Design, Synthesis And Magnetic Properties Of Micro And Nano-structured Iron Oxide

As one of the green materials and environment-friendly materials, iron oxide is nontoxic and unpolluted. It is important in varies of fields. In recent years, many new techniques have been developed in order to synthesize iron oxide with different shapes and properties. In this study, fantastic submicron and nano-structured iron oxide has been synthesized through thermal treatment of the iron film assisted by oxalic acid. The iron film is (110) preferential prepared on glass substrate by magnetron sputtering. The experimental conditions leading to different morphologies and the possible growth mechanisms as well as the magnetic properties have been investigated in detail. The main results are listed as follows:Firstly, oxalic acid was dropped on the surface of iron nano film. After thermal treatment at temperatures between 100℃and 600℃under ambient conditions, micro- and nano-structured iron oxide with different morphologies, such as polyhedron, blade-like and ball-flower, were obtained. Iron oxide is hard to form under 300℃; Fe3O4 is formed between 300℃and 400℃;α-Fe2O3 is prevailing above 500℃. The most homogeneous distribution of surface morphology is obtained in the method of wetting instead of dropping oxalic acid. With the heating rate of 10℃/min, the samples consist of uniform micro-sized polyhedron as prevalent morphology at temperatures between 100℃and 300℃; While between 300 and 400℃, with a lower heating rate, the prevalent morphology is blade-like nanostructure and the blades become wider and thicker as the heating temperature increases. Thicker film tends to induce rod-like nanostructure with larger aspect ratio.In the contact mode of scanning probe microscope, the original morphologies of unannealed samples wetting with merely distilled water and with 0.75 M oxalic acid were obtained, respectively. The surface of the former is full of round granule while the latter is in the shape of rhomb. Thus, oxalic acid is demonstrated to be crucial for the formation of polyhedron with rhombic cross section. The polyhedron and ball-flower microstructure is formed in a process of"nucleation–upgrowth–conglomeration-self assembled"at low temperatures and blade-like nanostructure is formed in a diffusion process at high temperatures.The magnetic properties of iron oxide were also investigated. It is found that the coercivity increases at first and then decreases with the increasing heating temperature, a maximum shows up at 300℃, and the magnetization decreases gradually. The easy magnetization axis lies in the surface of film.