Fabrication and characterization of Fe nano-particles by sonochemistry method

The structure and magnetic properties of Fe nano-particles prepared by the sonochemistry method were systematically studied. The power of sonicator played an important role in the microstructure and magnetic properties of the nano-particles. Initial X-ray powder diffraction patterns of Fe nano-particles prepared with a power of 180 W and 450 W exhibited amorphous-like diffraction peaks. TEM images showed that the average particle size of Fe nano-particles made with 180 W is 2-3 nm and increases to 5-6 nm with 450 W. The amorphous and superparamagnetic nature of the Fe nano-particles has been confirmed by TEM, SAD and magnetometry measurements. The saturation magnetization (Ms) of the 2-3 nm Fe nano-particles is only 0.414 T. Increasing the power to 450 W, the Ms of Fe nano-particles with the size of 5-6 nm can reach the value of 0.958 T. To obtain fully crystalline particles, the Fe nano-particles were annealed at 923 K for 2 min. After annealing, the Ms increased to 1.807 T. TEM results show that the amorphous-like Fe nano-particles have been transformed to crystalline bcc α-Fe.