Interfacial sensitivity and zero-bias anomalies in magnetic tunnel junctions

Large zero-bias resistance anomalies as well as an extremely strong decrease of magnetoresistance were observed in Co/Al2O3/Co magnetic tunnel junctions with thin Cr interfacial layers. The tunnel magnetoresistance decays exponentially with nominal Cr interlayer thickness with a length scale of 0.1 nm. The magnetoresistance decay, as well as some aspects of the zero-bias anomalies, can be understood by considering a strong spin-dependent modification of the density of states at Co/Cr interfaces and existing models for zero-bias anomalies. The effect of the density of states modification is also observed in the transport of the metallic electrodes alone, confirming the key role of the Co/Cr interface. However, several aspects of the zero-bias anomalies cannot be explained at present, suggesting perhaps a novel form of the Kondo resonance.