Two years after the prediction of a giant spin Hall effect for the dilute Cu(Bi) alloy [Gradhand et al., Phys. Rev. B 81, 245109 (2010)], a comparably strong effect was measured in thin films of Cu(Bi) alloys by Niimi et al. [Phys. Rev. Lett. 109, 156602 (2012)]. Both theory and experiment consider the skew-scattering mechanism to be responsible, however they obtain opposite sign for the spin Hall angle. Based on a detailed analysis of existing theoretical results, we explore differences between theory and experiment.

We present ab initio calculations of the skew-scattering contribution to the spin Hall effect for freestanding fcc Au(111) films. Their thickness is varied between 1 and 32 monolayers, and Pt atoms are considered as substitutional impurities and adatoms. The obtained spin Hall angle drastically changes with varying impurity positions in the film. Impurities in the adatom position play a special role reversing sign of the spin Hall angle. In addition, we show that Pt adatoms on one-monolayer noble metal films cause a gigantic spin Hall angle up to 18%, which is attributed to the lack of interband transitions.