Charge order in LuFe2O4: Antiferroelectric ground state and coupling to magnetism

X-ray scattering by multiferroic LuFe2O4 is reported. Below 320K, superstructure reflections indicate an incommensurate charge order with propagation close to (131332). The corresponding charge configuration, also found by electronic structure calculations as most stable, contains polar Fe/O double layers with antiferroelectric stacking. Diffuse scattering at 360K, with (13130) propagation, indicates ferroelectric short-range correlations between neighboring double layers. The temperature dependence of the incommensuration indicates that charge order and magnetism are coupled.