Critical currents and rapid measurements of magnetic relaxation in superconducting thin films

A fast DC magnetisation technique using a Hall effect probe is described. It is used for measuring thin film critical currents and their relaxation as functions of temperature. At fixed temperature it has been used to take current relaxation data over 6 decades of timescale in under 3 h, much faster than standard magnetisation techniques. Using a thin film ring geometry we deduce E− J characteristics extending down to 10 −14 V/cm. Magnetic relaxation measurements made on over 300 films consistently reveal a sharp divergence near to T c . At lower temperatures the relaxation rate is found to vary with film growth temperature and annealing conditions. The effect of field line curvature has been measured and its significance for our results is discussed.