Scaling of intrinsic Gilbert damping with spin-orbital coupling strength

We have experimentally and theoretically investigated the dependence of the intrinsic Gilbert damping parameter ${\alpha }_0$ on the spin-orbital coupling strength $\xi$ by using L1${}_0$ ordered FePd${}_{1-\mathrm{x}}$Pt${}_{\mathrm{x}}$ ternary alloy films with perpendicular magnetic anisotropy. With the time-resolved magneto-optical Kerr effect, ${\alpha }_0$ is found to increase by more than a factor of ten when $x$ varies from 0 to 1.0. Since changes of other leading parameters are found to be neglected, the ${\alpha }_0$ has for the first time been proven to be proportional to ${\xi }^2$.