title: 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 Fe3O4 nanoparticles via superparamagnetic relaxation. We observed that the cut-off frequency can be enhanced from 5.3 GHz for Fe3O4 to 6.9 GHz forFe3O4@SiO2 core-shell structure superparamagnetic nanoparticles, which are much higher than the natural resonance frequency of 1.3 GHz for Fe3O4 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.
authors.affiliation: State Key Laboratory of Magnetism and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Ning-Ning
authors.initials: NN
authors.lastname: Song
authors.forename: Hai-Tao
authors.initials: HT
authors.lastname: Yang
authors.forename: Hao-Liang
authors.initials: HL
authors.lastname: Liu
authors.forename: Xiao
authors.initials: X
authors.lastname: Ren
authors.forename: Hao-Feng
authors.initials: HF
authors.lastname: Ding
authors.forename: Xiang-Qun
authors.initials: XQ
authors.lastname: Zhang
authors.forename: Zhao-Hua
authors.initials: ZH
authors.lastname: Cheng