Controllable fabrication of nanoscale magnetic metal ordered structures and microwave absorption materials under synergetic irradiation and magnetic fields

The focus of nanoscience and nanotechnology is gradually shifting from the synthesis of individual components to their assembly into larger systems with well-defined structures, as assemblies of nanoscaled building blocks with some specific structures usually present collective optical, electronic, catalytic, and magnetic properties that are distinctly different from the corresponding individual nanoparticles. Although various methods have been used to prepare abundant shape-controlled metals and metallic compounds, γ-irradiation remains a very unique method for the preparation of metals, alloys, metal oxides, sulfides, and inorganic/polymer nanocomposites. We here demonstrate the preparation of magnetic nanomateirals and composite microwave absorbing materials through the γ-irradiation route. It is found out that a proper magnetic field can induce the prepared magnetic nanoparticles to align into well-defined stick or chain structures, where randomly dispersed nanoparticles are obtained without the application of magnetic field. The alignment of the magnetic nanoparticles gives rise to increased magnetization and coercivity due to the enhancement in shape anisotropy. Meanwhile, compared with the scattered nanoparticles, stronger electromagnetic wave absorption properties can also be realized in the aligned nanostructures, caused by the geometrical effect. (author)