Diffusion based degradation mechanisms in giant magnetoresistive spin   valves
  Spin valve systems based on the giant magnetoresistive (GMR) effect as used for example in hard disks and automotive applications consist of several functional metallic thin film layers. We have identified by secondary ion mass spectrometry (SIMS) two main degradation mechanisms: One is related to oxygen diffusion through a protective cap layer, and the other one is interdiffusion directly at the functional layers of the GMR stack. By choosing a suitable material as cap layer (TaN), the oxidation effect can be suppressed. 
M. Hawraneck, J. Zimmer, W. Raberg, K. Pruegl, S. Schmitt, T. Bever,   S. Flege, and L. Alff