Controlled Synthesis And Physical Properties Of Magnetic Nanomaterials

In this dissertation, solution-based routes were employed to realize the chemical synthesis of magnetic nanomaterials, and magnetic properties of the nanomaterials were studied systemically. Size, shape and morphology of the magnetic nanomaterials were controlled effectively through modulating the nucleation stage and crystal growth stage, and/or by tuning the starting materials' concentration. Hydrothermal method was employed to synthesize one-dimensional nanostructures of potassium manganese oxides, and transport properties of one single nanowire were studied. In addition, chemically colloidal methods were also employed to synthesize high quality Zr_1-xCe_xO₂ solid-solution nanoparticles and copper sulfide nanoplates.1. In the first section of this thesis, we discuss the latest development of the solution-based chemical synthesis methods and magnetic properties of magnetic nanomaterials. The theory and mechanism of chemically colloidal method which is used to synthesize nanomaterials with controlled size and shape are systemically reviewed. In addition, we review the latest experiment and theory research on magnetic properties that are affected by size effect and surface effect.2. A high-temperature solution-phase route, in which oleylamine was used as solvent and surfactant and metallorganic acetylacetones were used as precursors, was employed to synthesize monodispered nanomaterials of magnetic transition metal oxides: CoO, MnO, and CoMn₂O₄. The sizes of CoO and CoMn₂O₄ nanocrystals were controlled by tuning the kinetics of crystal growth. Remarkably, CoO nanocrystals changed from spherical shape to quasi-cubic shape when ten equivalent of water was introduced into the reaction medium. The morphologies of 3D hierarchical MnO nanocrystals were controlled by tuning the nucleation rate, which was implemented by modulating the heating rate and intensity of refluxing. Owning to the dipolar interactions between nanoparticles, the blocking temperatures didn't increase linearly with increasing particle size in the CoO and CoMn₂O₄ nanocrystal systems.