Size influence to the high-frequency properties of granular magnetite nanoparticles

We fabricate granular Fe₃O₄ nanoparticles with tunable particles sizes ranging from 20 to 250 nm using the solvothermal method. Magnetic stirring during the fabrication can further reduce the size of the particle. To investigate the high-frequency dynamic magnetic properties, the complex permeability and complex permittivity of the composites are measured in a frequency range of 1-15 GHz, and the reflection loss can be obtained through further calculation. The results show that the granular size strongly influences the permeability and the absorbing property of the material. The intrinsic permeability can be derived from the extended Bruggeman effective medium theory. The Fe₃O₄ nanoparticles assisted by magnetic stirring with a size of 20 nm shows high performance in absorption compared with other bigger counterparts prepared without magnetic stirring.