Significant modification of Co-59 hyperfine fields assigned to specific structural changes in sputtered Co/Au and Co/Cu multilayers

Magnetron sputtered Co/Cu and Co/Au multilayers (MLs) with low-field giant magnetoresistance were grown on SINx underlayers. Spin-echo Co-59 nuclear m agnetic resonance (NMR) spectra reveal an fee Co layer stacking for the Co/ Cu multilayers whereas the Co/Au spectra exhibit a unique profile that cann ot be assigned to any of the known bulk crystalline or glassy Co structures . Analysis of the Co/Au superlattice reflections, observed with x-ray diffr action (XRD), indicates that Co layers (d(Co)) expand significantly relativ e to close-packed lattice values and provide evidence for a reduced atomic density. The complementary study with XRD and NMR measurements has revealed a metastable Co nanostructure in the as-prepared Co/Au MLs, [S0163-1829(99 )00913-3].