Recently magnetic nanoparticles due to exclusive and useful characteristics have been used in different fields. There are different synthesis techniques proportional to the researcher’s purpose. In this study we choosed sol-gel auto-combustion method because of high homogeneity and purity of particles and ability to work in rather low temperatures. This study consist of three parts. In the first part we have investigated the effect of Zn on the structural and magnetic properties of cobalt ferrite nanoparticles in the form of Co 1-x Zn x Fe 2 O 4 (x=0, 0.1, 0.3, 0.5, 0.7). In the second part the effect of sintering temperature at 350 and 1000 o C and then in the third part the effect of Polyvinylpyrolidone (PVP) coating on structural and magnetic properties of Co 0.3 Zn 0.7 Fe 2 O 4 ferrite nanoparticles annealed at 350 o C have been studied using analysis such as XRD, FTIR, FE-SEM, TEM, VSM and ac susceptibility. The XRD patterns of the samples annealed at 350 o C indicated irregular behavior in lattice constant changes. This irregular behavior is attributed to the cation distribution among spinel sites. The lattice constant of the samples annealed at 1000 o C indicated a regular linear behavior that can be attributed to the redistribution of cations. The VSM of 350 o C sintered nanoparticles showed that by increasing Zn doping level the magnetization and coercivity decrease. Magnetization decreases due to the reduction of octahedral sites’ magnetization and the increase of the magnetization of tetrahedral sits. But in nanoparticles which was annealed at 1000 o C, by increasing Zn doping level up to x=0.3, the magnetization increased and it decreased by further increase in x. The increase of magnetization for x 0.3 is due to the increase of octahedral and the decrease of tetrahedral sites’ magnetization. On the other hand the magnetization’s reduction after x=0.3 due to the weakening of the superexchange interaction at the octahedral sites. XRD patterns of PVP coated Co 0.3 Zn 0.7 Fe 2 O 4 nanoparticles indicated no change in structural phase of nanoparticles and after coating the crystallite size decreased. Magnetic measurements indicated that with increasing the content of PVP, magnetization decreased due to the reduction of the effective mass.
