Investigation of Mixed Valence State of Sm1-xB6 and Sm1-xLaxB6 by XANES

S. Gabánia, K. Flachbarta, J. Bednarčíkb, E. Welterb, V. Filipovc, N. Shitsevalovac aCentre of Low Temp. Physics, Institute of Experimental Physics SAS, Watsonova 47, 04001 Košice, Slovakia bDeutsches Elektronen Synchrotron DESY, Notkestrasse 85, 22603 Hamburg, Germany cInstitute for Problems of Materials Science, NASU, Krzhyzhanovsky 3, 03680 Kiev, Ukraine

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We investigated the valence states of samarium ions in Sm deficient Sm1-xB6 (x=0.03, 0.05, 0.08, 0.1 and 0.2) sintered samples, in single crystalline solid solutions Sm1-xLaxB6 (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.

DOI: 10.12693/APhysPolA.126.338 PACS numbers: 78.70.Dm, 71.28.+d, 71.27.+a