The origin of the spiral spin-order in perovskite multiferroic manganites RMnO3 (RE= Tb or Dy) is here investigated using a two eg-orbitals double-exchange model. Our main result is that the experimentally observed spiral phase can be stabilized by introducing a relatively weak next-nearest-neighbor superexchange coupling (∼10 of the nearest-neighbor superexchange). Moreover, the Jahn-Teller lattice distortion is also shown to be essential to obtain a realistic spiral period. Supporting our conclusions, the generic phase diagram of undoped perovskite manganites is obtained using Monte Carlo simulations, showing phase transitions from the A-type antiferromagnet, to the spiral phase, and finally to the E-type antiferromagnet, with decreasing size of the R ions. These results are qualitatively explained by the enhanced relative intensity of the superexchanges.
@article{arxiv.0807.2395,
title = {Origin of the multiferroic spiral spin-order in the RMnO3 perovskites},
author = {Shuai Dong and Rong Yu and Seiji Yunoki and J. -M. Liu and Elbio Dagotto},
journal= {arXiv preprint arXiv:0807.2395},
year = {2008}
}