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Issue 5, 2009
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Nanocrystalline Co30Fe70 alloy synthesized by alkalide reduction

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Abstract

Co30Fe70 nanocrystallites have been synthesized by alkalide co-reduction of Co2+ and Fe3+. As produced, the material consists of highly pyrophoric 4.0 nm nanocrystals with a narrow (<12%) size distribution, that are superparamagnetic with an average blocking temperature <TB> of ∼20 K prior to removal of the by-products in which they are embedded. Removal of the by-products allows magnetic interactions between the particles with a consequent increase in the transition temperature to greater than 300 K. Annealing at temperatures higher than 300 °C under vacuum resulted in agglomeration and particle growth; annealing above 500 °C resulted in a change in the shape of the particles to largely rectangular prisms with little further growth above 700 °C. Ms increased with increasing annealing temperature reaching values as large as ∼89% of the bulk value (245 emu/g) after annealing at 700 °C while retaining low Mr and Hc. While rapid exposure of the Co30Fe70 nanocrystallites to air resulted in spontaneous combustion, gradual, slow exposure over a period of one week resulted in the formation of a thin surface coating of CoFe2O4, or air stable “core-shell” alloy–oxide nanocrystallites.

Graphical abstract: Nanocrystalline Co30Fe70 alloy synthesized by alkalide reduction

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Publication details

The article was received on 09 Sep 2008, accepted on 30 Oct 2008 and first published on 10 Dec 2008


Article type: Paper
DOI: 10.1039/B815751K
Citation: J. Mater. Chem., 2009,19, 611-616
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    Nanocrystalline Co30Fe70 alloy synthesized by alkalide reduction

    K. E. Mooney and M. J. Wagner, J. Mater. Chem., 2009, 19, 611
    DOI: 10.1039/B815751K

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