JPH05198020A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enable recording at a low magnetic field and to improve stability at the time of reproducing by forming a recording layer which has a specific or higher coercive force and the magnetic wall antimagnetic force smaller by a specific value or above than the coercive force at room temp. CONSTITUTION:A dielectric layer 12, the recording layer 13, a reflection film 15, a protective film layer 16, etc., are successively formed on a substrate 11. The recording layer 13 is formed of NdDyFeCo, etc., having >=5.0kOe coercive force and the magnetic wall antimagnetic force smaller by >=2.0kOe than the coercive force. The coercive force of the layer 13 is changed by changing the compsn. ratios of the NdDyFeCo and the magnetic wall antimagnetic force is lowered by executing reverse sputtering of the layer 12 before forming the layer 13 after the formation of the layer 12 and changing the time of the reverse sputtering. As a result, C/N is satd. by the small magnetic field at the time of recording and the stability of data at the time of reproducing is assured.

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 used in a magneto-optical memory or the like, and more particularly to a magneto-optical recording medium having a small magnetic field required for recording.

[0002]

2. Description of the Related Art In a ferromagnetic thin film having an easy axis of magnetization in a direction perpendicular to the film surface, a small inversion having a direction perpendicular to the film surface uniformly magnetized to S pole or N pole and a magnetic pole in the opposite direction. You can create magnetic domains. The presence or absence of this reversed magnetic domain is [1],
If it corresponds to [0], such a ferromagnetic thin film can be used as a high-density magnetic recording medium. Among such ferromagnetic thin films, a thin film having a large coercive force at room temperature and having a Curie point or magnetic compensation temperature relatively close to room temperature is generated by a light beam using the Curie point or magnetic compensation temperature. Since it is possible to record information by forming an inverted magnetic domain at an arbitrary position, it is used as a magneto-optical disk memory. With regard to the recording medium of this magneto-optical disk memory, in recent years, a new signal is directly superimposed on the previous signal without passing through the erasing process due to the need for shortening the processing time and the need for real-time recording of voice and moving images. There has been a strong demand for realization of a write-overwrite method, and several methods have already been proposed. As one of the overwrite methods, a magnetic field modulation recording method in which a laser beam is continuously irradiated with a constant power to modulate a magnetic field with a recording signal is regarded as the most promising.

[0003]

As described in the prior art, it is now strongly desired to develop a recording medium for overwrite used in the magnetic field modulation method. However, since the magnetic field required for recording is too high, the conventional recording media have problems such as a large device, slow access time, and large power consumption when actually used for magnetic field modulation. Was impossible. In addition, existing media that can be recorded in a low magnetic field have a problem in terms of data stability during reproduction. Therefore, in order to solve these problems, it is an object of the present invention to provide a magneto-optical recording medium for magnetic field modulation, which can record in a low magnetic field and is stable during reproduction.

[0004]

According to the present invention, in order to reduce the recording magnetic field, the domain wall coercive force of the recording layer is made smaller than the coercive force by 2.0 kOe or more to ensure the stability of data during reproduction. In addition, the coercive force is set to be 5.0 kOe or more.

[0005]

EXAMPLES The present invention will be described below based on examples.
The structure of the magneto-optical recording medium for magnetic field modulation used in the present invention is shown in FIG.
As shown in Fig. 1, a polycarbonate substrate 1 with a thickness of 1.2 mm
1, a dielectric layer 12 made of AlSiN, an NdDyFeCo recording layer 13, and an AlS layer by sputtering.
The iN protective layer 14 and the AlTi reflective film 15 were sequentially formed.
Here, the respective film thicknesses are 60 nm, 20 nm, 20 nm, 60 nm
Is. Further thereon, an ultraviolet curable resin was formed as a protective film 16 with a thickness of 10 μm by spin coating. Table 1 shows the coercive force and domain wall coercive force of the recording layers of the media used in Examples and Comparative Examples. However, the symbols in Table 1 and the symbols of the characteristic curves in FIGS. 2 and 3 are made to match.

The coercive force of the recording layer is NdDyFeCo.
Is changed by changing the composition ratio of, and after the dielectric layer 12 is attached in order to reduce the domain wall coercive force of the recording layer,
The reverse sputtering of the dielectric layer 12 is performed before attaching the recording layer 13, and the domain wall coercive force is changed by changing the reverse sputtering time.

With respect to these media, the rotation speed of the substrate is 1800 rpm, the recording radius position is 30 mm, and the recording frequency is 1.0 MH.
z, laser power during recording 7.0 mW, applied magnetic field during recording 1
Recording was performed at 0 Oe to 280 Oe, and reproduction was performed at a laser output of 1.0 mW.

FIG. 2 shows that the medium of the present invention has a recording magnetic field of 75 Oe.
It is shown that C / N is saturated in a magnetic field lower than the conventional one. The domain wall coercive force of the recording layer is 2.
Table 1 that does not satisfy the condition of the present invention that it is smaller than 0 kOe
Looking at the media of (5), (6), and (7),
Compared to the media of (1), (2), (3), and (4), C
A higher recording magnetic field is required for / N to saturate. Further, even if the mediums (1) and (3) having the same coercive force and smaller domain wall coercive force as the media (2) and (4) just satisfying the condition of the difference between the domain wall coercive force and the coercive force in the present invention,
No significant difference is observed between (2) and (4).

Next, in order to check the stability of the data during reproduction, the rotational speed of the substrate, the recording radial position, the recording frequency, and the laser output during recording are the same as above, and the applied magnetic field during recording is 250 Oe.
Recording was carried out under the conditions described above, and the laser was continuously irradiated with an output of 2.5 mW under an external magnetic field of 400 Oe for 0 to 60 minutes before the reproduction, and thereafter, was reproduced with a laser output of 1.0 mW. Figure 3
Indicates that the medium of the present invention has no problem in terms of stability when reproducing data. Looking at media (7), (8), and (9) whose coercive force is less than 5.0 kOe, it can be seen that the stability during reproduction is poor.

[0010]

[Table 1]

[0011]

By using the medium of the present invention, C / N is saturated with a smaller magnetic field during recording. Furthermore, the stability of the data during playback can be secured.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a magneto-optical recording medium for magnetic field modulation used in the present invention.

FIG. 2 is a characteristic diagram showing the recording magnetic field dependence of C / N of the medium of the present invention.

FIG. 3 is a characteristic diagram showing the dependency of C / N on irradiation time when a medium of the present invention is continuously irradiated with laser.

[Explanation of symbols]

 11 substrate 12 dielectric layer 13 recording layer 14 protective layer 15 reflective film 16 protective film

Claims (1)

[Claims] 1. The coercive force of the recording layer at room temperature is 5.0 kOe.
Above, and the coercive force of the domain wall is 2.0 kOe more than the coercive force.
A magneto-optical recording medium characterized by being smaller than the above.