Electronic and magnetic structures of the ferroelectric compound PbBaFe2O5

By using first-principles electronic and magnetic as well as ferroelectric property calculations on the ferroelectric compound PbBaFe2O5, we find that the ground states of the two PbBaFe2O5 phases, the space group Imma and Pnma phases, exhibit an antiferromagnetic structure with a propagation vector [0, 1 2, 1 2] state and the magnetic moment of 3.99 mu(B) on Fe atoms, which are in good agreement with neutron diffraction experiments. In addition, we find that this magnetic ordering state is an insulating state with an energy gap of 2.24 (2.62) eV for the Imma (Pnma) phase. These findings can be tested by future optical measurements. Furthermore, the parameters of magnetic exchange coupling are also evaluated to illustrate the nature of frustrated magnetic behaviors based on the localized Heisenberg model. Finally, we discuss whether the presence of an improper geometric spin frustration causes the appearance of ferroelectricity.