Magnetic Impurities in Superconductors; La(Ce)Sn_3−xPb_x and La_1−yY_y(Ce) Systems

Abstract

The dependences of the superconducting transition temperature and specific heat jump on the Ce impurity concentration have been reported for the superconducting La(Ce)Sn_3−xPb_x and La_1−yY_y(Ce) systems. The magnetic-nonmagnetic transition of the Ce impurities in these alloy systems has been observed by varying the host composition. These results are compared with not only the Müller-Hartmann and Zittartz theory but also the recent Matsuura, Ichinose and Nagaoka theory. It is concluded that the alloys with T_K⁄T_c0\gtrsim10² behave as if they were nonmagnetic in the superconducting state. The behavior of the initial depression of the specific heat jump in the transition region from magnetic to nonmagnetic is discussed.