Field-induced strain under load in Ni-Mn-Ga magnetic shape memory materials

Single-crystal Ni2MnGa shows a nearly 0.2% strain under a magnetic field of 8 kOe at -8 degrees C. Polycrystalline samples have been prepared near stoichiometry to study the composition dependence of the magnetic and elastic properties. A narrow band of compositions has been found having a range of Curie and martensitic transformation temperatures, T-c and T-0, extending to above room temperature. The compressive stress-strain characteristics in variable transverse field were studied in samples selected to have T-0 just below room temperature. Stress-induced martensite was observed as expected and the magnetic field was applied under fixed load for various stresses. A transverse field of 3200 Oe caused the sample to strain under load doing work that increased up to 1.3 J/kg with increasing volume fraction of stress-induced martensite. (C) 1998 American Institute of Physics. [S0021-8979(98)41211-8].