Ferroelectricity in an Ising Chain Magnet

Abstract

We report discovery of collinear-magnetism-driven ferroelectricity in the Ising chain magnet ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{O}}_{6}$ ($x\ensuremath{\approx}0.96$). Neutron diffraction shows that ${\mathrm{Co}}^{2+}$ and ${\mathrm{Mn}}^{4+}$ ions alternating along the chains exhibit an up-up-down-down ($\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$) magnetic order. The ferroelectricity results from the inversion symmetry breaking in the $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$ spin chain with an alternating charge order. Unlike in spiral magnetoelectrics where antisymmetric exchange coupling is active, the symmetry breaking in ${\mathrm{Ca}}_{3}(\mathrm{Co},\mathrm{Mn}{)}_{2}{\mathrm{O}}_{6}$ occurs through exchange striction associated with symmetric superexchange.