Enhanced static magnetic properties, multiresonance behaviour and novel frequency-selective surface absorption properties of hierarchical flower-like hexagonal close-packed Co superstructures

Hierarchical flower-like hexagonal close-packed Co superstructures were prepared using a hydrothermal approach without surfactants and complex precursors, and their static magnetic and microwave electromagnetic properties were investigated. The enhanced saturation magnetisation and coercivity were owing to the low surface spin disorder and the cooperative action between the coupling effect and the spatial confinement effect, respectively. The hierarchically equivalent circuit and frequency-selective surface (FSS) were applied for the first time to interpret multiresonance behaviours and nesting microwave absorption peaks of hierarchical flower-like Co/wax composites. Given the presence of hierarchical tuning loops, the composites exhibited three strong absorption peaks over 14-18-GHz. Three zero absorption peaks (corresponding to transmission) and nesting microwave absorption peaks can also be observed on the reflection loss (R_L) plots of the composites. Such absorption and transmission of the FSS are attributed to the hierarchical flower-like Co superstructures that function as randomly distributed patches in the wax matrix.