Influence of SiO2 matrix and annealing time on properties of Ni-ferrite nanoparticles

Nickel ferrite nanoparticles dispersed in SiO2 matrix have been synthesized by using sol–gel method. Influence of SiO2 concentration and annealing time on properties of nickel ferrite nanoparticles have been studied in detail in order to synthesize small (diameter around 10 nm) nickel ferrite nanoparticles with improved magnetic properties. Structural characterization includes X-ray diffraction (XRD) and transmission electron microscopy (TEM). Magnetic measurements have been done using SQUID-magnetometer. Average particle size decreases with increasing SiO2 matrix concentration, while it shows an increasing trend with increasing annealing time. The decrease of particle size at higher SiO2 concentration is due to large number of nucleation centers which finally restrict the nanoparticle growth. Saturation magnetization shows a decreasing trend with increasing SiO2 matrix concentration, while coercivity behaves oppositely and is attributed to increased number of disordered surface spins in small nanoparticles. Magnetic properties of the small nanoparticles have been improved on increasing annealing time with a corresponding increase in crystallite size. Therefore control over nanoparticle size, nanoparticle distribution, and magnetic properties could be achieved using optimum SiO2 matrix concentration and annealing time.

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