Giant Improper Ferroelectricity in the Ferroaxial Magnet CaMn7O12

In rhombohedral ${\mathrm{CaMn}}_{7}{\mathrm{O}}_{12}$, an improper ferroelectric polarization of magnitude $2870\text{ }\text{ }\ensuremath{\mu}\mathrm{C}\text{ }{\mathrm{m}}^{\ensuremath{-}2}$ is induced by an incommensurate helical magnetic structure that evolves below ${T}_{\mathrm{N}1}=90\text{... View More