Abstract The effect of core size on the magnetic behavior of nanoparticle assemblies of γ-Fe2O3 core/SiO2 shell morphology is investigated. Long-range magnetostatic interactions are probed in two highly monodispersed experimental test systems of spherical nanoparticles with core diameters of 10 nm and 12.5 nm, and a shell thickness varying from 0 nm (bare particles) to ∼ 50 nm. Zero-Field-Cooled magnetization curves are calculated by employing the Monte Carlo simulation technique in a mesoscopic-scale model for the assembly, assuming spin collinearity and coherent spin-reversal mechanisms. Simulation results reproduce the trend in the behavior of the Zero-Field-Cooled magnetization versus T curves in good qualitative agreement with the experimental findings. They also demonstrate that the increase of the magnetic core size results in a shift of the maximum magnetization peak, Tmax, to higher temperatures due to enhanced dipolar coupling. The results shed light on how interparticle distance and magnetic core size influence the value of Tmax through collective behavior and its transition to a single-particle superparamagnetic blocking temperature, TB, as the assembly becomes magnetically diluted with increasing shell thickness.

中文翻译：

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尺寸对 γ-Fe2O3 核/SiO2 壳纳米粒子组装体磁行为的影响

摘要 研究了核尺寸对γ-Fe2O3 核/SiO2 壳形貌纳米粒子组装体磁行为的影响。在两个高度单分散的球形纳米粒子实验测试系统中探测了长程静磁相互作用，其核直径为 10 nm 和 12.5 nm，壳厚度从 0 nm（裸粒子）到 50 nm 不等。零场冷却磁化曲线是通过在组件的介观尺度模型中采用蒙特卡罗模拟技术来计算的，假设自旋共线性和相干自旋反转机制。仿真结果再现了零场冷却磁化强度与 T 曲线的行为趋势，与实验结果具有良好的定性一致性。他们还证明，由于增强的偶极耦合，磁芯尺寸的增加导致最大磁化峰值 Tmax 向更高温度移动。结果揭示了粒子间距离和磁核尺寸如何通过集体行为及其向单粒子超顺磁性阻塞温度 TB 的转变影响 Tmax 的值，因为组件随着壳厚度的增加而被磁性稀释。