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$_{\rm eff}$ and effective damping constant $\alpha_{\rm eff}$ 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 $C_{\rm M}$ of the GdFeCo, while the estimated g$_{\rm eff}$ and $\alpha_{\rm eff}$ increased around the angular momentum compensation composition $C_{\rm A}$. The compositional dependences of g $_{\rm eff}$ and $\alpha_{\rm eff}$ were roughly described by a mean-field model. The g$_{\rm eff}$ and $\alpha_{\rm eff}$ 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 $C_{\rm M}$. The FMR method was unable to excite the magnetization near $C_{\rm M}$ because of the small net magnetization.