Dependence of inverse-spin Hall effect and spin-rectified voltage on tantalum thickness in Ta/CoFeB bilayer structure

Abstract

Ta-layer thickness (tTa) dependence of the measured DC voltage V from the inverse-spin Hall effect (ISHE) in Ta/CoFeB bilayer structure is experimentally investigated using the ferromagnetic resonance in the TE011 resonant cavity. The ISHE signals excluding the spin-rectified effect (SRE) were separated from the fitted curve of V against tTa. For tTa ≈ λTa (Ta-spin diffusion length = 2.7 nm), the deviation in ISHE voltage VISH between the experimental and theoretical values is significantly increased because of the large SRE contribution, which also results in a large deviation in the spin Hall angle θSH (from 10% to 40%). However, when tTa ≫ λTa, the VISH values are consistent with theoretical values because the SRE terms become negligible, which subsequently improves the accuracy of the obtained θSH within 4% deviation. The results will provide an outline for an accurate estimation of the θSH for materials with small λ value, which would be useful for utilizing the spin Hall effect in a 3-terminal spintronic devices in which magnetization can be controlled by in-plane current.