3 d transition metal substituted Fe 3 Se 4 : prediction of potential permanent magnet.

It is crucial for modern condensed matter physics to be able to effectively manipulate magnetism, as well as for permanent applications in general. The pristine Fe 3 Se 4 is known to meet all the criteria for a good permanent magnet (PM), but its energy product(BH)maxis quite low due to its low magnetization. Based on density functional theory calculations, we report on improved magnetic properties of promising transition metal (TM) substituted Fe 3 Se 4 systems (TM 0.5 Fe 2.5 Se 4 and TM 1 Fe 2 Se 4 , with TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn). The stability of the compounds is determined using phonon density of states and enthalpy of formation calculations. We predict an enhanced magnetization as well as uniaxial magnetic anisotropy energy (MAE) for TM substituted Fe 3 Se 4 , reaching a maximum value ofKu= 1.416 MJ m -3 for V 1 Fe 2 Se 4 . We investigate the electronic structure of the compounds, and explore the source of the improved MAE. The enhanced MAE in V 1 Fe 2 Se 4 is attributed to the in-plane 3 d orbitals near the Fermi level, E F , which alters the overall electronic bands. Site-resolved contributions toKushow that the Fe2 sublattice contributes considerably to the overall uniaxial anisotropy in V 1 Fe 2 Se 4 , whereas the Se sublattice contribution shifts from planar anisotropy in Fe 3 Se 4 to uniaxial. Such improvements in uniaxial MAE, together with improved structural stability, make V 1 Fe 2 Se 4 a promising choice for rare-earth-free PMs.