A novel foil actuator using the magnetic shape memory effect

Abstract

A novel foil actuator of 15 × 3 mm2 lateral dimensions is presented making use of the magnetic shapememory (MSM) effect. The actuation material is a Ni–Mn–Ga foil of200 µm thickness that has been fabricated by cutting of a bulk Ni–Mn–Ga(100) single crystalconsisting of 10 M martensite variants at room temperature. Stress–strain experiments ontensile test structures demonstrate that the stress needed for reorientation of martensitevariants is about 1.2 MPa. The low twinning stress allows magnetic-field-induced variantswitching, the basic mechanism of MSM actuation. A Ni–Mn–Ga foil actuator isfabricated by lithography and hybrid integration. The actuator shows a maximummagneto-strain of 4.9%, which is limited by the constraints of fixation and loading. Upontensile loading at 1.5 MPa, linear actuation cycles are generated with an actuationstroke of 2.2%. The foil actuator is used as a benchmark system for modelingthe coupled magneto–mechanical behavior of MSM actuation. We present finiteelement simulations based on a thermodynamic Gibbs free-energy model thatqualitatively describes the observed tensile stress-dependence of magneto-strain.