Structural and Magnetic properties of Ultrafine CoFe 2 O 4 Nanoparticles

Nanosized Cobalt ferrite (CoFe 2 O 4 ) particles are prepared through the sol-gel method using polyvinyl alcohol (PVA) as a chelating agent. The powder as prepared is annealed at three different temperatures (400 o C, 500 o C and 1000 o C) for one hour. The X-ray diffraction patterns confirm the spinel structure of the samples. The XRD patterns of the samples indicate broad peaks and the full width at half maximum decreased with increasing annealing temperature. Infrared (IR) spectra of the samples confirm the presence of metal - oxygen complexes within the spinel lattice. The average particle size obtained from TEM micrographs demonstrates ultrafine particles having spherical morphology. The particle size of the annealed samples is in between 4.5-6.8 nm. The saturation magnetization (M s ) and remnant magnetization (M r ) of the samples show dependence on particle size and crystallinity of the samples. The highest saturation magnetization (78.1 emu/g) is achieved for the sample annealed at 1000 0 C having average particle size of 6.8 nm. The high saturation magnetization of the samples suggests the present method is suitable for obtaining nanocrystalline magnetic ferrites which is desirable for practical applications.

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