High-Magnetic-Field XMCD as a Novel Tool for the Study of Valence Fluctuation Phenomena—Application to Eu-based Intermetallic Compounds

X-ray magnetic circular dichroism (XMCD) in Eu-based valence fluctuating compounds, EuNi 2 (Si 1− x Ge x ) 2 ( x =0.82, 0.85) and EuNi 2 P 2 are investigated at high magnetic fields up to 40 T. Distinct two XMCD peaks corresponding to different valence states, i.e., Eu 2+ and Eu 3+ states are observed in EuNi 2 (Si 1− x Ge x ) 2 ( x =0.82) and EuNi 2 P 2 at the L absorption edges (2 p →5 d ). This suggests that the Eu 5 d electrons are magnetically polarized in the both valence states. Since Eu 3+ state has nonmagnetic ground state J =0, where J is total angular momentum, finite XMCD of Eu 3+ state can be closely related to the magnetic polarization of the conduction electrons that is induced by the local magnetic moments of Eu 2+ ( J =7/2) state through the strong hybridization.