Mechanism of Lattice-Distortion-Induced Electric-Polarization Flop in the Multiferroic Perovskite Manganites

We theoretically study a competition between two types of spin cycloids (ab-plane and bc-plane ones) in the multiferroic perovskite manganites, which is an origin of intriguing tnagnetoelectric phenomena in these compounds. Analysis of a microscopic model using the Monte-Carlo method reveals that their competition originates from a conflict between the single-ion anisotropy and the Dzyaloshinsky-Moriya interaction. It is demonstrated that the conflict can be controlled by tuning the second-neighbor spin exchanges through the GdFeO3-type distortion, which leads to a cycloidal-plane flop from ab to be observed in the solid-solution systems like Eu1-xYxMnO3 and Gd1-xTbxMnO3 with increasing x.