INFLUENCE OF THE MIXED-VALENCES STATE ON THE MAGNETIC EXCITATION SPECTRUM OF SMB6-BASED COMPOUNDS

A series of experimental studies of the dynamical magnetic response of Sm in SmB6-based mixed-valence (MV) systems has been carried out by i nelastic neutron scattering on poly- and single-crystalline, double-is otopic (Sm-154, B-11), samples. In addition to two strongly damped hig h-energy peaks associated with the inter-multiplet transitions of Sm2 and Sm3+, pure SmB6 exhibits a very specific low-energy excitation at 14 meV. These features can be ascribed to the formation of the MV gro und state. To study the effect of a variation of the average valence u psilon on the magnetic excitation spectra, solid solutions have been s tudied in which 2+ or 3+ ions are substituted for Sm. The intensities of the inter-multiplet excitations change roughly in accordance with t he variation of upsilon. Systematic changes are observed in the positi on of the low-energy peak, and in the Q and T dependences of its inten sity. Further information concerning the energy, anisotropy, and the Q and T dependences of the low-energy excitation was obtained from trip le-axis experiments on single crystals of Sm1-xLaxB6 (x = 0.10, 0.22) at ambient pressure and SmB6 at P = 0.5 GPa. The transformations obser ved in the low-energy part of the spectra suggest a relation between t he average valence and the degree of delocalization (or hybridization strength) for the ''loosely bound'' f-electron state formed around the Sm ion, which is a characteristic feature of the MV ground state. (C) 1997 Academic Press.