Strengthening nanocomposite magnetism through microemulsion synthesis

The magnetic strength and versatility of heterostructures generated via a simple microemulsion cluster-formation technique is demonstrated. This approach allows optimization of individual component magnetic nanoparticles prior to heterostructuring, expediting the discovery and optimization of hybrid magnetic materials. The efficacy of this method is validated through a magnetic study of nanoparticle clusters combining antiferromagnetic CoO and superparamagnetic CoFe₂O₄ nanoparticles with tunable particle ratio and size. An enhancement of coercivity compared with pure CoFe₂O₄ nanoparticles indicates that close interparticle contacts are achieved. Upon annealing, an exchange bias field of 0.32 T was observed—over twice that achieved in any other colloidally-synthesized system. Additionally, the unique microstructure is defined during cluster formation and thus protects magnetic coercivity during the annealing process. Overall, this work demonstrates a general approach for quickly exploring magnetic parameter space, designing interparticle functionality, and working towards the construction of high-value bulk magnets with low materials and processing cost.