Weak ferromagnetism in morphotropic phase boundary of BiFeO3-based materials

The weak ferromagnetism in BiFeO3 classically arises from the canting of the antiferromagnetically aligned Fe3+ spins by the Dzyaloshinskii-Moriya (DM) interaction. Here, we observed an abnormally weak ferromagnetism in morphotropic phase boundary (MPB) compounds of BiFeO3, which could not be fulfilled by sole DM interaction. The magnetic properties were studied for two different polymorphs of the rhombohedral/orthorhombic (R -O) and rhombohedral/tetragonal (R -T) structures. The R -T composition displays a superior weak ferromagnetism over the R -O one at a small applied magnetic field (10 kOe), while a comparable value is observed in a high magnetic field (70 kOe). The phase switching controlled by external stimuli revealed that magnetization is caused by both the weak ferromagnetism associated with DM interaction and the ferromagnetic component related to the phase boundary spins located at the superficial region of the coexisting structural phases.