Magnetically-Driven Ferroelectric Atomic Displacements in perovskite like YMnO3

Magnetically-driven ferroelectric atomic displacements of the order of 10${}^{-3}Angstromhavebeenobservedinorthorhombic(perovskitelike)YMnO$_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.