Improper ferroelectricity (trimerization) in the hexagonal manganites RMnO3 leads to a network of coupled structural and magnetic vortices that induce domain wall magnetoelectricity and magnetization neither of which, however, occurs in the bulk. Here we combined first-principles calculations, group-theoretic techniques, and microscopic spin models to show how the trimerization not only induces a polarization but also a bulk magnetization and bulk magnetoelectric (ME) effect. This results in the existence of a bulk linear ME vortex structure or a bulk ME coupling such that if direction of polarization reverses so does magnetization. To measure the predicted ME vortex, we suggest RMnO3 under large magnetic field. We suggest a family of materials, the hexagonal RFeO3 ferrites, also display the predicted phenomena in their ground state.
@article{arxiv.1302.1099,
title = {Bulk magnetoelectricity in the hexagonal manganites and ferrites},
author = {Hena Das and Aleksander L. Wysocki and Yanan Geng and Weida Wu and Craig J. Fennie},
journal= {arXiv preprint arXiv:1302.1099},
year = {2015}
}