Ferrites are ferrimagnetic materials, a broad class of magnetic oxides with its remarkable structural, electrical, and magnetic properties making them suitable for a variety of applications. These properties strongly depend upon the method of preparation. Sol-gel method is having countless advantages over other methods to obtain the ferrite with desired nanoarchitecture. In this chapter, the effects of

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CoCr x Fe 2Àx O 4 (0 e x e 1.0) was synthesized by solÀgel auto combustion method using nitrates of respective elements and by keeping 1:3 ratio of metal nitrate to citrate. Representative sample was investigated by thermogravimeter/ differential thermal analyzer (TG/DTA); then, all samples were annealed at 500 °C for 4 h. The broad peaks in the X-ray diffraction patters (XRD) and evaluation of transmission electron microscopy (TEM) indicate a fine particle nature of the particles. Scanning electron microscopy (SEM) analysis and EDAX indicated that the samples were homogeneous and had the expected FeÀCoÀCr ratios. The lattice parameter, bulk density, and particle size are decreased, whereas the X-ray density, specific surface area, and porosity tend to increase with increasing Cr 3+ substitution. Cation distribution was estimated using XRD and by employing Bertaut method. Fourier transform infrared spectroscopy (FT-IR) is employed to determine the local symmetry in crystalline solids and to shed light on the ordering phenomenon. Saturation magnetization determined from vibrating sample magnetometer (VSM) decreases linearly with Cr 3+ concentration, suggesting that the superexchange interaction Fe(A)ÀOÀFe(B) link is stronger than that for the Fe(A)ÀOÀCr(B) link. Coercivity in the Cr-doped cobalt ferrites was larger than that in pure CoFe 2 O 4 compositions.

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