Using THz spectroscopy, we show that the spin-wave spectrum of multiferroic BiFeO3 in its high-field canted antiferromagnetic state is well described by a spin model that violates rhombohedral symmetry. We demonstrate that the monoclinic distortion of the canted antiferromagnetic state is induced by the single-ion magnetoelastic coupling between the lattice and the two nearly anti-parallel spins. The revised spin model for BiFeO3 contains two new single-ion anisotropy terms that violate rhombohedral symmetry and depend on the direction of the magnetic field.
@article{arxiv.2012.09178,
title = {The Magnetoelastic Distortion of Multiferroic BiFeO$_3$ in the Canted Antiferromagnetic State},
author = {Toomas Rõõm and Johan Viirok and Laur Peedu and Urmas Nagel and Daniel G. Farkas and David Szaller and Vilmos Kocsis and Sandor Bordács and Istvan Kézsmárki and Dymtro L. Kamenskyi and Hans Engelkamp and Mike Ozerov and Dmitry Smirnov and Jurek Krzystek and Komalavalli Thirunavukkuarasu and Yasuko Ozaki and Yasuhide Tomioka and Toshimitsu Ito and Trinanjan Datta and Randy S. Fishman},
journal= {arXiv preprint arXiv:2012.09178},
year = {2020}
}