Magnetoelectric phase diagrams of the rare-earth (R) Mn perovskites RMnO3 are theoretically studied by focusing on crucial roles of the symmetric magnetostriction or the Peierls-type spin-phonon coupling through extending our previous work. We first construct a microscopic classical Heisenberg model for RMnO3 including the frustrated spin exchanges, single-ion anisotropy, and Dzyaloshinskii-Moriya interaction. We also incorporate the lattice degree of freedom coupled to the Mn spins via the Peierls-type magnetostriction. By analyzing this model using the replica-exchange Monte Carlo technique, we reproduce the entire phase diagram of RMnO3 in the plane of temperature and magnitude of the orthorhombic lattice distortion. Surprisingly it is found that in the ab-plane spiral spin phase, the (S•S)-type magnetostriction plays an important role for the ferroelectric order with polarization P a whose contribution is comparable to or larger than the contribution from the (S×S)-type magnetostriction, whereas in the bc-plane spiral phase, the ferroelectric order with P c is purely of (S×S) origin. This explains much larger P in the ab-plane spiral phase than the bc-plane spiral phase as observed experimentally and gives a clue how to enhance the magnetoelectric coupling in the spin-spiral-based multiferroics. We also predict a noncollinear deformation of the E-type spin structure resulting in the finite (S×S) contribution to the ferroelectric order with P a, and a wide coexisting regime of the commensurate E and incommensurate spiral states, which resolve several experimental puzzles.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2011 Oct 5|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics