CoFe/Ir/CoFe artificial antiferromagnetic sandwich as a hard magnetic layer in hard-soft GMR sensors

We report on the magnetic and transport properties of CoFe_{3 nm}/Ir_{0.5 nm}/CoFe_{3 nm} and CoFe_{1.5 nm} /Ir_{0.5 nm}/CoFe_{3 nm} sandwiches, grown by ion beam sputtering. The sandwich with identical CoFe thicknesses presents a small rigidity and no plateau around zero field. For the same coupling strength, this rigidity and the plateau are strongly improved for the sandwich with asymmetrical CoFe thicknesses. In both cases, when the thicker layer is on the top or on the bottom of the AAF, coercive fields H_c of 600 Oe are obtained. However, the GMR plateau is only slightly improved for asymmetric sandwiches, probably due to lateral coupling fluctuations. Roughness analysis and TEM observations have been made in order to confirm the last hypothesis