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

Abstract

In this paper, both the leaf-like dendritic Co_xFe_1−x (x = 0.1, 0.3, 0.5 and 0.7) alloys and novel grain-like dendritic nanostructure Co_0.9Fe_0.1 alloy and ε-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 Co_xFe_1−x grow along three of the six equivalent <110> directions. However, for grain-like dendritic hcp ε-Co, their six branches grow along the six equivalent <101> directions, and the trunks are oriented preferably along [0002] direction. The electromagnetic absorption (EMA) performance of leaf-like structure Co_xFe_1−x alloys are obviously enhanced with Co content increase from −21.7 dB for Co_0.1Fe_0.9 to −59.1 dB for Co_0.5Fe_0.5. Meanwhile, the response frequency of maximum reflection loss (RL) shifts to the higher band. In the case of grain-like dendritic Co_0.9Fe_0.1 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 Co_xFe_1−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.