Contactless Determination of Critical Current Density of Superconducting Films

Superconducting films are a fundamental part of wires for high field solenoid winding, cables for lossless electric current transport, or superconducting electronics. We discuss an inductive method of contactless estimation of the critical depinning current density in films and its temperature dependence. The method is based on a measurement of the magnetic moment of the film induced in an applied ac magnetic field oriented perpendicularly to the film. Mapping of the ac susceptibility computed on the basis of model magnetization loops and measured magnetization loops as a function of the applied field and temperature allows unambiguously find the critical current density and its temperature dependence. This way, for example, a flux line pinning strength can be assess. The obtained results are important both for development of models and materials with a high critical depinning current density. Also, the contactless measurement of the induced magnetic moment allows a continuous production quality control.