Implications of antiphase boundaries (APBs) on the strain relaxation and magnetotransport properties of Fe3o4 hetero-epitaxial thin films

Abstract

The strain relaxation and magneto transport properties of epitaxial magnetite (Fe3O4) thin films were studied. Epitaxial Fe3O4 film s were grown on MgO and MgAl2O4 substrates using an Oxygen plasma assisted Molecular beam epitaxy (MBE) system. Characterisation of the films were done using techniques such as Reflection high energy electron diffraction (RHEED), High resolution X-ray diffractom eter (HRXRD), Vibrating sample magnetometer (VSM), Low temperature resistivity measurements, and Raman Spectroscopy. Our studies on strain relaxation behaviour of epitaxial Fe3O4 thin films grown on MgO (100) substrates reveal that the films do not exhibit strain relaxation up to 700 nm thickness, which is much larger than the strain relaxation critical thickness, tc, (70nm) predicted by the most accepted model based on mismatch strain. In contrast, the model predictions of strain relaxation behaviour are consistent with our results for Fe3O4 films grown on MgAl2O4 (100). The observed anomalous strain relaxation behaviour is attributed to the presence of antiphase boundaries (APBs) which lead to the formation of areas within the film that have opposite sign of stress. The stress compensation by the APBs reduces the effective stress experienced by the films. Even though APBs are not expected in Fe3O4 films grown on MgAl2O4, TEM studies revealed the presence of APBs. We suggest that these APBs are formed not because of symmetry difference but because of the staking faults generated by strain relaxation due to the large mismatch between the thin film and substrate.