Dynamical properties of magnetization reversal in exchange-coupled NiO/Co bilayers

Real time dynamic magnetization reversal measurements at room temperature have been performed on polycrystalline exchange-coupled NiO/Co bilayers over 10 decades of applied field sweep rates. Domain wall displacement and domain nucleation regimes govern the magnetization reversal at low and high sweep rates, respectively. The crossover between the two regimes depends on the relative thickness of the two layers. Thicker Co favors propagation, whereas thicker NiO favors nucleation. The coupling energy at the interface was found to be inversely proportional to the square root of the area corresponding to the activation (Barkhausen) volume. These results are consistent with a model of exchange anisotropy in which a randomness of the coupling along the ferromagnetic (F)/antiferromagnetic (AF) interface is combined with a thermally activated switching process of the AF magnetization.