Opportunities for Chromatic Aberration Corrected High-Resolution Transmission Electron Microscopy, Lorentz Microscopy and Electron Holography of Magnetic Minerals

High spatial resolution structural information about magnetic minerals can be obtained using spherical aberration (CS) corrected transmission electron microscopy (TEM), while local magnetic information can be obtained using complementary TEM techniques such as Lorentz microscopy and off-axis electron holography [1]. Figure 1 shows Lorentz TEM (out-of-focus) images of a magnetite (Fe3O4) specimen acquired at 300 kV without the use of CS correction. The images were recorded below the Verwey transition, at which the magnetocrystalline anisotropy increases by an order of magnitude and the magnetic easy axis switches from the <111> directions of the parent cubic phase to the [001] direction of the low temperature monoclinic phase. In extended crystals examined at low temperature, μm-scale monoclinic twin domains that are separated from each other by jagged twin walls are observed. The domains are subdivided by lamellar twins, which join at their ends to form needle twins that move in response to thermal or magnetoelastic stress by the advancement and retraction of the needle tips. Figures 1 (c) to (f) show a 180 ° magnetic domain wall being driven to the right by an applied magnetic field, resulting in the conversion of a conventional 90 ° domain wall into a ‘divergent ’ 90 ° domain wall. In individual nanocrystals that can only a single magnetic domain, we observe competing effects on the magnetic microstructure of shape anisotropy an