Magnetization Reversal in Exchange Biased IrMn/Fe Ring Arrays

We investigated the effect of exchange bias on the magnetization reversal behavior in ring-shaped IrMn/ Fe lithographic structures. The magnetic anisotropy geometry of the exchange biased ring is revealed by fitting for the angular dependence of the exchange bias, H eb, and coercivity, H c. Magnetic force microscopy images obtained at different field values along the hysteresis loop show that along the bias direction, the ring exhibits a magnetic reversal via nonuniform domain nucleation while perpendicular to the bias direction, the magnetic reversal occurs via coherent rotation. The difference in magnetic switching modes for these two field orientations is confirmed by micromagnetic simulations and interpreted by the effective field model.