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Tunable doping of a metal with molecular spins


The mutual interaction of localized magnetic moments and their interplay with itinerant conduction electrons in a solid are central to many phenomena in condensed-matter physics, including magnetic ordering and related many-body phenomena such as the Kondo effect1, the Ruderman–Kittel–Kasuya–Yoshida interaction2 and carrier-induced ferromagnetism in diluted magnetic semiconductors3. The strength and relative importance of these spin phenomena are determined by the magnitude and sign of the exchange interaction between the localized magnetic moments and also by the mean distance between them. Detailed studies of such systems require the ability to tune the mean distance between the localized magnetic moments, which is equivalent to being able to control the concentration of magnetic impurities in the host material. Here, we present a method for doping a gold film with localized magnetic moments that involves depositing a monolayer of a metal terpyridine complex onto the film. The metal ions in the complexes can be cobalt or zinc, and the concentration of magnetic impurities in the gold film can be controlled by varying the relative amounts of cobalt complexes (which carry a spin) and zinc complexes (which have zero spin). Kondo and weak localization measurements demonstrate that the magnetic impurity concentration can be systematically varied up to 800 ppm without any sign of inter-impurity interaction. Moreover, we find no evidence for the unwanted clustering that is often produced when using alternative methods.

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Figure 1: The Kondo effect for different concentrations of impurities.
Figure 2: Tunable molecular spin doping.
Figure 3: Magnetoresistance and weak localization.

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The authors thank W.J.M. Naber, R.M.J. van Damme, A. Brinkman, C.A. Nijhuis and C. Bäuerle for discussions. We acknowledge financial support from the ERC (grant no. 240433), the NWO VIDI programme (grant nos 07580 and 10246) and the NWO-CW ECHO programme (grant no. 700.55.029).

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Authors and Affiliations



T.G., D.A. and S.K.B. carried out the experiments, fabricated the devices and performed the data analysis. M.D.Y. synthesized the organometallic complexes and prepared the monolayers. E.S. assisted with data analysis. W.G.v.d.W. conceived the experiments, and planned and supervised the project. J.H. supervised the chemical synthesis. A.H.V. supervised the synthesis and characterization of the molecules. M.P.d.J. contributed to planning and supervision. All authors discussed the results, provided important insights and helped with the writing of the manuscript.

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Correspondence to J. Huskens or W. G. van der Wiel.

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The authors declare no competing financial interests.

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Gang, T., Yilmaz, M., Ataç, D. et al. Tunable doping of a metal with molecular spins. Nature Nanotech 7, 232–236 (2012).

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