Reversal asymmetry and anomalous magnetic viscosity in exchange-bias systems

Employing vector magnetometry, interaction plots and model simulations, we probe the magnetization reversal in Co/Cu/IrMn exchange-biased trilayers. In the films with thin or no Cu spacer, the magnetization reversal is governed by domain-wall motion along one branch of the easy-axis hysteresis loop and by coherent rotation along the other. For thicker Cu spacers, both magnetization paths are dominated by coherent rotation. The latter also appears to be responsible for the reversal when the magnetic field is applied away from the exchange-bias direction for all films. We reveal a delayed domain-wall reversal along the descending-field path as compared to that predicted for coherent rotation. By exploiting in-field interaction plots, we evidenced a correlation between the asymmetric reversal and the exchange-bias coupling. Anomalous viscosity along recoil curves is detected and attributed to strong ferromagnetic coupling into the ferromagnet. The anomaly tends to fade away with the increase in the bias.