Soft-x-ray magnetic circular dichroism under pulsed high magnetic fields at Eu M _4;5 edges of mixed valence compound EuNi ₂(Si _0:18Ge _0:82) ₂

By applying our new experimental technique of X-ray absorption spectroscopy (XAS) and its X-ray magnetic circular dichroism (XMCD) in the soft-X-ray region under high pulsed magnetic fields of up to 21.3 T, we measured the XAS and XMCD spectra at the Eu M _4;5 edges of EuNi ₂(Si _0:18Ge _0:82)2. The measured spectra are analyzed by taking into account the atomic multiplet structures to clarify the mixed valence properties, which are caused by the hybridization between Eu ²⁺ and Eu ³⁺ configurations. We obtain the field dependence of the average valence number from the XAS spectra and that of the magnetizations of Eu ²⁺ and Eu ³⁺ components separately using the spin and orbital sum rules from the XMCD spectra. These results are in good agreement with theoretical ones calculated with a modified single-impurity Anderson model. The present study reveals the key to solving a puzzling problem that was posed in previous XAS and XMCD experiments in the hard-X-ray region.