A novel foil actuator using the magnetic shape memory effect

A novel foil actuator of 15 × 3 mm2 lateral dimensions is presented making use of the magnetic shape memory (MSM) effect. The actuation material is a Ni–Mn–Ga foil of 200 µm thickness that has been fabricated by cutting of a bulk Ni–Mn–Ga(100) single crystal consisting of 10 M martensite variants at room temperature. Stress–strain experiments on tensile test structures demonstrate that the stress needed for reorientation of martensite variants is about 1.2 MPa. The low twinning stress allows magnetic-field-induced variant switching, the basic mechanism of MSM actuation. A Ni–Mn–Ga foil actuator is fabricated by lithography and hybrid integration. The actuator shows a maximum magneto-strain of 4.9%, which is limited by the constraints of fixation and loading. Upon tensile loading at 1.5 MPa, linear actuation cycles are generated with an actuation stroke of 2.2%. The foil actuator is used as a benchmark system for modeling the coupled magneto–mechanical behavior of MSM actuation. We present finite element simulations based on a thermodynamic Gibbs free-energy model that qualitatively describes the observed tensile stress-dependence of magneto-strain.