Enhancement of magnetic and ferroelectric properties of BiFeO₃ by Er and transition element (Mn, Co) co-doping

BiFeO₃(BFO), Bi_0.8Er_0.2FeO₃ (BEFO), Bi_0.8Er_0.2Fe_0.9Mn_0.1O ₃ (BEFMO) and Bi_0.8Er_0.2Fe_0.9Co _0.1O₃(BEFCO) nanoparticles were prepared by sol-gel method having an average size of 200 nm for BFO, under100 nm for BEFO and under 60 nm for BEFMO and BEFCO. Phase transition from a rhombohedral symmetry (R3c) for BFO to an orthorhombic symmetry (Ibmm) for BEFO, BEFMO and BEFCO has been observed. The phase transformation combined with size reduction has significantly improved both ferroelectric and ferromagnetic behaviors of the doped samples in a similar way. The formation of dipolar defect complexes (DDCs) in the doped samples also contributes to the improved ferroelectric property with saturated polarization (Ps) of 0.375 μC/cm² and remanent polarization (Pr) of 0.244 μC/cm² for BEFMO. Size effect may also impact the simultaneously developed Pr for BEFMO and BEFCO. Owning to the interactions between the ferromagnetic and antiferromagnetic microdomains, improved saturated magnetization (Ms) and remanent magnetization (Mr) are also observed in BEFMO.