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

Abstract

We report an investigation on the mixed-valence state for $\mathrm{Yb}X{\mathrm{Cu}}_{4}$ compounds with $X$ = Mg, Cd, In, and Sn. The x-ray diffraction measurements on $X$ = Sn have revealed a cubic ${\mathrm{AuBe}}_{5}$-type structure with the lattice constant $a=7.123\phantom{\rule{4pt}{0ex}}\AA{}$. The Kondo temperature of $X$ = Sn is determined to be ${T}_{\mathrm{K}}=503$ K from the value of magnetic susceptibility. We have observed a mixing of the ${\mathrm{Yb}}^{2+}$ and ${\mathrm{Yb}}^{3+}$ 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 $\mathrm{Yb}X{\mathrm{Cu}}_{4}$. Our data clearly exhibit correlations among the energy of the ${\mathrm{Yb}}^{3+}$ 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 $\mathrm{Yb}X{\mathrm{Cu}}_{4}$ by controlling the number of the Yb $4f$ electrons.