Low field giant magnetoresistance in discontinuous magnetic multilayers

Giant magnetoresistance of order 4%–6% has been observed in fields of 5–10 Oe at room temperature in annealed multilayers of Ni80Fe20/Ag prepared by magnetron sputtering. For a wide range of NiFe and Ag thicknesses, no giant magnetoresistance was observed in the unannealed films. We attribute the appearance of giant magnetoresistance to a magnetostatic interlayer interaction that promotes antiparallel order of the moments in adjacent layers fostered by a breakup of the NiFe layers. We discuss the effects of variations in the underlayers, spacer thickness, and the sputtering process on the magnetoresistance. Our results suggest that maximizing magnetoresistance and minimizing hysteresis require samples with continuous Ag layers that prevent contact between the NiFe layers and NiFe layers that are discontinuous but not too severly disrupted.