Characterization of Ultrathin Fe–Co Layer Grown on Amorphous Co–Fe–B by In situ Reflective High-Energy Electron Diffraction

The textured MgO(001) tunnel barrier grown on CoFeB is a fundamental building block for spintronic devices such as magnetic tunnel junctions. Although the insertion of an ultrathin Fe-Co layer between an MgO layer and a bottom CoFeB layer is a common technique for improving the magnetoresistance effect, the characteristics of this technique remain unclear. We systematically investigated the as-grown structure of Fe-Co by reflective high-energy electron diffraction and found that a highly textured MgO(001) is formed only on an amorphous Fe-Co surface. The diffusion of B atoms from underlying CoFeB into Fe-Co is what makes the as-grown Fe-Co layer amorphous. (C) 2013 The Japan Society of Applied Physics