Tailoring Structural, Electronic, and Magnetic Properties of Fe3O4 and MnZn-Ferrites through Metal/Non-metal Doping: A DFT plus U Study

Nanoscale spinel-structured ferrites, especially when doped with metal or nonmetal ions, have attracted significant attention due to their tunable functional properties, making them indispensable for advanced applications in high-frequency electronics and energy conversion systems. Among these, manganese-zinc (MnZn) ferrites exhibit remarkable versatility, driving extensive theoretical and experimental research. This study presents a systematic investigation utilizing spin-polarized density functional theory with Hubbard correction (DFT+U) within the generalized gradient approximation (GGA+U), employing the Perdew-Burke-Ernzerhof (PBE) functional, to analyze the electronic, magnetic, and structural properties of Fe3O4 and doped MnZn-ferrites of the form (Zn x 2+Mn y 2+Fe1-x-y 3+)A(M x Fe2x-1 3+)BO4 2- and (M x Fe1-x 3+)A(Zn x 2+Mn x 2+Fe2-x-y 3+)BO4 2-, where M represents transition metals (Ti, V, Co, Mo, La) and nonmetals (Ca, Si, Sn, Bi). The findings demonstrate that Mn/Zn doping exerts a pronounced influence on lattice distortions, with crystallographic deformation minimized and structural stability maximized under equimolar Mn:Zn substitution, as evidenced in the Mn4Zn4Fe2O4 composition. Formation energy calculations further suggest that transition-metal doping enhances the stability of the ferrite structures. Electronic structure analysis demonstrates that dopant selection critically governs band gap characteristics. Specifically, Ca-, Si-, V-, and Sn-doped systems exhibit half-metallic properties, whereas Mn4Zn4 and Mn8Zn8-ferrites configurations retain their semiconducting nature. Computational analysis of magnetocrystalline anisotropy energy (MAE) reveals a preferential alignment of the easy magnetization axis (EMA) along the crystallographic [001] direction (Z-axis) across all doped Mn4Zn4Fe2O4 systems with the exception of Ca-doped configurations. Notably, transition-metal dopants (V, Co, Ti, and Mo) in Mn8Zn8Fe8O4 exhibit robust uniaxial anisotropy, as evidenced by positive MAE values (0.25-3.5 meV/atom). This anisotropy arises from spin-orbit coupling-enhanced orbital polarization and asymmetric d-electron redistribution at dopant sites, which stabilizes the [001]-oriented magnetization.