Iron oxide nanoparticles were synthesized by coprecipitation method using ammonia as precipitation agent. Most researchers usually add ammonia into the iron salt solution but in this work the salt solution drop wise has been added to the ammonia and the new obtained results were compared with those of other researches. Magnetic properties of nanoparticles were measured by VSM. The effect of reaction temperature and concentration of reactants on the size and magnetic properties of nanoparticles were investigated. The size of particles was calculated by Sherrer formula and magnetic data, and then compared with the size of nanoparticles obtained by TEM. The size of produced nanoparticles ranged from 8 to 17 nanometer and their saturation magnetizations were between 65.5 to 72.5 emu/gr. It was found that increasing reaction temperature increases saturation magnetization of nanoparticles, but variation of concentration of ammonia did not change the saturation magnetization. Saturation magnetization observed here were more than the values reported by others.

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