  The effective spin-mixing conductance (G_eff) of a heavy metal/ferromagnet
(HM/FM) interface characterizes the efficiency of the interfacial spin
transport.Accurately determining G_eff is critical to the quantitative
understanding of measurements of direct and inverse spin Hall effects. G_eff is
typically ascertained from the inverse dependence of magnetic damping on the FM
thickness under the assumption that spin pumping is the dominant mechanism
affecting this dependence.Here we report that, this assumption fails badly in
many in-plane magnetized prototypical HM/FM systems in the nm-scale thickness
regime. Instead, the majority of the damping is from two-magnon scattering at
the FM interface, while spin-memory-loss scattering at the interface can also
be significant.If these two effects are neglected, the results will be an
unphysical "giant" apparent G_eff and hence considerable underestimation of
both the spin Hall ratio and the spin Hall conductivity in inverse/direct spin
Hall experiments.
