Domain Walls and Twin Boundaries in Ferromagnetic Shape Memory Alloys

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This renewal award by the Division of Materials Research to Carnegie-Mellon University is to apply electron microscopic techniques to ferromagnetic shape memory alloys (FSMA) and intermetallics, and in particular to try to understand the nature of the tweed structures. With this award, Professor De Graef will study the physical and magnetic microstructure of alloys of Nickel-Manganese-Gallium and Cobalt-Nickel-Gallium, with an emphasis on compositions with near room temperature phase transformations. The microscopy techniques, which were developed by the investigator, will be used for simultaneously imaging twins and other crystal defects that move during FSMA actuation, and the magnetic domain walls that drive the twin boundary motion. Proposed research would contribute significantly to the fundamental understanding of the mechanisms that couple the magnetic field to the atomic displacements associated with the actuation in ferromagnetic shape memory alloys. FSMA area is of considerable interest for potential applications of them as high-strain, moderate-frequency actuators and sensors Science developed by this award would shed light into our understanding of the motion of magnetic domains and twin boundaries. The characterization tools and methods developed by this project for ferromagnetic shape memory alloys will also have a positive impact on the ability to characterize magnetic recording media. There would be significant contributions for graduate education, course development, and teaching of advanced materials characterization by the proposed studies. Development of an interactive web-based site with the help of undergraduate students from both Materials Science and Engineering and Computer departments for an undergraduate textbook on crystallography and diffraction would be part of this project.