Facile synthesis of a hierarchical multi-layered CNT-NiFe 2 O 4 @MnO 2 composite with enhanced microwave absorbing performance

The assembly of magnetic and dielectric materials around carbon nanotubes (CNTs) can create specific microstructures, leading to materials with relatively high microwave absorbing properties. Here, through a facile process, nickel iron oxide (NiFe 2 O 4 ) is synthesized and placed on the surface of CNTs and this material is covered with manganese oxide (MnO 2 ). In this hierarchical multi-layered nanomaterial (CNT-NiFe 2 O 4 @MnO 2 ) produced though a two-step wet chemistry method followed by calcination at 200 ℃, CNTs are uniformly covered by NiFe 2 O 4 nanoparticles formed in situ over which the MnO 2 layer is deposited. Although CNT-NiFe 2 O 4 @MnO 2 exhibits weaker soft magnetic performance, its magnetic attenuation is higher than for CNT-NiFe 2 O 4. Structural effects produce differences between the constant and alternating magnetic properties of these materials. With a reflection loss (RL) of −17 dB and effective absorption bandwidth of 3.8 GHz, the microwave absorption of CNT-NiFe 2 O 4 @MnO 2 is superior to that of CNTs and CNT-NiFe 2 O 4. The hierarchical multi-layered structure increases the phase interface area and rearranges magnetic particles, leading respectively to higher interface polarization and natural resonance. The conductive mesh structure induces magnetic coupling which attenuates the electromagnetic field. This material employs a new approach to design and synthesize carbon-based hierarchical multi-layered microstructures with high microwave absorption.