INVESTIGATION OF THE RESPONSE OF SUPERCONDUCTING QUANTUM INTERFERENCEDEVICES TO TEMPERATURE-VARIATION

We have measured the temperature dependent change delta Phi/delta T in the flux signal of a superconducting quantum interference device (SQU ID) operating in a flux locked loop. Thin film niobium de SQUIDs were used for these investigations. One and the same device could be operat ed either as de or rf SQUID allowing one to compare the effect of temp erature variation in both modes of operation. We have found that relax ation of trapped flux appears to be the dominant result of temperature variation. The asymmetry of the two critical junction currents in de SQUID operation could be seen, as well as an influence of an external magnetic field on delta Phi/delta T. This influence was an order of ma gnitude smaller when the device was operated as an rf SQUID, compared to de SQUID operation. By the use of a high frequency demagnetization process, delta Phi/delta T could be reduced from typical values of abo ut 0.3 Phi(0)/K to less than 0.05 Phi(0)/K in certain cases. (C) 1997 American Institute of Physics.