Abstract
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.
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