Sandwich molecular nanowires: on-surface synthesis, structure and magnetism

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In focus of the project are sandwich molecular nanowires consisting of a periodic sequence of 4f rare earth metal cations, ionically bound and eightfold coordinated to planar aromatic anions, based on the cyclooctatetraene (C8H8, briefly Cot) molecule as ligand. These one dimensional entities are conceptually distinct from the two dimensional organometallic coordination networks as well as from zero dimensional organometallic molecular magnets Due to the hybridization of the metal atomic states and the extended pi-orbitals of the Cot molecule, the metal ions in the wire couple magnetically. Therefore, these systems could be more stable magnetic units than single molecule magnets, and could display larger magnetic anisotropy with correspondingly higher blocking temperatures.The first objective of the proposed research is to explore the versatility of a new on-surface synthesis method enabling us to create these one dimensional organometallic nanowires under clean conditions on a substrate and thereby making them accessible to detailed investigation for the first time. Starting from the paradigmatic Eu-Cot case we will (i) test different rare earth, earth alkali, and 3d metals, (ii) vary the ligand molecule, or attach functional groups to it, and (iii) use different substrates and doping methods. For the interesting cases, where we go beyond explorative experiments, structure and growth mechanism will be carefully analyzed to optimize the growth and thus the purity and quality of the wire product.The second objective is to understand the physics of metal 4f (or 3d) electrons interacting with molecular pi-systems. To this end, and for selected systems, we will experimentally characterize the electronic and magnetic properties of the sandwich molecular wires in detail, including band structure, band gaps, magnetic moments, magnetic anisotropy, as well as magnetic coupling and compare these results to dedicated ab initio calculations. We are convinced that this process of bringing experiment and theory to interaction will provide improved concepts for the synthesis. The third objective will serve as a guideline within the activities subordinated to the first two objectives, namely to create stable magnetic units with a potential use for spintronic applications. This implies to keep in focus magnetic anisotropy as well as the magnetic coupling strength of the metal centers in the wires, to pay attention to growth on insulating substrates, and finally to try to manipulate and contact wires in order to measure spin-polarized transport.