Structural and magnetic equilibrium properties of a semi-dilute suspension of magnetic multicore nanoparticles

The idea to create smart magnetically controllable nanostructured materials is highly appealing from both fundamental science point of view and application perspectives. Ample investigations of singledomain magnetic nanoparticles embedded in liquid and gel-like magneto-passive carriers revealed a plethora of new phenomena from controllable equilibrium self-assembly to a designed heat dissipation on the application of AC magnetic fields. However, all the effects in such systems are limited by the physical energy and entropy scales of nanoparticles and are very sensitive to temperature changes and confinement. As a result, among new types of complex magnetic materials, magnetic multicore nanoparticles (MMNPs) made of rigidly bound single-domain nanograins were proposed. The properties of such systems are resulting from inter-grain and grain-field interactions, and are not yet fully understood. In this study, employing Langevin dynamics computer simulations, we analyse the interplay of the aforementioned interactions in a dilute suspension of MMNPs made of grains with negligible magnetic anisotropy. We find that the stronger are the inter-grain interactions the lower is the initial magnetic response of MMNPs. The response is though hindered, rather than suppressed: at a certain intensity of an applied magnetic field a sufficient degree of the alignment of the grain magnetic moments and the field is achieved and a large-scale self-assembly accompanied by a rapid growth of magnetisation is observed. The strength of interactions essential for this crossover is much higher than that for a suspension of single-domain grains with the same concentration and magnetic saturation. (c) 2022 Elsevier B.V. All rights reserved.