Theory and experiment of microwave-assisted magnetization switching in perpendicular magnetic nanodots

In this paper, we review the theory and experiment on microwave-assisted magnetization switching in perpendicular magnetic nanodots. Within the framework of the single-macrospin model, the switching condition under radio frequency fields can be analytically derived from the steady-state solutions of the Landau-Lifshitz-Gilbert equation. When the Gilbert damping is not so large, this analysis perfectly coincides with the Stoner-Wohlfarth model under the rotating frame. This calculation also predicts the critical frequency above which no microwave assistance effect is operative. While the above analysis almost explains the experimental results on nanodots of a Co/Pt multilayer, the nanodots exhibits unusual size-dependent switching behaviors. For the dot as small as 50 nm, the switching behaviors agree with the analytical calculations based on the single-macrospin model. In contrast, for the dot diameter > 100 nm, the significantly enhanced assistance effect is observed. This enhancement for larger dot can be explained by excitation of spatially nonuniform precessional motion in the dots.