JPH0589540A - Magneto-optical recording medium and magneto-optical recording method - Google Patents

Abstract

(57) [Abstract] [Purpose] The problem in the method of overwriting by utilizing the temperature difference in the film thickness direction of the recording film during laser light irradiation was solved, and the temperature difference in the film thickness direction during recording was reduced. Also enables good overwriting, thins the recording film, and enables high-speed recording. [Structure] A magneto-optical recording medium having characteristics as shown in FIG. 2 and having a two-layer recording layer in which an exchange coupling force acts between both layers is used. One layer in advance for this medium
The magnetization direction of the (second magnetic layer) is aligned in one direction, and while applying a magnetic field in a predetermined direction, a laser beam whose power is modulated into at least two values corresponding to a recording signal is irradiated. When irradiated with laser light at a low power level, the other layer (first
The magnetization of the magnetic layer is oriented in the direction opposite to the magnetic field, and the irradiation of the laser beam at the high power level causes the magnetization of the other layer (first magnetic layer) to be oriented in the same direction as the magnetic field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording medium and a magneto-optical recording method.

[0002]

2. Description of the Related Art In the present magneto-optical recording method, when recording information,
There is a problem that it takes time because three steps of erasing, recording and collating are required. In order to solve this problem, the following overwrite method has been proposed.

(I) Magnetic field modulation system This is a system in which the intensity of the irradiation laser beam is kept constant and the polarity of the applied magnetic field is reversed at high speed according to the recorded information for recording (Japanese Patent Laid-Open Nos. 63-204532 and 63-63). -76135
No. In this method, since the polarity of the applied magnetic field must be reversed at high speed, the power for generating the magnetic field required for recording is increased from a position distant from the medium surface to some extent, and it is difficult to increase the frequency. Although a method of bringing the magnetic head close to the medium surface has also been proposed, this method loses the merit of non-contact inherent in the optical disk.

(Ii) Exchange-coupling two-layer film system A system in which a magneto-optical recording medium having a two-layer film of a rare earth metal-transition metal amorphous alloy as a recording film is used and overwrite is performed by utilizing exchange coupling between the two layers. (JP-A-62-62
-175948, etc.). Specifically, for example, TbF
Using a magneto-optical recording medium having a recording layer made of e and an auxiliary layer made of TbFeCo, initialization is performed, and then overwriting is realized by applying an external magnetic field and irradiating a laser beam having a different power. Is. This method has a problem that a large magnetic field is required for initialization.

In order to solve the above problem of the exchange coupling two-layer film system, a system which does not require initialization has been proposed (JJAP.,
Vol.283, 331-374 (1989)). This method uses the temperature difference in the film thickness direction of the recording film at the time of laser light irradiation to perform overwriting, but when the film thickness of the recording film becomes thinner, the temperature difference becomes smaller and Light becomes difficult. Therefore, it is disadvantageous for high-speed recording in which the recording film must be thin to improve recording sensitivity.

The present invention has been made in view of the above-mentioned circumstances of the prior art, and solves the above-mentioned problem in the method of overwriting by utilizing the temperature difference in the film thickness direction of the recording film at the time of laser light irradiation. However, it is possible to provide a magneto-optical recording medium and a magneto-optical recording method that enable good overwriting even when the temperature difference in the film thickness direction at the time of recording is small, make the recording film thin, and enable high-speed recording. To aim.

[0007]

To achieve the above object, according to the present invention, two or more magnetic layers made of an amorphous alloy containing a rare earth metal and an iron group transition metal as a main component are laminated on a substrate. Of these, at least two layers are perpendicular magnetization films, and when these two layers are the first magnetic layer and the second magnetic layer in the light incident direction, respectively, the first magnetic layer and the second magnetic layer are The layers are exchange-coupled, the Curie temperature of the second magnetic layer is higher than the Curie temperature of the first magnetic layer, and both the first magnetic layer and the second magnetic layer have a compensation point. There is provided a magneto-optical recording medium characterized in that the compensation temperature of the body layer is between room temperature and its Curie temperature. In the above structure, the compensation temperature of the first magnetic layer is the first
It is preferably 20 to 80 ° C. lower than the Curie temperature of the magnetic layer.

Further, according to the present invention, the above-mentioned magneto-optical recording medium is used, and the magnetization direction of the second magnetic layer is previously aligned in one direction, and the magnetic moment of the magnetic moment above the compensation point of the second magnetic layer is While applying a magnetic field in the opposite direction to the recording signal, a laser beam whose power is modulated into at least two values corresponding to the recording signal is emitted, and the temperature of the first magnetic layer is changed by irradiating the laser beam with a low power. The magnetic moment of the first magnetic layer is oriented in the direction opposite to the magnetic field by the exchange coupling force from the second magnetic layer and the temperature is raised to near the Curie temperature, and the first magnetic layer is irradiated with high-power laser light. Of the magneto-optical recording is performed by increasing the temperature of the magnetic field above the Curie temperature and orienting the direction of the magnetic moment of the first magnetic layer in the same direction as the magnetic field by the magnetic field. Recording method is provided.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, direct overwrite is performed by utilizing the temperature difference in the film thickness direction of the recording film during laser irradiation. First, the magneto-optical recording medium used in the present invention will be described.

FIG. 1 is a sectional view schematically showing the most basic layer structure of a magneto-optical recording medium used in the present invention. A first magnetic layer 2 and a second magnetic layer 3 are formed on a substrate 1. Are laminated so that the recording / reproducing laser beam 4 is incident from the substrate 1 side. First magnetic layer 2 and second magnetic layer 3
Is composed of a perpendicular magnetization film made of an amorphous alloy of a rare earth metal (Dy, Tb, Gd, Nd, etc.) and an iron group transition metal (Fe, Co, Ni), respectively, and an exchange coupling force between both layers 2 and 3. Is working. The magnetic characteristics are as shown in FIG. That is, the Curie temperature Tc ₂ of the second magnetic layer 3 is higher than the Curie temperature Tc ₁ of the first magnetic layer 2, and both the first magnetic layer 2 and the second magnetic layer 3 have compensation points. The compensation temperature Tcomp 1 of the magnetic layer ₁ is between room temperature Tr and its Curie temperature Tc ₁ . The difference ΔT between the compensation temperature Tcomp ₁ and the Curie temperature Tc ₁ is 20 to 80 ° C.
The effect is particularly large in this range. Examples of the combination of the materials of the first magnetic layer 2 and the second magnetic layer 3 that satisfy the above conditions include, for example, TbFeCo, TbFeCo, and DyF.
eCo and TbFeCo, TbDyFeCo and TbFeC
o, TbDyFeCo, TbDyFeCo, NdTbF
Examples thereof include eCo and TbFeCo, DyFeCo and GdTbFe, and the like.

As the substrate 1, glass, glass provided with a guide track of an ultraviolet curable resin, polycarbonate, polymethylmethacrylate, epoxy resin or the like can be used.

In addition to the layer structure shown in FIG. 1, as shown in FIG. 3, an intermediate layer, a protective layer, a reflective layer,
The dielectric layer, the guide track layer, the protective substrate, etc. may be provided in an appropriate combination, or the third magnetic layer, the fourth magnetic layer, etc. may be provided. Further, two sheets having these structures may be stuck together to form a double-sided recordable medium.

Next, a recording method using the magneto-optical recording medium having the above structure will be described. To describe the recording method,
In advance, the second magnetic layer 3 of the magneto-optical recording medium having the above structure
The magnetic moments of are aligned in one direction. As a method for aligning, there are methods such as applying a strong magnetic field, magneto-optical recording, and raising the temperature to apply a magnetic field. When recording,
A magnetic field Hex is applied in a direction opposite to the magnetic moment of the second magnetic layer 3 which is aligned in advance and is equal to or higher than the compensation point.
Then, as shown in FIG. 4, the recording laser power is changed at a minimum binary level in accordance with the recording signal. When changing at a binary level, a laser power value that raises the first magnetic layer 2 of the recording medium to a temperature Tb near its Curie temperature Tc ₁ is used as the low-level value Pb.
Here, Tc ₁ −50 ° C. ≦ Tb ≦ Tc ₁ + 30 ° C. is suitable. Further, as the value of the high level Pa, a laser power value that raises the temperature of the first magnetic layer 2 to a temperature Ta equal to or higher than its Curie temperature Tc ₁ is used. Where Tc ₁ + 30 ° C
≦ Tb ≦ Tc ₂ is suitable. However, since the temperature on the medium surface at the time of recording cannot be measured, these values are all estimated values. In addition to the method of changing the level as shown in FIG. 4, it is also possible to deal with it by changing the duty of the pulse train as shown in FIG.

In the laser light irradiation of the low power level Pb,
The temperature around the interface between the second magnetic layer 3 and the first magnetic layer 2 and the second magnetic layer 3 is lower than Tb, the exchange coupling force from the second magnetic layer 3 is strong, and the first magnetic layer The magnetic moment of 2 is directed in the direction opposite to the magnetic field Hex as shown in FIG. On the other hand, when irradiated with laser light of high power level Pa, the first magnetic layer 2 rises to Ta and crosses Tc ₁ in the cooling process.
The temperatures near the second magnetic layer 3 and the interface are almost equal,
Since the exchange coupling force from the magnetic layer 3 is weak, the magnetic moment of the first magnetic layer 2 is directed in the direction of the magnetic field Hex. Overwriting is possible as described above. In FIG. 6, arrows indicate the directions of the magnetic moment of each layer. Further, when the interface is shown by a broken line, the two layers are in exchange coupling, and when shown by a solid line, the interface domain wall exists. FIG. 6 shows the case where the magnetic moment of rare earth is dominant in the first magnetic layer and the magnetic moment of the iron group transition metal is dominant in the second magnetic layer.
The state in which the arrows of the two layers face in opposite directions is the state of exchange coupling.

[0015]

According to the present invention, because of the above construction, the following remarkable effects can be obtained. (1) A good overwrite is possible. (2) High-speed recording is possible without changing the magnetic field. (3) Non-contact and highly reliable. (4) Initialization by a magnetic field is not required, which is advantageous for downsizing the device. (5) Overwriting is possible even if the temperature difference in the film thickness direction of the recording film at the time of recording is small, the recording film can be made thin, recording sensitivity can be improved, and high-speed recording can be easily performed.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing the most basic layer structure of a magneto-optical recording medium used in the present invention.

FIG. 2 is a diagram showing magnetic characteristics of the recording medium of FIG.

FIG. 3 is a cross-sectional view showing another layer configuration example of a magneto-optical recording medium that can be used in the present invention.

FIG. 4 is a diagram showing an example of a laser light irradiation method.

FIG. 5 is a diagram showing another example of a laser light irradiation method.

FIG. 6 is a diagram illustrating a recording process in the present invention.

[Explanation of symbols]

 1 Substrate 2 First Magnetic Material Layer 3 Second Magnetic Material Layer 4 Laser Light

Front page continuation (72) Inventor Ms. Kurosawa 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A two or more magnetic material layer made of an amorphous alloy containing a rare earth metal and an iron group transition metal as a main component is laminated on a substrate, at least two of which are perpendicular magnetization films. When the layers are the first magnetic layer and the second magnetic layer from the light incident direction, respectively, the first magnetic layer and the second magnetic layer are exchange-coupled, and the Curie temperature of the second magnetic layer is It is higher than the Curie temperature of the first magnetic layer, both the first magnetic layer and the second magnetic layer have a compensation point, and the compensation temperature of the first magnetic layer is between room temperature and its Curie temperature. A characteristic magneto-optical recording medium. 2. The magneto-optical recording medium according to claim 1, wherein the compensation temperature of the first magnetic layer is 20 to 80 ° C. lower than the Curie temperature of the first magnetic layer. 3. The magneto-optical recording medium according to claim 1 or 2 is used, and the magnetization direction of the second magnetic layer is aligned in one direction in advance, and the magnetic moment is equal to or more than the compensation point of the second magnetic layer. While applying a magnetic field in the direction opposite to the direction of, the laser light whose power is modulated to at least two values corresponding to the recording signal is irradiated, and the temperature of the first magnetic layer is changed by the irradiation of the low power laser light. The magnetic moment of the first magnetic layer is oriented in the direction opposite to the magnetic field by the exchange coupling force from the second magnetic layer and the temperature is raised to near the Curie temperature. Magneto-optical recording capable of overwriting is performed by raising the temperature of the layer above its Curie temperature and orienting the direction of the magnetic moment of the first magnetic layer in the same direction as the magnetic field by the magnetic field. Recording method.