The Mixed Valence States in the Unconventional Heavy Fermion Compound SmOs₄Sb₁₂

Abstract

The X-ray absorption spectra of the heavy fermion compounds SmFe₄P₁₂ and SmOs₄Sb₁₂ have been measured near the Sm L₃-edge at selected temperatures below 300 K. The spectra show the valence of Sm ions in SmFe₄P₁₂ to be trivalent between 14 and 300 K with no significant temperature dependence. In contrast, that in SmOs₄Sb₁₂ is 2.83 at 300 K and shows a significant decrease below 150 K, indicating an important role of the nonmagnetic Sm²⁺ ions in the heavy fermion state that are insensitive to an applied magnetic field.