In columnar order quadrupole perovskites A₂A′A′′B₄O₁₂ hybrid improper ferroelectricity emerges through A-site cation ordering across anti-displaced structural columns. This novel form of polar order couples to an intrinsic proper ferroelectric instability associated with underbonded magnetic A′ Mn²⁺ ions, giving rise to a biased, asymmetric switching response under applied electric field that coexists at low temperature with antiferromagnetism.

Abstract

We show that cation ordering on A site columns, oppositely displaced via coupling to B site octahedral tilts, results in a polar phase of the columnar perovskite (NaY)MnMnTi₄O₁₂. This scheme is similar to hybrid improper ferroelectricity found in layered perovskites, and can be considered a realisation of hybrid improper ferroelectricity in columnar perovskites. The cation ordering is controlled by annealing temperature and when present it also polarises the local dipoles associated with pseudo-Jahn–Teller active Mn²⁺ ions to establish an additional ferroelectric order out of an otherwise disordered dipolar glass. Below T_N≈12 K, Mn²⁺ spins order, making the columnar perovskites rare systems in which ordered electric and magnetic dipoles may reside on the same transition metal sublattice.