Magnetic Field Induced Strain in Ni-Mn-Ga Wires and Foam

Magnetic shape-memory alloys change shape in the presence of a variable magnetic field. Ni-Mn-Ga is a magnetic shape memory alloy that displays magnetic field induced strain of up to 10%. Ni-Mn-Ga wires and foams are particularly interesting because they are lightweight and can be processed to small dimensions. We characterized thermal, magnetic, and magneto-mechanical properties of Ni-Mn-Ga wires and foams which were made to different compositions and with different processing techniques. The composition drastically impacts the Curie temperature (Tc) and martensite transformation temperature (TM). The Curie temperature of wires with Ni content between 51.5 and 54.5 at.-% was around 80°C -100°C. For compositions with Ni content between 57.1 and 66.7 at.-%, the Tc ranged between 5 and 45°C. Additionally, the loss of 8-10% Mn during fiber production decreased the martensite transformation temperature by up to 100°C from 80°C to -20°C.