Dipolar-Distribution Cavity γ-Fe O @C@α-MnO Nanospindle with Broadened Microwave Absorption Bandwidth by Chemically Etching.

Developing microwave absorption materials with ultrawide bandwidth and low density still remains a challenge, which restricts their actual application in electromagnetic signal anticontamination and defense stealth technology. Here a series of olive-like γ-Fe O @C core-shell spindles with different shell thickness and γ-Fe O @C@α-MnO spindles with different volumes of dipolar-distribution cavities were successfully prepared. Both series of absorbers exhibit excellent absorption properties. The γ-Fe O @C@α-MnO spindle with controllable cavity volume exhibits an effective absorption (<-10 dB) bandwidth as wide as 9.2 GHz due to the chemically dipolar etching of the core. Reflection loss of the γ-Fe O @C spindle reaches as high as -45 dB because of the optimized electromagnetic impedance balance between polymer shell and γ-Fe O core. Intrinsic ferromagnetism of the anisotropy spindle is confirmed by electron holography. Strong coupling of magnetic flux stray lines between spindles is directly imaged. This unique morphology and facile etching technique might facilitate the study of core-shell type microwave absorbers.