Self-Assembly of Magnetic Nanochains in an Intrinsic Magnetic Dipole Force-Dominated Regime

Magnetic nanoparticle chains offer the anisotropic magnetic properties that are often desirable for micro- and nanoscale systems; however, to date, large-scale fabrication of these nanochains is limited by the need for an external magnetic field during the synthesis. In this work, the unique self-assembly of nanoparticles into chains as a result of their intrinsic dipolar interactions only is examined. In particular, it is shown that in a high concentration reaction regime, the dipole–dipole coupling between two neighboring magnetic iron cobalt (FeCo) nanocubes, was significantly strengthened due to small separation between particles and their high magnetic moments. This dipole–dipole interaction enables the independent alignment and synthesis of magnetic FeCo nanochains without the assistance of any templates, surfactants, or even external magnetic field. Furthermore, the precursor concentration (M] = 0.016, 0.021, 0.032, 0.048, 0.064, and 0.096 m ) that dictates the degree of dipole interaction is examined—a property dependent on particle size and inter-particle distance. By varying the spinner speed, it is demonstrated that the balance between magnetic dipole coupling and fluid dynamics can be used to understand the self-assembly process and control the final structural topology from that of dimers to linear chains (with aspect ratio >10:1) and even to branched networks. Simulations unveil the magnetic and fluid force landscapes that determine the individual nanoparticle interactions and provide a general insight into predicting the resulting nanochain morphology. This work uncovers the enormous potential of an intrinsic magnetic dipole-induced assembly, which is expected to open new doors for efficient fabrication of 1D magnetic materials, and the potential for more complex assemblies with further studies.