Electrical Spin Injection and Detection in Mn$_{5}$Ge$_{3}$/Ge/Mn$_{5}$Ge$_{3}$ Nanowire Transistors

We report the electrical spin injection and detection in Ge nanowire transistors with single-crystalline Mn$_{5}$Ge$_{3}$ as the ferromagnetic source/drain contacts. The magnetoresistance (MR) of the Mn$_{5}$Ge$_{3}$/Ge/Mn$_{5}$Ge$_{3}$ nanowire transistor was found to be largely affected by the applied bias. Specifically, negative and hysteretic MR curves were observed under a large current bias from 2 K up to 50 K, clearly indicating successful spin injection into the Ge nanowire. In addition, the MR amplitude was found to exponentially decay with the Ge channel length. The fitting of MR further revealed a spin diffusion length of about 480 nm and a spin lifetime exceeding 244 ps at 10 K in $p$-type Ge nanowires, which are much larger than those reported for bulk $p$-type Ge. Our study of the spin transport in the Ge nanowire transistor points to a possible realization of spin-based transistors, and it may also open up new opportunities to create novel nanowire-based spintronic devices.