Tunable hierarchical Fe nanowires with a facile template-free approach for enhanced microwave absorption performance

We demonstrate a facile, template-free route for Fe nanowires (NWs) with an average diameter of 100 nm through magnetic-field-assisted hydrothermal conditions. The aspect ratio of the Fe NWs reaches 50. Fe NWs are constructed with interconnected bead-like nanospheres, which are composed of primary nanocrystals (NCs) with an average size of 8 nm. This shows that the polycrystalline Fe NWs have a body-centred cubic (bcc) structure with preferential growth on the < 110 > zone axis. Such hierarchical structures involve orientational growth in the presence of an external magnetic field. The molarity of the reducing agent, reaction time and temperature, are further investigated to understand the influence of these parameters on the growth process of Fe NWs. Compared with those of Fe nanoparticles (NPs), the magnetic properties of Fe NWs show both higher saturation magnetization (154.03 emu g(-1)) and coercivity (360.84 Oe). The peak value of reflection loss (RL) reaches up to -27.28 dB at 3.68 GHz, indicating the excellent microwave absorption performance of the Fe NWs for low gigahertz usage (2-6 GHz). This mild approach to control Fe NWs is easy to scale-up for other iron-related magnetic nanodevice applications.