Commensurate Dy magnetic ordering associated with incommensurate lattice distortion in multiferroic DyMnO3

Synchrotron x-ray diffraction and resonant magnetic scattering experiments on a single crystal of orthorhombic DyMnO3 have been carried out between 4 and 40 K. Below T-N(Dy)=5 K, the Dy magnetic moments order in a commensurate structure with propagation vector 0.5 b(*). Simultaneous with the Dy magnetic ordering, an incommensurate lattice modulation with propagation vector 0.905 b(*) evolves while the original Mn induced modulation is suppressed and shifts from 0.78 b(*) to 0.81 b(*). This points to a strong interference of Mn and Dy induced structural distortions in DyMnO3 besides a magnetic coupling between the Mn and Dy magnetic moments.