Structure and magnetism of cluster ensembles on metal surfaces: Microscopic theory of the fundamental interactions

• Applicants: Professor Dr. Gustavo M. Pastor; Professor Dr. Valeri Stepanyuk
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2012 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 210162829

The structural and magnetic properties of interacting 3d transition-metal clusters on noble-metal surfaces are investigated by combining first-principles and model quantum theory. The substrate-mediated binding energies and magnetic couplings between clusters are determined in the framework of the Green’s functions Korringa-Kohn-Rostoker (GF-KKR) approach to density-functional theory (DFT). The effects of spin-orbit interactions and noncollinear magnetic order are determined in the framework of selfconsistent tight-binding theory. A systematic study is performed as a function of experimentally relevant parameters such as particle size N (e.g., FeN, CoN, and CrN), type of substrate (e.g., different Cu, Ag and Au surfaces), intercluster distance, relative orientation of the clusters (both structural and magnetic), and surface coverage. Special attention is paid to quantum electronic-structure effects, particularly in the small-size nonscalable regime. Simple effective cluster-interaction models are derived on the basis of the ab initio GFKKR calculations in order to determine the structural relaxation in the nanostructure. The fundamental magnetic properties of interacting clusters, such as the spin and orbital magnetic moments, possible complex noncollinear magnetic orders, and magnetic anisotropy energy are determined for the optimized geometries. The effects of interactions and relaxation on the magnetic properties are analyzed in detail. The results are compared with current experiments (e.g., STM, STS, MOKE and XMCD). The present combination of complementary theoretical tools aims to achieve a microscopic understanding of cluster interactions at surfaces and contribute to refine the design of new cluster materials with tailored magnetic properties.

• DFG Programme: Research Grants