Usov N A, Serebryakova O N, Tarasov V P
National University of Science and Technology "MISIS", 119049, Moscow, Russia.
Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, IZMIRAN, 108480, Troitsk, Moscow, Russia.
Nanoscale Res Lett. 2017 Aug 14;12(1):489. doi: 10.1186/s11671-017-2263-x.
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 V/V , where N is the average number of the particles in the cluster, V is the nanoparticle volume, and V 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.
利用朗道 - 栗弗席兹随机方程计算了交变磁场中各种随机氧化铁纳米颗粒簇稀集合体的比吸收率。该方法同时考虑了纳米颗粒磁矩的热涨落以及簇中纳米颗粒之间的磁偶极相互作用。结果表明，对于通常的三维簇，磁偶极相互作用强度主要由簇的堆积密度η = N V / V 决定，其中N 是簇中粒子的平均数，V 是纳米颗粒体积，V 是簇体积。当簇的堆积密度在0.005 ≤ η < 0.4范围内增加时，低频磁滞回线面积和集合体比吸收率显著降低。随着η的增加，比吸收率对平均纳米颗粒直径的依赖性仍然存在，但变得不那么明显。对于生物介质中出现的纳米颗粒分形簇，除了吸收率大幅降低外，吸收最大值还向更小的颗粒直径移动。还发现，纳米颗粒表面非磁性壳层厚度增加时，分形簇的比吸收率会明显增加。
