Effects of Paramagnetic Impurities on Superconducting Properties in the La3-xGdxAl System

Effects of the magnetic impurity on superconducting properties were investigated on the La 3- x Gd x Al system. The superconducting transition temperature T c , the upper critical field H c2 and the magnetic susceptibility in the normal state were measured for various concentrations of gadolinium. A remarkable departure of the T c versus impurity concentration curve from the Abrikosov-Gor'kov curve was found in the region of high impurity concentrations (>0.4 at.% GD). Magnetic susceptibility versus temperature curves of compounds with Gd concentrations large enough to suppress the superconductivity showed no peak above 4.2°K. The H c2 versus temperature curve of the compound with 0.3 at.% Gd crossed the curve of La 3 Al. The upper critical field at 0°K, H c2 (0), had a maximum at a certain Gd concentration near La 3 Al. This fact is qualitatively explained by the theory of Fulde-Maki.