Hard X-ray Photoemission Spectroscopy of Temperature-Induced Valence Transition in EuNi₂(Si_0.20Ge_0.80)₂

抄録

We investigate the temperature-induced mixed valence transition in EuNi₂(Si_0.20Ge_0.80)₂ using Hard X-ray (5940 eV) photoemission spectroscopy (HX-PES), with a probing depth larger than 5 nm. The Eu 3d, Ni 2p and Ge 2p core-level states are studied below and above the critical valence transition temperature, T_v=80 K. HX-PES spectra at 40 K and 120 K show the mixed valence transition, with clear changes in the divalent and trivalent Eu 3d chemically shifted features, and negligible changes in the Ni 2p and Ge 2p states. The Eu 3d spectral shapes match very well with the results of the atomic calculations of the Eu²⁺ and Eu³⁺ configurations, confirming intra-atomic multiplet 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 accord with the results of bulk Eu L-edge X-ray absorption spectroscopy measurements.