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Active materials such as piezoelectrics are established in the field of microsystems application despite their low achievable strains which often require the integration of additional gear mechanisms. The ongoing search for new active materials has focused on magnetic shape memory (MSM) alloys such as NiMnGa since they combine macroscopic strains of up to 10% with a cycling frequency well above the frequencies of conventional thermal shape memory alloys. The present review focuses on preparation and analysis of NiMnGa films that can eventually be integrated in microsystems. Single crystal like films are prepared by epitaxial growth on suitable substrate materials. Since the magnetically induced reorientation of variants is blocked by a rigid substrate, we present different methods for releasing films from the substrates. We show that the sacrificial layer technology is the most promising approach. Further processing of the freestanding film requires a microtechnology which is adjusted to the film laminate structure. The properties of the freestanding films are compared with films on a rigid substrate. Although we observe stress‐induced twin boundary motion, the twinning stress is too high to be overcome by an external magnetic field. Therefore, it is necessary to develop suitable training methods to reduce the twinning stress below 2 MPa to enable the activation of the material by means of an external magnetic field.

A novel foil actuator of 15 × 3 mm 2 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.

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