Spin polarization and barrier-oxidation effects at the Co ∕alumina interface in magnetic tunnel junctions

The electronic structure and polarization in magnetic tunnel junctions prepared with varying degrees of barrier-layer oxidation have been studied using x-ray absorption spectroscopy across the Co L 2 , 3 absorption edges. It was found that the Co electronic structure near the Co ∕alumina interface tended to that of cobalt oxide as the barrier oxidation time was increased. However, the net Co 3 d spin polarization, determined from x-ray magnetic circular dichroism, increased for moderate oxidation times compared to that obtained for an under-oxidized Co ∕ Al interface. It is proposed that the expected dilution of the measured polarization due to the formation of (room temperature) paramagnetic cobalt oxide, is offset by an increase in the Co 3 d spin-polarization of the interface layer as the interface bonding changes from Co - Al to Co - O with increasing oxidation times.