Thickness dependence of the structure and magnetization of BiFeO3 thin films on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) substrate

The structural dependence of magnetization in BiFeO3 thin films deposited on (LaAlO3)(0.3)(Sr2AlTaO6)(0.7) (001) substrate has been investigated in the film thickness (t) range of 40-500 nm. High-resolution x-ray-diffraction studies reveal a thickness dependent structural transition from a fully strained tetragonal phase for films with t <= 75 nm to a partially strained and/or relaxed rhombohedral phase in films thicker than 110 nm, via a coexistence of fully and partially strained phases in the thickness of 75 > t > 110 nm. The fully strained phase could also be partially induced in 110-nm films by increasing the post-deposition O-2 annealing pressure. The films >= 110 nm were found to possess a thickness independent bulklike magnetic moment. A weak enhancement in magnetic moment (up to similar to 0.1 mu(B)) is observed in fully strained films (t <= 75 nm) and in excessive O-2-annealed 110-nm films having a fraction of strained phase. These results suggest that by a considerably weak magnetic moment in the pseudomorphic strained phase arises from the epitaxial strain induced canted antiferromagnetic structure. This study resolves a much debated issue of strain induced magnetic moment in BiFeO3 thin films.