40t soft X-ray spectroscopies on magnetic-field-induced valence transition in Eu(Rh_1-xIr_x)₂Si₂ (x = 0.3)

A magnetic-field-induced valence transition of Eu(Rh_1-xIr_x)₂Si₂ (x = 0.3) has been examined using soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements up to 39.3 T. At 9K, the Eu valence number takes a value of 2.65 (±0.03) at 0 T and decreases abruptly to 2.33 (±0.03) at the transition around 22 T. Above the transition field, the magnetization of the Eu²⁺ component saturates, although the Van Vleck paramagnetism of the Eu³⁺ linearly increases and reaches 0.65 μB=Eu³⁺ at 39 T. The valence determined by XAS and the saturation value of the bulk magnetization are mutually consistent. It is found that the transition field determined by XMCD differs from that of the bulk magnetization. To interpret the discrepancy, we discuss the sample inhomogeneity and the effect of the surface state.