JP2000322783A - Magnetooptical recording medium, its recording and recording/reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medium which can reduce a diamagnetic field while holding strong magnetostatic bonding between a reproducing layer and a recording layer and enables recording in a low recording magnetic field, a recording method and a recording and reproducing device therefore. SOLUTION: A magnetooptical recording medium has at least the recording layer, a disconnecting layer 2 and the reproducing layer 1 on a substrate, magnetization directions corresponding to information are recorded on the recording layer and the magnetization directions of the recording layer is transferred to the reproducing layer 1 by a magnetostatic bonding force from the recording layer at a temperature above room temperature. In the magnetooptical recording medium, the recording layer is constituted of plural layers which are consisting of alloys of rare earth metals and transition metals and are exchanging-bonded to each other and further includes a layer 4 having rare earth metal dominant magnetization at least at room temperature and a layer 3 having transition metal dominant magnetization at the ambient temperature.

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 used for recording information, a recording method thereof, and a recording / reproducing apparatus.

[0002]

2. Description of the Related Art A magneto-optical recording medium has been put to practical use as a high-density, low-cost rewritable information recording medium. In particular, a medium using a recording layer made of an amorphous alloy of a rare earth element and a transition metal shows very excellent characteristics. Magneto-optical disks are extremely large-capacity recording media, but with the increase in the amount of information in society, further increase in capacity is desired. In general, the recording density of an optical disc is determined by the size of the spot of the reproduction light. Since the spot size can be reduced as the wavelength of the laser becomes shorter, studies on shortening the wavelength of the laser are underway. However, it is very difficult and the use of the short wavelength laser is a high cost factor. Becomes

On the other hand, so-called super-resolution techniques have been attempted in recent years to obtain a resolution higher than that determined by the wavelength of the laser by various means. One of them is a magnetically induced super resoluti
on, hereinafter referred to as MSR). This method basically includes a layer on which information is recorded (recording layer) and a layer for reproducing information (reproducing layer). Recording is performed on the recording layer.
During reproduction, the magnetization direction of the recording layer is transferred to the reproduction layer and read. According to this method, it is possible to reduce the interference of the waveform of the reproduced signal by utilizing the temperature distribution in the reproduction light spot and deforming the magnetic domain of the reproduction layer by the temperature distribution, thereby improving the quality of the high-density recording information. Can be played well.

[0004] There are various forms of the MSR system, and one of them is disclosed in Japanese Patent Laid-Open No. 7-1470.
No. 29, a method called “inversion type MSR” using a medium composed of three layers exchange-coupled to each other, a reproducing layer having a low coercive force, a cutting layer having a low Curie temperature, and a recording layer having a high Curie temperature and a large coercive force. is suggesting. In the inversion type MSR system, the reproducing layer and the recording layer are exchange-coupled through the cutting layer at a low temperature portion in the reproducing light spot. At this time, the direction of the sublattice magnetization of the reproducing layer matches the direction of the sublattice magnetization of the recording layer.

On the other hand, in a high temperature part, the exchange coupling between the reproducing layer and the recording layer is broken because the temperature of the cutting layer exceeds the Curie temperature. For this reason, the magnetostatic coupling is dominant in the relationship between the reproducing layer and the recording layer, and the magnetization direction of the reproducing layer matches the magnetization direction of the recording layer. Therefore, if both the reproducing layer and the recording layer are predominant in rare earth metal magnetization (RE rich) or both are transition metal magnetization predominant (TM rich), the magnetization directions of the reproducing layer and the recording layer are the same. However, when the reproducing layer is RE-rich and the recording layer is TM-rich, there is a difference between the case where the sublattice magnetization directions of the reproducing layer and the recording layer are matched and the case where the magnetization directions of the reproducing layer and the recording layer are matched. The magnetization state of the reproducing layer is reversed.

That is, when the medium is heated by irradiating the reproducing light, the magnetization of the reproducing layer first appears due to exchange coupling with the recording layer at a low temperature portion, and when further heated to a high temperature, the exchange coupling is broken and the magnetization of the reproducing layer is reversed. I do. In high-density perpendicular magnetic recording, the inverted magnetization functions to reinforce signals with adjacent marks that have not been inverted, so that high resolution can be realized. Further, in the inversion type MSR system, the signal intensity is maximized not at the center of the mark (magnetic domain) but at the end of the mark (boundary of the magnetic domain) as in the case of the magnetic disk. The end can be easily detected. For this reason, there is a cost advantage that the mark length modulation recording signal can be reproduced by using the signal detection system circuit of the inexpensive magnetic disk as it is.

On the other hand, as one of the MSR methods, a non-magnetic blocking layer is provided between a recording layer and a reproducing layer as disclosed in JP-A-8-221818, and the magnetization direction of the recording layer is reproduced only by the magnetostatic coupling force. A method called “magnetostatic coupling CAD” for transferring to a layer has also been proposed. In the magnetostatic coupling CAD method, the reproducing layer has in-plane magnetization at a low temperature, and becomes a perpendicular magnetization film as the temperature increases and the magnetization decreases. Therefore, the magnetization of the recording layer is transferred to the reproducing layer only at a high temperature, and the signal can be read. In this method, the transfer of the magnetization direction of the recording layer is not performed at a low temperature, so that signal interference (crosstalk) with an adjacent track outside the recording track is performed.
In that it can be reduced.

[0008]

SUMMARY OF THE INVENTION The above-mentioned inverted MSR
In the method of transferring the magnetization direction of the recording layer to the reproducing layer using the magnetostatic coupling force, such as the method or the magnetostatic coupling CAD method, in order to preferably perform reproduction, a source of the magnetostatic coupling force is used.
It is necessary to increase the leakage magnetic field applied from the recording layer to the reproduction layer. This can be achieved by increasing the magnetization of the recording layer and the reproducing layer. For example, in the case of a reversal type MSR in which the reproducing layer is RE-rich and the recording layer is TM-rich, the recording layer is set such that the composition ratio of the rare earth and the transition metal is larger than the compensating composition in which the magnetizations of both cancel each other (TM rich). )
You can do it on the side. However, when a composition suitable for such reproduction is used, a problem occurs at the time of recording information.

In a region where the magnetization of the recording layer is uniform in a uniform direction, the magnetic flux from the surface layer magnet of the recording layer acts as a demagnetizing field inside the recording layer, that is, a force for forming reversal magnetization. For this reason, unintended magnetization reversal occurs even when no external magnetic field is applied or against the external magnetic field. As the larger magnetization is applied to the recording layer, the demagnetizing field increases at the same time, so that such magnetization reversal is more likely to occur, and a larger recording / erasing magnetic field is required at the time of recording / erasing. Incidentally, magneto-optical recording includes a light modulation recording method and a magnetic field modulation recording method. The former performs recording by changing the intensity of light to be irradiated, and the latter performs recording by changing (inverting) the recording magnetic field while keeping the light intensity constant.

[0010] The above-described magnetization reversal due to the demagnetizing field is extremely inconvenient, especially for magnetic field modulation recording. This is because the recording magnetic field must be larger than the demagnetizing field in order to perform the recording accurately, but if the recording magnetic field is increased, it is difficult to change the recording magnetic field at a high speed, which makes high-speed recording difficult. Therefore, when high-speed recording is performed, the magnetic field intensity must be weak. At this time, the influence of the magnetization reversal due to the demagnetizing field becomes a problem. In light modulation recording, a demagnetizing field is convenient when forming a recording magnetic domain in an erased area,
Too large a demagnetizing field still poses a problem for uniform erasure.

In order to reduce the demagnetizing field, the magnetization of the recording layer may be reduced, and it is said that a conventional medium has a composition near the compensation composition. However, this also reduces the leakage magnetic field during reproduction, which adversely affects the reproduction characteristics due to the principle of super-resolution using magnetostatic coupling. Specifically, the transfer of the magnetization direction to the reproducing layer tends to be insufficient. That is, conventionally, it has been difficult for an MSR using magnetostatic coupling to achieve both characteristics suitable for magnetic field modulation recording and transferability to a reproduction layer.

[0012]

Means for Solving the Problems The present inventors have studied and found that
By making the recording layer a multi-layer configuration with different characteristics,
The present inventors have found that both recording under a low recording magnetic field and good transferability to the reproducing layer can be achieved, and the present invention has been accomplished. That is, the gist of the present invention is that the recording layer has at least a recording layer, a cutting layer, and a reproducing layer, a magnetization direction corresponding to information is recorded on the recording layer, and magnetostatic coupling from the recording layer at a temperature equal to or higher than room temperature. A magneto-optical recording medium in which a magnetization direction of a recording layer is transferred to a reproducing layer by a force, wherein the recording layer is composed of a plurality of layers made of an alloy of a rare earth metal and a transition metal and exchange-coupled to each other,
The present invention also provides a magneto-optical recording medium characterized by including at least a layer having rare earth metal dominant magnetization at room temperature and a layer having transition metal dominant magnetization at room temperature.

Another aspect of the present invention resides in a recording method for a magneto-optical recording medium, characterized by using such a magneto-optical recording medium and recording information on the magneto-optical recording medium by a magnetic field modulation recording method. Still another aspect of the present invention resides in a recording / reproducing apparatus comprising such a magneto-optical recording medium and a floating or contact magnetic head.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The magneto-optical recording medium of the present invention has a recording layer on which a magnetization direction corresponding to information is recorded on a substrate, a cutting layer, and a magnetization direction of the recording layer by a magnetostatic coupling force from the recording layer at a temperature equal to or higher than room temperature. Has a reproducing layer to be transferred, and the recording layer is a plurality of layers of two or more layers. It is to be noted that the number of recording layers may be three or more as necessary.

Next, the present invention will be described with reference to the drawings. FIG. 2 shows an example of a layer configuration of a conventional magneto-optical recording medium. It comprises a reproducing layer 1, a cutting layer 2, and a recording layer 13, and a magnetostatic coupling force 5 and a demagnetizing field 16 of the recording layer act between the layers. As described above, when the magnetization of the recording layer is increased, the demagnetizing field 16 is increased, and the recording magnetic field required for recording / erasing is also increased. Conversely, when the magnetization of the recording layer is reduced, the magnetostatic coupling force 5 is reduced, which has an adverse effect on reproduction. This is because the magnetostatic coupling force 5 and the demagnetizing field 16
Is also generated from the surface magnetons of the recording layer.

Considering the difference between the demagnetizing field 16 and the magnetostatic coupling force 5 shown in FIG. 2, the demagnetizing field 16 is a force that a part of the recording layer 13 receives from the surrounding recording layer itself. 5 is a force between the recording layer 13 and the reproducing layer 1. Magnets are generated on both surfaces of the recording layer (and also between the recording layers in the case of a multilayer recording layer), but the demagnetizing field 16 of the recording layer itself is affected by magnetic fields from all the magnetons.

FIG. 1 shows an example of the layer structure of the magneto-optical recording medium of the present invention. It comprises a reproducing layer 1, a cutting layer 2, a first recording layer 3, and a second recording layer 4, with a magnetostatic coupling force 5,
The demagnetizing field 6 of the first recording layer and the demagnetizing field 7 of the second recording layer operate. A layer closer to the reproduction layer is called a first recording layer, and a layer farther from the reproduction layer is called a second recording layer. When the recording layer is divided into two layers as shown in FIG. 1 and the first recording layer 3 is dominated by transition metal magnetization and the second recording layer 4 is dominated by rare earth metal magnetization and exchange-coupled to each other, the demagnetizing field 6 , 7 cancel each other out and can be reduced as a sum. Most of the demagnetizing field is generated from the room temperature around the recording part (heating part).
It is necessary to reduce the magnetization at room temperature. Therefore, at room temperature, the first recording layer 3 needs to have transition metal magnetization dominance, and the second recording layer 4 needs to have rare earth metal magnetization dominance. Note that room temperature is typically about 25 ° C.

On the other hand, since the magnetostatic coupling force 5 is a coupling between the recording layer and the reproducing layer 1 outside the recording layer, it is affected by the magnetic field from the first recording layer 3 near the reproducing layer 1 (that is, the reproducing layer of the recording layer). Magnetic flux from the magnet on the side surface) is much stronger than the influence from the second recording layer 4 located far away. This can be well understood by considering that the strength of the magnetic field is inversely proportional to the square of the distance. Therefore, by using the lamination of the first recording layer 3 with the transition metal magnetization dominant and the second recording layer 4 with the rare earth metal magnetization dominant, it is possible to suppress the total sum of the recording layer magnetization while maintaining a strong magnetostatic coupling force. In addition, the demagnetizing field (sum of the demagnetizing fields 6, 7) can be reduced.

In an alloy of a rare earth metal and a transition metal,
In general, when the temperature is increased, the rare earth metal magnetization decreases quickly, and the rare earth metal magnetization is changed to the transition metal magnetization dominant. The temperature at which the magnetization of the rare earth metal and the transition metal perfectly balance is called the compensation temperature. At lower temperatures, the rare earth metal magnetization becomes dominant, and at higher temperatures, the transition metal magnetization becomes dominant. Therefore, when reproduction is performed while raising the temperature of the medium, the transition layer magnetization becomes stronger in the entire recording layer, so that a stronger magnetostatic coupling force than at room temperature can be obtained.

There are two methods for recording on such a medium: an optical modulation method in which recording information is carried on an optical pulse, and a magnetic field modulation method in which recording information is carried in the direction of a magnetic field.
When the present invention is used for magnetic field modulation recording in that the recording magnetic field can be reduced, high-speed recording is easily performed, and the effect is particularly large. When a magnetic field of rare earth metal dominant magnetization is generated from the recording layer to make magnetostatic coupling with the reproducing layer, the first recording layer should have rare earth metal magnetization dominance and the second recording layer should have transition metal magnetization dominance. Is also possible. At this time, since the magnetization of the first recording layer decreases as the temperature rises, it is effective to use the MSR method in which the magnetostatic coupling force is desired to be reduced at a high temperature.

Hereinafter, the characteristics of each layer will be described in more detail by taking the inversion type MSR system and the magnetostatic coupling CAD system as examples. However, the present invention is applicable to all types of recording systems using magnetostatic coupling, and the present invention is not limited to these examples. Inversion type MSR method and magnetostatic coupling CA
In the D system, the reproducing layer preferably has a composition in which rare earth metal magnetization is dominant. In the reversal type MSR, this is an essential condition for reversing the directions of the exchange coupling force and the magnetostatic coupling force. Further, in the magnetostatic coupling CAD system, it is an essential condition that the film is an in-plane magnetic film at a low temperature and changes to a perpendicular magnetic film due to a decrease in magnetization at a high temperature.

Materials used for such a reproducing layer include GdFeCo, GdCo, GdFe, and GdDyF.
e, GdDyCo, GdDyFeCo, GdTbFe,
GdTbCo, GdTbFeCo, DyFeCo, Dy
Co, TbCo, TbFeCo, TbDyFeCo, T
An alloy of a rare earth metal such as bDyCo and a transition metal is used. Among them, it is preferable to use an alloy containing Gd from the viewpoint of the Curie temperature and the coercive force. Particularly preferred is Gd
FeCo and GdFe. Curie temperature is 2
It is preferably at least 50 ° C. A magnetic material such as PtCo or a superlattice of Pt and Co can be laminated on the reproducing layer. These have large Kerr rotation angles at short wavelengths,
It can be applied to a high density recording medium using a blue laser or the like.

In order to increase the perpendicular magnetic anisotropy of the reproducing layer, it is preferable to apply a certain film stress to the magnetic layer to generate the anisotropy by the inverse magnetostriction effect. Is preferable because the magnetization easily stands perpendicularly. Preferably 100 nm or less, more preferably 70 nm or less,
Particularly preferably, it is 60 nm or less. However, if it is too thin, the leakage magnetic flux becomes small and the magnetostatic coupling force decreases, so it is preferably at least 10 nm, more preferably at least 15 nm, particularly preferably at least 20 nm.

A cutting layer for cutting exchange coupling is provided between the reproducing layer and the recording layer. In the inversion type MSR system, the cutting layer is a layer having a lower Curie temperature than the recording layer and the reproducing layer, and blocks exchange coupling at a high temperature exceeding the Curie temperature. In the magnetostatic coupling CAD method, a non-magnetic film is mainly used so as to block exchange coupling in all temperature regions. In the inversion type MSR method, a cutting layer having a lower Curie temperature than the reproducing layer and the recording layer is used. The Curie temperature Tc2 of the cutting layer is preferably about 90 to 180 ° C. T
If c2 is too low, the signal from the exchange-coupled area (low-temperature area in the reproduction light spot) will be small, while if c2 is too high, high reproduction power and high recording power will be required.

The inversion type MSR type cutting layer preferably has a high perpendicular magnetic anisotropy and generates a strong force in the magnetization of the reproducing layer. Materials used for the cutting layer include TbFe,
TbFeCo, DyFeCo, DyFe, TbDyFe
An alloy of a rare earth such as Co and a transition metal is preferable. The film thickness is 2
It is preferably not less than nm and not more than 30 nm. If it is too thin, the interruption of exchange coupling is insufficient, and if it is too thick, the magnetic flux of the magnetostatic coupling does not reach.

In the magnetostatic coupling CAD system, a metal, a dielectric or the like is used for the cutting layer. For example, Al, Ta, Cr,
Ti, W, Si, Pt, Cu, Si ₃ N ₄ , AlN, T
iN, carbon, hydrogenated carbon and the like. However, those having high magnetic permeability, such as Fe and Ni, are not preferable because they do not transmit the magnetic flux to the reproducing layer and reduce the magnetostatic coupling. The thickness is preferably 2 nm or more and 30 nm or less. If it is too thin, the interruption of exchange coupling is insufficient, and if it is too thick, the magnetic flux of the magnetostatic coupling does not reach.

In the present invention, the recording layer is composed of two or more layers, and has both a layer in which transition metal magnetization is dominant and a layer in which rare earth metal magnetization is dominant. At room temperature, the magnetizations of the recording layers cancel each other out, and the magnetization of the entire recording layer becomes 1 with no domain wall between the layers.
It is preferably not more than 00 emu / cc. More preferably, it is 80 emu / cc or less. In the inversion type MSR method, since it is desired to couple the transition metal dominant magnetization to the reproducing layer having rare earth metal dominant magnetization, the first recording layer closest to the reproducing layer has transition metal dominant at room temperature. preferable.

In the magnetostatically coupled CAD system, either rare-earth metal magnetization or transition metal magnetization may be predominant at room temperature. However, in the case of rare-earth metal magnetization predominant at room temperature, there is a problem that magnetization is reduced at high temperature during reproduction. It is preferred that the transition metal magnetization is dominant. The number of recording layers in the recording layer may be three or more if the rare earth metal magnetization predominant layer and the transition metal magnetization predominant layer are included, but two layers are preferable from the viewpoint of simplicity in production. .

Since the recording layers are layers in which recording is stably stored, it is necessary that each recording layer has a Curie temperature that is not deteriorated by heating by reproducing light. When the two recording layers are a combination of a layer having a low coercive force (for example, GdFeCo) and a layer having a high coercive force (for example, TbFeCo), if recording is performed on the high coercive force layer, the information is transferred to the low coercive force layer by exchange coupling force. Therefore, the recording sensitivity is determined by the high coercivity layer.

Therefore, if the Curie temperature of the high coercive force layer is too high, the laser power required for recording becomes too large, and therefore the Curie temperature of the high coercive force layer is preferably low. It is also necessary that the recording layer has high perpendicular magnetic anisotropy in order to give a strong force to the magnetization of the reproducing layer.
It is necessary that at least one of the two recording layers has a high coercive force and that recording can be stably stored. This high coercivity recording layer is made of TbFeCo, TbCo, DyF
eCo, TbDyFeCo, GdTbFe, GdTbF
eCo and the like are preferably used. Among them, TbFeCo is particularly preferable because of its high perpendicular magnetic anisotropy and large coercive force. The layers other than the high coercive force layer may have a small coercive force alone as long as they are exchange-coupled to the high coercive force layer. For example, GdFe, GdFeCo, GdCo, etc. The thickness of each recording layer is 20 nm or more, preferably 100 nm or less, more preferably 25 nm or more, and 70 nm or less. If the recording layer is too thin, a sufficient static magnetic field cannot be generated. On the other hand, if the thickness is too large, the sensitivity and productivity deteriorate.

The recording layer formed by combining the low coercive force layer having a high Curie temperature with the first recording layer and the high coercive force layer having a lower Curie temperature as the second recording layer has the Curie temperature of the second recording layer during reproduction. This is a particularly preferable mode because even when the temperature rises to the vicinity, strong magnetostatic coupling can be obtained without lowering the magnetization of the first recording layer. In this case, specifically, GdFeCo is used as the first recording layer, and TbF is used as the second recording layer.
eCo is preferably used. If the high coercivity layer has transition metal magnetization dominance, the coercive force may decrease during reproduction and recording may be easily lost. Therefore, the high coercivity layer preferably has rare earth metal magnetization dominance.

If the magnetization of each recording layer is too large, the readout signal characteristics are reduced due to a decrease in perpendicular magnetic anisotropy. Therefore, it is not preferable to use a composition that is extremely far from the compensation composition for the recording layer. Therefore, it is preferable that the transition metal magnetization dominant layer in the recording layer contains 18% or more of the rare earth metal. More preferably, it is at least 19%. It is particularly preferably at least 20%. The upper limit of the rare earth metal composition is the compensation composition. The rare earth metal magnetization dominant layer contains three rare earth metals.
It is preferable to contain 2% or less. More preferably, 3
It is at most 1%, particularly preferably at least 26% and at most 30%. The lower limit of the rare earth metal composition is the compensation composition. still,
In this specification, the composition is expressed by atomic percent.

When an alloy of a rare earth metal and a transition metal is used for the above magnetic layer, it is very easily oxidized. Therefore, it is preferable to adopt a mode in which protective layers are provided on both sides of the magnetic layer. As the protective layer, Si oxide, Al oxide, Ta oxide, T oxide
A simple substance such as i, Si nitride, Al nitride, Si carbide or a mixture thereof is preferably used. The thickness of the protective layer is preferably about 50 nm to 150 nm. After forming the protective layer on the substrate side, the magnetic anisotropy of the magnetic layer can be improved by plasma etching the surface.

The provision of a high thermal conductive material made of Al, Cu, Au, Ag, or the like or an alloy mainly composed of Al, Cu, Au, or the like as a heat dissipation layer directly or through a protective layer on the recording layer side of the magnetic layer is not suitable for reproduction. This is a desirable configuration for stabilizing the heat distribution at the time. The thickness of the heat radiation layer is 10 nm to 100
About nm is preferable. In order to more reliably generate the magnetostatic coupling force, a layer having a higher magnetic permeability than the recording layer, for example, Fe, Ni, Co, FeNi,
AlSiFe, etc., directly or through a non-magnetic layer
It may be provided about 50 nm. Due to the effect of these layers, the leakage magnetic flux of the recording layer is more efficiently generated and coupled to the reproducing layer. If the recording layer is in direct contact with the recording layer, the perpendicular magnetic anisotropy of the recording layer is reduced.

Since the present invention is a method for increasing the magnetostatic coupling force without deteriorating the recording magnetic field dependence, other than a medium in which the magnetization direction of the recording layer is transferred to the reproducing layer only by the magnetostatic coupling force, It is also possible to use a medium in which the magnetostatic coupling force assists the exchange coupling force, for example, a RAD medium or a double mask RAD medium.

A recording / reproducing apparatus using the above-described magneto-optical recording medium will be described. As a recording and playback device,
Conventionally used, an optical head is provided on the opposite side of the recording surface of the optical disk substrate, and the so-called substrate surface incidence method is used in which the reproducing light or the recording light emitted from the optical head reaches the recording surface through the substrate. There is a film surface incidence method in which an optical head is provided on the recording surface side, which has been recently proposed. The latter allows the head to be close to the recording surface, and is preferable for high-density recording and high-speed reproduction.

In the substrate surface incidence method, an optical head is provided with an objective lens controlled in the optical axis direction by an actuator in order to focus light on a recording surface. Is usually provided with an interval of about 1 mm. In the case of magnetic field modulation recording, a floating magnetic head or a contact magnetic head is usually provided on the recording surface side. In the film surface incidence method, one or two or more optical disks fixed coaxially are built in, and a floating type or contact type optical head is provided to face each recording surface, and the recording surface side without passing through the substrate. Irradiates light from A floating magnetic head or a contact magnetic head used for magnetic field modulation recording is also provided on the recording surface side.

In the conventional substrate surface incidence method, the numerical aperture of the objective lens could not be increased because the aberration of the light spot was increased due to the inclination of the substrate and the variation in the thickness of the substrate. By doing so, it is possible to increase the numerical aperture of the objective lens and reduce the light spot, thereby increasing the capacity of the optical disk and enabling high-speed access like a hard disk. Further, in the film surface incidence method, a magneto-optical recording / magnetic reproducing method has been proposed in which recording is performed while heating with a laser beam during recording, and reading is performed only with a magnetic head without using light during reproduction. According to these recording / reproducing apparatuses using the magneto-optical recording medium of the present invention, high-density recording and high-speed recording / reproducing can be performed.

[0039]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention.

Example 1 A polycarbonate substrate having a guide groove with a track pitch of 0.85 μm was introduced into a sputtering apparatus to produce an inverted type MSR medium, and evacuated to a degree of vacuum of 5 × 10 ⁻⁵ Pa or less. . Thereafter, 80 nm of Ta oxide was formed on the substrate as a protective layer by using reactive sputtering. Next, a 30 nm reproducing layer made of Gd ₃₅ (Fe ₈₀ Co ₂₀ ) ₆₅ , a 10 nm cut layer made of Tb ₂₀ (Fe ₉₅ Co ₅ ) ₈₀ , and Gd ₂₂ (Fe ₈₀ Co ₂₀ ) ₇₈ are formed on Ta oxide. 30 nm first recording layer, Tb ₂₆ (Fe ₈₀ Co ₂₀ ) ₇₄
A second recording layer of 80 nm was formed. Finally, SiN
A protective layer having a thickness of 50 nm was provided.

When the Curie temperatures of the reproducing layer, the cutting layer, the first recording layer, and the second recording layer were measured, each of them was 300 ° C. or more.
The temperature was 150 ° C, 300 ° C or more, and 270 ° C. At room temperature, the magnetization of the rare earth metal was dominant in the reproducing layer. The cut layer was dominated by the transition metal magnetization at room temperature. First
The recording layer had a transition metal dominance at room temperature, and the coercive force was almost zero. The second recording layer had a predominance of rare earth metal magnetization at room temperature and a coercive force of 8 kOe. The magnetization of the entire recording layer was 50 emu / cc at room temperature due to the predominance of rare earth metal magnetization.

First, light modulation recording was performed on the disk thus manufactured. The CN ratio was evaluated using an evaluator having a wavelength of 680 nm and a numerical aperture of 0.55. The recording conditions were a linear velocity of 8 m / s, a frequency of 10.53 MHz (mark length 0.38
μm) to perform recording. 8 before recording
Erasing was performed by applying a magnetic field of 300 Oe in the erasing direction with an erasing power of mW. When the reproduction power Pr was 1.5 mW, normal reproduction (non-super-resolution reproduction) was performed, and the CN ratio was 28 dB. At a Pr of 2.6 mW or more, the effect of super-resolution appeared.
Assuming that Pr is 3.0 mW, the CN ratio becomes maximum and is 49.5.
dB was obtained.

While changing the recording magnetic field (Hw) strength, C
FIG. 3 shows the result of measuring the change in NR. The recording power was set so as to obtain the maximum CN ratio. + Is the direction of the erasing magnetic field, and-is the direction of the recording magnetic field. In order to be used for magnetic field modulation recording, the magnetization must be accurately directed in the direction of the recording magnetic field. Therefore, the CN ratio is saturated at a low recording direction magnetic field, and the CN ratio is completely reduced at a low erasing direction magnetic field (that is, no recording is performed). )It is necessary. Assuming that the magnetic field intensity at which the CN ratio is within 1 dB from the maximum value in the recording direction magnetic field is Hw1 and the magnetic field intensity at which recording is not performed in the erasing direction magnetic field is Hw2, Hw1 is −50 Oe, and Hw2 is Hw2.
Was 140 Oe.

Next, magnetic field modulation recording was performed using a floating magnetic head. The reproduction optical system is the same as in the case of light modulation. Recording was performed by irradiating 7 mW continuous recording light while applying a recording magnetic field having the same frequency as the recording light pulse of light modulation at the same linear velocity as in the case of light modulation. FIG. 4 shows the results. Fifteen
With a recording magnetic field of 0 Oe, a CN ratio of 49.8 dB was obtained.

Example 2 A disc was prepared in the same manner as in Example 1 except that the composition of the first recording layer was changed to Gd ₁₇ (Fe ₈₀ Co ₂₀ ) ₈₃ and the composition of the second recording layer was changed to Tb ₃₁ (Fe ₈₀ Co ₂₀ ) _69. Was prepared. The magnetization of the entire recording layer was dominated by transition metal magnetization at room temperature, and was 80 emu / cc. When this disk was evaluated by optical modulation recording in the same manner as in Example 1, Hw1 was -120 Oe and Hw2 was 280
Oe and the highest CN ratio were 46.4 dB.

Example 3 A sputtering device was used to produce a magnetostatically coupled CAD medium.
With a guide groove with a track pitch of 0.85 μm
Introduction of a carbonate substrate, 5 × 10^-FiveTrue below Pa
Evacuation was performed to the air. Then, as a protective layer on the substrate
Forming 80nm Ta oxide using reactive sputtering
did. Next, on the oxidized Ta, Gd₃₂(Fe ₈₀Co₂₀)₆₈Yo
30 nm reproduction layer, Si_ThreeN_Four10nm consisting of
Cutting layer, Gd₂₀(Fe₈₀Co₂₀)₇₈30nm
First recording layer, Tb₂₈(Fe₈₀Co₂₀)₇₄Consisting of 60
nm second recording layer was provided. Finally Si_ThreeN_FourConsists of
A 50 nm protective layer was provided.

The Curie temperatures of the reproducing layer, the first recording layer, and the second recording layer were measured.
As described above, the temperature was 270 ° C. At room temperature, the magnetization of the rare earth metal was dominant in the reproducing layer. In the first recording layer, the transition metal magnetization was dominant at room temperature, and the coercive force was almost zero. In the second recording layer, rare-earth metal magnetization is dominant at room temperature, and the coercive force is 5
kOe. The magnetization of the entire recording layer was 40 emu / cc due to the transition metal magnetization dominance at room temperature.

First, optical modulation recording was performed on the disk manufactured as described above. The CN ratio was evaluated using an evaluator having a wavelength of 680 nm and a numerical aperture of 0.55. The recording conditions were a linear velocity of 8 m / s, a frequency of 10.53 MHz (mark length 0.38
μm) to perform recording. 8 before recording
Erasing was performed by applying a magnetic field of 300 Oe in the erasing direction with an erasing power of mW.

When the reproduction power Pr was set to 1.5 mW, normal reproduction was performed, and the CN ratio was 26 dB. Pr2.4
At mW or more, the effect of super-resolution appeared. When Pr was 2.8 mW, the CN ratio became the maximum, and 42.3 dB was obtained.
The change in CNR was measured while changing the recording magnetic field (Hw) strength. The recording power was set so as to obtain the maximum CN ratio. Hw1 was -80 Oe and Hw2 was 170 Oe.

Next, magnetic field modulation recording was performed using a floating magnetic head. The reproduction optical system is the same as in the case of light modulation. Recording was performed by irradiating 7 mW continuous recording light while applying a recording magnetic field having the same frequency as the recording light pulse of light modulation at the same linear velocity as in the case of light modulation. FIG. 5 shows the results. 18
A CN ratio of 43.2 dB was obtained with a recording magnetic field of 0 Oe.

Example 4 The first recording layer and the second recording layer were formed of Tb ₂₀ (Fe ₈₀ Co ₂₀ ) ₈₀
The first recording layer of 80 nm made of Gd ₃₀ (Fe ₈₀ C
o ₂₀ ) A disc was produced in the same manner as in Example 1, except that the second recording layer was made of ₇₀ and having a thickness of 30 nm. 1st recording layer, 2nd
When the Curie temperatures of the recording layers were measured,
℃, 300 ℃ or more. The first recording layer had a transition metal magnetization dominance at room temperature and a coercive force of 7.5 kOe. In the second recording layer, rare-earth metal magnetization was dominant at room temperature, and the coercive force was almost zero. The magnetization of the entire recording layer was 50 emu / cc due to the transition metal magnetization dominance at room temperature. When this disk was evaluated in the same manner as in Example 1, Hw1 was -80.
Oe and Hw2 are 250 Oe, and the highest CNR is 48.
It was 8 dB.

COMPARATIVE EXAMPLE 1 In order to produce an inverted type MSR medium, a polycarbonate substrate having a guide groove having a track pitch of 0.85 μm was introduced into a sputtering apparatus, and evacuation was performed to a degree of vacuum of 5 × 10 ⁻⁵ Pa or less. Was. Thereafter, 80 nm of Ta oxide was formed on the substrate as a protective layer by using reactive sputtering. Next, a 30 nm reproducing layer made of Gd ₃₅ (Fe ₈₀ Co ₂₀ ) ₆₅ , a 10 nm cut layer made of Tb ₂₀ (Fe ₉₅ Co ₅ ) ₈₀ , and Tb _x (Fe ₈₀ Co ₂₀ ) _{100-X are formed} on the oxidized Ta.
An 80 nm recording layer was formed. Finally, a 50 nm protective layer made of SiN was provided. X is 20 to 27
(%).

The Curie temperatures of the reproducing layer, the cut layer and the recording layer were measured.
° C. At room temperature, the magnetization of the rare earth metal was dominant in the reproducing layer. The cut layer was dominated by the transition metal magnetization at room temperature. In the recording layer, at room temperature, the compensation composition was around X = 24 (%). The disk manufactured in this manner was evaluated by light modulation recording in the same manner as in Example 1. The results are shown in Table 1.

[0054]

[Table 1]

Next, magnetic field modulation recording was performed using a floating magnetic head. The reproduction optical system is the same as in the case of light modulation. Recording was performed by irradiating 7 mW continuous recording light while applying a recording magnetic field having the same frequency as the recording light pulse of light modulation at the same linear velocity as in the case of light modulation. However, none of them could record at a low magnetic field and obtain a high CN ratio.

[0056]

According to the present invention, it is possible to provide a medium capable of recording at a low recording magnetic field by reducing the demagnetizing field while maintaining strong magnetostatic coupling between the reproducing layer and the recording layer. . In particular, when used for magnetic field modulation recording, high-speed recording can be performed with a low recording magnetic field.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the mechanism of a magnetostatically coupled super-resolution medium of the present invention.

FIG. 2 is an explanatory view of a mechanism of a conventional magnetostatically coupled super-resolution medium.

FIG. 3 shows recording magnetic field dependence in optical modulation recording in Example 1.

FIG. 4 shows recording magnetic field dependency in magnetic field modulation recording in Example 1.

FIG. 5 shows recording magnetic field dependency in magnetic field modulation recording in Example 3.

FIG. 6 shows recording magnetic field dependence in magnetic field modulation recording in Comparative Example 1.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 reproducing layer 2 cutting layer 3 first recording layer 4 second recording layer 5 magnetostatic coupling force 6 demagnetizing field of first recording layer 7 demagnetizing field of second recording layer 13 recording layer 16 demagnetizing field of recording layer

Claims (5)

[Claims] 1. A recording medium comprising at least a recording layer, a cutting layer, and a reproducing layer on a substrate, wherein a magnetization direction corresponding to information is recorded on the recording layer, and reproduction is performed by a magnetostatic coupling force from the recording layer at a temperature equal to or higher than room temperature. A magneto-optical recording medium in which the magnetization direction of a recording layer is transferred to a layer, wherein the recording layer is composed of a plurality of layers made of an alloy of a rare earth metal and a transition metal and exchange-coupled to each other, and at least at room temperature is a rare earth element. A magneto-optical recording medium comprising a layer having a metal dominant magnetization and a layer having a transition metal dominant magnetization at room temperature. 2. The magneto-optical recording medium according to claim 1, wherein a layer of the recording layer closest to the reproducing layer has a transition metal dominant magnetization at room temperature. 3. The layer having a rare earth metal dominant magnetization,
3. The magneto-optical recording medium according to claim 1, wherein the coercive force is larger than that of the layer having the transition metal dominant magnetization. 4. A method for recording information on a magneto-optical recording medium using the magneto-optical recording medium according to claim 1, wherein information is recorded by a magnetic field modulation recording method. 5. A recording / reproducing apparatus comprising the magneto-optical recording medium according to claim 1 and a floating or contact magnetic head.