JPH0453047A - Optical memory element - Google Patents

Abstract

PURPOSE:To increase a Kerr rotating angle and to improve C/N by forming a memory film of exchange bonded two-layered films of an amorphous thin film of rare earths transition metals and the amorphous thin film of rare earths transition metals having a different compsn. CONSTITUTION:Both of the amorphous thin films of the rare earths and transi tion metals which are the 1st layer and the 2nd layerconsist of the TM rich compsn. ratio having the sub-lattice magnetization MsTM of the transition metal TM larger than the sub-lattice magnetization MsRE of the rare earths metal RE. The magnitude of the Kerr rotating angle is mainly proportional to the magnitude of the sub-lattice magnetization MsTM of the transition metal TM. In addition, the respective layers maintain the respective magnetic characteristics by adopting the constitution of the two-layered films. The exchange bonding strength acts effective and the coercive force is intensified. Then, the perfor mance index is increased and the excellent recording characteristics are obtd.

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to an optical memory element that stores, reproduces, erases, etc. information by irradiating it with light such as a laser. .

(b) Conventional technology Magneto-optical storage media using thin films of amorphous alloys of rare earths and transition metals do not have sufficient readout characteristics;
Various improvement measures are being considered.

As an example, a method has been proposed in which a reflective film is provided on the optical memory 1 on the substrate (reflective film structure). This method (which aims to improve the figure of merit by combining the Maker effect and the Faraday effect) has previously been considered for use with magnetic garnet, which is nearly transparent in the visible light range and has a small light absorption coefficient. When using this method in a magnetic storage medium, the optimum film thickness is around 200 layers due to the magnitude of its absorption coefficient.

Furthermore, as another example, an exchange-coupled magneto-optical storage medium (magnetic double-layer film medium) having a two-layer structure consisting of a read layer and a write layer has been proposed. This method aims to improve the figure of merit by using a magneto-optical storage medium with a large Kerr rotation angle for the readout layer, and the readout layer medium is shot using GdFe.

GclFeCo, TbFeCo, etc. are used, and TbFeXDyFe, TbFeCo, etc. are used for the write layer. In addition, the film thicknesses of the read layer and write layer are each 500 mm, considering the size of Kerr rotation angle and the effect of exchange coupling force.
A: Most often, the number of people in the two layers is 1,000.

In recent years, the application of magneto-optical disks that use such storage media to store, reproduce, erase, etc. information has required even higher performance, and in particular, in the field of analog recording, for example, When used for video recording, a higher C/N value is desired because a single frequency is recorded and the larger the C/N value at one time, the higher the quality of the reproduced image.

(c) Problems to be Solved by the Invention However, the C/P ratio is higher than that of the conventional magneto-optical recording medium.
A magneto-optical storage medium that achieves the N value has not been developed to date.

Therefore, as an attempt, a reflective film structure magneto-optical storage medium (reflective film structure magnetic double-layer film magneto-optical storage medium) using a magnetic double-layer film as a storage medium, which is a combination of the elements on the two sides, can be considered.

However, since the optimal film thickness of the magnetic double-layer film and the optimal film thickness of the storage medium with the reflective film structure are significantly different, it has been difficult to actually design a magnetic double-layer film magneto-optical storage medium with the reflective film structure. . Furthermore, even if a design could be made, it was unknown whether the C/N value would exceed the conventional value.

An object of the present invention is to enable optimization of the above-mentioned reflective film structure magnetic double-layer film magneto-optical storage medium, and to achieve performance exceeding the C/N value obtained by the two examples shown in the [Prior Art] section. An object of the present invention is to provide a magneto-optical storage medium having the following features.

(d) Means and operation for solving the problems Thus, according to the present invention, a dielectric film, a magneto-optical memory film, a dielectric film, and a reflective film are laminated in this order on a substrate, and the magneto-optical memory film is a first layer consisting of a rare earth transition metal amorphous thin film, and a first layer
It is an exchange-coupled two-layer film with a second layer consisting of a rare earth transition metal amorphous thin film having a composition different from that of the first layer, and the first layer has the following composition formula: % formula % (wherein, X = 5 to 25 at I %, Y=1.8~3
0 atm%, Z=16 to 24 atm%) and the sublattice magnetization M S TX of the transition metal TM is rare earth gold@RE.
The second layer also has a sublattice magnetization M s of the transition metal TM.
It is characterized by being made of a rare earth transition metal alloy having a composition in which tM is larger than the sublattice magnetization MsR1 of the rare earth metal RE, and further, the film thickness of the first layer and the second layer is each 160 Å or more and the total thickness is 500 Å or less. An optical storage element is provided.

According to the above medium configuration, the first layer acts as a reading layer with a large Kerr rotation angle, and the second layer acts as a writing layer, and both the reading layer and the writing layer have a TM-rich composition ratio. sublattice magnetization M of the transition metal TM.
S T O is the sublattice magnetization of rare earth metal RE M S RE
When the two-layer film structure has a smaller (RE-rich) composition ratio, the relative Bekar rotation angle becomes larger.

Furthermore, by controlling the thicknesses of the reading layer and the writing layer within the above ranges, it is possible to obtain magnetic properties as an exchange-coupled two-layer film, and also to obtain the same effect when used as a reflective film structure. Therefore, the C/N ratio can be improved by this reflective film structure magnetic double-layer film magneto-optical storage medium.

The first layer of rare earth transition metal amorphous thin film in the present invention is:
The following composition: (G d +oo-xD 3'x) z (F e 1
．． 0O-YCQY) l1l-Z (wherein, X=5-25
atm%, Y=18~30atn%, Z=16~2
4 atm%). Here, the composition ratio of GdDyFeCo, coercive force (He), Kerr rotation angle (θh), and magnetization (M
s) is shown in Table 1. In this way, in the above composition range, the Kerr rotation angle θk is 0.48 degrees or more, and the composition ratio of GdDyFeCo and lie, θ
In addition, it is possible to exceed the Kerr rotation angle of 046 degrees for FeCo in relation to Ms.

(Left below) On the other hand, as the rare earth transition metal amorphous thin film of the second layer in the present invention, those made of various rare earth transition metal alloys that are used in the writing layer of ordinary exchange-coupled two-layer films can be used. , for example TbFe, DyFeCo, ThFeCo
Examples include alloys.

Both the first layer and the second M rare earth transition metal amorphous thin film have a composition in which the sublattice magnetization M S TM of the transition metal TM is larger than the sublattice magnetization M S *x of the rare earth metal RE, that is, a TM rich composition ratio. Consisting of

Here, conventionally, magnetic double-layer film media have the following types:
As shown in (b), the read layer RL and the write layer WL
As shown in FIGS. 2(a) and 2(b), the magnetizations Ms□ and Mst of the read layer RL and the write layer WL are parallel to each other (P type), and the magnetizations M s , , MS!
There is a type (A type) in which the directions are opposite to each other. Since the magnetic double layer film medium of the present invention is used in a reflective film structure,
The reproduction laser beam will be transmitted through the magnetic double layer film medium. Therefore, the amount of reproduced signal detected is affected not only by the recording state of the reading layer but also by the recording state of the writing layer. In addition, the magnitude of the Kerr rotation angle is mainly proportional to the magnitude of the sublattice magnetization M S TH of the transition metal TM within the range of perpendicular magnetization, and the direction of the magnetization M S TH is aligned between the two layers. is larger. That is, Fig. 1 (a
), it can be seen that the TM-rich composition ratio on the read layer and write layer results in the largest amount of reproduced signal. Based on this knowledge, in the present invention, the first layer and the second layer
Both layers have a TM-rich composition ratio.

Note that each of these layers is formed by vapor deposition, sputtering, CVD.
It can be formed into a thin film on a dielectric film by a known method such as.

In the present invention, the first layer and the second layer each have a thickness of 16
The total wrinkles are set to be 0 Å or more, and the total wrinkles are set to be not more than SOO Å. Here, GdDyF' eC.

Regarding the medium single layer film, Table 2 shows the experimental results of the relationship between the film thickness and the coercive force Hc. From this, it can be seen that the film thickness necessary for perpendicular magnetization is at least around 85 mm, and the coercive force Ha increases with the film thickness. However, the magnitude of the coercive force He is considered to be saturated at a certain film thickness or more.

Table 2 Table 3 Next, we investigated the thickness of each layer, which is the most important point in the structure of a two-layer film, so that each layer maintains its own magnetic properties and that the exchange coupling force works effectively between the two layers. The experimental results are shown in Table 3. The experimental method was to examine the change in coercive force He of the read layer RL and the write layer WL when they were made into a single layer and when they were made into two layers, respectively, from a hysteresis loop between an external magnetic field and Kerr rotation angle and Faraday rotation angle. Therefore, we experimentally determined that a film exhibiting a hysteresis loop as shown in FIG. 3 is a two-layer film structure that satisfies the above characteristics, and is marked with an O in the table. From this, it can be seen that the thickness of each layer is required to be approximately 160A or more.

Furthermore, from an optical point of view, the total thickness of the two layers of a two-layer film medium is limited; in other words, in a reflective film structure, the laser light passes through the two-layer film medium, and after being reflected by the reflective film, Since the laser beam must pass through the double-layer film medium again, considering the attenuation of the laser light intensity during this process, the total thickness of the double-layer film must be 500 Å or less in order to obtain the effect of the reflective film structure. I understand that. From the above, it is necessary that the total thickness of the two-layer film of the two-layer film medium be 320 Å or more and 500 Å or less.

(e) Examples Embodiments of the present invention will be described below with reference to the drawings.

Figure 4 shows a magneto-optical disk, where 1 is a transparent substrate made of glass, polycarbonate, acrylic, etc.
On this transparent substrate l, an aluminum nitride (AIN) film 2, which is a first transparent dielectric film, is formed to have a thickness of, for example, 97 nm, and on this AIN film 2, a readout layer, which is an earth-transition metal magneto-optical storage medium, is formed. gadolinium, dysprosium,
An iron, cobalt (GdDyFeCo) alloy thin film 3 is formed to have a thickness of, for example, 20 rpm, and this GdDyFeC.

On the alloy thin film 3, a terbium, dysprosium, iron, cobalt (TbDyFeCo) alloy thin film 4 serving as a writing layer, which is a rare earth transition metal magneto-optical storage medium, has a film thickness of, for example, 20 nm.
nn, and on this TbDyFeCo alloy thin film [14], an AIN film 5, which is a second transparent dielectric film, is formed to have a film thickness of, for example, 3.
Further, on this A I N film 5, an aluminum (A1) film 6 as a reflective film is formed with a film thickness of 50 nm, for example.
m is formed.

Here, the composition ratio of the readout layer 3 is (c dseD y+
+) ls (P e ?ICOt+) 5zatff
i%, and the composition ratio of the writing layer 4 is (Tb7oDyi
o) (Feioc.

This is the TM-rich composition ratio near the compensation composition of Il+).

Furthermore, the eleventh and second transparent dielectric films are set to enhance the Kerr rotation angle and Faraday rotation angle with respect to laser light incident from the substrate side, and to increase the apparent Kerr rotation angle.

Although each of the above layers is formed by a sputtering method, the film forming method may be a vacuum evaporation method, an ion blating method, or the like in addition to the sputtering method. Table 4 shows the changes in the coercive force He of a single layer and the coercive force He of the two layers combined in each of the magnetic double layer films having the above structure.

(Left below) Reflectance in Table 4, θ is the Kerr rotation angle of the storage medium) or C/N,
It is well known that there is a relationship of rRXθkcx:C/N. The measurement wavelength was 830 nm, and the results were measured on a land surface with a width of 10 μm.

From this, it can be seen that each layer maintains its respective magnetic properties and that the exchange coupling force is working effectively between the two layers.

FIG. 5 shows a magneto-optical disk structure with a film structure used to compare the figure of merit with the magneto-optical disk (a) using a reflective film structure magnetic double-layer film magneto-optical storage medium of the present invention. In the figure,
(b) shows a disk with a three-layer film structure commonly used in magneto-optical disks, (e) shows a disk with a reflective film structure, and (d) shows a disk with a normal magnetic double-layer structure. Here, 1 is a glass substrate, 7
8 is a transparent dielectric film, 8 is a readout layer magneto-optical storage film, 9 is a write layer magneto-optical storage film, 10 is a magneto-optical storage film, and 11 is a reflective film. Table 5 shows each magneto-optical disk') (1
) Shows the difference in performance index due to difference in structure. Here, the figure of merit rRXθk (R is the storage medium Table 5) From this, the reflective film structure magnetic double-layer film disk of the present invention (a
) has the largest figure of merit and is found to have excellent recording characteristics.

Table 6 shows the measurement results of the C/N value of the reflective film structure magnetic double layer film disk. Two disks having the above structure were used, with the reflective film side facing inward and glued together with an adhesive.

The recording and reproducing conditions were: disk rotation speed 1800 rpm, recording frequency 6.5 MHz, recording radius 55 mm, recording power 8.4 mW, auxiliary magnetic field 1500 e, and reproducing power 1.5.
mW.

The C/N value in Table 6 exceeds 53 dB, achieving a very large value. Furthermore, it has been experimentally found that if a medium with a large coercive force near the compensation composition is used as the writing layer, the writing noise of the disk can be suppressed to a small level.

Note that the dielectric film according to the present invention may include S in addition to ALN.
An i0%SiN film or the like may also be used. Further, as the reflective film, other than AI, Cu, Ag, Au, Ti, Cr films, etc. may be used.

(F) Effects of the Invention According to the configuration of the present invention, it is possible to achieve both the effect of improving the C/N value of both the reflective film structure and the magnetic double-layer film structure, which has been considered difficult in the past. A disk with excellent recording and reproducing characteristics can be manufactured. And for example,
It also becomes possible to develop discs for analog recording with high image quality and long duration.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1(a) and 1(b) are explanatory diagrams showing the magnetization state in a P-type exchange-coupled double-layer film. Figure 2 (a, )
, (b) is an explanatory diagram showing the magnetization state in an A-type exchange-coupled bilayer film. FIG. 3 is an explanatory diagram showing a magnetic hysteresis loop in an optical storage element according to the present invention. FIG. 4 is a schematic longitudinal sectional view of a magneto-optical disk according to an embodiment of the present invention. FIG. 5(a) is a schematic longitudinal sectional view of the magneto-optical disk of the present invention, and FIGS. 5(b) to 5(d) are respectively,
FIG. 1 is a schematic vertical cross-sectional view of a conventional magneto-optical disk. l...Transparent substrate, 2,5...AIN film, 3...GdDyFaCo alloy thin film, TdDy
FeCo alloy thin film, ・AI film. Figures (a) (b) , -, , , 1-m-- (C) (d)

Claims (1)

[Claims] 1. A dielectric film, a magneto-optical memory film, a dielectric film, and a reflective film are laminated in this order on a substrate, and the magneto-optical memory film is made of an amorphous thin film of a rare earth transition metal. It is an exchange-coupled two-layer film consisting of a first layer and a second layer made of a rare earth transition metal amorphous thin film having a composition different from that of the first layer, and the first layer has the following compositional formula: (Gd_1_0_0_−_XDy_X) ＿Z(Fe_1
_0_0_-_YCo_Y)_1_0_0_-_z (wherein, X = 5 to 25 atm%, Y = 18 to 30 atm%,
Z = 16 to 24 atm%), and the sublattice magnetization Ms_T_M of the transition metal TM is larger than the sublattice magnetization Ms_R_E of the rare earth metal RE,
The second layer is also made of a rare earth transition metal alloy having a composition in which the sublattice magnetization Ms_T_M of the transition metal TM is larger than the sublattice magnetization Ms_R_E of the rare earth metal RE, and furthermore, the film thicknesses of the first layer and the second layer are each 160 Å. An optical memory element having the above properties and a total thickness of 500 Å or less.