Shape-Dependent Magnetic Properties and Phase Transformation of Annealed Iron Oxide Nanoparticles

After investigation of different methods to synthesize magnetic nanoparticles (MNPs), finding methods to control their magnetic properties and to optimize their characteristics remains challenging. Heat treatment has been introduced as a perfect method that can affect the shape and size of MNPs and thus their magnetic properties. In this work, iron oxide (Fe₂O₃) nanoparticles with various shapes were produced by means of a microwave-assisted method, with use of cost-effective and non-toxic chemicals. These particles were then annealed at different temperatures, i.e., 300°C, 500°C, and 800°C, for 2 h in the presence of air. The results indicated that heated samples exhibited weaker magnetic properties than those of non-heated samples. Both x-ray diffraction and Raman analysis results of the annealed samples indicated that the Fe₂O₃ particles were well crystalline, with transformation in phases. Transmission electron microscopy images indicated that all the annealed particles were spherical, regardless of their initial shapes.