2, University of California, San Diego, San Diego, California, United States
Nanoparticle (NP) clusters generated via a facile microemulsion method has proven promising for a wide variety of applications. Herein, we demonstrate how nanoclustering of CoO and CoFe2O4 NPs can lead to synergistic interfacial effects. Different from core/shell methods, our method can optimize magnetic NPs as individual components before clustering, facilitating the improvement of novel magnetic materials. The advantage of this method is showed through studying the magnetic properties of nanoclusters combining antiferromagnetic CoO and superparamagnetic CoFe2O4 NPs with tunable size and ratio. It shows that close interparticle interactions is achieved with an enhancement of coercivity compared with pure CoFe2O4 NPs. In addition, a large exchange bias field of 0.32 T was observed after annealing, which is more than twice larger than that in any other related systems. Furthermore, Scanning electron microscope (SEM) images reveal a compartmentalized microstructure of nanoclusters that may help maintain magnetic coercivity after the annealing process. Overall, this work develops a general approach for studying the magnetic interactions within NPs, functionalizing NP assemblies, and constructing high energy product, low cost bulk magnets.