Shape-dependent microwave permeability of Fe₃O₄nanoparticles: a combined experimental and theoretical study

Abstract

Shape anisotropy is crucial for the microwave permeability of magnetic nanoparticles. In this work, we conduct a systematic study on the shape-dependent microwave permeability of magnetic nanoparticles. Three kinds of Fe3O4 nanoparticles with different geometric shapes (rod, disc, and octahedron) are fabricated by chemical methods and their permeability is investigated through both theoretical calculation and experiment. The results suggest that the rod could exhibit the highest resonance frequency (fr), while the lowest resonance frequency could be found in the octahedron. An opposite trend is observed in the initial permeability (μ0). In order to confirm the experimental permeability, we establish an improved LL-G model, which could take both the shape anisotropy and magnetic domain structure into account by introducing a local effective anisotropy field (Heff). The good agreement between the calculated and experimental permeability proves that the model can reproduce shape-dependent microwave permeability of magnetic nanoparticles. More importantly, no fitting process is involved in this model, enabling us to predict the permeability of magnetic nanostructures independent of experiment results.

Frequency-induced negative magnetic susceptibility in epoxy/magnetite nanocomposites

“…* email: thschang@phys.nthu.edu.tw; crchang@phys.ntu.edu.tw frequency is greater than a threshold frequency. Although this theory is not the only possible explanation and needs more experimental exploration 21,22 , it can explain the coexistence of superparamagnetism at low frequencies and diamagnetism at high frequencies as to why we adopt it to explain our results.…”

Nanoscaled self-alignment of Fe3O4nanodiscs in ultrathin rGO films with engineered conductivity for electromagnetic interference shielding

“…The resonance peak was ascribed to the natural resonance of the Fe 3 O 4 nanodisc. 26 It is known that the μ″ is crucial for the magnetic loss and usually equals to zero for non-magnetic materials. 47 The broad resonance peak of the μ″ curve in Fig.…”

“…25 Besides the intrinsic magnetic parameters, it is strongly related to the geometric shape, the so called shape anisotropy. 26 Among different shapes, flake-or disc-shaped magnetic particles could exhibit higher permeability at higher frequencies compared with isotropic nanoparticles. 26,27 The permeability can be further enhanced by a factor of almost 2 when alignment is achieved.…”

“…26 Among different shapes, flake-or disc-shaped magnetic particles could exhibit higher permeability at higher frequencies compared with isotropic nanoparticles. 26,27 The permeability can be further enhanced by a factor of almost 2 when alignment is achieved. 28,29 Furthermore, the disc shaped particles could be very thin in thickness.…”

Shape-Evolution and Growth Mechanism of Fe3O4Polyhedrons

“…Polyhedral micro-and nanoparticles with specific facets have attracted considerable attention because of their abundant size-and shape-dependent physical and chemical properties [1][2][3][4]. Magnetite (Fe 3 O 4 ), a traditional material, has found many applications, such as magnetic fluids [5,6] and microwave absorption [7,8].…”