Large negative magnetoresistance in a ferromagnetic shape memory alloy: Ni2+xMn1-xGa.

5% negative magnetoresistance (MR) at room temperature has been observed in bulk Ni2+xMn1-xGa. This indicates the possibility of using Ni2+xMn1-xGa as magnetic sensors. We have measured MR in the ferromagnetic state for different compositions (x=0–0.2) in the austenitic, premartensitic, and martensitic phases. MR is found to increase with x. While MR for x=0 varies almost linearly in the austenitic and premartensitic phases, in the martensitic phase it shows a cusplike shape. This has been explained by the changes in twin and domain structures in the martensitic phase. In the austenitic phase, which does not have twin structure, MR agrees with theory based on s-d scattering model. [ABSTRACT FROM AUTHOR]