where V is the sample volume, and the strength of spin-coil coupling is given by G = µ 0 2 ηQ, where η, γ h , Q, and µ 0 are respectively the filling factor, the gyromagnetic ratio, the quality factor and the vacuum permeability. The corresponding radiation damping rate is γ rd = µ 0 2 γ h ηQm 0 , where m 0 is the magnitude of the average magnetization density: