Magnetically-Driven Ferroelectric Atomic Displacements in perovskite   like YMnO3
  Magnetically-driven ferroelectric atomic displacements of the order of 10$^{-3} Angstrom have been observed in orthorhombic (perovskite like) YMnO$_3$ by a single-crystal synchrotron x-ray diffraction. The refined polar structure shows the characteristic bond alternation driven by the exchange striction in staggered Mn-O-Mn arrays with $\uparrow\uparrow\downarrow\downarrow$ type ordering, giving rise to a spontaneous polarization along a-axis. First-principles calculations based on the Berry phase method as well as on the experimentally refined crystal structure can reproduce the observed polarization value. 
D. Okuyama, S. Ishiwata, Y. Takahashi, K. Yamauchi, S. Picozzi, K.   Sugimoto, H. Sakai, M. Takata, R. Shimano, Y. Taguchi, ...
cond-mat.str-el