Cycloidal spin order in the a-axis polarized ferroelectric phase of orthorhombic perovskite manganite

The ferroelectric state in an orthorhombic perovskite RMnO3 (R = Gd(0.7)b(0.3)) was proved by neutron scattering studies to show the cycloidal spin state with the ab-spiral plane and the spin-helicity dependent polarization vector along the a axis, sharing the microscopic origin (inverse Dzyaloshinskii-Moriya interaction) with the more widely observed P vertical bar vertical bar c state (e.g., for R = Tb and Dy) with the bc-spiral plane. The magnetic-field induced polarization flop from P vertical bar vertical bar c to P vertical bar vertical bar a as well known for RMnO3 is thus assigned to the orthogonal flop of the spin spiral plane from bc to ab.