Synthesis and characterization of multiferroic BiMn7O12

We report on the high-pressure synthesis of BiMn7O12, a manganite displaying a "quadruple-perovskite" structure. Structural characterization of single-crystal samples shows a distorted and asymmetrical coordination around the Bi atom due to presence of the 6s2 lone pair, resulting in noncentrosymmetric space group Im, leading to a permanent electrical dipole moment and ferroelectric properties. On the other hand, magnetic characterization reveals antiferromagnetic transitions in agreement with the isostructural compounds, and the dielectric constant shows anomalies matching the magnetic transition temperatures. BiMn7O12 is therefore a promising multiferroic material, with evidence of coupling between magnetic and dielectric properties.