Observation of a second metastable spin-ordered state in ferrimagnet Cu₂OSeO₃

dc and ac magnetization measurements were performed on single-crystal Cu₂OSeO₃ under magnetic field (H) and hydrostatic pressure (P) conditions. Increasing H shifts the ferrimagnetic transition observed at T_C~60 K to a higher-temperature region. Moreover, the T_C increases linearly and magnetization is enhanced with P. Features of the ladder in the M-vs-H curve or the peak in the dM/dH-vs-H curve are observed at H _SF~0.5 kOe, suggesting a competing ordered state under magnetic fields below T_C. Remarkably, a second shoulder is observed at ∼1 kOe in the dM/dH-vs-H curve, revealing another metastable spin-ordered state in Cu₂OSeO₃. This state is retained and enhanced by applying pressure. As H rises to 55 T, no further slope changes in the M-H curve are observed. These magnetic properties indicate a complex spin orientation in the geometrically spin-frustrated system Cu₂OSeO₃.