Extrinsic Spin Hall Effects in Cu induced by Ir impurity

The spin Hall effect (SHE) is one of the important phenomena in spintronics since it enables to create spin currents in non-magnetic materials without using a ferromagnet. Recently-reported large SHEs in Pt and Au have triggered the search for a larger SHE in metallic devices. The mechanism of the large SHEs, however, have not been figured out yet ; whether it is intrinsic or extrinsic, if it is extrinsic whether it stems from the skew scattering mechanism or the side jump one. In this work, we focus on the extrinsic SHE. By adding Ir impurity into pure Cu, we have studied the impurity concentration dependence of the SHE in CuIr. We have used the lateral spin valve structure which consists of two Py wires and a CuIr middle wire.This device allows to estimate precisely how much spin currents are injected into CuIr. By flowing electric current from Py to one of the Cu electrodes, pure spin currents are injected into the CuIr middle wire and we are able to measure the inverse SHE. No SHE has been observed when there is no Ir impurity. With increasing the Ir impurity, however, the SH resistivity increases linearly with the resistivity of CuIr. This linear dependence strongly indicates that the SHE in CuIr is due to the skew scattering mechanism. From the slope of the SHE resistivity vs CuIr resistivity curve, it turns out that the SH angle in this system is 1.5%, which is consistent with the previous anomalous Hall effect measurement in CuMnIr.