Time dependence of magnetization reversal when beginning with pre-existing nucleation sites

We use measurements of time and field dependent magnetization reversal in Co/Pd multilayers with perpendicular anisotropy to detect the presence of dilute enclaves of opposite magnetization within a magnetized ferromagnet. Such enclaves are stable due to dipolar fields generated by the surrounding material, and their presence at the onset of reversal can speed the process by orders of magnitude. The field required to suppress these nuclei and reach true magnetic saturation is found to be an order of magnitude higher than the observable macroscopic saturation field. Fatuzzo-Labrune model is extended to describe magnetization reversal starting with ready nucleation domains.