Spin-polarized ferromagnetic features of the Bi12Fe0.5Co0.5O20 sillenite material

This paper reports on an experimental and theoretical study of the sillenite-type material Bi 12 Fe 0.5 Co 0.5 O 20 , synthesized by solid-state reaction method. Structural analysis by X-ray diffraction and Rietveld refinement confirmed the majority formation of the cubic I23 phase. Microstructural and compositional characterization by SEM and EDS revealed submicrometric granular morphology and a stoichiometry close to the nominal value. Ab initio calculations based on DFT with GGA+U correction revealed that the material simultaneously exhibits spin-polarized ferromagnetic behavior with semiconducting character in the majority spin channel with a direct gap of ∼2.4 eV for one spin polarization and conductive character for the opposite, as well as a total magnetic moment of 5.43 μ B per cell. The optical response determined by diffuse reflectance showed an effective gap of ∼1.16 eV, in agreement with the theoretical results. Based on the p–d exchange mechanisms and the density of states at the Fermi level, the Curie temperature is estimated to be in the range of 350–500 K, which guarantees the operability of the material at conditions close to and above room temperature. These results position Bi 12 Fe 0.5 Co 0.5 O 20 as a promising multifunctional material for applications in spintronic and optomagnetic devices. • Spin-polarized ferromagnetism induced in Bi 12 Fe 0 . 5 Co 0 . 5 O 20 sillenite • FM ground state confirmed • Asymmetric spin channels: semiconducting (↑) and metallic (↓) • Spin polarization at EF ∼70%, relevant for spin transport • Tunable electronic and optical properties via TM substitution