Ferroelectricity in an Ising Chain Magnet

We report discovery of collinear-magnetism-driven ferroelectricity in the Ising chain magnet Ca₃Co_2-xMnₓO₆ (x≈0.96). Neutron diffraction shows that Co²⁺ and Mn⁴⁺ ions alternating along the chains exhibit an up-up-down-down (↑↑↓↓) magnetic order. The ferroelectricity results from the inversion symmetry breaking in the ↑↑↓↓ spin chain with an alternating charge order. Unlike in spiral magnetoelectrics where antisymmetric exchange coupling is active, the symmetry breaking in Ca₃(Co,Mn)₂O₆ occurs through exchange striction associated with symmetric superexchange.