  The spin ordering and spin-charge coupling in LuFe2O4 were investigated on
the basis of density functional calculations and Monte Carlo simulations. The
2:1 ferrimagnetism arises from the strong antiferromagnetic intra-sheet
Fe3+-Fe3+ and Fe3+ -Fe2+ as well as some substantial antiferromagnetic
Fe2+-Fe3+ inter-sheet spin exchange interactions. The giant magnetocapacitance
at room temperature and the enhanced electric polarization at 240 K of LuFe2O4
are explained by the strong spin-charge coupling.
