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.Comment: Submitted to Nature Communication