Collective magnetic excitations in mixed-valence Sm0.83Y0.17S -: art. no. 153201

The magnetic spectral response of black-phase mixed-valence Sm0.83Y0.17S has been measured by inelastic neutron scattering on a single crystal. Two magnetic peaks are observed in the energy range of the Sm2+ spin-orbit transition (25-40 meV). Both of them exhibit significant dispersion along the three main symmetry directions, reminiscent of the spin-orbit exciton branch found in pure divalent SmS. The results can be reproduced by a simple phenomenological model taking into account the existence of sizable Sm-Sm exchange interactions, and a microscopic mechanism is proposed on the basis of the local-bound-state theory developed previously for SmB6.