JP2642656B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention records information by forming bits of reversed magnetic domains using a laser beam and an external magnetic field, thereby forming a polarized laser beam. The present invention relates to a magneto-optical recording medium for reading information by using a magneto-optical effect.

[Conventional technology]

Conventionally, in a magneto-optical recording medium, a single magnetic material having a low Curie temperature, easy recording, a high coercive force, high storage stability, a large magneto-optical Kerr rotation angle, and good read characteristics has been found. This is difficult, and a magneto-optical recording medium in which two different magnetic materials are laminated while separating the functions required for that purpose has been proposed (JP-A-57-7865).
No. 2).

This recording medium is composed of two layers, a high coercive force layer of Tb-Fe having a low Curie temperature capable of perpendicular magnetization, and a low coercive force layer of Gd-Fe having a high Curie temperature capable of perpendicular magnetization. The low coercive force layers are exchange-coupled to each other. Then, information is recorded and stored in the high coercive force layer having a low Curie temperature, and the recorded information is transferred to the low coercive force layer, and has a high Curie temperature and a large low coercive force of the magneto-optical Kerr rotation angle. Reading of information is performed in the layer.

As the structural material of the exchange-coupling two-layer film, in addition to the above, a high coercive force layer such as Tb-Fe, which is predominant in iron group sublattice magnetization, and a low coercive force layer, which is also Gd-Fe-Co in which iron group sublattice magnetization predominates Tb-Fe, Tb-Fe-Co predominant in rare-earth sublattice magnetization having a compensation temperature between room temperature and Curie temperature as a high coercive force layer comprising a magneto-optical recording medium comprising
Alternatively, a magneto-optical recording medium comprising Dy-Fe-Co, Gd-Fe or Gd-Fe-Co in which the iron-group sublattice magnetization is dominant as a low coercivity layer has been proposed.

Such a magneto-optical recording medium, like other recording media, poses a problem not only in recording / reproducing characteristics but also in recording stability. When considering the stability of recorded information, it is necessary to consider not only room temperature but also stability at a temperature slightly higher than room temperature. Because there are various sources of heat in the magneto-optical drive device, the temperature may rise to about 50 to 60 ° C. among them, and it is weak enough not to record information when reading information This is because reading is performed by irradiating the medium with laser light, but a certain degree of temperature rise of the medium is inevitable. Further, this is because, in each operation of the drive device, it is necessary to perform reading in a state where a bias magnetic field for recording / erasing is applied. Therefore, in a drive device of about 50 to 60 ° C., even if the temperature of the medium is further increased by the reading light under the application of the bias magnetic field, the recorded information needs to be stable.

[Problems to be solved by the invention]

Exchange-coupled two-layer films using rare earth-iron group amorphous alloys that require such characteristics include roughly four types of media.

(1) High coercivity layer is predominant in rare-earth sublattice magnetization, low coercivity layer is predominant in rare-earth sublattice magnetization (2) High coercivity layer is predominant in iron group sublattice magnetization, low coercivity layer is predominant in rare earth sublattice magnetization (3) The high coercivity layer is predominant in iron group sublattice magnetization, the low coercivity layer is predominant in iron group sublattice magnetization. (4) The high coercivity layer is predominant in rare earth sublattice magnetization, and the low coercivity layer is predominant in iron group sublattice magnetization. The media of (1) and (2), in which the coercivity layer is dominant in rare earth sublattice magnetization, have poor recording / reproducing characteristics. The media (3) and (4) have good recording / reproducing characteristics, but have different recording stability.

In general, in an exchange-coupled two-layer film, the magnetization process (coercive force) of each layer changes considerably compared to a single-layer film due to exchange interaction between the two layers. The magnetization reversal magnetic field changed by the two layers is called an apparent coercive force. In the case of the combination of the high coercive force layer and the low coercive force layer in question here, the apparent coercive force of the low coercive force layer increases in any of the media (3) and (4),
The stability of recorded information in the low coercivity layer is improved.

However, the magnetization process of the high coercivity layer also changes due to the exchange interaction from the low coercivity layer, but in the medium (3), the apparent coercivity decreases as compared with the case of the single layer film,
In the medium (4), the apparent coercive force increases. Therefore, in the medium (3), the apparent coercive force is reduced, and there is a problem in the stability of recorded information. Also,
In the medium of (4), the high coercive force layer is preferably a rare earth iron-group amorphous alloy in which the rare earth sublattice magnetization is dominant and has a compensation temperature between room temperature and Curie temperature from the recording / reproducing characteristics. At a temperature between the temperature and the Curie temperature, the magnetism changes to (3), and there is a problem in the stability of recorded information in this temperature range.

As described above, the recording stability of the medium (4) is considerably improved as compared with the medium (3), but the recording stability becomes a problem within the above-mentioned range and is still insufficient for practical use.

[Means for solving the problem]

The present invention that solves the above-mentioned problems of the prior art includes a high coercive force layer made of a rare earth-iron group amorphous alloy having a low Curie temperature capable of perpendicular magnetization and a rare earth-iron group non-magnetic material having a high Curie temperature capable of perpendicular magnetization. A low-coercivity layer made of a crystalline alloy, wherein the high-coercivity layer and the low-coercivity layer are exchange-coupled in a magneto-optical recording medium, wherein the low-coercivity layer contains Gd and Dy, and The low coercivity layer is predominant in iron group sublattice magnetization, the high coercivity layer is predominant in rare earth sublattice magnetization, and the high coercivity layer has a compensation temperature between room temperature and Curie temperature. Magneto-optical recording medium.

By using such a medium, recording is easy,
A medium having good read characteristics and excellent stability of recorded information can be obtained.

Hereinafter, the present invention will be described in detail. In the exchange-coupled two-layer film for the magneto-optical recording medium, as factors affecting the stability of the recorded information, the Curie temperature of the high coercivity layer, the magnitude of the apparent coercive force of the high coercivity layer, and the thickness of each layer,
It was found at the stage of creation of the present invention that the coercive force of the low coercive force layer was large.

The first factor that affects the stability of recorded information is the Curie temperature of the high coercivity layer. The higher the Curie temperature, the higher the stability of the recorded information, but the lower the recording sensitivity. Desirable Curie temperature of the high coercivity layer is 100 ° C. or higher, more preferably 130 ° C. or higher, and still more preferably 150 ° C. or higher. As the rare earth element of the high coercive force layer, it is preferable to use a non-S state element such as Tb or Dy in order to enlarge the coercive force layer. The Curie temperatures of Tb-Fe and Dy-Fe are each about 130
° C, about 70 ° C, and by further adding Co,
Curie temperature can be controlled freely.

The Curie temperatures of Tb- (Fe _100-X Co _X ) and Dy- (Fe _100-Y Co _Y ) are approximately expressed as 130 + 6X (° C.) 70 + 6Y (° C.). Co may be added so as to reach the Curie temperature.

The second factor that affects the stability of recorded information is the apparent coercive force of the high coercivity layer. In order to stabilize the recorded information based on this factor, the high coercivity layer has the rare earth sublattice magnetization dominance, the low coercivity layer has the iron group sublattice magnetization dominance (the medium of (4)), and the high coercivity layer has It is preferable to use an exchange-coupled bilayer film having a compensation temperature between the Curie temperature and the Curie temperature. Between room temperature and the compensation temperature, the apparent coercive force of the high coercive force layer becomes larger than the coercive force of a single layer due to the two layers, and the recording stability increases. However, there is a problem between the compensation temperature and the Curie temperature because the apparent coercive force decreases.

A third factor that affects the stability of recorded information is the thickness of each layer. For example, the thickness of the low coercivity layer and the thickness of the high coercivity layer are reduced to 400Å, 600Å, or even 300Å, 700Å, and the thickness of the high coercivity layer is set to be less than 500 膜厚 and 500 保, respectively. Thickness improves recording stability. However, if the thickness of the low coercive force layer is too thin, the magneto-optical effect is reduced, and the reproduction characteristics are deteriorated.

As described above, it has been found that the magnitude of the coercive force of the low coercive force layer is also involved as a factor affecting the stability of the recording characteristics.

Conventionally, it has been considered that it is preferable to use an element in the S state as the rare earth element of the low coercive force layer in order to reduce the coercive force. Elements in the S state include Eu and Gd, but Gd is mainly used because Eu has high reactivity.

Among alloys using Gd, Gd-Fe has a Curie temperature of about 22.
Although it is as high as 0 ° C. and suitable for a low coercive force layer, the addition of Co increases the Curie temperature, increases the magneto-optical Kerr rotation angle, and improves readout characteristics. However, Gd
In-(Fe _100-Z Co _Z ), Z50 is considered desirable because Z30 decreases the iron group magnetic moment.

The present invention relates to Gd-Fe, Gd-Fe
Attempts to add Dy, a non-S state element, to -Co, found that the stability of recorded information was improved due to the change in coercive force of the low coercive force layer, which was completed. .

That is, the low coercivity layer of the exchange-coupled two-layer film is Gd-Fe, Gd
-Fe-Co has too small coercive force, and Tb-Fe-Co, Dy
-Fe-Co has too large a coercive force.

Therefore, Gd-Dy-Fe, Gd-
When Dy-Fe-Co was used, it was found that the recording / reproducing characteristics were hardly changed, and that the recording stability, especially the durability against the deterioration of the recorded information due to the reproducing light was improved.

Other base elements of Gd-Dy are mainly Fe and Co, but Ni,
Cr, Ti, Al, Si, Pt, In, Cu and the like may be added. Gd
The amount of -Dy added is (Gd-Dy) _X M _1-X (M is Fe, Co, etc.
(X: atomic%) is preferably about 0.15 <X <0.30.

〔Example〕

Example 1 To prevent oxidation and obtain an interference effect, a Si ₃ N ₄
700 °, Gd-Dy-Fe-Co as a low coercive force layer, 400 °, Tb-Fe-Co as a high coercive force layer, 600 °, and Si ₃ N ₄ for oxidation prevention, 700 °, continuously without breaking vacuum. The film was formed using a magnetron sputtering apparatus to produce a magneto-optical disk having an exchange-coupled two-layer film. Gd, Dy, Tb, Fe ₇₀ Co ₃₀ and Fe ₉₄ Co ₆ were used as targets for the magnetic layer.
d, Dy and Fe ₇₀ Co ₃₀ are used to deposit Tb-Fe-Co, and Tb and Fe
It was formed the Tb-Fe-Co with a ₉₄ Co _6. The composition ratio of Gd and Dy or the composition ratio of rare earth and iron group was controlled by changing the power applied to the target. (Gd _X Dy
_{X of the} ( _100-X )-(Fe _100-Y Co _Y ) film was about 75 and Y was about 30. The Ar gas pressure was 0.15 Pa, the deposition rate of Si ₃ N ₄ was about 40 ° / min, and the deposition rate of each magnetic layer was about 100 ° / min. The interface domain wall energy density of the fabricated exchange-coupling bilayer film was about ² erg / cm ² , confirming that good exchange interaction was working between both layers.

The recording and playback characteristics of the disc are 1500 revolutions and a radius of 60 mm
Was measured using a bias magnetic field of 200 Oe.

The low coercivity layer is Gd-Dy-Fe-Co with iron group sub-lattice magnetization dominant and its saturation magnetization is 50-200 emu / cm ³ , and the high coercivity layer is rare earth sub-lattice magnetization dominant Tb-Fe-Co and its saturation magnetization Is 25 to 175 emu
/ cm ³ range, recording sensitivity is about 6.8mW, playback CN ratio is about 56d
B and good recording / reproducing characteristics were obtained.

The maximum power at which the recorded information did not deteriorate was as high as about 2.7 mW in a magnetic field of 600 Oe.

Comparative Example 1 As a comparison with Example 1, the same target was used, and the low coercive force layer was Gd-Fe-Co in which the iron group sublattice magnetization was dominant,
The saturation magnetization is 50 to 150 emu / cm ³ , and the high coercivity layer is
When a disc having the same characteristics as that of the above was produced, the recording sensitivity was about 6.7 mW and the playback CN ratio was about 58 dB, and good recording and playback characteristics were obtained.However, the maximum playback power in a 600 Oe magnetic field was about It was as low as 2.1mW.

Example 2 Gd, Dy, Fe ₇₀ Co ₃₀ and Fe ₈₅ were used as targets for the magnetic layer.
Using Co ₁₅ , Gd, Dy and Fe ₇₀ Co ₃₀ as a low coercive force layer, Gd-Dy-Fe-Co is deposited, and Dy and Fe as a high coercive force layer.
Using ₈₅ Co _15, it was deposited Dy-Fe-Co. All other conditions are the same as in the embodiment.

The coercivity layer has a saturation magnetization of 50 to 200 emu / cm ³ in Gd-Dy-Fe-Co in which iron group sublattice magnetization is dominant, and the saturation magnetization in Dy-Fe-Co in which the high coercivity layer has rare earth sublattice magnetization dominance. 25-175emu / c
The range of m ^3, the recording sensitivity is about 6.5 mW, the reproduction CN ratio is about 56dB
And good recording / reproducing characteristics were obtained.

The maximum power at which the recorded information did not deteriorate was as high as about 2.6 mW in a magnetic field of 600 Oe.

Comparative Example 2 As a comparison with Example 2, using the same target, the low coercive force layer was made of Gd-Fe-Co in which the iron group sublattice magnetization was dominant,
The saturation magnetization is 50 to 150 emu / cm ³ , and the high coercivity layer is
When a disc having the same characteristics as that of the above was produced, the recording sensitivity was about 6.7 mW and the reproduction CN ratio was about 56 dB, and good recording and reproduction characteristics were obtained.However, the maximum reproduction power in a 600 Oe magnetic field was about It was as low as 1.9mW.

Example 3 In Example 1, x was set to 50, and the other conditions were the same, except that the low coercive force layer was Gd-Fe-Co in which the iron group sublattice magnetization was dominant and the saturation magnetization was 50 to 250 emu / cm ^3. , The high coercivity layer is rare earth sublattice magnetization dominant Tb-Fe-Co whose saturation magnetization is
When a disk having a range of 25 to 175 emu / cm ³ was produced, the recording sensitivity was about 7.0 mW and the reproducing CN was about 55 dB, and good recording and reproducing characteristics were obtained. The maximum read power in a 600 Oe magnetic field was as high as about 2.9 mW.

〔The invention's effect〕

As described in detail above, in the exchange coupling bilayer film for magneto-optical recording, by using a specific rare earth-iron group amorphous alloy containing Gd and Dy as the low coercive force layer, the recording / reproducing characteristics are improved. It is possible to obtain a magneto-optical recording medium which is excellent and has excellent stability of recorded information, especially durability against deterioration of information due to reproduction light.

Claims (1)

(57) [Claims] A high coercive force layer comprising a rare earth-iron group amorphous alloy having a low Curie temperature capable of perpendicular magnetization and a low coercive force comprising a rare earth-iron group amorphous alloy having a high Curie temperature capable of perpendicular magnetization. A magneto-optical recording medium, wherein the high coercivity layer and the low coercivity layer are exchange-coupled to each other, wherein the low coercivity layer contains Gd and Dy, and the low coercivity layer is an iron group. A magneto-optical recording medium, wherein the sub-lattice magnetization is dominant, the high coercivity layer is a rare earth sub-lattice magnetization dominant, and the high coercivity layer has a compensation temperature between room temperature and Curie temperature.