Effects of halogen substitutes on the electronic and magnetic properties of BiFeO3

Abstract

To observe the high-temperature ferro-electricity at room-temperature, we used a halogen to create a 2p-hole for improving O–Fe p–d electronic transition, and calculated the systematic variations in electronic and magnetic properties using first-principle calculation. The systems prefer to charge disproportionate as Fe³⁺–O²⁻–Fe²⁺ with the highly localized halogen concentration increasing, where the O-site halogen creates a 2p-hole to disproportionate Fe charge from Fe³⁺-d⁵ orbital with a full-filled triple degeneracy orbits (t_2g) orbital to Fe²⁺-d⁵–d⁰ with a partially filled t_2g orbital. Whatever at room-temperature or high-temperature phase, the halogen substitutes, typically, for F (or Cl)-doping, induce the electrons to transfer from O-2p⁴ → unoccupied Fe³⁺-3d⁵ to O-2p⁴→Bi³⁺-6p³, while the ferromagnetic (FM)–anti-ferromagnetic (AFM) phase transits at about 1 atom per cell. Furthermore, to retain O–Fe electron transfer process, we applied the crystallographic anisotropy to produce the strong Fe–O orbital hybridization which offsets the effect of 2p-hole, and it causes more significant O-2p⁴ → unoccupied Fe³⁺-d⁵ electronic transitions at the valence band. This study opens a new perspective to the development of multiferroic devices with independent temperature.