The Loop-Stage-Dependent Exchange Bias Training Effect in FeNi/FeMn Bilayers

The loop-stage-dependent exchange bias training effect has been systematically studied in the polycrystalline FeNi/FeMn bilayers. According to the ferromagnet (FM) magnetization states, an entire magnetic hysteresis loop can be divided into four different stages: 1) positive saturation stage; 2) descending branch; 3) negative saturation stage; and 4) ascending branch. The loop-stage-dependent training effect was studied by probing the instant variation of the exchange field and the coercivity after adding a short waiting time At on a specific loop-stage. Our experimental results unambiguously show that this training effect strongly depends on the stage that the waiting time is assigned on and the quantity of At as well. Based on the macroscopic two-level relaxation model, these phenomena can be well explained by considering different switching probabilities of the interfacial uncompensated antiferromagnetic spins during different FM magnetization reversal processes.