Calculation of exchange integrals and electronic structure of manganese ferrite (MnFe2O4)

The exchange integrals of manganese ferrite (MnFe2O4) are calculated with the density functional theory method for both normal and inverse spinel structures. The functional is chosen to be a mixture of Becke exchange and Fock exchange with variable weight (w). The exchange integrals J(AB) (the exchange integral between the nearest neighbor A and B sites) and J(BB) (the exchange integral between nearest neighbor B sites) are calculated by substituting the total energies of different magnetic ground states into the Heisenberg model. The calculated value of J(AB) is in agreement with experimental values measured by neutron diffraction and nuclear magnetic resonance. Also, the parameters U (Coulomb repulsion energy) and E-g (band gap) are extracted from density of states plotted versus w. Our calculated band gap shows that MnFe2O4 is a complex insulator in contrast to previous local spin density approximation and generalized gradient approximation calculations which predicted it to be metallic. (C) 2003 American Institute of Physics.