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 M-s, magnetic anisotropy constant k(u), and the twin reorientation stress sigma(tw), namely, 57.6 A m(2)/kg, 1.4x10(5) J/m(3), 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. (C) 2002 American Institute of Physics.