Temperature dependent X-ray absorption spectroscopy of the valence transition in EuNi2(SiO.20Ge0.80)2

We investigate the temperature induced mixed valence transition in EuNi2(SiO.2Ge0.8)2 using Eu 3d-4f X-ray absorption spectroscopy (XAS). The unoccupied 4f states are studied as a function of temperature (27-120K), across the critical valence temperature, . The Eu 3d-4f X-ray absorption spectra show systematic changes of the mixed valency with temperature. The Eu2+ and Eu3+ spectral features match very well with atomic multiplet calculations. The observed non-integral mean valence changes systematically from 2.70+/-0.03 (27K) to 2.35+/-0.03 (120K), consistent with bulk-sensitive measurements.