Spin transport in Ge nanowires for diluted magnetic semiconductor-based nonvolatile transpinor

Spintronic devices, in particular spin field-effect transistors (spinFETs), have been researched for decades as a promising candidate to replace Si transistors with potentially low power dissipation and low variability. In this paper, we propose a nonvolatile spin-base transistor (transpinor) based on diluted magnetic semiconductor (DMS) with electric field-controlled paramagnetism-to-ferromagnetism phase transition. To realize the transpinor, we demonstrate the electrical spin injection into Ge nanowires using both ferromagnetic Mn₅Ge₃ Schottky contacts and Fe/MgO tunnel junctions. We observe much longer spin lifetimes and diffusion lengths in Ge nanowires compared with bulk Ge. Furthermore, we successfully grow the single-crystalline Mn_xGe_1-x DMS nanowires using pattern-assisted molecular beam epitaxy (MBE). The Mn_xGe_1-x nanowires exhibit a Curie temperature above 400 K, and the ferromagnetism can be further modulated by an external gate voltage. The demonstrated electric field-controlled ferromagnetism, along with the successful spin injection into Ge nanowires, paves the road to build the proposed transpinor.