Magnetic nano-chains — Properties, processing and prospects

Hierarchical assemblies of magnetic materials have attracted a great deal of interest due to their unique structures, particular physical properties and potential technological applications. In particular, one-dimensional (1D) magnetic assemblies of nanoparticles (NPs) have been a particularly active area of research in recent years, both from a theoretical and experimental point of view. Compared with zero-dimensional NPs or so-called "single NPs", 1D NP nanochains display exacerbated magnetic properties and provide aligned and parallel surface functionalities, suitable for various technological sectors, notably in the medical and environmental fields.

The aim of this article is to carry out an in-depth bibliographical survey of the state of the art concerning one-dimensional assemblies of individual magnetic NPs. In a first section, we recall some essential characteristics of magnetic NPs and the importance of modeling involving particle systems with dipolar interactions. These interactions are at the origin of collective effects in magnetic NP assemblies, due to their long range, and help explain chain formation in certain cases. So, beyond a fundamental investigation of the various processes, a good understanding of dipolar effects can also have a predictive character. In a second section, we present the various experimental strategies that have been developed in recent years to obtain these organizations: directed dipolar self-assembly, assembly induced by a magnetic field, or synthesis assisted by the use of a "chemical mold" (or template), the chemical assembly of particles presenting two different functionalities or physical methods such as electrospinning or using microfluidic systems. Some of these strategies can be combined, notably the use of a magnetic field, which can help direct chain formation in all the strategies considered. The last part of the article presents the various applications of these nanochains, particularly in the life and environmental sciences.