Exchange Bias in Bilayer and Multilayer NiFe/IrMn

The exchange bias effect in bilayer and multilayer samples of NiFe/IrMn was studied. Using techniques such as torque magnetometry, anisotropic magnetoresistance, and magnetization curves, a simple model valid for polycrystalline samples was used to fit the experimental curves. The model considers, beyond the stable grains, the presence of unstable ones at the ferro/antiferromagnetic interface, which gives rise to rotational hysteresis in the torque curves. From the obtained parameters, it was possible to evaluate and compare how the stacking of the layers affects the coupling of the ferromagnetic layers with the two kinds of interfacial grains.