Apparent Spin Polarization Decay in Cu-DustedCo/Al2O3/CoTunnel Junctions

Abstract

$\mathrm{Co}/{\mathrm{Al}}_2{\mathrm{O}}_3/\mathrm{Co}$ magnetic tunnel junctions with an interfacial Cu layer have been investigated with in situ growth characterization and ex situ magnetotransport measurements. Cu interlayers grown on Co give an approximately exponential decay of the tunneling magnetoresistance with $\xi \approx 0.26\mathrm{nm}$ while those grown on ${\mathrm{Al}}_2{\mathrm{O}}_3$ have a decay length of 0.70 nm. The difference in decay lengths can be explained by different growth morphologies, and in this way clarifies a present disagreement in the literature. For monolayer coverage of Cu, we show that the tunneling spin polarization is suppressed by at least a factor of 2 compared to Co and beyond $\approx 5\mathrm{ML}$ it becomes vanishingly small.