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

Single-crystal ${\mathrm{Ni}}_{\mathrm{2}}\mathrm{MnGa}$ shows a nearly 0.2% strain under a magnetic field of 8 kOe at $\text{−8\hspace{0.17em}°}\mathrm{C}.$ 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.