Improved epitaxial growth and multiferroic properties of Bi₃Fe₂Mn₂O using CeO₂ re-seeding layers

In ferroelectric and multiferroic-based devices, it is often necessary to grow thicker films for enhanced properties. For certain phases that rely on substrate strain for growth, such thicker film growths beyond the typical thin film regime could be challenging. As an example, the Bi₃Fe₂Mn₂O (BFMO) Aurivillius supercell (SC) phase possesses highly desirable multiferroic (i.e., ferromagnetic and ferroelectric) properties and a unique layered structure but relies heavily on substrate strain. Beyond the thin film regime (approximately 100 nm), a less desirable pseudo-cubic (PC) phase is formed. In this work, a novel heterogeneous re-seeding method is applied to maintain the strained growth in this SC phase beyond the thin film regime, thus enabling the growth of thick BFMO SC phase films. The insertion of periodic CeO₂ interlayers reintroduces the heteroepitaxial strain and effectively re-initiates the growth of the SC phase. The thick BFMO SC phase maintains the overall multiferroic and interesting anisotropic optical properties, even exceeding those of the typical 100 nm SC film. This re-seeding method can be effectively adopted with other SC systems or strain-dependent thin films, thus introducing practical applications of the new SC phases without thickness limitations.