Temperature-induced valence transition in EuNi 2(Si 0.20Ge 0.80) 2 studied by hard X-ray photoemission spectroscopy

Abstract

The temperature-induced mixed valence transition in EuNi 2(Si 0.20Ge 0.80) 2 has been investigated by hard X-ray (5940 eV) photoemission spectroscopy (HX-PES) for fractured surfaces, with a probing depth larger than 5 nm. The Eu 3d core-level states are studied below and above the critical valence transition temperature, T v = 80 K. The HX-PES spectra at 40 and 120 K show the mixed valence transition, with clear changes in the divalent and trivalent Eu 3d chemically shifted features. The Eu 3d HX-PES spectra indicate a mean valence of 2.70 ± 0.03 at 40 K which changes to 2.40 ± 0.03 at 120 K, in good accordance with the results of bulk Eu III-edge X-ray absorption spectroscopy measurements.