Disentanglement of Spin Orbit Torques Originated from Spin Hall Effect and Rashba-Edelstein Effect Using Harmonic Hall Measurements

We report on the quantitative separation of the spin orbit torques (SOTs) originated from the spin Hall effect (SHE) and the Rashba-Edelstein effect (REE), by performing the Harmonic Hall measurements for epitaxial platinum/cobalt (Pt/Co) bilayers. The damping-like (DL-) and field-like (FL-)SOT efficiencies (ξDL and ξFL ) are quantified respectively by fitting the SOT data with corresponding spin-diffusion equation. As a result, the ξDL originated from the Pt bulk region (ξDL0) decreases significantly with decreasing temperature, while the ξFL from the substrate (sub.)/Pt (ξFL1) and Pt/Co (ξFL2) interface barely change, suggesting that the origin of FL-SOT is the REE instead of the SHE; the sign of ξFL1 is opposite to ξFL2, which is consistent with the REE where the direction of the spin accumulation depends on the interfacial electric field induced by broken inversion symmetry. Moreover, the ξDL induced by sub./Pt (ξDL1) and Pt/Co (ξDL2) interfaces are found to be about 1 order of magnitude smaller than maximum ξDL0 , while their sign are consistent with respective ξFL (ξFL1 and ξFL2 ). Our work presents a thorough disentanglement of the SOTs in heavy metal/ferromagnet bilayers in which both SHE and REE are present, and provides deterministic answers to the fundamental question on their physical origin.