JPH04181534A - Magnetooptical recording medium and method - Google Patents

Abstract

PURPOSE:To achieve higher reliability by arranging a recording layer comprising a double-layer film which is laminated with a memory layer comprising a ferromagnetic film exhibiting vertical magnetic anisotropy and an auxiliary layer that exhibits an anti-ferromagnetic phase at a room temperature and a ferromagnetic phase at a higher temperature than the room temperature to present a specified relationship between Curie temperatures of the two layers. CONSTITUTION:A recording medium is provided with a protective film 2 on a transparent support 1 and a ferromagnetic film 3 exhibiting vertical magnetic anisotropy thereon. An anti-ferromagnetic film 4 is provided on the film as exhibiting an anti-ferromagnetic phase at a room temperature and a ferromagnetic phase at a higher temperature than the room temperature with the generation of a magnetic phase transision and a protective film 5 is provided thereon. When Curie temperature of the ferromagnetic film 3 is represented by TC2, it is necessary to satisfy a relation of TC1<TC2. With such an arrangement, a magnetiooptical recording medium can be provided which allows overwriting with easy designing of a medium along with excellent preservation stability and higher reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overwritable magneto-optical recording medium and a magneto-optical recording method.

[Problems to be solved by conventional techniques and inventions] 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
This 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 each trunk, but it has drawbacks such as complicating the device configuration and increasing costs. have. In addition, the two-layer film method uses a two-layer film as the recording layer of a magneto-optical recording medium to achieve overwriting.
It is disclosed in Japanese Patent No. 5948 and the like. The system described in the publication includes, for example, a memory layer made of TbFe and a TbFe layer.
Using a magneto-optical recording medium with a two-layer recording layer and an auxiliary layer made of FeCo, after initialization, overwriting is attempted by applying an external magnetic field and irradiating with a laser beam of different power. It is something. 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 adjust the medium temperature T (T1.2 is the Curie temperature of the auxiliary layer). ), apply a recording magnetic field (in the opposite direction to the initialization magnetic field) to reverse the magnetization of the auxiliary layer, and as the medium cools, the magnetization is transferred to the memory layer. and irradiate with a low-power laser beam to raise the medium temperature to TC, < T < TC2 (TCl is the Curie temperature of the memory layer), and transfer the magnetization direction of the auxiliary layer to the memory layer. Therefore, with this method, there are problems such as difficulty in medium design and susceptibility to the influence of external magnetic fields when the medium is stored.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and provide a magneto-optical recording medium and a magneto-optical recording method that are highly reliable, have a simple medium configuration, and can be overwritten with a single laser beam. .

[Means to solve the problem]

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 that is an antiferromagnetic film at room temperature and undergoes a magnetic phase transition at a temperature higher than room temperature to become ferromagnetic. It consists of a two-layer film laminated with an auxiliary layer made of an antiferromagnetic film showing a phase, and the Curie temperature of the memory layer is TCl,
When the Curie temperature of the auxiliary layer is TC2, TC1<T
A magneto-optical recording medium is provided which is characterized by having a recording layer that satisfies the relationship C2.

Further, according to the present invention, there is provided a memory layer made of a ferromagnetic film exhibiting perpendicular magnetic anisotropy, and an antiferromagnetic film that is an antiferromagnetic film at room temperature and exhibits a ferromagnetic phase by causing a magnetic phase transition at a temperature higher than room temperature. It consists of an auxiliary layer made of a magnetic film and an intermediate layer interposed between the memory layer and the auxiliary layer to adjust the exchange coupling force between the two layers, and the Curie temperature of the memory layer is set to TC1. When the Curie temperature of the auxiliary layer is TC2, TC<T. A magneto-optical recording medium is provided which is characterized by having a recording layer that satisfies the following two relationships.

Furthermore, according to the present invention, the magneto-optical recording medium described above is used, and during recording, a high-power laser beam is irradiated to raise the medium temperature to around the Curie temperature TC2 of the auxiliary layer, and an external magnetic field Her is applied. During erasing, a low power laser beam is irradiated to raise the medium temperature to around the Curie temperature TCl of the memory layer, and the same external magnetic field Her as during recording is applied, and the magnetization of the auxiliary layer is aligned in one direction. An overwritable magneto-optical recording method is provided, which is characterized in that initialization is performed using an initialization magnetic field H i when the medium temperature drops after recording or erasing.

The present invention will be explained in detail below based on the drawings.

The magneto-optical recording medium of the present invention (the recording medium of claim 1) has a recording layer comprising 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 an antiferromagnetic film exhibiting an antiferromagnetic film at room temperature and a magnetic phase at a temperature higher than room temperature. It is formed by laminating an antiferromagnetic film that undergoes a transition and exhibits a ferromagnetic phase. FIG. 1 shows an example of the structure of such a magneto-optical recording medium. This recording medium is made of Si3N4, Sin, etc. on a transparent support made of glass, plastic, ceramics, etc.
Protective film 2 made of SiO
0OA), a ferromagnetic film 3 (film thickness 100A to 5000A) exhibiting perpendicular magnetic anisotropy is provided thereon, and an antiferromagnetic film 3 (film thickness 100A to 5000A) exhibiting perpendicular magnetic anisotropy is provided thereon, and an antiferromagnetic film is formed on top of it at room temperature, and a magnetic phase transition occurs when the temperature is raised above room temperature. Antiferromagnetic film 4 (thickness: 100 mm) exhibiting a ferromagnetic phase
A-1000OA), and furthermore, Si3N4
, Sin, 5i02, etc. (film thickness 10
0A-500OA). Each film can be formed by a sputtering method, a vapor deposition method, an ion blating method, or the like. The ferromagnetic film 3 is made of, for example, Tb-Fe, Gd
-Fe, Dy-Fe, Gd-Tb-Fe, Tb-Fe-
Co, Gd-Fe-Co, Dy-Fe-Co
, Tb-Dy-Fe-Co, Gd-Tb-Fe
- Rare earth-transition metal-based amorphous films such as Go, or Mn-B i , Mn-Cu-B i , Co
It can be constructed from a polycrystalline film such as spinel ferrite Ba ferrite. The antiferromagnetic film 4 is made of, for example, Mn2.
It can be constructed using Sb, Mn□-, 5bYx (Y=Cr, Ti, V, etc.).

These ferromagnetic film 3 and antiferromagnetic film 4 must have thermomagnetic properties as shown in FIG. In addition, the ferromagnetic film 3
If the Curie temperature of the antiferromagnetic film 4 is TCl, and the Curie temperature of the antiferromagnetic film 4 is TC2, it is necessary to satisfy the relationship TCr<TC2.

Next, a magneto-optical recording method using the above magneto-optical recording medium will be explained.

For recording, a high-power laser beam is irradiated onto the area to be recorded to adjust the medium temperature to the Curie temperature TC2 of the antiferromagnetic film 4.
At the same time, the external magnetic field Hew is applied. 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 changed to near the TCZ by irradiation with a high power laser beam. Ferromagnetic film 3 to increase temperature
Then, the magnetization disappears, and the antiferromagnetic film 4 becomes magnetized with a small upward magnitude. At this time, since the external magnetic field Hex is applied downward, its magnetization is reversed and becomes downward, and this downward magnetization is transferred to the TCI during the cooling process.
When it reaches the vicinity, it is transferred to the ferromagnetic film 3 and held as it is. At this time, the magnetization of the antiferromagnetic film 4 becomes an antiferromagnetic film when the temperature returns to room temperature, so the apparent magnetization becomes zero, but since antiferromagnetic coupling exists, a large magnetic field is applied from the outside. is stable without being reversed, and at room temperature the magnetization of the antiferromagnetic film 4 is the same as that of the ferromagnetic film 3.
Since it does not affect the magnetization of the magnet, reliability is improved.

Note that FIG. 3 shows the magnetization state when the temperature is lowered after recording.

Erasing is performed by irradiating the area to be erased with a low power laser beam to raise the medium temperature near the Curie temperature TCl of the ferromagnetic film 3, and applying an external magnetic field Hex (
Figure 3(b)). When the medium temperature approaches TC, the magnitude of magnetization of the antiferromagnetic film 4, which has been initialized in advance and faces upward, becomes larger than the magnitude of magnetization of the ferromagnetic film 3, which faces downward (antiferromagnetic film Since the magnitude of the coercive force HCZ of 4 is larger than the magnitude of the external magnetic field Hex, the magnetization of the antiferromagnetic film 4 is transferred to the ferromagnetic film 4, the magnetization of the ferromagnetic film 3 is directed upward, and erasing is performed.

The magnetization of the antiferromagnetic film 4 is initialized as shown in FIG. 3(a) when the medium temperature drops after recording/erasing, that is, when the medium temperature is below TC1 (above the phase transition temperature). This is done by aligning the magnetization of the antiferromagnetic film 4 upward using the initialization magnetic field Hini (the direction of application is opposite to the external magnetic field New).

Further, reproduction is performed by irradiating a laser beam with a power level that makes the medium temperature lower than TCl.

Next, another type of magneto-optical recording medium according to the present invention (claim 2
(recording medium) will be explained. This magneto-optical recording medium has a memory layer in which the recording layer is made of a ferromagnetic film exhibiting perpendicular magnetic anisotropy, and an antiferromagnetic film at room temperature, which undergoes a magnetic phase transition and exhibits a ferromagnetic phase at temperatures higher than room temperature. It consists of an antiferromagnetic film and an intermediate layer therebetween that adjusts the exchange coupling force between both layers. FIG. 4 shows an example of the structure of such a magneto-optical recording medium. In this recording medium, a protective film 2 is provided on a transparent support l similar to that shown in FIG. An intermediate layer 6 is provided to adjust the exchange coupling force with the magnetic film 4, and an antiferromagnetic film is provided on the intermediate layer 6 to adjust the exchange coupling force with the magnetic film 4, and an antiferromagnetic film is formed thereon at room temperature, and when the temperature is raised above room temperature, a magnetic phase transition occurs and the antiferromagnetic film exhibits a ferromagnetic phase. It is constructed by providing a ferromagnetic film 4 and further providing a protective film 5 thereon. Each film other than the intermediate layer 6 can be constructed in the same manner as that shown in FIG. The intermediate layer 6 is provided to adjust the exchange coupling force between the ferromagnetic film 3 and the antiferromagnetic film 4, and is made of a non-magnetic material that does not deteriorate the magnetic films 3 and 4. Preferably, the material is a magnetic material having in-plane magnetic anisotropy. Specifically, such materials include Si, An, ^g,
＾u, Cu, Fe, Co, Ni, Cr, 5i-N, AQ
-N, Fe-N, etc. can be mentioned. If the thickness of the intermediate layer 6 is too thin, the exchange coupling force acting between the two magnetic layers 3 and 4 will become large and a large initializing magnetic field HIn+ will be required, which is undesirable. Since the exchange coupling force between 4 and 4 becomes too small and causes problems in recording and erasing, a value of about several A-100 A is appropriate.

Each operation of recording, erasing, reproducing, and initializing this magneto-optical recording medium is performed in the same manner as the recording medium of FIG. 1 (FIG. 5 shows an explanatory diagram of the operation corresponding to FIG. 3). When initializing this magneto-optical recording medium at the initialization temperature Tin1, the magnetic properties of the ferromagnetic film (memory layer) 3 and antiferromagnetic film (auxiliary layer) 4 must satisfy the following conditions. , the thickness of the intermediate layer 6 is controlled so as to satisfy the conditions.

δW ) (cl >HO2> − Ms-h where HCI is the coercive force of the ferromagnetic film 3, HCl is the coercive force of the antiferromagnetic film 4, δW is the domain wall energy between both films 3.4, and Ms is the antiferromagnetic film 3. The saturation magnetization of the ferromagnetic film 4 is shown, and all of these values are for old Ti, and b is the film thickness of the antiferromagnetic film 4.

Further, reproduction is performed by irradiating a laser beam with a power level that makes the medium temperature lower than TCl.

Although the configuration examples of the magneto-optical recording medium of the present invention have been described above, the present invention is not limited to these, and various modifications and changes are possible.1 For example, a reflective film may be provided on the protective film 5. The protective film 2.5 may be provided, or the protective film 2.5 may be appropriately removed.

〔Example〕

Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these two examples.

(Example 1) Polycarbonate substrate with group (diameter 130 mm)
The following films were sequentially laminated thereon in vacuum by a 102-element magnetron sputtering method to obtain a recording medium having the structure shown in FIG.

1 Protective film: Si3N4 film (100OA) Ferromagnetic film: Tbo-z+ (Feo, *zCoo, os)
o, ys film (800A) antiferromagnetic film: Mn1.6SbC
ro, 4 films (100OA) protective film: 3 i 3N4 film (
100OA) The Curie temperature TCl of the ferromagnetic film and the Curie temperature TC2 of the antiferromagnetic film were as follows.

TC1 =] 60°C TC2 = 240°C The temperature at which the magnetic phase transition from the antiferromagnetic film to the ferromagnetic phase in one antiferromagnetic film was 50°C.

The recording medium obtained as described above was driven at a linear speed of 10 m/sec, and an initializing magnetic field H i = 2 KOe and an external magnetic field Her = 4000 e (in the same direction during recording and erasing) were applied. IMHz signals were recorded and reproduced by changing the irradiation laser power as follows during erasing, erasing, and reproducing, and the recording/reproducing characteristics were evaluated.

Laser power during recording +7, 5 taW Laser power during erasure: 5.5 mW Laser backlash during reproduction: 2rnW As a result, the C/N ratio was 47 dB. Furthermore, when overwriting was performed on the recording medium at a recording frequency of 2 MHz under the same conditions, a good C/N ratio of 46 dB was obtained.

(Example 2) Polycarbonate substrate with group (diameter 130++o
The following films were sequentially laminated on top of (n) in a vacuum by a 102-element magnetron sputtering method to obtain a recording medium having the structure shown in FIG.

Protective film: Si3N4 film (1000 people) Ferromagnetic film 'Tb0-21 (Fl!0-92C00-01
1) O-79 film (600A) intermediate film: 5i3N4 (IO
A) Antiferromagnetic M: Mn1.6SbCro, 4 films (150OA
) Protective film + 5i3N4 film (100OA) Curie temperature of ferromagnetic film TCl, Curie temperature of antiferromagnetic film 11:, TC2 and magnetic phase transition temperature Tp of antiferromagnetic film
e was as follows.

TC+=16 (1°C TC2=240°C Tpc-50°C The recording medium obtained as above was driven at a linear velocity of 10 ml/sec, and the initializing magnetic field Hini-2KOe and the external magnetic field He
x = 4000e (in the same direction during recording and erasing), and changing the irradiation laser power as shown below during recording, erasing, and reproducing to record and reproduce a 1 Mtb signal, and record/reproduce characteristics. Laser power during 1° recording: 8 cW Laser power during erasing: 5 mW Laser power during reproducing: ImW As a result, the C/N ratio was 47 dB. Furthermore, when overwriting was performed on the recording medium at a recording frequency of 2M)It under the same conditions, a good C/N ratio of 46 dB was obtained.

〔Effect of the invention〕

According to the present invention, by having the above structure, it is possible to provide a magneto-optical recording medium and a magneto-optical recording method that have excellent storage stability, are highly reliable, and can be overwritten with easy medium design.

Furthermore, if an intermediate layer is provided between the memory layer and the auxiliary layer, the exchange coupling force acting between the memory layer and the auxiliary layer can be adjusted appropriately, so that the initialization magnetic field Hini can be reduced. Media design becomes easier.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the layer structure of the magneto-optical recording medium according to the present invention, and FIG. 2 is a diagram showing the temperature characteristics of the saturation magnetization My of the ferromagnetic film and antiferromagnetic film of the magneto-optical recording medium of the present invention. , FIG. 3 is a diagram showing the magnetization state of the recording medium of FIG. 1 during initialization, recording, and erasing, and FIG. 4 is a cross-sectional view showing the layer structure of another type of magneto-optical recording medium according to the present invention. , FIG. 5 is a diagram showing the magnetization state of the recording medium of FIG. 4 at the time of initialization, recording, and erasing. l...Support 2.5...Protective film 3...Ferromagnetic film (memory layer) 4...Antiferromagnetic film (auxiliary layer) 6...Intermediate layer

Claims (3)

[Claims] (1) A memory layer consisting of a ferromagnetic film that exhibits perpendicular magnetic anisotropy, and an auxiliary layer consisting of an antiferromagnetic film that exhibits an antiferromagnetic phase at room temperature and undergoes a magnetic phase transition and exhibits a ferromagnetic phase at temperatures higher than room temperature. The Curie temperature of the memory layer is T_C_1, and the Curie temperature of the auxiliary layer is T_C_
1. A magneto-optical recording medium characterized by having a recording layer that satisfies the relationship T_C_1<T_C_2 when T_C_1<T_C_2. (2) A memory layer consisting of a ferromagnetic film that exhibits perpendicular magnetic anisotropy, and an auxiliary layer consisting of an antiferromagnetic film that exhibits an antiferromagnetic phase at room temperature and undergoes a magnetic phase transition and exhibits a ferromagnetic phase at temperatures higher than room temperature. and an intermediate layer interposed between the two layers to adjust the exchange coupling force between the memory layer and the auxiliary layer, and the Curie temperature of the memory layer is T_C_1 and the Curie temperature of the auxiliary layer is T_C_2. A magneto-optical recording medium characterized by having a recording layer that sometimes satisfies the relationship T_C_1<T_C_2. (3) using the magneto-optical recording medium according to claim 1 or 2,
During recording, the medium temperature is the Curie temperature of the auxiliary layer T_C_2
A high-power laser beam that raises the temperature of the memory layer to around T_C_1 is irradiated, and an external magnetic field Hex is applied, and during erasing, a low-power laser beam that raises the medium temperature to around the Curie temperature T_C_1 of the memory layer is applied. Initialization is performed by applying the same external magnetic field Hex as during recording, and aligning the magnetization of the auxiliary layer in one direction.
An overwritable magneto-optical recording method characterized in that it is carried out using an overwritable magneto-optical recording method.