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Combining molecular electronics with spintronics represents one of the most exciting avenues in building future nanoelectronic devices. In this context, the design of nanoscale spintronic elements in multifunctional devices relies on a clear theoretical understanding of the physics at the electrode-molecule interfaces and in particular, the functionality of specific molecules in a given organic-metal surface environment. The density functional theory provides a framework where a realistic understanding of these systems with predictive power can be expected. However, only very recent functionals can properly describe the exchange correlation of the organic molecule-metal interface reliably including the van der Waals interaction. We show that this has a great influence on the flat absorption of aromatic molecules on metal surfaces. We will present a conceptual study to understand and how to tailor the magnetic properties at a hybrid organic-ferromagnetic interface by adsorbing organic molecules containing π(pz)-electrons onto a magnetic substrate. For such hybrid systems, the magnetic properties like molecular magnetic moments and their spatial orientation can be specifically tuned by substituting the H atoms with more electronegative atoms like Cl and F. Our first-principles calculations demonstrate that, by employing an appropriate chemical functionalization of organic molecules adsorbed on a ferromagnetic surface, a fine tuning of the spin-unbalanced electronic structure can be achieved. For example, by using molecular substituents with different electronegativity attached to π-conjugated systems adsorbed on a ferromagnetic surface, the electrons with a specific spin [i.e. up (↑) and down (↓)] can selectively be injected at the molecular site from the same ferromagnetic substrate. Even more important, we show that there is direct correspondence between the substituent's electronegativity and the size of the induced molecular magnetic moment. As regarding the stability of the magnetization direction of the hybrid organic-ferromagnetic system, we demonstrate that the adsorbed hydrogenated molecules destabilize more the out-of-plane magnetization of the ferromagnetic surface as compared to molecules containing more electronegative atoms as Cl and F which could also enhance it. Ultimately, this allows us to precisely engineer the magnetic properties of the hybrid organic-ferromagnetic interfaces which can be further exploited to design more efficient spintronic devices based on organic molecules. References: [1] N. Atodiresei, P. H. Dederichs, Y. Mokrousov, L. Bergqvist, G. Bihlmayer, S. Blügel, Physical Review Letters 100, 117207 (2008). [2] N. Atodiresei, V. Caciuc, P. Lazic, S. Blügel, Physical Review Letters 102, 136809 (2009). [3] N. Atodiresei, J. Brede, P. Lazic, V. Caciuc, G. Hoffmann, R. Wiesendanger, S. Blügel, Physical Review Letters 105, 066601 (2010). [4] J. Brede, N. Atodiresei, S. Kuck, P. Lazic, V. Caciuc, Y. Morikawa, G. Hoffmann, S. Blügel, R. Wiesendanger, Physical Review Letters 105, 047204 (2010). |
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