Setting temperature effect in polycrystalline exchange-biased IrMn/CoFe bilayers

We study the effect of atomic interdiffusion on the exchange bias of polycrystalline IrMn/(⁵⁷Fe + CoFe) multilayers due to the thermal setting process of exchange coupling during field annealing. Depth-resolved ⁵⁷Fe conversion electron Mössbauer spectroscopy was used to quantify atomic interdiffusion. Vibrating sample magnetometry was used to monitor the variation of exchange bias and magnetisation. It was found that interface sharpness is only affected above ∼350 °C. Three different stages for the setting of exchange bias can be inferred from our results. At the lower setting temperatures (up to 350 °C), the effect of field annealing involves alignment of spins and interfacial coupling due to the setting of both antiferromagnetic (AF) bulk and interface without significant interdiffusion. At a second stage (350–450 °C), where AF ordering dominates over diffusion effects, atomic migration and increased setting of AF spins co-exist to produce a peak in exchange bias field and coercivity. On a third stage (>450 °C), severe chemical intermixing reduces significantly the F/AF coupling.