Quenching of Giant Magnetoresistance by Interface Roughening and Alloying in Annealed [(Nix Fe1-x ) yAu1-y]/Au Multilayers

Antiferromagnetically coupled permalloy/Au multilayers display giant magnetoresistance (GMR) with large changes in resistance in very low fields. We show that thermal annealing of such structures, exhibiting GMR, leads to a quenching of the magnetoresistance. The detailed structure of the permalloy/Au interfaces has been probed using high-resolution cross-section transmission electron microscopy. On annealing, the Au layers interdiffuse into the permalloy layers, which leads both to rougher permalloy/Au interfaces and to “thinner” Au spacer layers. We infer that the latter results in ferromagnetic coupling of the permalloy layers, which accounts for the reduced GMR.