Using first-principle calculations and kinetic Monte Carlo simulation, we study the local and averaged hysteresis in tiny clusters of k magnetic nanoparticles (MNPs) or k-mers. We also analyze the variation of local dipolar field acting on the constituent nanoparticles as a function of the external magnetic field. The dipolar interaction is found to promote chain-like arrangement in such a cluster. Irrespective of cluster size, the local hysteresis response depends strongly on the corresponding dipolar field acting on a nanoparticle. In a small k-mer, there is a wide variation in local hysteresis as a function of nanoparticle position. On the other hand, the local hysteresis is more uniform for larger k-mer, except for MNPs at the boundary. In the case of superparamagnetic nanoparticle and weak dipolar interaction, the local hysteresis loop area Ai is minimal and depends weakly on the k-mer size. While for ferromagnetic counterpart, Ai is considerably large even for weakly interacting MNPs. The value of Ai is found to be directly proportional to the dipolar field acting on the nanoparticle. The dipolar interaction and k-mer size also enhance the coercivity and remanence. There is always an increase in Ai with cluster size and dipolar interaction strength. Similarly, the averaged hysteresis loop area A also depends strongly on the k-mer size, particle size and dipolar interaction strength. A and Ai always increase with k-mer size and dipolar interaction strength. Interestingly, the value of A saturates for k≥20 and considerable dipolar interaction irrespective of particle size. We believe that this work would help understand the intricate role of dipolar interaction on hysteresis and the organizational structure of MNPs and their usage in drug delivery and hyperthermia applications.

中文翻译：

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在偶极相互作用的磁性纳米粒子的小簇中调整局部滞后

使用第一性原理计算和动力学蒙特卡罗模拟，我们研究了微小簇中的局部和平均滞后ķ磁性纳米粒子 (MNP) 或ķ-mers。我们还分析了作为外部磁场函数作用于组成纳米颗粒的局部偶极场的变化。发现偶极相互作用促进了这种簇中的链状排列。无论簇大小如何，局部滞后响应强烈依赖于作用在纳米粒子上的相应偶极场。在一个小ķ-mer，局部滞后作为纳米粒子位置的函数存在很大变化。另一方面，局部滞后对于较大的ķ-mer，边界处的 MNP 除外。在超顺磁性纳米粒子和弱偶极相互作用的情况下，局部磁滞回线区域一种一世是最小的并且弱依赖于ķ-mer 大小。而对于铁磁对应物，一种一世即使对于弱相互作用的 MNP 也相当大。的价值一种一世发现与作用在纳米颗粒上的偶极场成正比。偶极相互作用和ķ-mer尺寸也增强了矫顽力和剩磁。总是有增加的一种一世具有簇大小和偶极相互作用强度。同样，平均磁滞回线面积一种也强烈依赖于ķ聚体尺寸、粒径和偶极相互作用强度。一种和一种一世总是增加ķ聚体大小和偶极相互作用强度。有趣的是，价值一种饱和ķ≥20和相当大的偶极相互作用，与粒径无关。我们相信这项工作将有助于了解偶极相互作用对滞后的复杂作用以及 MNP 的组织结构及其在药物输送和热疗应用中的用途。