Interaction Effects in Assembly of Magnetic Nanoparticles

Abstract

A specific absorption rate of a dilute assembly of various random clusters of iron oxide nanoparticles in alternating magnetic field has been calculated using Landau–Lifshitz stochastic equation. This approach simultaneously takes into account both the presence of thermal fluctuations of the nanoparticle magnetic moments and magneto-dipole interaction between the nanoparticles of the clusters. It is shown that for usual 3D clusters, the intensity of the magneto-dipole interaction is determined mainly by the cluster packing density η = N p V/V cl, where N p is the average number of the particles in the cluster, V is the nanoparticle volume, and V cl is the cluster volume. The area of the low frequency hysteresis loop and the assembly-specific absorption rate have been found to be considerably reduced when the packing density of the clusters increases in the range of 0.005 ≤ η < 0.4. The dependence of the specific absorption rate on the mean nanoparticle diameter is retained with an increase of η, but becomes less pronounced. For fractal clusters of nanoparticles, which arise in biological media, in addition to a considerable reduction of the absorption rate, the absorption maximum is shifted to smaller particle diameters. It is found also that the specific absorption rate of fractal clusters increases appreciably with an increase of the thickness of nonmagnetic shells at the nanoparticle surfaces.

Specific Absorption Rate of Fractal-like Aggregates of Magnetic Nanopaticles

“…6 shows, for all cases considered there is an optimal diameter of the nanoparticles corresponding to the maximal SAR value. In addition, in accordance with the results obtained previously [6] for fractal clusters of PC type with relatively small number of magnetic nanoparticles, N = 90, the maximal SAR value increases as a function of the non magnetic shell thickness L .…”

“…One of the reasons of such behavior is the property of magnetic particles to agglomerate [4] and to form fractal-like structures [5] at in-vivo conditions. As a result, SAR of an assembly of magnetic nanoparticles distributed in tissue decreases considerably under the influence of strong magneto-dipole interactions between the nanoparticles of the cluster [4,6]. It is well known [7] that two different types of fractal clusters can be constructed.…”

Equilibrium magnetization of a quasispherical cluster of single-domain particles

“…Dashed lines are from the analytical model given by Eqs. (28) and (39). Dotted line is the Langevin function [Eq.…”

“…For simplicity, it is sometimes assumed that microspheres and nanoclusters contain non-interacting and magnetically isotropic single-domain particles 7,[20][21][22] . However, in recent years quasi-spherical rigid clusters of different sizes have been actively studied via numerical simulations 11,[23][24][25][26][27][28] . And it has been repeatedly demonstrated that interactions between embedded particles as well as their magnetic anisotropy can have a noticeable impact on the cluster static 11,[23][24][25] and dynamic [25][26][27][28] magnetic properties.…”

Specific Absorption Rate of Assembly of Magnetite Nanoparticles with Cubic Magnetic Anisotropy

“…The numerical simulations are performed by solving stochastic Landau-Lifshitz (LL) equation [7][8][9]. This approach takes into account both thermal fluctuations of the particle magnetic moments and strong magnetodipole interaction [10][11] in assemblies of dense fractal-like aggregates of nanoparticles. It has been discovered recently [12] that fractal clusters of nanoparticles originate in biological cells loaded with magnetic nanoparticles.…”