Superconductivity and spin fluctuations inM−Zrmetallic glasses (M=Cu,Ni,Co,andFe)

Abstract

The superconducting transition temperature, upper critical field, and magnetic susceptibility have been measured in four binary metallic glass systems: Cu-Zr, Ni-Zr, Co-Zr, and Fe-Zr. For each alloy system, a full and continuous range of Zr-rich compositions accessible by melt spinning has been examined. For Cu-Zr, the range is $0.75>x>\mathrm{}0.30\mathrm{}$; for Ni-Zr, $0.80>x>\mathrm{}0.30\mathrm{}$; for Co-Zr, $0.80>x>\mathrm{}0.48\mathrm{}$, and for Fe-Zr, $0.80>x>\mathrm{}0.55\mathrm{}$ ($x$ being the concentration of Zr in at.%). The results show clearly the influence of spin fluctuations in reducing the superconducting transition temperature. The data have been successfully analyzed using a modified form of the McMillan equation together with expressions for the Stoner enhanced magnetic susceptibility and the Ginsburg-Landau-Abrikosov-Gor'kov expression for the upper critical field.