JPH06101155B2 - Magneto-optical recording / reproducing method - Google Patents

Description

The present invention relates to a magneto-optical recording / reproducing method using different wavelengths for writing and reading.

[Conventional technology]

Conventionally, a rare earth-transition metal amorphous alloy is well known as a magneto-optical recording medium. For example, the TbFeCo ternary medium is
It is an excellent recording medium having a Curie temperature of about 170 ° C. and a large Kerr rotation. However, with a single magnetic layer, the recording sensitivity and the SN ratio (signal, inos) during reading are insufficient, preventing reflection on the surface of the magnetic layer to improve thermal efficiency, and at the same time the car rotation angle due to the car enhancement effect. It is necessary to have an antireflection film that can increase JP 56-1569
In the single-layer antireflection film proposed in Japanese Patent Laid-Open No. 43, etc., the minimum value of the reflectance and the enhanced Kerr rotation angle obtained in a practical dielectric material and film thickness range are limited, and the recording sensitivity and the The effect on improving the SN ratio during reading is limited. Further, in the antireflection of the multilayer structure proposed in Japanese Patent Laid-Open No. 59-227054, it is possible to reduce the minimum value of the reflectance to zero, and good recording sensitivity can be obtained and When the ratio is close to zero, a large Kerr rotation angle is obtained and a high S / N ratio is obtained. However, in order to read the recorded information without destroying it, there is an upper limit to the laser light intensity at the time of reading, and accordingly, a reflectance of a certain value or more with respect to the wavelength of the laser is required. On the contrary, if the Curie temperature of the medium is increased so that reading can be performed with a high light intensity, the recording sensitivity will be deteriorated.

[Problems to be solved by the invention]

In this way, when writing and reading to / from a magneto-optical recording medium with a light source of one wavelength, there is a limit to simultaneously improving the recording sensitivity and the SN ratio at the time of reading even in a medium having an antireflection film with a multilayer structure. However, there is no sufficient effect.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a magneto-optical recording / reproducing method in which the writing efficiency is improved and the SN ratio at the time of reading is improved.

[Means for solving problems]

In the magneto-optical recording / reproducing method of the present invention, a magneto-optical recording medium including a substrate, an antireflection film provided on the substrate, and a recording magnetic film provided on the antireflection film has a reflectance of the antireflection film. Writing is performed on the recording magnetic film at a small first wavelength, and reading is performed from the recording magnetic film at a second wavelength having a large reflectance with respect to the antireflection film.

[Action]

In the present invention, by using different wavelengths for writing and reading, the wavelength for writing has a small reflectance with respect to the antireflection film, for example, zero or its vicinity,
It is possible to increase the writing efficiency and obtain a sufficient reflected light intensity and a high SN ratio at the time of reading. Furthermore, by increasing the writing efficiency, it is possible to compensate for the decrease in recording sensitivity that accompanies an increase in the Curie temperature of the medium, achieve a low reflectance and increase the SN ratio by increasing the intensity of the laser light for reading.

〔Example〕

As the first wavelength and the second wavelength according to the present invention, for example, a semiconductor laser capable of switching and simultaneous oscillation at two wavelengths is disclosed in, for example, the publication {App1.Phys.Lett, Vo1,4.
9, No.24 (1629)} Obtained by the GaAs laser announced by Tokuda et al., Which switches at wavelengths of 804 nm and 844 nm.

Needless to say, the wavelengths oscillated by different lasers may be used.

As the substrate according to the present invention, for example, glass, plastic, or the like that is transparent to the writing and reading wavelengths is used.

If the antireflection film according to the present invention is, for example, a single layer,
As shown in FIG. 1, when the refractive index of the substrate is ns and the refractive index of the magnetic layer is nm, the refractive index n and the film thickness d of the antireflection film are (1)
It is generally known that it is given by a formula.

Here, λ indicates the wavelength of light, and ns <n <nm.

In reality, there are few suitable substances that satisfy the expression (1) and are suitable for practical use with respect to the values of ns and nm, and there is a limit to reducing the reflectance. 1 is a sectional view of a magneto-optical recording medium according to an embodiment of the present invention, in which (1) is a substrate and (2) is
Is an antireflection film, (3) is a recording magnetic film, and the arrow indicates the traveling direction of light.

Therefore, in order to increase the antireflection effect, it is effective to make the antireflection film into a multi-layered structure. For example, if two-layer films with refractive indices n ₁ and n ₂ are made under the condition of nd = λ / 4, the Reflectance is And to prevent reflection You can choose like. Thereby, the reflectance can be reduced to 1% or less. Generally, in order to enhance these effects, a method of alternately stacking high refractive index layers (H) and low refractive index layers (L) is adopted.

FIG. 2 is a sectional view of a magneto-optical recording medium according to another embodiment of the present invention, in which (22), (24) and (26) are high refractive index films,
(23) and (25) are low refractive index films.

Example 1 In FIG. 1, a glass or plastic substrate is used as the substrate (1), Si ₃ N ₄ is used as the antireflection film (2), and TbFeCo is used as the recording magnetic film (3). The Si ₃ N ₄ antireflection film has a minimum reflectance for the first wavelength of 800 nm,
The Kerr rotation angle is 70 nm, which is the maximum value, and the recording magnetic film is 10 nm.
It is 0 nm. FIG. 3 is a characteristic diagram showing the wavelength dependence of the reflectance R and the Kerr rotation angle θk for the magneto-optical recording medium according to the embodiment of the present invention.

In the figure, the horizontal axis is the wavelength (nm), and the vertical axis is the reflectance (%) and the Kerr rotation angle (deg.) For the reflectance of 17% at the first wavelength of 800 nm and the reflectance of 18.5% at the second wavelength of 850 nm.
Indicates. When this medium was written at the first wavelength and read at the second wavelength, the SN ratio at the time of reading was almost the same as that at the time of writing and reading at the second wavelength only, and the recording sensitivity at the time of writing was improved. I was able to improve it by about 0.5%.

However, as can be seen from FIG. 3, when the antireflection film is a single layer, it is attempted to obtain a physicochemically stable and highly durable film for an ordinary substrate (n = 1.5 to 1.8). Then the materials are limited. In addition, it is difficult for the reflectance to have a minimum value of 10% or less in a practical film thickness (thickness from the minimum film thickness at which a uniform film can be obtained to a film thickness at which film formation is not difficult), and the wavelength dependence is gentle. Therefore, a sufficient difference in reflectance between the first wavelength and the second wavelength cannot be obtained. Therefore, in order to fully exert the advantages of writing and reading at two wavelengths, it is desirable to use an antireflection film having a multilayer structure with a sharp rise in wavelength dependence.

Example 2 As the antireflection film in the magneto-optical recording medium, a high refractive index film such as a Ta ₂ O ₅ film having a refractive index of 2.0, a ZrO ₂ film having a refractive power of 1.9, and TiO ₂ are used.
₂ film, low refractive index film such as SiO ₂ film with a refractive index of 1.45, MgF ₂ film with a refractive index of 1.38, and 804 nm using a GaAs laser.
And get 844 nm.

Here, in FIG. 2, high refractive index films (22), (24) and (26) and low refractive indexes (23) and (25) are provided on a glass substrate or a plastic substrate (1) at a wavelength of 804 nm. A magneto-optical recording medium according to another embodiment of the present invention is provided in which five layers (HLHLH) are alternately provided with a film thickness of λ / 4, and further a TbFeCo ternary amorphous recording magnetic layer (3) is provided. A characteristic diagram showing the wavelength dependence of the reflectance is obtained in FIG.

In the figure, the horizontal axis represents wavelength (nm) and the vertical axis represents reflectance (%). As is clear from FIG. 4, the reflectance was reduced to about 4% at the first wavelength of 804 nm. On the other hand, the second wavelength 844n
The reflectivity at m is about 20 to 30%, and by writing at the first wavelength and reading at the second wavelength, the optimum light intensity at the time of writing is kept at about the same while maintaining the conventional read light intensity and high SN ratio. It could be reduced by 10%.

Moreover, by increasing the Curie temperature of the recording magnetic medium by about 5%, the conventional light intensity during writing is reduced by about 4% and the light intensity during reading is increased by about 4%.
The ratio could be increased by about 2%.

〔The invention's effect〕

As described above, the present invention provides a magneto-optical recording medium including a substrate, an antireflection film provided on the substrate, and a recording magnetic film provided on the antireflection film. By writing to the recording magnetic film at one wavelength and reading from the recording magnetic film at the second wavelength having a large reflectance with respect to the antireflection film, the writing efficiency is improved and the SN ratio at the time of reading is improved. It is possible to obtain a magneto-optical recording / reproducing method.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium according to an embodiment of the present invention, FIG. 2 is a sectional view of a magneto-optical recording medium according to another embodiment of the present invention, and FIG. 3 is an embodiment of the present invention. The magneto-optical recording medium according to the example has a reflectance (%) and a Kerr rotation angle (de
FIG. 4 is a characteristic diagram showing the wavelength (nm) dependence of g), and FIG. 4 is the reflectance (%) of the magneto-optical recording medium according to another embodiment of the present invention.
The characteristic view which shows the wavelength dependence of is shown. In the figure, (1) is a substrate, (2) is an antireflection film,
(3) shows a recording magnetic film. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] 1. A magneto-optical recording medium comprising a substrate, an antireflection film provided on the substrate, and a recording magnetic film provided on the antireflection film, at a first wavelength having a small reflectance with respect to the antireflection film. A magneto-optical recording / reproducing method of writing to the recording magnetic film and reading from the recording magnetic film at a second wavelength having a large reflectance with respect to the antireflection film. 2. The magneto-optical recording / reproducing method according to claim 1, wherein the antireflection film has a multi-layer structure. 3. The antireflection film has a minimum reflectance or a value close to it for the first wavelength for writing, and the second reflectance for reading
The magneto-optical recording / reproducing method according to claim 1 or 2, wherein the reflectance is about 20 to 30% with respect to the wavelength.