  We present room temperature ferromagnetic resonance (FMR) studies of
polycrystalline ||Pt/10 nm Cu/t Co/10 nm Cu/Pt|| films as a function of Co
layer thickness (1 < t < 10 nm) grown by evaporation and magnetron sputtering.
FMR was studied with a high frequency broadband coplanar waveguide (up to 25
GHz) using a flip-chip method. The resonance field and the linewidth were
measured as a function of the ferromagnetic layer thickness. The evaporated
films exhibit a lower magnetization density (Ms = 1131 emu/cm^3) compared to
the sputtered films (Ms= 1333 emu/cm^3), with practically equal perpendicular
surface anisotropy (Ks ~ -0.5 erg/cm^2). For both series of films, a strong
increase of the linewidth was observed for Co layer thickness below 3 nm. For
films with a ferromagnetic layer thinner than 4 nm, the damping of the
sputtered films is larger than that of the evaporated films. The thickness
dependence of the linewidth can be understood in term of the spin pumping
effect, from which the interface spin mixing conductance
g^{\uparrow\downarrow}S^{-1} is deduced.
