Exchange bias model including setting process: Investigation of antiferromagnetic alignment fraction due to thermal activation

摘要

An exchange bias (EB) model taking the setting process into account is developed to study the effect of the crucial parameters, such as the AFM anisotropy constant (K-AF), the setting temperature (T-set), and the physical microstructure on the exchange bias field of an AFM/FM system. The magnetization dynamics of the EB system is treated using the kinetic Monte Carlo approach and by integrating the Landau- Lifshitz-Gilbert equation for AFM and FM layers, respectively. We first investigate the variation of the exchange bias field (H-EB) as a function of K-AF in the IrMn/CoFe system. It is found that H-EB strongly depends on the energy barrier dispersion determined by dispersions of K-AF and the grain volume. It is shown that the H-EB is affected by the physical microstructure of the IrMn layer: film thickness and grain diameter. We also demonstrate that the maximum setting fraction (f(set)) related to H-EB can be achieved by optimizing the value of K-AF and T-set. The simulation results of the setting process are in good agreement with previous experimental works. This confirms the validity of the EB model, including the setting process that can be used as a powerful tool for the application of spintronics, especially for read sensor design to achieve high thermal stability with scaling down of components.