Synthesis, Mössbauer Spectra and Magnetic Properties of Quasi-One-Dimensional Fe₃O₄ Nanowires

Quasi-one-dimensional Fe₃O₄ nanowires in diameter of about 200 nm were assembled into anodic aluminium oxide templates via electrodepositing and heat-treating processes. The nanowires have a polycrystalline spinel structure with a = 8.317Å, and each nanowire is composed of fine Fe₃O₄ crystallites with size of about 30 nm. The magnetic moments of Fe₃O₄ crystallites in nanowires have a preferred orientation leaning to the wire axis but not parallel to the wire axis. Mössbauer spectra (MS) were used to verify the presence of Fe₃O₄ further and the existence of superparamagnetic particles in nanowires. A perpendicular magnetic anisotropy was observed obviously. Temperature dependence of the magnetic moments (M-T) shows that the Verwey transition for the Fe₃O₄ nanowires occurs at 50 K, and the behaviour of the M-T curve is different from that of other magnetite materials. These characteristic magnetic properties of Fe₃O₄ nanowires are mainly due to the reduced dimension and the configuration of preferred orientation in the nanowires caused by the shape anisotropy.