Abstract
The magnetic properties of the ground state of a low-density free-electron gas in three dimensions have been the subject of theoretical speculation and controversy for seven decades1. Not only is this a difficult theoretical problem to solve, it is also a problem which has not hitherto been directly addressed experimentally. Here we report measurements on electron-doped calcium hexaboride (CaB6) which, we argue, show that—at a density of 7× 1019 electrons cm−3—the ground state is ferromagnetically polarized with a saturation moment of 0.07 µB per electron. Surprisingly, the magnetic ordering temperature of this itinerant ferromagnet is 600 K, of the order of the Fermi temperature of the electron gas.
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Acknowledgements
Z.F. thanks E. Abrahams, G. Aeppli, L. Gor'kov, P. Kumar, E. Manousakis, G. Ortiz and D. Pines for discussions. Work at NHMFL was supported by the NSF; work at Los Alamos was done under the auspices of the US Department of Energy; and the work at ETH Zürich was supported by the Schweizerische Nationalfonds zur Förderung der wissenschaftlichen Forschung.
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Young, D., Hall, D., Torelli, M. et al. High-temperature weak ferromagnetism in a low-density free-electron gas. Nature 397, 412–414 (1999). https://doi.org/10.1038/17081
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DOI: https://doi.org/10.1038/17081
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