Variation of magnetoresistance in Ni_2+xMn_1−xGa with composition

Abstract

The magnetoresistance (MR) of Ni_2+xMn_1−xGa (−1≤x≤0.35) ferromagnetic shape memory alloy shows a large increase in magnitude at room temperature (RT) with increasing x. For Mn₂NiGa (x=−1), MR at 8 T is −0.2%, while for Ni_2.35Mn_0.65Ga (x=0.35), it is −7.3%. Thus, MR of Ni_2+xMn_1−xGa can be varied over one order of magnitude by changing composition (x). Considering that the Curie temperature (T_C) varies with x, the MR behavior in the austenitic phase is explained on the basis of the s-d scattering model. By fitting the MR at 8 T in the austenitic phase for different x and T, a (T/T_C)⁶ power law dependence is obtained. In contrast to the monotonic MR variation with x, the magnetization at RT is highest for Ni₂MnGa (x=0) and decreases for both Ni and Mn excess compositions.