Hard X-ray Photoemission Spectroscopy of Temperature-Induced Valence Transition in EuNi_2(Si_<0.20>Ge<0.80>)_2(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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We investigate the temperature-induced mixed valence transition in EuNi_2(Si_<0.20>Ge<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 1p and Ge 2p core-level states are studied below and above the critical valence transition temperature, Tv = 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 Eu^<2+> and Eu^<3+> configurations, confirming intra-atomic multiple! 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.
社団法人日本物理学会の論文
2004-10-15