JPH06187680A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium having high recording sensitivity, a high CN ratio of signal at the time of reproducing, and high recording power margin. CONSTITUTION:The magneto-optical recording medium consists of a first and second magnetic layers magnetically coupled with each other. Each magnetic layer consists of a heavy rare earth-transition metal alloy having perpendicular magnetic anisotropy. The first magnetic layer has a relatively high Curie temp. (Tc1) lower coercive force (Hc1) at room temp. The second magnetic layer has a relatively lower Curie temp. (Tc2) and a higher coercive force (Hc2) at room temp. The saturation magnetization (Ms1) of the first magnetic layer at the Curie temp. Tc2 of the second magnetic layer is specified to 130<=Ms<=175 (emu/cc).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium. More specifically, the present invention relates to a magneto-optical recording medium useful for computers, audio equipment, measuring equipment and the like.

[0002]

2. Description of the Related Art Recently, an optical recording / reproducing method satisfying various requirements such as high density, large capacity, high access speed, high recording speed, high reproducing speed and the like, and an optical recording / reproducing method used therefor. Efforts have been made to develop recording devices, playback devices and recording media. Among various optical recording / reproducing methods, the magneto-optical recording / reproducing method is capable of erasing the information after recording the information once, and further recording new information after erasing the information. Is full of greatest appeal because of the unique advantage of being repeatable.

The magneto-optical recording medium used in this magneto-optical recording / reproducing method generally uses a magnetic thin film having perpendicular magnetic anisotropy in the recording layer. And as a magnetic thin film,
Typically, GdFe, GdCo, GdFeCo, TBFe, TbCo, TbFeCo
It is known to be composed of an amorphous heavy rare earth-transition metal alloy such as. The initialization, recording, and reproducing methods for this magneto-optical recording medium are performed in the following procedure. That is, the initialization is performed by setting the magnetization direction of the recording layer to either the upward direction or the downward direction. Recording is performed by heating a part of the recording layer near the Curie point with a laser beam whose diameter is reduced to about 1 micron, and using the recording magnetic field Hb to form a mark having magnetization in the opposite direction. . The recorded information is expressed by the presence or absence of this mark and / or the mark length. Then, this recorded information is reproduced by using the polarization of the laser beam depending on the Kerr rotation angle θk of the recording layer.

Generally, however, a high-performance recording layer having a low Curie point, easy recording, a large coercive force, a high storage stability, a large θk, and a high CN ratio during reproduction. It is difficult to realize the above with only one magnetic material. Therefore, the function required for the recording layer is divided into, for example, a recording layer (or recording holding layer) in a narrow sense and a reproducing layer, and a magnetic material having a suitable composition is selected for each of the two-layer magneto-optical recording. A medium has been proposed. One of the two-layer film magneto-optical recording media of this type is the two-layer film magneto-optical recording medium disclosed in JP-A-57-78652. This two-layer film magneto-optical recording medium is a magnetic layer having a relatively high Curie temperature and a relatively low coercive force (low coercive force layer) and a magnetic layer having a relatively low Curie temperature and a relatively high coercive force. (High coercive force layer) and a two-layer film, and the high coercive force layer and the low coercive force layer are exchange-coupled to each other. In this double-layered magneto-optical recording medium, since recording is performed in the vicinity of the low Curie temperature of the high coercive force layer, the recording sensitivity is high, and the recorded information is recorded from the side of the low coercive force layer having a high Curie temperature and a large Kerr rotation angle θk. The recorded data has a high CN ratio due to the reproduction of the. Further, since the information is stored in the high coercive force layer, the information storage property is also excellent.

However, recently, in this double-layered magneto-optical recording medium, when the recording laser power is smaller than the optimum recording power, there occurs a phenomenon that marks to be recorded are not recorded at a certain ratio and are lost. I've found it easy. When recording on a magneto-optical recording medium, the larger the recording laser power, the longer the mark to be recorded. The recording power (P
The recording power at which the time length of the signal coincides with the light emission time in w) is called the optimum recording power, and when the mark length recording is performed by magneto-optical recording, it is desirable that the recording optimum recording power is used.

However, in an actual recording / reproducing apparatus, the recording power often deviates from the optimum recording power for various reasons. Therefore, it is desirable that the mark be surely recorded even if the recording power deviates from the optimum value by about ± 20%. However, in the conventional double-layered magneto-optical recording medium as described above, the recording power is 15% from the optimum recording power. When it was reduced by about%, there was a missing mark to be recorded.

The present invention has been made in view of the above circumstances, solves the problems in the prior art, and even if the recording power is smaller than the optimum recording power,
An object of the present invention is to provide an improved magneto-optical recording medium capable of surely providing a mark for recording information.

[0008]

In order to solve the above-mentioned problems, the present invention provides a first magnetic layer and a second magnetic layer each made of an amorphous heavy rare earth-transition metal alloy having perpendicular magnetic anisotropy. The first magnetic layer has a relatively high Curie temperature (Tc1) and a relatively low coercive force (Hc1) at room temperature. Is the magnitude of the saturation magnetization of the first magnetic layer at the Curie temperature Tc2 of the second magnetic layer in a magneto-optical recording medium having a relatively low Curie temperature (Tc2) and a relatively high coercive force (Hc2) at room temperature. Provided is a magneto-optical recording medium characterized in that (Ms1) is 130 ≤ Ms1 ≤ 175 (emu / cc).

That is, the present invention provides a low coercive force layer (first
Saturation magnetization Ms1 at Curie temperature Tc2 of magnetic layer)
If the recording power is set to 130 (emu / cc) or more, even if the recording power is 15% or more smaller than the optimum recording power, no marks are lost and the optical signal with a good CN ratio of the reproduced signal is obtained. It was completed based on the finding that a magnetic recording medium can be obtained. And, in this case, GdFe and GdFeC are used for the first magnetic layer.
O, GdCo, GdTbFeCo, GdDy, etc. are desirable. Of these, GdFeCo with the highest Curie temperature and large Ms1 is the first.
Most suitable for magnetic layers.

Further, in the present invention, in order to realize a high Curie temperature and a large Ms1, it is desirable that the ratio of Co in the transition metal is large, and the ratio of the number of Fe and Co atoms is changed.
When Fe: Co = 1-X: X, X ≧ 0.30 is desirable.

[0011]

According to the present invention, even if the recording power is smaller than the optimum recording power by, for example, 15% to 25%, no mark drop is observed and the CN ratio of the reproduced signal is good. The reason why the medium is obtained is considered as follows. That is, first, in the two-layer film magneto-optical recording medium, a temperature higher than the Curie temperature (Tc2) of the second magnetic layer of the high coercive force layer reverses the magnetization of the first magnetic layer of the low coercive force layer, and when the temperature is lowered, the high coercive force is increased. Recording is performed in the process of transferring to a layer.

It is considered that the missing of the mark occurs when the temperature rise of the magneto-optical recording medium is insufficient and the reversal of the magnetization of the first magnetic layer of the low coercive force layer is not performed well. On the other hand, a demagnetizing field created by the recording film itself acts on the magnetic recording film. This demagnetizing field acts in a direction to help the magnetization of the recording film to face the direction of the recording magnetic field Hb, and its magnitude increases in proportion to the magnitude of the magnetization.

Since the vicinity of the recording mark is heated to a temperature near the Curie temperature Tc2 of the second magnetic layer,
Large Ms1 at this temperature helps recording by the demagnetizing field. Even if the recording power is small and the temperature rise of the medium is insufficient, if the magnitude Ms1 of the saturation magnetization of the first magnetic layer at a temperature near Tc2 is large, the mark is reliably formed with the help of the demagnetizing field. It

From the above, it is considered that in the conventional double-layered magneto-optical medium, Ms1 at a temperature near Tc2 was small, and thus the recording mark was likely to be lost. On the other hand, if Ms1 is too large, then a phenomenon occurs in which a minute magnetic domain facing the initialization direction appears in the recording mark, and the noise component during data reproduction increases. This phenomenon is observed when Ms1 at Tc2 is larger than 175 (emu / cc). From these, Ms1 in Tc2 must be 130 (emu / cc) or more and 175 (emu / cc) or less. The present invention is based on the above new knowledge of the magneto-optical recording action.

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

[0016]

Example 1 As shown in FIG. 1, a disk-shaped glass substrate (10) having a thickness of 1.2 mm and a diameter of 300 mm was set in a vacuum chamber of a three-dimensional magnetron sputtering apparatus to form a magnetic film. Filmed

After evacuating the interior of the vacuum chamber to 5 × 10 ^-5 Pa, Ar gas was introduced to adjust the Ar gas pressure to 2 × 10 ^-1 Pa.
Sputtering was carried out while holding at. First SiN
Using the target, a SiN protective film layer (11) having a film thickness of 70 nm was formed on the substrate. Then, using a GdFeCo alloy target, Gd _22.6 (Fe with a thickness of 50 nm was formed on the protective film layer (11).
₇₀ Co ₃₀ ) _77.4 (subscript represents atomic%) 1st
A magnetic layer (low coercive force layer) (12) was formed. On top of that, a Tb ₂₃ Fe ₇₇ film with a thickness of 50 nm was formed using a TbFe alloy target.
A second magnetic film (high coercive force layer) (13) was formed. Finally, a protective film layer (14) having a film thickness of 70 nm was formed again using a SiN target.

The Curie temperature of each magnetic layer thus formed is 400 ° C. or higher for the first magnetic layer (12) and the Curie temperature for the second magnetic layer (1)
3) was 140 ° C. In addition, 14 of the first magnetic layer (12)
The Ms1 at 0 ° C was 152 (emu / cc). For this disc under the conditions of linear velocity of 15 m / s and recording magnetic field of 300 Oe 7.
When recording a 5MHz signal, the optimum recording power is
It was 6.20 mW.

Next, the recording power was reduced by about 20% to 4.95 mW.
Was recorded. Is there any missing mark?
It was. Furthermore, the recording power is reduced by 0.05 mW each.
However, when the mark was lost, the recording power was 4.90 mW.
First seen. That is, -2 for the optimum recording power
No mark was lost until the recording power was 0%. Examples 2-5 In the same procedure as in Example 1, Gd: (Fe of the first magnetic layer (12) was₇₀
Co₃₀) Is changed to produce a magneto-optical recording medium.
It was Change the atomic% of Gd to 22.0, 22.4, 22.7, 23.1
It was Recording on this magneto-optical recording medium under the same conditions as in Example 1.
Composition at the time of recording, Ms1, optimum recording power, recording power
Mark was first observed when the
Mark missing start power, which is the recording power when measured,
And what percentage of laser power
From the optimum recording power that indicates whether it is warned
The amount of deviation was measured.

The results are shown in Table 1.

[0021]

[Table 1]

Example 6 By the same procedure as in Example 1, the first magnetic layer (12) has a thickness of 50.
Gd ₂₂ (Fe ₆₀ Co ₄₀ ) ₇₈ nm, and the thickness of the second magnetic layer (13) is
A magnetic film was formed as 50 nm Tb ₂₀ Fe ₇₆ Co ₄ . The Curie temperature of each magnetic layer formed in this way is determined by the first magnetic layer (1
2) was 400 ° C. or higher, and the second magnetic layer (13) was 175 ° C. The Ms1 of the first magnetic layer at 175 ° C is 173 (emu / c
It was c). When a signal of 7.5 MHz was recorded on this disk under the conditions of a linear velocity of 15 m / s, a recording power of 6.7 mW and a recording magnetic field of 300 Oe, the optimum recording power was 8.10 mW.

Further, when recording was performed while gradually lowering the recording power, no mark was lost until the recording power was 6.05 mW. That is, -2 for the optimum recording power
It means that no marks were lost until the recording power was 5%.

[0024]

As described in detail above, according to the present invention, it is possible to provide a magneto-optical recording medium having a high recording sensitivity, a high CN ratio of a signal during reproduction, and a large recording power margin.

[Brief description of drawings]

FIG. 1 is a sectional view of a recording medium as an example.

[Explanation of symbols]

 Reference Signs List 10 substrate 11 protective film layer 12 first magnetic layer (low coercive force layer) 13 second magnetic layer (high coercive force layer) 14 protective film layer

Claims (3)

[Claims] 1. A first magnetic layer and a second magnetic layer, each of which is composed of an amorphous heavy rare earth-transition metal alloy having perpendicular magnetic anisotropy, are magnetically coupled and laminated. The magnetic layer has a relatively high Curie temperature (Tc1) and a relatively low coercive force (Hc1) at room temperature, and the second magnetic layer has a relatively low Curie temperature (Tc2) and a relatively low room temperature. In a magneto-optical recording medium having a high coercive force (Hc2), the magnitude of saturation magnetization (Ms1) of the first magnetic layer at the Curie temperature Tc2 of the second magnetic layer is 130 ≤ Ms1 ≤ 175 (emu / cc). A magneto-optical recording medium characterized by the above. 2. The magneto-optical recording medium according to claim 1, wherein the main component of the first magnetic layer is Gd, Fe and / or Co. 3. The light according to claim 2, wherein when the ratio of the number of Fe and Co atoms contained in the first magnetic layer is Fe: Co = 1-X: X, X ≧ 0.30. Magnetic recording medium.