Giant improper ferroelectricity in the ferroaxial magnet CaMn7O12

Now published in Physical Review Letters!

In rhombohedral CaMn7O12, an improper ferroelectric polarization of magnitude 2870 μC m−2 is induced by an incommensurate helical magnetic structure that evolves below TN1 = 90 K. The electric polarization was found to be constrained to the high symmetry three-fold 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.

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R. D. Johnson, L. C. Chapon, D. D. Khalyavin, P. Manuel, P. G. Radaelli, and C. Martin, Physical Review Letters 108, 067201 (2012)