Abstract
The iron selenides are important because of their superconducting properties. Here, an unexpected
phenomenon is predicted to occur in an iron-selenide compound with a quasi-one-dimensional ladder
geometry: BaFe2Se3 should be a magnetic ferrielectric system, driven by its magnetic block order via
exchange striction. A robust performance (high TC and large polarization) is expected. Different from most
multiferroics, BaFe2Se3 is ferrielectric, with a polarization that mostly cancels between ladders. However,
its strong magnetostriction still produces a net polarization that is large (∼0.1 μC=cm2) as compared with
most magnetic multiferroics. Its fully ferroelectric state, with energy only slightly higher than the
ferrielectric, has a giant improper polarization ∼2–3 μC=cm2.
