The effect of doped elements on the martensitic transformation in Ni–Mn–Ga magneticshape memory alloy

Abstract

Ni–Mn–Ga alloy is a new actuator material due to the fact that its shape memoryeffect can be controlled by magnetic field in addition to the conventional controlsby temperature and stress. However, the alloy shows relatively low martensitictransformation and Curie temperatures. In this paper, we report the results ofadding small amounts of Fe, Co and Tb to NiMnGa alloys. The effect of smalladditions of these doped elements on the martensitic transformation temperatureis remarkable, but the Heusler structure of the alloys remains unchanged. ForNi50Mn27Ga23−xFex (x = 0,1,2) with partial replacement of Ga by Fe, the martensitic transformationtemperatures increase with increase of the Fe content, and so does the Curietemperature. This phenomenon of increasing both the martensitic transformationtemperatures and the Curie temperature was found for the first time. ForNi47Mn31X1Ga21 (X = Fe,Co), Fe and Co substitution for Mn, Fe increases the martensitic transformationtemperature but decreases the Curie temperature, while Co has the opposite effect. ForNi48Mn33Ga18Tb1, the addition of the rare earth element Tb decreases the martensitic transformationtemperature and the Curie temperature remarkably. Therefore, the transformationtemperatures of the alloys can be improved by these doping methods.