The migration process of magnetic nanoparticles and colloids in solution under the influence of magnetic field gradients, which is also known as magnetophoresis, is an essential step in the separation technology used in various biomedical and engineering applications. Many works have demonstrated that in specific situations, separation can be performed easily with the weak magnetic field gradients created by permanent magnets, a process known as low-gradient magnetic separation (LGMS). Due to the level of complexity involved, it is not possible to understand the observed kinetics of LGMS within the classical view of magnetophoresis. Our experimental and theoretical investigations in the last years unravelled the existence of two novel physical effects that speed up the magnetophoresis kinetics and explain the observed feasibility of LGMS. Those two effects are (i) cooperative magnetophoresis (due to the cooperative motion of strongly interacting particles) and (ii) magnetophoresis-induced convection (fluid dynamics instability originating from inhomogeneous magnetic gradients). In this feature article, we present a unified view of magnetophoresis based on the extensive research done on these effects. We present the physical basis of each effect and also propose a classification of magnetophoresis into four distinct regimes. This classification is based on the range of values of two dimensionless quantities, namely, aggregation parameter N* and magnetic Grashof number Gr_m, which include all of the dependency of LGMS on various physical parameters (such as particle properties, thermodynamic parameters, fluid properties, and magnetic field properties). This analysis provides a holistic view of the classification of transport mechanisms in LGMS, which could be particularly useful in the design of magnetic separators for engineering applications.

中文翻译：

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磁性理论下磁性纳米颗粒分离的统一视图。

磁性纳米粒子和胶体在磁场梯度的影响下在溶液中的迁移过程（也称为磁泳）是在各种生物医学和工程应用中使用的分离技术中必不可少的步骤。许多工作表明，在特定情况下，可以轻松地利用永磁体产生的弱磁场梯度进行分离，这一过程称为低梯度磁分离（LGMS）。由于涉及的复杂程度，不可能在经典的磁泳观点内理解所观察到的LGMS动力学。近年来，我们的实验和理论研究揭示了两种新的物理效应的存在，这些效应加快了磁致动力学，并解释了LGMS的可行性。这两个效应是（i）协同磁致变热（由于强相互作用粒子的协同运动）和（ii）磁致变热引起的对流（源于不均匀磁梯度的流体动力学不稳定）。在这篇专题文章中，基于对这些效应的广泛研究，我们提出了一种磁磁效应的统一观点。我们介绍了每种效应的物理基础，还提出了将磁泳分为四个不同的机制的分类。该分类基于两个无量纲量的值的范围，即聚合参数 在这篇专题文章中，基于对这些效应的广泛研究，我们提出了一种磁磁效应的统一观点。我们介绍了每种效应的物理基础，还提出了将磁泳分为四个不同的机制的分类。该分类基于两个无量纲量的值的范围，即聚合参数 在这篇专题文章中，基于对这些效应的广泛研究，我们提出了一种磁磁效应的统一观点。我们介绍了每种效应的物理基础，还提出了将磁泳分为四个不同的机制的分类。此分类基于两个无量纲值的值范围，即聚合参数N *和磁格拉索夫数Gr _m，其中包括LGMS对各种物理参数（例如粒子特性，热力学参数，流体特性和磁场特性）的所有依赖性。该分析提供了LGMS中运输机制分类的整体视图，这在设计用于工程应用的磁选机时可能特别有用。