Abstract The magnetic properties of a real system of magnetite nanoparticles with controlled interparticle distances via a silica shell are modeled by the modification of existing theoretical models that describe ideal non-interacting superparamagnetic systems. In this work, the variation of the blocking temperature as a function of the interparticle separation is explained through a phenomenological model where the interaction is taken into account through a dipolar field that modifies the intrinsic anisotropy field of the system. Moreover, it is observed that the field-dependent magnetization of the studied samples does not fulfill the universal scaling law of superparamagnetic systems, in which the magnetization is well described by the classic Langevin model, even for the less interacting samples. However, when the actual temperature of the system is modified by a temperature factor comprised by two terms that account for dipolar and anisotropy contributions, the magnetization curves satisfactorily comply with the scaling law. The results suggest that the interaction increases the anisotropy barrier and the developed approach allows to distinguish the effect of this contribution from the anisotropic contribution on the magnetic properties studied in this system. By means of this study it is demonstrated that models like the Interacting Superparamagnetic model must be carefully used to describe correctly a non-interacting system because the latter can account for a false interaction that is not present from blocking temperature measurements.

中文翻译：

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结合偶极和各向异性贡献以正确描述磁性纳米粒子真实系统的磁性

摘要 通过对描述理想非相互作用超顺磁系统的现有理论模型的修改，模拟了通过二氧化硅壳控制粒子间距离的磁铁矿纳米粒子的真实系统的磁性。在这项工作中，阻塞温度的变化作为粒子间分离的函数是通过现象学模型来解释的，其中通过偶极场来考虑相互作用，该偶极场修改了系统的固有各向异性场。此外，观察到所研究样品的场相关磁化强度不满足超顺磁系统的通用标度定律，其中经典朗之万模型很好地描述了磁化强度，即使对于相互作用较少的样品也是如此。然而，当系统的实际温度被一个温度因子修改时，该温度因子由两个解释偶极和各向异性贡献的项组成，磁化曲线令人满意地符合标度定律。结果表明，相互作用增加了各向异性势垒，并且开发的方法允许将这种贡献与各向异性贡献对在该系统中研究的磁特性的影响区分开来。通过这项研究，表明必须谨慎使用相互作用超顺磁模型等模型来正确描述非相互作用系统，因为后者可以解释阻塞温度测量中不存在的错误相互作用。