Polyacrylamide-assisted Solvothermal Synthesis Of Magnetic Cobalt Nanowires

Nanostructured Co has been a subject of intensive research in recent years because of their unique electrical and magnetic properties and potential applications in a wide range of fields, such as high-density magnetic recording, magnetic separation, magnetic storge, magnetic fluids, medical diagnosis and catalysis. It is well-known that electronic and magnetic properties of these materials are strongly dependent on their structure, size, morphology and.crystal form. Hence, it is of scientific significance to fabricate nanostructured Co with high aspect ratio via a simple, mild technique. This work focuses on the high-yield solvothermal synthesis of magnetic Co nanowires with extremely high coercive force in presence of structure-directing agent. The main results are as follows:Magnetic 1D cobalt nanowires with high aspect ratio and uniform size were successfully fabricated in high-yield via a facile solvothermal approach in presence of acrylamide as the structure-directing agent in ethylene glycol(EG)- ethylene diamine(EDA) mixed solutions. The crystalline phase, morphology and size of the products can be easily controlled through properly monitoring the synthetic parameters including reaction temperature, reaction time, the amount of acrylamide, the volume ratio of EG/EDA and concentrations of NaOH) and are characterized by XRD、EDX、SEM、TEM and HRTEM techqiue. The optimal experimental conditions of Co nanowires were obtained as follows: T = 200 ℃, t = 10 h, 6 M NaOH, ethylene glycol/ethylenediamine = 1:5(volume ratio), and 0.3 g acrylamide.Magnetic properties of the as-obtained products were measured at room temperature using a Quantum Design Superconducting Quantum Interference Device magnetometer(SQUID, PMS-XL-5T, 300 K). The product exhibits an excellent ferromagnetic behavior with a saturation magnetization(Ms) of 149 emu/g, a remnant magnetization(Mr) of 49 emu/g, residual magnetization of 0.33, and an extremely high coercive force(Hc) of 365 Oe. It was noteworthy that Co nanowire showed markedly enhanced coercivities than the values of the spherical and bulky Co counterparts(a few tens of Oersteds), flower-like submicrospheres(90 Oe) and hollow mesospheres(66 Oe). It was even much larger than those of the previously reported 1D chains of Co hexagonal intercrossed microplatelets(169 Oe). The remarkable enhancement of Hc could be attributed to the high shape anisotropy of 1D hcp Co nanowires with high aspect ratio. The as-synthesized hcp Co nanowires are very promising for applications in a variety of fields such as magnetic recording, magnetic separation, magnetic storge and so on.