▎ 摘　　要

The thin-film heterostructures or nanocomposites exhibit vastly different properties from those observed in bulk systems. Herein, in a nanocomposite of reduced graphene oxide (RGO) and BiFeO3 (BFO), the remnant ferroelectric polarization is found to follow nonmonotonic magnetic field dependence at room temperature as the applied magnetic field is swept across 0-20 kOe on a pristine sample. Bulk BiFeO3, in contrast, exhibits monotonic suppression of polarization under magnetic field. The remanent ferroelectric polarization, in the present case, is determined, primarily, from powder neutron diffraction patterns recorded under 0-20 kOe field. The nanosized (approximate to 20 nm) particles of BFO are anchored onto the graphene sheets of RGO via Fe-C bonds with concomitant rise in covalency in the Fe-O bonds. Field-dependent competition between positive and negative magnetoelectric coupling arising from magnetostriction due to, respectively, interface and bulk magnetization appears to have given rise to the observed nonmonotonic field dependence of polarization. The emergence of Fe-C bonds and consequent change in the magnetic and electronic structure of the interface region have influenced coupling between ferroelectric and magnetic properties remarkably and thus creates a new way of tuning the magnetoelectric properties via reconstruction of interfaces in nanocomposites or heterostructures of graphene/single-phase-multiferroic systems.