Investigation of mixed valence state of Sm1-xB6 and Sm1-xLaxB6 by XANES

Abstract

We investigated the valence states of samarium ions in Sm deficient Sm 1-xB6 (x = 0.03, 0.05, 0.08, 0.1 and 0.2) sintered samples, in single crystalline solid solutions Sm1-xLa xB6 (x = 0.16, 0.28, 0.4, 0.55 and 0.7) as well as in a SmB6 single crystal by X-ray absorption near edge structure (XANES) between 4.2 and 300 K. It was shown that the mixed valence state vSm of Sm-ions (vSm ≈ 2.51 for SmB6 at 4.2 K) in deficient samples is changed but maintained up to a concentration of 20% of vacancies and up to a concentration of 70% in samples doped with trivalent La-ions, and that in both cases it increases with temperature. On the other hand, the value of vSm increases with increasing vacancy level, whereas it decreases with increasing La3+ substitution. The obtained dependences of Sm-valence in SmB6 on vacancy as well as on La3+ ion concentration are in good agreement with susceptibility measurements and exact numerical calculation of the spinless Falicov-Kimball model in two dimensions.