Layered structure and related magnetic properties for annealed Fe/Ir(111) ultrathin films

After annealing treatments for fcc-Fe/Ir(111) below 600 K, the surface layers remain pseudomorphic. The Ir(111) substrate plays an important role on the expanded Fe lattice. At temperatures between 750 and 800 K, the surface composition shows a stable state and a c(2 × 4) structure is observed. We discover a layered structure composed of some Fe atoms on the top of a Fe_0.5Ir_0.5 interfacial alloy supported on the Ir(111) substrate. The competition between the negative formation heat of Fe_0.5Ir_0.5 and surface free energy of Fe causes the formation of layered structure. The existence of ferromagnetic dead layer coincides with the formation of fcc-Fe for ultrathin Fe on Fe_0.5Ir_0.5/Ir(111). For Fe films thicker than three monolayers, the linear increase of the Kerr intensity versus the Fe coverage is related to the growing of bcc-Fe on the surface where the Fe layer is incoherent to the underlying Fe_0.5Ir_0.5/Ir(111). These results emphasize the importance of the substrate induced strain and layered structure of Fe/Fe_0.5Ir_0.5/Ir(111) on the magnetic properties and provide valuable information for future applications.