JPH04370552A - Magneto-optical recording method - Google Patents

Abstract

PURPOSE:To facilitate medium constitution and to attain overwriting with good reliability with a single laser beam, single bias magnetic field or without bias magnetic fields. CONSTITUTION:The magneto-optical recording medium constituted by using a ferromagnetic film 3 which exhibits perpendicular magnetic anisotropy and a diaferromagnetic film 4 which exhibits a diaferromagnetic phase at room temp. and exhibits a ferromagnetic phase by generating magnetic phase transition at about the Curie temp. of this ferromagnetic film 3 on a base 1 is used. Recording is executed by irradiating the medium with a laser under such conditions under which the ferromagnetic film 3 heats up to the temp. lower than the temp. to generate the magnetic phase transition. Erasing is executed by irradiating the medium with the laser under such conditions under which both of the ferromagnetic film 3 and the diaferromagnetic film 4 heat up to the temp. above the temp. to generate the magnetic phase transition. The recorded information is reproduced by irradiating the medium with the laser beam of the power than at the time of erasing.

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 method.

0002

[Prior art and problems to be solved by the invention] In recent years,
As rewritable optical recording media, magneto-optical recording media that utilize the magneto-optical effect have been actively researched and developed, and some have even been put into practical use. This magneto-optical recording medium has the advantages of large-capacity, high-density recording, non-contact recording and playback, and ease of access, as well as the ability to overwrite, making it suitable for document information files, video/still image files, and computers. It is expected to be used for memory, etc. In order to make a magneto-optical recording medium a recording medium with performance equal to or better than that of a magnetic disk, there are several technical issues, and one of the major ones is overwriting technology. Currently proposed overwriting techniques are broadly classified into magnetic field modulation methods and optical modulation methods (multi-beam method, two-layer film method, etc.) depending on the recording method.

The magnetic field modulation method is a method in which recording is performed by reversing the polarity of the applied magnetic field depending on the recorded information. In this method, since the magnetic field must be reversed at high speed, it is necessary to use a floating type magnetic head, making it difficult to exchange the medium.

On the other hand, the optical modulation method is a method in which recording is performed by turning on/off or modulating the intensity of the irradiated laser beam depending on the recording information. Among these methods, the multi-beam method is a pseudo-overwrite method that uses two to three laser beams and reverses the direction of the magnetic field every rotation to record/erase on a track-by-track basis, but the device configuration is complicated. It has disadvantages such as increasing the cost and increasing the cost. In addition, in the two-layer film method, the recording layer of the magneto-optical recording medium is a two-layer film,
This technique attempts to achieve overwriting, and is disclosed in, for example, Japanese Patent Laid-Open No. 175948/1983. The method described in the publication uses a magneto-optical recording medium equipped with a two-layer recording layer, for example, a memory layer made of TbFe and an auxiliary layer made of TbFeCo, and after initialization, the external magnetic field is applied. This is an attempt to achieve overwriting by irradiating laser beams with different application and powers. That is, in this method, prior to recording, the magnetization of the auxiliary layer is aligned in one direction using an initializing magnetic field, and a high-power laser beam is irradiated to raise the medium temperature T such that T>Tc2 (Tc2 is the Curie temperature of the auxiliary layer). Recording is performed by heating the medium to a certain temperature, applying a recording magnetic field (in the opposite direction to the initializing magnetic field) to reverse the magnetization of the auxiliary layer, and transferring the magnetization to the memory layer as the medium cools. , the medium temperature is adjusted to Tc1<T<Tc2 (Tc
1 is the Curie temperature of the memory layer), and erasing is performed by transferring the magnetization direction of the auxiliary layer to the memory layer. Therefore, this method has problems such as difficulty in media design.

The present invention solves the above-mentioned drawbacks of the prior art and provides a magneto-optical recording method that allows for simple media design and reliable overwriting using a single laser beam, a single magnetic field, or no magnetic field. The purpose is to

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a memory layer made of a ferromagnetic film exhibiting perpendicular magnetic anisotropy, and a memory layer consisting of a ferromagnetic film exhibiting perpendicular magnetic anisotropy, and a memory layer comprising a ferromagnetic film exhibiting perpendicular magnetic anisotropy, and During recording, a magneto-optical recording medium is used which has a recording layer consisting of a two-layer film laminated with an auxiliary layer consisting of an antiferromagnetic film that undergoes a magnetic phase transition and exhibits a ferromagnetic phase at a temperature near the Curie temperature of the memory layer. , laser irradiation is performed under conditions such that only the memory layer is heated to a temperature below the temperature at which the magnetic phase transition of the antiferromagnetic film occurs, and during erasing, both the memory layer and the auxiliary layer undergo the magnetic phase transition of the antiferromagnetic film. Provided is a magneto-optical recording method characterized in that laser irradiation is performed under conditions such that the temperature is raised to a temperature higher than that at which .

The present invention will be explained in detail below with reference to the drawings. The magneto-optical recording medium used in the present invention has a memory layer consisting of a ferromagnetic film exhibiting perpendicular magnetic anisotropy, and a temperature near the Curie temperature of the memory layer exhibiting an antiferromagnetic phase at room temperature and higher than room temperature. It is formed by laminating an auxiliary layer made of an antiferromagnetic film that causes a magnetic phase transition and exhibits a ferromagnetic phase. FIG. 1 shows an example of the configuration of such a magneto-optical recording medium. This recording medium has a protective film 2 (thickness: 100 Å to 5000 Å) made of Si3N4, SiO, SiO2, etc. formed on a transparent support 1 made of glass, plastic, ceramics, etc., and exhibits perpendicular magnetic anisotropy. Ferromagnetic film 3 (film thickness 100 Å to 500 Å
0 Å), on which an antiferromagnetic film 4 exhibits an antiferromagnetic phase at room temperature and undergoes a magnetic phase transition at a temperature higher than room temperature and near the Curie temperature of the ferromagnetic film 3 to exhibit a ferromagnetic phase. (
A protective film 5 (thickness: 100 Å to 10,000 Å) made of Si3N4, SiO, SiO2, etc. is provided thereon.
The film thickness is 100 Å to 5000 Å). Each film can be formed by sputtering, vapor deposition, ion plating, or the like. The ferromagnetic film 3 is made of, for example, Tb-F.
e, Gd-Fe, Dy-Fe, Gd-Tb-Fe, Tb
-Dy-Fe, Gd-Dy-Fe, Tb-Fe-Co,
Gd-Fe-Co, Dy-Fe-Co, Tb-Dy-F
e-Co, Gd-Tb-Fe-Co, Gd-Dy-Fe
It can be composed of a rare earth-transition metal based amorphous film such as -Co or a polycrystalline film such as Co-Pt or Co-Cr. The antiferromagnetic film 4 is made of, for example, Mn2Sb,
It can be configured using (Mn)pSb(Y)q (where Y=Cr, Ti, V, etc., p=2-q). In this case, the material is preferably selected so that the thermal conductivity of the antiferromagnetic film 4 is lower than that of the ferromagnetic film 3. Further, the ferromagnetic film 3 and the antiferromagnetic film 4 must have the temperature characteristics of coercive force as shown in FIG. That is, the Curie temperature of the ferromagnetic film 3 is Tc1, the Curie temperature of the antiferromagnetic film 4 is Tc2, and the magnetic phase transition temperature of the antiferromagnetic film 4 is Tp.
c. When the ferromagnetic film 3 is irradiated with a laser and the temperature is raised to around Tc1, the demagnetizing field from the surrounding magnetization that acts on that part is Hd, the bias magnetic field in the opposite direction to Hd is Hex, and further ferromagnetic The relationship with the coercive force Hc1 of the film 3 is Hc1=
The temperature at which Hd-Hex is obtained is Ta, and the temperature at which the relationship with the coercive force Hc2 of the antiferromagnetic film 4 becomes Hc2=Hd-Hex (T
When Tb is a temperature higher than pc, the following relationship holds true. When Ta>T, Hc1>Hd-Hex When Ta≦T<Tpc, Hc1≦Hd-HexTpc≦
When T<Tb, Hc2≧Hd−Hex

The layer structure of the magneto-optical recording medium of the present invention is not limited to that shown in FIG. 1, and various modifications and changes are possible.
For example, a reflective film may be provided on the protective film 5, or the protective films 2 and 5 may be appropriately removed. Further, an intermediate layer may be provided between the ferromagnetic film 3 and the antiferromagnetic film 4 to adjust the magnetic interaction between the two layers.

Next, a magneto-optical recording method using the above magneto-optical recording medium will be explained. Recording is performed under laser irradiation conditions such that only the ferromagnetic film 3 is heated to a temperature of Ta≦Tw<Tpc (Tw: temperature during recording) as shown in FIG. 3(a). At this time, the antiferromagnetic film 4 has a magnetic phase transition point Tpc
Since the temperature is lower, the antiferromagnetic phase apparently has zero magnetization and the ferromagnetic film 3 is not affected. Here, the part of the ferromagnetic film 3 that is irradiated with the laser is influenced by the reflected field Hd from the surrounding magnetization, and is magnetized in a direction opposite to the saturation direction (downward in the figure), and in the process of decreasing the film temperature. be frozen. During recording, a bias magnetic field Hex acts in the opposite direction to the demagnetizing field, but since Hex is set to a value smaller than Hd or to 0, recording is always performed in the direction of the demagnetizing field.

Erasing is performed by irradiating the ferromagnetic film 3 and the antiferromagnetic film 4 with a laser so that the temperature is such that Tpc≦Te<Tb (Te: temperature during erasing) as shown in FIG. 3(b). . At this time, a magnetic phase transition occurs in the antiferromagnetic film 4, changing from the antiferromagnetic phase to the ferromagnetic phase, and moving in the saturation direction (upward in the figure).
The magnetization of the antiferromagnetic film 4 is transferred to the ferromagnetic film 3 as the film temperature decreases. At this time, the ferromagnetic film 3
If the thermal conductivity of the antiferromagnetic film 4 is made higher than that of the antiferromagnetic film 4, the temperature of the ferromagnetic film 3 will drop quickly, whereas the temperature of the antiferromagnetic film 4 will drop slightly slower. The magnetization of 4 exists until the magnetization of the ferromagnetic film 3 becomes large and is not recorded. Further, the bias magnetic field Hex is not necessary if the magnetization of the antiferromagnetic film 4 is sufficiently large. The temperature range for erasing is Tpc≦Te<Tb, and when the temperature is raised above Tb, the magnetization direction of the antiferromagnetic film 4 changes in the direction of the demagnetizing field Hd (
It is not possible to raise the temperature above Tb because it will point downward (in the figure) and will not be able to be erased. Further, reproduction is performed by irradiating a laser at a power level such that the medium temperature is below Ta.

[0011]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples illustrated herein. Grooved polycarbonate substrate (diameter 13
The following films were sequentially laminated on the recording medium (0 mm) by RF binary magnetron sputtering method in vacuum to obtain a recording medium. Protective film: Si3N4 film (1000 Å) Ferromagnetic film: Dy0.2 (Fe0.90Co0.10)0
．． 8 films (600 Å) Antiferromagnetic film: Mn1.8SbCr0.2 film (1500 Å
) Protective film: Si3N4 film (1000Å)

The Curie temperature Tc1 of the ferromagnetic film, the Curie temperature Tc2 of the antiferromagnetic film, the magnetic phase transition temperature Tpc, and Ta and Tb shown in FIG. 2 were determined as follows. Tc1=120℃ Tc2=240℃ Tpc=110℃ Ta≒70℃ Tb≒180℃

[0013] The recording medium obtained as described above was processed at a linear velocity of 10
The device was driven at a speed of 1 MHz per second, an external magnetic field Hex = 100 Oe (same direction during recording and erasing) was applied, and the irradiation laser power was changed as shown below during recording, erasing, and reproducing. Signals were recorded and reproduced, and recording/reproduction characteristics were evaluated. Laser power during recording: 4 mW Laser power during erasing: 8 mW Laser power during reproducing: 1 mW As a result, the C/N ratio was 47 dB. Furthermore, when overwriting was performed on the same recording medium under the same conditions at a recording frequency of 2 MHz, a good C/N ratio of 46 dB was obtained.

[0014]

According to the present invention, with the above structure, overwriting can be performed with high reliability using a single beam, a single magnetic field, or no magnetic field.

[Brief explanation of drawings]

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

FIG. 2 is a diagram showing the temperature characteristics of the coercive force Hc of the ferromagnetic film and antiferromagnetic film of the magneto-optical recording medium of the present invention.

[Fig. 3] (a) shows the magnetization state during recording, and (b)
) is a diagram showing the magnetization state during erasing.

[Explanation of symbols]

1 Support 2,5 Protective film 3 Ferromagnetic film (memory layer) 4 Antiferromagnetic film (auxiliary layer)

Claims (1)

[Claims] 1. A memory layer consisting of a ferromagnetic film exhibiting perpendicular magnetic anisotropy, and a memory layer that exhibits an antiferromagnetic phase at room temperature and undergoes a magnetic phase transition at a temperature near the Curie temperature of the memory layer, which is higher than room temperature, and becomes ferromagnetic. A magneto-optical recording medium is used which has a recording layer consisting of a two-layer film laminated with an auxiliary layer consisting of an antiferromagnetic film exhibiting a phase. During recording, only the memory layer is heated to a temperature lower than the temperature at which the magnetic phase transition of the antiferromagnetic film occurs. Laser irradiation is performed under conditions that raise the temperature to the temperature below, and during erasing, laser irradiation is performed under conditions that raise the temperature of both the memory layer and the auxiliary layer to a temperature that exceeds the temperature at which the magnetic phase transition of the antiferromagnetic film occurs. Characteristic magneto-optical recording method.