Journal
NATURE NANOTECHNOLOGY
Volume 4, Issue 10, Pages 681-687Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/nnano.2009.221
Keywords
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Funding
- US National Science Foundation [CHE 0628252-CRC, DGE-0504573]
- Gaussian Inc
- Dreyfus Foundation
- University of Washington
- Swiss National Science Foundation [PBBE2-115064]
- Center for Ecogenetics and Environmental Health UW Center [P30 ES07033]
- National Institutes of Environmental Health Sciences, NIH
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Electrical control over the magnetic states of doped semiconductor nanostructures could enable new spin-based information processing technologies. To this end, extensive research has recently been devoted to examination of carrier-mediated magnetic ordering effects in substrate-supported quantum dots at cryogenic temperatures, with carriers introduced transiently by photon absorption. The relatively weak interactions found between dopants and charge carriers have suggested that gated magnetism in quantum dots will be limited to cryogenic temperatures. Here, we report the observation of a large, reversible, room-temperature magnetic response to charge state in free-standing colloidal ZnO nanocrystals doped with Mn2+ ions. Injected electrons activate new ferromagnetic Mn2+-Mn2+ Interactions that are strong enough to overcome antiferromagnetic coupling between nearest-neighbour dopants, making the full magnetic moments of all dopants observable. Analysis shows that this large effect occurs in spite of small pairwise electron-Mn2+ exchange energies, because of competing electron-mediated ferromagnetic interactions involving distant Mn2+ ions in the same nanocrystal.
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