Epitaxial growth of Ni on Cu(0 0 1) with the assistance of O-surfactant and its magnetism compared to Ni/Cu(0 0 1)

The growth of Ni films deposited on a reconstructed (√2×2√2)R45° O/Cu(0 0 1) is examined. It is shown that deposition of Ni changes the surface symmetry to c(2 × 2) and that oxygen always floats on the film surface. No NiO is formed. Surface roughness decreases and the growth mode is closer to ideal layer-by-layer, as compared to that of Ni/Cu(0 0 1) indicating a surfactant activity of oxygen. Furthermore, the critical thickness for dislocation formation is larger than that for Ni/Cu(0 0 1), which points to a less defective film structure. The improved growth patterns are accompanied by a shift of the spin reorientation transition from in- to out-of-film plane by about 5 monolayers. In the film plane, the easy axis of the magnetization switches from the [1 1 0] direction for Ni/Cu(0 0 1), to the [1 0 0] direction for Ni on preoxidized Cu. We attribute these characteristics to modifications of the film surface by the floating oxygen.