Effect of post annealing on spin accumulation and transport signals in Co₂FeSi/MgO/ n ⁺-Si on insulator devices

The post annealing temperature dependence of spin accumulation and transport signals in Co₂FeSi/MgO/n⁺-Si on insulator were investigated. The spin signals were detected using 3- and 4-terminal Hanle, 2-terminal local and 4-terminal nonlocal magnetoresistance measurements. The post annealing temperature (T_A) dependence of the magnitude in 3-terminal narrow Hanle signals is nearly constant up to T_A < 400°C, however a slight decrease above T_A ≥ 400°C is observed. This behavior is consistent with the T_A dependence of the magnitude of 4-terminal nonlocal magnetoresistance (MR) signals. The spin polarization estimated from the 3-terminal narrow Hanle signals and the magnitude of 2-terminal local MR signals show a slight improvement with increasing post annealing temperature with a peak at around 325°C and then start reducing slowly. The slight increase in the spin signal would be due to high spin polarization of Co₂FeSi as a result of structural ordering. The 2-terminal local MR signals do not vary significantly by annealing between as-deposited and T_A = 400°C, indicating the robustness of our device. This result would be useful for future Si spintronics devices.