Exceeding natural resonance frequency limit of monodisperse Fe3O4 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.

Fractal Frequency-Selective Surface Embedded Thin Broadband Microwave Absorber Coatings Using Heterogeneous Composites

“…Several exchange resonance peaks have been reported for ferromagnetic nanoparticles ( 100 nm) [76], which support the existence of exchange resonance in present composites, as the particle size of Fe O is less than 100 nm. Finally, it is noticed that the multiresonant dielectrics and magnetic peaks observed in Fe O -Ti composites bear a strong resemblance to the results reported by other researchers for similar kinds of materials [57]- [60], [72], [73], [77], [78].…”

“…Natural and exchange resonance are two well-known resonance phenomenon [73]- [75]. However, natural resonance is dominant at lower frequencies than exchange resonance [74].…”

“…Apart from this, another important concept relating to excellent absorption is interface effect, i.e., exchange coupling interaction between different phases present in the composite. Many recent studies investigated the behavior of ferromagnetic particles in combination with a dielectric matrix material for the microwave absorption [50], [55], [57]- [61], [73], [77], [82]. More specifically, less coating thickness ( mm) and wide absorption bandwidth ( dB) of C1, C2, and C3 makes them extraordinary as compared to above referred works.…”

Flowerlike iron oxide nanostructures and their application in microwave absorption

“…Surface anisotropy and exchange energy caused by the exchange effect between grains have been proven to be important for nanocrystalline particles [25]. Generally speaking, the multiresonance phenomena were contributed from the natural resonance and exchange resonance [26,27]. In Fig.…”

Mixed Brownian alignment and Néel rotations in superparamagnetic iron oxide nanoparticle suspensions driven by an ac field

“…The measurement techniques are discussed in Sec. II C. We used the bulk value for the gyromagnetic ratio of 1.3 GHz/T as opposed to the single electron value [31]. The best fit to experimental data was achieved using a mean anisotropy constant of 3.4 kJ/m 3 with a 3 kJ/m 3 standard deviation, which is consistent with recent measurements of similar samples [32].…”