Synchrotron X-ray spectroscopy study on the valence state and magnetization in α-YbAl_1-xFe_xB₄ (x = 0.115) at low temperatures and high magnetic fields

Valence fluctuation phenomena in rare-earth intermetallic compounds have attracted attention because the quantum criticality of the valence transition has been proposed theoretically. Recently, it was found that β-YbAlB₄ shows quantum criticality without tuning and has a strong mixed-valence state. In this study, we measured the magnetization curve and X-ray magnetoabsorption in α-YbAl_1-xFe_xB₄ (x = 0.115), which is a locally isostructural polymorph of β-YbAlB₄. The magnetization and X-ray experiments were performed in fields up to 55 and 40 T, respectively. A small increase in the Yb valence was observed at fields where the magnetization curve exhibited a change in slope.