Magnetic field dependence of magnetization reversal in ColPt multilayers was qmmtitatively investigated. Serial
samples of ColPt multilayers were prepared by dc-magnetron sputtering under various Ar pressures. Magnetization
reversal was monitored by magnetization viscosity measurement and direct domain observation using a
magneto-optical microscope system, and the wall-motion speed V and the nucIeation rate R were determined
using a domain reversal model based on time-resolved domain reversal pattems. Both V and R were found to be
exponentially dependent on the applied reversing field. From the exponential dependencies, the activation volumes
for wall motion and nucIeation could be determined, based on a thermally activated relaxation model, and
the wall-motion activation volume was found to be slightIy larger than the nucIeation activation volume.