SURFACE AND STEP MAGNETIC-ANISOTROPY

Cu(11n) surfaces vicinal to Cu(001) are characterized by (001) terrace s separated by monoatomic steps. Growth of thin epitaxial magnetic fil ms on such terraced substrates, e.g., Co/Cu(I 1 13), leads to unexpect ed magnetic anisotropy associated with the surface steps. This anisotr opy remains largely unexplained, and is of potential technological imp ortance. We have studied the anisotropy of fcc Co/Cu (1113) films usin g in-situ magneto-optical Kerr effect (MOKE), and find an in-plane uni axial anisotropy favoring magnetization parallel to the steps. The str ength of this anisotropy decreases with increasing film thickness. In this paper we focus on the interpretation of this anisotropy in terms of the Neel model. The Neel anisotropy energy for such a film has the form E(film) = E(bulk) - 2E(surface)/t - 2E(step)/(td), where t and d are film thickness and terrace width, respectively. The last term incl udes contributions from sites at both the upper edge and inner comer o f the step and makes the dominant contribution to the step-induced ani sotropy. This model properly accounts for the preferred direction of m agnetization parallel to the steps in Co/Cu(1113). bcc Fe/W vicinal to (001) shows a preference for in-plane magnetization perpendicular to the steps for t < 2.5 monolayers. The Neel model also predicts this an isotropy for a bcc Fe film provided the magnetization lies in the film plane, not in the (001) plane.