Mixing of discretized states in quantum magnets has a radical impact on their properties. Managing this effect is key for spintronics in the quantum limit. Magnetic fields can modify state mixing and, for example, mitigate destabilizing effects in single-molecule magnets1,2. The exchange bias field3,4 has been proposed as a mechanism for localized control of individual nanomagnets5,6. Here, we demonstrate that exchange coupling with the magnetic tip of a scanning tunnelling microscope provides continuous tuning of spin state mixing in an individual nanomagnet. By directly measuring spin relaxation time with electronic pump–probe spectroscopy7, we find that the exchange interaction acts analogously to a local magnetic field that can be applied to a specific atom. It can be tuned in strength by up to several tesla and cancel external magnetic fields, thereby demonstrating the feasibility of complete control over individual quantum magnets with atomically localized exchange coupling.
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The authors thank S. Heinze, C. Hübner and D. Pfannkuche for discussions, and E. Weckert and H. Dosch (Deutsches Elektronen-Synchrotron) for providing laboratory space. D.J.C. and J.A.J.B. acknowledge postdoctoral fellowships from the Alexander von Humboldt Foundation. J.A.J.B. acknowledges support from the Natural Sciences and Engineering Research Council of Canada.
The authors declare no competing financial interests.
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Yan, S., Choi, DJ., Burgess, J. et al. Control of quantum magnets by atomic exchange bias. Nature Nanotech 10, 40–45 (2015). https://doi.org/10.1038/nnano.2014.281
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