Abstract： Oil soluble Fe₃O₄ nano-particles with particle size less than 10 nm were prepared by the simple coprecipitation method. The structure and properties of the Fe₃O₄ nano-particles were characterized. Effect of adding methods of NH₃·H₂O on morphology and yield of the Fe₃O₄ nano-particles was discussed. The results show that the inverse spinel Fe₃O₄ nano-particles are coated by oleic acid and can be dissolved in a variety of organic solvents. Magnetic hysteresis loops indicate that the Fe₃O₄ nano-particles are superparamagnetic materials. Growth and yield of the Fe₃O₄nano-particles are significantly influenced by modifying adding methods of NH₃·H₂O.

Keywords: chemical coprecipitation method; Fe₃O₄ nano-particle; magnetic materials