Giant field-induced reversible strain in magnetic shape memory NiMnGa alloy

TLDR

Field‑induced strain in NiMnGa alloys diminishes as external compressive stress along the expansion direction increases. In martensitic Ni48Mn31Ga21, a 5.1 % reversible strain is achieved at 480 kA/m, but a 3 MPa compressive load suppresses it; the strain and abrupt magnetization change arise from twin‑variant reconfiguration, as confirmed by optical imaging.

Abstract

A room temperature extensional strain of 5.1% was observed in martensitic Ni/sub 48/Mn/sub 31/Ga/sub 21/ alloy in the magnetic field of 480 kA/m. The magnitude of field-induced strain decreases with increasing external compressive stress applied in the direction of expansion. The compressive stress of about 3 MPa prevents the development of the substantial field-induced strain. Magnetization curves obtained by VSM exhibit an abrupt magnetization change and a transient hysteresis in the first quadrant. Large reversible field-induced strain and the abrupt magnetization change are due to the rearrangement or redistribution of martensitic twin variants by the applied magnetic field. It was confirmed by optical observation of movement and nucleation of martensitic twin boundaries.