Magnetic field-directed self-assembly of FePt-based nanoparticles at the liquid–air interface

The self-assembly of nanoparticles is a prominent strategy for fabricating nanomaterials and nanodevices. Herein, FePt-based nanoparticles are self-assembled at a diethylene glycol–air interface, under an applied in-plane static magnetic field. The effect of the field on the self-assembly is apparent at a field strength of 60 mT, whereby nanoparticles arranged into randomly oriented nanoparticle chains. Increasing the field strength to 90–120 mT resulted in the nanoparticle chains becoming increasingly disintegrated, and large islands form at the expense of the uniform nanoparticle monolayer. The pattern arising from self-assembly is described based on the drag force and ligand–ligand interactions, which compete with van der Waals forces and magnetic dipole interactions induced by the applied magnetic field.