Temperature resolved structural investigation of sintered NiMnGa Ferromagnetic Shape Memory Alloys

NiMnGa alloys are FeSMA where the thermoelastic martensitic transformation (TMT) is correlated to the ferromagnetic transition and the Curie Temperature (Tc). Materials where the Tc is overlapped to the TMT temperature have attracted interest for multifunctional properties as magnetocaloric and magnetomechanical coupling. Due to the high brittleness of these systems, attention has been devoted to sintering routes. The tuning of the grain and microstructure gives a modulation of TMT temperatures, and the shift of its temperatures to overlap with Tc. The correlation of magnetic and martensitic transition could be influenced by local order of ferromagnetic and paramagnetic state. The stored energy due to the sintering process could induce structural distortion that influence the magnetic order. An investigation of microstructure and a description of its cell parameter is interesting in NiMnGa samples, where the Tc and the TMT temperatures are far or near to be overlapped.