Charge Order in LuFe2O4: Antiferroelectric Ground State and Coupling to Magnetism

X- ray scattering by multiferroic LuFe2O4 is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to (1/3 1/3 3/2). 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 360 K, with (1/3 1/3 0) propagation, indicates ferroelectric short- range correlations between neighboring double layers. The temperature dependence of the incommensuration indicates that charge order and magnetism are coupled.