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 magnetoelectric 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 GdFeO ₃-type distortion, which leads to a cycloidal-plane flop from ab to bc observed in the solid-solution systems like Eu _1-xY _xMnO ₃ and Gd _1-xTb _xMnO ₃ with increasing x.