Ferromagnetic shape memory in the NiMnGa system
Strain versus field measurements for a ferromagnetic shape memory alloy in the NiMnGa system demonstrate the largest magnetostrictive strains to date of nearly 1.3%. These strains are achieved in the martensitic state through field-induced variant rearrangement. An experimental apparatus is described that provides biaxial magnetic fields and uniaxial compressive prestress with temperature control while recording microstructural changes with optical microscopy. The magnetostrictive response is found to be sensitive to the initial state induced by stress-biasing the martensitic variant structure, and exhibits rate effects related to twin boundary mobility. Experiments performed with constant stress demonstrate work output capacity. Experimental results are interpreted by using a theory based on minimization of a micromagnetic energy functional that includes applied field, stress, and demagnetization energies. It is found that the theory provides a good qualitative description of material behavior, but significantly overpredicts the amount of strain produced. Issues concerning the martensitic magnetic anisotropy and variant nucleation are discussed with regard to this discrepancy.
- Research Organization:
- Univ. of Minnesota, Minneapolis, MN (US)
- Sponsoring Organization:
- US Department of the Navy, Office of Naval Research (ONR); Advanced Research Projects Agency; National Science Foundation (NSF)
- OSTI ID:
- 20000596
- Journal Information:
- IEEE Transactions on Magnetics (Institute of Electrical and Electronics Engineers), Vol. 35, Issue 5Pt3; Other Information: PBD: Sep 1999; ISSN 0018-9464
- Country of Publication:
- United States
- Language:
- English
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