Inelastic Neutron Scattering Studies on the Crystal Field Excitations in Superconducting NdFeAsO0.85F0.15

Inelastic neutron scattering experiments were performed on polycrystalline samples of NdFeAsO0.85F0.15over a wide temperature range (3 K–250 K). Based on the analysis of the experimental data, a Nd3+CF energy level scheme is proposed to give a consistent explanation about the observed CF transitions. The observed extra ground-state CF transitions could not be simply explained by the transitions between five Kramers doublets split from the Nd3+ 4I9/2ground state in theC4vpoint symmetry. A reliable explanation would be a superposition of crystal fields due to different local symmetries around the Nd3+ions induced by the fluorine doping.