Temperature and bias dependence of Hanle effect in CoFe/MgO/composite Ge

We have investigated the temperature and bias dependence of the Hanle effect in a composite n-type Ge system consisting of a heavily doped surface layer and a moderately doped Ge substrate, using three-terminal Hanle measurements. A large spin signal of ∼5.1 $kΩμm2$ and a spin lifetime of ∼105 ps are obtained at 300 K. The spin signal, spin lifetime, and their asymmetries with respect to the bias polarity have been measured over a temperature range from 5 K to 300 K. Intriguingly, an inverted Hanle effect, indicating the sign inversion of spin polarization in Ge, is observed at low temperature.