Dependence of the dielectric function and electronic properties on the Co layer thickness in giant-magnetoresistance Co/Au multilayers

Abstract

A series of Co/Au multilayers, which exhibit (111) texture and low-field giant magnetoresistance (GMR), were examined with spectroscopic ellipsometry (SE) in a range of Co layer thicknesses ${(t}_{\mathrm{Co}}).$ The obtained optical dielectric functions show a systematic variation with increasing ${t}_{\mathrm{Co}}.$ Analysis of the optical transitions reveals nonmonotonic variations in plasma frequency ${\ensuremath{\omega}}_{p}$ and the interband parameters with increasing ${t}_{\mathrm{Co}}.$ These anomalies in the electronic states reflect drastic changes in Co layering above 1.5 nm of ${t}_{\mathrm{Co}}.$ The complementary study of SE and GMR measurements, on similar Co/Cu and Co/Au multilayers with (111) texture, provide experimental evidence that an interplay between spin-dependent interface and bulk scattering contributions can explain the observed linear decrease of GMR with increasing ${t}_{\mathrm{Co}}.$