Observation of unequal activation volumes of wall-motion and nucleation processes in Co/Pd multilayers.

We report the difference in activation volumes of wall-motion and nucleation processes in Co/Pd multilayers. Each activation volume was estimated from field dependence of wall-motion speed and nucleation rate, obtained by real-time domain imaging using a magneto-optical Kerr effect microscope. Delicate analysis shows that the two activation volumes are generally unequal and the ratio between the volumes varies noticeably from 0.9 to 1.1 with change of the multilayered structure. We found that the inequality in the two activation volumes has a crucial influence on magnetization reversal behavior: a process having a smaller activation volume dominates.