Reversible structural transition in monocrystalline Ni2FeGa microwires for shape-memory applications

We report on the production and characterization of Heusler-based Ni2FeGa microwires exhibiting two - way shape memory effect. The microwires are characterized by a monocrystalline structure with a strong preferred crystallographic orientation that shows [1 1 1] axis parallel to the wire's axis for high-temperature L2(1) austenite phase, while the [0 1 7] axis is preferred for low-temperature monoclinic phase. Variation of crystallographic axis (and corresponding easy magnetization axis) leads to 1600% variation of magnetic permeability due to a 2% strain in axial direction. Such straining is reversible immediately after production without the necessity of further thermal treatment. These properties give the microwire function of very sensitive SMART actuators that can be easily produced in a large amount.