Investigation of microstructural and functional properties of polycrystalline samples of NiMnGaCu ferromagnetica shape memory alloy

In the last 20 years Magnetic Shape Memory Alloys (MSMA) attracted increasing attention for their different properties and smart functions. Starting from the first and most important system NiMnGa, a long series of quaternary alloys was developed to improve the performance of these materials in the Giant Magnetrostrictive Effect (or Magnetic Field Induction Strain), Magnetic Shape Memory effect, Magnetocaloric and Magnetoresistive properties and also Elastocaloric response. Some alloys like NiMnInCo, NiMnSn or NiMnGaCo showed interesting giant magnetocaloric effect using the superimposition in temperature of magnetic transition and thermoelastic martensitic transformation; in this way under magnetic field the resulting entropy variation (DS) is maximized by the overlapping of these two physical transitions in the material. Therefore, these alloys open new perspective in the development of devices for magnetic solid state refrigeration. In the last years NiMnGaCu showed interesting magnetocaloric properties and the Ni50Mn18,5Cu6.5Ga25 (at%) alloys gives rise to thehighest magnetic DS: -81.75 J/KgK at 302.5 K by magnetic field change of 9 T. This results that was obtained near room temperature is very important for the development of applications. In our work we prepared polycrystalline samples of the latter quaternary Ni50Mn18,5Cu6.5Ga25 alloy, where Cu is in substitution of Mn. By different kind of thermal treatments we modulated the microstructure of the alloy and we investigated the correlation between microstructural and functional properties. Magnetocaloric response was measured and a complete calorimetric and structural characterization was utilized to investigate this possible correlation. Moreover, to study the overcoming of brittleness problems, mechanical measurements completes the informations about the optimization of the material for future development of applications.