JPH02273348A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To attain the high recording density and reproduced output of the magneto-optical recording medium alternately laminated with thin films respectively essentially consisting of rare earth metals and transition metals by specifying the film thickness values per layer of the former. CONSTITUTION:Periodic multilayered films 2 of 1,000Angstrom thickness alternately laminated with Tb films 3 and FeCo films 4 as recording layers are formed on a glass substrate 1 having 1.2mm thickness and a protective layer 5 of 800Angstrom thickness consisting of an Si3N4 film is formed thereon. The film thicknesses DTb and DFeCo per layer respectively of the films 3 and 4 are specified by selecting the number of circuit boards, the DC electric power to be supplied, and 1.1. to 2.5 sputtering rate ratio of the film 4 to the film 3 by two dimensional DC magnetron sputter method, by which the film thickness DTb is specified in the range of 3.5Angstrom near the atom diameter of Tb to 10.8Angstrom which is 3 times this thickness. The high Kerr rotating angle thetak is thus obtd. at the low Curie temp. Tc and the high sensitivity and high reproduced output are obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magneto-optical recording medium, particularly a magnetic film having an axis of easy magnetization perpendicular to the film surface as a recording layer, which is irradiated with a light beam such as a laser. The present invention relates to a magneto-optical recording medium in which information can be recorded by creating reversed magnetic domains in a region and read out using the magneto-optic effect.

[Conventional technology]

Conventional magneto-optical recording media are attracting attention as a type of large-capacity file memory, and because they have the advantage of being able to rewrite recorded information, they are widely used as code data file memory, image file memory, etc. A wide range of applications are being actively researched in various places. The recording medium is T.
b, rare earth metal RE such as Gd5Dy, Ho, Fe,
RE-TM based amorphous magnetic alloy thin film created by combination with transition metal TM such as Co and Ni has high recording sensitivity, low grain boundary noise, and magnetic anisotropy in the direction perpendicular to the film surface. It is considered the most promising because it has advantages such as easy production of membranes.

Magneto-optical recording media using TbFeCo or CdTbFe in the recording layer are already at a practical level for code data files that can be used even at relatively low data transfer rates.

In recent years, one of the improvements in the performance of magneto-optical recording media is an increase in the data transfer rate.

This is particularly strongly required in the field of recording and reproducing large amounts of data in real time, such as image files.

In order to increase the data transfer rate, it is necessary to obtain sufficient recording and reproduction signals when the disk rotates at high speed, so the recording layer is required to have higher recording sensitivity and reproduction output than conventional ones.

Information is recorded on the recording layer by magnetizing it in one direction and irradiating it with a laser beam to raise the temperature of the medium to the Curie temperature T.
This is done by increasing the magnetic field to near c and forming inverted magnetic domains using an externally applied magnetic field and a demagnetizing field of the recording layer.

Therefore, in order to make the recording layer highly sensitive, the Curie temperature Tc
needs to be lowered.

On the other hand, reproduction is performed using the magneto-optical effect.

In other words, information is read from the recording layer by utilizing the rotation of the polarization plane of the reflected light from the medium depending on the presence or absence of reversed magnetic domains in the recording layer.In order to obtain high reproduction output, it is necessary to It is necessary to increase the rotation angle of the surface, that is, the Kerr rotation angle θ.

[Problem to be solved by the invention]

However, in order to meet the demand for higher data transfer rates, the conventional magneto-optical recording medium described above requires a recording layer having a low Curie temperature Tc and a high Kerr rotation angle θ. In conventional 'RETM-based amorphous magnetic alloy thin films represented by TbFe+TbFeCo, the Kerr rotation angle θ generally tends to decrease as the Curie temperature Tc decreases. (See Uchiyama et al., 1985 IEEJ National Conference S.3-1.) For example, RE, which is often used for code data files.
Kerr rotation angle θ of a recording layer having a composition near 20 at%
, is 0.37 degrees when the Curie temperature Tc is 200℃, but when the Curie temperature Tc is lowered to 150℃, it becomes 0.
．． The temperature drops to 30 degrees. As described above, conventional recording media have the following drawback: when aiming for high sensitivity, the reproduction output decreases significantly.

[Means to solve the problem]

The magneto-optical recording medium of the present invention is a magneto-optical recording medium whose recording layer is a periodic multilayer film in which rare earth metal thin films and thin films mainly composed of transition metals are laminated alternately. The film thickness value per layer is configured to be larger than the diameter of the rare earth atom and smaller than three times the diameter of the rare earth atom.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention.

The magneto-optical recording medium shown in FIG. 1 has a recording layer of Tb3 and FeC on a glass substrate 1 with a thickness of 1.2 mm.

A periodic multilayer film 2 with a thickness of 100 OA is formed by alternately stacking films 4, and a periodic multilayer film 2 with a thickness of 80 OA consisting of a Si3N4 film is formed on top of this.
A protective layer 5 of 0 persons is formed.

The recording layer is manufactured by a binary DC madanetron sputtering method. In the production apparatus shown in FIG. 2, the recording layer is formed on the substrate 1.
While rotating, target 8 of Tb and F e 90
It is produced by simultaneously supplying DC power to COlo's Targetera I/9 and performing simultaneous film formation (both are battered).

The Tb film 3 and FeC determine the periodic structure of the recording film.

Each of the films 4 has a film thickness DT □. . .

is selected depending on the substrate rotation speed, the DC input power, and the sputtering rate ratio R of the FeCo film 4 to the Tb film 3.

Table 1 shows the main sputtering conditions.

Table 1 Sputtering conditions si3] Protective layer 5 of 800 mm thick made of J4 film is
Using a Si target, a mixed gas of Ar and N2 (50%
By reactive sputtering using N2) as the sputtering gas,
Power density 8w/cut, sputtering gas pressure 2.5X10
'Made with Pa.

FIG. 3 shows the relationship between the Curie temperature Tc and Kerr rotation angle θ of the recording film and the film thickness DTb per layer of the Tb film 3 when the sputtering rate ratio R (FeCo/Tb) is 1.15.
and 1.25. In either case, the film thickness D
From 35 people whose Tb is close to the atomic diameter of Tb to 1 which is about three times that
In the range of 0.8 people, the Curie temperature Tc is equal to the film thickness DTb
It can be seen that the Kerr rotation angle θ decreases as θ increases, but the Kerr rotation angle θ remains almost unchanged.

The decrease in Curie temperature Tc with increase in film thickness DTb is
A sputter rate ratio R of 1.25 is more significant than 1.15.

Further, the recording film had magnetic anisotropy in the direction perpendicular to the film surface within a range where the film thickness I)Tb was smaller than 10.8 mm.

For example, the film thickness DTb is 8, and the sputtering rate ratio R is 1.2.
In the case of No. 5, a recording film having a Curie temperature Tc of 150° C. and a Kerr rotation angle θ of 0.4° is obtained.

In another embodiment shown in FIG. 4, the diameter is 130 mm and the thickness is 1
．． This recording film is placed on a 2 mm polycarbonate substrate 14 with a protective layer 5 of 800 mm thick made of Si3N4 film.
and 15, and the recording and reproducing characteristics were measured.

The recording and reproducing characteristics were evaluated using a PIN-differential optical system with an objective lens of NAo 5, a peripheral speed of 11.3 m/s (disc rotation speed 180 Orpm, radius 60 mm), a recording frequency of 2.5 MHz, and a recording pulse duty. 50% and a bias magnetic field of 2500e. As a result, 7 mW was obtained as the optimum recording power at which the second harmonic distortion of the carrier wave was minimized.

This value is based on the conventional standard recording film (Tc=200°C, θ,
= 0.37 degrees), the recording sensitivity was 2 to 3 mW lower, and a significantly higher recording sensitivity was achieved.

In addition, the CNR is 56 to 57, which is 1 to 2 dB higher than the conventional one.
dB was obtained.

Here, the rare earth metal thin film and the thin film containing transition metal as main components are not limited to those described above. For example, as rare earth metal thin films, Dy film, Gd film, GdTb alloy film, as thin films mainly composed of transition metals, Fe film, Co
Similar effects were observed even when a film or FeCoTi alloy film was used.

〔Effect of the invention〕

Since the magneto-optical recording medium of the present invention can obtain a high Kerr rotation angle θ at a low Curie temperature Tc, it has the advantage of being able to obtain high recording sensitivity and high reproduction output.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG.
FIG. 3 is a characteristic diagram of the embodiment shown in FIG. 1, and FIG. 4 is a sectional view showing another embodiment of the present invention. 1.14... Substrate, 2... Periodic multilayer film, 3...
...Tb film, 4...FeCo film, 5,15
...Protective film, 6...Substrate boulder, 7...
... Sputter chamber, 8.9 ... Targetera l-110, 11 ... Target holder, 1
2,1.3...DC power supply, θ Yu...Carr rotation angle, Tc...Curie temperature. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] A substrate, and a rare earth metal thin film and a thin film mainly composed of a transition metal, each of which has a thickness value per layer of the rare earth metal thin film larger than the rare earth atom diameter and less than three times the rare earth atom diameter, are alternately formed on the substrate. What is claimed is: 1. A magneto-optical recording medium comprising a periodic multilayer film and a protective layer formed to cover the periodic multilayer film.