Incidence of in situ annealing on the nanoscale topographical/electrical properties of the tunnel barrier in sputtered epitaxial Fe/MgO/Fe multilayers

Technological improvements in the magnetotransport performance of Fe/MgO/Fe stacks require nanoscale control over the topographical and electrical properties of the ultrathin MgO barrier. We have statistically investigated the incidence of in situ annealing of the lower Fe layer on the nanoscale topographical/electrical properties of Fe/MgO bilayers and the structural and magnetic properties of Fe/MgO/Fe/Co multilayers prepared by sputtering. This annealing step improves the crystal quality of both the lower Fe and the upper Fe/Co layers, leading to an enhanced saturated magnetic moment. Finally, this annealing step substantially mitigates the presence of nanohills on the lower Fe layer and improves the uniformity of the height and/or the thickness of the MgO tunnel barrier. Our results pave the way for studies of nanoscale transport on micrometre-sized devices through a better understanding of, and control over, nanoscale hotspots in the tunnel barrier.