Sign determination of spin polarization in L2 ₁-ordered Co ₂FeSi using a Pt-based spin Hall device

So far, we have demonstrated markedly high spin polarizations (∼0.8) in one of the L2 ₁-ordered Heusler compounds, Co ₂FeSi (CFS), by detecting pure spin currents using nonlocal spin-valve measurements. Here, we experimentally determine the sign of the spin polarization in the L2 ₁-ordered CFS using the electrical spin Hall effect (SHE) measurements in a lateral device with Pt. Inverse SHE signals with a positive-sign hysteresis loop are clearly detected at 20 K. Since the spin Hall conductivity of Pt is the positive sign, the pure spin current generated by the CFS electrode with L2 ₁-ordered structures has positive spin polarization. The SHE measurement is a powerful tool to determine the sign of the spin polarization in unknown spin injectors.