JPH0731828B2 - Photothermal magnetic recording medium - Google Patents

Description

The present invention relates to a magneto-optical recording medium used in, for example, a magneto-optical memory or a magnetic display element.

[Prior Art] Conventionally, as a recording medium capable of high-density recording, a magneto-optical recording medium using a rare earth transition metal thin film having an easy axis of magnetization in the direction perpendicular to the film surface has been studied. Above all, SN during playback
As a medium having a good ratio and high recording sensitivity, Japanese Patent Laid-Open No. 56-1535
Japanese Patent Laid-Open Publication No. 46-46 proposes a two-layer structure recording medium comprising a writing layer having a high coercive force and a reading layer having a large magneto-optical effect. FIG. 2 is a sectional view of a conventional magneto-optical recording medium having such a two-layer structure. In the figure, (1) is a substrate, (2) is a write layer, (3) is a read layer, and (4) is transparent. Protective layer,
(5) is a laser beam used for reading, (6)
(7) is an arrow indicating the direction of the transition metal sublattice magnetization in each of the layers (2) and (3).

Next, the operation relating to the information reading of the above conventional example will be described. Information is recorded in a magnetization pattern indicating whether the magnetization direction is upward or downward. First, the laser light (5) is read from the transparent protective layer (4) side to the readout layer (3).
Incident on. When the laser light is reflected, its polarization direction rotates by the Kerr rotation angle due to the magneto-optical effect. The rotation of the polarization direction is converted into an electric signal by the photoelectric conversion element after the light amount is changed by the analyzer. That is, the magnetization pattern of the medium is reproduced as an electric signal.

[Problems to be solved by the invention]

In the above example, it is desirable to use a rare earth sublattice magnetization dominant layer having excellent recording characteristics as the writing layer (2) and a transition metal sublattice magnetization dominant layer having a large magneto-optical effect as the reading layer (3). However, in this case, there are the following problems. That is, the energy required for reversing the magnetization of the read layer (3) is the coercive force energy Ec, and the directions (6) and (7) of the transition metal sublattice magnetizations of the write layer (2) and the read layer (3) are opposite to each other. At times, the magnetic energy stored at the interface between both layers (2) and (3) due to the conversion force is Ew.
Then, in the case of Ec> Ew, the transition metal sublattice magnetization of the read layer does not face the same direction due to the exchange force with respect to the direction (6) of the transition metal sublattice magnetization of the write layer. As shown, the directions of transition metal sublattice magnetization in both layers (6) (7)
Face in opposite directions. In this case, there is a problem that the Kerr rotation angle of the reading layer is partially offset by the Kerr rotation angle of the writing layer having the opposite sign, the Kerr rotation angle as a whole is reduced, and the reproduction signal strength is lowered.

The present invention has been made in order to solve the above problems, and obtains a magneto-thermomagnetic recording medium having a high reproduction signal intensity by effectively utilizing excellent writing characteristics and a large Kerr rotation angle of a read layer. Is intended.

[Means for solving problems]

The magneto-optical recording medium of the present invention has an easy axis of magnetization in the direction perpendicular to the film surface, a writing layer made of a rare earth transition metal having a rare earth sublattice magnetization dominant, and an easy axis of magnetization in the direction perpendicular to the film surface, In a case where a read layer made of a rare earth transition metal having a dominant transition metal sublattice magnetization is laminated on a substrate, when the directions of the transition metal sublattice magnetizations of the write layer and the read layer are opposite, The magnetic energy stored at the interface is larger than the coercive energy of the read layer.

[Action]

According to the present invention, when the writing layer and the reading layer have opposite transition metal sublattice magnetization directions in the usage state such as room temperature, the rare earth metal sublattice magnetization predominant layer and the transition metal sublattice magnetization predominant layer are exchanged by the exchange force. Since the magnetic energy stored at the layer interface is larger than the coercive force energy of the layer in which the transition metal sublattice magnetization is dominant, the directions of the transition metal sublattice magnetization of both layers contributing to the Kerr rotation angle are oriented in the same direction. In addition, the Kerr rotation angles of both layers are not canceled and a large reproduction signal strength can be obtained.

〔Example〕

 The present invention will be specifically described below with reference to examples.

Embodiment 1 FIG. 1 is a cross-sectional view of a magneto-optical recording medium according to an embodiment of the present invention, (1) is a transparent substrate made of polycarbonate, (2) is a sub-lattice magnetism-dominant writing layer of a basic earth metal, (3)
Is a read layer in which the transition metal sublattice magnetization is dominant, and the composition of both layers is write layer (2): Tb ₂₄ (Fe ₉₅ Co ₅ ) ₇₆ read layer (3): Tb ₁₈ (Fe ₈₀ Co ₂₀ ) ₈₂ . (4) is a Si-N film which is a transparent protective layer, and each layer (2), (3) and (4) was produced by the sputtering method.
Regarding (5), (6), and (7), the second example showing the conventional example
It is exactly the same as the figure.

The magnetic energy (Ew) stored when the directions of the transition metal sublattice magnetizations of the write layer (2) and the read layer (3) in the magneto-optical recording medium having the above-described structure are opposite to each other is , 5 erg / cm ² , which was higher than the coercive force energy (Ec) of the readout layer, 1.8 erg / cm ² . At this time, the directions (6) and (7) of the transition metal sublattice magnetizations of the two layers (2) and (3) are opposed to the opposite directions to each other, for example, against the coercive force energy. )
If the magnetizations of the two layers are oriented in the same direction, the energy possessed by them will be lower, and as a result, the transition metal sublattice magnetizations of both layers will always be oriented in the same direction as shown in FIG. When reproducing, the laser beam (5) emits light to the readout layer (3).
The polarization azimuth is rotated by, and a part of the light is transmitted through the read layer and is reflected by the write layer (in the case of 2, the polarization azimuth is also rotated and reflected, but the rotation directions are the read layer (3) and the write layer (2). As a result, the Kerr rotation angles in both layers (2) and (3) are not offset but rather added and the Kerr rotation angle as a whole becomes a large value. From 1.2 times compared to recording media
A reproduction signal strength of about 1.5 times was obtained.

Conventional Example In FIG. 2, the composition of the write layer (2) and the read layer (3) is: write layer: Dy ₂₄ Fe ₇₆ read layer: Gd ₁₈ Co ₈₂ . In this case, Ew was 0.7 and Ec was 0.9, and the magnetic energy (Ew) did not exceed the coercive force energy (Ec) as in the above-mentioned Examples.

Examples 2 to 5 Photothermomagnetic recording media of other examples of the present invention were obtained in the same manner as in Example 1 except that the write layer (2) and the read layer (3) were made of the materials shown in the table. . Also, in the above table,
The values of Ew and Ec when the combinations of materials shown in the table are used are also shown at the same time. Even in these combinations, Ew showed a value larger than Ec, and the transition metal sublattice magnetization directions (6) and (7) in both layers (2) and (3) were oriented in the same direction. Therefore, similar to Example 1, a reproduction signal intensity 1.1 to 1.3 times larger than that of the magneto-optical recording medium in the conventional example was obtained.

Although reproduction was performed from the side of the protective layer (4) in the above example, the positions of the read layer (3) and the write layer (2) were exchanged, and laser light (5) was emitted from the transparent substrate (1) side. The same effect can be obtained even when the light beam is incident to perform reproduction.
In that case, the effect of the present invention is not changed even if an optical interference layer such as a Si-N film is provided between the readout layer (3) and the transparent substrate (1).

The energy Ew stored at the interface between the writing layer (2) and the reading layer (3) is a value determined by the materials forming both layers and the cleanliness of the interface between both layers, and the coercive energy of the reading layer. Ec is the saturation magnetization of the read layer,
It is expressed as twice the product of coercive force and film thickness. Therefore, the user should properly select the above-mentioned saturation magnetization, coercive force, film thickness, etc. within the range satisfying the condition of Ec <Ew, and use the composition and material other than those in the above-mentioned examples as the read layer and the write layer. You can

〔The invention's effect〕

As described above, the present invention has a writing layer made of a rare earth transition metal having a rare earth sublattice magnetization dominant axis and an easy axis of magnetization in a direction perpendicular to the film surface, and a transition layer having a magnetization easy axis in the direction perpendicular to the film surface. In a structure in which a read layer composed of a rare earth transition metal having a metal sublattice magnetization predominant is laminated on a substrate, when the directions of the transition metal sublattice magnetizations of the write layer and the read layer are opposite to each other, the interface between the layers is formed. When the magnetic energy stored in the read layer is larger than the coercive force energy of the read layer, it is possible to effectively utilize the large Kerr rotation angle of the read layer to obtain a magneto-thermomagnetic recording medium having a high reproduction signal intensity.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional magneto-optical recording medium. In the figure, (1) is a substrate, (2) is a writing layer, (3) is a reading layer, and (6) and (7) are arrows showing the directions of transition metal sublattice magnetization in the writing layer and the reading layer, respectively. is there. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A rare-earth sublattice write layer having an easy axis of magnetization in the direction perpendicular to the film surface and a transition metal sublattice having an easy axis of magnetization in the direction perpendicular to the film surface. In a structure in which a read layer made of a rare earth transition metal having a dominant magnetization is laminated on a substrate, the magnetic field stored in the interface between the write layer and the read layer when the directions of the transition metal sublattice magnetizations are opposite. Energy is greater than the coercive energy of the read layer.