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

Epitaxial Fe films, with thickness in the range between 2.5 and 12 Angstrom , were grown in UHV conditions on the 7 x 7 reconstructed (111)-Si surface, with a Cu 35 Angstrom thick buffer layer, using the so-called metal-metal epitaxy on silicon (MMES). Kikuchi electron diffraction showed that the gro wth of Fe on Cu/Si(111) occurs first by formation of a pseudomorphic film o f gamma-Fe(111), about two to three atomic layers thick, and by the success ive growth of bcc Fe(110) domains in the Kurdjumov-Sachs orientation, in ag reement with our previous low-energy electron diffraction observations. Ker r effect measurements carried out at low temperatures (20-150 K) revealed t hat Fe films thinner than 5-6 Angstrom are ferromagnetic with an easy axis magnetization orthogonal to the film plane. With increasing Fe thickness, i n coincidence with the fcc-to-bcc structural transformation, the easy axis switches to the in-plane orientation over a finite range of thickness. (C) 2000 Elsevier Science B.V. All rights reserved.