Microscopic Observation of Heavy Quasiparticle Formation in the Intermediate Valence Compound EuNi2P2: 31P NMR Study

We report P-31 NMR measurements under various magnetic fields up to 7T for the intermediate valence compound EuNi2P2, which shows heavy electronic states at low temperatures. In the high-temperature region above 40 K. the Knight shift followed the Curie-Weiss law reflecting localized 4f states. In addition, the behavior corresponding to the temperature variation of the average valence of Eu was observed in the nuclear spin-lattice relaxation rate 1/T-1. With the occurrence of the Kondo effect, 1/T-1 was clearly reduced below 40K, and the Knight shift becomes almost constant at low temperatures. From these results, the formation of heavy quasiparticles by the hybridization of Eu 4f electrons and conduction electrons was clarified from microscopic viewpoints. Furthermore, a characteristic spin fluctuation was observed at low temperatures, which would be associated with valence fluctuations caused by the intermediate valence state of EuNi2P2.