LT 21 Proceedings of the 21st International Conference on Low Temperature Physics Prague, August 8-14, 1996

Part $5 - Techniques and applications: Cryodeviees and magnetometers

T h e f l u x g a t e m a g n e t o m e t e r f o r c r y o g e n i c s

Sergey V.Uchaikin

Particle Pliysics Laboratory, Joint Institute for Nuclear Research, Dubna, Moscow reg., 141980, Russia

Tile report presents a fiuxgate magnetometer based on the metal glass sensor for high resolution measurements at the temperature range of 4.2 - 300 K. The details of the design and construction of the sensors are given. Tile white noise level of 20 pT/(Hz) z12 has been obtained with the 1/f corner frequency of 5 Hz at 4.2 K using the ring core sensors as a null-detector for the magnetic field.

1. I N T R O D U C T I O N

The superconducting shields are used if it is nec- essary in any experiment to create the magnetic vac- uum. The HTS shields allow to achieve the magnetic vacuum at the liquid nitrogen temperature. To cre- ate the HTSC shield is a complicated technological multifactor process to be improved [1]. To investi- gate the ItTSC shields the fluxgate has been created and studied at the low temperatures.

2. F L U X G A T E N O I S E

It is known that the magnetic noises of the flux- gate sensors are basically defined by the Barkhausen noise. This noise appears due to the spasmodic change of the core magnetization. Different circles of magnetization have different parameters of sud- den changes and that is why the magnetic noise ap- pears. This noise increases by 3 times at 77 K and by 10 times at 4.2 K for supermalloy cores [2]. This is explained by increasing magnetic anisotropy of su- permalloy [3]. Metal glass seems a more preferable material at low temperatures because of the less mag- netic anisotropy. We have investigated the tempera- ture dependence of the noise spectrum of the fluxgate with the metal glass core.

3. C O N S T R U C T I O N AND E X P E R I M E N T

The sensor core was manufactured from the 20 jim metal glass ribbon. The ring was glued under pressure and etching to exclude the edge short.

The standard fluxgate electronics scheme was used. The output signal on the second harmonic of the excitation current is amplified by the lock-in.

In fig.1 the fluxgate noise spectrums at the tem- perature of 297 K, 77 K H 4.2 K are shown. The

C 1 0 =-: ~ N -l-

&

5 1 0 z Z

o b z

1 0 - t

4.2K

77K

297K

FREQUENCY z

Figure 1: The fiuxgate noises at the different tem- peratures.

"white" noise increases while the temperature de- creases and is by 3 times more at 4.2 K.

4. C O N C L U S I O N S

The temperature dependence of the noise spec- trum has been investigated for the fluxgate sensor with the metal glass core. The investigation has shown that the metal glass cores are more preferable than those made of supermalloy at the low temper- atures.

R E F E R E N C E S

[1] V.Polushkin, A.Buev, H.Koch. In: Studies of

Czechoslovak Journal of Physics, Vol. 46 (1996), Suppl. $5 2809

high-To Superconductors, Ed. by V.Narlikar, 1995.

[2] S.I.Bondarenko, V.I.Sheremet, S.S.Vinogradov, V.V.Ryabovo]. Journal of Technical Physics 45 127 (in Russian).

[3] Yu.V.Afanas'ev. Fluxgates. Leningrad, Ener- goatomizdat, 1986 (in Russian).

2~10 Czech. J. Phys. 46 (1996), Suppl. S5