Interfacial Density of States in Magnetic Tunnel Junctions

Abstract

Large zero-bias resistance anomalies as well as a collapse of magnetoresistance were observed in $\mathrm{Co}/{\mathrm{Al}}_2{\mathrm{O}}_3/\mathrm{Co}$ magnetic tunnel junctions with thin Cr interfacial layers. The tunnel magnetoresistance decays exponentially with nominal Cr interlayer thickness with a length scale of $\sim 1Å$ more than twice as fast as for Cu interlayers. The strong suppression of magnetoresistance, as well as the zero-bias anomalies, can be understood by considering a strong spin-dependent modification of the density of states at Co/Cr interfaces. The role of the interfacial density of states is shown by the use of specially engineered structures. Similar effects are predicted and observed in junctions with Ru interfacial layers.