Crystal field excitations in the filled skutterudite

We have performed inelastic neutron scattering experiment on a powder sample of the ferromagnetic filled skutterudite compound NdOs 4 Sb 12 in order to clarify the crystal-field (CF) states of 4f electrons in this system. At lowest temperature 15 K, two inelastic peaks have been observed at energy transfers 23.0 and 30.2 meV. The intensity of these two peaks decreases with increasing temperature, as expected for excitations from the CF ground state. This observation of CF excitations evidences the localized character of 4f electrons in NdOs 4 Sb 12 . From this result and the bulk magnetic susceptibility of NdOs 4 Sb 12 , possible CF level schemes are discussed.