The effect of Co substitution on the structural and magnetic properties of lithium ferrite synthesized by an autocombustion method

Nanoparticles of Li0.5 - 0.5xCoxFe2.5 - 0.5xO4 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) were synthesized by the solution combustion method. The influence of Co substitution on the structural, morphological and magnetic properties of the prepared samples was studied. The XRD studies confirm the formation of single phase cubic spinet structure of the ferrite samples. Their lattice constants vary linearly from 8.31 angstrom (x-0) to 8.35 angstrom (x=0.6) with increasing Co2+ content, due to the ionic volume differences of Co2+, Fe3+ and Li1+ ions. Also, the bond lengths and site radii of octahedral and tetrahedral sites are found to increase linearly with Co2+ content. The crystallite sizes of all the prepared samples estimated from the full width half maximum (FWHM) of the strongest reflection of the planes (311) almost remain constant with the increase of Co2+ content. The surface morphology of the prepared ferrite samples show that some of the particles have a cubic and the others have a spherical shape. The average particle sizes of the samples obtained from SEM micrographs show an initial increase up to the sample of x=0.3 and then it decreases slightly. The magnetic properties of the samples have been studied by measuring M-H plots. Moreover, the saturation magnetization, remnant magnetization, and coercivity of the prepared samples increase up to the sample of x=0.3 (140.1 emu/g, 49.4 emu/g and 714.05 Oe, respectively) and then they decrease again. The variation in the experimental magnetic moment mu(B) (exp) with Co2+ content is explained on the basis of Neel's two sub-lattice model. Furthermore, the initial permeability of the prepared samples increases with increasing Co2+ content up to the sample of x=0.3 and then a slight decrease is observed again. (C) 2015 Elsevier B.V. All rights reserved