Imaging of magnetic nanodots on self-organized semiconductor substrates

Arrays of magnetic nanodots have been prepared by evaporation in ultrahigh vacuum onto self-organized templates consisting of nanometric pyramids of SiGe alloy previously grown on Si(001). Co was deposited by molecular beam epitaxy at grazing incidence, so that preferential deposition occurs on the island facets facing the Co flux. The films' structural and magnetic morphology has been characterized by means of mirror electron microscopy and x-ray photoemission electron microscopy with magnetic circular dichroism. The morphology of the Co deposit is dictated by the surface template. The Co dots are elongated along the direction perpendicular to deposition due to geometrical factors of the surface at grazing incidence and via steering by the surface steps, and this promotes an uniaxial magnetic anisotropy in this direction. The dots are ferromagnetic and single domain at room temperature. Macroscopic magnetic domains composed of several dots are observed. This indicates that the dipolar interaction between them is stronger than the coercivity and the exchange interaction is minimized.