Stability and thermal reaction of GMR NiFe/Cu thin films

Giant magneto-resistance model systems of NiFe/Cu multilayer stacks with 2 nm single layer thickness were deposited onto needle-shaped W tips using ion beam sputtering and analyzed by atom probe tomography after appropriate heat treatments. Owing to the outstanding sensitivity of the method, even minor chemical modifications on the nanometer scale can be detected. Although annealing treatments at temperatures up to 250 °C already result in a dramatic decrease of magneto-resistivity, no major structural or chemical transformation of the initial layer system is found. Instead, a slight decrease of the concentration slope at the interfaces is observed, which is attributed to short range interdiffusion induced by non-equilibrium point defects. Annealing at higher temperatures up to 500 °C/40 min still preserves a clear layer structure. However, appreciable amounts of Ni are dissolved inside the Cu layers. In the presence of grain boundaries, the onset of significant grain boundary diffusion occurs at about 350 °C.