Structural instability of FeCo ultrathin films grown on MgO(100)

Structures and their stability of FeCo ultrathin films grown on MgO(100) were investigated. Atomic force microscopy observations revealed dramatic structural changes from a continuous ultrathin layer to coarse islands by low temperature annealing. The results suggest that the thin layered structures of Fe based alloys as grown on MgO(100) are not so stable as expected from the relatively small lattice mismatch between Fe based alloys and MgO. This possibly explains annealing temperature dependence of tunnel magnetoresistance observed in a Fe/MgO/Fe(100) junction.