Giant spin-to-charge conversion in germanium tin epilayers

We report a study of the spin-to-charge current conversion in compressively strained Ge1-xSnx alloy epilayers as a function of the Sn concentration by means of the inverse spin Hall effect (ISHE). The spin current is generated by spin-pumping effect (SPE) from a thin NiFe layer driven into ferromagnetic resonance (FMR). By simultaneously measuring the magnetic damping of the NiFe layer and the ISHE-induced charge current we extract two key spintronics parameters: the spin Hall angle and the effective spin mixing conductance. Our results reveal a giant spin-to-charge conversion and a non-monotonic dependence of the charge current signal on the Sn concentration, consistent with the variation in the magnetic damping observed in FMR. The values of spin Hall angle are comparable to those reported for heavy metals such as Pt and Ta. Furthermore, we show that the spin conductivity at the Au/GeSn interface can be enhanced by tuning the Sn concentration.