Layer-by-layer epitaxial growth of polar FeO(111) thin films on MgO(111)

► Epitaxial FeO layers are grown by molecular beam epitaxy on MgO(111). ► The successful stabilization of polar FeO films as thick as 16 monolayers (ML) is presented. ► CEMS measurements as a function of the film thickness demonstrate a size-effect-induced evolution of the hyperfine parameters. ► Ex situ CEMS investigation confirmed the magnetic ordering of the wüstite thin film phase at 80 K.