Processing Routes Toward Textured Polycrystals in Ferromagnetic Shape Memory Alloys

NiMnGa single crystals can produce large strain in moderate magnetic fields. It is the scope of this article to demonstrate, that also polycrystalline materials can show strain in a magnetic field, so called MFIS (magnetic field-induced strain). In order to design functional polycrystalline materials the interactions of twin boundaries and grain boundaries have to be understood. Therefore, different ways of introducing a texture into NiMnGa polycrystals are presented. The different kinds of texture and the consequences for the corresponding materials are discussed. Moreover, thermal, magnetic, and/or mechanical training concepts are presented and their working principle is explained. Several possibilities of evaluating the MFIS capability of the resulting samples are displayed. Finally methods of increasing the strain further are discussed.