Synthesis of hierarchical dendritic micro-nano structure CoxFe1-x alloy with tunable electromagnetic absorption performance

In this paper, both the leaf-like dendritic CoxFe1-x (x = 0.1, 0.3, 0.5 and 0.7) alloys and novel grain-like dendritic nanostructure Co0.9Fe0.1 alloy and epsilon-Co were synthesized by an electric field-induced and electrochemical reduction method under over-polarization current. The formation of these two dendritic structures is not only attributed to the electric-field strength and ion concentration gradient, but also related to their crystalline structure. The trunks and branches of leaf-like dendritic bcc CoxFe1-x grow along three of the six equivalent < 110 > directions. However, for grain-like dendritic hcp epsilon-Co, their six branches grow along the six equivalent < 10 (1) over bar1 > directions, and the trunks are oriented preferably along [0002] direction. The electromagnetic absorption (EMA) performance of leaf-like structure CoxFe1-x alloys are obviously enhanced with Co content increase from -21.7 dB for Co0.1Fe0.9 to -59.1 dB for Co0.5Fe0.5. Meanwhile, the response frequency of maximum reflection loss (RL) shifts to the higher band. In the case of grain-like dendritic Co0.9Fe0.1 alloy, it has the widest frequency band from 5 to 18 GHz with RL < -20 dB due to the mixed phase composition. We ascribe the enhancement of dendritic CoxFe1-x alloys' EMA performance to the different elemental compositions, crystalline structures, surface anisotropy and crystal defects, which contribute to enhancing the effective complementarities between dielectric loss and magnetic loss.