Quantum tunnelling of the magnetization in a monolayer of oriented single-molecule magnets

Abstract

A fundamental step towards atomic- or molecular-scale spintronic devices has recently been made by demonstrating that the spin of an individual atom deposited on a surface1, or of a small paramagnetic molecule embedded in a nanojunction2, can be externally controlled. An appealing next step is the extension of such a capability to the field of information storage, by taking advantage of the magnetic bistability and rich quantum behaviour of single-molecule magnets3,4,5,6 (SMMs). Recently, a proof of concept that the magnetic memory effect is retained when SMMs are chemically anchored to a metallic surface7 was provided. However, control of the nanoscale organization of these complex systems is required for SMMs to be integrated into molecular spintronic devices8,9. Here we show that a preferential orientation of Fe4 complexes on a gold surface can be achieved by chemical tailoring. As a result, the most striking quantum feature of SMMs—their stepped hysteresis loop, which results from resonant quantum tunnelling of the magnetization5,6—can be clearly detected using synchrotron-based spectroscopic techniques. With the aid of multiple theoretical approaches, we relate the angular dependence of the quantum tunnelling resonances to the adsorption geometry, and demonstrate that molecules predominantly lie with their easy axes close to the surface normal. Our findings prove that the quantum spin dynamics can be observed in SMMs chemically grafted to surfaces, and offer a tool to reveal the organization of matter at the nanoscale.

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Figure 1: Structure of Fe 4 clusters.
Figure 2: X-ray absorption and dichroic spectra.
Figure 3: Periodic DFT-optimized structure of a Fe 4 C 5 cluster on an unreconstructed Au(111) surface.
Figure 4: Magnetic hysteresis loops.

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Acknowledgements

We acknowledge D. Gatteschi and J. Villain for discussions. F. Scheurer, J. P. Kappler, B. Muller, F. Nolting and N. Brookes are acknowledged for their contribution to the development of the synchrotron experimental set-ups used in this work. This work is based on experiments performed at the Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland, and the European Synchrotron Radiation Facility, Grenoble, France. The research leading to these results received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 226716, through the projects MolSpinQIP (FP7-ICT-2007-C-211284) and ERANET ‘NanoSci-ERA: Nanoscience in European Research Area’, from the Italian CNR, through the Commessa PM.P05.012, from the Italian MIUR, through the project PRIN 2008, and from Ente CRF. DFT calculations were carried out within the DEISA Extreme Computing Initiative projects AMNOS and QUNA.

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R.S., A.C. and M.M. designed the project; C.D. and A.C. synthesized the SMMs; L.S., A.C., F.P. and R.S. carried out the bulk magnetic characterization and analyses; M.M. and F.P. prepared the monolayers and performed the STM characterization and analysis; M.M., F.P., Ph.S., E.O., L.J., J.C.C. and R.S. performed the XMCD and XNLD experiments; F.T. performed the DFT calculations; Ph.S. and M.-A.A. performed the LFM calculations; and R.S. simulated the hysteresis curves.

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Correspondence to R. Sessoli.

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The authors declare no competing financial interests.

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Mannini, M., Pineider, F., Danieli, C. et al. Quantum tunnelling of the magnetization in a monolayer of oriented single-molecule magnets. Nature 468, 417–421 (2010). https://doi.org/10.1038/nature09478

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