JP2985641B2 - Magneto-optical recording medium and reproducing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording and reproducing information, and more particularly, to reproducing a reproduction signal from only a part of a reproduction light irradiation area at the time of reproduction. The present invention relates to a magneto-optical recording medium capable of recording and reproducing information at a high density and a reproducing method therefor.

[0002]

2. Description of the Related Art A magneto-optical recording medium has a high recording density, a low cost,
It has been put to practical use as a rewritable information recording medium. In particular, a medium using a recording layer of an amorphous alloy of a rare earth element and a transition metal exhibits extremely excellent recording / reproducing 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 a normal case, 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 beam becomes shorter, studies have been made on shortening the wavelength of the laser beam, but this is extremely difficult at this stage.

On the other hand, in recent years, so-called super-resolution techniques have been attempted to achieve finer resolution determined by the wavelength of a laser by various means.
One of them is the use of a magneto-optical disk and the super-resolution (Magnetically induced Super Res
olution, hereinafter referred to as MSR. ) The method has been reported.

One form of this system uses a medium composed of three layers exchange-coupled to each other: a reproducing layer having a small coercive force, a cutting layer having a low Curie temperature, and a recording layer having a high Curie temperature and a large coercive force. When heated by the reproducing light while applying the reproducing magnetic field, the exchange coupling between the respective magnetic layers is cut at the high temperature portion of the medium.

[0006] Since the coercive force of the reproducing layer alone is small, the magnetization is uniformly oriented in the direction of the reproducing magnetic field in the high temperature portion, and the recorded bits are erased. As a result, only the low-temperature portion is reproduced, and as a result, the high-temperature portion is masked, so that the reproduction range is narrowed. Becomes possible.

The erased recording bit is automatically restored by being transferred from the recording layer when the medium temperature is lowered and exchange coupling is restored. This method detects the signal in front of the reproduction light spot, so Front Aperture Detec
and FAD. A drawback of the FAD method is that a considerably large reproducing magnetic field (Hr) is required during reproduction. At this time, the reproducing magnetic field usually needs to be 24000 A / m or more, and there is a disadvantage that the bits recorded in the recording layer become unstable because reproduction is performed while applying a strong reproducing magnetic field.

Further, there is a possibility that a magnetic field larger than the magnetic field required for recording is required for reproduction, which is a major obstacle in reducing the size of the magnetic head and simplifying the apparatus.
In particular, in magnetic field modulation recording, the recording magnetic field is often 10000 A / m or less, and the application of the reproducing magnetic field imposes a heavy burden on the magnetic head.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a super-resolution in which a magnetic field required for reproduction can be small and a high CN ratio (carrier-to-noise ratio, hereinafter CNR) can be obtained. And a reproducing method therefor. In order to solve the problem of the reproducing magnetic field, the present applicant has previously reduced the Kerr rotation angle of the mask portion of the FAD medium, thereby obtaining a medium that achieves a super-resolution effect without using a reproducing magnetic field and a recording and reproducing method. A method was proposed (for example, Japanese Patent Application No. 5-196248, "Magneto-optical recording medium and recording / reproducing method").

In the present invention, a mask is formed by a force for eliminating domain wall energy at the time of reproduction to obtain a super-resolution effect, and an attempt is made to achieve super-resolution reproduction that requires a small reproduction magnetic field and obtains a high CNR. It is.

The gist of the present invention is that a magnetic layer composed of at least three layers of a reproducing layer, a cutting layer and a recording layer, which are exchange-coupled to each other, is provided on a substrate in this order.
When the Curie temperatures of the recording layers are Tc1, Tc2, and Tc3, respectively, Tc1, Tc2, and Tc3 are equal to or higher than room temperature. In the magneto-optical recording medium that satisfies the relationship of Tc1> Tc2, Tc3> Tc2, the reproducing layer has Gd, Gd in GdFeCo is composed of an amorphous alloy of rare earth metal and transition metal mainly composed of Fe and Co.
The molar fraction of 27-35% der of is, the external magnetic field is 1000
The medium is partially heated by the reproduction light under the condition of 0 A / m or less.
By doing so, the previously recorded magnetic domain of a specific magnetization direction
Only the magneto-optical recording medium is characterized in that it is smaller than at low temperatures . Further, another gist of the present invention is that
Using a magnetic recording medium, the external magnetic field during reproduction is 10,000A
/ M or less, the medium is heated by the irradiation of reproduction light,
Light that is reproduced while reducing the magnetic domains
A method for reproducing a magnetic recording medium. Further, according to the present invention,
Another point is that the above-described magneto-optical recording medium is used for recording.
First, irradiate continuous light while applying a magnetic field in a certain direction.
To align the magnetization in one direction, and then apply a magnetic field in the opposite direction.
Irradiating pulse light according to the information while applying
Recording by forming magnetic domains by reverse magnetization
When reproducing, the external magnetic field is 10,000 A / m or less.
Then, the medium is heated by irradiating the reproducing light, and the recorded magnetic domain is
Magneto-optical recording characterized by reproducing while reducing the size
The present invention resides in a recording and reproducing method for a medium.

The magneto-optical recording / reproducing method of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a magneto-optical recording medium for illustrating the principle of magneto-optical recording and reproduction of the present invention, and FIG. 2 is a plan view thereof. In the magneto-optical recording medium of the present invention, the exchange-coupled magnetic layers including at least three layers of the reproducing layer 1, the cutting layer 2, and the recording layer 3 are provided on the substrate in this order. The Curie temperatures of the reproducing layer 1, the cutting layer 2, and the recording layer 3 are each set to Tc.
When Tc2 and Tc3 are set, Tc1, Tc2, and Tc3 are equal to or higher than room temperature, and satisfy the relations of Tc1> Tc2 and Tc3> Tc2.

When recording is performed on this magneto-optical recording medium, first, a continuous magnetic field is applied while applying a magnetic field in a certain direction to align the magnetization direction in one direction (erase). Next, while applying a magnetic field in the opposite direction, irradiate pulse light according to the information,
A magnetic domain is formed by magnetization in the direction opposite to the erasure (recording).
In FIG. 1 and FIG.
Have substantially the same size in the recording layer 3 and the reproduction layer 1.

When the reproducing light 6 shown in the figure is irradiated while applying a weak magnetic field Hr to reproduce the recording, when the exchange coupling force between the recording layer 3 and the reproducing layer 1 becomes small or disappears, In this region 8, the magnetic domain moves in the direction of 5 in the direction of decreasing the domain wall area in the high temperature region by the force for reducing the domain wall energy in the reproducing layer, which was suppressed by the exchange coupling force at the time of low temperature.

At this time, since the magnetic domain in the recording direction is surrounded by the magnetic domain in the erasing direction, the reduction of the magnetic domain in the recording direction always becomes the energy stabilizing direction. Therefore,
When reproducing a magnetic domain in the recording direction, the high temperature portion does not contribute to the reproduction signal, and the "mask" conventionally obtained by applying a strong reproducing magnetic field can be obtained by applying a very weak reproducing magnetic field.

In this case, in order to promote the stabilization of the domain wall energy when the magnetic domain is reduced, it is desirable that the intermediate region 10 between the adjacent recording tracks 9 is also erased in advance in the same direction as the erase. Here, in the case of land recording, the intermediate region is a groove portion, and in the case of groove recording, the intermediate region is a land portion.

When reproducing a long recorded magnetic domain, the effect of stabilizing the energy by the reduction in the vicinity of the center of the magnetic domain is reduced, so that a "mask" may not be formed. However, even in this case, since the magnetic domain is reduced at both ends of the recording magnetic domain and a mask is generated, the signal separating performance from the adjacent recording magnetic domain is improved and the super-resolution effect is obtained. In order to increase the force for moving the domain wall, it is desirable that the periphery of the recording magnetic domain is uniformly magnetized in the direction opposite to the recording magnetic domain.

This is because, if a domain wall exists between the recording domain and the area other than the recording domain, the expansion of the recording domain may reduce the domain wall energy. Only when the circumference is uniform, the magnetization direction and size of the mask become uniform. Therefore, it is preferable that an intermediate region (for example, a groove portion in the case of land recording and a land portion in the case of groove recording) separating the recording tracks is uniformly magnetized in the erasing direction.

In order to obtain such a medium, the energy reduction by eliminating the domain wall in the portion heated to a high temperature by the reproduction light is larger than the increase in the magnetostatic energy due to the uniform magnetization direction, and Must have enough power to overcome holding power. In order to sufficiently increase the magnetostatic energy, the reproducing layer needs to have high perpendicular magnetic anisotropy, and the perpendicular magnetic anisotropy is preferably 8 × 10 ⁵ erg / cm ³ or more during reproduction. . The magnetostatic energy is preferably 1 erg / cm ² or more. However, if the magnetostatic energy is too large, it is difficult to transfer the information in the recording layer to the reproducing layer, so that it is preferably 10 erg / cm2 or less.

The perpendicular magnetic anisotropy and the magnetostatic energy can be adjusted by conditions such as gas pressure during film formation. When the magnetic domain is reduced and the magnetization direction is made uniform, the magnetostatic energy increases. In order to suppress this increase as much as possible, it is necessary that the magnetization of the reproducing layer becomes small in the vicinity of Tc2, so that the magnetostatic energy becomes very small.

For this reason, it is preferable that the reproducing layer has a composition in which the magnetization of the rare earth metal is predominant at room temperature, and the magnetization decreases as the temperature rises. The preferred volume susceptibility of the reproducing layer at Tc2 is 2
It is at most 00 emu / cm ^2, more preferably at most 150 emu / cm ² . As a substance used for such a reproducing layer, G
dFeCo as the main component, and Ti, Cr, M
An amorphous alloy of a rare earth metal and a transition metal to which elements such as o and Tb are added in a total amount of 5 mol% or less is used.

As for the composition, the molar concentration of Gd in GdFeCo is 27% or more. However, if the molar concentration of Gd is too large, the CNR is remarkably reduced. Preferably it is 28% or more and 34% or less. The Curie temperature is preferably 250 ° C. or higher.
In order to increase the perpendicular magnetic anisotropy of the reproducing layer, it is preferable to give the magnetic layer some film stress to generate the anisotropy by the inverse magnetostriction effect.

If the film stress is too large, the durability of the film is adversely affected, so that it is 1 × 10 ⁹ dyne / cm ² or more and 5 × 10 ⁹ dyne / c.
It is preferably at most m ² . It is preferable that the thickness of the reproducing layer is thin because the force applied to the magnetization is large. However, if it is too thin, the reproduction signal becomes small, so
nm or less is preferable. More preferably, 12 nm or more,
It is 35 nm or less.

The cut layer must have a Curie temperature lower than those of the reproducing layer and the recording layer. The Curie temperature of the cutting layer is preferably about 100 to 180 ° C. The reproducing layer preferably has a high perpendicular magnetic anisotropy and generates a strong force in the magnetization of the reproducing layer.

The substances used include TbFe, Tb
FeCo, DyFeCo, DyFe, TbDyFeCo
And alloys of rare earths and transition metals. The film thickness is 2 nm
As described above, the thickness is preferably 30 nm or less. The recording layer is
Since it is a layer that stably stores data, it is necessary that the layer has a Curie temperature that does not deteriorate with a reproduction beam.

The Curie temperature is preferably about 200 to 280 ° C. If the Curie temperature is too high, the laser power required for recording will be too strong. The recording layer needs to have high perpendicular magnetic anisotropy in order to give a strong force to the magnetization of the reproducing layer. The material of the recording layer is T
bFeCo, TbCo, DyFeCo, TbDyFeC
An alloy of a rare earth and a transition metal such as o, GdTbFe, GdTbFeCo is preferably used.

TbFeCo is particularly preferably used.
It is. The thickness of the recording layer is preferably 10 nm or more and 50 nm or less. When an alloy of a rare earth metal and a transition metal is used, the magnetic layer is very easily oxidized. Therefore, it is preferable to adopt a form in which protective films are provided on both sides of the magnetic layer. As the protective film, Si oxide, Al oxide, Ta oxide,
A simple substance such as Ti oxide, Si nitride, Al nitride, Si carbide or a mixture thereof is preferably used.

The thickness of the protective film is preferably about 50 to 150 nm. After forming the protective film on the substrate side, the magnetic anisotropy of the magnetic layer can be improved by plasma etching the surface. A heat radiation layer directly on the recording layer side of the magnetic layer or via a protective layer, such as Al, Cu, Au, Ag or the like;
Providing a high thermal conductive material made of an alloy mainly composed of such a material is a desirable configuration for stabilizing the mask during reproduction.

The thickness of the heat radiation layer is preferably about 10 nm to 100 nm.

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, however, are not intended to limit the scope of the invention. Example 1 A light-transmitting polycarbonate resin substrate having a thickness of 1.2 mm and a guide groove of 1.6 μm was used as a substrate.

This is placed in a sputtering apparatus at 5 × 10 ^-5.
Evacuation was performed until the degree of vacuum became Pa or less. Thereafter, a tantalum oxide thin film was formed as a dielectric layer on the substrate by a reactive sputtering method. Next, the surface was etched with high-frequency plasma at an output of 100 W for 5 minutes to smooth the surface.

The initial film thickness was set so that the thickness of the tantalum oxide layer after etching was about 85 nm. Next, on the tantalum oxide layer, a reproducing layer 3 made of amorphous having a composition of Gd ₂₈ (Fe ₈₀ Co ₂₀ ) ₇₂ (atomic%, Co concentration in the 3d transition metal is 20 atomic%) and having a thickness of 35 nm, Tb
₂₀ Fe ₈₀ than become cut layer having a thickness of 10nm 4, Tb ₂₁ (F
A recording layer 5 made of e ₈₀ Co ₂₀ ) ₇₉ and having a thickness of 38 nm, and a dielectric layer made of SiN and having a thickness of ₇₈ nm were sequentially formed by sputtering.

Each of the magnetic layers is made of Gd ₂₈ (Fe ₈₀ Co).
₂₀ ) ₇₂ only, Tb ₂₀ Fe ₈₀ only, Tb ₂₁ (Fe ₈₀ C
o ₂₀ ) X-ray diffraction was performed on a sample prepared in the same manner as above except that only ₇₉ was used, and no peak indicating crystallinity was observed. The magnetic curl loop was measured for these samples while increasing the temperature, and the Curie points were measured. The Curie points were 220 ° C. or higher (reproducing layer), about 120 ° C. (cutting layer), and 22 ° C., respectively.
It was found that the temperature was 0 ° C. or higher (recording layer).

First, high-density recording having a frequency component equal to or higher than the cut-off spatial frequency was performed on a medium having such a configuration using an evaluator having a wavelength of 830 nm and a numerical aperture of 0.55. The recording power was 9 mW, the linear velocity was 7 m / s, and the frequency was 7 MHz. After this recording operation, reproduction was performed at a reproduction power of 2.4 mW while changing the intensity of the external magnetic field, and the CNR was measured. As a result, the minimum required Hr to obtain a CNR of 45 dB was 1.6 kA / m, and the maximum reached CNR was 49.2 dB.

Example 2 A film was prepared in the same manner as in Example 1 except that the reproducing layer was an amorphous alloy of Gd ₃₀ (Fe ₈₀ Co ₂₀ ) _{70 having} a thickness of 35 nm. The Curie temperature of the reproducing layer was 220 ° C. or higher. When this was evaluated for magnetic properties in the same manner as in Example 1, 45 dB or more was obtained even at a reproduction magnetic field of 0,
The NR was 47.6 dB.

Example 3 A film was produced in the same manner as in Example 1 except that the reproducing layer was made of Gd ₃₃ (Fe ₈₀ Co ₂₀ ) ₆₇ , an amorphous alloy having a thickness of 35 nm. The Curie temperature of the reproducing layer was 220 ° C. or higher. When this was evaluated for magnetic properties in the same manner as in Example 1, 45 dB or more was obtained even at a reproduction magnetic field of 0,
The NR was 48.5 dB.

COMPARATIVE EXAMPLE 1 The same procedure as in Example 1 was carried out except that the reproducing layer was an amorphous alloy of Gd ₂₄ (Fe ₈₀ Co ₂₀ ) _{76 having} a thickness of 35 nm. The Curie temperature of the reproducing layer was 220 ° C. or higher. When the magnetic properties were evaluated in the same manner as in Example 1, the minimum Hr required to obtain a CNR of 45 dB was 3
7.0 kA / m, and the highest attainable CNR is 50.2 dB
Met.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the reproducing layer was an amorphous alloy of Gd ₂₆ (Fe ₈₀ Co ₂₀ ) _{74 having} a thickness of 35 nm. The Curie temperature of the reproducing layer was 220 ° C. or higher. When the magnetic properties were evaluated in the same manner as in Example 1, the minimum Hr required to obtain a CNR of 45 dB was 3
1.3 kA / m, the highest CNR reached is 50.3 dB
Met.

Comparative Example 3 The same procedure as in Example 1 was carried out except that the reproducing layer was an amorphous alloy of Gd ₃₆ (Fe ₈₀ Co ₂₀ ) _{64 having} a thickness of 35 nm.

The Curie temperature of the reproducing layer was 220 ° C. or higher. The magnetic properties were evaluated in the same manner as in Example 1. As a result, even when Hr was changed in the range of 0 to 64 kA / m, C
The NR did not reach 45 dB. In addition, the highest attainment C
The NR was 40.5 dB. Figure 3 shows the results of these evaluations.
Shown in The solid line indicates the minimum magnetic field strength (kA / m) required to obtain a CNR of 45 dB, and the broken line indicates the highest attained CNR (d
B) is shown. As is clear from FIG. 3, even in the state where the reproducing magnetic field is weak, a high CNR can be obtained by the super-resolution effect in the example having the predetermined Gd composition.

[0041]

According to the magneto-optical recording medium and the recording / reproducing method of the present invention, the effect of super-resolution can be obtained even when the reproducing magnetic field is weak, and the long-term stability of the recording bit can be obtained as compared with the conventional super-resolution medium. It is possible to obtain excellent effects in terms of performance and miniaturization of the drive.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a magneto-optical reproducing method according to the present invention.

FIG. 2 is a plan view showing a magneto-optical reproducing method according to the present invention.

FIG. 3 shows 45d in Examples and Comparative Examples of the present invention.
Minimum Hr and maximum reached CN required to obtain CNR of B
The dependence of R on the Gd ratio in the reproducing layer.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 reproducing layer 2 cutting layer 3 recording layer 4 recording magnetic domain 5 moving direction of domain wall 6 reproducing light 7 moving direction of reproducing light 8 high temperature section 9 recording track 10 intermediate area

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 11/10 506 G11B 11/10 586

Claims (3)

(57) [Claims] A magnetic layer exchange-coupled with at least three layers of a reproducing layer, a cutting layer and a recording layer is provided in this order on a substrate, and the Curie temperatures of the reproducing layer, the cutting layer and the recording layer are each set to Tc1. , Tc2, and Tc3, Tc
1, Tc2 and Tc3 are higher than room temperature, and in a magneto-optical recording medium satisfying the relationship of Tc1> Tc2, Tc3> Tc2, the reproducing layer is made of an amorphous alloy of a rare earth metal and a transition metal mainly composed of Gd, Fe and Co. , GdFeCo
Ri mole fraction from 27 to 35% der of Gd in the external magnetic field by the reproducing light under the following conditions 10000 A / m
By partially heating the medium, the pre-recorded features
A magneto-optical recording medium characterized in that only magnetic domains having a fixed magnetization direction are reduced as compared with a low temperature . 2. Use of the magneto-optical recording medium according to claim 1.
When the external magnetic field during reproduction is 10,000 A / m or less,
The medium is heated by light irradiation, and the recorded magnetic domains are reduced.
Reproduction of a magneto-optical recording medium,
Raw method . 3. At least a reproducing layer, a cutting layer, and a
The magnetic layers exchange-coupled to each other consisting of three recording layers are
Are provided in this order, the curability of the reproducing layer, the cutting layer, and the recording layer
-When the temperatures are Tc1, Tc2 and Tc3, respectively,
1, Tc2 and Tc3 are higher than room temperature , satisfy the relation of Tc1> Tc2, Tc3> Tc2 , and the reproducing layer is composed of Gd, Fe and C
amorphous alloy of rare earth metal and transition metal mainly composed of o
Made of gold, and the molar fraction of Gd in GdFeCo is 27 to
35% recording / reproducing method for a magneto-optical recording medium.
Te, the time of recording, first continuous light while applying a magnetic field in a predetermined direction
To align the magnetization in one direction, and then in the opposite direction.
Irradiating pulse light according to information while applying a magnetic field,
By forming magnetic domains due to magnetization in the opposite direction to erasure,
In the case of reproduction, when the external magnetic field is 10,000 A / m or less,
The medium is heated by light irradiation, and the recorded magnetic domains are reduced.
Recording on a magneto-optical recording medium characterized in that reproduction is performed while
Recording and playback method.