Strain relaxation inFe3O4/MgAl2O4heterostructures: Mechanism for formation of antiphase boundaries in an epitaxial system with identical symmetries of film and substrate

Strain relaxation studies in epitaxial magnetite, ${\text{Fe}}_3{\text{O}}_4$, thin films grown on ${\text{MgAl}}_2{\text{O}}_4$(100) substrates are reported. The study shows that the films were relaxed in line with the theoretical model prediction with a critical thickness, $t_{\text{c}}=5\text{nm}$. Antiphase boundaries (APBs) are not expected to form in ${\text{Fe}}_3{\text{O}}_4$ films grown on ${\text{MgAl}}_2{\text{O}}_4$ substrates because both film and substrate have the same crystal symmetry. In contrast, our study reveals the formation of APBs within the ${\text{Fe}}_3{\text{O}}_4$ films. Our analysis shows that the APBs in a ${\text{Fe}}_3{\text{O}}_4/{\text{MgAl}}_2{\text{O}}_4$ heteroepitaxial system are formed by partial dislocations, which accommodate the misfit. This formation mechanism of APBs is fundamentally different from the one found in the ${\text{Fe}}_3{\text{O}}_4/\text{MgO}$ system, where APBs are formed as a consequence of equivalent nucleation sites on the MgO substrate separated by nontranslational vectors of the ${\text{Fe}}_3{\text{O}}_4$ lattice. The mechanism for the formation of antiphase boundaries through partial dislocations should be applicable to a wide range of epitaxial systems having identical symmetries of the film and the substrate and significant lattice mismatch.