Inelastic neutron scattering and muon spin relaxation investigations of the deuterated Kondo lattices CeNiSnD_x

CeNiSn is a Kondo semimetal where a gap opens at low temperatures due to hybridization between 4f and conduction electrons, but a full insulating state fails to develop. Upon the insertion of hydrogen, long range magnetic order is induced. Here we report zero-field muon-spin relaxation and inelastic neutron scattering measurements of polycrystalline samples of the deuterides CeNiSnD_x (x=1.0, 1.8). The muon-spin relaxation results confirm magnetic ordering in the whole sample of CeNiSnD below around 4.7 K, while inelastic neutron scattering reveals two well-defined crystalline-electric field (CEF) excitations at around 13 meV and 34 meV in CeNiSnD, and 5 meV and 27 meV for CeNiSnD_1.8. These results suggest that hydrogenation leads to the localization of the Ce-4f electrons, giving rise to long-range magnetic order. We propose CEF level schemes for both systems, which predict a ground state moment of 0.96μ_ B/Ce within the ab-plane for CeNiSnD_1.8 and a saturated moment of 1.26μ_ B/Ce along the easy c axis for CeNiSnD, that account for the observed magnetic properties.