Superhigh strains by variant reorientation in the nonmodulated ferromagnetic NiMnGa alloys

Superhigh strains of 15% for the Ni53Mn25Ga22 and 13.5% for the Ni54Mn23Ga23 with the nonmodulated martensite structure were achieved by variant reorientation. A strong magnetic anisotropy exists in the prefabricated single variant with the easy axis along the contraction [001] direction of the high-temperature cubic phase. A higher austenitic transformation temperature was found in the single variant comparing with the original multivariant sample. The same order of magnitude for the saturation magnetization Ms, magnetic anisotropy constant ku, and the twin reorientation stress σtw, namely, 57.6 A m2/kg, 1.4×105 J/m3, and approximately 20 MPa, respectively, as those in 5M martensite indicate that it is reasonable to expect a much higher magnetic field-induced-strain in the nonmodulated NiMnGa alloys.