Superconductivity, normal-state resistivity, and magnetic susceptibility of amorphous Zr-Co alloys

Disordered Zr-Co alloys are studied in the concentration range from 45 to 80 at. % Zr. Particular experimental concerns are described including the control of nonuniform sample cross section, possible aging effects, and the influence of small crystallites on one sample surface. Results are obtained for the concentration dependence of the first peak in the structure factor, the superconducting transition temperature $T_c$, the temperature and field dependence of the magnetic susceptibility χ in the range 4.2–300 K and 0–1.5 T, and for the normal-state resistivity and its temperature dependence dρ/dT at 270 K. χ is found to be field dependent, behavior which is ascribed to ferromagnetic clusters. The weight fraction of these clusters increases with decreasing temperature and decreasing Zr concentration and amounts to at most 0.2 wt. % at 45 at. % Zr close to the ferromagnetic phase boundary. ‖dρ/dT‖ decreases with decreasing Zr concentration and approaches 0 close to the ferromagnetic phase boundary. This behavior is well described by the observed $T_c$ and a model which relates dρ/dT to the electron-phonon interaction λ. The decrease of $T_c$ is mainly due to a decreasing λ.