  We report remarkable multiferroic effects in polycrystalline Bi2Fe4O9.
High-resolution X-ray diffraction shows that this compound has orthorhombic
structure. Magnetic measurements confirm an antiferromagnetic transition around
260 K. A pronounced inverse S-shape anomaly in the loss tangent of dielectric
measurement is observed near the Neel temperature. This feature shifts with the
application of magnetic field. These anomalies are indicative of substantial
coupling between the electric and magnetic orders in this compound.
