Superconducting properties of Nb3Ge thin films prepared by coevaporation

Nb3Ge films with thicknesses between 60 and 800 nm were deposited onto heated sapphire substrates by thermal coevaporation. Stoichiometric Nb3Ge samples crystallize in a single-phase A15 structure with a lattice parameter of 5.14 A. Critical current densities and upper critical magnetic inductions were measured as a function of temperature, film thickness, and magnetic field orientation. The critical currents and fields show maxima for parallel field orientation. This is due to the random orientation of the crystallites. With decreasing thickness an increasing second maximum for normal field orientation is observed. This behavior can be explained by additional precipitates caused by internal stress