Orbitally ordered states evolving coincidentally with structural distortions and magnetic ordering provide a novel route to controlling electronic and magnetic properties of materials through external fields. We report an unprecedented magneto-orbital helix in CaMn7O12, found to give rise to the largest magnetically induced ferroelectric polarisation measured to date. Characterisation of the structural modulation using x-ray diffraction, and analysis of magnetic exchange shows that orbital order is crucial in stabilising a chiral magnetic structure, thus allowing for electric polarisation. Additionally, the presence of a global structural rotation enables the coupling between this polarisation and magnetic helicity required for multiferrocitiy. These novel principles open up the possibility of discovering new high-temperature multiferroics.
@article{arxiv.1208.0775,
title = {Magneto-orbital helices and multiferroicity},
author = {N. J. Perks and R. D. Johnson and C. Martin and L. C. Chapon and P. G. Radaelli},
journal= {arXiv preprint arXiv:1208.0775},
year = {2012}
}