Effect of interface roughness on hysteresis loops of ultrathin Co films from 2 to 30 ML on Cu(001) surfaces

Abstract

Ultrathin Co films have been grown on a smooth Cu(001) surface and a rough Cu(001) surface by molecular beam epitaxy (MBE). Using high-resolution low-energy electron diffraction (HRLEED) angular profile measurement and a kinematic LEED model, we quantitatively extracted the interface width w, the roughness exponent α film and the lateral correlation length ξ for Co films grown on a smooth Cu surface from 2 up to 30 ML thick. Corresponding magnetic properties, including the Kerr intensity I k, coercivity H c and d〈M〉 dH H = H c (the slope of the hysteresis loop at H = H c) were obtained from hysteresis loops measured by the surface magneto-optic Kerr effect (SMOKE). For 2 to 7 ML thick Co films grown on the rough Cu surface the hysteresis loop shape is much less square-like compared with that of Co films grown on teh smooth Cu surface; the Kerr intensity I k is a factor of 3–4 smaller than that of the smooth film; the H c value is ≈3 times larger than that of the smooth film. H c is almost thickness independent in the 2–7 ML regime, in contrast to that of the smooth film in the same thickness region. The difference in magnetic properties can be qualtitatively explained in terms of the quantitative roughness parameters associated with the Co films.