  We report on magnetic domain wall velocity measurements in ultrathin
Pt/Co(0.5-0.8 nm)/Pt films with perpendicular anisotropy over a large range of
applied magnetic fields. The complete velocity-field characteristics are
obtained, enabling an examination of the transition between thermally activated
creep and viscous flow: motion regimes predicted from general theories for
driven elastic interfaces in weakly disordered media. The dissipation limited
flow regime is found to be consistent with precessional domain wall motion,
analysis of which yields values for the damping parameter, $\alpha$.
