Role of antisite disorder on intrinsic Gilbert damping in L 1 0 FePt films

The impact of antisite disorder $x$ on the intrinsic Gilbert damping ${\ensuremath{\alpha}}_{0}$ in well-ordered $L{1}_{0\phantom{\rule{0.16em}{0ex}}}$ FePt films is investigated by time-resolved magneto-optical Kerr effect. The variation of $x$ mainly affects the electron scattering rate $1/{\ensuremath{\tau}}_{\mathrm{e}}$, while other leading parameters remain unchanged. The experimentally observed linear dependence of ${\ensuremath{\alpha}}_{0}$ on $1/{\ensuremath{\tau}}_{\mathrm{e}}$ indicates that spin relaxation is through electron interband transitions, as predicted by the spin-orbit coupling torque correlation model. Measurements at low temperature show that ${\ensuremath{\alpha}}_{0}$ remains unchanged with temperature even for FePt with very high chemical order, indicating that electron-phonon scattering is negligible. Moreover, as $x$ decreases, the perpendicular magnetic anisotropy increases, and the Landau $g$ factor exhibits a negative shift due to an increase in orbital momentum anisotropy. Our results will facilitate the design and exploration of magnetic alloys with large magnetic anisotropy and desirable damping properties.