Fabrication and magnetic behavior of Co/Cu multilayered nanowires
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Bethanie J.H. Stadler Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (Received 3 April 2006; accepted 23 June 2006)
Multilayered Co/Cu nanowires were fabricated using anodic alumina templates, containing 40-nm-diameter nanopores, and electrochemical deposition. The Cu layer thickness was varied to study the resulting differences in coercivity and magnetization reversal. Magnetization versus field loops both parallel and perpendicular to an applied field were measured to investigate the mechanisms of magnetization reversal. It was found that the coercivity decreased with increasing Cu thickness. In addition, the magnetization reversal appeared to be a combination of rotation and spin flipping, which was dependent on the Cu thickness and on the angle of the nanowires with the applied field.
I. INTRODUCTION
Nanostructured materials are promising subjects, as they provide novel properties over their bulk counterparts and potential applications in nanoscale devices. Recent progress on magnetism and magnetic materials has made magnetic nanostructures, including magnetic nanowires, a particularly interesting class of materials for both scientific and technological explorations.1 Many kinds of magnetic nanowires such as Co, Fe, and FeNi have been developed for study of both their unique properties and potential applications.2–5 The diameter of these nanowires can be tailored from a few nanometers to a few hundred nanometers with lengths as high as 100 m. Recently, multilayered nanowires have been used for current perpendicular to the plane (CPP) giant magnetoresistance (GMR), which is predicted to have a larger GMR effect than the normal current in the plane structures (CIP).3,6 CPP structures are of interest not only for GMR but also a new phenomenon, currentintroduced magnetization switching (CIMS), which has potential applications in magnetic random access memory (MRAM). There are various techniques for fabricating nanowires, including E-beam lithography techniques, step growth, and template-assisted electrodeposition. Of
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0348 2870
J. Mater. Res., Vol. 21, No. 11, Nov 2006
these, electrodeposition is the fastest and most costeffective way to produce large quantities of magnetic nanowires. Most work in electrodeposited multilayered nanowires has focused on the GMR effect.2,6,7 In this paper, we present new measurements of the magnetization reversal process in multilayered nanowires with 40-nm diameters using vibrating sample magnetometry (VSM). Usually, magnetization versus field (M-H) hysterisis loops show only the magnetic moment along the sweep direction of the applied magnetic field. In this work, two components of magnetic moment (parallel and perpendicular to the sweep field) were measured to understand the magnetization reversal mechanism in multilayered nanowires. The Cu thickness dependence was investigated by keeping the Co thickness fixed at 5 nm while v
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