Apparent spin polarization decay in Cu-dusted Co/Al2O3/Co tunnel junctions

Co/Al2O3/Co magnetic tunnel junctions with an interfacial Cu layer have bee n investigated with in situ growth characterization and ex situ magnetotran sport measurements. Cu interlayers grown on Co give an approximately expone ntial decay of the tunneling magnetoresistance with xi approximate to 0.26 nm while those grown on Al2O3 have a decay length of 0.70 nm. The differenc e in decay lengths can be explained by different growth morphologies, and i n this way clarifies a present disagreement in the literature. For monolaye r coverage of Cu, we show that the tunneling spin polarization is suppresse d by at least a factor of 2 compared to Co and beyond approximate to 5 ML i t becomes vanishingly small.