Specific Heat Study of Superconducting Alloys with Magnetic Impurities, La3-xGdxAl System

The effects of magnetic impurities on superconductors La 3- x Gd x Al containing up to 2 at. % Gd have been studied extensively mainly by specific heat measurements. In the investigated range of temperature and impurity concentration, the superconducting transition temperature T c as a function of impurity concentration agrees well with the theoretical curve of Abrikosov and Gor'kov. The magnetic ordering temperature T M observed as the temperature at which the specific heat reaches maximum is lower than T c in the present study. Absence of the departure from Abrikosov and Gor'kov curve results in the fact that the magnetic ordering has no effect on T c in the temperature range above T M . Generally the upper critical field H c2 decreases linearly with increasing Gd content. The examination of the behaviors of H c2 gives the possible presence of the magnetic ordering on H c2 below the studied temperature range. The nature of the magnetic ordering is discussed.