Ferromagnetic Shape Memory in the NiMnGa System
by
R. Tickle, R.D. James, T. Shield, M. Wuttig, V.V. Kokorin, P. Schumacher
in
IEEE J. Magnetics, , 1998.
AEM Report Number 1998-1
Keywords: ferromagnetic shape memory, giant magnetostrictive materials, cubic-tetetragonal transformation, magnetomechanical properties
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Abstract:
Strain field measurements for a shape memory alloy in the system demonstrate the largest tive strains to date of nearly 1.3%. These strains are in the martensitic state through field-induced variant rearrangement. An experimental apparatus is described that provides magnetic fields and uniaxial compressive with temperature control while recording changes optical microscopy. The magnetostrictive response is found be sensitive to the initial state induced by stress-biasing the martensitic variant and exhibits rate related twin boundary mobility. Experiments performed with constant stress demonstrate work output results are interpreted using a theory based on minimization of a micro- magnetic energy functional that includes applied field, stress, and demagnetization energies. is found that the theory provides a good qualitative description of behavior, but significantly overpredicts the amount strain produced. Issues concerning the martensitic magnetic and variant nucleation are discussed with regard this discrepancy.
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