Antiphase domain boundaries in thin films of magnetite

Films of Fe3O4 were prepared by sputter deposition onto MgO substrates of both [100] and [110] orientations. The films used in this study were mainly 50 nm thick. X-ray diffraction, Mossbauer spectroscopy, and other techniques revealed that the films were stoichiometric single crystals. Electron microscopy showed that the films were essentially dislocation free. Despite this high degree of perfection, the magnetic properties of the films were inconsistent with bulk single crystal properties. For example, the magnetization of the films did not saturate in fields as large as 7 Tesla, while bulk single crystals saturate by 0.1 Tesla. The films were removed from the substrates in a reactive bath and examined in a transmission electron microcope. It is observed that the films contain a high density of antiphase domain boundaries (APBs), spaced several tens of nanometers apart. The APBs tend to lie in the {110} planes. Preliminary modeling indicates that the APBs could produce the anomalous high field behavior. The electron diffraction patterns repeatedly showed unusually prominent diffraction spots that are not allowed by the standard kinematical structure factor. These extra spots appeared in several zone axes in films of the two growth orientations that were studied. They also appeared, albeit with less intensity, in a specimen that was thinned from a bulk single crystal that did not exhibit APBs.