Estimating spin diffusion length and spin Hall angle from spin pumping-induced inverse spin Hall voltages

摘要

There exists considerable confusion in estimating the spin diffusion lengthof materials with high spin-orbit coupling from spin pumping experiments. Fordesigning functional devices, it is important to determine the spin diffusionlength with sufficient accuracy from experimental results. An inaccurateestimation of spin diffusion length also affects the estimation of otherparameters (e.g., spin mixing conductance, spin Hall angle) concomitantly. Thespin diffusion length for platinum (Pt) has been reported in literature in awide range of 0.5 - 14 nm, and particularly it is a constant value independentof Pt's thickness. Here, the key reasonings behind such wide range of reportedvalues of spin diffusion length have been identified comprehensively.Particularly, it is shown here that a thickness-dependent conductivity and spindiffusion length is necessary to simultaneously match the experimental resultsof effective spin mixing conductance and inverse spin Hall voltage due to spinpumping. Such thickness-dependent spin diffusion length is tantamount toElliott-Yafet spin relaxation mechanism, which bodes well for transitionalmetals. This conclusion is not altered even when there is significantinterfacial spin memory loss. Furthermore, the variations in the estimatedparameters are also studied, which is important for technological applications.