Abstract
Collective magnetic properties are usually associated with the d or f electrons that carry the individual magnetic moments. A fully spin-polarized ground state based on π electrons has been predicted in half-filled flat-band organic materials, but has remained experimentally challenging to realize. Here we show that isolated tetracyano- p-quinodimethane molecules deposited on graphene epitaxially grown on Ru(0001) acquire charge from the substrate and develop a magnetic moment of 0.4 μB per molecule. The magnetic moment survives even when the molecules form into a dimer or a monolayer, with a value of 0.18 μB per molecule for the monolayer. The self-assembled molecular monolayer develops spatially extended spin-split electronic bands, and we visualized the ground-state spin alignment using spin-polarized scanning tunnelling microscopy. The observation of long-range magnetic order in an organic layer adsorbed on graphene paves the way for incorporating magnetic functionalities into graphene.
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Acknowledgements
Financial support by the Ministerio de Educación y Ciencia through projects CONSOLIDER-INGENIO 2010 on Molecular Nanoscience, FIS2010-18847, FIS2010-15127 and CTQ2010-17006 and Comunidad de Madrid through the programme NANOBIOMAGNET S2009/MAT1726 is gratefully acknowledged. S.B. would like to acknowledge the FPU Grant AP-2007-001157. D.S. and M.G. would like to acknowledge the FPI-UAM programme.
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The experiments were carried out primarily by M.G. and S.B., with important contributions by F.C. The calculations were performed mainly by D.S. with contributions by C.D. and M.A., and F.M. leading the theoretical approach. N.M. selected the specific chemical system. The data analysis was carried out by A.L.V.d.P., who also contributed to the writing of the manuscript. R.M. developed the physical idea and wrote the paper.
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Garnica, M., Stradi, D., Barja, S. et al. Long-range magnetic order in a purely organic 2D layer adsorbed on epitaxial graphene. Nature Phys 9, 368–374 (2013). https://doi.org/10.1038/nphys2610
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DOI: https://doi.org/10.1038/nphys2610
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