Anomalous magnetotransport behavior in Fe-doped MnNiGe alloys

The electrical dc transport properties of hexagonal magnetic equiatomic alloys of nominal composition ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{NiGe}$ $(x=0.2\phantom{\rule{4pt}{0ex}}\text{and}\phantom{\rule{4pt}{0ex}}0.25)$ have been investigated experimentally as well as theoretically using first-principles electronic structure calculations. Thermal hysteresis in the magnetization data indicates that the alloys undergo a first-order martensitic transition. Both the alloys show unusual nonmetallic resistivity behavior and a noticeable amount of training effect in resistivity when thermally cycled through the first-order martensitic transition. We observe moderate negative magnetoresistance ($\ensuremath{\sim}\ensuremath{-}11.5$% for 150 kOe) at 5 K (well below the martensitic transition temperature) associated with clear virgin line effect for both the alloys. We have adapted different flavors of density functional theory approach to understand the experimentally observed nonmetallic transport behavior.