Superconducting properties of thermally-relaxed Zr_80Co_20 metallic glass.

We have studied the effect of thermal relaxation on the superconducting properties of Zr_80Co_20 metallic glass by means of differential scanning calorimetry and electrical resistivity measurements in the vicinity of the superconducting transition temperature T_c. Experimental values for the crystallisation temperature and activation energy of the crystallisation processes were derived by studying these processes at different heating rates. The T_c of the Zr_80Co_20 metallic glass thermally relaxed with a heating rate of 60 K/min to slightly below its first crystallisation exotherm is higher than in unrelaxed Zr_80Co_20 metallic glass, whereas in all other thermally relaxed samples Tc decreases with decreasing heating rates and increasing temperature of relaxation. The homogeneity of the thermally relaxed Zr_80Co_20 metallic glass is discussed by using the superconducting transition width as a criterion. The superconducting transitions of thermally relaxed Zr_80Co_20 metallic glass samples are characterised by a sharp fall in electrical resistance. This suggests that the samples are homogeneous on a spatial scale of less than the zero-temperature coherence length ζ0.