Break Snoek limit via superparamagnetic coupling in Fe3O4/silica multiple-core/shell nanoparticles

Natural materials that maintain significant permeability at microwave frequencies are a challenge due to the Snoek limit, but manipulation of matter-microwave interaction in artificial composites provides a possibility to achieve breakthroughs. Herein, we synthesized Fe3O4/silica core/shell nanoparticles comprised of multiple Fe3O4 cores in each particle (denoted as multiple-Fe3O4/silica). In comparison to conventional magnetic natural resonance at megahertz frequencies, the resonance of multiple-Fe3O4/silica composite appears at 9.3 GHz relying on superparamagnetic coupling, which is the highest value reported currently. Our study opens up a fantastic avenue for optimizing micromagnetism by nanoscale architectures.