Scaling laws for the critical current density of NbN films in high magnetic fields

Abstract

The authors have measured the critical current density (J/sub c/) of two NbN films (500-AA and 1550-AA thick) as a function of temperature in magnetic fields up to 25 T using transport measurements. In both films, the functional form of the volume pinning force F/sub p/ obeys the Fietz-Webb scaling law throughout the entire magnetic field and temperature range. Values of J/sub c/ derived from DC magnetization data using Bean's model show qualitative agreement with the transport measurements throughout the superconducting phase. Despite the marked granularity in the microstructure of these films, the results are interpreted as evidence that a flux pinning mechanism determines the transport current density in NbN films in high magnetic fields. >