Structural, magnetic and Mossbauer spectral studies of nanosize aluminum substituted nickel zinc ferrites

Nanosize aluminum substituted nickel zinc ferrites were prepared through aerosol route and characterized using TEM, XRD, magnetic measurements and Mossbauer spectroscopy. The particle size of as obtained samples was found to be similar to 10 nm which increases up to similar to 85 nm upon annealing at 1200 degrees C. The unit cell parameter 'a' decreases linearly with concentration of aluminum due to the small ionic radius of aluminum. The saturation magnetization for all the samples after annealing at 1200 degrees C lies in the range 12.9-72.6 emu/g and decreases linearly with concentration of aluminum. Room temperature Mossbauer spectra of all as obtained samples of ferrite compositions exhibited a broad doublet suggesting super paramagnetic nature. This doublet is further resolved into two doublets and assigned to the surface region and internal region atoms of the particles. The samples annealed at 1200 degrees C show broad sextets, which were fitted with five sextets, indicating different local environment of both tetrahedrally and octahedrally coordinated Fe cation. (C) 2005 Elsevier B.V. All rights reserved.