Preparation and characterization of nanosize nickel-substituted cobalt ferrites (Co1-xNixFe2O4)

Nanosize nickel-substituted cobalt ferrites were prepared using aerosol route and characterized by TEM, XRD, magnetic and Mossbauer spectroscopy. The particle size of as obtained samples was found to be similar to 10 nm which increases upto similar to 80 nm on annealing at 1200 degrees C. The unit cell parameter 'a' decreases linearly with the nickel concentration due to smaller ionic radius of nickel. The saturation magnetization for all the samples after annealing at 1200 degrees C lies in the range 47.6-84.5 emu/g. Room temperature Mossbauer spectra of as obtained samples exhibit a broad doublet, suggesting super paramagnetic nature of the sample. The broad doublet is further resolved into two doublets corresponding to the iron atoms residing at the surface and internal regions of the particle. The samples annealed at 1200 C showed broad sextet, which is resolved into two sextets, corresponding to tetrahedrally and octahedrally coordinated Fe cations. Cation distribution calculated using XRD and Mossbauer data indicates a decrease in Fe3+(oct.)/Fe3+(tet.) ratio with increasing nickel concentration. (c) 2005 Elsevier Inc. All rights reserved.