Control of perpendicular magnetic anisotropy and intrinsic Gilbert damping in $L1_{0} $ordered FePt(Pd) thin films

The dependence of perpendicular magnetic anisotropy (PMA) and intrinsic Gilbert damping $\alpha_{0} $ on some leading parameters, such as spin-orbital coupling strength $\xi $, are investigated in $L1_{0} $ ordered FePt(Pd) thin films by time-resolved magneto-optical Kerr effect measurements and spin dependent ab initio calculations. Continuous tuning of PMA and $\alpha_{0} $ over a wide range of magnitude is realized by modulating the chemical substitution and ordering. Spin orbital coupling strength can be effectively adjusted by replacing Pt with Pd atoms, which keeps other leading parameters with negligible changes. Measured PMA and $\alpha_{0} $ from experiment are proportional to $\xi^{1.6}$ and $\xi ^{2}$ at 200K, while first principle calculations predict for both a quadratic dependence on $\xi $. The degree of chemical order in real samples can also significantly affect PMA and $\alpha_{0} $through leading parameters other than spin orbital coupling strength.