Establishing room-temperature multiferroic behaviour in bismuth-based perovskites

In the search of single-phase multiferroic materials at room temperature, a ceramic system with composition 0.5(0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃)-0.5BiFe_0.8Mn_0.2O₃ (BNT-6BT-5BFO2M) was fabricated via the solid-state reaction route, and its crystal structure, dielectric, ferroelectric, and magnetic properties were studied. The results indicate that the ceramic can be considered a single-phase perovskite system with ferroelectric and ferromagnetic characteristics at room temperature. The ferroelectricity is evidenced by the switching of ferroelectric domains, as imaged by piezoresponse force microscopy (PFM). The presence of a weak ferromagnetism is manifested by a non-negligible remnant magnetization in the magnetization-magnetic field loops. The spontaneous net magnetization is mediated by the presence of Mn⁴⁺ ions, which may introduce ferromagnetic Fe³⁺-O-Mn⁴⁺ double-exchange interactions in the system. The PFM images taken during the application of a magnetic field of 2000 Oe revealed that the ferroelectric domain structure at room temperature can be significantly influenced by the magnetic field, reflecting the presence of a magnetoelectric effect that allows the occurrence of magnetic field-induced polarization reorientation.