Magnetic Properties and Spontaneous Polarization of La-, Mn- and N-Doped Tetragonal BiFeO₃: A First-Principles Study.

Multiferroic materials have been receiving attention for their potential applications in multifunctional devices. Chemical substitution is an effective method for improving the physical properties of BiFeO₃ (BFO). However, different experimental results have been reported for Lanthanum- (La-) and Manganese (Mn) -doped BFO ceramics. Here, we systematically studied the magnetic properties and spontaneous polarization of La-, Mn-, and Nitrogen (N) -doped tetragonal BiFeO₃ using density functional theory with the generalized gradient approximation and U-value method. The calculated results demonstrated that the systems show ferromagnetism with Mn and N doping, whereas no magnetization was found with La doping in G- and C-type antiferromagnetic orderings. Our research further revealed that the ferromagnetism is attributed to the - orbital hybridization. Berry-phase polarization calculations predicted a large polarization of 149.2 µC/cm² along the [001] direction of pure tetragonal BFO. We found that La and N substitution had little influence on the spontaneous polarization, whereas Mn substitution reduced the spontaneous polarization. The reduced energy barrier heights of the doped systems indicate the reduced stability of the off-centering ferroelectricity against the thermal agitation. These findings provide greater understanding for controlling and tuning the multiferroic properties of BFO.