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Transport properties studies of magnetic tunnel junctions performed on electrodeposited single and double barrier structures like Ni-NiO-Co, Ni-NiO-CoNi-NiO-Co show a broad distribution of magnetoresistance values from +60% to -25%. The range of results can be understood in terms of tunneling via localized states in the single barrier. Calculations based on Landauer-Büttiker theory explain this behavior in terms of disorder-driven statistical variations in magnetoresistance with a finite probability of the inversion of tunnel magnetoresistance sign due to resonant tunneling. Double barrier structures show two level switching of resistance with changing applied bias. The magnitude and sometimes the sign of magnetoresistance is different for high-resistance and low-resistance states. Charge build-up mechanism, filament formation and rupture, quantum well states, and changes in the magnetic states of the CoNi "island" are proposed to explain this behavior.
