Mixed-valence state of the rare-earth compounds YbXCu4 (X = Mg, Cd, In, and Sn): Magnetic susceptibility, x-ray diffraction, and x-ray absorption spectroscopy investigations

We report an investigation on the mixed-valence state for YbXCu4 compounds with X = Mg, Cd, In, and Sn. The x-ray diffraction measurements on X = Sn have revealed a cubic AuBe5-type structure with the lattice constant a = 7.123 angstrom. The Kondo temperature of X = Sn is determined to be TK = 503 K from the value of magnetic susceptibility. We have observed a mixing of the Yb2+ and Yb3+ electronic states from the x-ray absorption spectra at 300 K and a change in their relative intensities with varying X atoms, indicating a different degree of valence mixing in YbXCu4. Our data clearly exhibit correlations among the energy of the Yb3+ peak, the degree of valence mixing, and the Kondo temperature. These results suggest that the 5p electrons of X atoms play an important role in the mixed-valence state of YbXCu4 by controlling the number of the Yb 4f electrons.