Giant magnetoresistance and structure of electrodeposited Co/Cu multilayers: The influence of layer thicknesses and Cu deposition potential

N. Rajasekaran, J. Mani, B. G. Tóth, G. Molnár, S. Mohan, L. Péter, I. Bakonyi

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Abstract

The giantmagnetoresistance (GMR) and structurewas investigated for electrodeposited Co/Cumultilayers prepared by a conventional galvanostatic/potentiostatic pulse combination from a pure sulfate electrolytewith various layer thicknesses, total multilayer thickness and Cu deposition potential. X-ray diffraction (XRD) measurements revealed superlattice satellite reflections for many of the multilayers having sufficiently large thickness (at least 2 nm) of both constituent layers. The bilayer repeats derived from the positions of the visible superlattice reflections were typically 10-20% higher than the nominal values. The observed GMR was found to be dominated by the multilayer-like ferromagnetic (FM) contribution even for multilayers without visible superlattice satellites. There was always also a modest superparamagnetic (SPM) contribution to the GMR and this term was the largest for multilayers with very thin (0.5 nm) magnetic layers containing apparently a small amount of magnetically decoupled SPM regions. No oscillatory GMR behavior with spacer thickness was observed at any magnetic layer thickness. The saturation of the coercivity as measured by the peak position of the MR(H) curves indicated a complete decoupling of magnetic layers for large spacer thicknesses. The GMR increased with total multilayer thickness which could be ascribed to an increasing SPM contribution to the GMR due to an increasing surface roughness, also indicated by the increasing coercivity. For multilayers with Cu layers deposited at more and more positive potentials, the GMRFMterm increased and the GMRSPMterm decreased. At the same time, a corresponding reduction of surface roughness measured with atomic force microscopy indicated an improvement of the multilayer structural quality which was, however, not accompanied by an increase of the superlattice reflection intensities. The present results underline that whereas the structural quality as characterized by the surface roughness generally correlates fairly well with the magnitude of the GMR, the microstructural features determining the amplitude of superlattice reflections apparently do not have a direct influence on the GMR.

Original languageEnglish
Pages (from-to)D204-D212
JournalJournal of the Electrochemical Society
Volume162
Issue number6
DOIs
Publication statusPublished - Jan 1 2015

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ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Surfaces, Coatings and Films
  • Electrochemistry
  • Materials Chemistry

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