We present results for ferromagnetic resonance measurements in ultrathin magnetic films. Our aim is to investigate quantitatively the damping of spin motions where different sources of damping are present. We investigate a polycrystalline 10-nm-thick Co film grown on GaAs using microwave frequencies between 4 and 24 GHz and different orientations of the static magnetic field. We discuss the role of Gilbert and two-magnon dampings (activated by defects in the film) within the theoretical framework presented some years ago by Arias and Mills [Phys. Rev. B 60, 7395 (1999)] and its extension to the case in which the magnetization is tipped out of the film plane [P. Landeros, R. E. Arias, and D. L. Mills, Phys. Rev. B 77, 214405 (2008)]. It is found that linewidth vs. field angle data are well reproduced by the theory for several frequencies and we obtain information about fundamental parameters as well as the role of defects in the dynamical response of the prototype Co system.

• Received 19 May 2009

DOI:https://doi.org/10.1103/PhysRevB.80.224421