Intermixing effects in ultrathin barrier magnetic tunneling junctions

Ultrathin tunneling barrier magnetic tunneling junctions were fabricated to study the intermixing effects of ferromagnetic layer, NiFe, and barrier precursor aluminum. Both bottom ferromagnetic layer (NiFe) and aluminum were grown epitaxially on a Pt buffered sapphire (0001) substrate. Grazing incidence x-ray reflectometry indicated an intermixing layer of 0.6 nm (∼3 atomic layers) between the NiFe and Al. Junction barrier height and width were extracted from both $\mathrm{R(T)}$ curve and zero-bias conductance. Nonideal oxidation of the intermixing region degrades the device performance, and poses a fundamental limit to the optimization of ultrathin barrier tunnel junctions.