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.