Superconducting properties of Nb3Ge thin films prepared by cosputtering

Abstract

Nb/sub 3/Ge films with thicknesses between 0.5 and 1.5 ..mu..m have been deposited on heated sapphire substrates by dc sputtering in a pure argon atmosphere. With a maximum superconducting onset temperature T/sub c/=22.7 K, these high-T/sub c/ samples crystallize in a single-phase A15 structure with lattice parameters down to 5.14 A. Critical current densities and upper critical magnetic inductions have been measured as a function of magnetic field orientation, temperature, and film thickness. The anisotropies of the critical currents and fields depend on the microstructure of the samples and show maxima for the field orientation normal to the sample surface in those films that exhibit columnar growth of the crystallites normal to the substrate. The temperature, field, and angular dependences of the pinning forces in these films are compared to existing pinning theories.