Effect of interface roughness on exchange coupling in polycrystalline Co/CoO bilayer structure: An in-situ investigation

The effect of interface roughness on exchange-bias (EB) properties of polycrystalline Co/CoO bilayer structure has been studied in-situ. Isothermal annealing of a 135 angstrom thick Co layer under the partial pressure of pure oxygen at 573K results in the formation of a 35 angstrom thick CoO layer, the surface roughness of which increases with the increasing annealing time. Bilayers were characterized in-situ using magneto-optic Kerr effect, reflection high energy electron diffraction, and x-ray reflectivity for their magnetic and structural properties during each stage of bilayer growth. Combined analysis revealed that the increase in the roughness from 7 +/- 0.5 angstrom to 13 +/- angstrom causes the exchange bias field (H-EB) to decrease from 171 Oe to 81 Oe, whereas coercivity (HC) increases up to 616 Oe. In contrast to some earlier studies on polycrystalline films, where H-EB increased with roughness due to the increase in the uncompensated spins at ferromagnetic-antiferromagnetic (AFM) layer interface, in the present case, dependence of H-EB and HC on the roughness is attributed to the disorder at the interface of AFM layer, which leads to a decrease in H-EB due to weakening of the effective spin coupling at the interface. Present in-situ experiments make it possible to study the variations in EB properties with the interface roughness in a single sample, and thus avoiding the possibility of the sample to sample variation in the morphological properties along with the change in the interface roughness. Published by AIP Publishing.