Superconducting Properties of Nb sub 3Ge Thin Films Prepared by Cosputtering

Nb sub 3Ge films with thicknesses between 0.5 and 1.5 mu m have deposited on heated sapphire substrates by d.c. sputtering in a pure Ar atmosphere. With a max. superconducting onset temp. T sub c = 22.7 these high-T sub c samples crystallize in a single-phase A15 structure with lattice parameters down to 5.14 A. Critical current and upper critical magnetic inductions have been measured as a function of magnetic field orientation, temp. and film thickness. The anisotropies of the critical currents and fields depend on the microstructure of the samples and show max. for the field orientation normal to the sample surface in those films that exhibit columnar growth of the crystallites normal to the substrate. The temp., field and angular dependences of the pinning forces in these films are compared to exsisting pinning theories.36 refs.--AA