Scaling of spin relaxation and angular momentum dissipation in permalloy nanowires

We study the relationship between the damping (alpha) and the nonadiabaticity of the spin transport (beta) in permalloy nanowires. alpha is engineered by Ho doping, and from the characteristics of the current-induced domain-wall velocity, determined by high-resolution x-ray magnetic circular-dichroism photoemission electron microscopy, beta due to spin relaxation is measured. We find that beta scales with alpha and conclude that the spin relaxation that leads to nonadiabatic spin torque originates from the same underlying mechanism as the angular momentum dissipation that causes viscous damping.