Thickness dependence of Hall transport in Ni1.15Mn0.85Sb thin films on silicon

Highly spin polarized Heusler alloys, NiMnSb and Co2MnSi, attract a great deal of interest as potential spin injectors for spintronic applications. Spintronic devices require control of interfacial properties at the ferromagnet:semiconductor contact. To address this issue we report a systematic study of the ordinary and anomalous Hall effect, in Ni1.15Mn0.85Sb films on silicon, as a function of film thickness. In contrast to the bulk stoichiometric material, the Hall carriers in these films become increasingly electron-like as the film thickness decreases, and as the temperature increases from 50 K toward room temperature. High field Hall measurements confirm that this is representative of the majority transport carriers. This suggests that current injected from a NiMnSb:semiconductor interface may not necessarily carry the bulk spin polarization. The films also show a low temperature upturn in the resistivity, which is linked to a discontinuity in the anomalous Hall coefficient. Overall these trends indicate that the application of Heusler alloys as spin injectors will require strictly controlled interfacial engineering, which is likely to be demanding in these ternary alloys.