Joint Research group of Institute for Solid State Physics, University of Tokyo (ISSP), Yokohama National University (YNU) and JAEA have revealed spin-chirality-driven ferroelectricity on the perfect triangular lattice antiferromagnet RbFe(MoO₄)₂ by using pulsed high-field magnet in YNU and wide-angle neutron diffractometer WAND of Oak Ridge National Laboratory (ORNL).

This is the first example in which the ferroelectricity originates predominantly from the spin chirality on the triangular lattice, and it is due to a completely new mechanism for magnetoferroelectricity that cannot be explained by conventional theory. The results of this research are expected to lead to the development of next-generation of energy-saving memories and new optical devices. 30 September, 2012 Press releases

YMn₂O₅ is one of multiferroic compounds, and two coupling mechanisms between magnetism and ferroelectricity have been proposed. One is the exchange striction mechanism where the polarization is proportional to the scalar product of neighboring spins. Another is the mechanism due to the cycloidal spin structure which breaks the inversion symmetry, where the polarization is proportional to the vector product of neighboring spins.

Joint Research group of Tohoku University and JAEA have performed simultaneous measurements of magnetic chirality by using polarized neutrons and electric polarization on the multiferroic material YMn₂O₅, and succeeded in distinguishing the electric polarization originated from the magnetic exchange striction and that originated from the cycloidal spin structure by taking advantage of the characteristics of polarized neutrons. Furthermore, we found that two kinds of polarization by the both mechanisms occur in this material. This result is the first example to reveal the existence of multiferroic phenomena involving multiple electric polarization mechanisms.