The invention relates to magneto-optical structures applicable in systems for optical processing of information, in sensors and converters of magnetic field. The technical result is comprised in increase of resolution and sensitivity, ensuring high value of Faraday rotation of polarized light and high speed of operation when pulses of external magnetic field are applied. In the magneto-optical structure, comprised of underlay 1 formed of a mono-crystal of gadolinium-gallium ferrite-garnet, on which deposed is a film 2 of bismuth containing gallium ferrite-garnet with vector 3 of magnetization lying in the plane of the film, crystallographic axis [100] 5 of the underlay mono-crystal 1 is offset relative to the perpendicular 4 to the underlay plane at an angle not exceeding the magnitude of deflection to the crystallographic axis [210] 6, preferably in the range from 0 deg to 4 deg inclusive, and the bismuth containing ferrite-garnet is doped with rare-earth elements, preferably thulium, gadolinium, lutetium or their combinations.

BACKGROUND OF THE INVENTION 
The invention relates to magneto-optical structures designated to 
application in systems for optical processing of information, and can be 
utilized for building sensors, converters of magnetic field, and other 
devices of similar purpose. 
At the present time, ferrite-garnet materials containing bismuth in form of 
thin or multi-layer films (foils) are widely known, and are used for 
visualization and observation of magnetic fields. 
In particular, epitaxial films containing bismuth are used for observation 
of magnetic fields from various sources, as well as for processing of 
information in magneto-optical devices and systems [1,2]. Such epitaxial 
films are structures grown on mono-crystalline underlay of gadolinium 
gallium garnet (GGG) having their crystallographic orientation in the 
usual plane [111], [110] or [210]. 
Well known are magneto-optical films with garnet structure of 
(Bi,Y,Tm,Gd).sub.3 (Fe,Ga).sub.5 O.sub.12, applicable to display devices, 
optical devices for data processing, and storage components [3]. As 
presented on FIG. 1, such film 1, epitaxially grown on a GGG underlay 2 
with [111] orientation, has a mono-axial anisotropy directed along 
orientation line [111]. The faraday rotation coefficient of such a film, 
measured with a going-through 546.1 nanometer wavelength light, is of the 
order of 3 deg/micrometer. Such a film exhibits a B-H hysteresis of the 
Faraday rotation as a function of the field applied along the [111] axis. 
The field magnitude, required for switching the film between opposite 
saturation states, varies in the range of 30-400 E. 
A film, similar to the one presented by FIG. 1, has mono-axial direction of 
magnetization, i.e. vector 3 of the magnetization is oriented 
perpendicular to the film plane. Characteristic of such films is the 
"labyrinth" domain structure, schematically presented on FIG. 1. It forms 
in absence of external magnetic field H.sub.ext, perpendicular to the film 
plane, or when such field is weak. 
When external field H.sub.ext of sufficient level is applied to film 1, its 
domain structure changes, approximately representing the form of the 
magnetic flux coming from the corresponding source. This is the base 
principle of visualization of magnetic field using ferrite-garnet films 
containing bismuth. Inclusion of bismuth in the composition of the 
ferrite-garnet film improves its magneto-optical properties. The 
relatively low resolution of such films, the limited resolution caused by 
the width of stripe domains, can be considered a disadvantage. The width 
of stripe domains can be reduced by increasing the saturation 
magnetization 4PM.sub.s of the film. This, however, results in strong 
reduction of sensitivity of such film to the external magnetic field 
H.sub.ext. The saturation magnetization 4PM.sub.s can also be increased by 
reducing the thickness of the film. Such approach, however, leads to the 
reduction of Faraday rotation of polarized light vector making observation 
of the visualized magnetic field difficult. Resolution achieved with 
mono-axial ferrite-garnet films containing bismuth is not better than 1.2 
micrometers for magnetic field sources having signal/noise ratio in the 
range of 45-50 dB. 
Also known are magneto-optical structures with bismuth containing 
ferrite-garnet films, in which magnetization vector M is oriented along 
the film plane, so called films with "easy plane" [4,5]. Such a structure 
is schematically presented on FIG. 2. Usually a GGG mono-crystal or GGG 
with complex substitution by Ca Mg Zr, or any other mono-crystalline 
dielectric material with similar crystal parameters of crystal lattice 
serves as underlay 2 for such a film. Orientation of the underlay for 
ferrite-garnet films with "easy plane" of magnetization can be [111], 
[210], or [100]. Under influence of perpendicular component of the 
external magnetic field H.sub.1ext the vector 3 of magnetization M 
deflects from the film plane at certain angle which depends on the 
magnitude of the external field H.sub.1ext. The angle of Faraday rotation 
of light polarization vector is proportional to the angle between M and 
the film plane, and proportional to the H.sub.1ext. 
The main advantages of films with "easy plane" are high resolution and 
capability to achieve deep optical modulation, i.e. to obtain higher 
contrast image of the magnetic field. This capability is bound to the 
higher values of the Faraday rotation. However, in order to achieve such 
values it is necessary to introduce higher number of bismuth ions into the 
crystallographic lattice of the film. On the other hand, increasing the 
number of bismuth ions increases anisotropy of the field H.sub.a of the 
ferrite-garnet film and, in result, raises the value of the H.sub.1ext 
field necessary for obtaining the desired angle of vector M rotation. In 
the other words, sensitivity of the film goes down. Furthermore, in result 
of introducing bismuth ions in the film composition above certain number, 
the film becomes mono-axial. 
SUMMARY OF THE INVENTION 
The purpose of the invention is to create a magneto-optical structure, 
primarily for utilization in sensors of magnetic fields, capable of 
overcoming the disadvantages of the analogous structures known in the 
previous level of technology. The achievable technical result of the 
invention should be improvement of resolution and sensitivity, providing a 
high value of Faraday rotation of a polarized light, and high speed of 
operation when the external magnetic field has a pulse form. 
The desired result is achieved in a way, in which a magneto-optical 
thin-film structure has an underlay of garnet structure, on which 
deposited is a film of a magnetic material magnetization vector of which 
lies in the film plane, with a bismuth containing gallium ferrite-garnet 
chosen as the film material; the structure distinct by the fact that the 
underlay is formed from a mono-crystalline gadolinium gallium garnet, 
crystallographic axis [100] of which is offset with respect to the 
perpendicular to the underlay plane and, correspondingly, with respect to 
the plane of the film of the ferrite-garnet containing bismuth by the 
angle A, which doesn't exceed the magnitude of deflection from the 
direction of the crystallographic axis [210], and with the ferrite-garnet 
containing bismuth doped with rare-art elements. 
At the same time, the angle A, between crystallographic axis [100] of the 
mono-crystalline underlay and the perpendicular to the plane of the 
underlay with the film of bismuth containing ferrite-garnet, which is 
measured in direction towards the crystallographic axis [210] of the 
underlay mono-crystal, is preferably chosen in the range 0 deg&lt;A&lt;=4 deg. 
In addition, as the doping rare-earth elements may be chosen the elements 
from the group comprised of thulium, lutetium and gadolinium either 
separately or their combinations. Finally, the magnetic material of the 
film preferably contains 0.8 to 0.85 bismuth ions and 1.1 to 1.15 gallium 
ions per each formulary unit of the crystalline structure of the 
aforementioned material.

DETAILED DESCRIPTION 
Assumptions, according to the invention, regarding orientation of the 
underlay and composition of the layer deposited on it, the magnetic 
material film, ensure optimal parameters for anisotropy field H.sub.a, 
saturation magnetization 4PM.sub.s, Faraday rotation coefficient Q.sub.F, 
and magnetic Q factor Q=2H.sub.a /4PM.sub.s, preserving minimal values of 
H.sub.a and 4PM.sub.s. 
As result of the research and experiments conducted by the inventors in 
order to learn the influence of changes in the orientation of the underlay 
on the anisotropy field H.sub.a and on the sensitivity Q.sub.F /H.sub.1ext 
it has been discovered, that the aforementioned orientation of the 
underlay, presented on FIG. 3, characterized by the angle A between 
perpendicular 4 to the of plane of the underlay 1 with the deposited film 
2 and the crystallographic axis [100] 5 falling in the range within 4 deg 
as measured in direction of the crystallographic axis [210] 6 provides 
best results in the aspect of sensitivity Q.sub.F /H.sub.1ext. When 
increasing the underlay 1 orientation angle A from 0 deg to 4 deg, 
inclusive, anisotropy field gradually decreases and sensitivity Q.sub.F 
/H.sub.1ext rapidly raises. With further deflection of the underlay 
orientation beyond 4 deg, the top layer of the ferrite-garnet film changes 
magnetization direction to perpendicular to the film plane. In particular, 
with the magnitude of deflection from orientation [100] equal to 6 deg the 
epitaxial mono-crystalline film in its entire thickness becomes magnetized 
along a single axis and the "labyrinth" domain structure appears (FIG. 1), 
as in the usual ferrite-garnet films of the [111] orientation. 
The orientation angle of magnetization M.sub.s vector 3 of film 2 measured 
from a perpendicular direction to a position within film 2 plane, i.e. 
from the orientation of magnetization M.sub.s vector 3 shown on FIG. 1 
towards its orientation shown on FIG. 2, also depends on the number of 
bismuth and gallium ions in the composition of the mono-crystalline layer 
and on the conditions of the film growth and methods of the film growth or 
deposition. When the content of gallium is less than 1.1 ion per one 
formulary unit of the mono-crystalline structure the saturation 
magnetization becomes large (4PM.sub.s &gt;200 Gauss). In such case, magnetic 
Q factor of the film drops (Q-factor&lt;1), sensitivity drops sharply and 
higher values of H.sub.1ext are needed in order to defect the M.sub.s 
vector from the [100] direction. Increasing the number of gallium ions 
beyond 1.15 ions per one formulary unit (4PM.sub.s .about.=70 Gauss) the 
magnetic Q factor becomes greater than 1, and vector M.sub.s is in a 
position perpendicular to the film plane ("labyrinth" domain structure). A 
limitation of bismuth content is a result of the requirement of greater 
values of the Faraday rotation coefficient, and is determined by the 
values of H.sub.a and 4PM.sub.s. At less than 0.8 ions per one formulary 
unit the films have low values of Q.sub.F. This disadvantage is directly 
related to the content of bismuth in the crystalline lattice. However, 
when the bismuth content becomes higher than 0.85 ions per one formulary 
unit, the a.sub.F parameter of the lattice becomes higher than the a.sub.S 
parameter of the underlay lattice, and that causes significant stress 
anisotropy along the plane determined by the crystallographic axis [100], 
and sensitivity of the films deceases. At the same time, magneto-optical Q 
factor Q.sub.F /alpha, where alpha is optical amplification, also goes 
down. 
Example of a substantial implementation. 
According to the invention, a magneto-optical structure has been formed, 
which consisted of an underlay on which thin epitaxial films have been 
grown according to the composition 
RE.sub.3,0-0,81 Bi.sub.0,81 Fe.sub.3,85 Ga.sub.1,15 O.sub.12,0 
where RE--rare-earth elements. 
The films were grown by the way of liquid phase epitaxy on a 
mono-crystalline GGG underlay. The above determined deflection angle of 
the underlay orientation with respect to the crystallographic axis [100] 
varied in the range between 0 deg and 6 deg, and further away an underlay 
with orientation [210] was used. 
Mono-crystalline films were grown with the following ratios of the alloy 
components: 
R.sub.1 =RE.sub.2 O.sub.3 /Fe.sub.2 O.sub.3 =34.0 
R.sub.2 =Fe.sub.2 O.sub.3 /Ga.sub.2 O.sub.3 =6.47 
R.sub.3 =PbO/Bi.sub.2 O.sub.3 =1.0 
R.sub.4 =0.095 
R.sub.5 =PbO/B.sub.2 O.sub.3 =4.17 
Growth temperature 720 deg C. 
Underlay rotational speed 120 rev/min. 
Thickness of the films 3.0 micrometers. 
The films according to the composition presented above had the following 
optimal parameters: 
at H.sub.1ext =20 E sensitivity equal 0.55 angle deg/micrometer 
at H.sub.1ext =100 E sensitivity equal 0.65 angle deg/micrometer 
The following table reports parameters of films according to the above 
position grown on underlays with various deflection angles of the 
orientation with respect to the plane determined by the crystallographic 
axis [100]. 
______________________________________ 
Deflection 
angle of Position Q.sub.F (deg/mm) Q.sub.F (deg/mm) 
orientation of M.sub.s at H.sub.1ext = at H.sub.1ext = 
Resolution 
(deg) vector 20 E 150 E (mm) 
______________________________________ 
0,[100] 
In the film 
0.2 0.38 0.45 
plane 
1 as above 0.44 0.53 0.45 
3 as above 0.48 0.56 0.45 
4 as above 0.55 0.65 0.45 
6 Perpendicu- 0.62 0.68 &gt;1.5 
lar in the 
range of 
the film 
sub-layer 
[210] Perpendicu- labyrinth labyrinth &gt;2 
lar to the domain domain 
film plane structure structure 
______________________________________ 
The results reported in the table show that position of the magnetization 
vector M along the film plane is preserved up to the value of the 
deflection angle between perpendicular to the underlay plane and the 
crystallographic axis [100], equal 4 deg, inclusive. At the value of the 
angle equal 6 deg a sub-layer appears, beginning at the open surface of 
the film, which has a magnetization vector M, perpendicular to the film 
plane. Further increase of the angle in direction of the [210] axis leads 
to the film having across its entire thickness vector M perpendicular to 
the film plane. 
The following are various sources of information on the topic of the 
invention: 
1. Scott G. B., IEEE Transactions on Magnetics, Vol. MAG-12, No.4, 
pp.292-310, 1976. 
2. Tolksdorf W., Thin Solid Films, Vol.114, No.1-2, pp.33-43, 1984. 
3. Gualtieri D. M. and Tumelty P. F., J.Appl.Phys. 57(1), Apr. 15, 1985, 
pp.3879-3881. 
4. Gusev M. Y., Publications in [Journal of Phycisists Society], Vol.14, 
No.18, pp.1659-1662, 1988. 
5. T. Mizumoto at al., IEEE Transactions on Magnetics., Vol. 29, No.6, 
November 1993, pp.3417-3419.