On the exact crystal structure of exchange-biased Fe3O4–CoO nanoaggregates produced by seed-mediated growth in polyol. Issue 21 (6th May 2016)

• Record Type: Journal Article
• Authors: Gaudisson, T.; Sayed-Hassan, R.; Yaacoub, N.; Franceschin, G.; Nowak, S.; Grenèche, J.-M.; Menguy, N.; Sainctavit, Ph.; Ammar, S.
• Is Part Of: CrystEngComm. Volume 18:Issue 21(2016)
• Page Start: 3799
• Page End: 3807
• Publication Date: 2016-05-06
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/c6ce00700g
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : The nucleation and growth mechanism of exchange-biased magnetically contrasted highly crystallized and perfectly epitaxied Fe3 O4 –CoO nanoaggregates was investigated using local probe analysis. Abstract : The nucleation and growth mechanism of exchange-biased magnetically contrasted highly crystallized and perfectly epitaxied Fe3 O4 –CoO nanoaggregates was investigated using local probe analysis, namely 57 Fe 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 Co 2+ cation diffusion into the spinel lattice leading to the formation of Co x Fe3− x O4 core single crystals around which CoO nanocrystals start growing. Conversely, in the in situ route, it is driven by Co 2+ cation reactivity with unreacted dissolved Fe 3+, conducted to the coating of the preformed Fe3 O4 cores by a CoFe2 O4 -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.