Field induced spin frustration and magnetic coupling in BiFeO3-based ceramics

The external magnetic field is used to tune the spin states at the phase boundary (PB) of two structures coex-istence in BiFeO3-based ceramics. It is shown that the PB spins are able to transform from the unfrustrated to frustrated states under applied magnetic field with a magnitude larger than a critical value, which consequently causes a continuous increase in the net magnetization during a sweep decrease of magnetic field. The frustrated PB spins form a ferromagnetic spin configuration thus leading to a magnetic exchange interaction with the intrinsic antiferromagnetic spins giving rise to a vertical magnetization shift, field step-dependent hysteresis loop, and training effects. The unique properties of PB spins allows to control the coercivity and magnetization by magnetic field.