Room temperature observation of high spin polarization in post annealed Co₂FeSi/MgO/n+-Si on insulator devices

The post annealing temperature dependence of room temperature spin signals in Co₂FeSi/MgO/n+-Si on insulator fabricated on Si(2×1) surface was investigated. For the devices fabricated on the Si(2×1) surface, the large and reliable three- and four-terminals spin signals were obtained even at room temperature. The magnitude of three-terminal narrow Hanle signals has a peak around 325 °C with respect to post annealing temperature. The trend of increasing spin accumulation signal with decreasing bias voltage was observed for both as deposited and sample annealed at 325 °C in the bias voltage range 600-800mV. The enhancement of three- and four-terminals non-local magnetoresistance (MR) for post annealed sample at 325 °C, indicates that the spin polarization increases due to the structural ordering of Heusler alloy Co₂FeSi. As a result, we observed large spin injection efficiency into Si (P > 41.7%) even at room temperature. These results will pave a way to the future Si spintronics devices such a spin-MOSFET.