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Issue 21, 2016
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On the exact crystal structure of exchange-biased Fe3O4–CoO nanoaggregates produced by seed-mediated growth in polyol

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Abstract

The nucleation and growth mechanism of exchange-biased magnetically contrasted highly crystallized and perfectly epitaxied Fe3O4–CoO nanoaggregates was investigated using local probe analysis, namely 57Fe Mössbauer and L2,3 Co XMCD spectroscopies, and advanced magnetometry. The granular nanocomposites were produced by a two-step chemical route. Spinel iron oxide nanoparticles were first synthesised by forced hydrolysis of iron acetate in a polyol and then used as seeds for rock-salt cobalt monoxide nanocrystalline growth. In one case, this crystallochemical step is carried out by separating the seeds, washing and drying them before mixing them in a fresh polyol solution of cobalt precursors. In another case, it is conducted by introducing, directly in the seed reaction solution, the cobalt precursors in the same Fe/Co nominal atomic ratio. It appears that the composite formation proceeds differently in the two cases. It is driven, in the ex situ route, by Co2+ cation diffusion into the spinel lattice leading to the formation of CoxFe3−xO4 core single crystals around which CoO nanocrystals start growing. Conversely, in the in situ route, it is driven by Co2+ cation reactivity with unreacted dissolved Fe3+, conducted to the coating of the preformed Fe3O4 cores by a CoFe2O4-like thin interlayer, itself decorated by outer CoO nanocrystals. These reaction schemes are well confirmed by magnetometry experiments. The low-temperature magnetic properties of the produced composites are consistent with the establishment of an exchange-bias feature into hard-magnet@antiferromagnet and soft-magnet@hard-magnet@antiferromagnet structures, respectively.

Graphical abstract: On the exact crystal structure of exchange-biased Fe3O4–CoO nanoaggregates produced by seed-mediated growth in polyol

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Publication details

The article was received on 29 Mar 2016, accepted on 19 Apr 2016 and first published on 19 Apr 2016


Article type: Paper
DOI: 10.1039/C6CE00700G
Citation: CrystEngComm, 2016,18, 3799-3807

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    On the exact crystal structure of exchange-biased Fe3O4–CoO nanoaggregates produced by seed-mediated growth in polyol

    T. Gaudisson, R. Sayed-Hassan, N. Yaacoub, G. Franceschin, S. Nowak, J.-M. Grenèche, N. Menguy, Ph. Sainctavit and S. Ammar, CrystEngComm, 2016, 18, 3799
    DOI: 10.1039/C6CE00700G

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