Investigation of Twin Boundaries and Magnetic Tongues Using AFM and MFM

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Dr. Peter Mullner and Dr. William B. Knowlton


Atomic probe microscopy techniques are developed to characterize magnetic and crystallographic domain structures of magnetic shape memory alloys. The intent is to correlate the magnetic domains of the material with the crystallographic domains. The data was collected with a Digital Instruments Dimension 3000 atomic force microscope. A comparison of the topographic and magnetic data reveal a direct correlation between the height and phase images, i.e. a direct correlation between the magnetic and the crystallographic domain structure. Crystallographic twins appear as parallel bands of ridges and valleys with planar facets. On every other facet, the crystallographic c direction is parallel to the surface and perpendicular to the ridges and valleys. On the other facets, the crystallographic c direction is perpendicular to the surface. The magnetic moments are parallel to the crystallographic c direction, which is the direction of easy magnetization. On the facets with c parallel to the surface, magnetic "tongue-shaped" features were found, which are anchored at the ridges. Using this information, a three dimensional model of the twin microstructure and the magnetic domain structure is being developed.

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