domain magnification reproduction with simple constitution and has a high recording density and high reliability and its reproducing method. SOLUTION: This magneto-optical recording medium is constituted by laminating a transparent dielectric layer 12, a reproducing layer 5, an intermediate layer 6, a recording layer 7 and a protective layer 13 in this order on a disk substrate 11 and is divided to a servo region having pits 1... for tracking control by a sample servo tracking method and a data region free of ruggendess for recording information. Since the data region is devoid of the ruggedness, the magnetic walls of the reproduction magnetic domains 10 formed in the reproducing layer 5 are not subjected to pinning. Then, the magnetic wall movement in the reproducing layer 5 is made free and even if the track pitch is narrowed, the expansion of the reproduction magnetic domains 10 is well embodied.

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 for recording / reproducing information by modulating light or a magnetic field, and a reproducing method therefor.
The present invention relates to a magneto-optical recording medium in which a magnetic domain of a recording layer is enlarged and transferred to a reproducing layer during reproduction, and a reproducing method therefor.

[0002]

2. Description of the Related Art A magneto-optical recording medium using a magneto-optical effect is known as a large-capacity information recording medium that can be repeatedly rewritten. In order to further increase the recording density of this magneto-optical recording medium, various studies and studies have been made.

[0003] In a magneto-optical disk, which is one form of a magneto-optical recording medium, in order to read recorded bits on the disk, a light beam must be accurately focused on target recorded bits. For this reason, it is necessary to control the spot of the light beam in the radial direction of the disk by using a tracking servo for recording and reproduction on the magneto-optical disk. In this control, a deviation of the light beam from a predetermined position on the disk is called a tracking error.

Various techniques are known as a method for detecting this tracking error. Among them, a general technique is referred to as a push-pull method in which a guide groove is provided in a disk substrate of a magneto-optical disk to perform control. Is the way.
This method irradiates a part of a light beam to a guide groove formed in a disk, detects a tracking error of the disk from the intensity distribution of the diffracted light reflected from the guide groove, and outputs a control signal of a beam spot irradiation position and a control signal. This is a method for obtaining a tracking error signal.

The push-pull method is advantageous for high-density recording of a magneto-optical disk, and is often used for recording and reproduction on a conventional magneto-optical recording medium. Therefore, studies have been made on the length and depth of the guide groove so as to improve both the characteristics of the tracking error signal obtained by this method and the characteristics of the magneto-optical signal which is the information reproduction signal. It is known that these appropriate sizes are determined to some extent from the size of the beam spot and the like. For example, when a general beam spot is used, the width is on the order of 0.6 μm to 1 μm, and the depth is on the order of tens to 100 nm. The size of the beam spot is determined by the wavelength of light, the aperture ratio of the condenser lens, and the like.

As another method for detecting a tracking error, there is a sample servo tracking method using a track wobbling method. This sample servo
In the tracking method, the reproduction of the information recorded in the data area and the tracking control using the servo area are performed by being completely separated in time and space. Therefore, on the magneto-optical disk, areas called servo bytes in which servo information is written in advance are provided at predetermined intervals, separated from the areas where information is recorded. In this servo byte, a clock pit for generating a clock and a servo pit for detecting a tracking error signal are embedded.

On both sides of one track of this magneto-optical disk, two servo pits are formed at equal distances from the track. These two servo pits are shifted from each other in the circumferential direction of the disk. And, when recording / reproducing this disc,
The objective lens of the optical pickup is controlled so that the amount of reflected light from each servo pit becomes equal. This allows the beam spot to follow the track at the center of the two servo pits.

In this sample servo tracking method, if a plurality of servo pits are included in a beam spot, it is impossible to distinguish the reflected light of each servo pit. For this reason, in order to increase the recording density of the magneto-optical disk, it is necessary to devise the positional relationship of the servo pits on the track and the like.

Japanese Patent Application Laid-Open No. 6-60408 discloses a tracking device employing the above-described sample servo tracking method. This device uses wobble pits (servo pits) on adjacent tracks on the optical disc.
, And by switching the polarity of the tracking error signal obtained from the wobble pit between adjacent tracks, tracking control in a small servo area is performed. For this reason, in this conventional apparatus, it is possible to increase the recording density in the track direction (radial direction of the disk) by narrowing the track pitch of the optical disk.

By the way, with respect to the beam diameter of the light beam,
When the diameter of the recording bit, which is the recording magnetic domain, and the interval between the recording bits decrease, the reproduction characteristics of the magneto-optical recording medium deteriorate. The cause is that adjacent recording bits enter the beam diameter of the light beam condensed on the recording bits to be reproduced, and it becomes impossible to separate and reproduce individual recording bits.

In order to prevent this deterioration, see “Summary of the 20th Annual Meeting of the Japan Society of Applied Magnetics (1996), 22pE-4,
"Ultrahigh-density magneto-optical disk by magnetic domain expansion reproduction" discloses a magneto-optical disk having a configuration in which a non-magnetic intermediate layer is interposed between a recording layer and a reproduction layer, and a reproduction method therefor. In this magneto-optical disk, a magnetic domain larger than the magnetic domain of the recording layer is transferred to the reproducing layer by a magnetic field generated from the recording layer. Then, information is reproduced from this reproduction layer. The reproducing method in which the magnetic domains of the recording layer are enlarged to the reproducing layer and the magnetic domains formed in the reproducing layer are read by the light beam is called magnetic domain enlarged reproduction.

FIG. 5 is an explanatory diagram for explaining the magnetic domain enlargement reproduction. Various methods have been proposed as a magnetic domain enlarging / reproducing method.
Within the time when the (recording bit) is in the beam spot 111, this recording magnetic domain 109
An external magnetic field is applied in the same direction as the magnetization direction. As a result, as shown in FIG. 5, the small recording magnetic domain 109 can be enlargedly transferred as the reproducing magnetic domain 110 to the high-temperature portion HP of the reproducing layer 105 and read. Therefore, in this magnetic domain expansion reproduction method, since most of the portion irradiated with the beam spot 111 becomes the reproduction magnetic domain 110, acquisition of reproduction signal characteristics higher than normal reproduction and high-density recording of the magneto-optical disk can be simultaneously performed. It will be realized. In FIG. 5,
The magnetization of the portion other than the upward recording magnetic domain 109 is all downward.

[0013]

However, a magneto-optical disk employing this magnetic domain enlarging / reproducing method uses the above-described push-pull method for tracking control, that is, a substrate using a guide groove in the magneto-optical disk. In the case where is used, the following problems occur.

That is, the magnetic film and the dielectric film of the magneto-optical disk are laminated by sputtering or vapor deposition on the substrate surface on which the guide groove is formed. For this reason, these magnetic films and dielectric films are also laminated not in a uniform planar shape but in an uneven shape of the guide groove.

FIG. 6 is an explanatory view showing a magneto-optical recording medium having a reproducing layer 105, an intermediate layer 106, and a recording layer 107 formed in such an uneven shape, and FIG. FIG. 3 is an explanatory diagram showing a disk surface of a magneto-optical disk. As shown in FIG. 6, the magneto-optical disk is formed with groove portions 102 as guide grooves, and land portions 10 between the groove portions 102 and the guide grooves.
Information is recorded in 3 and so on. Further, in the groove section 102 on the right side in the figure, the recording magnetic domain 109 of the recording layer 107 is enlarged and transferred to the reproducing layer 105 as the reproducing magnetic domain 110, and the reproducing magnetic domain 110 is in a perpendicular magnetization state.

As shown in the magnetic bubble theory, if there is unevenness in a portion in the perpendicular magnetization state like the reproducing magnetic domain 110 shown in FIG. 1, a magnetic pole is generated in this portion, and the reproducing magnetic domain 110
The magnetic force is applied to. Therefore, an obstacle occurs in the movement of the domain wall of the reproducing magnetic domain 110 in the reproducing layer 105, that is, the expansion of the reproducing magnetic domain 110 formed in the reproducing layer 105. This obstacle is particularly caused at the corners of the groove (groove portion 102).
The boundary between the magnetic domain wall and the land portion 103) is notable, and in some cases, the domain wall is pinned (fixed) at this portion.

When a magnetic film or a dielectric film is formed, particles are incident on the side wall surface of the guide groove almost in parallel.
Therefore, these films become very thin on the side wall surface. Therefore, the magnetic film on the side wall surface has poor magnetic properties as compared with the magnetic film in the portion other than the side wall surface, and the poor magnetic characteristics cause obstacles to domain wall movement in the same manner as described above.

Accordingly, when an external magnetic field is applied to such a magneto-optical disk to move the domain wall of the magnetic domain in the reproducing layer, as shown in FIG.
The reproducing magnetic domain 110 formed in the groove 102 does not become larger than the width of the groove 102. That is,
The domain wall is pinned at the corner of the guide groove, and does not spread to the land 103. Therefore, the reproduction magnetic domain 110
Cannot be transferred to a desired range. Therefore, since the reproducing magnetic domain 110 cannot be formed largely in the beam spot 111, the characteristic of the reproducing signal deteriorates, and the object of the magnetic domain enlarging reproducing method of enlarging and reproducing fine magnetic domains is achieved. You can't do that.

In such a configuration of the magneto-optical disk (configuration having a guide groove), there is a method of increasing the external magnetic field applied during reproduction in order to prevent the above-described pinning of the domain wall. When such a large external magnetic field is applied,
The influence of the magnetic force generated by the shape of the guide groove becomes relatively negligible and pinning of the domain wall can be prevented.

However, applying an external magnetic field having a magnitude larger than that required for magnetic domain expansion reproduction is disadvantageous in terms of the configuration and cost of the apparatus. In addition, since a large external magnetic field also hinders the magnetostatic coupling between the recording layer and the reproducing layer, the recording magnetic domain cannot be accurately expanded to the reproducing layer.

In order to prevent the pinning, there is a method of increasing the track pitch within a range where a tracking error signal is obtained, and positioning the corner of the guide groove as outside of the beam spot as possible. In this method, the loss of the reproduced signal is reduced even when the domain wall pinning occurs. However, this method is not desirable because it limits the density increase in the track direction (disc radial direction).

There are other problems with the push-pull method. To increase the density of the magneto-optical disk, it is conceivable to reduce the track pitch or the width of the guide groove and arrange the tracks at a high density in the disk radial direction. However, if the width of the guide groove is reduced to form a fine groove shape, there is a problem that optical noise is generated during reproduction. That is, as the width of the guide groove decreases, the area of the adjacent track entering the beam spot increases. Since the distance from the optical pickup to the track to be played is different from the distance from this optical pickup to the adjacent track, the optical pickup receives reflected light mixed with a lot of light having different phases, and noise is generated in the reproduced signal. It will happen. Further, in the magneto-optical disk having such a fine groove shape, the magnetic domain of the reproducing layer is likely to be pinned when the magnetic domain expansion reproduction is performed.

Further, it is difficult to process the irregularities of the guide groove into a perfect rectangle. Therefore, the shape of the side wall is easily rounded, which causes a problem of generation of noise. Also, in a magneto-optical disk having an incomplete guide groove on a dull side wall, if the track pitch is narrowed for higher density,
Since the side wall of the guide groove approaches the center of the beam spot, noise is further increased.

In the push-pull method, a DC offset occurs in the tracking error signal due to a shift of the optical axis of the objective lens, a radial inclination of the disk, and an unbalance in the shape of the guide groove. This DC offset causes an abnormal tracking operation.

For high-density recording, a land / groove recording method for recording data on both lands (between guide grooves) and grooves (within guide grooves) has been proposed. In this method, it is difficult to detect a focus error signal using an astigmatism method because the depth of the data area is different and the shape of the guide groove is not a perfect rectangle. Therefore, it is necessary to adjust the focus offset, and it becomes difficult to control the optical pickup. Further, since the land and the groove have different optical characteristics, it is necessary to adjust optically and circuitally at the time of recording / reproducing.

As described above, in the conventional push-pull method using a guide groove, it has been difficult to satisfactorily perform magnetic domain expansion reproduction. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and a magneto-optical recording medium having high recording density and high reliability, realizing good magnetic domain expansion reproduction with a simple configuration, and a reproducing method thereof. Is to provide.

[0027]

In order to achieve the above-mentioned object, a magneto-optical recording medium according to the first aspect of the present invention comprises a recording layer having magnetic domains for recording information, a recording layer having a predetermined temperature, As described above, in the magneto-optical recording medium having the reproducing layer that is magnetostatically coupled to the recording layer and expands and transfers the magnetic domain of the recording layer, the servo area for detecting a tracking error is separated from the servo area. And a data area having a planar shape for recording information, which is formed as described above.

In the above-described magneto-optical recording medium, during reproduction,
The magnetic domain of the recording layer is enlarged and transferred to the reproducing layer, and a magnetic domain larger than the magnetic domain of the recording layer is formed in the reproducing layer. By reading this large magnetic domain with a light beam, a good reproduction signal can be obtained. The magneto-optical recording medium includes a servo area for detecting a tracking error and a data area for recording information. This data area is formed separately from the servo area, and has a planar shape with no irregularities. That is, the data area of this configuration does not have irregularities such as the guide grooves that hinder the expansion of the magnetic domains formed in the reproducing layer.

In the above-described reproduction performed by enlarging and transferring magnetic domains to the reproducing layer, it is necessary to move the domain walls of the magnetic domains in the reproducing layer within a very short time. In the above-mentioned magneto-optical recording medium, since there is no unevenness that hinders the expansion of the magnetic domain in the reproducing layer, the domain wall of this magnetic domain can move freely. Therefore, the expansion of the magnetic domain of the reproducing layer can be satisfactorily realized, so that a good reproducing signal characteristic can be obtained even if the track pitch is narrowed. Thereby, the above-described magneto-optical recording medium is a highly reliable magneto-optical recording medium capable of high-density recording as compared with a magneto-optical recording medium in which irregularities such as grooves based on a push-pull method are formed in a data area. Has become. Since the data area of the above-mentioned magneto-optical recording medium has a planar shape with no irregularities, it is easy to manufacture the master disk of the magneto-optical recording medium and the magneto-optical recording medium, and the productivity can be increased.

Further, in the magneto-optical recording medium according to the second aspect, in addition to the configuration of the first aspect, the reproducing layer has an in-plane magnetization state at room temperature and a perpendicular magnetization state at a high temperature. And According to the above configuration, the reproducing layer of the magneto-optical recording medium has an in-plane magnetization state at room temperature and a perpendicular magnetization state at high temperature. Therefore, the portion of the beam spot irradiated with the central portion and heated to a high temperature is in a perpendicular magnetization state, and is magnetostatically coupled with the magnetization of the recording magnetic domain in the recording layer to form an enlarged magnetic domain. In addition, portions other than this portion, that is, portions that are not at a high temperature, such as a portion where the end portion of the beam spot is irradiated, are in an in-plane magnetization state and interact with the magnetization of the recording magnetic domain in the recording layer. do not do. That is, the recording layer is masked. Therefore, since a magneto-optical signal is not generated from a portion other than the enlarged magnetic domain in the reproducing layer, such as a portion where the end of the beam spot is irradiated, a reproduced signal with less noise can be obtained. it can.

According to a third aspect of the present invention, in the magneto-optical recording medium according to the first aspect, the servo area is provided with irregularities for performing tracking control by a sample servo tracking method. It is characterized by having. According to the above configuration, the servo area is provided with irregularities for performing tracking control by the sample servo tracking method. Then, at the time of recording / reproducing, tracking control is performed by irradiating a beam spot onto the irregularities and detecting the amount of reflected light. In the sample servo tracking method, reproduction of information recorded in a data area and tracking control using the servo area are performed in a completely separated manner in time and space. Therefore, the tracking control of the magneto-optical recording medium in which the servo area and the data area are separated as described in claim 1 can be favorably performed.

In the tracking control using the irregularities, when the data area is irradiated with the beam spot, the irregularities in the servo area are not irradiated with the beam spot. Therefore, the reflected light from the irregularities does not mix with the reflected light from the beam spot for reproducing the information, so that good reproduced signal characteristics can be obtained.

A magneto-optical recording medium according to a fourth aspect of the present invention is characterized in that, in addition to the configuration of the third aspect, the irregularities are formed of pits. According to the above configuration, the irregularities are formed of pits. Since these pits are formed based on the sample servo tracking method as described above, tracking control can be efficiently performed with a small number of pits. In addition, since such a pit can be easily formed and a magneto-optical recording medium provided with a pit has been put to practical use, a conventional magneto-optical recording medium can be applied, and the cost can be reduced at a low cost. The described magneto-optical recording medium can be manufactured.

A magneto-optical recording medium according to a fifth aspect of the present invention is characterized in that, in addition to the configuration of the third aspect, the irregularities are formed by lands and grooves formed based on a push-pull method. According to the above configuration, the irregularities are formed by the grooves, which are the guide grooves formed based on the push-pull method, and the lands between the grooves. Therefore, the tracking control of the magneto-optical recording medium is a combination of the sample servo tracking method and the push-pull method. That is, this tracking control is performed separately from reproduction of information,
This is performed based on light reflected from lands and grooves formed in the servo area.

Thus, the portions common to the conventional magneto-optical recording medium for magnetic domain expansion reproduction are increased, and the conventional magneto-optical recording medium can be applied as the magneto-optical recording medium according to the third aspect. Therefore, the magneto-optical recording medium according to claim 3 can be manufactured at low cost. Further, since the tracking control is similar to that of the conventional magneto-optical recording medium, compatibility with the magneto-optical recording medium can be improved.

According to a sixth aspect of the present invention, there is provided a reproducing method for a magneto-optical recording medium, comprising: a recording layer having a magnetic domain for recording information; A reproducing layer for transferring magnetic domains of the recording layer, wherein the magnetic domains of the recording layer are enlarged and transferred to the reproducing layer to form magnetic domains larger than the magnetic domains of the recording layer on the reproducing layer. The method is characterized in that the magnetic domain is irradiated with a beam spot and information is read, while tracking control is performed by a sample servo tracking method.

According to the above-described method, the transfer of the magnetic domain in the recording layer to the reproducing layer is an enlarged transfer in which the magnetic domain formed in the reproducing layer is larger than the magnetic domain of the recording layer. This enlargement transfer is performed, for example, by applying an external magnetic field in the same direction as the magnetization direction of the magnetic domain while the magnetic domain of the recording layer to be reproduced passes through the inside of the beam spot.

In order to enlarge the magnetic domains of the reproducing layer to a desired size, irregularities such as guide grooves used for tracking control by the push-pull method are formed in the area where information is recorded. Preferably, it is not. Therefore, in the above method, tracking control by the sample servo tracking method is performed. That is, as the magneto-optical recording medium for reproduction, a region in which the magnetic domain of the reproduction layer is formed and the region for performing tracking control are separated from each other, and tracking control is performed separately from reproduction of information. ing. As a result, the magnetic domains formed in the reproducing layer are reproduced while being enlarged to a desired size, and a good reproduction signal can be obtained, and the tracking control can be performed well.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. FIG. 1B is a cross-sectional view schematically showing the configuration of a magneto-optical disk (hereinafter, referred to as the present magneto-optical disk) which is a magneto-optical recording medium according to the present embodiment. As shown in this figure, the present magneto-optical disk has a disk substrate 1
1, a transparent dielectric layer 12, a reproducing layer 5, an intermediate layer 6, a recording layer 7, and a protective layer 13 are laminated in this order. Although not shown, a protective film (protective coat) made of an organic resin is formed on the protective layer 13 to protect the entire magneto-optical disk.

FIG. 1A is an explanatory diagram showing the outline of the structure of the reproducing layer 5, the intermediate layer 6, and the recording layer 7 in the present magneto-optical disk and the state of each of the layers 5 to 7 during reproduction. . As shown in this figure, the magneto-optical disk is divided into a servo area and a data area. The data area is an area for recording information, and has a planar shape without unevenness. The servo area is an area for tracking control using the track wobbling method, that is, tracking control using the sample servo tracking method, and has pits 1.

FIG. 2 is an explanatory diagram showing the shape of the disk surface of the present magneto-optical disk. As shown in this figure, these pits 1 are track 2 that beam spot 4 follows.
Are formed to be shifted from each other in the circumferential direction. .. Are not formed in the data area, but are formed only in the servo area. Therefore, pit 1 ...
Is completely separated from the data area,
When information is reproduced, these pits 1 are not irradiated with a light beam. Therefore, the reflected light of the pits 1 does not mix with the reflected light for reproducing information. These pits 1 are used not only for information reproduction but also for tracking control at the time of recording.

The characteristics of the layers 5 to 7 and 11 to 13 shown in FIG. 1B which constitute the magneto-optical disk will be described below. The disk substrate 11 includes a portion having pits 1... Serving as a substrate in a servo area, and a flat portion having no irregularities serving as a substrate in a data area. For example, polycarbonate is used as a material.

The transparent dielectric layer 12 is formed on the disk substrate 11 by sputtering or depositing nitride or the like. The transparent dielectric layer 12 enhances the Kerr rotation angle generated by the reflection of light on the reproducing layer 5 by using an optical interference phenomenon. Therefore, the transparent dielectric layer 1
For 2, a light-transmitting material is used. The transparent dielectric layer 12 also has a function of protecting a rare earth / transition metal alloy that is easily oxidized. The protective layer 13 has a function of protecting a rare earth / transition metal alloy that is easily oxidized, and is formed by sputtering or depositing a nitride or the like on the recording layer 7.

The recording layer 7 is a perpendicular magnetization film formed by sputtering or depositing an amorphous magnetic alloy made of a rare earth transition metal. Then, FIG.
As shown in FIG.
have. The recording layer 7 in FIG.
Is a portion where only one is formed, so that the magnetization of the portion other than the recording magnetic domain 9 in the drawing is all downward. This recording layer 7 is a magnetic layer whose magnetization increases at high temperatures. Therefore, when a light beam is irradiated during reproduction, the temperature of the portion corresponding to the center of the beam spot 4 becomes high, and the magnetization of this portion increases. Then, since the magnetic field generated from this portion increases due to the increase in the magnetization, the recording magnetic domain 9 in this portion can be transferred to the reproducing layer 5.

The reproducing layer 5 is a magnetic film formed by sputtering or vapor-depositing an amorphous magnetic alloy made of a rare-earth transition metal and having an in-plane magnetization state at room temperature and a perpendicular magnetization state at high temperature. Therefore, as shown in FIG. 1A, when a light beam is applied to the reproducing layer 5 at the time of reproducing, a high temperature portion HP in a perpendicular magnetization state is formed near the center of the beam spot 4. The other portions are in an in-plane magnetization state to mask the magnetization of the recording layer 7. Then, in the high-temperature portion HP, the recording magnetic domain 9 is enlarged and transferred by the magnetostatic coupling with the magnetization of the recording magnetic domain 9 in the high-temperature portion of the recording layer 7 to form a reproduction magnetic domain 10. Then, the reproducing magnetic domain 10 is read by a light beam, and a reproducing signal is generated. Therefore, while one recording magnetic domain 9 of the recording layer 7 passes through the beam spot 4, it is necessary that this recording magnetic domain 9 is enlarged and transferred to the reproducing layer 5, and the magnetic characteristics of each of the layers 5, 7 An apparatus for reproducing a magnetic disk is adjusted so as to enable this enlarged transfer.

The intermediate layer 6 is provided such that the magnetic exchange coupling between the recording layer 7 and the reproducing layer 5 is interrupted, and the magnetostatic coupling is a dominant interaction between the two layers 5. And a non-magnetic material is used. This intermediate layer 6 can improve the magnetic field sensitivity during recording.

The reproduction of the magneto-optical disk as described above is performed as follows.
It is performed as follows. As shown in FIG. 1A, when the light beam is condensed by the objective lens 8 and irradiated on the reproducing layer 5 from the disk substrate 11 side of the present magneto-optical disk,
The high-temperature portion HP is formed in the reproducing layer 5. Further, the magnetization of the high-temperature portion of the recording layer 7 corresponding to the center of the beam spot 4 of the light beam (the magnetization of the recording magnetic domain 9 in the figure) increases. Then, the high-temperature portion HP of the reproducing layer 5 is in a perpendicular magnetization state, and the magnetostatic coupling with the magnetization of the high-temperature portion of the recording magnetic domain 9 in the recording layer 7 causes the recording magnetic domain 9 to be enlarged and transferred to the high-temperature portion HP, thereby causing the reproducing magnetic domain 10 to move. It is formed. The light beam is reflected by the reproducing magnetic domain 10 and becomes reflected light including a magneto-optical signal.
A reproduction signal is formed based on the reflected light. Further, the formation of the reproduction magnetic domain 10 is performed by applying an external magnetic field to the high-temperature portion HP in the same direction as the magnetization of the recording magnetic domain 9.

After the reproduction magnetic domain 10 is reproduced, the high-temperature portion HP moves by the rotation of the magneto-optical disk, and another recording magnetic domain (not shown) is similarly transferred to the reproduction layer 5 and reproduced. Thus, in the present magneto-optical disk, the enlarged transfer of the recording magnetic domain of the recording layer 7 to the reproducing layer 5 is repeated.

The tracking control is performed by receiving the reflected light of the light beam from the pits 1... Formed in the servo area formed on the disk substrate 11. That is, since the beam spot 4 passes through the center of the track 2, the track 2
The pits 1.1 on both sides are sequentially irradiated. And these pits 1.1, which are shifted from the track 2 by the same distance,
The tracking control is performed so that the reflected light amounts are equal.

As described above, the present magneto-optical disk is a magnetic domain expansion reproduction magneto-optical disk employing the sample servo tracking method for tracking control. Therefore, it is advantageous in the following points as compared with a conventional magneto-optical disk for land-groove recording, which employs a push-pull method for tracking control, like a magneto-optical disk for magnetic domain expansion reproduction.

First, by making the data area a flat surface without unevenness, it is possible to eliminate the domain wall pinning which has conventionally occurred at the corner of the guide groove. This makes it possible to freely move the domain wall in the reproducing layer 5 and to favorably form the reproducing magnetic domain 10.

When the tracking control is performed by the push-pull method, the magnetic domain transfer is more restricted as the track pitch becomes narrower because of the guide grooves. However, in the magneto-optical disk employing the sample servo tracking method, although the recording density in the circumferential direction of the disk is slightly reduced, it is possible to increase the density in the radial direction of the disk. Therefore, the recording density of the present magneto-optical disk can be higher than that of a magneto-optical disk employing the push-pull method. In addition, since the data area has a flat shape without unevenness, it is easy to manufacture the master disk of the present magneto-optical disk and also easily manufacture the magneto-optical disk. Therefore,
This magneto-optical disk is a magneto-optical disk with high productivity.

Further, in the magneto-optical disk employing the push-pull method, when the track pitch is narrowed to increase the density, the generation of noise due to the guide groove cannot be avoided. However, in the present magneto-optical disk, the occurrence of this noise can be suppressed by setting the data area to a flat surface without unevenness.

In the sample servo tracking method employed in the present magneto-optical disk, a DC offset, which has been a problem in the push-pull method using a guide groove, does not occur. In addition, since the optical axis shift becomes strong, the accuracy of the optical system can be greatly reduced. Further, since the inclination of the magneto-optical disk is increased, the compatibility of the magneto-optical disk is improved.
This is advantageous for high-density recording. Further, since the servo area and the data area are completely separated in time and space, there is no interference between the reproduction signal and the tracking error signal. That is, since the tracking error signal does not change during recording and reproduction of information, extremely stable recording and reproduction can be realized.

Further, in the present magneto-optical disk, since the data area is a flat surface without unevenness, it is not necessary to adjust the focus offset for each adjacent track. Accordingly, the control of the optical pickup is simple, and there is no difference in the optical characteristics of the adjacent tracks, so that the reproducing apparatus can be made simple in optical and circuit terms.

Hereinafter, measurements performed to verify the characteristics of magnetic domain expansion reproduction in the present magneto-optical disk will be described. First, the sample # 1 of this magneto-optical disk and the comparative samples # 1 and # 2 used for this measurement will be described.

Sample # 1 performs tracking error detection by the sample servo tracking method.
This is a sample of the present magneto-optical disk. This sample # 1
Here, polycarbonate is used as the material of the disk substrate 11, AlN is used as the material of the transparent dielectric layer 12, GdFeCo is used as the material of the reproducing layer 5, and Al is used as the material of the intermediate layer 6.
N, TbFeCo is used as a material of the recording layer 7, and AlN is used as a material of the protective layer 13.
The magnetic properties of each layer are adjusted to enable magnetic domain expansion reproduction. The data area of sample # 1 is
It has a flat shape without unevenness like a guide groove.

The comparative samples # 1 and # 2 have a transparent dielectric layer made of AlN and a recording made of TbFeCo on a disk substrate having guide grooves (grooves) for the push-pull method, similarly to the present magneto-optical disk. In this configuration, a layer, an intermediate layer made of AlN, a reproducing layer made of GdFeCo, and a protective layer made of AlN are provided. Although the structure of these comparative samples # 1 and # 2 is the same, in the measurement described below, the reproduction of the comparative sample # 1 is normal reproduction performed without applying an external magnetic field, while the reproduction of the comparative sample # 2 is performed. And magnetic domain expansion reproduction performed by applying an external magnetic field.

Note that the sample No. 1 and the comparative sample No.
The track pitch of 1.♯2 was 0.7 μm in common. The land width, groove width, and groove depth of Comparative Sample # 1 and Comparative Sample # 2 were the same, the land width and groove width were 0.7 μm, and the groove depth was 40 nm. This is to make the recording densities in the data areas of the comparative sample # 1 and the comparative sample # 2 equal. Land / groove recording was performed on these comparative samples # 1 and # 2.

The measuring method and the result are shown below. In the following measurement, a semiconductor laser having a wavelength of 680 nm and an aperture ratio NA were used.
Has an objective lens of 0.55, and the beam spot diameter is 1
An optical pickup of μm was used. In each sample, an isolated pattern was recorded so that only one recording magnetic domain was included in the beam spot, and measurement was performed by reproducing this pattern. The magnetic domain expansion reproduction for sample # 1 and comparative sample # 2 is performed by applying an external magnetic field of 200 Oe in the same direction as the magnetization direction of this recording magnetic domain while one recording magnetic domain passes through the inside of the beam spot. I went.

FIG. 3 is a graph showing the measurement results of the mark length dependence of the CNR (signal-to-noise ratio) of Sample # 1 and Comparative Samples # 1 and # 2. CN shown here
The mark length dependency of R represents a signal-to-noise ratio when a recorded magnetic domain having a length corresponding to the mark length is reproduced.
This recording magnetic domain is recorded as an isolated pattern as described above.

As shown in this figure, the mark length is 0.3 μm
The CNR of the sample # 1 was 31.0 dB, that of the sample # 1 was 41.0 dB, and that of the comparison sample # 2 was 33.0 dB.
Is 40.5 dB, and the CNRs of sample # 1, comparative sample # 2, and comparative sample # 1 are 7.0 dB.
A difference of B to 8.0 dB was observed.

In this measurement, since the recording magnetic domain is recorded as an isolated pattern, in the comparative sample # 1 subjected to normal reproduction (reproduction other than magnetic domain expansion reproduction), the recording magnetic domain of the recording layer has the same size as the reproduction layer. Transcribed. Therefore, the isolated reproducing magnetic domain of 0.3 μm formed in the reproducing layer was reproduced. On the other hand, in Sample # 1 and Comparative Sample # 2, the magnetic domain expansion reproduction was performed by appropriately applying an external magnetic field, and thus the reproduced magnetic domain subjected to the enlargement transfer was reproduced. It is thought that it became big.

From this figure, there is no significant difference in CNR between the sample # 1 subjected to the magnetic domain expansion reproduction and the comparison sample # 2. This is because the track pitch was not a small value of 0.7 μm as compared with the beam spot diameter of about 1 μm, so even if pinning of the domain wall in the reproducing magnetic domain occurred in Comparative Sample # 2, the effect was small. It is considered that the presence or absence of unevenness due to the land and groove did not affect the reproduction signal characteristics.

FIG. 4 shows that the track pitch of sample # 1 and comparative samples # 1 and # 2 is 0.5 μm to 0.2 μm.
In the range of 7 μm, the CN at the mark length of 0.3 μm
It is a graph which shows the result of having measured R. The track pitch of sample # 1 was narrowed by using the conventional technique disclosed in Japanese Patent Application Laid-Open No. 6-60408. The groove depth of the comparative samples # 1 and # 2 was 40 nm. Also,
The land and groove widths of the comparative samples # 1 and # 2 are the same as the track pitch.

As shown in FIG. 4, the comparative samples {1
The CNR of No. 2 decreases as the track pitch decreases. This is considered to be due to the generation of noise due to the miniaturization of the groove shape. In land and groove records,
As the track pitch decreases, the area of the adjacent track entering the beam spot increases. Therefore, since the distance to the optical pickup differs between the land and the groove, the optical pickup receives reflected light mixed with a lot of light having different phases. Thus, it is considered that the noise of the reproduction signal increased in these comparative samples # 1 and # 2.

The grooves and lands of the comparative samples # 1 and # 2 are not perfect rectangles, but the sidewalls have a distorted shape, and it is considered that noise due to this dulling has occurred. Also, when the track pitch becomes narrower, it is considered that the side wall of the groove approaches the center of the beam spot in these comparative samples # 1 and # 2, and this also causes noise.

In comparison sample # 1, comparison sample # 2 has a remarkable decrease in CNR due to the narrower track pitch. The reason is considered as follows. That is, in magnetic domain expansion reproduction, one of the recording layers
Each time one recording magnetic domain passes through the beam spot, the magnetic domain of the reproducing layer expands or contracts, that is, the domain wall of the reproducing magnetic domain moves. During this movement, if the domain wall is pinned due to the uneven shape of the land and the groove, the domain wall cannot cross the boundary between the land and the groove. Therefore, the movement of the domain wall of the reproducing magnetic domain in the reproducing layer in the radial direction of the disk is limited to the width of the land or groove in which the reproducing magnetic domain is formed. The area of the reproducing magnetic domain is also limited to this width. Therefore, the reproduced magnetic domain is not sufficiently enlarged, and the reproduced signal is significantly deteriorated.

The deterioration of the reproduction signal due to the restriction of the size of the reproduction magnetic domain by the land or groove width is a serious problem if the width is not so small as to the beam spot diameter. No. However, if the width is reduced in order to increase the density of the magneto-optical disk, the area of the reproducing magnetic domain with respect to the beam spot diameter becomes smaller, so that the characteristics of the reproducing signal are significantly deteriorated.

Therefore, when the track pitch is 0.5 μm, in the comparative sample # 2, since the reproducing magnetic domain is expanded in the circumferential direction of the disk, the CNR value is larger than that in the comparative sample # 1. However, it can be seen that the effect of domain expansion in Comparative Sample # 2 is insufficient compared to Sample # 1. In sample # 1, the value of CNR remains high even when the track pitch becomes small. This is because the sample servo tracking method is used for the tracking control, and the data area is a flat surface without unevenness, so that there is no problem in expanding the reproduction magnetic domain.

As described above, in sample # 1, since domain wall pinning does not occur during magnetic domain expansion reproduction, even when the track pitch becomes narrower, reproduction magnetic domains can be favorably expanded, and reproduction signal characteristics deteriorate. Nothing. Therefore, even when the track pitch is narrowed and the density in the disk radial direction is increased, it is possible to maintain good magnetic domain expansion reproduction.

The magneto-optical recording medium of the present invention is not limited to the configuration of the magneto-optical disk. Any film configuration may be used as long as magnetic domain expansion reproduction is possible. That is, a recording layer 7 composed of a perpendicular magnetization film for recording information as magnetic domains and a recording layer 7 for irradiating a light beam prior to the recording layer 7 for transferring the recorded magnetic domains in an enlarged or reduced manner are provided. It suffices to include two layers of the reproduced layer 5. In addition, a more preferable configuration is provided if an intermediate layer 6 is provided between the two layers 5 and 7 in order to break the exchange coupling between the recording layer 7 and the reproducing layer 5. Further, in order to prevent the magnetization in the recording layer 7 other than the magnetization of the recording magnetic domain 9 involved in the reproduction from being transferred to the reproduction layer 5, a gap between the reproduction layer 5 and the recording layer 7 is provided.
If a mask layer for applying a magnetic mask is provided, a more preferable configuration is obtained.

In the present magneto-optical disk, the reproducing layer 5 is an in-plane magnetic film at room temperature and is in a perpendicular magnetization state at high temperature. However, the magneto-optical recording medium of the present invention is not limited to this. Absent. As long as the portion irradiated with the beam spot is in a perpendicular magnetization state, the other portions may be in any state. However, if the low-temperature portion is in the in-plane magnetization state, this portion does not transfer the magnetization of the recording layer 7, and no magneto-optical signal is generated therefrom. Therefore, a reproduced signal with less noise can be obtained.

Although the pits 1... Are formed in the servo area of the magneto-optical disk, the configuration for detecting the tracking error signal in the magneto-optical recording medium of the present invention is not limited to this. Absent. In other words, this configuration may be any configuration as long as it has an uneven shape in the servo area, and may be, for example, a guide groove. This guide groove is not formed in the data area, but is formed only in the servo area. When the magneto-optical recording medium of the present invention has a shape in which a guide groove is formed in the servo area, the common part with the conventional magneto-optical recording medium employing the push-pull method is increased, so that the compatibility with this magneto-optical recording medium is increased. Can be enhanced.

The protective layer 1 of the present magneto-optical disk
3 and a protective film (not shown) will be described below. The protective layer 13 is provided in contact with the recording layer 7,
It is formed to a thickness on the order of nm by sputtering. The protective layer 13 is for preventing the recording layer 7 from being oxidized. On the other hand, the protective film (protective coat) is made of an organic resin, and has a thickness on the order of μm. This protective film is a film for protecting the entire magneto-optical disk from shock and moisture. Therefore, although the protective layer 13 and the protective film are formed continuously, the protective layer 13 is formed in the final step of sputtering, while the protective film is formed in the coating step. Process. Thus, the protective layer 13 and the protective film are completely different members.

The reproduction of the magneto-optical disk may be performed as follows. That is, as shown in FIG. 1, when the light beam is condensed by the objective lens 8 and the beam spot 4 irradiates the reproducing layer 5 of the present magneto-optical disk, a high-temperature portion HP is formed in the reproducing layer 5. Then, in the high-temperature portion HP, the reproducing layer 5 is in a perpendicular magnetization state, and one recording magnetic domain 9 is enlarged and transferred by magnetostatic coupling with the magnetization of the recording magnetic domain 9 in the recording layer 7, thereby forming the reproducing magnetic domain 10.
The formation of the reproducing magnetic domain 10 is performed by applying external magnetization to the high-temperature portion HP in the same direction as the magnetization of the recording magnetic domain 9. Then, after the reproduction magnetic domain 10 is reproduced,
Immediately, a magnetic field is applied to the high-temperature portion HP in a direction opposite to the recording magnetic field, and the reproduced reproduction magnetic domain 10 is erased. Thereafter, the high-temperature portion HP moves due to the rotation of the magneto-optical disk, and another recording magnetic domain 9 is similarly reproduced. in this way,
By inverting and applying an external magnetic field at a high speed, the transfer and erasure of the recording layer 7 to the recording magnetic domain 9 and the reproduction layer 5 can be performed.
It can be repeated at high speed.

The magneto-optical recording medium of the present invention may have the following configuration. That is, a servo area for detecting a tracking error signal in a magneto-optical recording medium having at least a reproducing layer in which a signal reproducing area is in a perpendicular magnetization state and a recording layer made of a perpendicular magnetic film which is magnetostatically coupled to the reproducing layer. And a data area for reading and writing data are completely separated in time and space, and at least the data area may be a flat surface without unevenness.

[0078]

As described above, in the magneto-optical recording medium according to the first aspect of the present invention, a servo area for detecting a tracking error, and information recording formed separately from the servo area. And a data area having a planar shape for performing the following.

As a result, since there is no unevenness in the data area which hinders the expansion of the magnetic domain, the expansion of the magnetic domain of the reproducing layer can be satisfactorily realized, and a good reproduction signal characteristic can be obtained even if the track pitch is narrowed. Becomes possible. As a result, compared to a magneto-optical recording medium in which unevenness such as grooves based on the push-pull method is formed in the data area, the recording density can be increased, and the reliability of reproduction can be increased. It works. In addition, since the data area has a planar shape without any irregularities, it is easy to manufacture the master disk of the magneto-optical recording medium and the magneto-optical recording medium, and also has an effect that high productivity can be realized.

Further, in the magneto-optical recording medium according to the second aspect, in addition to the configuration according to the first aspect, the reproducing layer has an in-plane magnetization state at room temperature and a perpendicular magnetization state at high temperature. .

Thus, in addition to the effect of the first aspect, since the portion in the in-plane magnetization state masks the recording layer, no magneto-optical signal is generated from the end of the beam spot.
This produces an effect that a reproduced signal with less noise can be obtained.

Further, in the magneto-optical recording medium according to the third aspect, in addition to the configuration of the first aspect, the servo area is provided with irregularities for performing tracking control by a sample servo tracking method. Configuration.

Thus, in addition to the effect of the first aspect, tracking control of the magneto-optical recording medium for performing magnetic domain expansion reproduction in which the servo area and the data area are separated can be favorably performed. It works.

The magneto-optical recording medium according to a fourth aspect of the present invention has a configuration in which the irregularities are formed of pits in addition to the configuration of the third aspect.

As a result, in addition to the effect of the third aspect, it is possible to efficiently perform tracking control with a small number of pits, and to manufacture the magneto-optical recording medium of the third aspect at low cost. It also has the effect of being able to do so.

The magneto-optical recording medium according to the fifth aspect has, in addition to the configuration of the third aspect, a configuration in which the irregularities are formed by lands and grooves formed based on a push-pull method.

Thus, a conventional magneto-optical recording medium can be applied as the magneto-optical recording medium according to the third aspect. Therefore, in addition to the effect of the third aspect, the magneto-optical recording medium according to the third aspect can be manufactured at low cost, and the tracking control is similar to that of the conventional magneto-optical recording medium. Therefore, an effect that compatibility with the magneto-optical recording medium can be improved can be obtained.

According to the reproducing method of the magneto-optical recording medium of the present invention, the recording layer having a magnetic domain for recording information is magnetostatically coupled with the recording layer at a predetermined temperature or higher. A reproducing layer for transferring magnetic domains of the recording layer, wherein the magnetic domains of the recording layer are enlarged and transferred to the reproducing layer to form magnetic domains larger than the magnetic domains of the recording layer on the reproducing layer. In this method, the magnetic domain is irradiated with a beam spot to read information, and at the same time, tracking control is performed by a sample servo tracking method.

As a result, it is possible to reproduce a magnetic domain formed in the reproducing layer while enlarging the magnetic domain to a desired size, to obtain a good reproduction signal, and to perform an excellent tracking control.

[Brief description of the drawings]

FIG. 1A is an explanatory diagram showing a schematic configuration of a magneto-optical recording medium according to an embodiment of the present invention and a state at the time of reproduction, and FIG. FIG. 3 is a cross-sectional view illustrating a layer configuration of a recording medium.

FIG. 2 is an explanatory view schematically showing a shape of a disk surface in the magneto-optical recording medium shown in FIGS. 1 (a) and 1 (b).

FIG. 3 is a graph showing the mark length dependence of the CNR of the sample of the magneto-optical recording medium shown in FIGS. 1A and 1B and the sample of the comparative example.

FIG. 4 is a graph showing the track pitch dependence of the CNR between the sample of the magneto-optical recording medium shown in FIGS. 1A and 1B and the sample of the comparative example.

FIG. 5 is an explanatory diagram showing an outline of a configuration of a conventional magneto-optical recording medium capable of magnetic domain expansion reproduction and a reproducing state of the magneto-optical recording medium.

FIG. 6 is an explanatory diagram showing a configuration of a conventional magneto-optical recording medium that is tracking-controlled by a push-pull method.

FIG. 7 is an explanatory diagram showing pinning of a domain wall that occurs when magnetic domain expansion reproduction is performed on the magneto-optical recording medium shown in FIG. 6;

[Explanation of symbols]

 Reference Signs List 1 pit 2 track 4 beam spot 5 reproducing layer 6 intermediate layer 7 recording layer 9 recording magnetic domain 10 reproducing magnetic domain 11 disk substrate 12 transparent dielectric layer 13 protective layer

Claims (6)

[Claims] 1. A recording layer having a magnetic domain for recording information, and a reproducing layer which is magnetostatically coupled to the recording layer when the temperature reaches a predetermined temperature or higher, and enlarges and transfers the magnetic domain of the recording layer. A magneto-optical recording medium, comprising: a servo area for detecting a tracking error; and a planar data area formed separately from the servo area for recording information. recoding media. 2. The magneto-optical recording medium according to claim 1, wherein the reproducing layer has an in-plane magnetization state at room temperature and a perpendicular magnetization state at high temperature. 3. A sample servo system according to claim 1, wherein:
2. The magneto-optical recording medium according to claim 1, wherein the recording medium has irregularities for performing tracking control by a tracking method. 4. The magneto-optical recording medium according to claim 3, wherein said irregularities are formed of pits. 5. The magneto-optical recording medium according to claim 3, wherein said irregularities are formed by guide grooves. 6. A magneto-optical recording device comprising: a recording layer having a magnetic domain for recording information; and a reproducing layer for transferring a magnetic domain of the recording layer by magnetostatic coupling with the recording layer when a predetermined temperature or more is reached. A method of reproducing a medium, wherein a magnetic domain of a recording layer is enlarged and transferred to a reproducing layer to form a magnetic domain larger than a magnetic domain of the recording layer on the reproducing layer, and the magnetic domain is irradiated with a beam spot to read information. A reproducing method for a magneto-optical recording medium, wherein tracking control is performed by a sample servo tracking method.