The paramagnetic response of mixed-valence samarium hexaboride has been studied by inelastic neutron scattering using a low-absorption double-isotope single crystal of 154Sm11 B6. Measurements were performed for energy transfers 0

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Inelastic-neutron-scattering spectra were measured on the polycrystalline double isotopic sample '%m "B6 in a wide range of the energy transfer. The intermukiplet transitions corresponding to f 6 and f 5 configurations of the intermediate-valent state of the Sm ion, as well as a low-energy excitation with unusual momentum transfer and temperature dependences have been observed in the magnetic part of the scattering function.

All acoustic and the lowest optic branches in three main symmetry directions have been determined by inelastic neutron scattering at room temperature using a double isotope monocrystal 1saSm11B6. In comparison with the integer valence system La& the phonons are softer, and the LA branches exhibit remarkable anomalies. These features are interpreted on the basis of a specific coupling of the lattice vibrations with the dipole (f-d) and monopole (f-D excitations of the Sm shells, the latter being characteristic for the mixed valence semiconductor. A weak broad signal has been observed in the energy gap between acoustic and optic modes, which can be ascribed to an additional mode appearing due to the nonadiabatic interaction of phonons with valence fluctuations.

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