Enhanced magnetic coercivity of α-Fe2O3 obtained from carbonated 2-line ferrihydrite
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We report the physical properties of α-Fe2O3 (hematite), synthesized by dry-heating (350–1,000 °C) of a new, poorly ordered iron oxyhydroxide precursor compound that we name carbonated 2-line ferrihydrite. This precursor was characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, electron microscopy, and thermogravimetric analysis, whereas the α-Fe2O3 was studied with X-ray diffraction, scanning and transmission electron microscopy, and magnetic techniques. α-Fe2O3 synthesized at 350 °C consisted of single-nanocrystal particles (length × width 20 ± 6 nm (L) × 15 ± 4 nm (W)), which at room temperature exhibited very narrow hysteresis loops of low coercivities (<300 Oe). However, α-Fe2O3 synthesized at higher temperatures (1,000 °C) was composed of larger nanocrystalline particle aggregates (352 ± 109 nm (L) × 277 ± 103 nm (W)) that also showed wide-open hysteresis loops of high magnetic coercivities (~5 kOe). We suggest that these synthesis-temperature-dependent coercivity values are a consequence of the subparticle structure induced by the different particle and crystallite size growth rates at increasing annealing temperature.
KeywordsHematite Ferrihydrite High coercivity Carbonate Microstructure
This research was supported by the Spanish Ministry of Economy and Competitivity (MICINN-12-MAT2011-27573-C04-02) and the Marie Curie EU-FP6 MINGRO Research and Training Network under contract MRTNCT-2006-035488. The authors would like to thank the Cohen Laboratories at the School of Earth and Environment and the Leeds Electron Microscopy and Spectroscopy Centre (LEMAS) at the Faculty of Engineering (University of Leeds). The help of David Martínez Blanco (Scientific-Technical Services of the University of Oviedo, Spain) with the magnetic measurements is also acknowledged.
- Coelho AA (2003) TOPAS: General profile and structure analysis software for powder diffraction dataGoogle Scholar
- Farmer VC (1974) The infrared spectra of minerals. Mineralogical society monograph, vol 4. Mineralogical Society of Great Britain & Ireland, TwickenhamGoogle Scholar
- Galwey AK, Brown ME (1999) Decomposition of carbonates. Thermal decomposition of ionic solids. Elsevier B.V. Ed, In, pp 345–364Google Scholar
- Lu BL, Xu XY, Wu D, Sun YH (2008) Preparation and characterization of porous alpha-Fe2O3 nanodisks. Chin J Inorg Chem 24:1690–1694Google Scholar
- Michel FM, Barrón V, Torrent J, Morales MP, Serna CJ, Boily JF, Liu Q, Ambrosini A, Cismasu AC, Brown GE Jr (2010) Ordered ferrimagnetic form of ferrihydrite reveals links among structure, composition, and magnetism. P Natl Acad Sci USA 107:2787–2792. doi: 10.1073/pnas.0910170107 CrossRefGoogle Scholar
- Scherrer P (1918) Estimation of the size and internal structure of colloidal particles by means of röntgen. Nachr Ges Wiss Götingen Math-Pys Kl 2:96–100Google Scholar