FEM simulation of a Ni–Mn–Ga film bridge actuator

This paper explores the use of the magnetic shape memory (MSM) effect for actuation of a free-standing film bridge by coupled finite element simulations in the framework of a Gibbs free energy model. The material of interest is a Ni–Mn–Ga film showing a 10M tetragonal martensite structure. Two actuation mechanisms (I and II) are considered depending on the magnetic field configuration and the method of stress biasing. In mechanism I, tensile stress is generated by a mechanical point load in out-ofplane direction applied in the film bridge center. In this case, magnetic field-induced reorientation (MIR) requires a magnetic field along the long axis of the film bridge. We show that only a partial MIR effect is possible for mechanism I as the magnetic field has to counteract the applied mechanical force. For mechanism II, variant reorientation and stress biasing are accomplished by different magnetic fields applied along the short axis of the film bridge allowing complete MIR.