Enhanced Coercivity in Co-Rich Near-Stoichiometric CoxFe3-xO4+δ Nanoparticles Prepared in Large Batches

http://pubs.acs.org/doi/abs/10.1021/cm070827t

Chem. Mater., 2007, 19 (20), pp 4957–4963
German Salazar-Alvarez, Richard T. Olsson, Jordi Sort, Waldemar A. A. Macedo, José D. Ardisson, Maria Dolors Baró, Ulf W. Gedde, and Josep Nogués

DOI: 10.1021/cm070827t

Abstract:
The relationship between the structure and composition with the magnetic properties of near stoichiometric cobalt ferrite nanoparticles Co_xFe_3-xO_4+δ (0.85 < x < 1.1) prepared in large batches with average sizes in the range 60−210 nm has been investigated. Chemical analysis and Rietveld refinement of the X-ray diffraction data in conjunction with Mössbauer spectroscopy allowed us to identify an interplay between particle size, microstructure (concentration of interstitial ions, microstrain, cation arrangement in octahedral and tetrahedral sites), and composition, which sensitively controls the magnetic properties such as coercivity and saturation magnetization. In all cases, cobalt-rich compositions resulted in a higher coercivity, whereas lower degrees of inversion and higher iron contents led to slightly higher saturation magnetization values.