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. 
M. Angst, R.P. Hermann, A.D. Christianson, M.D. Lumsden, C. Lee, M.-H.   Whangbo, J.-W. Kim, P.J. Ryan, S.E. Nagler, W. Tian...