Magnetic devices are often subject to thermal processing steps, such as field cooling to setexchange bias and annealing to crystallize amorphous magnetic electrodes. These processing stepsmay result in interdiffusion and the subsequent deterioration of magnetic properties. In this study,we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystallinethin-film structures using atom probe tomography. Images taken after annealing at 400 C for60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundariesfor the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 C showed further Mn diffu-sion into Co grains. At the IrMn/Pt interface, annealing at 500 C led to a type B behavior since Mndiffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration ofthe films’ exchange bias properties upon annealing was correlated to the observed diffusion. Inparticular, the topmost Pt capping layer thickness turned out to be crucial since a fasterdeterioration of the exchange bias properties for thicker caps was observed. This is consistent with theidea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.