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Control of single-spin magnetic anisotropy by exchange coupling

Nature Nanotechnology volume 9, pages 64–68 (2014)Cite this article

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Abstract

The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be affected strongly by this interaction. Although this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation1, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons2 in water molecules in a host's tissue3. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data-storage devices4, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magnetic anisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be renormalized controllably. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be tuned electronically. These effects may play a significant role in the development of spintronic devices5 in which an individual magnetic atom or molecule is coupled to conducting leads.

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Figure 1: Spectroscopy of Co on a large (18.6 × 20.5 nm2) Cu2N island.
Figure 2: Generalized Anderson model of the Co electrons coupled to a bath of conduction electrons.
Figure 3: Magnetic-field dependence of differential conductance spectra of Co on 18.6 × 20.5 nm2 Cu2N island.

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Acknowledgements

We acknowledge B. E. M. Bryant, A. J. Fisher, K. J. Franke, A. J. Heinrich, M. Hybertsen, S. Loth and A. F. Otte for discussions and B. E. M. Bryant for support during the experiments. J.F-R. acknowledges the hospitality of the Max-Planck-Institut für Mikrostrukturphysik Halle. Also, J.F-R. is on leave from Departamento de Física Aplicada, Universidad de Alicante, Spain. This work was supported by the Engineering and Physical Sciences Research Council, UK (EP/D063604/1 and EP/H002022/1), Ministry of Science and Education Spain (FIS2010-21883-C02-01, MAT2010-19236, CONSOLIDER CSD2007-0010 and Programa de Movilidad Postdoctoral), European Commission FP7 Programme (PER-GA-2009-251791) and GV grant Prometeo 2012-11.

Author information

Author notes

  1. M. Reyes Calvo

    Present address: Present address: Department of Physics, Stanford University, Stanford, California 94305, USA,

  2. Jenny C. Oberg and M. Reyes Calvo: These authors contributed equally to this work

Authors and Affiliations

  1. London Centre for Nanotechnology, University College London, London, WC1H 0AH, UK

    Jenny C. Oberg, M. Reyes Calvo & Cyrus F. Hirjibehedin

  2. Department of Physics and Astronomy, University College London, London, WC1E 6BT, UK

    Jenny C. Oberg & Cyrus F. Hirjibehedin

  3. International Iberian Nanotechnology Laboratory, Braga, 4715-330, Portugal

    Fernando Delgado & Joaquín Fernández-Rossier

  4. Instituto de Nanociencia de Aragón and Laboratorio de Microscopías Avanzadas, Universidad de Zaragoza, Zaragoza, 50018, Spain

    María Moro-Lagares & David Serrate

  5. Departamento de Física de la Materia Condensada, Universidad de Zaragoza, Zaragoza, 50009, Spain

    María Moro-Lagares & David Serrate

  6. Max-Planck-Institut für Mikrostrukturphysik, Halle, 06120, Germany

    David Jacob

  7. Department of Chemistry, University College London, London, WC1H 0AJ, UK

    Cyrus F. Hirjibehedin

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Contributions

J.C.O, M.R.C. and C.F.H. conceived the experiments. J.C.O. and M.R.C. performed the primary experiments and the data analysis, supervised by C.F.H. Additional experiments were performed by J.C.O. with the assistance of M.M. and supervised by D.S. and C.F.H. F.D. performed the perturbative calculations of exchange-induced modification of magnetic anisotropy, as proposed by J.F-R. D.J. implemented and performed the Anderson model calculations in the OCA as proposed by J.F-R. All authors discussed the results and participated in writing the manuscript.

Corresponding author

Correspondence to Cyrus F. Hirjibehedin.

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The authors declare no competing financial interests.

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Oberg, J., Calvo, M., Delgado, F. et al. Control of single-spin magnetic anisotropy by exchange coupling. Nature Nanotech 9, 64–68 (2014). https://doi.org/10.1038/nnano.2013.264

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