JPH0664762B2 - Magneto-optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magneto-optical recording medium for recording / reproducing with semiconductor laser light.

2. Description of the Related Art In recent years, magneto-optical recording media that perform magnetic recording and reproduction with semiconductor laser light have been researched and developed for high density recording. The most basic type of magneto-optical recording medium is a heat-resistant transparent substrate such as quartz glass provided with a magnetic film that can be magnetized perpendicularly to the substrate surface by a method such as sputtering or vacuum deposition. . Here, as the material of the magnetic film, a magnetic substance made of an amorphous alloy of a rare earth metal and a transition metal (for example, a Tb-Fe alloy) is mainly used. Recording and reproduction on such a magneto-optical recording medium are performed as follows. That is, recording is performed by irradiating and heating the magnetic film with laser light modulated by a binary signal by utilizing the rapid change characteristic of the coercive force corresponding to the temperature change in the vicinity of the Curie temperature or the compensation temperature of the magnetic film to change the direction of magnetization. It is performed by reversing. In addition, for reproduction, polarized laser light is applied to the magnetic film thus recorded in reverse, and the polarization plane is rotated according to the direction of magnetization by utilizing the difference in the magneto-optical effect of the magnetic film. Is detected as.

In the above recording / reproducing method, the rotation angle of the polarization plane is further increased by the transmission of the reflected light, that is, sputtering is performed on the magnetic film for the purpose of obtaining a high reproduction output by the Faraday effect, and the Al is formed by a method such as vacuum deposition. It has also been proposed to use a recording medium provided with a reflective film of Cu, Ag, Pt, Au or the like.

Since all of the magneto-optical recording media using the amorphous alloy magnetic material described above have high recording sensitivity, there is an advantage that recording can be performed at high speed (at a frequency of 1 MHz) by using a semiconductor laser beam, but it is amorphous. Since a fine alloy magnetic material, especially a rare earth metal component, is susceptible to oxidative corrosion, a material without a protective film has a major drawback that the magneto-optical characteristics of the magnetic film deteriorate with time. In order to prevent this, a protective layer such as SiO, SiO ₂ is provided on the amorphous magnetic film (the formation method is generally vacuum deposition, sputtering, etc. as in the case of the magnetic film).
It is also known that when forming a magnetic film or a protective layer,
O ₂ remaining in the vacuum, on the magnetic film is oxidized and corroded with time by O _2, H ₂ O or the like contained in Tagetsuto of O _2, H ₂ O or the like and alloy magnetic body that is adsorbed on the substrate surface, This oxidative corrosion is further promoted by light and heat during recording. Further, the amorphous magnetic material has a drawback that it is easily crystallized by heat, which easily deteriorates the magneto-optical quantity characteristic. Since these defects are caused by the material of the magnetic film, the same applies to the recording medium provided with the protective film. Further, in this type of recording medium, the effect of improving the reproduction output by the reflection method was also insufficient.

It is an object of the present invention to provide a magneto-optical recording medium which has almost no deterioration in magneto-optical characteristics due to aging or heat and has high recording sensitivity and improved reproduction output.

Structure The present invention is a magneto-optical recording medium having a magnetic layer and a reflective layer on a heat-resistant substrate, the magnetic layer is represented by the general formula (1) (However, at least one of Me = Ba, Pb, Sr, M _I = Ga, A
at least one of l, Mn and Cr, M _II = Sc, Ta, T
i, Zn, In, Bi, Sm, Gd, indicates at least one or more kinds of Co, m, n ionic valence of each M _I and M _II, x, y substituted atoms each M _I and M _II Where A, x, and y are 5 ≦ A ≦ 6, 0 <x ≦ 1.0,
It is within the range of 0 <y ≦ 0.5. ) Or a metal oxide magnetic material represented by the following general formula (2) [Co _y ] [MxFe _1-x ] _3-y O ₄ (2) (providing at least one or more of M = Mn, Al, Cr) , X, y are the numbers of substitution atoms of Co and M, n is the ionic valence of M, and x and y are in the range of 0 <x ≦ 0.8 and 0.2 <y <1.0.) It is characterized in that it is made of a magnetic material, and that the magnetic layer is sandwiched by a translucent refractive index dielectric layer having an absolute refractive index of 1.7 or more.

The magnetic material or magnetic film used in the magneto-optical recording medium must have magneto-optical characteristics (appropriate Curie temperature, coercive force, etc.) that can be recorded and reproduced by semiconductor laser light, but particularly high recording sensitivity. In order to obtain the above, the Curie temperature Tc must be low, and the coercive force Hc must be appropriately high in order to maintain the recorded memory stable. Generally, the proper range of Tc and Hc is 100-350 ℃ for Tc, Hc
About 300 to 6000 is considered to be Elsted.

Conventionally, hexagonal and spinel metal oxide magnetic materials have been studied as magnetic bubble materials. Of the hexagonal ones, for example, those represented by the general formula (3) MeO · A [Fe ₂ O ₃ ] (3) (where Me and A are the same as those in the general formula (1)) are known, and spinel CoFe ₂ O ₄ is known in the system. The present inventor has paid attention to the fact that this type of magnetic material is an oxide itself, and therefore there is no fear of oxidative deterioration. However, these have a Kyrie temperature Tc
Since it is as high as 450 ° C. or higher, recording with a semiconductor laser beam is difficult as described above, and it cannot be applied as it is as a material for a magneto-optical recording medium. Therefore, the present inventor has conducted various studies, and when a part of the Fe atoms of the magnetic material of the general formula (3) and CoFe ₂ O ₄ is replaced with a specific other metal atom, Tc is lowered, and the Tc is decreased. The metal oxide magnetic material of the general formulas (1) and (2) satisfying the above-mentioned appropriate ranges of Tc and Hc required for the magnetic layer was found.

Further, the present inventor focused on using a material having a Faraday effect for the purpose of improving the reproduction output in a magneto-optical recording medium having a conventional reflective layer, and SiO, TiO ₂ , ThO ₂ , as the material. By using a high refractive index inorganic transparent dielectric material such as CeO ₂ , SiO ₂ and TiO, and by sandwiching the magnetic layer with these as a translucent high refractive index dielectric layer, it has been found that the above object can be achieved. It was the invention.

Next, the basic layer structure of the present invention will be described, centering on the characteristics of the magnetic layer sandwiched by the translucent high refractive index dielectric layer. 1 to 6 are schematic cross-sectional views of a magneto-optical recording medium, in which FIG. 1 shows one without a transparent high refractive index dielectric layer, and FIGS. 2 and 3 show magnetic layers. Of the present invention having a light-transmitting high-refractive-index dielectric layer on one surface thereof, and FIGS. 4 to 6 show the one according to the present invention in which the magnetic layer is sandwiched between the light-transmitting high-refractive-index dielectric layers. In the figure, 1 is a heat resistant substrate, 2 is a reflective layer, 3 is a magnetic layer,
4 is a protective layer, 5 and 5'are transparent high refractive index dielectric layers, 6 is a laser beam, 7 is a void layer, and 8 is a spacer.

FIG. 1 shows a recording medium in which a reflective layer 2, a magnetic layer 3 and a protective layer 4 are sequentially laminated on a heat resistant substrate 1. When the recording medium is irradiated with the laser beam 6 from a substantially vertical direction and the reflected light from the recording medium is received as a reproduction signal by, for example, a photodiode, the Kerr rotation angle of the reflected light from the magnetic layer 3 And the Faraday rotation angle transmitted through the magnetic layer 3, reflected by the reflective layer 2, and transmitted again by the magnetic layer 3. And will overlap. The Kerr rotation angle and the Faraday rotation angle are based on the rotation of the polarization plane depending on the magnetization direction of the magnetic layer 3. However, the Kerr rotation angle and the Faraday rotation angle have opposite magnetization directions and opposite polarization plane rotations. Direction.
Therefore It can be said that taking out only the good reproduction characteristics. FIG. 2 shows a light-transmitting high-refractive-index dielectric layer 5 provided on the magnetic layer 3. Here, the thickness of the transparent high refractive index dielectric layer 5 is d
₁ , the absolute refractive index is n, the refractive index of the magnetic layer 3 is n ₁ , and the refractive index of the protective layer 4 is n ₂ , d ₁ = λ (2N + 1) / 4n (λ
Is the wavelength of the laser light, When the above condition is satisfied, the reflected light from the translucent high refractive index dielectric layer 5 And reflected light from the magnetic layer 3 Will offset each other. FIG. 3 shows a transparent high refractive index dielectric layer 5 ′ provided between the reflective layer 2 and the magnetic layer 3. Here, when the thickness of the transparent high refractive index dielectric layer 5'is d ₂ , the refractive index of the magnetic layer 3 is n ₁ , and the refractive index of the reflective layer is n ₃ , If you are satisfied with Will be synergistic.

For this reason, when the translucent high refractive index dielectric layers 5 and 5'are provided so as to sandwich the magnetic layer 3 as shown in FIG. And offset the And can be synergistic. This makes it possible to increase the Faraday rotation angle and improve the reproduction output. It is desirable that the thicknesses of the translucent high refractive index dielectric layers 5 and 5'satisfy the above-mentioned d ₁ = λ (4N + 1) / 4n and d ₂ = λ (2N + 1) / 2n. The present invention can also be applied to those having a pre-groove as shown in FIGS. 5 and 6, and FIG. 5 shows that the above-mentioned layers are laminated on the substrate 1 with the pre-groove to obtain a light-transmitting high refractive index. A void layer 7 is provided between the dielectric layer 5 and the protective layer 4. In FIG. 6, the protective layer 4 has a pre-groove, and the air gap layer 7 is provided between the reflective layer 2 and the translucent high refractive index dielectric layer 5 ′, and the laser light is irradiated from the substrate 1 side. It

The magnetic layer of the present invention comprises the metal oxide magnetic material represented by the general formula (1) or (2), and specific examples thereof include the following.

These metal oxide magnetic materials include Fe ₂ O ₃ or Co ₂ O _{3 and the} like, a predetermined amount of an oxide of a predetermined metal atom is mixed and pulverized, and this is put into a mold of an appropriate shape and then molded, Made by sintering at a temperature of 1400 ° C.

In order to form a magnetic layer using the metal oxide magnetic material as described above, depending on the type of substrate, generally, the magnetic material is targeted on a transparent substrate at a substrate temperature of 400 to 600 ° C.
Then, it may be deposited to a film thickness of about 0.1 to 10 μm by a method such as sputtering, vacuum deposition, or ion plating.
In some cases, the magnetic layer may be formed at a substrate temperature of less than 400 ° C. However, in this case, after forming the magnetic layer, it is necessary to perform heat treatment at 400 to 700 [deg.] C. on this, while applying a magnetic field in some cases, for perpendicular magnetization. Here, as the material of the substrate, general glass, quartz glass; GG
G; Sapphire; Lithium tantalate; Crystallized transparent glass; Pyrex glass; Single crystal silicon with or without surface oxidation treatment; Al ₂ O ₃ , Al ₂ O ₃ .MgO, MgO, LiF, Y ₂
Transparent ceramic materials such as O ₃ · LiF, BeO, ZrO ₂ · Y ₂ O ₃ , ThO ₂ · CaO; inorganic materials such as inorganic silicon materials (eg Toshiba Silicon Tosguard, Sumitomo Chemical Sumiceram P) can be used. .

The translucent high refractive index dielectric layer is made of an inorganic transparent dielectric material having an absolute refractive index of 1.7 or more. Ce as an inorganic transparent dielectric material
O ₂ (2.2), ZrO ₂ (2.1), CeF ₃ (1.7), MgO (1.74), TiO ₂ (2.5), Al
₂ O ₃ (1.7), Bi ₂ O ₃ (1.9), WO ₃ (2.0), ZnS (2.1), SiO (2.0), Si ₃
N ₄ (2.3) etc. are used. The value in () shows an absolute refractive index. As in the case of the magnetic layer, the transparent high-refractive-index dielectric layer may be formed by depositing the above-mentioned materials by a method such as sputtering, vacuum deposition, or ion plating.

The reflection layer is the same as before, such as Cu, Al, Ag, Au, Ni, Pt, TeOx, TeC, SeA.
s, TeAs, TiN, TaN, CrN, cyanine dye, phthalocyanine dye, etc. The method of forming the reflective layer is exactly the same as the conventional method.
The material may be deposited to a film thickness of about 0.02 to 0.5 μm by a method such as sputtering, vacuum deposition, or ion plating. The reflective layer thus obtained has the function of reflecting the laser beam transmitted through the magnetic layer and increasing the Faraday effect by transmitting it through the magnetic layer again, and improving the reproduction output like the translucent high refractive index dielectric layer. Have

The protective layer is composed of SiO, SiO ₂ , TiN, SiN, TaN, acrylic resin, polyurethane resin, polycarbonate resin, polyether sulfone resin, polyamide resin, epoxy resin, etc. as in the conventional case. The method for forming the protective layer is the same as the conventional method,
In the case of resin, it is formed by a coating method, and in other cases, it is formed by adhering to a target surface with a film thickness of about 0.1 to 10 μm by a method such as vacuum deposition, sputtering, ion plating and the like.

Advantageous Effects According to the present invention, a metal oxide magnetic material that has no risk of oxidative deterioration in a magnetic layer and has an appropriate Curie temperature and coercive force as a material for a magneto-optical recording medium is used.
Since the magnetic layer is sandwiched by the translucent high-refractive-index dielectric layer, the magneto-optical characteristics are not deteriorated with time, and the recording sensitivity is high. In addition, a sufficient reproduction output can be obtained by improving the Faraday effect.

Example 1 On a heat-resistant quartz substrate, Ag having a film thickness of 500Å was deposited as a reflective layer by a vapor deposition method. A transparent high-refractive-index dielectric layer SiO having a film thickness of 1300 Å was deposited thereon by a sputtering method, and the above-mentioned NO.
A magnetic layer of 3000 Å was deposited by the sputtering method to form a magnetic layer, and a polymethylmethacrylate protective plate was bonded onto the magnetic layer to obtain a magneto-optical recording medium.

Example 2 A film having a thickness of 10 as a reflective layer was formed on a substrate with Ni electroformed guide track.
00Å Al was deposited by vapor deposition. CeO ₂ with a film thickness of 1000 Å was deposited on this by the sputtering method, and then the above NO.1 to NO.
A magnetic layer was formed by depositing 16 magnetic substances with a thickness of 5000Å to form a magnetic layer, and further CeO ₂ was deposited with a thickness of 1000Å, and this was bonded to a polymethylmethacrylate protective substrate via a spacer to obtain a magneto-optical recording medium.

Example 3 A SiO ₂ film having a film thickness of 1000 Å was deposited on a Vycor glass substrate by a sputtering method, then the magnetic materials of Nos. 1 to 16 were adhered to a film thickness of 5000 Å, and TiO ₂ was deposited to a film thickness of 1000 Å. It adhered to obtain a recording body. On the other hand, a film with a thickness of 1000 Å a was deposited as a reflective layer on a polymethylmethacrylate substrate with a guide track obtained by the indaction method by a vapor deposition method. A magneto-optical recording medium was obtained by bonding the reflective layer side of the pre-groove plastic substrate with the reflective layer and the translucent high refractive index dielectric layer TiO ₂ side of the recording body via a spacer.

Next, the magneto-optical recording medium obtained as described above is magnetized in one direction, and then the external magnetic field opposite to the direction of this magnetism is 0.
Recording was carried out by irradiating a semiconductor laser beam with an output of 20 mW with a pulse of 1 MHz and magnetically reversing while applying 5K erst, and in each case, a minute bit was recorded. Next, when a laser output of 2 mW was applied and the reflected light from the recording bit of the medium was received by the Abaracia Photodiode through the detector, a signal was reproduced.

[Brief description of drawings]

1 to 6 are schematic sectional views of a magneto-optical recording medium,
Of these, FIGS. 4 to 6 show those according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Heat resistant substrate, 2 ... Reflective layer 3 ... Magnetic layer, 4 ... Protective layer 5, 5 '... Translucent high refractive index dielectric layer

Claims (2)

[Claims] 1. In a magneto-optical recording medium having a magnetic layer and a reflective layer on a heat-resistant substrate, the magnetic layer has a general formula. (However, at least one of Me = Ba, Pb, Sr, M _I = Ga, A
at least one of l, Mn and Cr, M _II = Sc, Ta, Ti, Zn, In,
Bi, Sm, Gd, and Co represent at least one kind, m and n respectively represent the ionic valences of M _I and M _II , x and y respectively represent the number of substitution atoms of M _I and M _II , and A and x , Y is 5 ≦ A, respectively
It is within the range of ≦ 6, 0 <x ≦ 1.0 ≦, 0 <y ≦ 0.5. ) A magneto-optical recording medium comprising a metal oxide magnetic material represented by the formula (3), wherein the magnetic layer is sandwiched by a translucent high refractive index dielectric layer having an absolute refractive index of 1.7 or more. 2. A magneto-optical recording medium having a magnetic layer and a reflective layer on a heat-resistant substrate, wherein the magnetic layer has the general formula [Co _y ] [MxFe _1-x ] _3-y O ₄ (where M = Mn , Al, Cr at least one or more, x,
y is the number of substituted atoms of Co and M, n is the ionic valence of M, and x and y are in the range of 0 ≦ x ≦ 0.8 and 0.2 <y <1.0. ) A magneto-optical recording medium comprising a metal oxide magnetic material represented by the formula (3), wherein the magnetic layer is sandwiched by a translucent high refractive index dielectric layer having an absolute refractive index of 1.7 or more.