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

Abstract

Thermoelastic and strain-induced martensitic transformations of single crystalline Ni 49.7 Mn 29.1 Ga 21.2 magnetic shape memory alloys were investigated by simultaneous detection of the strain and magnetization. The transformation temperature to austenite was T A =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, K u =1.2×10 5 J/m 3 and the saturation magnetization increased, about 14%, compared with the parental austenite.