Giant magnetoresistance and structural study of permalloy/silver multilayers during rapid thermal annealing

The Giant Magnetoresistance effect with high field-sensitivity was recently discovered in multilayers of alternating ferromagnetic and non-ferromagnetic layers. Some of these layer structures may find industrial application in miniaturized sensor and high-density digital magnetic recording technologies which require materials with large changes in electrical resistance at low magnetic fields. In this paper we report on Rapid Thermal Annealing experiments done on a series of multilayers of alternating thin permalloy (Ni₈₀Fe₂₀) and silver films. The layers were sputter deposited on thermally oxidized Si (100) substrates. Samples were annealed in nitrogen at temperatures ranging from 280 to 340 °C for 30 seconds to 10 minutes, yielding magnetoresistance data as high as 5% and a maximum field sensitivity of 4.6% per kA·m^-1. X-Ray diffraction analysis, showing the gradual formation of an Ag (111) shoulder peak at 2θ = 38.3° upon annealing, supports a recently published hypothesis that the appearance of the GMR effect is anneal-induced by a change of the microstructure due to diffusion, causing notching and disruption of the permalloy layers in the superlattice.