JPH06139633A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide a magneto-optical recording medium fit for magnetic field modulated recording and ensuring low recording noise in the case of recording in a small external magnetic field. CONSTITUTION:When a recording layer 4 having perpendicular magnetic anisotropy, a relatively low Curie temp. or magnetic compensation temp. and relatively high coercive force and a regenerating layer 3 having perpendicular magnetic anisotropy, a relatively high Curie temp. or magnetic compensation temp. and relatively low coercive force are formed as adjacent layers to obtain a magneto-optical recording medium, an auxiliary layer 5 having intrasurface magnetic anisotropy is formed so that it is brought into contact with one of the regenerating layer 3 and the recording layer 4. The Curie temp. or magnetic compensation temp. of the auxiliary layer 5 is higher than that of the recording layer 4 and the coercive force of the layer 5 is lower than that of the recording layer 4.

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 medium,
In particular, the present invention relates to a magneto-optical recording medium with little recording noise even when recording is performed under a small external magnetic field.

[0002]

2. Description of the Related Art In a magneto-optical recording method, recording and reproduction are performed by using light and a magnetic material, and therefore, both the non-volatility and rewritability of magnetic recording and the high-density recording property of optical recording are combined. Therefore, practical application was desired. recent years,
As a recording medium used in the magneto-optical recording method, a disk-shaped magneto-optical recording medium having a magnetic layer made of an amorphous rare earth-transition metal alloy thin film has been put into practical use, and has begun to be used for storing a large-capacity data file, for example. There is. In this case, in order to achieve both high sensitivity and high CN (carrier-to-noise) ratio, the magnetic layer is not composed of a single-layer magnetic film, but a recording layer for holding the recording and a reproducing for reading the recording. Adjacent layers are provided. In this case, both the recording layer and the reproducing layer are magnetic thin films having an easy axis of magnetization perpendicular to the film surface, and the reproducing layer is higher than the Curie temperature or the magnetic compensation temperature, and the coercive force is compared. The recording layer is higher.

The term "Curie temperature or magnetic compensation temperature" refers to the Curie temperature for a magnetic material having no magnetic compensation temperature, and the magnetic compensation higher than the ambient temperature and lower than the Curie temperature. A magnetic substance having a temperature means this magnetic compensation temperature. In any case, when the temperature is raised from the ambient temperature, the magnetization as a ferromagnetic material or a ferrimagnetic material disappears at least in appearance at this “Curie temperature or magnetic compensation temperature”.

Recording on these magneto-optical recording media is generally performed by the CAV (constant rotation speed) method. In the case of the CAV method, since the number of rotations of the medium is constant, the recording mark length is different between the inner peripheral portion and the outer peripheral portion of the disk-shaped medium, which limits the increase in recording capacity. Therefore, as a recording method capable of further increasing the capacity, recording with a fixed mark length M
-A CAV (modified CAV) method was devised. In this method, the recording frequency is changed between the outer circumference and the inner circumference of a disk-shaped magneto-optical recording medium to make the recording mark length constant. Further, a pit edge recording method has also been proposed in which information of "0" and "1" is associated with the ends of recorded pits.

In parallel with the increase in recording capacity, it is required to shorten the time required for recording / reproducing per unit recording amount. To meet this demand, it is necessary to realize a recording process that does not require an erasing operation, that is, an overwrite function. As a recording method capable of overwriting, there is a magnetic field modulation method that modulates a magnetic field according to data to be recorded. Promising.

[0006]

In the magnetic field modulation method, since a modulation magnetic field is generally generated using a coil, the external magnetic field applied to the medium during recording is relatively small. Therefore, the magneto-optical recording medium used in this system is desired to have high magnetic field sensitivity. However, in the magneto-optical recording media which have been studied so far, the recording noise tends to be larger when recording is performed with a smaller external magnetic field, as the magnetic field sensitivity is higher. For this reason, when recording is performed on such a magneto-optical recording medium by the magnetic field modulation method, the level of recording noise increases, and eventually a magneto-optical recording medium suitable for the magnetic field modulation method cannot be obtained. . An object of the present invention is to provide a magneto-optical recording medium which is suitable for recording by a magnetic field modulation method and has a small recording noise when recording with a small external magnetic field.

[0007]

The magneto-optical recording medium of the present invention has a recording layer having an easy axis of magnetization perpendicular to the film surface and a Curie temperature which is provided adjacent to the recording layer as compared with the recording layer. A reproducing layer having a high magnetic compensation temperature, a coercive force smaller than that of the recording layer, and an easy axis of magnetization perpendicular to the film surface, and a transparent layer that holds the recording layer and the reproducing layer and is disposed on the light incident side. In a magneto-optical recording medium having a substrate and a metal reflective layer for reflecting light that has entered from the transparent substrate side and has passed through the recording layer and the reproducing layer, a Curie temperature or a magnetic property higher than that of the recording layer is provided. An auxiliary layer having a high compensation temperature, a coercive force smaller than that of the recording layer and an easy axis parallel to the film surface is provided in contact with either the recording layer or the reproducing layer.

[0008]

The magneto-optical recording medium of the present invention is in contact with either the recording layer or the reproducing layer, has in-plane magnetic anisotropy, has a higher Curie temperature or magnetic compensation temperature than the recording layer, and has a high storage temperature. Since the auxiliary layer having a small magnetic force is provided, the recording noise when recording with a small external magnetic field is reduced, as will be apparent from the examples described later.

The recording layer, the reproducing layer, and the auxiliary layer are magnetic thin films, and when these layers are made of, for example, various metallic magnetic materials, they are easily affected by oxidation. Therefore, in order to prevent the oxidation and improve the light interference effect, between the magnetic multilayer film constituted by the recording layer, the reproducing layer and the auxiliary layer and the transparent substrate, and between the magnetic multilayer film and the metal reflective layer, It is preferable to provide a dielectric layer for each.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic sectional view showing the structure of a magneto-optical recording medium according to an embodiment of the present invention.

This magneto-optical recording medium is formed on an optically transparent transparent substrate 1 made of glass or plastic.
In order to obtain the light interference effect and the corrosion prevention effect, the first dielectric layer 2 made of an inorganic dielectric material is provided. This first
The reproduction layer 3, the recording layer 4, and the auxiliary layer 5 are sequentially laminated on the dielectric layer 2 of FIG. 1, and the corrosion of the reproduction layer 3, the recording layer 4, and the auxiliary layer 5 is further formed on the auxiliary layer 5. A second dielectric layer 6 is provided for preventing and producing an interference effect of light, and a metal reflective layer 7 is provided on the second dielectric layer 6. The metal reflective layer 7 reflects the light, which is transmitted from the transparent substrate 1 side and transmitted through the reproducing layer 3, the recording layer 4, and the auxiliary layer 5, and redirects it toward the transparent substrate 1 side when reproducing data. In addition to the magnetic Kerr effect, the magnetic Faraday effect is used to contribute to the reproduced signal and the C / N (carrier noise ratio) of the reproduced signal is improved. Transparent substrate 1
When laminating each of these layers on top, it is desirable to continuously form each layer without breaking the vacuum using a continuous film forming apparatus.

Now, the reproducing layer 3, the recording layer 4, and the auxiliary layer 5 will be described. Each of these layers is a magnetic thin film, the reproducing layer 3 and the recording layer 4 have an easy axis of magnetization perpendicular to the film surface, and the auxiliary layer 5 has an easy axis of magnetization parallel to the film surface. When the reproducing layer 3 and the recording layer 4 are compared, the Curie temperature or the magnetic compensation temperature of the reproducing layer 3 is higher, and the coercive force of the recording layer 4 is higher. The reproducing layer 3 and the recording layer 4 are made of, for example, an amorphous rare earth transition metal alloy. On the other hand, the auxiliary layer 5 is higher in Curie temperature or compensation temperature than the recording layer 4 and smaller in coercive force than the recording layer 4. Examples of the material of the auxiliary layer 5 include R-Fe-Co-Cr (R is one or more elements selected from rare earth elements), Pt-Co, Mn-Sb.
And so on.

For recording on this magneto-optical recording medium, a laser beam is irradiated from the transparent substrate 1 side while applying a modulation magnetic field according to a data signal to be recorded from the outside, the irradiation point is heated, and at this irradiation point. This is performed by orienting the magnetization of the recording layer 4 and the reproducing layer 3 in the direction according to the modulation magnetic field.
Further, in reproducing the recorded signal, a laser beam, which is weaker and linearly polarized than the laser beam used at the time of recording, is irradiated from the transparent substrate 1 side, and the deflecting surface of the reflected light has a magnetic Kerr effect and a magnetic The rotation is detected by the Faraday effect.

Next, an example in which the magneto-optical recording medium of the present invention is actually manufactured will be described in comparison with a comparative example.

Example 1 A pregrooved polycarbonate substrate having a diameter of 130 mm is used as the transparent substrate 1, and this substrate is mounted on a magnetron sputtering apparatus having a plurality of targets. First, in order to obtain an antioxidant effect and an interference effect. Then, a SiN film having a thickness of 1100Å was formed as the first dielectric layer 2. Next, G with a thickness of 100Å
Reproduction layer 3 consisting of d-Fe-Co-Cr film, thickness 200Å
Recording layer 4 made of Tb-Fe-Co-Cr, Gd-Fe-Co-Cr having a thickness of 20Å to form an in-plane magnetized film
The auxiliary layer 5 made of a film was laminated in this order. Then, on the auxiliary layer 5, a SiN film having a thickness of 300Å is formed as the second dielectric layer 6 in order to enhance the oxidation prevention and the interference effect.
Finally, the metal reflection layer 5 made of an Al film having a thickness of 450 Å was formed to complete the magneto-optical recording medium. Each of these layers is continuously formed without breaking the vacuum.

In this magneto-optical recording medium, both the reproducing layer 3 and the recording layer 4 exhibit perpendicular magnetic anisotropy, the Curie temperature of the reproducing layer 3 is 370 ° C., and the coercive force is 100 Oe.
The Curie temperature of the recording layer 4 is 190 ° C., and the coercive force is 8 kOe.
Met. The Curie temperature of the auxiliary layer 5 is 220 ° C.,
The coercive force was 50 Oe.

Next, the magneto-optical recording medium was subjected to a recording / reproducing test by a magnetic field modulation recording system. In this recording / reproduction test, the magneto-optical recording medium was rotated at a rotation speed of 2400 rpm, and a radius of 36 mm from the center was measured at 6.2 mm.
Recording was performed by changing the intensity of the modulation magnetic field to various values at a modulation (carrier) frequency of MHz, and then recording was performed to measure the carrier and noise levels. The change in these levels with respect to the magnitude of the modulating magnetic field became as shown in the graph of FIG.

(Example 2) As the auxiliary layer 5, a thickness of 20Å
Example 1 except that the in-plane magnetized film made of Pt-Co is used.
A magneto-optical recording medium was prepared with the same material and structure as described above.
At this time, the Curie temperature of the auxiliary layer 5 was 210 ° C., and the coercive force was 80 Oe. A recording / reproducing test was conducted on this magneto-optical recording medium in the same manner as in Example 1. The results are shown in the graph of FIG.

(Example 3) As the auxiliary layer 5, a thickness of 20Å
Example 1 except that the in-plane magnetized film of Mn-Sb of
A magneto-optical recording medium was prepared in the same manner as. At this time, the Curie temperature of the auxiliary layer 5 was 220 ° C., and the coercive force was 50 Oe. A recording / reproducing test was conducted on this magneto-optical recording medium in the same manner as in Example 1. The results are shown in the graph of FIG.

(Example 4) In Example 1, the reproduction layer 3, the recording layer 4, and the auxiliary layer 5 were laminated from the transparent substrate 1 side, but here, the auxiliary layer 5 and the reproduction layer 3 are laminated from the transparent substrate 1 side. A magneto-optical recording medium was prepared in the same manner as in Example 1 except that the recording layer 4 was laminated. The compositions and film thicknesses of the reproducing layer 3, the recording layer 4, and the auxiliary layer 5 are the same as in Example 1. A recording / reproducing test was conducted on this magneto-optical recording medium in the same manner as in Example 1. The result is shown in the graph of FIG.

(Comparative Example 1) A magneto-optical recording medium was prepared in the same manner as in Example 1 except that the auxiliary layer 5 was not provided, and this magneto-optical recording medium was subjected to a recording / reproducing test in the same manner as in Example 1. I did. The result is shown in the graph of FIG.

From the graphs of Examples and Comparative Examples shown in FIG. 2, a magneto-optical recording medium provided with an auxiliary layer (Example 1)
4), even when the intensity of the modulation magnetic field was as small as 50 Oe or less, the noise level was almost constant regardless of the modulation magnetic field and was small at -60 dB or less. On the other hand, in the magneto-optical recording medium having no auxiliary layer (Comparative Example 1), the noise level increased as the modulating magnetic field decreased, and the noise level increased to about -50 dB in the vicinity of 10 Oe. From the above,
By providing an auxiliary layer in contact with either one of the recording layer and the reproducing layer, having an easy axis of magnetization parallel to the film surface and having a higher Curie temperature or magnetic compensation temperature and a smaller coercive force than the recording layer, It has been clarified that recording noise is reduced when recording is performed with a small external magnetic field.

[0023]

As described above, the present invention has in-plane magnetic anisotropy in contact with either the recording layer or the reproducing layer and has a higher Curie temperature or magnetic compensation temperature than the recording layer. Further, by providing the auxiliary layer having a small coercive force, recording noise when recording with a small external magnetic field is reduced, and there is an effect that a magneto-optical recording medium capable of good recording can be obtained by the magnetic field modulation method.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a magneto-optical recording medium according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a result of measuring changes in a carrier level and a noise level in a reproduced signal with respect to the intensity of a modulation magnetic field.

[Explanation of symbols]

 1 Transparent Substrate 2 First Dielectric Layer 3 Playback Layer 4 Recording Layer 5 Auxiliary Layer 6 Second Dielectric Layer 7 Metal Reflective Layer

Claims (3)

[Claims] 1. A recording layer having an easy axis of magnetization perpendicular to the film surface and a Curie temperature or magnetic compensation temperature higher than that of the recording layer provided adjacent to the recording layer and higher than that of the recording layer. A reproducing layer having a small magnetic force and having an easy axis of magnetization perpendicular to the film surface, a transparent substrate that holds the recording layer and the reproducing layer and is arranged on the light incident side, and the recording medium is incident from the transparent substrate side. In a magneto-optical recording medium having a layer and a metal reflective layer for reflecting light transmitted through the reproducing layer, the Curie temperature or the magnetic compensation temperature is higher than that of the recording layer and the coercive force is higher than that of the recording layer. A magneto-optical recording medium, characterized in that a small auxiliary layer having an easy axis of magnetization parallel to the film surface is provided in contact with either one of the recording layer and the reproducing layer. 2. The magneto-optical recording medium according to claim 1, wherein the reproducing layer is arranged closer to the transparent substrate than the recording layer. 3. A dielectric layer is provided between a magnetic multi-layered film composed of a recording layer, a reproducing layer and an auxiliary layer and a transparent substrate, and between the magnetic multi-layered film and a metal reflective layer. The magneto-optical recording medium according to claim 1.