Kinetics and intermediate phases in epitaxial growth of Fe3O4 films from deposition and thermal reduction

We have studied the kinetics of the transitions between the Fe2O3 and Fe3O4 phases as thin epilayers (similar to 2.5 nm) on Al2O3 (001) substrates using time-resolved reflection high energy electron diffraction. The different iron oxide phases were identified using a combination of in-situ and ex-situ characterizations. The transition from an alpha-Fe2O3 (001) epilayer to a Fe3O4 (111) epilayer through thermal reduction was found to be determined by the Fe-O bonding energy, resulting in a long time scale. The oxidation at high temperature converts a Fe3O4 (111) epilayer to an alpha-Fe2O3 (001) epilayer quickly; at low temperature, a gamma-Fe2O3 (111) epilayer was slowly generated instead. By repeating the deposition/thermal reduction processes, a thicker Fe3O4 (111) film was obtained, which exhibit high crystallinity and moderate magnetic coercivity. Published by AIP Publishing.