JP2919662B2 - Magneto-optical recording medium - 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 such as a rewritable magneto-optical disk. In the magneto-optical recording medium of the present invention, the recording layer is formed by alternately laminating a transition metal thin film and a rare earth metal thin film.

[0002]

2. Description of the Related Art (1) A magneto-optical disk having a recording layer made of a perpendicular magnetization film formed on a substrate has been proposed or provided as an optical disk capable of repeatedly recording and reproducing.
For recording on the magneto-optical disk, a desired portion of the recording layer is heated to a temperature above the Curie point by a laser beam to reduce the coercive force to 0, and then cooled under an external magnetic field. This is performed by directing the magnetization of the site (domain) in the direction of the external magnetic field (Curie point recording). In order to stabilize magnetization at room temperature, it is important that the coercive force Hc at room temperature is large. In the magneto-optical disk using a ferrimagnetic material as the recording layer, recording is performed by a compensation point recording method. The compensation point is the temperature at which the magnetization apparently becomes zero before reaching the Curie point. on the other hand,
The reproduction from the magneto-optical disk is performed by utilizing the rotation of the deflecting surface due to the magnetic Carr effect or the Faraday effect.

(2) It has been proposed to use a so-called alternating laminated film in which a transition metal thin film and a rare earth metal thin film are alternately laminated as the recording layer of the magneto-optical disk (Japanese Patent Laid-Open No. 60-1985). 237655, JP-A-61-108112, JP-A-59-217247, JP-A-62-26659,
JP-A-62-71041, JP-A-62-128041, JP-A-62-137753, JP-A-2-33744, etc.). These are considered in view of the fact that the above-mentioned alternately laminated film has superior characteristics with respect to the coercive force, the amount of magnetization, the magnetic Carr effect or the Faraday effect as compared with a single layer of an alloy of a rare earth metal and a transition metal. It was proposed.

[0004]

At the time of recording, the magneto-optical disk is heated at a high speed while the recording region (domain) is heated by a laser beam, and then cooled. The temperature of the domain due to the heating and cooling (= temperature at an arbitrary time) is not uniform in the rotation direction of the disk and the irradiation direction of the beam, but has a certain heat distribution. For this reason, there may be a case where the Curie point or the portion that does not reach the compensation temperature is formed in the peripheral portion of the domain, and even if it does, the time is different.

For this reason, there may be a portion where the direction of magnetization is not exactly aligned with the direction of the external magnetic field in the peripheral portion (edge) of the domain, and in such a case, it is likely to cause noise during reproduction. This tendency is particularly remarkable when the disk rotates at a high speed. The present invention aims to solve the above problems.

[0006]

According to the present invention, in a magneto-optical recording medium having a recording layer composed of an alternately laminated film of a transition metal thin film and a rare earth metal thin film on a substrate, the lamination cycle of the alternately laminated film is as follows: This is a magneto-optical recording medium which is formed so as to be shorter on the incident side of the laser beam and gradually longer as it goes away.

[0007] The lamination cycle of the alternately laminated film is about 1 to 1.5 [Å] on the shortest incidence side, and 40 to 50 [Å] on the longest side.
The degree is good, and during that time, it is good to gradually change so as to substantially conform to the compensation temperature characteristic (described later). The number of stacked layers is preferably about 50 to 400, and the total thickness of the alternately stacked films is about 20.
0 to 800 [Å] is good. With this configuration, the effects of the present invention can be obtained.

As the transition metal constituting the alternately laminated film, for example, an FeCo alloy can be used. As the rare earth metal, for example, a GdDy alloy can be used. Other than these, the present invention can be applied as long as it is a known material referred to as a constituent material of the alternately laminated film in the above-mentioned publication.

The substrate may be made of, for example, glass, polycarbonate (PC), polymethyl methacrylate, or epoxy resin. Any known material referred to as a constituent material of a substrate in a publication or the like can be used.

Also, a structure in which a dielectric (SiN or the like) film is formed between the substrate and the alternately laminated film so as to increase the Carr effect, etc., on the opposite surface side of the substrate so as to prevent oxidation of the alternately laminated film. A configuration in which a thin film of SiO, AlN, Si ₃ N ₄ or the like is formed as a protective film, and a configuration in which a Faraday effect is synergized with a Car effect by forming a reflective layer on the non-incident side, etc. The present invention can be applied.

[0011]

FIG. 2 is a compensation temperature characteristic diagram showing the relationship between the lamination period (Period) of the alternately laminated films and the compensation temperature (T _comp ).
As shown, the compensation temperature T _comp gradually decreases as the lamination cycle becomes longer. As described above, in the present invention, the lamination period is shorter on the incident side (the side where the heating amount is relatively large) of the laser beam, and is longer on the opposite side (the side where the heating amount is relatively small). And gradually changing between them. The rate of change of the lamination cycle is set to substantially correspond to the rate of change of the compensation temperature.

For this reason, in the domain heated by the laser beam at the time of recording, each portion including the peripheral portion reaches the compensation temperature at substantially the same time. For this reason, the direction of magnetization in the peripheral portion is also beautifully aligned with the direction of the external magnetic field, similarly to the central portion.

[0013]

Embodiments of the present invention will be described below. FIG. 1 is a diagram schematically showing a part of a cross section of a magneto-optical disk according to an embodiment, and FIG. 3 is a configuration explanatory view of a sputtering apparatus for producing the magneto-optical disk.

The magneto-optical disk shown in FIG.
Substrate 2, a protective film 1 formed of SiN on the polycarbonate substrate 2, a recording layer (perpendicular magnetization film) 3 formed on the SiN film, and And a protective film 4 formed of SiN. Note that the arrow LB indicates the laser beam.
Indicates the incident direction of the system.

The recording layer 3 is composed of an alternately laminated film GdDy-FeCo of GdDy (an alloy of gadolinium and dysprosium) and FeCo (an alloy of iron and cobalt). The laminating cycle is about 1 [Å] on the substrate 2 side and about 50 [Å] on the protective film 4 side, and during this period, the cycle is gradually increased in the direction of arrow a so that a total of 400 layers are laminated. ing. The total thickness of the recording layer 3 is 800
[Å]. The thickness of the protective film 1 is about 800 [Å], and the thickness of the protective film 4 is about 800 [Å].

The magneto-optical disk having such a configuration is manufactured by the apparatus shown in FIG. A substrate table 12 having a rotation mechanism and having a rotation speed freely controlled by a modulator 11 is provided above the vacuum-evacuated (approximately 10 ⁻⁷ [Torr]) sputtering apparatus 10. ing. The substrate 2 is mounted on the lower surface of the substrate table 12 at a position eccentric from the rotation axis. On the other hand, below the sputtering apparatus 10, GdDy3a is set on the target holding plate 14, and FeCo3b is set on the target holding plate 15, and these are separated by the shielding plate 13.

By using the apparatus 10 and performing sputtering by RF or DC while rotating the substrate table 12, the alternate laminated film 3 of GdDy-FeCo can be formed on the substrate 2. . Also, the lamination cycle can be set to a desired value by controlling the rotation speed of the substrate table 12.

For example, when the sputtering rate of the alternately laminated film 3 is set to 100 [Å / min] and the rotation speed of the substrate table 12 is gradually reduced from 100 [rpm] to 2 [rpm], A magneto-optical disk having the lamination cycle shown in FIG. 1 is obtained. In the magneto-optical disk prepared in this manner, the magnetization at the edges of the domains is uniformly aligned, and the noise is higher than that of the conventional magneto-optical disk (a magneto-optical disk in which the lamination cycle of the alternately stacked films is constant). Was reduced.

FIG. 4 shows the magneto-optical disk shown in FIG. 1 in which a reflection film 5 is formed on the side opposite to the substrate 2. In such a structure, the same effect as the magneto-optical disk of FIG. 1 was obtained.

[0020]

As described above, according to the present invention, the lamination cycle of the alternately laminated film (recording layer: perpendicular magnetization film) formed on the substrate is a laser.
It is shorter on the incident side of the beam and longer on the opposite side.
In the meantime, the temperature is gradually changed so as to correspond to the compensation temperature characteristic. For this reason, the time at which each portion of the domain formed in the alternately stacked film reaches the compensation temperature is substantially equal in both the edge portion and the central portion.

Therefore, at the time of recording involving heating by a laser beam, the direction of the magnetization of the domain is also precisely aligned with the direction of the external magnetic field at the edge. Therefore, noise at the time of reproduction is significantly reduced as compared with the related art, and recording can be performed with smaller power than the related art.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a cross-sectional structure of a magneto-optical disk according to an embodiment.

FIG. 2 is a graph showing compensation temperature characteristics.

FIG. 3 is an explanatory diagram of a sputtering apparatus for producing the magneto-optical disk.

FIG. 4 is an explanatory diagram schematically showing a cross-sectional structure of a magneto-optical disk according to another embodiment.

[Explanation of symbols]

1 protective film, 2 substrates, 3 recording layers (alternate layered film), 4 protective film, 5 reflective film,

Claims (1)

(57) [Claims] 1. In a magneto-optical recording medium having a recording layer composed of an alternately laminated film of a transition metal thin film and a rare earth metal thin film on a substrate, the lamination cycle of the alternately laminated film is such that the laser beam is incident on the laser beam incident side. A magneto-optical recording medium formed to be as short as possible and gradually longer as the distance increases.