Exceeding natural resonance frequency limit of monodisperse Fe 3 O 4 nanoparticles via superparamagnetic relaxation

Abstract

Magnetic nanoparticles have attracted much research interest in the past decades due to their potential applications in microwave devices. Here, we adopted a novel technique to tune cut-off frequency exceeding the natural resonance frequency limit of monodisperse Fe 3 O 4 nanoparticles via superparamagnetic relaxation. We observed that the cut-off frequency can be enhanced from 5.3â€...GHz for Fe 3 O 4 to 6.9â€...GHz forFe 3 O 4 @SiO 2 core-shell structure superparamagnetic nanoparticles, which are much higher than the natural resonance frequency of 1.3â€...GHz for Fe 3 O 4 bulk material. This finding not only provides us a new approach to enhance the resonance frequency beyond the Snoek's limit, but also extend the application for superparamagnetic nanoparticles to microwave devices.