Abstract: The observation of ferroelectric, ferromagnetic and ferroelastic phases in thin films of binary oxides attracts the broad interest of scientists and engineers. However, the theoretical consideration of physical nature of the observed behaviour was performed mainly for HfO2 thin films from the first principles, and in the framework of Landau-Ginzburg-Devonshire (LGD) phenomenological approach with a special attention to the role of oxygen vacancies in both cases. Allowing for generality of the LGD theory we applied it to the group of binary oxides in this work. The calculations have been performed in the assumption that oxygen vacancies, as elastic dipoles, can be partially transformed into electric dipoles due to the defect site-induced and/or surface-induced inversion symmetry breaking (via e.g. piezoelectric effect), and can “migrate” throughout the depth of an ultra-thin film. Since the many films of binary oxide are ferroelectric and ferromagnetic due to the oxygen vacancies, they can be multiferroics. Performed calculations have shown that thin films of binary oxides can be considered as new multiferroics with physical properties useful for broad spectra of applications in nanoelectronics and nanotechnology. The properties can be controlled by the choice of oxygen vacancies concentration, film thickness and special technological treatment, such as annealing.
Title: Origin of Ferroelectricity and Multiferroicity in Binary Oxide Thin Films
DOI: https://doi.org/10.1109/TUFFC.2020.2988361 IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control (2020) 68, 273-278