Effects of annealing on the microstructure and giant magnetoresistance of Co-Cu-based spin valves

The effect of annealing on the microstructure and giant magnetoresistive (G MR) properties of NiO/ Co/Cu/Co bottom spin valves is investigated using co nventional and high resolution transmission electron microscopy. The value of the GMR of these spin valves is observed to decrease from 12.2 to 2.7 pe t after annealing in a vacuum for 30 minutes at 335 degreesC. This decrease is attributed to an increase in the roughness of the Co and Cu layers. In annealed specimens, grain boundary grooving is also observed in the antifer romagnetic NiO pinning layer at the NiO/Co interface, and the location of t hese grooves correlates with waviness in the Co/Cu interfaces. An increase in the Neel "orange-peel" coupling between the ferromagnetic Co layers, res ulting from the increased roughness of the Co/Cu interfaces, accompanies th e degradation of the GMR.