Theoretical analysis of experimental valence and magnetization data around the field- and temperature-induced valence transitions of EuNi_2(Si_(0.18)Ge_(0.82))_2: Unified interpretation for the results from soft x-ray absorption, its magnetic circular dichroism, and magnetostatic measurements

摘要

We calculate the valence and the magnetization as functions of magnetic field and temperature for EuNi_2(Si_(0.18)Ge_(0.82))_2 with a single impurity Anderson model (SIAM), taking into account the effects of (i) the first-order nature of field- and temperature-induced valence transitions, (ii) magnetic impurities, and (iii) the Van Vleck paramagnetism for the Eu~(3+) state, as well as of the mixed valency between the Eu~(2+) and Eu~(3+) configurations. The results are in good agreement with recent experimental results by the soft X-ray absorption and X-ray magnetic circular dichroism experiments and also with available data of magnetization measurements. The present SIAM is an improved version of that used to analyze the field-dependent valence observed by hard X-ray absorption measurements. We point out a serious inconsistency between experimental data for the valence observed by hard X-ray experiments and the magnetization curve, but this inconsistency is removed by the new valence data observed by soft X-ray experiments.