Perpendicular magnetization in epitaxial Cu/Fe/Cu/Si(111) ultrathin films

Epitaxial Fe films, with thickness in the range between 2.5 and 12 Å, were grown in UHV conditions on the 7×7 reconstructed (111)-Si surface, with a Cu 35 Å thick buffer layer, using the so-called metal–metal epitaxy on silicon (MMES). Kikuchi electron diffraction showed that the growth of Fe on Cu/Si(111) occurs first by formation of a pseudomorphic film of γ-Fe(111), about two to three atomic layers thick, and by the successive growth of bcc Fe(110) domains in the Kurdjumov–Sachs orientation, in agreement with our previous low-energy electron diffraction observations. Kerr effect measurements carried out at low temperatures (20–150 K) revealed that Fe films thinner than 5–6 Å are ferromagnetic with an easy axis magnetization orthogonal to the film plane. With increasing Fe thickness, in coincidence with the fcc-to-bcc structural transformation, the easy axis switches to the in-plane orientation over a finite range of thickness.