The Development And Studies On Physical Properties Of Magnetic Shape Memory Alloys With Wide Martensitic Transformation Temperature Range

The structure,martensitic transformation and magnetic properties of alloys Mn₂NiGa with doped rare earth element Pr,Nd,Gd and Fe element were investigated in this paper.The magnetic properties of some alloys also studied by theoretical calculations.The rare earth element Pr was doped in the Mn₂NiGa alloy to replace Mn element,and then we found that Mn_50-xPr_xNi₂₅Ga₂₅?x=0.5,1,1.5,2,3,6.25?alloys consist of the matrix phase and the second phase?Pr-rich phase?.When the content of Pr is scarce?x?0.5?,there is little second phase.With an increase of the content of Pr?0.5<x?6.25?,the second phase becomes larger and trends to distribute along the grain boundaries.In this series of alloys,with the increasing of rare earth element Pr,the martensitic transformation temperature and inverse transformation temperature increase gradually,and nearly reach room temperature.Meanwhile,the temperature range of the phase transformation has also been gradually widened.The theoretical calculations show that the rare earth Pr atom prefers to occupy the Mn?A?site of Mn₂NiGa,and the magnetic moment of martensitic phase is lower than that of austenitic phase.The microstructure of Mn₅₀Ni_25-xNd?Pr?_xGa₂₅ alloys are composed by the matrix and the second phase?Nd?Pr?-rich phase?.With the increasing of Nd?Pr?content,the martensitic transformation temperature and inverse transformation temperature increase remarkably.Meanwhile,the temperature ranges of martensitic transformation also broaden.However,the saturation magnetization at 5K decreases with the increasing of rare earth elements.The Mn₄₈Ni_27-xFe_xGa₂₅?x=0,1,2,3,4?alloys were prepared by arc-melting.The study of Mn₄₈Ni_27-xFe_xGa₂₅5 alloys have shown that with the increasing of Fe content the magnetic structure and electron concentration change,which lead to an increase of the martensitic transformation temperature and inverse transformation temperature.Furthermore,the phase transition temperature range becomes wider and the thermal hysteresis also increases.However,the saturation magnetization at 5K has shown a decreasing trend with the increasing of Fe content.The rare earth element Gd was doped in the Mn₂NiGa alloy to replace Ga element,and then we studied the structure of Mn₅₀Ni₂₅Ga_25-xGd_x?x=0.1,0.2,0.3,0.5,1?alloys.At the same time,we found that the martensitic transformation temperature and inverse transformation temperature of Mn₅₀Ni₂₅Ga_25-xGd_x alloys gradually increase and nearly reach room temperature with the increasing of Gd content.