JP2562219B2 - Magneto-optical disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention is a rewritable magneto-optical disk recording / reproducing apparatus with enhanced circular dichroic effect for a read-only or write-once optical disk reproducing apparatus. The present invention relates to a magneto-optical disk in which the magnetic Kerr effect is enhanced.

[Conventional technology]

Magneto-optical disks have been actively researched and developed in recent years as large-capacity memories capable of rewriting recorded information. Among them, those using a rare earth-transition metal alloy thin film as a recording medium have entered the stage of practical application as digital memories. There is. In the magneto-optical disk memory using the rare earth-transition metal alloy thin film, the signal detecting means generally uses the so-called magnetic Kerr effect, which is the rotation of the polarization plane of light generated when linearly polarized light is incident on the magneto-optical disk. The method of converting the rotation of the plane of polarization into light intensity with an analyzer is adopted.

On the other hand, when circularly polarized light is made incident, the intensity and phase of light differ depending on the direction of magnetization.
A signal detection method using the chromatic effect is also theoretically conceivable, and there is an example in which a differential signal at a bit boundary is detected using a garnet film (Journal of Applied Magnetics of Japan, 12, 1988). However, when a rare earth-transition metal alloy thin film is used as the recording medium, the circular dichroic effect is very small and cannot be practically used as it is.

[Problems to be Solved by the Invention]

However, a rewritable magneto-optical disk that is premised on reproduction by linearly polarized light cannot be reproduced by a reproduction-only (ROM) or write-once (WORM) optical disk reproducing apparatus that is currently in practical use. That is, a magneto-optical disk recording / reproducing apparatus is required to reproduce the magneto-optical disk. In addition, there is a problem that the number of necessary parts increases with the reproduction by linearly polarized light, high precision is required at the time of assembly, and the cost tends to increase as a whole.

[Means for solving the problem]

In order to solve the above problems, a magneto-optical disk according to the present invention includes a first transparent dielectric film (eg, AlN film), a perpendicular magnetization film (for example, rare earth-transition metal alloy such as TbFeCo) for recording information, The second transparent dielectric film has a multilayer film structure in which a second transparent dielectric film (eg, AlN film) and a reflective film (eg, Al) are sequentially stacked, and the first reproduction light is incident on the second transparent dielectric film. The circular dichroic effect is enhanced when the second reproduction light having a wavelength different from that of the first reproduction light is incident, and the magnetic Kerr effect is enhanced. I am trying.

[Action]

According to the above configuration, the first reproduction light is incident when the reproduction is performed by the reproduction-only type or the write-once type optical disc reproducing apparatus by utilizing the interference effect generated according to the wavelength of the incident reproduction light due to the multilayer film structure. The circular dichroic effect is enhanced, and when the information is recorded by the rewritable magneto-optical disk recording / reproducing apparatus, the second reproducing light is incident to enhance the magnetic Kerr effect, thereby recording the information recorded on the perpendicular magnetization film. Can be read.

For example, even in a read-only type or write-once type optical disc reproducing apparatus which irradiates an optical disc with circularly polarized light or elliptically polarized light having a large ellipticity, the circular dichroic effect is enhanced by the multilayer film structure having the above configuration. Therefore, it is possible to reproduce the change in magnetization, which is a bit pattern recorded by the magneto-optical disc recording / reproducing apparatus, as a change in light intensity.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

As shown in FIG. 1, the magneto-optical disk according to the present invention includes a transparent protective substrate 1, a first nitride film 2 as a first transparent dielectric film, a perpendicular magnetization film 3, and a second transparent dielectric film as a second transparent dielectric film. Two
It has a multilayer film structure in which the nitride film 4 and the reflective film 5 are sequentially laminated.

The transparent protective substrate 1 is made of glass having a thickness of 1.2 mm, for example. Other materials for the transparent protective substrate 1 include PC (polycarbonate) and PMMA (polymethyl methac).
rylate), APO [amorphous poly-olefin] and the like.

The first nitride film 2 has, for example, a refractive index of 2.05 and a film thickness of 50.
Using nm AlN.

The perpendicular magnetization film 3 has a refractive index of [(3.20-3.55i) when the reproduction wavelength of the light source used (not shown) is 780 nm.
± (0.05-0.03i)], and when the reproduction wavelength is 390 nm, TbFeCo with a film thickness of 20 nm is used, which has a refractive index of [(2.5-2.4i) ± (0.008-0.025i)]. The material of the perpendicular magnetization film 3 may be a rare earth transition metal alloy such as GdTbFe or DyFeCo, an oxide magnetic material such as MnBi, MnBiCu, Bi substituted garnet or Co ferrite, PtMnSb or Pt / Co instead of TbFeCo. .

The reflective film 5 has a refractive index of (2-7i) when the reproduction light wavelength λ is 780 nm, and the reproduction light wavelength λ is 390 nm.
When, the film thickness is 50 nm, which gives a refractive index of (0.78-2.2i).
The Al layer is used. As the material of the reflective film 5, the above-mentioned Al
Instead of, Au, Ag, Cu, Ni, or Pt may be used.

As a material for the first nitride film 2 and the second nitride film 4, instead of AlN, SiN, ZnS, SiAlON, AlNGe, Si
It can be either O.

In the magneto-optical disk according to the present invention, the multi-layered film structure enhances the multi-layered film structure circular dichroic effect and the magnetic Kerr effect according to the wavelength of the incident reproducing light.

Here, the second nitride film 4 (AlN) has a refractive index of 2.05.
Then, the calculation results of the magnetic Kerr rotation angle θ _k and ellipticity ε when the film thickness is changed from 0 to 200 nm will be described below with reference to FIGS. 2 and 3, respectively. The ellipticity ε
Is a value determined by the complex reflectance due to the difference in the direction of the magnetization recorded in the perpendicular magnetization film 3. This is the second nitride film 4
This is because the film thickness of has a greater influence on the appearance of the magnetic Kerr effect than other film thicknesses. The above calculation result is AEBell
(IEEE, QE-14 (7), 1978) and other methods were referred to.
Note that FIG. 2 shows the characteristics when the wavelength λ of the reproduction light is 780 nm, and FIG. 3 shows the characteristics when the wavelength λ of the reproduction light is 390 nm.

As shown in FIG. 2, by setting the film thickness of the second nitride film 4 to 80 nm (see the arrow in the figure), the ellipticity ε should be about 2.1 (deg) with respect to the reproduction light having the wavelength of 780 nm. You can On the other hand, as shown in FIG. 3, the film thickness of the second nitride film 4 is
A wavelength of 390 nm is obtained by setting 80 nm (see arrow in the figure).
The magnetic Kerr rotation angle θ _k is about 0.44 (de
g) can be These magnetic Kerr rotation angles θ _k ,
And the ellipticity ε, when the simple TbFeCo thick film single layer structure is used (the ellipticity ε is about 0.1 when the reproduction light wavelength λ is 780 nm).
4 (deg), the magnetic Kerr rotation angle θ _k is about 0.17 (deg) when the reproduction light wavelength λ is 390 nm), the ellipticity ε is about 4.8 times, and the circular dichroic effect is enhanced. , The magnetic Kerr rotation angle θ _k is about 2.6 times, and the magnetic Kerr effect is enhanced.

From the above, when the magneto-optical disk has a multilayer film structure having the thickness of each layer as in this embodiment, the wavelength λ of the reproduction light is
The bit pattern magneto-optically recorded by using 390 nm can be reproduced by a reproduction-only optical disk reproducing device, for example, a current CD player (the reproduction light wavelength λ is 780 nm).

Here, as another example of the magneto-optical disk according to the present invention, the film thickness of each layer has the same four-layer film structure as in the above-described embodiment.
For example, the first nitride film 2 is 80 nm, the perpendicular magnetization film 3 is 20 nm, the second
When the nitride film 4 is set to 20 nm and the reflective film 5 is set to 50 nm, the ellipticity ε is 0.61 (deg) when the reproduction light wavelength λ is 390 nm, and the magnetic Kerr rotation angle when the reproduction light wavelength λ is 780 nm. θ
_k becomes 1.3 (deg). These magnetic Kerr rotation angles θ _k ,
And the ellipticity ε are measured with a simple TbFeCo thick film single layer structure (when the wavelength λ of the reproduction light is 390 nm, the ellipticity ε is about 0.3).
4 (deg), when the reproduction light wavelength λ is 780 nm, the magnetic Kerr rotation angle θ _k is about 0.43 (deg)), the ellipticity ε is about 1.8 times and the circular dichroic effect is enhanced. , The magnetic Kerr rotation angle θ _k is about 3.0 times, and the magnetic Kerr effect is enhanced.

Therefore, if a magneto-optical disk having the thickness of each of the above layers is used, the bit pattern recorded by the magneto-optical disk recording / reproducing apparatus using the reproducing light with the wavelength of 780 nm is used only for the reproduction with the reproducing light with the wavelength of 390 nm. It can be played back by an optical disc reproducing apparatus of the type or the write-once type. Note that the reproduction light having the wavelength of 780 nm is obtained by using, for example, a semiconductor laser of 40 mW, and the reproduction light having the wavelength of 390 nm is
For example, it is obtained by SHG (second harmonic generator) with 3mW output. Incidentally, the wavelength of the reproduction light is not limited to the above-mentioned wavelengths of 780 nm and 390 nm (one wavelength is 1/2 times the other wavelength).

Here, FIG. 4 shows a schematic configuration diagram of an optical system used for circular dichroic reproduction. In a circular dichroic recording medium, since circularly polarized light is incident and recorded information is detected as a difference in intensity of reflected light, the optical system has almost the same structure as a reproducing device for CD and VD.

In the circular dichroic reproduction optical system, as shown in FIG. 4, the reproduction light (linearly polarized light) emitted from the semiconductor laser 11 is 1 /
It is converted into circularly polarized light through the four-wave plate 12 and irradiated on the magneto-optical disk 13, and the reflected light is finally incident on the photodetector 14 and converted into an electric signal that changes according to the intensity of the reflected light. It is supposed to be done. As described above, the configuration can be simplified as compared with the conventional optical system using the magnetic Kerr effect, except that the quarter-wave plate 12 for changing to circularly polarized light is arranged. As a result, when the circular dichroic effect is used for the detection of the magneto-optical signal, the configuration of the optical system can be simplified and the magneto-optical disk drive can be downsized as compared with the case where the magnetic Kerr effect is used. Weight reduction is possible.

〔The invention's effect〕

As described above, the magneto-optical disk according to the present invention has the first
The transparent dielectric film, the perpendicular magnetization film for recording information, the second transparent dielectric film, and the reflective film have a multilayer film structure sequentially laminated, and the film thickness of the second transparent dielectric film is The circular dichroic effect is enhanced when the first reproduction light is incident, and the magnetic Kerr effect is enhanced when the second reproduction light having a wavelength different from that of the first reproduction light is incident. The configuration is set.

Therefore, due to the multilayer structure having the above-described structure, the first reproduction light is incident on the reproduction-only type or write-once type optical disk reproducing apparatus by utilizing the interference effect of the incident reproduction light, and the circular dichroism is caused. The effect is enhanced, and when the information is reproduced by the rewritable magneto-optical disk recording / reproducing apparatus, the second
Since reproducing light is incident to enhance the Kerr effect, the reproduction-only type (ROM) currently in practical use is used as the change in the intensity of the light, which is the change in magnetization that is the bit pattern recorded by the magneto-optical disk recording / reproducing apparatus. , Or write-once type (WOR
M) It can be played back by the optical disk playback device. Further, by using the magneto-optical disk, the structure of the optical system for reproduction can be simplified, high precision is not required at the time of assembly, and the cost can be reduced as a whole. .

[Brief description of drawings]

1 to 4 show one embodiment of the present invention. FIG. 1 is a sectional view of a magneto-optical disk having a multilayer film structure according to the present invention. FIG. 2 is an explanatory diagram showing the dependence of the magnetic Kerr rotation angle θ _k and ellipticity ε of the magneto-optical disk according to the present invention on the thickness of the second nitride film when irradiated with reproducing light having a wavelength of 780 nm. is there. FIG. 3 is an explanatory diagram showing the dependence of the magnetic Kerr rotation angle θ _k and the ellipticity ε of the magneto-optical disk according to the present invention on the thickness of the second nitride film when irradiated with reproducing light having a wavelength of 390 nm. is there. FIG. 4 is a schematic configuration diagram showing an optical system used for circular dichroic reproduction. Reference numeral 1 is a transparent protective substrate, 2 is a first nitride film (first transparent dielectric film), 3 is a perpendicular magnetization film, 4 is a second nitride film (second transparent dielectric film), and 5 is a reflective film.

Front Page Continuation (72) Inventor Toshio Ishikawa 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture (56) References JP-A-60-63747 (JP, A) JP-A-60-129951 (JP) , A) JP 62-73442 (JP, A) JP 2-50335 (JP, A)

Claims (1)

(57) [Claims] 1. A first transparent dielectric film, a perpendicular magnetization film for recording information, a second transparent dielectric film, and a reflective film, which have a multi-layered structure sequentially laminated, and the second transparent film. The film thickness of the dielectric film enhances the circular dichroic effect when the first reproduction light is incident, and the magnetic Kerr effect when the second reproduction light having a wavelength different from that of the first reproduction light is incident. A magneto-optical disk characterized by being set so as to enhance.