Stability, superconducting transition temperature, and residual resistivity of amorphous films ofLa100−xAuxalloys

Abstract

Amorphous films of ${\mathrm{La}}_{100-x}{\mathrm{Au}}_x$ alloys with $0\le x\le 32$ and thicknesses from 560 to 2100 Å were formed by vapor condensation on substrates at 4 K. The superconducting transition temperature decreased with increasing Au concentration, varying from 4.6 K for pure La films to 1.6 K for ${\mathrm{La}}_{68}$ ${\mathrm{Au}}_{32}$ films. The residual resistivity increased with increasing Au concentration, varying from 63 μΩ cm for pure La films to 208 μΩ cm for ${\mathrm{La}}_{68}$ ${\mathrm{Au}}_{32}$ films. The films were annealed to room temperature to determine the stability of the amorphous phase. By a comparison of transition temperatures, residual resistivities, and temperature dependence of the resistance before and after annealing, it was determined that amorphous films containing less than 26 at.% Au crystallized during annealing to room temperature, while films containing 26-32 at.% Au were stable in the amorphous phase at room temperature. The stability and superconducting transition temperatures were compared to those reported for liquid-quenched ${\mathrm{La}}_{100-x}{\mathrm{Au}}_x$ foils. It appears that the amorphous phase in the vapor-condensed films may be more homogeneously disordered than the reported amorphous phase in the liquid-quenched foils.