Polar atomic displacements in multiferroics observed via anomalous x-ray diffraction

The minute polar atomic displacements in multiferroics are shown to be within the reach of crystallography. A nonconventional methodology with anomalous x-ray diffraction is employed to investigate such displacements in DyMn2O5 with giant magnetoelectric coupling and two distinct Mn3+ and Mn4+ sites. Intensity differences of a selected Bragg reflection were measured as the direction of electric polarization is switched by a poling field. A significant differential effect, which is strongly enhanced at energies near and above the Mn K edge, was observed near and below the ferroelectric transition temperature, T-c similar to 40 K. The direct participation of ionic displacements in the ferroelectric polarization, particularly the Mn3+ sublattice, is demonstrated, dismissing a purely electronic mechanism for the multiferroicity.