Evidence of interfacial asymmetric spin scattering at ferromagnet-Pt interfaces

We measure the spin-charge interconversion by the spin Hall effect in various ferromagnetic/Pt nanodevices. The extracted effective spin Hall angles of Pt evolve drastically with the ferromagnetic (FM) materials (CoFe, Co, and NiFe), when assuming transparent interfaces and a bulk origin of the spin injection/detection by the FM elements. By carefully estimating the interface resistance, we show that it is quite large and cannot be neglected. We then evidence that the spin injection/detection at the FM/Pt interfaces are dominated by the spin polarization of the interfaces. We show that interfacial asymmetric spin scattering becomes the driving mechanism of the spin injection in our samples.