Microwave-assisted magnetization switching (MAS) processes for granular films were demonstrated by time integration of the Landau-Lifshitz-Gilbert equation. At low microwave frequencies, hysteresis loops become narrower, and at higher frequencies, an extra step occurs in the curves. In the case when the extra step occurs, saturation field increases to be comparable to that for non-MAS case, although switching field decreases. The occurrence of the extra step possibly originates from 'unstable switching process' predicted by Bertotti et al., and the magnetization contour maps indicated large un-switched agglomerates remains when MAS proceeds through the unstable switching process. The unstable switching processes are also observed even when dc incident angles are large.
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