Interface chemistry and structure of multiply oxidized barrier spin-tunnel junctions

Nb/Fe/Al(2)O(3)/CoFe/Nb spin-tunnel junctions fabricated using a multiple oxidation technique have been characterized using high spatial resolution electron microscopy techniques. Junction magnetoresistance values up to 6.2% at room temperature and 9.2% at 77 K were obtained for junctions fabricated using this technique. Energy dispersive x-ray spectroscopy and electron energy loss spectroscopy were used to study the chemistry and interface structure of the barrier layer; elemental mapping showed the degree of chemical homogeneity across the layers and high spatial resolution electron energy loss spectroscopy revealed changes in the oxidation state and d-shell occupancies of Fe and Co across the layers, which need to be considered when modelling the spin-tunneling effect. Pinholes across the barrier were also observed by high resolution electron microscopy. (C) 2000 American Institute of Physics. [S0021-8979(00)32408-2].