Core/Shell Metal/Heterogeneous Oxide Nanocapsules: The Empirical Formation Law and Tunable Electromagnetic Losses

We report an empirical thermodynamic law for the synthesis of core/shell metal/heterogeneous oxide nanocapsules, such as Fe/SiO2, Ni/SiO2, Fe/B2O3, Ni/B2O3, Fe/Al2O3, Fe/MnO2, Fe/Y2O3, Fe/CeO2, and Fe/La2O3, by arc-discharge evaporating a compressed mixture of Fe (or Ni) powders and the oxide powders of shell components. By integrating such dielectric oxide shells and magnetic metal cores in each particle, the electromagnetic losses can be artificially manipulated at the whole S-band, C-band, X-band, and Ku frequency ranges. The microscopic origins of the controllability of electromagnetic losses are ascribed to the specific matching and interfacial coupling between the magnetic cores and dielectric shells.