title: Giant improper ferroelectricity in the ferroaxial magnet CaMn7O12.
abstract: In rhombohedral CaMn7O12, an improper ferroelectric polarization of magnitude 2870  μC  m(-2) is induced by an incommensurate helical magnetic structure that evolves below T(N1)=90 K. The electric polarization was found to be constrained to the high symmetry threefold rotation axis of the crystal structure, perpendicular to the in-plane rotation of the magnetic moments. The multiferroicity is explained by the ferroaxial coupling mechanism, which in CaMn7O12 gives rise to the largest magnetically induced, electric polarization measured to date.
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom. r.johnson1@physics.ox.ac.uk
authors.forename: R D
authors.initials: RD
authors.lastname: Johnson
authors.forename: L C
authors.initials: LC
authors.lastname: Chapon
authors.forename: D D
authors.initials: DD
authors.lastname: Khalyavin
authors.forename: P
authors.initials: P
authors.lastname: Manuel
authors.forename: P G
authors.initials: PG
authors.lastname: Radaelli
authors.forename: C
authors.initials: C
authors.lastname: Martin