Anomalous strain relaxation behavior of Fe_3O4/MgO (100) heteroepitaxial system grown using molecular beam epitaxy

Strain relaxation studies in epitaxial magnetite (Fe3 O4) thin films grown on MgO (100) substrates using high-resolution x-ray diffraction and cross-sectional transmission electron microscopy reveal that the films remain fully coherent up to a thickness of 700 nm. This thickness is much greater than the critical thickness tc for strain relaxation estimated from mismatch strain. Anomalous strain relaxation behavior of Fe3 O4 MgO heteroepitaxy is attributed to the reduction in the effective stress experienced by the film due to the presence of antiphase boundaries (APBs) that enable the film to maintain coherency with the substrate at large thickness. However, the stress accommodation in the film depends upon the nature and density of the APBs.