Strain and interface effects in a novel bismuth-based self-assembled supercell structure

Bi₂FeMnO₆ (BFMO) thin films with both conventional pseudocubic structure and novel supercell structure have been grown on SrTiO₃ (001) substrates with different thicknesses of CeO₂ buffer layers (ranging from 6.7 to 50.0 nm) using pulsed laser deposition. The correlation between the thickness of the CeO₂ buffer layer and the structure of the BFMO films shows that the CeO₂ buffer layer, as thin as 6.7 nm, is sufficient in triggering the novel BFMO supercell structure. This may be ascribed to the interfacial strain between the BFMO supercell structure and the CeO₂ buffer layer which also serves as a seed layer. The buffer layer thickness is found to be critical to control the microstructure and magnetism of the formed BFMO supercell structures. Thin seed layers can produce a smoother interface between the BFMO film and the CeO₂ buffer layer, and therefore better ferrimagnetic properties. Our results have demonstrated that strain and interface could be utilized to generate novel thin film structures and to tune the functionalities of thin films.