Anomalous Hall effect in 3 d / 5 d multilayers mediated by interface scattering and nonlocal spin conductivity

We have evidenced unconventional anomalous Hall effects (AHEs) in $3d/5d$ (${\mathrm{Co}0.2\mathrm{nm}/\mathrm{Ni}0.6\mathrm{nm})}_{N}$ multilayers grown on a thin Pt layer or thin Au:W alloys with perpendicular magnetic anisotropy (PMA) properties. The inversion of AHEs observed with one Pt series is explained by considering the opposite sign of the effective spin-orbit coupling of Pt compared to Co/Ni combined with peculiar specular electronic reflections. Using advanced simulations methods for the description of the spin-current profiles based on the spin-dependent Boltzmann formalism, we extracted the spin-Hall angle (SHA) of Pt and Co/Ni of opposite sign. The extracted SHA for Pt, $+20%$, is opposite to the one of Co/Ni, giving rise to an effective AHE inversion for thin Co/Ni multilayers (with the number of repetition layers $Nl17$). The spin-Hall angle in Pt is found to be larger than the one previously measured by complementary spin-pumping inverse spin-Hall effect experiments in a geometry of current perpendicular to the plane. Whereas magnetic proximity effects cannot explain the effect, spin-current leakage and spin-orbit assisted electron scattering at Pt/(Co,Ni) interfaces fit the experiments. We also extract the main relevant electronic transport parameters governing the overall effects in current-in-plane (CIP) currents and demonstrate, in particular, that the specularity/nonspecularity in the electronic diffusion processes play an essential role to explain the observed results.