Properties of polycrystalline NiMnGa - alloys for application as magneto-mechanic actuator

Magnetic shape memory materials can deform by some percent via twin boundary motion under the influence of a magnetic field. This effect is well documented for single crystals of Ni-Mn-Ga alloys with compositions around Ni2MnGa. It is demonstrated that this effect can be achieved in textured polycrystalline samples as well, which can be produced much more efficient than single crystals. Directional solidified samples were subjected to thermal and thermo-mechanical treatment in order to adjust structure and microstructure. A shape change larger than 1 % was achieved in a Ni5oMn29Ga2i alloy by applying a magnetic field at room temperature.