NiMnGa polycrystalline magnetically activated shape memory alloy: A calorimetric investigation

A lot of attention is now being given to ferromagnetic shape memory alloys (also known as MSM-- magneto strained materials) as they can be used to achieve magnetically induced strains of more than a few percent. Such high strains are related not only to the driving effect of the external magnetic field on twin plane and phase boundary movement, but also to the possibility of promoting austenite- martensite transformation. Experiments reported in the literature refer mainly to single crystal and/or thin film specimens, very few deal with polycrystals. The aim of the present work was to investigate the behavior of polycrys- talline samples. For this purpose samples with two different compositions were prepared and charac- terized by Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Energy Dispersion Spectroscopy (EDS) and optical microscopy.