Mn diffusion and the thermal stability of tunneling spin polarization

We examine the role of Mn diffusion in the thermal stability of tunneling spin polarization P by directly measuring P of Al/AlO(x)/Co/FeMn and Al/AlO(x)/Co(90)Fe(10)/FeMn junctions using superconducting tunneling spectroscopy (STS). We confirm Mn diffusion in our junctions using x-ray photoelectron spectroscopy after an ultrahigh vacuum 500 degrees C anneal. Surprisingly, and in contrast to the current belief, no drop in P is observed using STS. Therefore, though Mn diffuses significantly, it cannot be solely responsible for the drop in tunneling magnetoresistance observed after postdeposition anneals above 300 degrees C. (c) 2005 American Institute of Physics.