The Influnce Of Adulteration On The Physical Properties Of Ferromagnetic Shape Memory Alloy Mn 2 NiGa

Ferromagnetic shape memory alloy is a type of smart material which is driven by the magnetic field. A series of ferromagnetic shape memory alloys were developed after the first ferromagnetic shape memory alloy Ni₂MnGa was studied. Their physical properties, like the crystal structure, martensite-transition and magnetic properties were investigated in details.Mn₂NiGa is a ferromagnetic shape memory alloy with a high content of Mn. Compared with Ni₂MnGa, it has the Hg₂CuTi crystal structure. In this structure, Mn(A) and Mn(B) is antiferromagnetic coupling, which has an influence on the magnetic field induced strain of the material by decreasing the saturation magnetization.It is well known that it can improve the property of the alloy by doping another element in a material. In this work, we focus on the Re-doped Mn₂NiGa alloys. We prepared Mn_50-xRe_xNi₂₅Ga₂₅(x=1,2,3,4,5,6) and Mn₅₀Ni_25-xRe_xGa₂₅(x=1,2,3,4,5,6) alloys. Their structures, martensitic transformation behaviors, magnetic property and some basic physical properties were studied. We find that the crystal lattice of these compounds, obviously the Mn₅₀Ni_25-xRe_xGa₂₅(x=1,2,3,4,5,6) alloys, is bigger than that of Mn₂NiGa. At the same time, this dopant has an influence on martensitic transformation temperature of the material. On the other hand, the compound contained Re is more sensitive to the stress and inclines to transform into stress-induced-martensite. The magnetic property has also a great change.Furthermore, we also studied the influence of Re on the physical properties of Mn₂NiGa by theoretical calculations. By calculating Mn₂ReGa and MnReNiGa which stand for the alloy substituted Re for Ni or Mn, we can speculate that Re is inclined to occupy A or C site of the crystal in Mn_50-xRe_xNi₂₅Ga₂₅(x=1,2,3,4,5,6) and Mn₅₀Ni_25-xRe_xGa₂₅(x=1,2,3,4,5,6), as the free energy is the lowest in the atomic arrangement. By these calculated results, we successfully explained the phenomenon that the property of the alloy has changed after being doped by Re.At the same time, we also has an investigation on Mn₂NiGa_0.9X_0.1(X=Al, Sn, Ge), Mn₅₀Ni_25-xTb_x Ga₂₅(x=1,2), Mn_50-xTb_xNi₂₅Ga₂₅(x=1,2), Mn₅₀Ni_25-x Dy_x Ga₂₅(x=1,2), Mn_50-xDy_xNi₂₅Ga₂₅(x=1,2) in experiment and found that the martensite in these alloys has two different types except Mn₂NiGa_0.9Sn_0.1 and Mn₂NiGa_0.9Ge_0.1. The martensitic transformation temperature of Mn₂NiGa_0.9Sn_0.1 and Mn₂NiGa_0.9Ge_0.1 is higher than that of Mn₂NiGa, but Sn changes the sensitivity of the material to stress, so we can not see the strong diffraction peaks of the martensitic phase in XRD patterns for Mn₂NiGa_0.9Sn_0.1 at the room temperature.