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Transition-metal dimers and physical limits on magnetic anisotropy


Recent advances in nanoscience have raised interest in the minimum bit size required for classical information storage. This bit size is determined by the necessity for bistability with suppressed quantum tunnelling and energy barriers that exceed ambient temperatures. In the case of magnetic information storage, much attention has centred on molecular magnets1 with bits consisting of about 100 atoms, magnetic uniaxial anisotropy energy barriers of about 50 K and very slow relaxation at low temperatures. Here, we draw attention to the remarkable magnetic properties of some transition-metal dimers, which have energy barriers approaching 500 K with only two atoms. The spin dynamics of these ultrasmall nanomagnets is strongly affected by a Berry phase, which arises from quasi-degeneracies at the electronic highest occupied molecular orbital energy. In a giant-spin approximation, this Berry phase makes the effective reversal barrier thicker.

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Figure 1: Electronic molecular orbital diagrams and plots of magnetic anisotropies with associated Berry curvature.


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We would like to thank D. Bishop, W. de Heer and J. Keto for helpful discussions. This work was supported in part by the Welch Foundation, the National Science Foundation under grant DMR-0606489, the Faculty of Natural Sciences at Kalmar University, the Swedish Research Council under Grant No. 621-2004-4439 and by the Office of Naval Research.

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Correspondence to Tor O. Strandberg.

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Strandberg, T., Canali, C. & MacDonald, A. Transition-metal dimers and physical limits on magnetic anisotropy. Nature Mater 6, 648–651 (2007).

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