Differences of the Magnetic Behavior and Microstructure between the Co Layers in the Ni Buffered Co/Cu/Co Sandwich and Their Effects on Giant Magnetoresistance

The magnetic behaviors and the microstructures of the two Co layers in the Ni buffered Co 55 A/Cu 35 A/Co 55 A sandwich were investigated by a vibrating sample magnetometer and high resolution transmission electron microscope. It was found that the structural quality of the two cobalt layers depends on their different `buffer' layers. The lower cobalt layer induced by the nickel layer formed high quality face-centered cubic (fcc) structure, while the upper cobalt layer grown upon the copper matrix produced only random-oriented fcc-Co structure. The different crystalline states between the two Co layers resulted in their different magnetic behaviors through the magnetostatic effect, which made it possible to achieve a maximum anti-aligned state and finally enhanced the giant magnetoresistance (GMR) effect in the Co/Cu/Co sandwich.