Inelastic Neutron Scattering Studies on the Crystal Field Excitations in Superconducting NdFeAsO 0.85 F 0.15

Inelastic neutron scattering experiments were performed on polycrystalline samples of NdFeAsO0.85F0.15 over a wide temperature range (3K-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+4I9/2 ground state in the C-4V point 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.