Alternating-Current Loss Measurements in Thin-Film Type II Superconductors

Abstract
An electrical technique is described for measuring the audio frequency power dissipation in superconducting thin films as a function of the ac current density, frequency, and applied dc magnetic field. This system has been used to study the ac losses in thin films of Nb and NbN, and also the ac and dc critical current densities in these materials. The results can be explained by assuming that both hysteresis and eddy current losses contribute.