Room temperature multiferroicity in Bi4.2K0.8Fe2O9+δ

Magnetoelectric multiferroics are materials that have coupled magnetic and electric dipole orders, which can bring novel physical phenomena and offer possibilities for new device functions. In this report, single-crystalline Bi4.2K0.8Fe2O9+delta nanobelts which are isostructural with the high-temperature superconductor Bi2Sr2CaCu2O8+delta are successfully grown by a hydrothermal method. The regular stacking of the rock salt slabs and the BiFeO3-like perovskite blocks along the c axis of the crystal makes the Bi4.2K0.8Fe2O9+delta nanobelts have a natural magnetoelectric-dielectric superlattice structure. The most striking result is that the bulk material made of the Bi4.2K0.8Fe2O9+delta nanobelts is of multiferroicity near room temperature accompanied with a structure anomaly. When an external magnetic field is applied, the electric polarization is greatly suppressed, and correspondingly, a large negative magnetocapacitance coefficient is observed around 270 K possibly due to the magnetoelectric coupling effect. Our result provides contributions to the development of single phase multiferroics.