Effects of atomic structures at Co2Fe(Al0.5,Si0.5)/Ge interfaces on spin-electronic properties

Efficient spin injection is essential for the development of ferromagnet—semiconductor spintronic devices with high performances, including spin transistors. Although the Co2Fe(Al0.5,Si0.5) (CFAS)/Ge hybrid structure has been identified as an outstanding platform for such devices, there is a lack of systematic analyses on the effects of the interface atomic structure on the spin-electronic properties. In this study, we investigate electronic and magnetic properties of CFAS/Ge (001) interfaces by density functional theory calculations under two possible scenarios, with atomically abrupt bulk-like interfaces and with intermixing at the interfaces. For two possible terminations in the case of abrupt interfaces, we show considerable reductions in spin polarization (SP), which is emphasized in the case of the —Fe—Si,Al/Ge interface, where the SP has reversed sign. Further, we show that Fe—Ge interdiffusion is most likely to occur at the interface, and that this intermixing does not largely affect the spin-electronic properties. In contrast, the model of interdiffusion affecting the Co sublattice in the CFAS film exhibits a reversed SP at the interface layers, but this is less likely to occur owing to the higher energy for such atomic swaps. Band alignment analyses show that interfaces with a small degree of Fe/Ge intermixing could be beneficial for the spin injection efficiency. This study demonstrates that the spin injection efficiency is strongly dependent on the ferromagnet—semiconductor interface atomic structure, and thus can guide further theoretical and experimental studies for development of spintronic devices with improved properties.