Thermal stability of nanoscale Co/Cu multilayers

The thermal stability of Co(2 nm)/Cu(2 nm) multilayers which exhibit the gi ant magnetoresistance (GMR) effect: has been investigated both experimental ly and theoretically. Conventional and analytical transmission electron mic roscopy, Auger spectroscopy and X-ray analysis revealed changes of the comp osition on the nanometer scale, the phase morphology as well as the grain s tructure of multilayers which arise during annealing up to 740 degreesC. Ab ove an annealing temperature of 300 degreesC, the onset of grain coarsening accompanied by a transition from a [111] to a [100] texture is observed. M oreover, a sharpening of the Co/Cu phase boundaries occurs during annealing up to 600 degreesC. Transmission electron microscopy observations revealed the coalescence of adjacent Co layers at 600 degreesC, and a complete disi ntegration of the layer morphology at 740 degreesC. Thermally induced chang es of the phase morphology were also analysed by means of Monte Carlo simul ations. With the assumption that the multilayer decomposition starts by a f ormation of Cu bridges through Co layers at grain boundaries, simulations o f the subsequent evolution of the phase morphology showed a recession of Co layers near grain boundaries which can lead to the localised fusion of adj acent Co layers as well as to a Co and Cu layer thickness coarsening.