Compositional dependence of g-factor and damping constant of (Gd_100-xRE_x)FeCo alloy films (RE = Yb, Tm, Er)

Time domain magnetization dynamics of (Gd_100-xRE_x)FeCo (RE = Yb, Tm, Er) alloy films with various compositions were measured by pump-probe method using a high energy ultra short pulse fiber laser, and their g-factors and damping constants were estimated. The g-factor of GdFeCo became large near the angular moment compensation point C_A, which is qualitatively consistent with the simple mean field model. On the other hand, the damping constants took a maximum near magnetization compensation point, which is not described by the mean field model. Substitution of Tm or Er for Gd results in the significant increase of damping constant; (Gd₉₀Tm₁₀)FeCo and (Gd₉₀Er₁₀)FeCo exhibit roughly 3-6 times large damping constant compared to GdFeCo, while (Gd₉₀Yb₁₀)FeCo has almost the same damping constant as GdFeCo. This means that the damping constant is significantly modified by the orbital moment of RE atoms.