JP2800444B2 - Magneto-optical recording medium and recording / reproducing method thereof - Google Patents

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 used for recording information and a recording / reproducing method for the medium.

[0002]

2. Description of the Related Art Optical disks have been applied in various fields as high-density, high-speed recording media. However, in consideration of use for moving images and the like and in consideration of competition with other recording media, higher-density recording is required. However, the spot diameter of the reproduction beam used for the optical disc is limited by the wavelength of the semiconductor laser used,
At the wavelength of about 780 nm currently used, it is about 1 μm. Therefore, when the interval between recording bits becomes narrower, surrounding bits are simultaneously read at the time of reading, so that the signal strength is significantly reduced. Even when the track pitch is reduced, crosstalk is increased for the same reason.

In order to solve these problems, it is only necessary to shorten the wavelength of the laser. However, the development of a semiconductor laser having a short wavelength is accompanied by extremely technical difficulties, and more time will be required in the future. Seem. Although there is a method of generating a second harmonic using a nonlinear optical element (SHG), it is difficult to generate sufficient power.
The above problem was exactly the same for a magneto-optical disk as a rewritable optical disk. However, a magazine "Nikkei Electronics" published in February 1991 reported a method for increasing the recording density while keeping the wavelength of the laser beam as it is. I have. This method is briefly summarized with reference to FIG. 2. a) Recording is performed on both layers by using two layers, the reproducing layer (1) and the recording layer (2). B) The magnetization of the reproducing layer is aligned using an initial magnetic field. C) A reproduction light (4) is irradiated while an external magnetic field (3) is applied, and the magnetization of the recording layer (2) is transferred to the reproduction layer (1) by the temperature rise. Therefore, in this method, since there is no bit in the reproduction layer that has not been reproduced yet during reproduction, signal leakage from surrounding bits is small and the recording density can be improved. Also, since there are no bits in adjacent tracks, the track pitch can be reduced.

[0004]

However, in this system, as shown in FIG. 2, since there are bits in the portion where the reproduction light has passed, it is impossible to completely eliminate signal leakage from surrounding bits. could not. That is, one side of the bit being read is in the erased state, but the other side has the bit, and the effect is half that of the state in which the entire periphery is erased. Therefore, the effect of improving the recording density has been insufficient.

[0005]

Means for Solving the Problems The present inventors provide a reproducing layer with specific magnetic characteristics and apply an initializing magnetic field during reproduction to initialize again a portion whose temperature has decreased after reproduction and to reproduce during reproduction. Succeeded in completely eliminating signal leakage from surrounding areas. The gist of the present invention is a magneto-optical recording medium having a reproducing layer and a recording layer formed of a perpendicular magnetization film on a substrate, wherein the reproducing layer and the recording layer are exchange-coupled to each other; (B) When the coercive force H _C1 of the reproducing layer and the coercive force H _{C2 of the} recording layer are equal to or higher than H _C1 <H _C2 (b) room temperature and equal to or lower than the Curie temperature T _{C2 of the} recording layer.

[0006]

(Equation 2)

[0007] A magneto-optical recording medium characterized by having a temperature T _R that satisfies the above relationship, and a recording / reproducing method characterized by performing recording / reproduction using the medium by the following method.

[0008] Recording is performed by changing the magnetization direction of the recording layer by modulating the recording light or modulating the magnetic field according to the binary information. By applying the initialization magnetic field Hini, the magnetization of the reproducing layer is aligned in one direction without changing the magnetization direction of the recording layer. The reproducing layer is irradiated with reproducing light from the reproducing layer while Hini is applied, so that the temperature of the reproducing layer is equal to or higher than room temperature and equal to or lower than T _C2 , and the temperature T satisfies the expression (A) according to claim 1. _The temperature rises to _R. As a result, the magnetic domain of the reproducing layer is reversed so that the domain wall disappears when there is a domain wall between the recording layer and the reproducing layer. Transfer to layer.
When the reproduction light passes and the temperature of the reproduction layer decreases, the magnetic domains of the reproduction layer are aligned in one direction again by Hini.

As shown in FIG. 1, the magnetic layer of the present invention stores information in the reproduction layer (1) and the recording layer (2), which are the two layers of the exchange-coupled reproduction layer (1) and recording layer (2). Recording can be easily performed by a normal light modulation recording method or a magnetic field modulation recording method. When information is reproduced, an initialization magnetic field (3) Hini that is large enough to initialize the reproduction layer (1) must be applied around the portion irradiated with the reproduction light (4). . Assuming that the exchange coupling energy between the reproducing layer (1) and the recording layer (2) is σ _W

[0010]

(Equation 3)

Must be satisfied. At this time, the condition that the recording on the recording layer does not disappear

[0012]

(Equation 4)

Equation (2) must be satisfied both at room temperature and in a state where the reproducing light is irradiated.

In the case of the present invention, it is not necessary for the reproducing layer to remain initialized when Hini disappears, and the reproducing layer may be changed so that the domain wall disappears. In the case of the above-mentioned known technique, Hini is initialized after the reproduction layer is initialized.
The playback layer must not change even when there is no

[0015]

(Equation 5)

Although the requirement for the reproducing layer has been severed due to the condition described above, such a restriction does not occur in the present invention.

The temperature at which the reproducing layer is irradiated with reproducing light is represented by T
_Let it be _R. At this time, the coercive force of the reproducing layer is H _C1R and the saturation magnetization is M _S1R . At low T _R than the Curie temperature of the higher recording layer than room temperature

[0018]

(Equation 6)

When the relationship is satisfied, the reproducing layer moves so as not to form a magnetic domain wall with the recording layer, and the information of the recording layer is transferred to the reproducing layer.

From formulas [1] and [4], the reproducing layer is

[0021]

(Equation 7)

It can be seen that when the condition is satisfied, an appropriate Hini can exist. When the temperature decreases due to the passage of the reproduction light, the condition of the expression (1) is satisfied again, and the reproduction layer is initialized.

By the above-mentioned movement, as shown in FIG. 1, recording bits are generated only in the portion heated by the reproduction light (4), and are not generated in other portions at all. And recording at a very high density becomes possible. The reproducing layer (1) used here is, for example, DyFe
Co, GdFeCo, GdFe, GdTbFe, GdT
Materials such as bFeCo and GdDyFeCo, from which low H 2 _C is easily obtained, are used. It is preferable that the coercive force (magnetization) greatly changes with temperature due to a slight temperature rise of the reproduction light (4).
GdFeCo or GdDyFeCo, GdTbFeC
Those having a large Gd content of o, GdFe and GdTbFe are preferably used.

The recording layer (2) has TbFeCo, Tb
A material such as Fe, TbDyFeCo, and GdTbFeCo, from which large H _C is easily obtained, is used. Reproduction layer (1)
An intermediate layer for controlling the exchange coupling force may be provided between the recording layer and the recording layer (2). By providing the intermediate layer, Hini can be reduced. As the intermediate layer, a layer having a smaller magnetic anisotropy than the reproducing layer (1) and the recording layer (2) is used. For example, GdFeCo or the like.

If the thickness of the reproducing layer (1) is too small, the coercive force becomes large and initialization becomes difficult. If the thickness is too large, the sensitivity is deteriorated. If the recording layer (2) is too thin, the magnetic domains become unstable, and if it is too thick, the sensitivity deteriorates. In the case of the present invention, since a strong magnet (Hini) is required to face the optical head at the time of reading, it may be difficult to invert the magnetic field corresponding to recording and erasing. In such a case, another head is prepared exclusively for recording or erasing. In this case, a great advantage is that overwriting can be apparently performed by the two heads.

It is a preferable embodiment to form protective films on both sides of the magnetic layer to prevent oxidation. As the protective film, a thin film of ceramics such as oxide, nitride, carbide, sulfide and the like is preferably used. Si ₃ N ₄ , AlN, TiO ₂ , T
a ₂ O ₅ , SiO ₂ , SiO, Al ₂ O ₃ , ZnS, S
iC, etc. Further, a protective film of an organic film such as an ultraviolet curable resin may be further provided thereon.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an example, a reproducing layer having a thickness of 500 ° (Gd _90
10 ) ₂₂ (Fe ₉₅ Co ₅ ) is used, and the recording layer is made of Tb ₂₁ (Fe ₉₀ Co ₁₀ ) ₇₉ of 500 ° C. at a Curie temperature of 200 ° C. When the reproducing power is 1.5 mW, the temperature of the reproducing layer rises to about 80 ° C. Table 1 shows the characteristics of the reproducing layer and the recording layer at room temperature and 80 ° C. At this time, the left side of equation (5) is

[0028]

(Equation 8)

The following expression (5) is satisfied. A value of 1.9 kOe or more and 2.5 kOe or less may be selected for Hini. The right side of equation (2) for the recording layer is 7 kO at room temperature.
e, and 5.5 kOe at 80 ° C., the magnetic domains of the recording layer are stably present without being affected by Hini.

[0030]

[Table 1]

[0031]

According to the present invention, it is possible to generate recording bits only in the reproducing portion in the reproducing layer, so that the recording density can be increased and the recording capacity can be drastically improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a reproduction method according to the present invention.

FIG. 2 is an explanatory diagram of a conventional reproducing method.

[Explanation of symbols]

 Reference Signs List 1 playback layer 2 recording layer 3 initialization magnetic field 4 playback light

Claims (2)

(57) [Claims] 1. A magneto-optical recording medium having a reproducing layer and a recording layer formed of a perpendicular magnetization film on a substrate, wherein the reproducing layer and the recording layer are exchange-coupled to each other.
A magneto-optical recording medium satisfying (b). (A) below in the Curie temperature T _C2 or less is the temperature of the coercive force H _C1 of the reproducing layer and the coercive force H _C2 of the recording layer is H _C1 <and recording layer by H _C2 (b) at or above room temperature at room temperature (A) There is a temperature T _R that satisfies the equation 2. A recording / reproducing method using the magneto-optical recording medium according to claim 1 to perform recording / reproducing by the following method. Recording is performed by changing the magnetization direction of the recording layer by modulating the recording light or the magnetic field according to the binary information. By applying the initialization magnetic field Hini, the magnetization of the reproducing layer is aligned in one direction without changing the magnetization direction of the recording layer. The reproducing layer is irradiated with reproducing light from the reproducing layer while Hini is applied, so that the temperature of the reproducing layer is equal to or higher than room temperature and equal to or lower than T _C2 , and the temperature T satisfies the expression (A) according to claim 1. _The temperature rises to _R. As a result, the magnetic domain of the reproducing layer is reversed so that the domain wall disappears when there is a domain wall between the recording layer and the reproducing layer. Transfer to layer. When the reproduction light passes and the temperature of the reproduction layer drops,
The magnetic domains of the reproducing layer are again aligned in one direction by Hini.