A scanning electron microscope (SEM) sturon me the magnetic domain structure of ion meteorites and their synthetic analogues

1976 Journal of geomagnetism and geoelectricity  
Magnetic domain observations were carried out on iron meteorites and on sputter-deposited thin films of meteoritic composition (10, 20% Ni-Fe), by two SEM techniques: 1) high voltage (30kV) backscattered electron mode and 2) low-voltage (2kV) secondary electron image. To confirm and complement these, 3) Bitter-powder patterns were also observed in reflected-light microscopy. High energy SEM magnetic contrast revealed parallel-oriented arrays of stripe domains in kamacite (k) regions, at 60 (for
more » ... <111> face) or 90 (for <100> face) to their taenite (t) boundaries, depending on the crystal orientation. Magnetic domain widths ranged from 15-25um in the Gibeon meteorite (finest octahedrite, 8% Ni-Fe, average k-bandwidth 0.2mm) to 40-80pm in the Odessa meteorite (coarsest octahedrite, 7.29% Ni-Fe, 3.3mm k-bands). Finer domain substructure (-10pm) was resolved by Bitter-pattern microscopy in Odessa, as magnetic grids in each k grain, whose orientation was discontinuous across boundaries. Based on low-energy SEM observations of Gibeon, it appears that each micro-kamacite grain in plessite regions is a single domain. By the same technique, 1-5um stripe domains separated by <0.5pm Bloch walls were resolved in a 2000 Ni-Fe film and 0.2-2gum domains with 90 "elbow" -walls, typical of Fe3O4, were observed in a laboratory-produced Fe3O4 film. The much finer scale of magnetic domain structure in meteorites, by comparison with their metallographic-compositional features, may explain the presence of stable paleoremanence in the coarsely crystalline iron meteorites. The application of even higher-voltage (50kV) SEM to similar studies of terrestrial, lunar, and meteoritic materials promises to reveal the bulk domain-structure of their magnetic carriers and may thus afford a better understanding of their paleomagnetic record.
doi:10.5636/jgg.28.31 fatcat:w7ktkcev4zcb3duvamol7r5n6a