Shape-controllable Synthesis And Magnetic Properties Of Micro/Nanostructured Ferromagnetic Metallic Materials

Morphology control of micro-/nanometer scale materials has attracted a great deal of attention because the properties of micro-/nanomaterials sensitively depend on their size and shape.Ferromagnetic metal materials,especially Fe,Co and Ni,have been studied for many years for their unique properties and potential applications.In this paper,some research works on the shape-controllable synthesis of micro/nanostructured ferromagnetic metals have been done.1.Synthesis of metallic Co microcrystals with flowerlike architectures via a hydrothermal routeWell-defined,three-dimensional(3D) flowerlike metallic Co microcrystals with several radiating hexagonal-tapered petals assembled by particles sized of 150-250 nm were fabricated via a facile hydrothermal reduction route under a fixed basic condition.The probable formation mechanism of the flowerlike Co microcrystals was discussed based on the experimental results.The flowerlike products exhibited ferromagnetic characteristics with a saturation magnetization of 128.1 emu/g and a coercivity of 232.5 Oe at room temperature.Compared to the coercivity value of bulk Co,the products displayed a remarkable enhanced value due to their special morphology.2.Controlled synthesis of Co nanostructures using an external magnetic fieldChainlike,spherical and flowerlike structures of hcp Co were synthesized via a facile template-free aqueous solution reduction approach under an external magnetic field at 60℃.The results demonstrated that reaction parameters such as the external magnetic field and the cobalt precursor concentration played an important role in controlling the morphology of the products.Compared with the coercivity value of bulk Co,the synthesized products displayed remarkable enhanced value due to their special morphology. 3.Controlled synthesis of FeNi₃ alloy nanostructures via reverse microemulsion-directed hydrothermal routesFeNi₃ alloy nanostructures were synthesized by hydrothermal methods in the surfactant/n-octane/n-hexanol/water quaternary reverse microemulsion system.The size and shape of the products could be controlled by changing the category and dosage of the surfactant.Spherical particles with diameter of～75 nm were prepared when PEG was used as the surfactant.Sea-urchin-like particles were obtained when CTAB was used as the surfactant.The single sea-urchin-like particle was constituted by lots of nanorods with diameter of～42 nm and a length of 0.4-1.2μm.Both of spherical and sea-urchin-like FeNi₃ samples exhibited typical ferromagnetic behavior at room temperature.The saturation magnetization value for them were 114.4 emu/g and 97.4 emu/g,respectively,while the coercivity value were 94.0 Oe and 329.0 Oe, respectively.