Magnetic and magnetoresistance studies of nanometric electrodeposited Co films and Co/Cu layered structures: influence of magnetic layer thickness

Zsurzsa, Sándor and Péter, László and Kiss, László Ferenc and Bakonyi, Imre (2017) Magnetic and magnetoresistance studies of nanometric electrodeposited Co films and Co/Cu layered structures: influence of magnetic layer thickness. JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 421. pp. 194-206. ISSN 0304-8853

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Abstract

The magnetic properties and the magnetoresistance behavior were investigated for electrodeposited nanoscale Co films, Co/Cu/Co sandwiches and Co/Cu multilayers with individual Co layer thicknesses ranging from 1 nm to 20 nm. The measured saturation magnetization values supported reasonably the validity of the nominal layer thicknesses. All three types of layered structure exhibited anisotropic magnetoresistance for thick magnetic layers whereas the Co/Cu/Co sandwiches and Co/Cu multilayers with thinner magnetic layers exhibited giant magnetoresistance (GMR), the GMR magnitude being the largest for the thinnest Co layers. The decreasing values of the relative remanence and the coercive field when reducing the Co layer thickness down to below about 3 nm indicated the presence of superparamagnetic (SPM) regions in the magnetic layers which could be more firmly evidenced for these samples by a decomposition of the magnetoresistance vs. field curves into a ferromagnetic and an SPM contribution. For thicker magnetic layers, the dependence of the coercivity (Hc) on magnetic layer thickness (d) could be described for each of the layered structure types by the usual equation Hc = Hco + a/d n with an exponent around n = 1. The common value of n suggests a similar mechanism for the magnetization reversal by domain wall motion in all three structure types and hints, at the same time, for the absence of coupling between magnetic layers in the Co/Cu/Co sandwiches and Co/Cu multilayers.

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