SU1674027A1 - Method for measurements of magnetic field strength - Google Patents

Abstract

The invention can be used to measure magnetic fields. The purpose of the invention is to increase the sensitivity of measurements by reducing the noise level. A device that implements the method contains a light source 1, a polarizer 2, a circuit 3 for creating a modulating field, a package of 4 magnetically uniaxial films, an analyzer 5, a photodetector 6, a resonant amplifier with an indicator 7. A pack of 4 magnetically uniaxial films is placed in the measured field a beam of polarized light and register a photo response at the exit of the film package. Simultaneously, the modulating field is affected, and the surface area of the films with one instantaneous direction of the magnetic field in the illumination area is equal to the surface area with the antiparallel instantaneous direction of the magnetic field. 2 Il.

Description

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The invention relates to magnetic measurements, in particular to methods for measuring a magnetic field based on detecting the displacement of domain walls in a sensitive element when introduced into a field of interest, and can be used to measure weak constant magnetic fields.

The purpose of the invention is to increase the sensitivity of the method by suppressing magnetic noise.

Fig. 1 shows a block diagram of a device implementing a method consisting of a light source 1, a polarizer 2, a circuit 3 for creating a modulating field, a multilayer sample 4, an analyzer 5, a photo-receiver 6, a resonant amplifier with an indicator 7.

FIG. 2a, b as an example, two schemes are presented that provide polarization modulation by a magnetic field,

having at any time the opposite directions in different areas of the film (the arrows indicate the instantaneous direction of the current flowing according to the scheme).

The method is carried out as follows.

A packet of magnetically uniaxial films with a domain structure is placed in the measured field, they are illuminated by a beam of polarized light, and a photo response is recorded at the output.

The expression of the change under the action of the field of the luminous flux that passed the package of 3 films and the analyzer has the following form:

(5 rl / 2D8 n2 5t4 -ZD22so8 Vsln4 /

A sin2 -4A3sln2Vsln32 y where D is the relative magnetization of the sensor occurring at the domain OVI shift

4 o

Yu

h |

for the following presentation it is essential that the value of L is associated with a change in the area of different polarity domains and therefore depends on the direction of the applied field;

V angle of installation of the analyzer with respect to the polarizer;

p is the Faraday angle of rotation of the polarization plane in one film.

The method is based on the use of nonlinear in A members contained in the photoresponse. Let there be two collinear magnetic fields applied to the sensor, measured and modulating, creating a total bias A -A n (t) A M.COSOI t. In this case, all the AM odd members are compensated, as in figure 2, the areas of the areas marked with a dot with a cross are equal and compensated. Then, at -45 °, the only variable component that has been stored with in the third member of the photoresponse, will take the form

-12 Dm-soz2 - sin3 2 y)

-6 А „А м sin3 2 р- cos 2 ft) t.

Thus, the measured field produces an amplitude modulation of the photoresponse received at carrier frequency 2 (a.

FORUMAWLAH AND ISLANDS

A method for measuring a magnetic film comprising placing a package of magneto-single-axis films in a measured magnetic field, illuminating it with a beam of plane-polarized light perpendicular to the plane of the film package, polarizing modulation of the light flux by an alternating magnetic field directed along the axis perpendicular to the plane of the films, and

registering a photo response at the exit of the film package, characterized in that. in order to increase the sensitivity of measurements, polarization modulation is carried out by a magnetic field, instantaneous

the direction of which is opposite in different areas of the illuminated surface, while the areas with different directions of the acting alternating magnetic field are equal to each other, the second harmonic of the modulation frequency is recorded.

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Claims (1)

5 Formula tions A method of measuring a magnetic field, including placing a packet of magnetically uniaxial films in a measured magnetic field, illuminating it with a beam of plane polarized light perpendicular to the plane of the packet of films, polarizing modulation of the light flux with alternating a magnetic field directed along an axis perpendicular to the plane of the films, and 15 15 recording a photoresponse at the exit of the film package, characterized in that. In order to increase the measurement sensitivity, polarization modulation is carried out by a magnetic field, the instantaneous direction of which is opposite in different parts of the illuminated surface, while the areas with different directions of the acting alternating magnetic field are equal, they record the second harmonic of the modulation frequency. Figure 1