Compositional Dependence of g-Factor and Damping Constant of GdFeCo Amorphous Alloy Films

Time-domain magnetization dynamics of sputtered GdFeCo (30 nm) amorphous alloy films was measured by pump-probe method using high-power ultra-short pulse fiber laser. The effective g-factor g _eff and effective damping constant alpha_eff of the GdFeCo films were estimated by using a numerical calculation of Landau-Lifshitz-Gilbert equation. The precessional frequency took a maximum near the magnetization compensation composition C _M of the GdFeCo, while the estimated g _eff and alpha_eff increased around the angular momentum compensation composition C _A. The compositional dependences of g _eff and alpha_eff were roughly described by a mean-field model. The g _eff and alpha_eff were also estimated from the ferromagnetic resonance (FMR) spectra, and the data from the FMR spectra agreed well with those from the pump-probe measurement except for the composition near C _M. The FMR method was unable to excite the magnetization near C _M because of the small net magnetization.