Origin of metamagnetism in skyrmion host Cu _2 OSeO _3

Skyrmion host chiral Cu _2 OSeO _3 has attracted researchers due to several intriguing properties. Observation of metamagnetism in low-temperature and low-field makes the magnetic properties of Cu _2 OSeO _3 more complex. Here, we present an investigation on metamagnetism in Cu _2 OSeO _3 by analyzing its structural and magnetic properties. Study of magnetic properties reveal spin-flip of one of the Cu ^2+ ions, embedded in square pyramidal CuO _5 polyhedra, due to the development of strain in low-temperature and low-field regime. The spin-flip is found to be the main reason for field-induced first-order metamagnetic transition. Magnetic phase diagram of Cu _2 OSeO _3 has been constructed with the help of magnetization analyses. It is argued that the metamagnetic hysteretic field region may be low-temperature skyrmion phase with additional spiral and tilted-conical phases. A tricritical point has been observed in the phase diagram at which first-order metamagnetic hysteretic field range ceases to exist.