HR: 10:50h
AN: GP12A-02 INVITED     [Abstracts]
TI: Magnetic Force Microscopy and Electron Back Scatter Diffraction Study of Pseudo-Single-Domain Grains of Magnetite
AU: * Pokhil, T
EM: tpokhil@nve.com
AF: NVE Corporation, 11409 Valley View Road, Eden Prairie, MN 55344-3617 United States
AU: Moskowitz, B M
EM: bmosk@umn.edu
AF: University of Minnesota, 291 Shepherd Labs, 100 Union St SE, Minneapolis, MN 55455 United States
AU: Jackson, M J
EM: irm@umn.edu
AF: University of Minnesota, 291 Shepherd Labs, 100 Union St SE, Minneapolis, MN 55455 United States
AU: Carter-Stiglitz, B S
EM: cart0196@umn.edu
AF: University of Minnesota, 291 Shepherd Labs, 100 Union St SE, Minneapolis, MN 55455 United States
AB: Magnetic domain structures in pseudo-single-domain (PSD) grains (5-20 μm) of magnetite (Fe₃O₄) were studied using magnetic force microscopy (MFM) and correlated with grain shapes and with crystallographic orientations determined by electron back scatter diffraction (EBSD). The magnetite grains, produced by the glass-ceramic method, are randomly oriented and dispersed in a nonmagnetic silicate matrix. The studies were focused on grains with magnetization mainly parallel to the sample surface. Domain wall (DW) types and crystallographic orientation of wall planes were identified using MFM and EBSD data. For instance, for a triple wall junction where three wall types (180°, 71° and 109° DW) intersect, the wall orientations were identified as following: the 180° wall is parallel to (112) type plane, the 71° wall to (110) type plane and the 109° wall to (001). Most of the studied grains were subdivided into domains by 180° DWs, which cross the entire grain without formation of closure domain structures at grain edges. Domain structures remained qualitatively the same after repeated AF demagnetization cycles. Most of the observed 180° walls were parallel to (110) type planes, most likely because such planes contain two easy axes, which reduces wall energy density. Close to grain edges, 180° DWs often deviated from (110) orientations by twisting around a [111] axis parallel to the magnetization in adjacent domains. This allows optimization (minimization of total) of wall energy density, wall area and stray field (magnetic charge at grain edges) and indicates that stress is a subordinate factor in causing wall bending. Our wall bending analysis is consistent with published micromagnetic calculations. The combined MFM and EBSD study allows the conclusion that remanent 3-D domain structures in PSD grains result from combined magnetostatic effect of all grain surfaces (shape anisotropy of the grain) and magnetocrystalline anisotropy.
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2005 Joint Assembly