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Exchange bias and room-temperature magnetic order in molecular layers

Abstract

Molecular semiconductors may exhibit antiferromagnetic correlations well below room temperature1,2,3. Although inorganic antiferromagnetic layers may exchange bias4 single-molecule magnets5, the reciprocal effect of an antiferromagnetic molecular layer magnetically pinning an inorganic ferromagnetic layer through exchange bias has so far not been observed. We report on the magnetic interplay, extending beyond the interface, between a cobalt ferromagnetic layer and a paramagnetic organic manganese phthalocyanine (MnPc) layer. These ferromagnetic/organic interfaces are called spinterfaces because spin polarization arises on them6,7,8. The robust magnetism of the Co/MnPc spinterface6,9 stabilizes antiferromagnetic ordering at room temperature within subsequent MnPc monolayers away from the interface. The inferred magnetic coupling strength is much larger than that found in similar bulk10,11, thin1 or ultrathin2 systems. In addition, at lower temperature, the antiferromagnetic MnPc layer induces an exchange bias on the Co film, which is magnetically pinned. These findings create new routes towards designing organic spintronic devices.

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Figure 1: FM coupling of the first-ML MnPc onto Co.
Figure 2: Antiferromagnetic ordering of the MnPc molecules.
Figure 3: Adsorption geometry and magnetic properties of the MnPc stacking on Co deduced from DFT calculations.
Figure 4: Exchange bias induced by MnPc.

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Acknowledgements

We thank B. Muller, A. Boulard, B. Leconte and C. Kieber for technical assistance. We thank D. Lacour and Y. Henry for scientific insight. We thank P. Rengasamy, G. Schmerber and C. Ulhaq for auxiliary measurements. We acknowledge funding from the Franco-German University and the Baden-Württemberg Stiftung in the framework of the Kompetenznetz für Funktionale Nanostrukturen (KFN), from the Alexander von Humboldt foundation, from the Institut Carnot MICA’s ‘Spinterface’ grant, from the Agence Nationale de la Recherche ANR-09-JCJC-0137 and ANR-11-LABX-0058 NIE and from the International Center for Frontier Research in Chemistry. The MBE chamber used during our beamtime on DEIMOS was funded by the Agence National de la Recherche; grant ANR-05-NANO-073. This work was performed using HPC resources from the Strasbourg Mesocenter and from GENCI-CINES Grant 2014-gem1100.

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M.G., S.B., E.B. and M.B. conceived and designed the experiments. J.A. purified the molecules. M.G., L.J., V.D.C., S.B., M.S., H.I., M.P., H.J., V.D.C., F.S., W.Weber, E.B. and M.B. carried out XAS measurements. M.G., S.B., M.B., V.D.C., U.H., W.Weber and E.B. carried out MOKE experiments. H.I., J.C. and W.Wulfhekel performed STM experiments. M.G. analysed the data. F.I. and M.A. performed the ab initio study. F.C., E.O., K.C. and P.O. performed control experiments. M.G., M.B. and E.B. co-wrote the paper. All the authors discussed the results and commented on the manuscript.

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Correspondence to Manuel Gruber, Eric Beaurepaire or Martin Bowen.

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The authors declare no competing financial interests.

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Gruber, M., Ibrahim, F., Boukari, S. et al. Exchange bias and room-temperature magnetic order in molecular layers. Nature Mater 14, 981–984 (2015). https://doi.org/10.1038/nmat4361

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