Magnetism and superconductivity in RPtSi (R=La, Ce, Nd, and Sm)

Abstract

Although many studies have been made on the nonmagnetic heavy fermion CePtSi belonging to the α-ThSi₂ structure, to the best of our knowledge no studies have been reported in the other rare-earth members of this series. In this paper, we report our resistivity, magnetization, and heat-capacity studies on NdPtSi and SmPtSi. We have established bulk antiferromagnetic ordering in NdPtSi below 3.8 K and ferromagnetic ordering in SmPtSi below 15 K. The heat-capacity studies show large contribution from the crystal-field effects. We have also established bulk superconductivity below 3.8 K in LaPtSi from resistivity, susceptibility, and heat-capacity studies. A detailed study of the influence of paramagnetic impurities (Nd and Ce) on the superconductivity of LaPtSi has been made. From this study, we are able to show that the superconducting transition temperature (T_c) decreases with the substitution of Nd impurities and this can be explained using Abrikosov and Gor'kov theory. On the other hand, Ce impurities show large depression of T_c which we ascribe to the Kondo effect due to Ce aotms with the Kondo temperature, T_k~0.25T_c. The observed data have been analyzed using recent quantum Monte Carlo calculations by Jarrel for superconductors with arbitrary T_k values.