Magnetic viscosity measurements reveal reversal asymmetry in exchange-biased bilayers

We have used time-dependent magnetization measurements to probe the asymmetry in the magnetizationreversal mechanisms in exchange-biased MnF2 /Fe bilayers. Analysis of the magnetic viscosity on the magnetizing and demagnetizing sides of the exchange-shifted hysteresis loops reveals a striking asymmetry. This is due to different mechanisms for reversal on the two sides of the loop as elucidated previously by polarizedneutron reflectometry and anisotropic-magnetoresistance measurements. The viscosity data reveal asymmetric features that are intrinsically related to the nature of the exchange anisotropy.