Employing ab initio electronic structure calculations we have investigated the magnetostrictive properties and the effect of epitaxial strain on the magnetic anisotropy (MA) of Au/FeCo/MgO heterostructure. Under small expansive strain on the FeCo layer the system exhibits an in-plane MA. The calculations reveal that the strain dependence of the MA is nonlinear and that the FeCo film undergoes a spin reorientation at a critical strain between 2 and 4%. The underlying mechanism is the strain-induced shift of the spin–orbit coupled d-states of the Fe atoms. We predict a giant magnetostriction coefficient of about 420 Â 10 À 6 in the heterostructure. Published by Elsevier B.V.