Magnetization Asymmetry in Exchange Bias Systems

We report on an experimental study on an observed asymmetry in the magnetization of a sputtered polycrystalline Co–Fe/Ir–Mn exchange bias system. Such asymmetries have been predicted by numerical modeling but have never been measured in detail. In particular, we observe the magnetization asymmetry to increase with decreasing temperature down to 5.5 K. Given that the bulk of the antiferromagnetic grains is known to be stable below 300 K, this indicates that the asymmetry derives from interface spin effects at the ferromagnetic/antiferromagnetic interface. As the temperature is reduced, a peak in magnetization asymmetry is observed below 10 K. We also observed that when measured at low temperature there is an increase in the hysteresis loop coercivity and the well-known training effect on the loop shift in exchange bias systems. These effects both derive from the ferromagnetic/antiferromagnetic interface.