Large negative magnetoresistance in a ferromagnetic shape memory alloy : Ni_{2+x}Mn_{1-x}Ga

TL;DR

This study reports a 5% negative magnetoresistance at room temperature in Ni_{2+x}Mn_{1-x}Ga, highlighting its potential for magnetic sensor applications and analyzing how MR varies across different phases and compositions.

Contribution

It provides the first detailed analysis of magnetoresistance behavior across phases in Ni_{2+x}Mn_{1-x}Ga and links MR changes to twin and domain structures.

Findings

MR increases with x in all phases

MR exhibits a cusp in the martensitic phase

MR in austenitic phase aligns with s-d scattering theory

Abstract

5% negative magnetoresistance (MR) at room temperature has been observed in bulk Ni_{2+x}Mn_{1-x}Ga. This indicates the possibility of using Ni_{2+x}Mn_{1-x}Ga as magnetic sensors. We have measured MR in the ferromagnetic state for different compositions (x=0-0.2) in the austenitic, pre-martensitic and martensitic phases. MR is found to increase with x. While MR for x=0 varies almost linearly in the austenitic and pre-martensitic phases, in the martensitic phase it shows a cusp-like 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.