JPH04219642A - Magneto-optical recording medium and method thereof - Google Patents

Abstract

PURPOSE:To obtain an overwrite reliable in single base beam and single bias magnetic field respectively by making easiness of medium constitution. CONSTITUTION:The ferromagnetic film 3 showing perpendicular magnetic anisotropy and diaferromagnetic film 4 showing intrasurface magnetic anisotropy, arising transition of magnetic phase in neiborhood of Curie temp. of relevant ferromagnetic film 3 and showing a perpendicular surface magnetic anisotropy in room temp. are laminated on to the supporting body 1. The medium is heated to higher than the magnetic phase transition temp. by irradiation of high power laser beam and the bias magnetic field having definite strength is added to be recorded, and then heated to lower temp. than the magnetic phase transition temp. by irradiating low power laser beam and adding the same bias magnetic field as the above to be erased. The recording information is reproduced by irradiating less power laser beam than in the case 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 medium and a 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 medium and magneto-optical recording which are highly reliable, have a simple medium configuration, and can be overwritten with a single laser beam and a single magnetic field. The purpose is to provide a method.

[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 comprising a ferromagnetic film exhibiting perpendicular magnetic anisotropy; It is characterized by having a recording layer made of a two-layer film laminated with an auxiliary layer made of an antiferromagnetic film that causes a magnetic phase transition at a temperature near the high Curie temperature of the memory layer and exhibits perpendicular magnetic anisotropy. A magneto-optical recording medium is provided.

Further, according to the present invention, the above magneto-optical recording medium is used, and during recording, a high power laser beam is irradiated to raise the temperature of the medium until the temperature exceeds the temperature at which the magnetic phase transition occurs, and an external A magnetic field Hex is applied, and during erasing, a low power laser beam is irradiated to raise the temperature of the medium until it reaches a temperature below the temperature at which the magnetic phase transition occurs, and at the same time, the same external magnetic field Hex as during recording is applied. An overwritable magneto-optical recording method is provided.

The present invention will be explained in detail below with reference to the drawings. The magneto-optical recording medium of the present invention has a memory layer in which the recording layer is made of a ferromagnetic film that exhibits perpendicular magnetic anisotropy, and a memory layer that exhibits in-plane magnetic anisotropy at room temperature and at a temperature near the Curie temperature of the memory layer that is higher than room temperature. It is formed by laminating an antiferromagnetic film that causes a magnetic phase transition and exhibits perpendicular magnetic anisotropy. FIG. 1 shows an example of the configuration of such a magneto-optical recording medium. This recording medium is made of Si3N on a transparent support 1 made of glass, plastic, ceramics, etc.
4. Protective film 2 made of SiO, SiO2, etc. (film thickness 10
0 Å to 5000 Å), and a ferromagnetic film 3 (film thickness 100 Å to 5000 Å) exhibiting perpendicular magnetic anisotropy is provided thereon.
On top of that, an antiferromagnetic film 4 ( Si
A protective film 5 (film thickness 100 Å to 5000 Å) made of 3N4, SiO, SiO2, etc. is provided. Each film can be formed by sputtering, vapor deposition, ion plating, or the like. The ferromagnetic film 3 is made of, for example, Tb-Fe,
Gd-Fe, Dy-Fe, Gd-Tb-Fe, Tb-D
y-Fe, Gd-Dy-Fe, Tb-Fe-Co, Gd
-Fe-Co, Dy-Fe-Co, Tb-Dy-Fe-
Co, Gd-Tb-Fe-Co, Gd-Dy-Fe-C
It can be composed of a rare earth-transition metal amorphous film such as O, or a polycrystalline film such as Mn-Bi, Mn-Cu-Bi, Co-Pt, Co spinel ferrite, Ba ferrite, etc. The antiferromagnetic film 4 is RCo (R=D
y, Nd, etc.) based film. These ferromagnetic film 3 and antiferromagnetic film 4 must have coercive force temperature characteristics 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 Tpc.
, if Ta is the temperature at which the coercive force Hc1 of the ferromagnetic film 3 and the bias magnetic field Hex are equal, and Tb is the temperature at which the coercive force Hc2 of the antiferromagnetic film 4 is equal to the bias magnetic field Hex, the following relationship is established. It has been established. When Tpc≦T<Tb, Hc2>
When Hc1+Hex Ta<T<Tpc
When Hc1<Hex T≦Ta
Hc1≧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. Alternatively, the protective films 2 and 5 may be appropriately removed.

Next, a magneto-optical recording method using the above magneto-optical recording medium will be explained. Recording is performed by irradiating the portion to be recorded with a high-power laser beam to raise the medium temperature to around the Curie temperature Tc1 of the ferromagnetic film 3, and by applying an external magnetic field Hex. The magnetization of the area to be recorded is such that the ferromagnetic film 3 is facing upward (or downward) and the antiferromagnetic film 4 is apparently zero under normal medium driving conditions, but it is increased to around Tc1 by high power laser beam irradiation. As the temperature rises, the magnetization in the ferromagnetic film 3 disappears or becomes almost zero, and a magnetic phase transition occurs in the antiferromagnetic film 4 (Tp
(c) changes from in-plane magnetic isomerism to perpendicular magnetic anisotropy, and moreover, magnetization occurs in the downward direction in the figure (in the opposite direction to the saturation magnetization). This downward magnetization is transferred to the ferromagnetic film 3 during the cooling process and is maintained as it is. FIG. 3(a) shows the magnetization state when the temperature is lowered after recording. The temperature range during recording is Tpc≦T<Tb, and if the temperature is raised above Tb, the magnetization direction of the antiferromagnetic film 4 will be directed toward the bias magnetic field Hex direction (upward in the figure), making it impossible to record. .

Erasing is performed by irradiating the area to be erased with a laser beam of lower power than during recording to lower the medium temperature such that Ta≦T<
This is performed by raising the temperature to Tpc and applying an external magnetic field Hex (FIG. 3(b)).

[0012] Since the magnetization of the auxiliary layer made of an antiferromagnetic film always points in the same direction, there is no need to initialize the magnetization, and overwriting with a single beam and a single magnetic field is possible. Become. Further, reproduction is performed by irradiating a laser beam with a power level that makes the medium temperature less than or equal to Ta.

[Example] 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. The following films were sequentially laminated in vacuum on a grooved polycarbonate substrate (diameter 130 mm) by RF binary magnetron sputtering to obtain a recording medium. Protective film: Si3N4 film (1000 Å) Ferromagnetic film: Tb0.2 (Fe0.98Co0.02) 0.8 film (
600 Å) Antiferromagnetic film: DyCo5 film (1500 Å
) Protective film: Si3N4 film (1000Å)

0014
] Curie temperature Tc1 of the ferromagnetic film, Curie temperature Tc2 and magnetic phase transition temperature Tpc of the antiferromagnetic film, temperature T at which the coercive force Hc1 of the ferromagnetic film and the bias magnetic field Hex are equal.
a. The temperature Tb at which the coercive force Hc2 of the antiferromagnetic film becomes equal to the bias magnetic field Hex was as follows. Tc1=130℃ Tc2=300℃ Tpc=100℃ Ta=70℃ Tb=180℃

[0015] 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 = 700 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: 6 mW Laser power during erasing: 4 mW Laser power during reproduction: 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 47 dB was obtained.

[0016]

According to the present invention, with the above structure, overwriting can be performed with a single beam and a single magnetic field with high reliability.

[Brief explanation of the drawing]

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 (2)

[Claims] 1. A memory layer consisting of a ferromagnetic film exhibiting perpendicular magnetic anisotropy, and a memory layer that exhibits in-plane magnetic anisotropy 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. 1. A magneto-optical recording medium characterized by having a recording layer made of a two-layer film laminated with an auxiliary layer made of an antiferromagnetic film exhibiting perpendicular magnetic anisotropy. 2. Using the magneto-optical recording medium according to claim 1, during recording, a high power laser beam is irradiated to raise the temperature of the medium until the temperature reaches the temperature at which the magnetic phase transition occurs, and an external magnetic field Hex is applied. is applied, and during erasing, a low power laser beam is irradiated to raise the temperature of the medium until it becomes below the temperature at which the magnetic phase transition occurs, and the same external magnetic field Hex as during recording is applied. A magneto-optical recording method that allows overwriting.