Mössbauer and magnetic study of Co x Fe3--x O4 nanoparticles

• Published in: Hyperfine interactions 2005-09, Vol.165 (1-4), p.61-67
• Main Authors: Estournès, C., D’Orléans, C., Rehspringer, J.-L., Manova, E., Kunev, B., Paneva, D., Mitov, I., Petrov, L., Kurmoo, M.
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Material chemistry
• ISSN: 0304-3843; 1572-9540
• DOI: 10.1007/s10751-006-9248-y

Magnetic nanoparticles of cobalt ferrites Co x Fe3−x O4 (x = 1 or 2) have been obtained either by mechanical milling or thermal treatment of pre-prepared layered double hydroxide carbonate x-LDH–CO3. Mechanical milling of the 1-LDH–CO3 leads to the large-scale preparation of nearly spherical nanoparticles of CoFe2O4, the size of which (5 to 20 nm) is controlled by the treatment time. Core-shell structure with surface spin-canting has been considered for the nanoparticles formed to explain the observed hysteresis loop shift (from ZFC–FC) in the magnetic properties. Annealing treatment of the 2-LDH–CO3 below 673 K results in the formation of nearly spherical pure Co2FeO4 nanoparticles. At 673 K and above, the LDH decomposition leads to the formation of a mixture of both spinels phases Co2FeO4 and CoFe2O4, the amount of the latter increases with annealing temperature. Unusually high magnetic hardness characterized by a 22 kOe coercive field at 1.8 K has been observed, which reflects the high intrinsic anisotropy for Co2FeO4.