Enhanced Coercivity in Co-Rich Near-Stoichiometric Co_xFe_3-xO_4+δ Nanoparticles Prepared in Large Batches

The relationship between the structure and composition with the magnetic properties of near stoichiometric cobalt ferrite nanoparticles Co x Fe 3 - x O 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.