Temperature dependent X-ray absorption spectroscopy of the valence transition in EuNi 2(Si 0.20Ge 0.80) 2

Abstract

We investigate the temperature induced mixed valence transition in EuNi 2(Si 0.2Ge 0.8) 2 using Eu 3d–4f X-ray absorption spectroscopy (XAS). The unoccupied 4f states are studied as a function of temperature (27–120 K), across the critical valence temperature, T v = 80 K . The Eu 3d–4f X-ray absorption spectra show systematic changes of the mixed valency with temperature. The Eu 2 + and Eu 3 + spectral features match very well with atomic multiplet calculations. The observed non-integral mean valence changes systematically from ∼ 2.70 ± 0.03 (27 K) to ∼ 2.35 ± 0.03 (120 K), consistent with bulk-sensitive measurements.