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Relay-Like Exchange Mechanism through a Spin Radical between TbPc2 Molecules and Graphene/Ni(111) Substrates

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journal contribution
posted on 11.10.2016, 00:00 by Simone Marocchi, Andrea Candini, David Klar, Willem Van den Heuvel, Haibei Huang, Filippo Troiani, Valdis Corradini, Roberto Biagi, Valentina De Renzi, Svetlana Klyatskaya, Kurt Kummer, Nicholas B. Brookes, Mario Ruben, Heiko Wende, Umberto del Pennino, Alessandro Soncini, Marco Affronte, Valerio Bellini
We investigate the electronic and magnetic properties of TbPc2 single ion magnets adsorbed on a graphene/Ni(111) substrate, by density functional theory (DFT), ab initio complete active space self-consistent field calculations, and X-ray magnetic circular dichroism (XMCD) experiments. Despite the presence of the graphene decoupling layer, a sizable antiferromagnetic coupling between Tb and Ni is observed in the XMCD experiments. The molecule–surface interaction is rationalized by the DFT analysis and is found to follow a relay-like communication pathway, where the radical spin on the organic Pc ligands mediates the interaction between Tb ion and Ni substrate spins. A model Hamiltonian which explicitly takes into account the presence of the spin radical is then developed, and the different magnetic interactions at play are assessed by first-principle calculations and by comparing the calculated magnetization curves with XMCD data. The relay-like mechanism is at the heart of the process through which the spin information contained in the Tb ion is sensed and exploited in carbon-based molecular spintronics devices.