Ferroelectric and Magnetic Properties of BiFeO3 Thin Films Deposited on SrTiO3 Substrate

BiFeO3 films were hetero-epitaxially grown on SrTiO3 substrate with a various orientation by pulse laser deposition. BiFeO3 films grown on (111) SrTiO3 substrate have a rhombohedral structure, identical to that of single crystals. On the other hand, films grown on (110) or (001) SrTiO3 substrate are monoclinically distorted from the rhombohedral structure due to the epitaxial constraint. The easy axis of spontaneous polarization is close to [111] for the variously oriented films. Dramatically enhanced polarization and magnetization have been found for BiFeO3 thin films grown on SrTiO3 substrate comparing to that of BiFeO3 crystals. The results are explained in terms of an epitaxially-induced transition between cycloidal and homogeneous spin states, via magneto-electric interactions.