Suchergebnisse

Turning graphene magnetic is a promising challenge to make it an active material for spintronics. Predictions state that graphene structures with specific shapes can spontaneously develop magnetism driven by Coulomb repulsion of π-electrons, but its experimental verification is demanding. Here, we report on the observation and manipulation of individual magnetic moments in graphene open-shell nanostructures on a gold surface. Using scanning tunneling spectroscopy, we detect the presence of single electron spins localized around certain zigzag sites of the carbon backbone via the Kondo effect. We find near-by spins coupled into a singlet ground state and quantify their exchange interaction via singlet-triplet inelastic electron excitations. Theoretical simulations picture how electron correlations result in spin-polarized radical states with the experimentally observed spatial distributions. Extra hydrogen atoms bound to radical sites quench their magnetic moment and switch the spin of the nanostructure in half-integer amounts. Our work demonstrates the intrinsic π-paramagnetism of graphene nanostructures ; We acknowledge financial support from Spanish AEI (MAT2016-78293-C6, FIS2017-83780-P, and the Maria de Maeztu Units of Excellence Program MDM-2016-0618), the Basque Government (Department of Education, Grant PI-2015-1-42), the EU project PAMS (610446), the Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016-2019, ED431G/09), and the European Regional Development Fund (ERDF) ; SI

We report on the construction and magnetic characterization of a fully functional hybrid molecular system composed of a single magnetic porphyrin molecule bonded to graphene nanoribbons with atomically precise contacts. We use on-surface synthesis to direct the hybrid creation by combining two molecular precursors on a gold surface. High-resolution imaging with a scanning tunneling microscope finds that the porphyrin core fuses into the graphene nanoribbons through the formation of new carbon rings at chemically predefined positions. These ensure the stability of the hybrid and the extension of the conjugated character of the ribbon into the molecule. By means of inelastic tunneling spectroscopy, we prove the survival of the magnetic functionality of the contacted porphyrin. The molecular spin appears unaffected by the graphenoid electrodes, and we simply observe that the magnetic anisotropy appears modified depending on the precise structure of the contacts. ; We acknowledge the financial support from Spanish Agencia Estatal de Investigación (AEI) (project nos. MAT2016-78293-C6 and FIS2015-62538-ERC, and the Maria de Maeztu Units of Excellence Programme MDM-2016-0618), the Basque Government (Department Industry, grant no. PI-2015-1-42), the European project PAMS (610446), the Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016 to 2019, ED431G/09), the European Research Council (grant agreement no. 635919), and the European Regional Development Fund ; SI

Scattering of electrons by localized spins is the ultimate process enabling detection and control of the magnetic state of a spin-doped material. At the molecular scale, scattering is mediated by the orbitals hosting the spin. Here we report the selective excitation of a molecular spin by tunneling through different molecular orbitals. Spatially resolved tunneling spectra on iron-porphyrins reveal that the inelastic spin excitation extends beyond the iron site, changing shape and symmetry along the molecule. Combining density functional theory simulations with a phenomenological scattering model, we show that the extension and lineshape of the inelastic signal are due to excitation pathways assisted by different frontier orbitals. By selecting the intramolecular site for electron injection, the relative weight of iron and pyrrole orbitals in the tunneling process is modified. Thus, the excitation mechanism, reflected by its spectral lineshape, depends on the degree of localization and energy alignment of the chosen molecular orbital. ; This work has been funded by the COST 15128 Molecular Spintronics project, by Marie Curie IF ARTE, by the Spanish Ministerio de Economía y Competitividad (MINECO) through the cooperative grant No. MAT2016-78293 and grant No. FIS2016-75862-P, and by the Basque Government (Dep. Industry, Grant PI-2015-1-42, Dep. Education, Grant PI-2016-1-27 and Grant IT-756-13), the EU project PAMS (610446), and the European Regional Development Fund (ERDF).