Origin of giant magnetoresistance contributions in electrodeposited Ni-Cu/Cu multilayers

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Abstract

The magnetoresistance (MR) and magnetization were studied at room temperature and down to 4.2K for Ni81Cu19(3nm)/Cu(d Cu) multilayers with 0.5nm≤dCu≤3nm and for a bulk Ni81Cu19 alloy, all produced by electrodeposition. For most of the multilayers, giant magnetoresistance (GMR) was observed with a maximum around 1-1.5nm Cu-layer thicknesses. The room-temperature MR curves consisted of a rapidly varying low-field component up to about 1kOe and a slowly varying high-field component persisting beyond 18kOe. For Cu-layer thicknesses around the maximum GMR, the low-field component dominated whereas for dCu > 1.5nm, it became comparable to or smaller than the high-field component. For the bulk alloy, anisotropic magnetoresistance was observed. According to the room-temperature magnetization curves, both the bulk alloy and the multilayers exhibited ferromagnetic (FM) behaviour with technical saturation around 1-3kOe. For the multilayers, the low-field MR curves with a small peak splitting were characteristic of uncoupled or weakly coupled magnetic layers. Magnetic measurements from 5 to 300K indicated that besides an FM contribution, these multilayers also exhibit a superparamagnetic (SPM) component with blocking temperature around 220K. From an analysis of the present results, the low-field MR component could be attributed to the FM domains with their magnetizations exhibiting a random in-plane distribution in the zero-field (demagnetized) state and the high-field MR component to a contribution due to SPM regions. All these considerations are supported by the complete saturation of the MR in a magnetic field of 4kOe at T=4.2K.

Original languageEnglish
Pages (from-to)156-167
Number of pages12
JournalJournal of Magnetism and Magnetic Materials
Volume269
Issue number2
DOIs
Publication statusPublished - Feb 1 2004

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Keywords

  • Electrodeposition
  • GMR
  • Ni-Cu/Cu multilayers
  • Superparamagnetism

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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