Thermal stability of antiferromagnetically coupled multilayers with Ru/Co and Cu/Co interfaces

The long-term thermal stability of the hard artificial antiferromagnetic su bsystem (AAF) found in giant magnetoresistance (GMR) and tunnel magnetoresi stance sensors based on Cu/Co/Ru/Co/Cu has been investigated using the comp lete sensor stack as well as of selected single layers. A striking asymmetr y between both types of Co layers in the single Co layer samples with respe ct to magnetic and transport properties is observed, which show a different dynamics for each upon annealing. Directly after deposition, the Co/Ru int erface is stronger mixed as compared to the Ru/Co interface, due to differe nce in sputter energies and order of growth. The different behavior upon an nealing has been interpreted by the difference in concentration gradients a nd lattice mismatch at the interfaces. Despite the strong mixing found at t he Co/Ru interface, the impact on the characteristics of the AAF, like the GMR signal and the rigidity is limited. Several causes, like the cohesion i n the AAF induced by its Co seed layer on the Cu and the limited availabili ty of Ru, are pointed out as likely origins of the improved stability of th e AAF as compared to the single Co layers. Possibilities to even further im prove the rigidity by carefully matching of anneal procedure and layer thic knesses are discussed. (C) 2001 American Institute of Physics.