Size effects and giant magnetoresistance in unannealed NiFe/Ag multilayer stripes

Abstract

We have observed giant magnetoresistance ͑GMR͒ in unannealed NiFe/Ag multilayer thin-film stripes. Rectangular stripes having constant thickness and a constant 11:1 length-to-width aspect ratio, but varying widths down to 0.5 m, were measured. Two types of multilayer configurations were tested, a system of five NiFe/Ag bilayers with 5.5-nm-thick Ag spacer layers, and a system of nine bilayers with 4.4-nm-thick Ag layers. In contrast to the characteristic of annealed NiFe/Ag multilayer stripes, the unnannealed stripes produced increasing GMR ratios for decreasing stripe sizes, with the 0.5-m-wide stripe of the five-bilayer system exhibiting a ⌬R/R of 2.5%. Barkhausen noise and response broadening also increased with decreasing stripe size, however. The results are discussed in terms of magnetostatic coupling of the NiFe layers within the stripes.

Width dependence of giant magnetoresistance in Cu/Co multilayer nanowires

“…Conversely, the saturation field continues to increase with decreasing wire width at the second and third antiferromagnetic maxima. This is attributable to a magnetostatic broadening effect, similar to that reported in unannealed NiFe/Ag multilayer stripes 6 and NiFe/Co/Cu/Co spin valves. 3 In the case of the first maxima, the interlayer exchange coupling dominates the energetics, so it is not surprising that increasing the wire aspect ratio from 40:1 to 120:1 produces no discernible change in H s .…”

“…Enhancement of the GMR amplitude has previously been achieved by patterning lines and dots as small as 0.7 m. [4][5][6] In our wire geometry, we do not expect to see the enhancement in antiferromagnetic coupling due to magnetic edge charge effects, like those observed in patterned dots. 5 For our narrowest wires, however, the strong shape anisotropy should prevent the formation of magnetic domains, which may enhance the amplitude of the GMR effect by allowing more perfect alignment of the magnetization of the Co layers.…”

Influence of sample width on the magnetoresistance and planar Hall effect of Co/Cu multilayers

“…In wide samples, the main subjects are either the magnetic coupling of the layers (linked to the process of magnetization on that account) [3][4][5][6] or the description of the magnetotransport processes in Current in Plane (CIP) or Current Perpendicular to Plane (CPP) conduction. 7,8 On the other hand, most authors that have dealt with very narrow spin-or pseudo spin-valve systems, probably stimulated by the perspective of applications, were mainly focused on the magnitude variation of the GMR, [9][10][11] not paying much attention to the changes in its magnetic field response.…”