Large positive magnetoresistance in nonstoichiometric NiMnSb thin films on silicon

摘要

We report a systematic study of the transport properties of pulsed-laser-deposited NiMnSb films on silicon as a function of film thickness. A low-temperature upturn is observed in the resistivity for film thicknesses of 130 nm and below. The resistivity minimum corresponds to the maximum in the positive magnetoresistance for all samples. As the film thickness decreases, the magnitude of both the resistivity upturn and the magnetoresistance increase. There is no feature associated with the upturn in the low-field Hall resistivity, which becomes systematically more electron dominated as the film thickness decreases and the temperature increases. This has implications for the use of NiMnSb as a spin injector for spintronic applications. The positive magnetoresistance of the 5 nm sample is greater than 100% at 200 K in 8 T. Further enhancement of the magnetoresistance occurs for field parallel, rather than perpendicular, to the film surface. The magnetoresistance behavior is compared to various model systems, including the band-gap tuning found in the silver chalcogenides, disorder-induced weak localization, and the emerging class of "bad metal" ferromagnets.