JPH05198033A - Magneto-optical recording system - Google Patents

Abstract

PURPOSE:To greatly improve C/N in the magneto-optical recording system which executes direct overwriting of data. CONSTITUTION:While a magneto-optical recording medium is transferred in order to execute the direct overwriting of the data, a bias magnetic field is impressed in the recording direction of bits and the recording medium is irradiated with a laser beam modulated in a power level and/or the pulse width between an erasing level and a writing level. The magneto-optical recording medium is constituted by forming a recording layer consisting of a perpendicularly magnetized film including an amorphous alloy of rare earths and transition metals on a transparent substrate having <=0.5[W/(m.K)] thermal conductivity or on a transparent substrate formed with a transparent high-polymer layer having <=0.5[W/(m.K)] thermal conductivity on a recording layer side. This recording layer has 20<=x<=28 rare earth compsn. ratio X (atom%). Fe or Fe and Co are used for the transition metal. Further, the bias magnetic field Hex(Oe) to be impressed is specified within a range of Hex<=800, Hex>=17X(X-24)<2>+100 and Hex<=30X(X-24)<2>+400.

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 system for recording, reproducing and erasing information by using light from a laser or the like. More specifically, the power level of the optical pulse and / or
Alternatively, the present invention relates to a magneto-optical recording method for performing direct overwrite by modulating the pulse width.

[0002]

2. Description of the Related Art Various researches and developments have been made on optical recording media as high-density and large-capacity information recording media. In particular, magneto-optical recording media capable of erasing information have a wide range of application fields, various materials and systems have been announced, and they have already been put to practical use.

When comparing a floppy disk, a hard disk, etc., with a magneto-optical recording medium in terms of characteristics, a major drawback of the magneto-optical recording medium is a direct-over in which old recorded information is erased and new information is written and recorded. The point is that writing (direct overwriting) is difficult.

As a direct overwrite technique for a magneto-optical recording medium, various systems have been proposed so far. Among them, JP-A 1-251357, J. App
l. Phys. Vol.63 No.8 (1988) 3844, IEEE TRANS. Mag
n.Vol.23 No.1 (1987) 171, Appl. Phys. Lett. Vol.4
9 No.8 (1986) 473, IEEE TRANS.Magn.Vol.25 No.5 (1
989) 3530, J. Appl. Phys. Vol. 69 No. 8 (1991) 4967
As described above, in a part of the domain wall boundary region heated by laser light irradiation, using a self-reversible magneto-optical recording layer capable of self-reversing the direction of the net remanent magnetization, in the absence of an external bias magnetic field, Optical pulse power level and /
Alternatively, the method of performing direct overwrite by modulating the pulse width between the erasing level and the writing level requires a drastic change in the structure of the optical system, magnets, etc. compared to the magneto-optical disk drive that is currently on the market. Without
This is the method that will receive the most attention as a future technology.

[0005]

DISCLOSURE OF THE INVENTION The present inventors actually conducted a confirmation test of direct overwrite by the above-mentioned conventional method. The medium used at that time is 130 mm in diameter,
On a polycarbonate resin (PC) substrate with a spiral groove with a thickness of 1.2 mm and a pitch of 1.6 μm,
Gd ₁₃ Tb ₁₃ Fe _{59 is used} as the aforementioned self-reversible magneto-optical recording layer.
Rare earth transition metal amorphous alloy magnetic thin film (thickness 150 nm) of Co ₁₅ (subscript indicates composition by atom%) is sandwiched by AlSiN film (thickness 80 nm) which is a transparent dielectric. .. The recording layer here is J. Appl. Phys. Vol. 63 No. 8
(1988) 3844 and IEEE TRANS.Magn.Vol.25 No.5 (1989)
It has exactly the same composition and magnetic properties as the GdTbFeCo film described in 3530.

According to the above-mentioned document, it is said that the direct overwrite operation is possible in the absence of an external bias magnetic field or in the presence of an external bias magnetic field of 120 Oe at maximum in the bit recording direction. Ie J. Appl. P
According to hys. Vol.63 No.8 (1988) 3844, when the external bias magnetic field is larger than 120 Oe, the margin of the erase pulse width disappears, and the erase becomes impossible and the direct overwrite becomes impossible. Have been described. Also, J. Appl. Phys. Vol.69 No.8 (1991) 4967 describes that the erase margin becomes narrower when the external magnetic field is increased.

After grasping such a point, a test of the direct overwrite operation of the above-mentioned medium was conducted. The rotation speed of the medium installed in the evaluation drive was set to a linear velocity of 5.65 m / sec at a position with a radius of 30 mm. Recording and erasing were performed with a 2 MHz pulse signal shown in FIG. 3 in the absence of an external bias magnetic field. At that time, the laser power using a laser having a wavelength of 830 nm was 8.0 mW during recording and 5.5 mW during erasing. After that, 1.0 mW of DC light, that is, continuous light was irradiated to measure the reproduction signal. At this time, the C / N of the reproduced signal was about 25 dB.

Subsequently, recording and erasing were performed on the same track on which this measurement was performed with a pulse signal of 1.5 MHz shown in FIG. 4 in the absence of an external bias magnetic field. That is, FIG.
The original signal according to (4) was directly overwritten with the signal in FIG. After that, 1.0 mW of DC light, that is, continuous light was irradiated to measure the reproduction signal. Then, the 2 MHz signal recorded at the beginning was completely erased, and only the 1.5 MHz signal was recorded. At this time, the C / N of the reproduced signal was about 25 dB.

Using another track, a direct overwrite operation test was conducted in the same manner as described above except that the external bias magnetic field 120 Oe was applied in the bit recording direction. Then, the result is not much different from that in the absence of the external bias magnetic field, and the C / N at direct overwrite was about 25 dB.

As described above, it was possible to confirm the basic direct overwrite operation by using the above-mentioned optical modulation method. However, regarding reproduction characteristics, C / N = 25
It is extremely low as dB, and in order to reach the level of practical use,
A significant improvement in C / N is an issue.

The present invention solves the above-mentioned problems, and in the magneto-optical recording system of optical modulation for direct overwriting of data by modulating the power level and / or pulse width of the above-mentioned optical pulse, C / N Intended for significant improvement.

[0012]

The magneto-optical recording method of the present invention is one of the domain wall boundary regions heated by laser light irradiation on a transparent substrate or a transparent substrate having a transparent polymer layer formed on the recording layer side. In the section, a magneto-optical recording medium having a recording layer formed of a perpendicular magnetization film containing a self-reversible rare earth transition metal amorphous alloy capable of self-reversing the direction of the net remanent magnetization is used, and the magneto-optical recording medium is transferred. Meanwhile, in a magneto-optical recording method in which a bias magnetic field is applied in the bit recording direction and direct overwriting of data is performed by irradiating laser light whose power level and / or pulse width is modulated between an erasing level and a writing level, The thermal conductivity of the transparent substrate is 0.5 [W / (m · K)] or less, or the thermal conductivity of the transparent polymer layer formed on the transparent substrate is
0.5 [W / (m · K)] or less, the rare earth composition ratio X (atom%) in the recording layer is 20.0 ≦ X ≦ 28.0, and the transition metal in the recording layer is Fe or Fe and Co. And the applied bias magnetic field Hex (Oe) is
Hex ≧ 17 × (X−24) ² +100, and Hex ≦ 30 × (X
-24) It is characterized by being ² + 400.

This has been clarified by the following studies by the present inventors. The same medium as that used in the confirmation test of the conventional method described above was used, and the same test as the confirmation test of the conventional method was performed except that the external fixed bias magnetic field was applied at 250 Oe in the recording direction of the bit. As a result, the C / N of the reproduced signal was about 31 dB, which was confirmed to be improved by about 6 dB compared to the above-mentioned conventional method.

Therefore, a medium in which the rare earth composition of the recording layer was changed was prepared, and the C / N was measured by changing the strength of the external fixed bias magnetic field. As a result, the rare earth composition ratio X (at
om%) and the external fixed bias magnetic field Hex (Oe),
20 ≦ X ≦ 28, Hex ≧ 17 × (X-24) ² +100, and H
It has been found that it may be within the range represented by ex ≦ 30 × (X−24) ² +400 (in the shaded area in FIG. 1). That is, by performing magneto-optical recording within this range, even if a recording layer having the same composition is used, the C / N is improved by at least 6 dB as compared with the case where the bias magnetic field is 0, etc. It has been clarified that a favorable effect can be obtained in the direct overwrite magneto-optical recording.

J. Appl. Phys. Vol. 63 No. 8 (1988) 3844
The condition indicated by is the area A (X = 2
6, 0 ≦ Hex ≦ 120). On the other hand, in the present invention, the range of the external fixed bias magnetic field when the rare earth composition ratio is 26 atom% is a region higher than the region A. And when applying the bias magnetic field of the strength of the present invention to the data and contents described in J. Appl. Phys. Vol. 63 No. 8 (1988) 3844, the external fixed bias magnetic field hinders the erase operation, The erase pulse width margin has completely disappeared,
It is thought that direct overwrite will be impossible. Nevertheless, in the present invention, direct overwriting is possible even when an external fixed bias magnetic field of 250 Oe is applied.

The cause of this difference is that the difference in the temperature profile in the recording layer causes a difference in the profile of the magnetic characteristics of the recording layer, and the self-reversal mechanism of the residual magnetization is different from that of the conventional method. It is thought to be because.

That is, in the study of Japanese Patent Application Laid-Open No. 1-251357, a sample formed on a flat glass substrate surface is used. On the other hand, in the test according to the present invention, the sample formed on the PC substrate having the groove is used. Therefore, it is considered that the two differ in the way of heat escape due to the difference in the substrate material, which causes the difference in the temperature profile in the recording layer.

In the study conducted by the present inventors, the diameter was actually
A recording layer of the same film composition and the same multilayer film structure as the above-mentioned test was formed on a glass substrate of λ = 1.0 [W / (m · K)] having a spiral groove of 130 mm in thickness, 1.2 mm in thickness and 1.6 μm pitch. Was formed, and an overwriting test was performed with an external bias magnetic field of 250 Oe applied in the bit recording direction, the reproduced signal C / N obtained was approximately 25 dB, and λ = approximately
It was 6 dB lower than when using a polycarbonate substrate of 0.2 [W / (m · K)].

This is because by using a polycarbonate substrate having a lower thermal conductivity than that of a glass substrate, the temperature distribution at the laser light irradiation portion becomes sharp, the shape of the domain formed in the recording layer is adjusted, and the C / N ratio is improved. I think that has improved. From this, it is preferable that the material of the transparent substrate has a thermal conductivity λ of 0.5 [W / (m · K)] or less.

As a material satisfying the above condition of λ ≦ 0.5 [W / (m · K)], an organic resin can be mentioned. Examples thereof include polycarbonate resin, acrylic resin, epoxy resin, 2-methylpentene resin, polyolefin resin, and copolymers thereof. Among them, polycarbonate resin is preferable in terms of mechanical strength, weather resistance, heat resistance, and moisture permeability.

The above-mentioned condition of thermal conductivity may be satisfied if the material in contact with the recording layer including the transparent dielectric layer is satisfied. Therefore, even if it is a glass substrate, the groove portion has λ ≦ 0.5 [W / (m
If the 2P glass substrate formed of the organic resin of (K)] is satisfied, the above conditions are satisfied and the glass substrate can be used.

Further, the shape of the temperature distribution is the thermal conductivity λ of the substrate.
It is thought that the lower is, the sharper
It is more preferable that λ ≦ 0.2 [W / (m · K)].

The shape of the temperature distribution is also affected by how to narrow down the laser light with which the medium is irradiated. That is, it is possible to make the temperature distribution of the laser light irradiation portion sharper by making the light flux narrower by reducing the numerical aperture of the optical system that narrows down the laser light.

Further, in the present invention, when the composition of the recording layer is changed as shown in FIG. 1, the external fixed bias magnetic field strength with which a high C / N is obtained changes greatly. Moreover, the present invention requires a magnetic field larger than the external fixed bias magnetic field described in Japanese Patent Application Laid-Open No. 1-251357. Moreover, according to the present invention, the significance thereof can be understood in that a higher C / N can be obtained as compared with the above-mentioned conventional method.

In FIG. 1, rare earth composition X <20 (at
om%) and X> 28 (atom%) range, direct overwrite operation cannot be obtained, so
It is excluded from the scope used as the present invention.

In the conventional magneto-optical recording medium which is not direct overwrite, the old information signal which has been recorded is completely erased once in the erasing process, and then a new signal is written. Therefore, in a conventional magneto-optical recording medium that is not direct overwrite, it is easy to obtain a high C / N when a newly written signal is reproduced. On the other hand, in a direct overwrite magneto-optical recording medium that directly writes new information while erasing recorded old information, the newly written signal is reproduced when the old signal is not completely erased. However, it was difficult to obtain a high C / N. However, in the present invention, a high C / N is obtained even when a newly rewritten signal is reproduced. In particular, the condition of the bias magnetic field in the present invention is X ≦ 28.0, H ≧ 220, Hex ≧ 130 × X
C / N of 31 dB or more is more preferable by setting it within the range represented by −3160 and Hex ≦ 100 × X−2100.

The external bias magnetic field strength is 800 Oe.
When a larger magnetic field is applied, expensive materials such as NdFeB must be used as the material of the permanent magnet, and inexpensive materials such as ferrite should be used in order to satisfy the requirement to mount a small magnet in the drive. When used, there is a problem that the size of the magnet becomes large. This is disadvantageous in terms of drive cost reduction and drive size reduction. Therefore, it is preferable to properly select the medium composition and perform magneto-optical recording at an external fixed bias magnetic field strength of 800 Oe or less.

The recording layer used in the present invention is a perpendicular magnetization capable of self-reversing the direction of the net remanent magnetization in the presence of a constant bias magnetic field in at least a part of the domain wall boundary region heated by laser light irradiation. Any film may be used. For example, TbFe, Gd of rare earth transition metal amorphous alloy system
Fe, DyFe, TbFeCo, GdFeCo, DyFeCo, DyTbFeCo, GdTbFe
Co, GdDyFeCo, GdDyTbFeCo, NdDyFeCo, NdDyTbFeCo, Nd
An amorphous alloy film containing a rare earth element such as Fe, PrFe, or CeFe and a transition metal such as Fe or Fe and Co as the main components can be given. The rare earths here include Gd and / or
The use of Tb is preferable because a high C / N can be stably obtained.

In the above-mentioned rare earth / transition metal amorphous alloy, as long as its perpendicular magnetic anisotropy is not lost, rare earth and Fe
There is no problem even if elements other than Co and Co are added up to 10 atom%. Examples of such elements include Ti, Zr, Hf, V,
Nb, Ta, Cr, Mo, W, Tc, Re, Ru, Os, Ir, Si, Ge, B
Examples thereof include i, Pd, Au, Ag, Cu and Pt. One or more of these rare earth elements and elements other than Fe and Co may be contained. In particular, it is preferable to add Ti, Zr, Hf, Ta, Cr and Re in order to prevent corrosion of the recording film itself due to oxidation.

In order to obtain a higher reproduction C / N, it is preferable that the recording layer has a compensation temperature Tcomp of 50 to 250 ° C. and a Curie temperature Tc of 100 to 350 ° C. Further, it is more preferable that Tcomp is 80 to 160 ° C and Curie temperature Tc is 200 to 250 ° C.

In addition to this, it is preferable to keep the perpendicular magnetic anisotropy constant Ku of the recording layer within the range of 2 to 3 (× 10 ⁶ erg / cc). This is because the C / N decreases at 2 (× 10 ⁶ erg / cc) or less, and the external fixed bias magnetic field must be at least 800 Oe at 3 (× 10 ⁶ erg / cc) or more.

When the thickness of the recording layer is less than 10 nm, there are many problems in terms of film structure such as film discontinuity and nonuniformity. On the other hand, if it is thicker than 200 nm, the heat capacity becomes large, and thus high laser power is required for recording and erasing. Therefore, the film thickness is preferably in the range of 10 to 200 nm.

When a transparent dielectric film is provided between the transparent substrate and the recording layer, the thermal conductivity λS of the substrate should be kept in order not to disturb the shape of the domain due to the temperature distribution. It is preferable that the relation between the thermal conductivity λd of the transparent dielectric layer and the thermal conductivity λR of the recording layer is λS ≦ λd ≦ λR.

Since the thermal conductivity λ R of the recording layer made of a rare earth transition metal amorphous alloy is approximately 20 to 50 [W / (m · K)], the thermal conductivity λ d [W / (M ・
The range of K)] is preferably 0.5 ≦ λd ≦ 20.

As the transparent dielectric, a material having a high refractive index n, that is, a material satisfying n ≧ 1.8, and more preferably n is used in order to enhance the Kerr effect enhancement.
Materials with ≧ 2.0 are preferred.

As such a transparent dielectric material, Al
N, MgF ₂ , ZnS, CeF ₃ , Si ₃ N ₄ , AlSiN, SiO,
_{SiO 2, Zr 2 O 3,} In 2 O 3, SnO 2, Ta 2 O 5, AlO
N, SiON, ZrON, InON, SnON, TaON or a mixture thereof can be applied. Especially in the point that the refractive index is 2.0 or more, AlSiN, ZnS, Zr ₂ O ₃ , Ta ₂ O ₅ , Zr
ON and TaON are preferable.

Further, the transparent dielectric layer is not limited to a single-layer film made of a single material of the above-mentioned materials, but a plurality of types of multi-layer films may be provided.

To further increase the reproduction signal C / N,
It is effective that the thickness of the entire recording layer is 15 nm or more and 100 nm or less, more preferably 60 nm or less, still more preferably 40 nm or less, and the metal reflection layer is provided on the opposite side of the recording layer from the substrate.

The metal reflective layer used here is C / N.
It is preferable to use a material having a higher reflectance than the recording layer with respect to the laser light of the drive head used for the evaluation in order to improve C / N. Specifically, the laser light wavelength used is 830 nm
The refractive index n and the extinction coefficient k which are optical constants at
It is preferred to choose a material such that 3.5 and k ≧ 3.5. More preferably n ≦ 2.5 and 4.5 ≦ k ≦ 8.5
In the medium prepared under these conditions, the Kerr effect enhancement is improved by improving the reflectance of the metal reflection layer, and C
Further improvement of / N can be realized.

On the other hand, when a signal is recorded by heating with a laser beam, if the thermal conductivity of the metal reflection layer is too high, the heat is diffused significantly and a strong laser power is required. Therefore, in order to enable signal recording with a semiconductor laser with a power of 10 mW or less, which is widely used at present, the thermal conductivity of the material used for the metal reflective layer is 100 [W / (m · K)] or less. It is preferably 80 [W / (m · K)] or less.

As a material satisfying such conditions, Al
Alternatively, an alloy in which Au is added to Ag, that is, an AlAu alloy or an AgAu alloy can be used. In addition, in these alloys
If the addition amount of Au is less than 0.5 atom%, the above-mentioned effect of lowering the thermal conductivity is small, and if it is more than 20 atom%, the above-mentioned decrease in light reflectance is large, which is disadvantageous in terms of C / N. Therefore, it is preferable to keep the Au content in the range of 0.5 to 20 atom%.

Further, in order to suppress the decrease of the reflectance within 2% as compared with the film of Al or Ag alone, and prevent the decrease of C / N, Au is used.
The content is preferably 0.5 to 15 atom%, more preferably 0.5 to 10 atom%.

In order to reduce the Au content in this way,
It is also important in terms of reducing the cost of targets and media.

Further, from the viewpoint of minimizing the Au content, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc,
It is preferable to supplementarily add one or more specific elements such as Re, Ru, Os, and Ir. The addition amount of the specific element should be kept within 5.0 atom%, and if it exceeds this amount, the reflectance of the metal reflection film is lowered and the C / N is also lowered. 5.0 atom%
Within this range, the decrease in reflectance at 830 nm, which is the wavelength of the semiconductor laser used in the magneto-optical recording / reproducing apparatus, is within 2%. On the other hand, if less than 0.3 atom%, Au
It is not possible to compensate for the increase in thermal conductivity due to the saving of. Therefore, the added amount of specific element is 0.3-5.0 atom%
It is necessary to set in the range of. Due to the addition of the specific element in this range, the reflectance of the reflective film is 2% compared with the film of Al or Ag alone when the added amount of Au is in the range of 0.5 to 10 atom%.
Within this range, the Au cost can be reduced, and at the same time, the thermal conductivity can be set in the range of 20 to 100 [W / (m · K)].

From the viewpoint of enhancing the durability of the metal reflective layer itself, Ti, Zr, Nb, and T are among the above-mentioned specific element groups.
Preferred are a, Cr and Re. The thickness range of these metal reflective layers is 1
Although it is 0 to 500 nm, it is preferably 30 to 200 nm, particularly preferably 40 to 40 nm in order to suppress the C / N decrease due to the decrease in reflectance and enable recording with a laser power of 10 mW.
It is 100 nm.

Further, by setting the Au composition and / or the specific element composition in the above composition range, the thermal conductivity thereof can be 100 [W / (m · K)] or less as described above, and the laser It is also possible to record signals with power of 10 mW or less.

The position where the metal reflection layer is provided is not particularly limited except that it is provided on the side opposite to the light incident surface of the magneto-optical recording layer. That is, one having a metal reflection layer directly provided on the magneto-optical recording layer, or one provided with a transparent dielectric layer interposed therebetween, and further, an inorganic protective layer such as a transparent dielectric layer and / or the like on the metal reflection layer. Those with an organic protective layer, etc.
Applicable to any configuration.

As the method for producing the above-mentioned transparent dielectric layer, recording layer, and inorganic thin film of the metal reflection layer, various thin film forming methods such as the known vacuum deposition method, PVD method such as sputtering method, or CVD method are applied. it can. However, the magneto-optical recording medium is preferably manufactured under the condition that the adhesiveness to the polymer substrate is particularly large in order to prevent the peeling which occurs in the high temperature and high humidity environment resistance test. For this purpose, the sputtering method is preferable.

As the organic protective layer, light and / or thermosetting resin, thermoplastic resin or the like can be applied and can be formed by a coating method or the like. The back surface protective layer provided on the opposite side of the recording layer from the substrate is preferably provided so as to cover at least the side surface of the recording layer.

In this system, the waveform of the laser pulse irradiated during recording / erasing, that is, overwriting, is shown in FIG.
It is not limited to such a shape. That is, the above-mentioned JP-A-1-
As disclosed in Japanese Patent No. 251357, the recording / erasing pulse in FIG. 3 may be continuously irradiated with a close-in-interval pulse train that is continuous in a close-in interval with a narrower pulse width. Further, it may be a waveform in which the optical pulse composed of the pulse train of the close interval and the continuous irradiation pulse described above are combined.

However, the power of the optical pulse described above needs to be appropriately set according to the recording sensitivity of the medium, that is, the Curie temperature of the recording layer, and the film structure.

Further, in the direct overwrite method of the present invention, the direct overwrite characteristics were measured by changing the linear velocity of the medium and changing the recording frequency so that the recording bit length was the same. The result was that the C / N improved with the increase. That is, the medium used in the above-mentioned test is used as it is, and the evaluation condition is 11.3 m at a radius of 30 mm.
Recording was performed at a linear velocity of / sec. Direct overwriting is performed in the presence of an external fixed bias magnetic field in the bit recording direction, using a laser with a wavelength of 830 nm, a laser power of 15 mW for recording, and a laser power of 9 mW for erasing, and using the waveform pulses shown in FIGS. The C / N at that time was measured. As a result, the C / N was about 35 dB, and it was possible to obtain a C / N improvement of 4 dB as compared with the case of performing at a low linear velocity.
The use at high linear velocity can improve the data transfer rate, which is a desirable direction for future technology.

[0053]

Examples 1 to 30 and Comparative Examples 1 to 66 The magneto-optical recording medium having the structure shown in FIG. 2 was prepared and evaluated on the substrate as follows. In the figure, 1 is a substrate, 2 is a transparent dielectric layer, 3 is a recording layer, 4 is a back transparent dielectric layer as an inorganic protective layer, and 5 is an organic protective layer.

A disk having a diameter of 130 mm and a thickness of 1.2 mm,
Has a groove of 1.6 μm pitch and has a thermal conductivity of 0.2 [W
/ (M · K)] polycarbonate resin (PC) disk substrate 1 is fixed in a vacuum chamber of a three-target high-frequency magnetron sputtering apparatus (SPF-430H type manufactured by Anerva Co.) to 4 × 10 ⁻⁷ Torr. Exhaust until In addition,
Substrate 1 was rotated at 15 rpm during film formation.

First, as the transparent dielectric layer 2, a target having a diameter of 100 mm and a thickness of 5 mm is formed of Al ₅₀ Si.
₅₀ (Appendix numbers indicate composition the atom%) using a sintered body of, by introducing Ar / N ₂ mixed gas (N ₂ 30 vol%) in a vacuum chamber, Ar / N ₂ so that the pressure 5 mTorr The mixed gas flow rate was adjusted. High frequency sputtering was performed at a discharge power of 100 W and a discharge frequency of 13.56 MHz to deposit a transparent dielectric layer 80 nm of Al ₂₃ Si ₂₃ N ₅₄ as the dielectric layer 2.

Subsequently, a target was used as the magneto-optical recording layer 3.
Using the alloy targets of GdTbFeCo and TbFeCo, Gd and Tb metal chips (5 × 5 × 1 mm) are appropriately arranged on the target, and the sputtering gas is Ar (purity 99.999%), except the above. About 15 rare-earth transition metal amorphous alloy films capable of self-inversion with the film composition shown in Tables 1 and 2 under the same discharge conditions as
0 nm was deposited.

Further, as the inorganic protective layer on the back surface, the target was returned to AlSi and the sputtering gas was Ar / N.
_The back transparent dielectric layer 4 made of an Al ₂₃ Si ₂₃ N ₅₄ film was deposited to a thickness of 80 nm under the same discharge conditions as the above-mentioned transparent dielectric layer 2 while changing to ₂ mixed gas (N ₂ 30 vol%).

This sample was taken out of the sputtering device and attached to a spin coater. While rotating the disk, apply an ultraviolet curable phenol novolac epoxy polyacrylate resin, and then pass through an ultraviolet irradiation device to cure the resin, and an organic protective layer of about 20 μm 5
Was established.

Recording / erasing, that is, overwriting characteristics and reproducing characteristics of this sample disk were measured. For the measurement, a magneto-optical recording / reproducing apparatus (DDU-10 manufactured by Pulstec) was used.
00) was used. Direct overwriting was carried out by rotating the disk so that the linear velocity at a position with a radius of 30 mm was 5.65 m / sec, and sequentially irradiating light pulses modulated as shown in FIGS. That is, the signal according to FIG. 3 was directly overwritten by the signal according to FIG. At this time, the external fixed bias magnetic field Hex
Was changed and the magnetic field strength at which the C / N was maximized was examined for each sample. Hex and C / N maximum values at that time are shown in Tables 1 and 2 (Examples 1 to 30).

On the other hand, overwriting was performed under the same evaluation conditions as in Examples 1 to 15 except that the disks used in Examples 1 to 30 were used and the external fixed bias magnetic field had the values shown in Tables 1 and 2. The C / N measurement results of the tests are shown in Tables 1-2 (Comparative Examples 1-66).

[0061]

[Examples 31 to 40] The media produced in Examples 6 to 10 and 16 to 20 were used as they were, the linear velocity was 11.3 m / sec, and the optical pulses in FIGS. 3 and 4 were changed to those in FIGS. 5 and 6. The values of Hex and C / N were obtained under exactly the same evaluation conditions as in Examples 1 to 30 except that direct overwriting was performed instead. The results are shown in Table 2.

[0062]

[Comparative Example 67] For comparison, the structure of Example 19 shown in FIG. 2 was the same as that of Example 1 except that the substrate was a glass substrate having a thermal conductivity of 1.0 [W / (m · K)]. A magneto-optical disk was produced. This was evaluated under the same conditions as in Example 19, Comparative Example 19 and Comparative Example 49, while changing the external fixed bias magnetic field. The result obtained in this regard is that the C / N of the reproduced signal is 25 when the external fixed bias magnetic field is 350 Oe.
dB, which was 19 dB when the external fixed bias magnetic field was 0 Oe and 100 Oe.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

As described above in detail, according to the present invention, even in a magneto-optical recording medium for direct overwriting using a recording layer having the same composition, by using the recording system according to the present invention, a reproduction signal This has a great effect that the C / N can be greatly improved.

[Brief description of drawings]

FIG. 1 Relationship between rare earth composition ratio of recording layer and external fixed bias magnetic field

FIG. 2 is a laminated structure of an example and a comparative example.

FIG. 3 is an optical pulse used for overwriting in Examples 1 to 30 and Comparative Examples 1 to 67.

FIG. 4 is an optical pulse used for overwriting in Examples 1 to 30 and Comparative Examples 1 to 67.

FIG. 5: Optical pulse used for overwriting in Examples 31 to 35

FIG. 6 is an optical pulse used for overwriting in Examples 31 to 35.

[Explanation of symbols]

 1 substrate 2 transparent dielectric layer 3 recording layer 4 back transparent dielectric layer 5 organic protective layer

Claims (10)

[Claims] 1. On a transparent substrate or a transparent substrate having a transparent polymer layer formed on the recording layer side, in a part of the domain wall boundary region heated by laser light irradiation, the direction of the net remanent magnetization can be self-reversed. Using a magneto-optical recording medium having a recording layer formed of a perpendicular magnetization film containing a reversible rare-earth transition metal amorphous alloy, while transferring the magneto-optical recording medium, a bias magnetic field is applied in the bit recording direction, In a magneto-optical recording method in which direct writing of data is performed by irradiating laser light whose power level and / or pulse width is modulated between an erasing level and a writing level, the transparent substrate has a thermal conductivity of 0.5 [W / ( m · K)] or less, or the thermal conductivity of the transparent polymer layer formed on the transparent substrate is 0.5 [W / (m · K)] or less, and the rare earth composition ratio in the recording layer. (The atom%) is 20.0 ≦ X ≦ 28.0, and the transition metal of the recording layer is Fe or Fe and
Co, and the bias magnetic field Hex (O
e) is Hex ≧ 17 × (X−24) ² +100, and Hex ≦ 3
A magneto-optical recording method characterized by 0 × (X-24) ² +400. 2. The magneto-optical recording method according to claim 1, wherein the bias magnetic field Hex (Oe) is Hex ≦ 800. 3. The bias magnetic field Hex (Oe) is H ≧ 220, H
3. The magneto-optical recording method according to claim 1, wherein ex ≧ 130 × X-3160 and Hex ≦ 100 × X-2100. 4. The rare earth element in the recording layer is Gd and / or Tb.
The magneto-optical recording method according to any one of claims 1 to 3, wherein 5. The thermal conductivity of the transparent substrate or the thermal conductivity of the transparent polymer layer formed on the recording layer side of the transparent substrate is 0.2 [W /
(M · K)] or less.
The magneto-optical recording method described in any one of the above. 6. The magneto-optical recording method according to claim 1, wherein the transparent substrate is made of polycarbonate resin. 7. The light according to claim 1, wherein the transparent substrate is made of a glass material, and a transparent polymer layer made of an ultraviolet curable resin is formed on the recording layer side of the transparent substrate. Magnetic recording method. 8. The magneto-optical recording according to claim 1, wherein the compensation temperature Tcomp of the recording layer is in the range of 50 to 250 ° C. and the Curie temperature Tc is 100 to 350 ° C. method. 9. The magneto-optical recording method according to claim 8, wherein the compensation temperature Tcomp of the recording layer is in the range of 80 to 160 ° C. and the Curie temperature Tc is 200 to 250 ° C. 10. The perpendicular magnetic anisotropy constant Ku of the recording layer is from 2 to.
3. It is 3 (× 10 ⁶ erg / cc).
9. The magneto-optical recording method according to any one of 9 to 9.