High-Magnetic-Field X-ray Absorption Spectroscopy of Field-Induced Valence Transition in YbInCu4

The magnetic field-induced valence transition in YbInCu 4 has been studied by X-ray absorption spectroscopy at the Yb L III -edge up to 41 T. The field-induced valence transition is clearly observed as a significant change in the absorption spectra. Magnetic field dependences of Yb valence at low temperatures are directly determined for the first time. It is found that the valence above the metamagnetic transition recovers from Yb 2.84+ to Yb 2.96+ which is identical to that in the high-temperature phase. Variation of the valence is also obtained in the B – T (magnetic field-temperature) plane at 0< B <41 T and 5< T <50 K.