  Recent advances in antiferromagnetic spin dynamics using rare-earth (RE) and
transition-metal (TM) ferrimagnets have attracted much interest for spintronic
devices with a high speed and density. In this study, the spin wave properties
in the magnetostatic backward volume mode and surface mode in RE-TM
ferrimagnetic $Gd_{x}Co_{1-x}$ films with various composition x are
investigated using spin wave spectroscopy. The obtained group velocity and
attenuation length are well explained by the ferromagnet-based spin wave theory
when the composition of $Gd_{x}Co_{1-x}$ is far from the compensation point.
