JPH0410256A - Magneto-optical recording medium and magneto-optical recording method - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium for many valued recording satisfying read/write conditions by executing ternary information recording by utilizing the difference in the recording threshold power of a 1st recording film and a 2nd recording film. CONSTITUTION:The state in which the directions of the magnetizations of the 1st recording film 3 and 2nd recording film 5 having >=2mW difference in the recording threshold power, 50 to 400Angstrom film thickness and the layers 2, 4, 5 consisting of transparent dielectric films existing at 50 to 500Angstrom between the layers are both directed upward is set as an initial state. The films 3, 5 are irradiated with a laser of the power larger than the threshold power of the film 3 and smaller than the threshold power of the film 5 from the film 3 side under the impression of the magnetic field at which the magnetization of the films 3, 5 cannot be inverted at room temp., by which only the magnetic of the film 3 is inverted. The power for the irradiation is increased to the power above the threshold power of the films 3, 5 and the magnetizations of both films 3, 5 are inverted. The ternary recording is executed by the various intensifies of the laser beam with which the films are irradiated in this way. The magneto-optical recording medium for many valued recording satisfying the read/write conditions is thus obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magneto-optical recording medium and a magneto-optical recording method, in particular,
The present invention relates to a magneto-optical recording medium and an optical recording method capable of recording ternary information in one recording pit.

[Conventional technology]

Magneto-optical disks have already been commercialized as large-capacity, randomly accessible, removable media files. In a conventional magneto-optical disk medium, the recording film is a single layer, and the direction of magnetization of the recording film is used as a recording mark. Some use dual-layer recording films, which are exchange-coupled two-layer film media to improve sensitivity or allow overrides.

It has been reported that multi-value recording is possible by using films with different coercive powers as multilayer films for multi-value recording.

[Problems to be solved by the invention] Multilevel recording is difficult with conventional single recording films or exchange-coupled recording films, and it is difficult to achieve high density due to the size of the laser spot due to the wavelength limit of laser light. There was a limit.

The report that multi-level recording is possible due to the difference in retention force (13th Japanese Society of Applied Magnetics, Abstracts of Academic Lectures (1989), p. 63) merely showed that multi-level recording is possible in principle; R/W (read/write) conditions, particularly readability, were not considered.

An object of the present invention is to provide a magneto-optical recording medium for multilevel recording and a magneto-optical recording method that satisfy R/W conditions.

[Means to solve the problem]

The present invention provides a magneto-optical disk medium having a perpendicular magnetization film as a recording film, wherein the recording film is composed of two layers, a first recording film and a second recording film,
There is a difference of 2IIIW or more between the recording threshold power of the first recording film and the recording threshold power of the second recording film, the layer thickness of each recording film layer is 50 Å or more and 400 Å or less, and
Between the layers, there is a layer of transparent dielectric film with a thickness of 50 Å or more.
It is characterized by having a metal reflective film on the side opposite to the direction of incidence of the read beam, with a recording film and a transparent dielectric film interposed therebetween.

Further, the present invention provides a method for applying magnetic field Hb of a magnitude that cannot reverse the magnetization of either the first recording film or the second recording film at room temperature to the magneto-optical recording medium from the first recording film side. A magneto-optical recording method comprising a process of irradiating light, the irradiation power of the light being "0", and a power P1 greater than or equal to a threshold power of a first recording film and less than a threshold power of a second recording film; The present invention is characterized in that three-value recording is performed by setting three values of power P2, which is equal to or higher than the threshold power of the first recording film and the second recording film.

[Effect]

In the present invention, ternary information is recorded by utilizing the difference in recording threshold power between the first recording film and the second recording film.

For example, the initial state is when the magnetization directions of the first recording film and the second recording film are both upward.

While applying a magnetic field Hb of such a magnitude that neither the magnetization of the first recording film nor the second recording film can be reversed at room temperature in the opposite direction to this direction of magnetization, the first recording film is By irradiating the laser with a power P1 that is greater than or equal to the threshold power and smaller than the threshold power of the second recording film, a first state in which only the magnetization of the first recording film is reversed can be realized.

Further, by setting the irradiation power to a power P2 that is higher than the threshold power of the first recording film and the second recording film, a second state in which the magnetization of both the first recording film and the second recording film are reversed can be realized. In order to return to the initial state, it is sufficient to set the direction of the applied magnetic field in the same direction as in the initial state and irradiate the laser with a power P2 that is higher than the threshold power of the first recording film and the second recording film. In other words, three-value recording can be realized by adjusting the strength of the irradiated laser beam.

Furthermore, the magnetic Kerr effect can be used to read information. The magnitude of the Kerr rotation angle varies depending on the magnetization direction and magnitude of the material. Therefore, the magnitudes of the Kerr rotation angles in the initial state, the first state, and the second state are different, and by setting the slice level corresponding to the magnitude of each Kerr rotation angle in the readout level, it is possible to It becomes possible to read out the first state and the second state separately.

[Example] (Example 1) FIG. 1 is a partial cross-sectional view showing the structure of a magneto-optical medium according to the present invention. A total of six transparent dielectric films 2, 4, 6, recording films 3, 5, and metal reflective films 7 are formed on a polycarbonate substrate 1.
It is made of laminated layers. 5tsN for transparent dielectric films 2 and 4.6
4 was produced by the reactive RF sputtering method. The first recording film 3 has (Nd+:+Dy57) 21 (F esaccxb
) tq amorphous film, and T b tz for the second recording film 5.
(Fe sec 020)? 11 Amorphous film, DC
Manufactured using the magnetron svanta method. The metal reflective film 7 was made of AI by DC sputtering. Table 1 shows the thickness and type of each layer in Example 1.

Next, the R/W characteristics of this magneto-optical medium were measured.

Substrate rotation speed 300Orpm, linear velocity 11n+/s, recording frequency 3.7MHz, bias magnetic field Hb = 3000
FIG. 2 shows the dependence of the carrier level (dBm) on the recording power (-) under the condition of e. Read power is 1mW
It is. The carrier level is saturated in two stages: in the recording power range of 4 to 5 mW and in the recording power range of 6.51 mW or higher.

At this time, the carrier level in the recording power range of 4 to 5d and the carrier level in the recording power of 6.5mW or more is 8.
There is a dB difference, and the carrier level is higher when the recording power is 6.51 or higher. Therefore, the recording power should be set to 0.4~
By using three levels: 5 mW (this is referred to as Pl) and 6.5 or more ridges (this is referred to as P2), it is possible to record three-value information in one pit, and the strength of the recording power can be changed. I was able to achieve 3-level recording. In addition, since the reproduction output corresponding to the recording power can be obtained, by providing a slice level corresponding to each reproduction output,
Playback of three-value recording can be realized.

(Example 2) A magneto-optical recording medium having the same medium configuration as in Example 1 except that only the film thickness of each layer was changed was manufactured by the same method. Table 2 shows the thickness and type of each layer in Example 2.

Show the type.

Next, the R/W characteristics of this magneto-optical medium were measured.

FIG. 3 shows the dependence of carrier level on recording power under the same conditions as in Example 1. The read power is 11. The carrier level is saturated in two stages: in the range of recording power of 3 to 4.5 mW and in the range of recording power of 6.5 mW or more. At this time, there is a difference of 7 dB between the carrier level in the range of recording power of 3 to 4.5n+H and the carrier level at recording power of 6.5 mW or higher, and the carrier level is higher at recording power of 6.5 mW or higher. Therefore, the recording power is 0.3 to 4.5a+W (this is set as Pl)
, and 6.5 mW or more (this is referred to as P2) in three stages, it became possible to record three-value information in one pit, and three-value recording was realized by varying the strength of the recording power. Information reading was achieved in the same manner as in Example 1.

(Example 3) A magneto-optical recording medium having the same medium configuration as in Example 1, but with only the film thickness of each layer changed, was manufactured in the same manner. Table 3 shows the thickness and type of each layer in Example 3. Next, the R/W characteristics of this magneto-optical medium were measured.

FIG. 4 shows the dependence of carrier level on recording power under the same conditions as in Example 1. Read power is 0.5mW
It is. The carrier level is saturated in two stages: in the range of recording power of 2.5 to 4d and in the range of recording power of 5.5 mW or more. At this time, there is a difference of 8 dB between the carrier level in the recording power range of 2.5 to 4 mW and the carrier level in the recording power range of 5.5 + wW, and the recording power is 5.51 mW.
The career level is higher than the above. Therefore, by setting the recording power to three levels: 0.2.5 to 41 (this is referred to as Pl) and 5.5 mW or more (this is referred to as P2), three-value information is recorded in one bit. This made it possible to realize three-value recording by varying the strength of the recording power. Information reading was achieved in the same manner as in Example 1.

〔Effect of the invention〕

As explained above, in the magneto-optical medium and magneto-optical recording method of the present invention, ternary recording is possible, so the recording density is improved by 1.5 times compared to conventional media.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view showing the film structure of the magneto-optical recording medium of the present invention, FIG. 2 is a diagram showing the recording power dependence of the carrier level in Example 1, and FIG. 3 is a diagram showing the dependence of the carrier level in Example 2. FIG. 4 is a diagram showing the recording power dependence of the carrier level in Example 3. FIG. 1...Substrate 2.4.6...Transparent dielectric film 3...First recording film 5...Second recording film 7...Metal reflective film

Claims (2)

[Claims] (1) In a magneto-optical disk medium whose recording film is a perpendicularly magnetized film, the recording film consists of two layers, a first recording film and a second recording film,
There is a difference of 2 mW or more between the recording threshold power of the first recording film and the recording threshold power of the second recording film, the layer thickness of each recording film layer is 50 Å or more and 400 Å or less, and A layer consisting of a transparent dielectric film with a thickness of 50 Å to 500 Å exists between the layers, and a metal reflective film is provided on the opposite side to the direction of incidence of the read beam via the recording film and the transparent dielectric film. magneto-optical recording medium. (2) While applying a magnetic field Hb of such a magnitude that the magnetization of neither the first recording film nor the second recording film can be reversed at room temperature to the magneto-optical recording medium according to claim 1, the first
A magneto-optical recording method comprising a process of irradiating light from the recording film side, wherein the irradiation power of the light is "0" and the threshold power of the second recording film is higher than or equal to the threshold power of the first recording film. A magneto-optical recording method characterized in that three-value recording is performed by setting a small power P1 and a power P2 higher than a threshold power of a first recording film and a second recording film.