Determination of the critical interspacing for the noninteracting magnetic nanoparticle system

Abstract

Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticlesThe dipole-dipole interactions of monodisperse Fe 3 O 4 nanoparticles ͑NPs͒ can be directly controlled by a uniform SiO 2 shell with different thickness, i.e., different interspacings. Thus, the interacting strength of a serial of Fe 3 O 4 -SiO 2 NPs system can be revealed by fitting the blocking temperature T B measured at ac fields to the Vogel-Fulcher law. The interspacing over five times of diameter for less than 8.0 nm Fe 3 O 4 NPs is the critical value to achieve a noninteracting system. Furthermore, a general equation to evaluate critical interspacing for noninteracting magnetic NPs systems with different sizes and saturation magnetizations was calculated by Monte Carlo method.

Controlling lateral nanomixing and velocity profile of dilute ferrofluid capillary flows in uniform stationary, oscillating and rotating magnetic fields

“…The fact that the average MNP particle-particle distance is about six times the MNP diameter (d p-p $ 95 nm for / = 0.0025) [1], particles interaction may be neglected [37,38] and the mixing phenomenon can be interpreted as resulting from the individual particle behavior under magnetic field. Fig.…”

Exceeding natural resonance frequency limit of monodisperse Fe3O4 nanoparticles via superparamagnetic relaxation

“…In contrast to conventional bulk microwave ferrites, the magnetic properties of superparamagnetic nanoparticles can be easily tuned by controlling the volume, shape, anisotropy, dipolar interaction between particles, and by applying exchange bias and electric field18192021. However, the effect of superparamagnetism on high frequency properties is not well understood.…”

Inception of vortical coherent structures from spinning magnetic nanoparticles in rotating magnetic fields – New nanofluid microscale mixing tool

“…Since the average distance between MNPs is several times greater than their diameter at the employed magnetic core volume fractions (from 129 nm to 60 nm for d p = 16 nm) [15], mutual interactions between MNPs at rest may be neglected [16,17] and the resulting phenomena can be interpreted as arising from the action of isolated nanoparticles under magnetic field. In the absence of magnetic field, the net (ensemble-average) spin vector is equal to zero because of the randomized MNP magnetic moments in all directions due to Brownian agitation.…”

“…Table 1 summarizes the properties of the original asreceived undiluted ferrofluids. Finally, although it was determined that cluster or chain formation during the course of experiments was highly unlikely at the utilized dilute concentrations [16,17], to verify particle stability throughout testing, particle size distributions for the employed concentrations of the different MNPs were also measured with the Zetasizer from samples before and after exposure to magnetic fields. No statistically significant difference was found between the aforementioned samples, confirming the absence of clusters or chain formation during the experiments.…”

“…Consequently, a time-varying magnetic field such as RMF with its ever changing directionality can exert an angular torque on MNPs, forcing gyration of the latter with respect to the surrounding liquid phase. In turn, provided the spinning MNPs are in a sufficiently dilute nanofluid suspension, where magnetic mutual interactions among MNPs are negligible [16,17], MNPs can transfer their momentum to the neighboring liquid molecules and thus locally generate an angular motion (or nanoconvective streams) in the liquid.…”