Surface magnetic structure of epitaxial magnetite thin films grown on MgO(001)

摘要

The crystallographic structure of antiphase domain boundaries (APBs) and the magnetic structure of large domains of magnetite (Fe_3O_4) thin films, which were epitaxially grown on MgO(001) substrates and annealed in an ambient condition, were investigated by scanning tunneling microscopy (STM), transmission electron microscopy (TEM), magnetic force microscopy (MFM), and scanning electron microscopy with polarization analysis (SEMPA). STM and TEM showed the morphology of the APBs in film surfaces and the bulk, whereas MFM and SEMPA showed the magnetic structure of the surfaces. As in previous paper reported by another group, STM and TEM observations revealed the antiphase domains on a scale from tens of nanometers to a few hundred nanometers. Also MFM measurement showed the magnetic domains on a scale of a few hundred nanometers and large-scale undulations of a few micrometers. Our SEMPA observations of the films displayed large-scale magnetic structures on a scale of a few hundred nanometers to a few micrometers. These large-scale magnetic structures are expected to be induced by the enlargement of magnetic domains that contain magnetic moments aligned along a magnetic easy axis. These moments have in-plane components that make the SEMPA images visible. An air-annealing process is needed to change magnetic couplings in APBs and to form large-scale magnetic ordering.