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专业: 金属非晶态、准晶和纳米晶

[交流] 【资源】最新一期nature: 铁磁金属的久保效应

Letter

Nature 458, 1150-1153 (30 April 2009) | doi:10.1038/nature07878;

The Kondo effect in ferromagnetic atomic contacts

M. Reyes Calvo1, Joaquín Fernández-Rossier1, Juan José Palacios1, David Jacob2, Douglas Natelson3 & Carlos Untiedt1

Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk, electronic conduction in these materials takes place mainly through the s and p electrons, whereas the magnetic moments are mostly in the narrow d-electron bands, where they tend to align. This general picture may change at the nanoscale because electrons at the surfaces of materials experience interactions that differ from those in the bulk. Here we show direct evidence for such changes: electronic transport in atomic-scale contacts of pure ferromagnets (iron, cobalt and nickel), despite their strong bulk ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of local magnetic moments by the conduction electrons below a characteristic temperature1. The Kondo effect creates a sharp resonance at the Fermi energy, affecting the electrical properties of the system; this appears as a Fano–Kondo resonance2 in the conductance characteristics as observed in other artificial nanostructures3, 4, 5, 6, 7, 8, 9, 10, 11. The study of hundreds of contacts shows material-dependent log-normal distributions of the resonance width that arise naturally from Kondo theory12. These resonances broaden and disappear with increasing temperature, also as in standard Kondo systems4, 5, 6, 7. Our observations, supported by calculations, imply that coordination changes can significantly modify magnetism at the nanoscale. Therefore, in addition to standard micromagnetic physics, strong electronic correlations along with atomic-scale geometry need to be considered when investigating the magnetic properties of magnetic nanostructures.

http://www.nature.com/nature/jou ... bs/nature07878.html

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