Nonmagnetic ground state of the superconductor PrPt2B2C and magnetic pairbreaking in La0.9R0.1Pt2B2C (R = Ce, Pr, Nd)

PrPt 2 B 2 C is an unusual superconducting member (T c ∼6 K) of quaternary borocarbide family. At high temperatures, Pr ions are found to carry magnetic moment, but so far no magnetic order is reported. We have investigated the nature of the electronic ground state of this material (nominal composition PrPt 2 1 B 2 4 C 1 . 2 ) through magnetic and heat capacity studies. We confirm that PrPt 2 B 2 C exhibits bulk superconductivity below 6 K. Our studies show that (non-Kramers) Pr ions at low temperatures are in the crystal field split singlet ground state (nonmagnetic) and there is no indication of an induced magnetic moment. In the nonmagnetic analogue superconductor LaPt 2 B 2 C (T c ∼10.5 K), we have studied magnetic pairbreaking by magnetic ions Ce, Pr, and Nd. We find severe pair-breaking caused by Ce ions suggesting an enhanced Ce-4f-conduction electron hybridization.