JPH10134428A - Magneto-optical recording medium, its reproducing method and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium with which reproducing beam intensity may be suppressed to a lower level, a C/N value is high, a recording speed is high and the sure reproduction of high-density recorded information is possible at the time of magnetic ultra-high resolution reproducing, its reproduction method as well as a process for producing the magnetooptical recording medium having sufficient recording durability. SOLUTION: This magneto-optical recording medium has the constitution that the recording medium has four layers of magnetic layers in order of at least a reproducing layer, reproducing intermediate layer, reproduction switching layer and memory layer and that the respective layers consist of magnetic materials mainly composed of rare earth metals and transition metals. The magneto-optical recording medium otherwise has the constitution that the recording medium has eight layers of the magnetic layers: a reproducing layer, reproducing intermediate layer, reproduction switching layer, memory layer, intermediate layer, recording layer, switching layer and initialization layer and that the respective layers consist of the magnetic materials mainly composed of the rare earth metals and transition metals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magneto-optical recording medium,
The present invention relates to a recycling method and a manufacturing method thereof.

[0002]

2. Description of the Related Art Information can be recorded at high density.
An optical recording medium capable of high-speed reproduction has attracted attention as a recording medium for audio and images, and further for a computer. Read-only CDs have become widespread for audio use, and in recent years have also rapidly spread for computer use. Also, a write-once type in which information can be recorded only once and a rewritable type (re-writable type) in which information once recorded can be rewritten many times have become widespread. In particular, one type of rewritable type magneto-optical recording medium is 100
It is possible to rewrite information more than ten thousand times, and it is widely used mainly as a computer recording medium. Recently, opportunities for recording or reproducing a large amount of information such as image information have been increasing. Under such circumstances, there is an increasing demand for recording more information on an optical recording medium or reproducing the information accurately. Various approaches have been taken to meet that demand.

First, in a disk, there is a method of reducing the track pitch in order to increase the recording density in the radial direction. For this purpose, it is necessary to reduce the recording mark width. Until now, the standard track pitch was 1.6 μm, but recently attempts have been made to reduce the track pitch, and 1.4 μm, 1.2 μm, and even 1.0 μm have been reported. Next, in order to increase the recording density in the circumferential direction, it is necessary to reduce the recording mark length. In order to reduce the width and length of the recording mark, the sensitivity of the recording medium is set so that the recording mark is formed only in the high energy area near the center of the recording beam. Can be formed. That is, when recording, if the composition of the magnetic layer is designed so that a recording mark is formed only in a high-temperature portion near the center of the recording beam, high-density recording can be performed.

However, the problem lies in reproduction. Reproduction is performed by optically detecting a mark in the beam spot. It is therefore necessary to always have basically only one mark in the beam. If a plurality of marks exist in the beam, the information will be mixed and the necessary information cannot be reproduced correctly. Such mixing of information in the beam spot is called optical crosstalk. That is, due to optical crosstalk, it is not possible to retrieve and reproduce only the information represented by the mark in a part of the beam spot.

[0005] For example, in the case of an infrared laser, the beam spot diameter can be narrowed to only about 1.0 µm by an ideal optical system. Therefore, in the radial direction, the track pitch is 1.4
If it is smaller than about μm, marks recorded on adjacent tracks will be reproduced simultaneously, and if the mark length or mark interval is considerably less than 1.0 μm, the preceding and succeeding marks will be reproduced simultaneously.

Therefore, it is conceivable to shorten the wavelength of the reproduction beam. It is known that how small a beam can be narrowed is proportional to the wavelength of the beam. By this means, the reproduction beam spot size is made smaller, thereby enabling the reproduction of information recorded at high density. If this is realized, the problem of optical crosstalk can be avoided. However, the wavelength of a semiconductor laser that can be used as a light source of an optical pickup has a limit in terms of its output and stability. For example, semiconductor lasers with a wavelength of 830 nm have been generally used in the past, but despite the fact that the wavelength was shortened by taking a considerable period of time, the wavelength of 680 nm only became mainstream recently. is there. That is, the reduction rate of the beam size due to the shortening of the wavelength is only 18%. Therefore, it is difficult to drastically reduce the beam spot size to 1/2 or 1/3 of the current size by this means.

However, there has been invented a recording / reproducing method and a medium capable of accurately reproducing information recorded at a considerably high density even if the size of the reproducing beam spot is the same as before. This is called super-resolution reproduction and medium. The basic idea of this method is as follows. Although the temperature of the recording medium rises due to the irradiation of the reproduction beam, since the medium is moving, the temperature on the rear side in the reproduction beam spot becomes relatively high due to the heat storage effect. If a part of the beam spot is masked using this characteristic of the temperature distribution and only the unmasked part is reproduced, only the information of a small part in the spot can be reproduced. That is, the reproducing beam spot size is substantially reduced. That is, information recorded at a considerably high density can be accurately reproduced. The principle of mask generation has been proposed based on magnetic super-resolution reproduction using a change in the magnetization direction due to a change in magnetic coupling force.In addition to this, a method based on a change in transmittance due to a phase change has also been announced. I have.

More specifically, (1) a FAD type in which a low-temperature portion in a reproduction beam spot, that is, an opening is provided in front of a traveling direction in a beam spot (a high-temperature portion becomes a mask) (Japanese Unexamined Patent Publication No. 93056) and (2) RAD type or CAD type in which the high temperature part, that is, the rear side in the beam spot becomes an opening (the low temperature part becomes a mask), and (3) Both the low temperature part and the high temperature part A double mask type, which becomes a mask and realizes a smaller opening, has been proposed.

Here, the principle of magnetic super-resolution reproduction utilizing a change in the magnetization direction due to a change in magnetic coupling force will be briefly described. First, the CAD type will be described with reference to FIG. FIG. 8B shows a cross section of a main portion of this type of magneto-optical recording medium and a temperature distribution of a portion irradiated with a reproducing beam. The magneto-optical recording medium has two magnetic layers, and information is recorded in the form of the perpendicular magnetization direction of the memory layer. A reproduction layer is provided on the memory layer. The magnetization of the reproducing layer is in-plane magnetization in a region below a predetermined temperature (low temperature region), but is the same as that of the memory layer in a region above the predetermined temperature (high temperature region) due to exchange coupling force with the magnetization of the memory layer. The direction becomes perpendicular magnetization. The predetermined temperature is:
The region which is perpendicularly magnetized by the reproduction beam irradiation is set to be a small region near the center of the temperature distribution. As a result, as shown in FIG. 8A, a mark is formed on the reproducing layer only in a high-temperature region of a part of the reproducing beam spot, and only that information is read. Then, even if the mark is within the reproduction beam spot, the mark that is out of the high temperature region is not read.

Next, the FAD type will be described with reference to FIG. FIG. 9B shows a cross section of a main portion of this type of magneto-optical recording medium and a temperature distribution of a portion irradiated with a reproducing beam. The magneto-optical recording medium has three magnetic layers, and information is recorded in the form of the perpendicular magnetization direction of the memory layer. On top of the memory layer is a playback switching layer (RS
Layer: so called to distinguish it from the overwriting switching layer), and a reproducing layer. The magnetization of the memory layer is transferred to the reproducing layer through the reproducing switching layer at a predetermined temperature or lower. However, above the Curie temperature of the reproducing switching layer, its magnetization disappears, so that the influence of the magnetization of the memory layer does not reach the reproducing layer. In this temperature region, the magnetization of the reproducing layer follows the reproducing magnetic field under the influence of the reproducing magnetic field. That is, since the magnetization of the reproducing layer is aligned with the direction of the reproducing magnetic field in the high-temperature region, the mark of the memory layer is not reproduced in this region, and the magnetization of the memory layer appears in the reproducing layer in the low-temperature region. Only the mark will be reproduced.

FIG. 10 shows a double mask type.
This will be described with reference to FIG. FIG. 10B shows a cross section of a main portion of this type of magneto-optical recording medium and a temperature distribution of a portion irradiated with the reproducing beam. The magneto-optical recording medium has three magnetic layers, and information is recorded in the form of the perpendicular magnetization direction of the memory layer. On top of the memory layer is a playback intermediate layer (RI
Layer: so called to distinguish it from the overwriting switching layer), and a reproducing layer. The magnetization of the reproduction switching layer is in-plane magnetization in a region below a predetermined temperature (low temperature region), but shows perpendicular magnetization in a region above a predetermined temperature (high temperature region). The magnetization disappears. Therefore, below the predetermined temperature, the magnetization of the memory layer does not reach the reproducing layer because the magnetization of the reproducing switching layer is in the in-plane direction. In this temperature range, the magnetization of the reproducing layer follows the reproducing magnetic field under the influence of the reproducing magnetic field. . In a temperature range from a predetermined temperature or higher to the Curie temperature of the reproducing switching layer, the magnetization of the memory layer is transferred to the reproducing layer through the reproducing switching layer by the exchange coupling force. When the temperature is higher than the Curie temperature of the reproducing switching layer, the magnetization of the memory layer does not reach the reproducing layer because the magnetization of the reproducing switching layer disappears. In this temperature region, the magnetization of the reproducing layer follows the reproducing magnetic field under the influence of the reproducing magnetic field. . That is, since the magnetization of the reproducing layer is aligned with the direction of the reproducing magnetic field in the low-temperature region and the high-temperature region, the mark of the memory layer is not reproduced in these regions, and the magnetization of the memory layer is transferred to the reproducing layer in the intermediate region. Therefore, only the marks that fall into this area are reproduced.

This type has an advantage that it can cope with the reproduction of information recorded at a higher density because the opening area can be made smaller than other types. In addition, with the fluctuation of the reproducing beam intensity, when the high temperature region increases, the low temperature region decreases, and when the high temperature region decreases, the low temperature region increases, so that the opening region does not change. Another advantage is that the reproduction signal characteristics are not easily affected by fluctuations in the reproduction beam intensity.

Conventionally, in order to rewrite information once recorded on a magneto-optical recording medium with new information, it is necessary in principle to erase the recorded information and then record the new information. Met. That is, it has not been possible to overwrite by directly rewriting to new information without erasing the information once recorded as in the case of rewriting information on a magnetic recording medium.

Therefore, the disadvantage is that the time required for rewriting information is lengthened by the amount required for erasing information, that is, the rewriting speed of information is slow. In order to overcome this disadvantage, a light modulation overwrite recording method capable of overwriting only by modulating the recording beam intensity, and an apparatus and a medium used therein have been invented. This invention has been filed for a patent in a number of countries, of which a patent has already been registered in the United States (JP-A-62-17594).
8 = DE3,619,618A1 = USP 5,239,524). Hereinafter, this invention will be referred to as "basic invention". Hereinafter, the present invention will be briefly described.

The overwritable magneto-optical recording medium used in this magneto-optical recording / reproducing method has a perpendicular magnetic anisotropy (perpendicular magnetic layer) as a layer for recording information.
orlayers). This magnetic layer is made of, for example, amorphous TbFe, TbFeCo, GdFe, GdFeCo, DyF
e, a heavy rare earth metal-transition metal amorphous alloy such as DyFeCo, etc., in which the magnetization of the heavy rare earth metal (RE sublattice magnetization) and the magnetization of the transition metal (TM sublattice magnetization) They are facing each other. The difference between these two sublattice magnetizations indicates the magnitude and direction of the magnetization as the magnetic layer.

As the magnetic layer, a layer (hereinafter, referred to as a memory layer or an M layer) basically serving as a recording and reproducing layer composed of a perpendicularly magnetizable magnetic thin film, and a recording auxiliary composed of a perpendicularly magnetizable magnetic thin film (Hereinafter referred to as a recording layer or a W layer), and both layers are exchange-coupled (exc
This is an overwritable multilayer magneto-optical recording medium capable of keeping only the magnetization of the W layer in a predetermined direction without changing the magnetization direction of the M layer at room temperature.

The W layer has a lower coercive force Hc and a higher Curie point Tc at room temperature than the M layer. Then, the information has a mark having a magnetization in the direction perpendicular to the substrate (referred to as “A direction”) in the M layer (and possibly also the W layer) and a magnetization in the opposite direction (referred to as “reverse A direction”). Record by mark. In this medium, the direction of magnetization of the W layer can be aligned in one direction by magnetic field means (for example, initialization magnetic field Hini.). In addition, at that time, the magnetization direction of the M layer does not reverse, and the magnetization direction of the W layer once aligned does not reverse even when subjected to the exchange coupling force from the M layer. The direction of magnetization of the M layer does not reverse even when subjected to exchange coupling force from the W layer aligned in one direction.

In the recording method according to the basic invention, the recording medium is arranged such that only the direction of magnetization of the W layer is aligned in one direction by a magnetic field means before recording. Then, the medium is irradiated with a beam pulse-modulated according to the binarized information. The beam intensity is controlled to two values, high level PH and low level PL,
This corresponds to the high and low levels of the pulse. This low level is higher than the reproduction level PR for irradiating the medium during reproduction. As is already known, it is common to turn on the laser at a "very low level" even when not recording, for example to access a predetermined recording location on the medium. This very low level also has a playback level PR
Is the same or similar level as.

At the temperature reached by the medium when the medium is irradiated with a low-level beam, the direction of magnetization of the W layer does not change, and the direction of magnetization of the M layer has a domain wall between the M layer and the W layer. Orientation of non-existent state. This is called a low-temperature process (L
The temperature range in which this process occurs is called a low-temperature process temperature (L process temperature) TL. on the other hand,
At a higher temperature reached by the medium when the medium is irradiated with a high-level beam, the direction of magnetization of the W layer follows the direction of the recording magnetic field, and the direction of magnetization of the M layer is between the M layer and the W layer. In which no domain wall exists. This is called a high temperature process (H process), and a temperature region in which this process occurs is called a high temperature process temperature (H process temperature) TH.

After the beam irradiation, the magnetization of the W layer imitated by the magnetic field means in the direction of the recording magnetic field by the high-level beam irradiation again imitates the direction of the magnetic field means. Therefore, if the direction of the magnetization of the magnetic field means and the direction of the recording magnetic field are reversed, new recording can be repeatedly recorded (that is, overwritten) on the already recorded M layer. This is the principle of light modulation overwrite magneto-optical recording.

In a slightly different expression, the contents described above form recording marks by high-level beam irradiation and erase recording marks by low-level beam irradiation, so that new information is overlaid on old information. It can also be said to write (overwrite). Thereafter, it has been proposed to provide an intermediate layer (I layer) between the M layer and the W layer for adjusting the exchange coupling force acting between them. Thereby, the overwrite operation can be realized more stably.
It has also been proposed to provide a reproducing layer (R layer) which is a magnetic layer having a larger magneto-optical effect on the beam irradiation side in contact with the M layer, and magnetically transfer information of the M layer to this layer for reproduction. . As a result, a better reproduction signal can be obtained.

Further, instead of the initialization magnetic field, an initialization layer (In
By providing a magnetic layer called an i.layer) and a magnetic layer called a switching layer (S layer) that controls the exchange coupling force between the Ini. layer and the W layer, the W layer can be initialized. Type (JP-A-63-268103 = USP 4,878,13
2) was invented and has already been put into practical use. By the way, a magneto-optical recording medium that can be overwritten and that can be reproduced with magnetic super-resolution has also been proposed (JP-A-6-13).
9639). This is because of the six magnetic layer configurations (R) of the recently commercialized overwritable magneto-optical recording medium described above.
Layer / M layer / I layer / W layer / S layer / Ini. Layer)
A reproduction switching layer (RS layer), which is a magnetic layer for controlling exchange coupling between the two layers, is provided between the layer and the M layer, and has a seven-layer magnetic layer configuration.

The overwrite recording operation of this medium is exactly the same as that of the previously commercialized overwritable magneto-optical recording medium having six magnetic layers which has been commercialized recently. That is, when a high-level beam is irradiated (ie, during the H process), a mark having a length corresponding to the irradiation time of the beam is formed on the recording layer (W layer). The marks formed on the recording layer are magnetically recorded on the memory layer (M layer), the reproduction switching layer (RS layer), and the reproduction layer (R layer) when the temperature of the medium decreases to the L process temperature after the beam irradiation. Transcribed. When the temperature of the medium further decreases, the magnetization of the recording layer also aligns in a predetermined direction by the action of the magnetization of the initialization layer which has been aligned in a predetermined direction in advance. That is, it is initialized.
When a low-level beam is irradiated (ie, during the L process), the magnetization is transferred to the memory layer, the reproduction switching layer, and the reproduction layer by the action of the magnetization of the recording layer aligned in a predetermined direction.

On the other hand, at the time of reproduction, the three layers of the reproduction layer, the reproduction switching layer, and the memory layer have the same function as that of the FAD type magnetic super-resolution reproduction described with reference to FIG. That is, by adding a reproduction switching layer which is a magnetic layer whose Curie temperature is lower than that of the memory layer to the six-layer overwrite magneto-optical recording medium, an overwrite magneto-optical recording medium capable of magnetic super-resolution reproduction can be obtained. Become.

[0025]

By the way, in magnetic super-resolution reproduction, in each of the RAD, CAD and FAD types, the aperture area (or mask area) changes due to the fluctuation of the irradiation beam intensity during reproduction. There is a problem that the reproduction signal characteristics fluctuate due to the fluctuation of the reproduction beam intensity.

In the double mask type, as described above, the reproduction signal characteristics are hardly affected by the fluctuation of the reproduction beam intensity. However, in this type, it is necessary to use a material having a high Curie temperature such as GdFe as the reproduction switching layer. In order to perform reproduction, it is necessary to raise the temperature above the Curie temperature of the reproduction switching layer, as described above, so that the reproduction beam intensity needs to be set high.
When the reproducing beam intensity is high, it is necessary to increase the recording beam intensity, which causes problems such as excessive modulation of a general semiconductor laser as a light source and an increase in power consumption of the recording / reproducing apparatus. is there.

Further, in the case of combining the optical super-resolution reproduction with the light modulation overwrite magneto-optical recording, there is the following problem. That is, in order to perform the light modulation overwriting, it is necessary to modulate the beam intensity into three levels of a high level PH and a low level PL, which are binary recording beam intensities at the time of recording, and a reproduction beam intensity Pr at the time of reproduction. . This means that the number of modulation levels of the beam intensity in the light modulation overwrite magneto-optical recording / reproduction is one more than the number of modulation levels of the beam intensity in the conventional non-overwrite magneto-optical recording / reproduction. On the other hand, the beam intensity that can be emitted from a general semiconductor laser as a light source naturally has an upper limit. For this reason, the intensity range (power margin) that can be set as each modulation level is narrower in the optical modulation overwrite magneto-optical recording / reproduction than in the conventional non-overwrite magneto-optical recording / reproduction. In other words, in the case of light modulation overwrite magneto-optical recording / reproducing, the intensity range that can be set as the reproducing level is narrower to the lower side as the low level exists between the high level and the reproducing level. However, in order to increase the C / N of the reproduction signal, the higher the reproduction beam intensity, the more advantageous. Therefore, the optical modulation overwrite magneto-optical reproduction is disadvantageous in this respect.

In magnetic super-resolution reproduction, as described above, the temperature distribution in the reproduction beam spot is used. Therefore, in principle, it is necessary to make the temperature distribution larger than a predetermined value. However, in light modulation overwrite magneto-optical recording / reproduction, the upper limit of the reproduction beam intensity must be kept low in principle due to the presence of a low level. Therefore, combining light modulation overwrite magneto-optical recording / reproduction with magnetic super-resolution reproduction Is difficult.

Further, a magneto-optical recording medium in which magnetic super-resolution reproduction is combined with light modulation overwriting has a problem that recording durability is not sufficient. The present invention solves the above-mentioned problems, and can reduce the intensity of the reproduction beam during magnetic super-resolution reproduction, and has a high C / N value, a high recording speed, and ensures the information recorded at high density. It is an object of the present invention to provide a magneto-optical recording medium capable of reproducing information at a high speed and a reproducing method therefor.
Another object of the present invention is to provide a method for manufacturing a magneto-optical recording medium having sufficient recording durability.

[0030]

In order to solve the above-mentioned problems, the present invention has at least four magnetic layers in the order of a reproduction layer, a reproduction intermediate layer, a reproduction switching layer, and a memory layer. A magneto-optical recording medium composed of a magnetic material mainly composed of a rare earth metal and a transition metal (FIG. 1).

Further, the magnetic recording medium has eight magnetic layers of a reproducing layer, a reproducing intermediate layer, a reproducing switching layer, a memory layer, an intermediate layer, a recording layer, a switching layer, and an initialization layer, each of which contains a rare earth metal and a transition metal. A magneto-optical recording medium composed of a main magnetic material (FIG. 2). It also has seven magnetic layers, a reproducing layer, a reproducing switching layer, a memory layer, an intermediate layer, a recording layer, a switching layer, and an initialization layer. Each of these layers is composed of a magnetic material mainly composed of a rare earth metal and a transition metal. In a magneto-optical recording medium capable of being overwritable and magnetically super-resolution capable of being exchange-coupled to each other, the memory layer has a laminated structure in which a region mainly composed of a rare earth metal and a region mainly composed of a transition metal are alternately repeated. And the reproducing layer has
A magneto-optical recording medium having an alloy structure in which a rare earth metal and a transition metal are mixed without bias is provided.

In producing the medium, a laminated structure is formed by simultaneously sputtering a target mainly composed of a rare earth metal and a target mainly composed of a transition metal, and by sputtering using an alloy target of a rare earth metal and a transition metal. The manufacturing method is to form an alloy structure. Further, when reproducing the medium, a reproducing method is used in which a reproducing level beam is irradiated and a reproducing magnetic field having a strength of 500 Oe or less is applied.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION The reproducing layer, the reproducing intermediate layer,
The principle of magnetic super-resolution reproduction in a magneto-optical recording medium having four magnetic layers in the order of a reproduction switching layer and a memory layer will be described with reference to FIGS. First, in a high-temperature region that occurs slightly behind the reproduction beam irradiation center position, the temperature becomes equal to or higher than the Curie temperature of the reproduction switching layer.
The magnetization of the reproduction switching layer disappears, and the exchange coupling force acting between the reproduction layer and the memory layer becomes zero or small. In any case, since the exchange coupling force acting between the reproducing layer and the memory layer is extremely small, the reversing magnetic field for reversing the magnetization of the reproducing layer can be reduced, and the function of the reproducing magnetic field larger than the reversing magnetic field can be reduced. Thereby, the magnetization of the reproducing layer is aligned in a predetermined direction. That is, a mask is formed in the high temperature region.

Further, in the low-temperature region in front of the reproduction beam irradiation center position and around the beam, since the magnetization of the reproduction intermediate layer is in the in-plane direction, the exchange coupling force acting between the reproduction layer and the memory layer becomes zero or small. Become. As a result, in these low temperature regions, the magnetization of the reproducing layer can be aligned in a predetermined direction by applying the reproducing magnetic field. At this time, the magnetization of the reproducing intermediate layer becomes in-plane magnetization (FIG. 3), or in a region where the magnetization of the memory layer is opposite to the reproducing magnetic field, the magnetization of the memory layer becomes the same direction as the reproducing magnetic field. In the region (2), the magnetization becomes perpendicular (the same direction as the reproducing magnetic field) (FIG. 4). That is, in any case, the mask is formed in the low temperature region.

Therefore, in the medium having this configuration, a mask is generated in a high-temperature region and at the same time a mask is generated around the beam. Due to the mask around the beam, information recorded on adjacent tracks is not reproduced at the same time. That is, since only the mark existing in the narrow area sandwiched between these two masks is reproduced, the crosstalk not only from the track direction but also from the adjacent track can be greatly reduced, which is more advantageous for narrowing the track pitch. In addition, the distance between marks can be further reduced, which is more advantageous for increasing the recording / reproducing density.

The thickness of the reproducing intermediate layer is preferably 2 to 60 nm,
~ 20 nm is more preferred. The thickness of the regeneration switching layer is 5
~ 50 nm is preferred. The material of the reproduction switching layer is preferably TbFeCo or TbFe containing 20% or less of Co in atomic%. The material of the reproducing intermediate layer is preferably GdFe or GdFeCo containing 20 to 40% of Gd by atomic%. The magnetization of the reproducing intermediate layer desirably exhibits in-plane magnetic anisotropy at a temperature lower than a predetermined temperature, and exhibits perpendicular magnetic anisotropy at a temperature higher than the predetermined temperature. The magnetization of the reproducing intermediate layer becomes an in-plane magnetization in a region lower than a predetermined temperature Tri, becomes a perpendicular magnetization in a region higher than the above Tri, and the Tri is a Curie temperature Tcr of the reproducing switching layer.
Desirably lower than s. More preferably, 40 <Tcrs-Tri <250.

In a magneto-optical recording medium having at least seven magnetic layers of a reproducing layer, a reproducing switching layer, a memory layer, an intermediate layer, a recording layer, a switching layer, and an initialization layer, the reproducing layer is composed of a rare earth metal and a transition metal. Preferably, the memory layer has a laminated structure in which regions mainly composed of rare earth metals and regions mainly composed of transition metals are alternately laminated. It is more effective if the recording layer has a laminated structure in addition to the memory layer. It is further desirable that the lamination cycle of the memory layer and the recording layer is a cycle in which the thickness of the region mainly composed of the rare earth metal is 2 to 10 degrees.

The relationship between the Curie temperature of the memory layer and the Curie temperature of the switching layer is as follows.
When m and Tcs are satisfied, it is desirable that Tcm−30 <Tcs <Tcm + 30 (unit: ° C.). Tcm-20 <Tcs <Tcm
+20 is more effective, and Tcm−10 <Tcs
<Tcm + 10 is even more effective. More preferably, a dielectric layer is formed on the initialization layer, and a metal layer is further formed thereon. The thickness of the metal layer is desirably 10 nm or more. The metal is preferably Al, and more preferably about 3% Ti is added.

When reproducing the medium, the medium is irradiated with a beam at the reproducing level and reproduced while applying a reproducing magnetic field having an absolute value of not more than 600 Oe. It may be constant.
In order to manufacture the above medium, it is desirable that the laminated structure is formed by binary simultaneous sputtering.

The present invention also includes a configuration in which no I layer is provided between the M layer and the W layer. Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

[0041]

Embodiment 1 A sputtering apparatus is prepared. 90mm in diameter
Is set on a substrate carrier of a sputtering apparatus. Guide grooves having a pitch of 1.1 μm are formed in a spiral shape on the surface of the substrate. Next, the substrate carrier on which the substrate is set is transported into the sputtering chamber of the sputtering device.

Next, the inside of the chamber is set to 5 × exp (−5) Pa
After evacuation to the following degree of vacuum, argon gas and nitrogen gas are introduced into the chamber, reactive sputtering is performed with a silicon target, and the silicon nitride layer is 70 nm thick.
Form a film. Next, while moving the substrate carrier to another sputtering chamber and introducing argon gas again,
Sputtering with GdFeCo alloy target,
A reproducing layer made of Gd25Fe60Co15 (atomic%, Gd25%, Fe60%, Co15%, the same applies hereinafter) has a thickness of 30 nm on the silicon nitride layer.
Form a film.

Next, sputtering is performed using a GdFeCo alloy target to form a 30-nm-thick reproducing intermediate layer of Gd29Fe67Co4 on the reproducing layer. The reproducing intermediate layer has a temperature of about 90 ° C. in the sacrificial temperature, an in-plane magnetization below it, and a perpendicular magnetization above it. In addition, in addition to the above-mentioned composition, a large number of samples in which the ratio of Gd is changed in the range of 15 to 45% and those in which the thickness is changed in the range of 0 to 100 nm are prepared. The Curie temperature changes as the composition fluctuates.

Next, sputtering is performed with a TbFeCo alloy target to form a reproduction switching layer of Tb20Fe76Co4 with a thickness of 20 nm on the reproduction intermediate layer. The Curie temperature of the regeneration switching layer is about 170 ° C. In addition, in addition to the above-mentioned composition, a large number of samples in which the ratio of Co is changed in the range of 0 to 30% and those in which the thickness is changed in the range of 0 to 80 nm are prepared. The Curie temperature changes as the composition fluctuates.

Next, sputtering is performed simultaneously with a target of Tb as a rare earth metal and an alloy target with Fe and Co as transition metals (referred to as binary simultaneous sputtering:
The substrate and the substrate carrier are simultaneously rotated while performing (FIG. 7), and a memory layer of Tb21Fe63Co16 having a structure in which a region mainly composed of Tb and a region mainly composed of FeCo are alternately laminated is formed to a thickness of 50 nm on the reproduction switching layer. I do.

Next, a silicon nitride layer having a thickness of 70 nm is formed on the initialization layer by the same procedure as that for forming the first silicon nitride layer.
Deposit a nm film. After forming a film by sputtering according to the above procedure, a resin protective film is further applied, and a magneto-optical disk having a magnetic layer configuration shown in FIG. 1 is prepared. The magneto-optical disk is initialized by adjusting the magnetization direction to a predetermined direction by an external magnetic field.

Next, a magneto-optical recording / reproducing apparatus is prepared. This device has an optical pickup having a recording magnetic field of 300 Oe and a semiconductor laser having a wavelength of 680 nm as a light source. Set the above magneto-optical disk in the magneto-optical recording / reproducing device,
Rotate at a linear speed of. The laser beam focused by the objective lens of the optical pickup is irradiated onto the disc surface while modulating the duty ratio to 50% between 9.0mW and 1.0mW, so that the mark length is 0.35μm and the distance between marks is 0.35μm. To record. Thereafter, reproduction is performed with a beam intensity of 3.0 mW while a magnetic field of 300 (Oe) is applied, and the C / N value is measured. It is confirmed that a sufficiently high C / N value is obtained and that magnetic super-resolution reproduction is performed favorably.

C / N is high when the thickness of the reproducing intermediate layer is 2 to 60 nm, and particularly higher when the thickness is 5 to 20 nm. Also,
When the thickness of the reproducing switching layer is 5 to 50 nm, the reproducing intermediate layer is GdFe or GdFeCo containing 20 to 40% of Gd by atomic%, and the reproducing switching layer contains 20% or less of Co by atomic% or C / N is also high in the case of TbFeCo or TbFe.

[0049]

Embodiment 2 A sputtering apparatus is prepared. 90mm in diameter
Is set on a substrate carrier of a sputtering apparatus. Guide grooves having a pitch of 1.1 μm are formed in a spiral shape on the surface of the substrate. Next, the substrate carrier on which the substrate is set is transported into the sputtering chamber of the sputtering device.

Next, the inside of the chamber is set to 5 × exp (−5) Pa
After evacuation to the following degree of vacuum, argon gas and nitrogen gas are introduced into the chamber, reactive sputtering is performed with a silicon target, and the silicon nitride layer is 70 nm thick.
Form a film. Next, while moving the substrate carrier to another sputtering chamber and introducing argon gas again,
Sputtering with GdFeCo alloy target,
A reproducing layer made of Gd22Fe52Co26 (atomic%, Gd22%, Fe52%, Co26%, the same applies hereinafter) has a thickness of 25 nm on the silicon nitride layer.
Form a film. The Curie temperature of this reproducing layer is 320 ° C.

Next, sputtering is performed using a TbFeCo alloy target, and a reproduction switching layer of Tb22Fe74Co4 is formed to a thickness of 10 nm on the reproduction layer. The Curie temperature of this regeneration switching layer is 140 ° C. Next, while simultaneously performing sputtering (binary simultaneous sputtering: see FIG. 7) with a target of Tb, which is a rare earth metal, and an alloy target of Fe and Co, which are transition metals, the substrate and the substrate carrier are rotated at the same time. A memory layer of Tb24Fe70Co6 having a structure in which regions and FeCo-based regions are alternately stacked is formed to a thickness of 25 nm on the reproduction switching layer. At this time, the number of rotations of the substrate carrier is changed, and samples having several kinds of different lamination periods are prepared. Incidentally, when the rotation speed of the substrate carrier is 50 rpm, the thickness of the region mainly composed of Tb is 4 °. The Curie temperature of this memory layer is 220 ° C.

Next, sputtering is performed with a GdFeCo alloy target to form an intermediate layer of Gd32Fe65Co3 on the memory layer to a thickness of 10 nm. Next, the substrate and the substrate carrier are simultaneously rotated while performing dual simultaneous sputtering with a target of Dy which is a rare earth metal and an alloy target of Fe and Co which are transition metals, so that a region mainly composed of Dy and a region mainly composed of FeCo are formed. Dy with a structure of alternately stacking
A recording layer of 24Fe49Co27 is formed on the intermediate layer to a thickness of 20 nm. Note that, at this time, the number of rotations of the substrate carrier is changed, and samples having several different lamination cycles are created. The Curie temperature of this recording layer is 300 ° C.

Next, sputtering is performed using a TbFeCo alloy target, and a switching layer of TbFeCo is formed to a thickness of 12 nm on the recording layer. At this time, TbFe of different composition
Table 3 shows the results of sputtering using a Co alloy target.
A plurality of samples having a switching layer having the composition shown in FIG. Depending on the composition, these switching layers have different Curie temperatures.

Next, the substrate and the substrate carrier are simultaneously rotated while performing simultaneous binary sputtering with a target of Tb which is a rare earth metal and a target of FeCo which is a transition metal, so that a region mainly composed of Tb and a region mainly composed of FeCo are formed. Initialization layer of Tb22Fe16Co62 having alternately laminated structure with thickness of 20
Deposit a nm film. The Curie temperature of this recording layer is 320 ° C.

Next, a silicon nitride layer having a thickness of 30 nm is formed on the initialization layer by the same procedure as that for forming the first silicon nitride layer.
Deposit a nm film. Finally, sputtering is performed using an Al target, and a metal layer of Al is formed on the silicon nitride layer. At this time, a plurality of samples having an Al layer having a thickness shown in Table 4 are prepared. After a film is formed by sputtering according to the above procedure, a resin protective film is further applied to form a magneto-optical disk having the configuration of the magnetic layer shown in FIG.

Next, a magneto-optical recording / reproducing apparatus is prepared. This device has an optical pickup having a recording magnetic field of 250 Oe and a semiconductor laser having a wavelength of 680 nm as a light source. Set the above magneto-optical disk in the magneto-optical recording / reproducing device,
Rotate at a linear speed of. The laser beam condensed by the objective lens of the optical pickup is adjusted to PH = 8.5 mW, PL =
Irradiation is performed on the disk surface while modulating with a first reference signal of 4.5 mW and a duty ratio of 50%, and recording is performed so that the mark length is 5 μm and the distance between marks is 5 μm.

Next, the frequency and the duty are changed to provide a second reference signal.
Overwrite recording is performed so that the distance between marks is 5 μm. Thereafter, reproduction is performed at a beam intensity of 1.5 mW, and the C / N value is measured. It can be determined from the C / N value whether or not the overwrite operation has been successfully performed. Next, the frequency and the duty are changed again to be the third reference signal, and the overwrite recording is performed again using this signal so that the mark length becomes 0.35 μm and the distance between marks becomes 0.35 μm. Then 50
Reproduction is performed with a beam intensity of 2.5 mW while a magnetic field of 0 (Oe) is applied, and the C / N value is measured. It can be determined from the C / N value whether super-resolution reproduction has been successfully performed.

Further, after the direction of the magnetic field was reversed (erasing direction), the disk was rotated 50,000 while irradiating the beam with a constant intensity of 12.0 mW (without modulation), and then the mark was marked by the third reference signal. Length 0.35μm, distance between marks 0.
Overwrite recording is performed again so that the thickness becomes 35 μm. Thereafter, reproduction is performed with a beam intensity of 2.5 mW while a magnetic field of 500 (Oe) is applied, and the C / N value is measured. The recording durability can be evaluated by the C / N value. Here, the reason for applying the magnetic field in the erasing direction is to prevent the magnetization reversal of the initialization layer.

Next, the above C / N value will be described. Table 1 shows the relationship between the lamination period of the memory layer and the C / N value. However, the composition of the switching layer is (Tb18Fe82) Co6,
The lamination cycle of the recording layer is 3 mm in the thickness of the region mainly composed of Dy.
The thickness of the Al layer is 30 nm. From Table 1, the lamination period is
Relatively high C / N when the thickness of the region mainly composed of Tb is about 4 to 8 mm
Value is obtained. However, when the lamination period is reduced to a thickness of 2 ° or less in the region mainly composed of Tb, the C / N value decreases. In this case, the C / N value in magnetic super-resolution reproduction in particular decreases remarkably. On the other hand, the thickness of the region mainly composed of Tb is
The C / N value similarly decreases even if the roughness is increased to a level exceeding 12 °. Then, when the lamination cycle becomes further coarse, overwriting is finally impossible.

Table 2 shows the relationship between the lamination period of the recording layer and the C / N value. However, the composition of the switching layer is (Tb18Fe82) Co
The stacking period of the memory layer is 4 ° in the thickness of the region mainly composed of Tb. The thickness of the Al layer is 30 nm. From Table 2, it can be seen that a relatively high C / N value can be obtained when the lamination period is about 4 to 8 ° in the thickness of the region mainly composed of Dy. However, the C / N value is low when the lamination period is out of the range of 2 to 10 ° in the thickness of the region mainly composed of Dy. In particular, when the lamination period is 14 ° or more in the thickness of the region mainly composed of Dy, overwriting becomes impossible.

Table 3 shows the relationship between the composition of the switching layer and the C / N value. Table 3 also shows how the Curie temperature changes with a change in the composition. However, the lamination period of the memory layer is 4 mm in the thickness of the region mainly composed of Tb, and the lamination period of the recording layer is 3 mm in the region mainly composed of Dy. The thickness of the Al layer is 30 nm. From Table 3, the Curie temperature Tcs of the switching layer is 220 ° C., which is the Curie temperature Tcm of the memory layer.
When the temperature falls below 30 ° C., the C / N value starts to decrease, and when the Curie temperature Tcs of the switching layer further decreases, overwriting becomes impossible. On the other hand, even when the Curie temperature Tcs of the switching layer is higher than 30 ° C. with respect to the Curie temperature Tcm of the memory layer of 220 ° C., the C / N value starts to decrease, and the Curie temperature Tcs of the switching layer further decreases. If it is higher than this, overwriting becomes impossible.

Next, Table 4 shows the relationship between the thickness of the Al layer and the C / N value. However, the composition of the switching layer is (Tb18Fe82) Co
6 The lamination period of the memory layer is 4 mm in the thickness of the region mainly composed of Tb, and the lamination period of the recording layer is 3 mm in the region mainly composed of Dy. As can be seen from Table 4, when the thickness of the Al layer is less than 10 nm, the C / N value decreases, and particularly, the C / N value at the time of reproducing a short recording mark by the third reference signal decreases significantly. When the thickness is 20 nm or more, a higher C / N value can be obtained.

Next, between the reproducing layer and the reproducing switching layer,
A sample (see FIG. 5) in which a reproduction intermediate layer of Gd26Fe72Co2 was formed to a thickness of 6 nm was prepared. Here, the composition of the switching layer is (Tb18Fe82) Co6. The lamination period of the memory layer is 4 ° in the thickness of the region mainly composed of Tb, and the lamination period of the recording layer is 4 ° in the thickness of the region mainly composed of Dy. The thickness of the Al layer is 30 nm.

The measurement of the C / N value is performed in exactly the same way as for the sample having no reproducing intermediate layer. Further, the magnitude of a magnetic field (reversal magnetic field) required to reverse the magnetization of the reproducing layer at room temperature is measured. Table 5 shows a comparison of the C / N value and the reversal magnetic field between the sample without the reproducing intermediate layer and the sample with the reproducing intermediate layer. Table 5 shows that there is no difference in the C / N value between the two, but the sample provided with the reproducing intermediate layer has a small reversal magnetic field.

The principle of magnetic super-resolution reproduction in a sample provided with a reproduction intermediate layer will be described in comparison with magnetic super-resolution reproduction in a sample without a reproduction intermediate layer. FIG. 6 shows a case where there is no reproduction intermediate layer, and FIG. 5 is an explanatory diagram of magnetic super-resolution reproduction when a reproduction intermediate layer is provided. First, when there is no reproducing intermediate layer, as shown in FIG. 6, the temperature of the reproducing switching layer becomes equal to or higher than the Curie temperature of the reproducing switching layer in a high temperature region generated slightly behind the center position of the reproducing beam irradiation. It disappears, and the exchange coupling force acting between the reproducing layer and the memory layer becomes zero or small. In any case,
When the exchange coupling force is extremely small, the reversal magnetic field for reversing the magnetization of the reproducing layer can be reduced, and in this state, the magnetization of the reproducing layer is aligned in a predetermined direction by the action of the reproducing magnetic field. That is, a mask is formed, and super-resolution reproduction is performed.

Here, when the reproducing intermediate layer is provided between the reproducing layer and the reproducing switching layer as shown in FIG. 5, the exchange coupling acting between the reproducing layer and the reproducing switching layer at a temperature as low as about room temperature can be achieved. Power can be reduced. As a result, even in a place other than the irradiation position of the reproduction beam, the magnetization of the reproduction layer can be aligned in a predetermined direction only by applying a reproduction magnetic field of about several hundred Oe. That is, in the medium having this configuration, a mask is generated in a high-temperature region and at the same time a mask is generated around the beam. By using the mask around the beam, information recorded on adjacent tracks is not reproduced at the same time, and crosstalk can be reduced. That is, it is more advantageous to narrow the track pitch. At the same time, since a mask is formed in the low-temperature portion in front of the reproduction beam, the distance between marks can be shortened, which is more advantageous for increasing the density of recording and reproduction.

A sample having the same structure as that of the sample except that the reproducing layer was formed by binary simultaneous sputtering without using an alloy target so that the lamination period was 4 ° in the thickness of the region mainly composed of Gd. When it is created and measured by the above procedure, overwriting is impossible regardless of the lamination cycle of the memory layer and the recording layer. It is considered that the magnetization of the overwritten recording layer is not transferred well to the memory layer, the first blocking layer, and the reproducing layer.

[0068]

According to the present invention, the reproducing beam intensity can be suppressed at the time of magnetic super-resolution reproduction, and the C / N value is high, the recording speed is high, and the information recorded at high density is reliably reproduced. It is possible to provide a magneto-optical recording medium and a reproducing method therefor. Further, it is possible to provide a method of manufacturing a magneto-optical recording medium capable of overwriting with light modulation having sufficient recording durability.

[0069]

[Table 1]

[0070]

[Table 2]

[0071]

[Table 3]

[0072]

[Table 4]

[0073]

[Table 5]

[Brief description of the drawings]

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

FIG. 2 is a vertical sectional view illustrating a configuration of a magneto-optical recording medium according to the present invention.

FIG. 3 is a vertical sectional view for explaining the principle of reproduction of the magneto-optical recording medium according to the present invention.

FIG. 4 is a vertical sectional view for explaining the principle of reproduction of the magneto-optical recording medium according to the present invention.

FIG. 5 is a vertical sectional view for explaining the principle of reproduction of the magneto-optical recording medium according to the present invention.

FIG. 6 is a vertical sectional view for explaining the principle of reproduction of the magneto-optical recording medium according to the present invention.

FIG. 7 is a conceptual diagram illustrating a binary simultaneous sputtering method.

FIG. 8 is a conceptual diagram illustrating the principle of reproduction of a magneto-optical recording medium capable of reproducing magnetic super-resolution of a CAD type.

FIG. 9 is a conceptual diagram illustrating the principle of reproduction of a magneto-optical recording medium capable of reproducing magnetic super-resolution of the FAD type.

FIG. 10 is a conceptual diagram illustrating the principle of reproduction of a magneto-optical recording medium capable of reproducing magnetic super-resolution of a double mask type.

Continued on the front page (72) Inventor Akio Omuro 3-2-2 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (72) Inventor Masahiro Furuta 3-2-2 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation Inside

Claims (23)

[Claims] 1. At least four magnetic layers in the order of a reproducing layer, a reproducing intermediate layer, a reproducing switching layer, and a memory layer, wherein each of the layers is made of a magnetic material mainly composed of a rare earth metal and a transition metal. Magneto-optical recording medium. 2. The magneto-optical recording medium according to claim 1, wherein the thickness of the reproducing intermediate layer is 2 to 60 nm. 3. The magneto-optical recording medium according to claim 1, wherein the reproduction switching layer has a thickness of 5 to 50 nm. 4. The magneto-optical recording medium according to claim 1, wherein the reproducing switching layer is made of TbFeCo or TbFe containing 20% or less of Co by atomic%. 5. The magneto-optical recording medium according to claim 1, wherein the reproducing intermediate layer is made of GdFe or GdFeCo containing 20 to 40% of Gd by atomic%. 6. The magneto-optical recording medium according to claim 1, wherein the magnetization of the reproducing intermediate layer exhibits in-plane magnetic anisotropy at a temperature lower than a predetermined temperature, and exhibits perpendicular magnetic anisotropy at a temperature higher than the predetermined temperature. Magneto-optical recording medium. 7. The magneto-optical recording medium according to claim 1, wherein the magnetization of the reproducing intermediate layer is in-plane magnetization in a region lower than a predetermined temperature Tri, is perpendicular magnetization in a region higher than the predetermined temperature Tri, and is equal to the tri-state magnetization. A magneto-optical recording medium characterized by having a temperature lower than the Curie temperature Tcrs of the reproducing switching layer. 8. The magneto-optical recording medium according to claim 7, wherein a relationship of 40 <Tcrs-Tri <250 is satisfied. 9. A magneto-optical recording medium having at least seven magnetic layers of a reproducing layer, a reproducing switching layer, a memory layer, an intermediate layer, a recording layer, a switching layer, and an initialization layer, wherein each of the layers is a rare earth metal and a transition metal. The playback layer has an alloy structure mainly composed of a rare earth metal and a transition metal, and the memory layer has a laminated structure in which a region mainly composed of a rare earth metal and a region mainly composed of a transition metal are alternately laminated. A magneto-optical recording medium characterized by the following. 10. At least eight magnetic layers of a reproducing layer, a reproducing intermediate layer, a reproducing switching layer, a memory layer, an intermediate layer, a recording layer, a switching layer, and an initialization layer, each of which is a rare earth metal and a transition metal A magneto-optical recording medium comprising a magnetic substance mainly composed of: 11. The magneto-optical recording medium according to claim 10, wherein the reproducing layer has an alloy structure mainly composed of a rare earth metal and a transition metal, and the memory layer has a region mainly composed of a rare earth metal and a region mainly composed of a transition metal. A magneto-optical recording medium having a laminated structure. 12. The magneto-optical recording medium according to claim 9, wherein the recording layer has a laminated structure in which a region mainly composed of a rare earth metal and a region mainly composed of a transition metal are alternately laminated. . 13. The magneto-optical recording medium according to claim 9, wherein the lamination period of the memory layer is a period in which the thickness of the region mainly composed of a rare earth metal is 2 to 10 degrees. Medium. 14. The magneto-optical recording medium according to claim 9, wherein the lamination cycle of the recording layer is such that the thickness of the region mainly composed of the rare earth metal is 2 to 10 degrees. 15. The magneto-optical recording medium according to claim 9, wherein when the Curie temperature of the memory layer and the Curie temperature of the switching layer are Tcm and Tcs, respectively, Tcm−30 <Tc
A magneto-optical recording medium satisfying s <Tcm + 30 (unit: ° C.). 16. The magneto-optical recording medium according to claim 9, wherein a dielectric layer is formed on the initialization layer, and a metal layer is further formed thereon. 17. The magneto-optical recording medium according to claim 16, wherein the thickness of the metal layer is 10 nm or more. 18. The magneto-optical recording medium according to claim 16, wherein the metal layer is made of Al. 19. The magneto-optical recording medium according to claim 18, wherein the metal layer is made of Al and Ti. 20. The reproducing method for reproducing a magneto-optical recording medium according to claim 1, 9 or 11, wherein the medium is irradiated with a reproducing level beam and a reproducing magnetic field having an absolute value of 600 Oe or less is applied. A reproduction method for a magneto-optical recording medium, wherein reproduction is performed while applying a voltage. 21. A reproducing method for reproducing a magneto-optical recording medium according to claim 20, wherein a linear velocity of the medium at a reproducing position is constant. 22. The method for manufacturing a magneto-optical recording medium according to claim 11, wherein the laminated structure of the memory layer is formed by forming a film by binary simultaneous sputtering. 23. The method for manufacturing a magneto-optical recording medium according to claim 12, wherein the laminated structure of the memory layer and the recording layer is 2
A method for manufacturing a magneto-optical recording medium, comprising forming a film by original simultaneous sputtering.