Thermal Stability of Nanoscale Co/Cu Multilayers

Abstract

Abstract The thermal stability of Co(2 nm)/Cu(2 nm) multilayers, which exhibit the giant magnetoresistance (GMR) effect, has been investigated both experimentally and theoretically. Conventional and analytical transmission electron microscopy, Auger spectroscopy and X-ray analysis revealed changes of the composition on the nanometer scale, the phase morphology as well as the grain structure of multilayers which arise during annealing up to 740 °C. Above an annealing temperature of 300 °C, the onset of grain coarsening accompanied by a transition from a 〈111〉 to a 〈100〉 texture is observed. Moreover, a sharpening of the Co/Cu phase boundaries occurs during annealing up to 600 °C. Transmission electron microscopy observations revealed the coalescence of adjacent Co layers at 600 °C, and a complete disintegration of the layer morphology at 740 °C. Thermally induced changes of the phase morphology were also analysed by means of Monte Carlo simulations. With the assumption that the multilayer decomposition starts by a formation of Cu bridges through Co layers at grain boundaries, simulations of the subsequent evolution of the phase morphology showed a recession of Co layers near grain boundaries which can lead to the localised fusion of adjacent Co layers as well as to a Co and Cu layer thickness coarsening.