Valence transition of EuRh₂Si₂

We have studied ¹⁵¹Eu Mössbauer effects on EuRh₂Si₂ at a high pressure of 1.0 GPa as well as at ambient pressure. The compound shows a temperature-induced valence transition from the Eu²⁺ state to the nearly Eu³⁺ state with decreasing temperature at P ≥ 1.0 GPa. The synchrotron-radiation-based Mössbauer spectroscopy is applied to the measurements under a high pressure. The Eu²⁺ ratio abruptly decreases at around 30 K reflecting the temperature-induced valence transition. We also observed a valence transition due to magnetic field by Mössbauer spectroscopy for the first time. It was found that a considerable amount (∼45%) of Eu atoms do not participate in the valence transition. We discuss the origin of these Eu atoms by calculating the magnetization based on the Mössbauer spectroscopy data.