Amorphous Nanoparticles: Synthesis, Crystallization Process, and Magnetic Properties

Amorphous CoFe₂O₄ nanoparticles have been successfully synthesized by the chemical microwave-assisted method. The crystallization process and the hard magnetic properties of prepared nanoparticles were systematically investigated in terms of thermal analysis and in situ measurement of magnetization dynamics. The as-prepared sample was amorphous, which was confirmed by various techniques, such as high resolution transmission electron microscopy, with electron diffraction and X-ray diffraction. The thermal analysis using differential scanning calorimetry showed that crystallization from CoFe₂O₄ amorphous state to CoFe₂O₄ crystalline started at 290°C. Crystallization activation energy was determined using the Kissinger model with a value of 1.09 eV. A study of the temperature dependence of magnetization supported the crystallization process of cobalt ferrite nanoparticles. Magnetic measurement indicated that the as-prepared amorphous particles were superparamagnetic. Compared with the bulk material, the observed value of saturation magnetization of the annealed sample was significantly low (27 emu/g) due to its nanocrystalline nature.