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

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.<>