JP3082240B2 - Recording method for magneto-optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording method for a magneto-optical recording medium using a reflection film whose reflectance changes when irradiated with light.

[Problems to be Solved by the Prior Art and the Invention] A magneto-optical recording medium such as a magneto-optical disk records information by irradiating a recording layer with a laser beam to form a magneto-optical inversion portion, And the information is read by detecting the change in the Kerr rotation angle of the reflected light. Therefore, the magnitude of the bit read signal is determined only by the change in the Kerr rotation angle. Since the amount of change in the car rotation angle is small, conventionally, it has been attempted to enhance the car rotation angle by providing a reflective layer made of aluminum or the like. However, even if such an enhanced film is provided, C /
Figure of merit R ^1/2 · θ _K which is an index of the magnitude of N (however,
It is difficult to sufficiently increase R (reflectance, θ _K is Kerr rotation angle), and it is impossible to expect a dramatic improvement in C / N.

The present invention has been made in view of such circumstances, and has as its object to provide a recording method for a magneto-optical recording medium capable of obtaining a large C / N.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a substrate,
A magneto-optical recording layer whose magnetization direction can be changed by irradiation with light; and a reflecting layer whose reflectance with respect to irradiation light for reading changes according to heating conditions by irradiation with the light. A recording method for a magneto-optical recording medium, characterized in that information is recorded by simultaneously causing a change in the magnetization direction of a layer and a change in the reflectance of the reflective layer.

[Operation] In the present invention, the temperatures of the magneto-optical recording layer and the reflective layer are locally increased by light irradiation, and recording bits (pits) are formed in these layers. In this case, in the portion of the recording bit corresponding to the magneto-optical recording layer, the direction of magnetization changes due to an external magnetic field, as in ordinary magneto-optical recording. Changes with respect to. Therefore, at the time of reading, a change in the Kerr rotation angle due to a change in the direction of magnetization and a change in the reflectance of the reflective layer can be superimposed, and the figure of merit can be increased. Obtainable. Information recorded in this manner is realized by irradiating light with different conditions to restore the magnetization direction of the magneto-optical recording layer and the reflectivity of the reflective layer in the recording bit.

[Example] Hereinafter, an example of the present invention will be described in detail.

FIG. 1 is a partial sectional view of a magneto-optical disk according to one embodiment of the present invention. The magneto-optical recording medium according to this embodiment includes a substrate 1, an enhancement layer 2 formed of a transparent dielectric material having a high refractive index, a magneto-optical recording layer 3, a reflective layer 4, and a protective layer 5 in this order. It is configured to be laminated.

The substrate 1 is formed of a transparent and stable material, for example, a polymer such as glass or polycarbonate.

The enhance layer 2 is a layer formed for the purpose of enhancing the Kerr rotation angle of the magneto-optical recording layer 3, and is formed of, for example, ZnS containing O and N. This ZnS
The refractive index of light in a transparent region, for example, light having a wavelength of 633 nm, is greater than 2.41 and has desirable characteristics as an enhanced film having a Kerr rotation angle.

The magneto-optical recording layer 3 preferably has an easy axis of magnetization perpendicular to the layer surface, and is made of, for example, a rare earth-transition metal amorphous alloy such as TbFeCo. The thickness of this recording layer is 20
It is preferably from 500 to 500 °.

The reflection layer 4 is formed of a substance whose reflectivity changes reversibly by heat treatment, for example, AgZn. AgZn usually has a silvery white color, but when heated to 290 ° C or higher and quenched, the crystal structure changes to pink, and those in the pink state are heated to 140-285 ° C and slowly cooled. Then, it has the property that the crystal structure returns to its original state and turns into silver-white again.
FIG. 4 shows the spectral reflectance of AgZn, where a shows the spectral reflectance when exhibiting silver white, and b shows the spectral reflectance when exhibiting pink. As is clear from the figure, the wavelength range (78
0 to 905 nm), there is a change in reflectance of 10% or more.

The protective layer 5 has a function of protecting the magneto-optical recording layer 3 and the reflective layer 4, and is, for example, ZnS containing O and N.
It is formed with.

When information is recorded on such a magneto-optical recording medium, a laser beam having a predetermined wavelength is irradiated as irradiation light onto the magneto-optical recording layer 3 and the reflection layer 4 from the substrate 1 side. In this case, a semiconductor laser can be used. Then, recording bits (pits) 7 are formed on the recording layer 3 and the reflection layer 4 by the irradiation of the laser beam. That is, the temperature of the portion corresponding to the recording layer 3 of the recording bit 7 rises to near the Curie temperature due to the light irradiation, and the magnetization is reversed under the influence of the external magnetic field. The color is changed from silver white to pink by heating and quenching by light irradiation.

In the case of this embodiment, the crystallization temperature (about 330 ° C.) of the TbFeCo alloy used for the magneto-optical recording layer 3 and the reflection layer 4
In addition to the fact that the transition temperature (290 ° C.) of AgZn used in the above is close to each other, and since the recording medium is a disk, it is necessary to strictly control the heating temperature by laser beam irradiation. For example, when recording information with constant writing conditions such as laser power, pulse width, and intensity of an external magnetic field, the rotation speed of the magneto-optical disk is switched according to the track position where information is to be recorded, and the linear velocity is changed. Are performed in the same manner. When recording information while keeping the rotation speed of the magneto-optical disk constant, the power of the laser and / or the intensity of the external magnetic field are also switched according to the track position where the information is to be recorded. The laser beam may be focused on the magneto-optical recording layer. However, as described above, the crystallization temperature of the TbFeCo alloy and the dislocation temperature of AgZn are close to each other. Temperature control becomes easy.

Information is reproduced by irradiating the recording layer with a relatively low-power laser beam using a semiconductor laser or the like, receiving the reflected light through a photoelectric conversion element via an analyzer, and converting the reflected light into an electric signal. Done. The C / N ratio of the reproduced signal is represented by a figure of merit R ^1/2 · θ _K (where R is the reflectance, θ _K
Is proportional to the car rotation angle). In the case of this embodiment, the recording layer 3
In the above, the direction of the Kerr rotation angle is reversed between the recording bit and the non-recording part, so that the amount of reflected light passing through the analyzer is different. Also, in the reflection layer 4, the recording bit and the non-recording part are as described above. Therefore, when a semiconductor laser is used as a reproduction laser, as described above, the reflectance for the laser beam wavelength range (780 to 905 nm) is 10%.
% Different. Therefore, in the reproduced signal obtained by photoelectrically converting these, both the change in the Kerr rotation angle and the reflectance change, and the conventional signal reproducing information only by the change in the Kerr rotation angle is substantially used. C / N than optical disc
Can be dramatically increased. The reflectivity of a conventional reflective layer formed of aluminum or the like does not change with the heat generated by the writing laser, and as a result, the reflectivity does not change due to light irradiation.

Erasure of information is performed by irradiating a laser beam with lower power than at the time of writing. In addition, since the laser beam at the time of erasing must be applied to a range that completely covers the recording bit, the pulse width is made wider than that at the time of recording. Along with this erasing laser beam irradiation,
By applying a magnetic field in a direction opposite to the external magnetic field at the time of recording, the magnetization of the portion of the recording bit 7 corresponding to the recording layer 3 is reversed, and is magnetized in the same direction as the non-recording portion. Further, since the portion of the recording bit 7 corresponding to the reflection layer 4 is heated to a lower temperature than during recording, the portion is gradually cooled and the color tone returns to the original silver white.

FIG. 3 schematically shows the process of recording and erasing at this time. Figure 3 shows time on the horizontal axis and temperature on the vertical axis.
It shows the recording and erasing laser pulses and also shows the direction of the external magnetic field. As shown in this figure, since the recording laser beam has a large power, it is heated to a high temperature and rapidly cooled. Also, since the erasing laser beam has a small power, it is heated to a lower temperature and relatively gradually cooled. By this heating condition, the reflection layer 4
AgZn reversibly changes between silver-white and pink. Further, at the time of such irradiation of the recording and erasing laser beams, an external magnetic field is applied in the illustrated direction, so that the magnetization of the recording bit portion of the recording layer 3 is reversed to a desired direction, Recording and erasing are also performed on the recording layer 3. Even if the order of lamination of the magneto-optical recording layer and the reflective layer is reversed, the same effect as in the above-described layer configuration can be obtained by setting the thickness of the reflective layer to 500 mm or less.

FIG. 2 is a partial sectional view showing a magneto-optical disk according to another embodiment. In this embodiment, a heat insulating layer 6 made of a dielectric such as ZnS containing O and N is interposed between the magneto-optical recording layer 3 and the reflective layer 4. The presence of the heat insulating layer 6 makes it possible to make the recording layer 3 and the reflective layer 4 different in local rise temperature due to laser irradiation. Therefore, according to this structure, the dislocation temperature of the color tone (reflectance) of the magneto-optical recording layer 3 such as AgZn as a material constituting the reflective layer is determined by setting the laser beam focusing position to the reflective layer 4. It is possible to use even a substance having a color tone transition temperature higher than the use limit temperature of the magneto-optical recording layer 3 as well as being close to the use critical temperature (crystallization temperature of the TbFeCo alloy). Such materials include CuAlNi alloys and Cu
AlAg alloy and the like. Moreover, in the optical disk having such a configuration, since recording bits can be formed on the recording layer 3 and the reflection layer 4, four recording states can be created by independently controlling the temperature of the formation of these bits. The recording density can be increased. In the case of this embodiment, as described above, the thickness of the
By setting the following, the same effect can be obtained even if the order of lamination of the magneto-optical recording layer and the reflective layer is reversed.

[Effects of the Invention] According to the present invention, when reading information, a change in the Kerr rotation angle due to a change in the direction of magnetization can be superimposed on a change in the reflectance of the reflective layer, thereby increasing the figure of merit. Can achieve a dramatic increase in C / N.
Therefore, it can be used as a recording method for an analog recording image file memory that requires a high C / N.

[Brief description of the drawings]

1 and 2 are partial sectional views showing a magneto-optical disk according to an embodiment of the present invention, and FIG. 3 shows a heating temperature and a pulse width by a laser beam during recording and erasing, and a direction of an external magnetic field. FIG. 4 is a diagram showing the spectral reflectance of AgZn. 1; substrate, 2; enhanced layer, 3; magneto-optical recording layer, 4; reflective layer,
5; protective layer, 6; thermal insulation layer, 7; recording bit

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI G11B 11/105 586 G11B 11/105 586B

Claims (6)

(57) [Claims] 1. A light comprising: a substrate; a magneto-optical recording layer whose magnetization direction can be changed by irradiation with light; and a reflection layer whose reflectance with respect to irradiation light for reading changes depending on heating conditions by irradiation with the light. In a recording method for a magnetic recording medium, information is recorded by simultaneously generating a change in the direction of magnetization of the magneto-optical recording layer and a change in the reflectance of the reflective layer by the light irradiation. Media recording method. 2. The recording method for a magneto-optical recording medium according to claim 1, wherein the reflection layer is formed of AgZn, CuAlNi, or CuAlAg. 3. The magneto-optical recording medium according to claim 1, further comprising an enhancement layer provided between the substrate and the magneto-optical recording layer for enhancing a Kerr rotation angle. Recording method. 4. A recording method for a magneto-optical recording medium according to claim 1, wherein said magneto-optical recording layer is provided between said substrate and said reflective layer. 5. A recording method for a magneto-optical recording medium according to claim 1, wherein said reflection layer is provided between said substrate and said magneto-optical recording layer. 6. A recording method for a magneto-optical recording medium according to claim 1, wherein said magneto-optical recording layer is formed of a rare earth-transition metal amorphous alloy.