Magnetic properties of stress-induced martensite and martensitic transformation in Ni–Mn–Ga magnetic shape memory alloy

Thermoelastic and strain-induced martensitic transformations of single crystalline Ni49.7Mn29.1Ga21.2 magnetic shape memory alloys were investigated by simultaneous detection of the strain and magnetization. The transformation temperature to austenite was TA=314 K. The thermoelastic transformation was shifted to higher temperature with increasing compressive stress with rate about 4 MPa/K. The effect of the moderate magnetic field up to 1 T on transformation was negligible. Very similar magnetic properties of thermally and stress-induced martensites measured in the field up to 1.2 T suggest an equivalence of the phases. Direct comparison of the magnetic properties of austenite and stress-induced martensite at constant temperature above the thermal martensitic transformation is made. At 317 K, the stress-induced martensite had a large uniaxial magnetic anisotropy, Ku=1.2×105 J/m3 and the saturation magnetization increased, about 14%, compared with the parental austenite.