JPS62214537A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease the noise level generated from a recording medium by adding B, Ge, Sr, Si to a rare earth transtion metal which is the essential compsn. of an amorphous photomagnetic recording layer in a manner as to attain the specified compsn., thereby forming the recording medium. CONSTITUTION:The amorphous photomagnetic recording film 6 which is formed on a substrate 4 and with which the direction of the magnetization is perpendicular to the film plane and has two values of either upward or downward is formed by using the rate earth transtion metal contg. at least >=1 kinds of heavy rare earth metals among Gd, Tb, Dy and Ho and at least >=1 kinds of transition metals of Fe and co and adding B, Ge, Sr, and Si to said compsn. in a manner as to attain the compsn. expressed by the formula. The recording film 6 is provided by sandwiching the same between protective films 5, 7 consisting of silicon nitride in order to protect the film against oxidation. the noise level generated from the recording medium is decreased at the time of making recording, reproduction and erasure by irradiating light to the photomagnetic recoding medium formed in the above-mentioned manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the composition of a magneto-optical recording layer of a magneto-optical recording medium.

[Conventional technology]

Research on magneto-optical memory is said to have its origins in 1957, when recording was performed on an MnB1 thin film using a hot pen, and the written magnetic domain was observed using the magneto-optic effect. Stimulated by the subsequent development of lasers, vigorous research has been carried out mainly on MnEi-based materials.
It was never put into practical use because the laser light source and its utilization technology were immature.

However, in the 1970s, advances in optical information processing related technology and research into new magnetic thin film materials such as amorphous rare earth transition metal alloy thin films led to Gd7e, 'I'bl
Alloy thin films such as Fe, DyFe, and GdCo have been developed. These materials generally have the following characteristics.

Compensation point recording magneto-optical recording media such as GdFe and GdCo have a larger Kerr rotation angle than Curie single-point recording magneto-optical recording media, and although they have excellent optical reproduction characteristics, their coercive force is small (several hundred oersteds). 1 tt It is not possible to stably obtain a minute bit with a diameter of about m, and T'b? e, Dy
Magneto-optical recording media for Currie single-point recording, such as Fe, have a large coercive force (several kilo Oersteds) and can stably obtain minute bits with a diameter of about 1 μm, contrary to the above, but have a small Kerr rotation angle and poor optical reproduction characteristics. It had drawbacks such as not being very good.

In order to compensate for the drawbacks of these binary alloy thin films, two methods have been attempted in the past.

1) Make it ternary or quaternary. For example, binary GdF
GdTbFe takes advantage of the advantages of e and TbPθ and compensates for the disadvantages.
Methods of diversification such as ternary alloys or GdTb1reO0 quaternary alloys. (Telegraph Handken'yR, cpMao-
44) 2) Method of creating a multilayer structure. A dielectric layer is layered on the recording medium to increase the Kerr effect due to multiple reflections. (Eng.EEK
Trans Magn MAG-16 (198
0 (356, Autumn Biological Science Conference Proceedings, 9p-P-9 (19
[Problems to be Solved by the Invention] However, in the above-mentioned prior art, although the Kerr rotation angle increases, the reflectance decreases, and the signal strength is not sufficiently large because it is the product of the Kerr rotation angle and the square root of the reflectance. There wasn't.

Therefore, since it is not possible to increase the signal strength, reduction of the noise level is currently expected.

The present invention is intended to solve these problems, and its purpose is to reduce the noise level generated from the medium, reduce the signal strength as much as possible, and improve the signal-to-noise ratio (C! The goal is to provide materials that can increase the /N).

[Means for solving problems]

The magneto-optical recording medium of the present invention has an amorphous magneto-optical recording layer in which the direction of magnetization is perpendicular to the film surface and has a binary value of upward or downward.
In a magneto-optical recording medium that performs recording, reproduction, and erasing by irradiating light, at least one of B, Gθ, Sr, and Si is added to the rare earth transition metal that is the main composition of the amorphous magneto-optical recording layer. It is characterized by adding elements and having the following composition and impurities.

(Rare earth transition metal), oo-a (BwGexSrySi
z).

0kuα< 15 at% 0≦Wkuj00at%0≦
X≦100 at% 0≦Y≦100 at%o<z×1ooat% W+X+7+Z: 100 at% [Action] Conventional media GdFe, TbF'e, DyFe
t'L A n M tP JJ /n Yakisaya X-1
b HIS-Ab 薯R11! l+ Since it is originally amorphous, there are no grain boundaries that cause media noise ψ
it is conceivable that. However, electron diffraction images of these rare earth transition metal thin films show that they are not completely amorphous. (
Journal of the Japanese Society of Applied Magnetics, Vo'1 B, No. 2.
1984s Television Engineers Society Technical Report VR59-5) In other words, although no ring is seen in the completely amorphous electron beam and diffraction image, the ring is actually observed although it is unclear. This seems to be because a part of the film is crystallized or in a state close to crystallization. Furthermore, when the HOCO film is viewed using a high-resolution electron microscope, it is observed that some crystallization does exist.

(J, ApplPhys, Vol. 57. No. 1
．． 15 April.

Therefore, according to the present invention, rare earth transition metals include B, Gθ
By adding at least one element among , Sr, and 81, amorphization is further promoted than in conventional media, noise from the medium is reduced (and a/N can be increased).

[Example 1] FIG. 1 shows Tb-? according to the present invention. FIG. 3 is a diagram showing the composition dependence of O/N when B is added to an e-alloy thin film. Furthermore, FIG. 2 is a diagram showing the composition dependence of the Kerr rotation angle, which was measured from the substrate side. A sputtering method was used to produce the medium, and a PC board with a pitch of 1.6 μm and a groove depth of 700× was used as the substrate. Tb and B chips were registered on the target, and a film was formed by DC3 magnetron sputtering.

The composition of Tb1Fe is Tb25Fe75 at%. The structure of the medium is shown in FIG. 4 is a PC board, 5 is a silicon nitride film 1000X, and 6 is Tb? eB membrane 400 people, 7
is a silicon nitride film 1oooX. Here TbFeB
The film was sandwiched with a silicon nitride film in Tl)11.
! Since the θB film is easily oxidized, it was used as a protective film and has no essential meaning for the present invention.

First, FIG. 1 will be explained. The conditions for writing and reading the medium are: Write Power 4 mW, Read
Power 1mW, bias magnetic field 4000e, rotation 'fk 450 rpm, frequency W! , I MB2, linear speed 2.5 tn/see e-bandwidth 50 to 111
It is z. 1 is carrier level/I/(0), 2 is carrier to noise ratio (C/N), and 3 is noise level (N)
It is. From this figure, the C/N is 8 at% B added.
It has increased to about 94B (improvement of 94B). If you look a little more closely, your career level will remain the same, but
The O/N ratio has increased because the noise level has decreased.

If the amount of B added is further increased, the noise level remains the same, but the carrier level decreases, resulting in 0/
It can be seen that N is decreasing. However, the amount of B added is 1
If it is less than 5at%, is it T'b? The C/N can be made larger than that of the medium with only e (without B addition). On the other hand, from Fig. 2, the dependence of the Kerr rotation angle (θk) on the amount of B added,
It can be seen that the dependence of the carrier level on the amount of B added is the same. In other words, there is no change in θ up to 8 at% B addition,
It decreases when it exceeds 8 at%. Note that the Kerr rotation angle shown here is not the original Kerr rotation angle of TbP8, but is enhanced by the silicon nitride film and becomes large.

From the above, it was found that by adding B to Tb1Fe, it was possible to reduce the noise level of the medium and relatively increase a/X.

In addition, Tb1Fe is Tb25 here? Although e75at% was used, other composition ratios'['b15? e85
at%, T'b30? A similar effect is exhibited even with a composition ratio such as e70at%.

[Example 2] Next, the results when Ge was added to the T b -7e alloy thin film will be shown. The experimental method, medium structure, etc. were the same as in Example 1. FIG. 4 is a graph showing the compositional dependence of C/H on Ge addition, and FIG. 5 is a graph showing the compositional dependence of θ on Ge addition. 8 in Figure 4 is carrier level, 9 is C/N1
10 indicates the noise level. From FIGS. 4 and 5, the same thing as in the first embodiment can be said. In other words, with the addition of Ge, the noise level of the medium decreases and the relative C/N
The C/N peak increases when Ge is Sat%
If Ge is added up to 15 at%, '
Only rbye (O/N of the medium without Ge addition can be made larger).

[Example 3] Next, the results when Sr was added to the 'rby6 alloy thin film are shown. The experimental method, medium structure, etc. were the same as in Example 1. FIG. 6 is a graph showing the compositional dependence of C/N on Sr addition, and FIG. 7 is a graph showing the compositional dependence of θ on Sr addition. , 11 in Figure 6 is carrier level, 12 is O/N
, 13 indicate the noise level, and from FIGS. 6 and 7, it can be said that the same thing as in the first embodiment can be said. In other words, with the addition of Sr, the noise level of the medium decreases and the C/
N will improve. And the O/H peak is Sr at 8at.
%, and if Sr is added up to 1 sat%,
Tb? It can be made larger than the ○/N of the medium with only e (without Sr addition).

[Example 4] Next, the results when 81 was added to the 'I'l) 76 alloy thin film are shown. The experimental method, medium structure, etc. were the same as in Example 1. FIG. 8 shows the composition dependence of a/N on addition of 81, and FIG. 9 shows the composition dependence of θ on addition of 81. 14 in Figure 8 is career level, 15 is C
/N%16 indicates the noise level. From FIGS. 8 and 9, the same thing as in the first embodiment can be said. In other words, with the addition of Si, the noise level of the medium decreases relative to r
ia7N will improve. The C/N peak is around 8 at% sl, and if Sl is added up to 1 sat%, the O of the medium with only 'rb1Pe (no Si addition)
/N can be made larger.

[Example 5] Furthermore, the results when B and Ge were added to the TbFe alloy thin film will be shown. The composition ratio of B and GS is 50; 50 at%. The experimental method, medium structure, etc. were the same as in Example 1. FIG. 10 is a diagram showing the compositional dependence of C/N on the addition of B-Go, and the previous diagram 11 is a diagram of the compositional dependence of θ on the addition of B-Go. 17 in Figure 10 is career level.
1B indicates O/N, and 19 indicates the noise level. Figure 10,
From FIG. 11, the same thing as in Example 1 can be said.

In other words, with the addition of B-Ge, the noise level of the medium decreases and c/N relatively improves. And O/
The peak of H is B-Ge near 8 at%, and B
If -Ge is added up to 15 at%, it can be made larger than 0/N of a medium containing only TbIre (no B-Ge addition).

Also, the ratio of B-Ge used this time is s o : s o
Although the ratio of B and Ge is at %, the effect of the present invention is the same regardless of the ratio of B and Ge. Furthermore, not only B-Ge but also B-8r, B-8i, Ge-8r
.

ee-3i, 8r-8i, B Ge78r, E-G
e −S i , G e −S r −S i ,
It goes without saying that a material to which B-Gs-Sr-31 is added is also acceptable, and the ratio thereof is also arbitrary.

Next, the present invention will be described where the rare earth transition metal alloy is other than Tl)76.

[Example 6] FIG. 12 shows Gd-Tb-11'θ-CO according to the present invention.
FIG. 3 is a diagram showing the composition dependence of C/N when B is added to an alloy film. The film formation method, medium structure, etc. are the same as in Example 1,
Is the composition Gd1λ5Tb12.5? It is e680o7at%. 20 in Figure 12 is medium level, 21 is O/N
, 22 indicate the noise level. From FIG. 12 and FIG. 13, the same thing as in the first embodiment can be said. However, the medium is 'l'
Since it is not a b7e binary element system but a Gd'I'bFeOoJ element system, θk is thicker and the O/N is larger than in Example 1.

Further, in addition to the addition of B, the effects of the present invention were observed in all the cases in which Go, 3r, Si, and their binary, penta, and quaternary elements were added, and the noise level was reduced.

In this example, TbFe, GdTb? I mentioned eCo, but GdFe, 'I"bFeoo, Gd?bI
Fe, T'b(So, GaCo, EIoOo, 'I'b
Dy? The present invention is effective if it is a heavy rare earth transition metal such as eOoDylFeOo. When the medium used in the Examples according to the present invention was observed under an electron microscope, all electron beam diffraction images were complete halo patterns, and no unclear rings were observed.

〔Effect of the invention〕

As described above, according to the present invention, Ga, Tl), Dy
, at least one heavy rare earth metal among HO;
and? In the magneto-optical recording film containing at least one transition metal among e, Co, B, Ge, 8r, Si
The noise level of the medium can be reduced by adding at least one element among the following.
/H can be improved.

Although only the PC board is shown in this example,
PMMA or epoxy resin substrates may be used, and glass substrates may also be used. Also, the structure of the medium is 5
The dielectric material may be S or 4 layers, and the dielectric material may be S instead of silicon nitride.
iO, SiO□.

Even if aluminum nitride, ZnS, etc. are used, the present invention will not be impaired in any way.

[Brief explanation of drawings]

Figure 11g1 is a diagram of the composition dependence of O/N when B is added to the 'l''b-1B alloy thin film. Figure 2 is the Kerr rotation when B is added to the Tb-Fe alloy thin film. A diagram of the composition dependence of the angle. Figure 3 is a diagram of the structure of the medium. Figure 4 is a diagram of the composition dependence of c / H when Ge is added to a Tb-713 alloy thin film. Figure 5 is a diagram of the composition dependence of Tb - A diagram of the composition dependence of the Kerr rotation angle when ()e is added to the IF e alloy thin film. Figure 6 is '1''bl! A diagram of the composition dependence of c/H when Sr is added to the 'e alloy thin film. Figure 7 shows Tb? FIG. 3 is a diagram showing the composition dependence of the Kerr rotation angle when Sr is added to the e-alloy thin film. Figure 8 shows Tb? O when Sl is added to the e-alloy thin film
A diagram of the composition dependence of /N. Figure 9 shows Tb? FIG. 3 is a diagram showing the composition dependence of the Kerr rotation angle when 31 is added to the a-alloy thin film. FIG. 10 is a graph showing the composition dependence of c/N when B-Ge is added to a TbIre alloy thin film. Figure 11 shows Tb? FIG. 3 is a diagram showing the composition dependence of the Kerr rotation angle when B-Ge is added to the e-alloy thin film. FIG. 12 shows G (L-1' b -II' e-00
A diagram showing the composition dependence of O/N when B is added to the alloy film. FIG. 13 shows Ga-T b-? FIG. 3 is a diagram showing the composition dependence of the Kerr rotation angle when B is added to the e-Oo alloy thin film. 1...Carrier (Cn2...Ratio of carrier to noise ((:!/N)3)
...Noise (N) 4...PC board 5...Silicon nitride film 1000^6------
- T 1) F e B film 400 or 7...Silicon nitride film 1000X8...Carrier (0) 9...Ratio of carrier to noise (0/N) 10.
...Noise (N) 11...Carrier (C) 12...Ratio of carrier to noise (C!/N)13...
・Noise (N) 14...Carrier (C) 15...Ratio of carrier to noise (0/N) 16...
Noise (N) 17... Carrier (1 18... Carrier to noise ratio (C!/N) 19...
・Noise (N) 20...Carrier (C) 21...Ratio of carrier to noise (0/N) 22...
Noise (N) Applicant: Seiko Epson Co., Ltd. 1 Fig. ζ Fig. 2 G-TI-Fe B 41 Assault Kiku 4 Fig. Winter S Fig. 6 Fig. % Fig. 7 (≧iBka,) % g Fig. Mikuzu wo diagram [circumstance is one]

Claims (2)

[Claims] (1) The direction of magnetization is perpendicular to the film surface and is either upward or downward.
In a magneto-optical recording medium in which recording, reproduction, and erasing is performed by irradiating light onto an amorphous magneto-optical recording layer that takes a value, B, G
1. A magneto-optical recording medium characterized in that it is doped with at least one element among e, Sr, and Si and has the following composition and impurities. (Rare earth transition metal)_1_0_0_-_α(Bw Ge
x SrySiz)_α 0<α≦15at%, 0≦W≦100at%0≦X≦
100at%, 0≦Y≦100at%0≦Z≦100a
t%, w+x+y+z=100at% (2) The rare earth transition metal is Gd, Tb, Dy, Ho
at least one heavy rare earth metal, and F
2. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium contains at least one transition metal among e and Ce.