Correlation of microstructure and giant magnetoresistance in electrodeposited Ni-Cu/Cu multilayers

Giant magnetoresistance (GMR) was observed in pulse-plated Ni 81 Cu 19 /Cu multilayers with a maximum GMR value of about 2 % for Ni - Cu layer thicknesses around 2 to 3 nm. A columnar growth of the multilayers was detected by transmission electron microscopy. The column width (grain size) was the largest for multilayers with the maximum GMR. It could also be established that the multilayer planes are often inclined at angle, which depends on the chemical modulation wavelength, with respect to the substrate plane. This definitely gives rise to a current-perpendicular-to-plane contribution to the GMR, offering a plausible explanation for the location of the maximum of the GMR vs thickness curve. The lattice constant mismatch between the Ni-Cu and Cu layers gives rise to considerable stresses which are relaxed, besides the formation of twinning and dislocation structures, also by an induced periodic lattice distortion (structural modulation) not completely coinciding with the chemical modulation in every direction.