High frequency study of core-shell and uncoated Fe3O4 nanoparticles

Nanoparticles of Fe3O4 (core) were synthesized and some were covered with a thin layer of Au (shell) to create a core-shell structure. The dynamic magnetic properties were studied using a vector network analyzer. It was found that, at a given applied magnetic field, the core-shell nanoparticles resonate at lower frequency compared to the uncoated Fe3O4 nanoparticles and the resonance frequency increased with increasing applied field for both the core-shell and the uncoated nanoparticles. Also, the core-shell nanoparticles exhibited additional resonances. Further, the core-shell nanoparticles exhibited a larger linewidth compared to the uncoated counterparts for all the particle sizes. The experimental absorption data have been compared with the results obtained from an effective medium theory.