Theoretical-Experimental Study of Magnetic and Optical Properties of Co-Doped BiFeO ₃

This study investigates the effects of cobalt doping on the structural, magnetic, electronic, and optical properties of BiFeO₃ using density functional theory (DFT) simulations. A 2 × 2 × 2 supercell containing 80 atoms was constructed, and nine distinct Co-Co configurations were systematically evaluated, considering different dopant separations, local spin orientations, and global magnetic orderings (antiferromagnetic, AFM, and ferromagnetic, FM). The BiFe_0.875Co_0.125O₃ solid solution is found to be most stable when the two Co ions are separated by 5.637 Å. The results show that Co doping effectively narrows the band gap of BiFeO₃, enhancing its optical absorption in the visible and near-infrared regions. New electronic states associated with the Co dopants are introduced near the Fermi level, leading to additional optical transitions at lower energies, 1.25 and 1.75 eV, together with a reduction of the main band gap to 2.55 eV. Furthermore, Co incorporation induces ferrimagnetic behavior with a total magnetic moment of 1.879 μ_B per 2 × 2 × 2 supercell (16 formula units). The first-principles calculations show qualitative agreement with previous experimental reports. Overall, these results highlight Co-doped BiFeO₃ as a viable candidate for optoelectronic and spintronic applications, showcasing enhanced optical properties and structural stability.