Growth and magnetism of low-dimensional metallic nanostructures on the Pt(997) surface

Abstract

The thesis presents experimental results on the growth and magnetism of metallic nanostructures on the vicinal Pt surface. The aim of the research project consists of two parts: First, to find conditions for growing nanostructures of dimensionalities from 1D to 2D initiated from the step edges of a vicinal surface. Second, to investigate the magnetic properties of the nanostructures and ultrathin films fabricated with the knowledge from the first part. The first part of the thesis studies molecular beam epitaxy (MBE) of Fe, Rh, Ru, and Mo nanostructures on the vicinal Pt(997) surface for various temperatures employing thermal energy He atom scattering (TEAS), Auger electron spectroscopy (AES) and low electron energy diffraction (LEED) as characterizing methods. The parameters for the growth of a wide variety of Fe nanostructures, from monatomic chains to monolayers and surface alloys, were obtained and a detailed comparison of Fe growth on Pt(997) and Pt(111) is presented. Rh deposition creates structures similar to the ones of Fe although with higher defect density. A complex growth mode involving double layer growth is observed for Ru. For Mo no ordered structures could be identified. In the second part of the thesis measurements by X-ray magnetic circular dichroism (XMCD) and magneto optical Kerr effect (MOKE) were employed as probes to the magnetic properties of the structures. Ultrathin Fe films show different magnetic properties depending on the step density of the substrate. The relation between magnetism and structure is shown by the comparison of films on Pt(997) and Pt(111). The variety of Fe structures characterized in the first part is investigated finding an increase of orbital magnetic moments when the dimension and thus the coordination in the structure is reduced. It is shown that a stabilization of the magnetization in Fe nanostructures which is reflected by an increased remanence and coercivity is achieved simply by alloying with Pt from the substrate. Finally, it is demonstrated that well measurable magnetic moments are induced in the Pt for a FePt alloy with a total Fe coverage of only 0.5 ML. The Pt moments are found to couple collinearly to the Fe moments.