Synthesis And Micromagnetic Simulation Of Biomedical Fe₃O₄ Nano-ellipsoids With Magnetic Vortex State

Recently, the magnetic vortex-state nanoparticles, due to unique vortex domain structure and more excellent magnetic properties, has been concerned widely in biomedical applications such as magnetic resonance imaging ?MRI?, magnetic hyperthermia etc. This thesis takes ellipsoidal magnetite nanoparticles ?EMPs? as the study subject to discuss its preparation and characterization, and to investigate its magnetic vortex configurations and the magnetization reversal behaviors by means of the micro-magnetic simulation software OOMMF ?object-oriented micro-magnetic framework?. The detailed contents and methods are as follows:?1? Preparation and characterization of the EMPs. The EMPs are prepared by two-step synthesis which includes the hydrothermal process of preparing a-Fe₂O₃ ellipsoidal nanoparticles and the hydrogen thennal reduction that these a-Fe^Ch nanoparticles are used as template and converted into Fe₃O₄ phase. During the hydrothermal process, through controlling the concentrations of the reactants, the ?Fe₂O₃ ellipsoidal nanoparticles with different aspect ratio can be obtained. In respect of the characterization of the EMPs, the shape and size of EMPs have been observed by the scanning electron microscope ?SEM? and the transmission electron microscope ?TEM?. The phase analysis has been performed through high-resolution TEM, selected area electron diffraction ?SAED? and X-ray diffractometer ?XRD? etc. The magnetic properties of EMPs have been tested by vibrating sample magnetometer ?VSM?. Particularly, the magnetic vortex domain structure of EMPs has been verified through Lorenz TEM experimentally.?2? The micro-magnetic simulation of EMPs. Firstly, a magnetization vortex state is observed in EMPs with different aspect ratio ?p = a/b = 1.0,1.5,2.0?. Secondly, the remanence phase diagram of EMPs with major axis a from 60 nm to 260 nm and minor axis b varying between 60 nm and 130 nm is obtained as a function of major axis a and minor axis b, which identifies a vortex phase and a single-domain phase. Thirdly, the angle-dependence of single EMP with different orientations related to the direction of external magnetic field is investigated and the simulated hysteresis loops and the switching fields are obtained as a function of angle ?. Finally, the inter-particle interaction of double EMPs is investigated by changing the inter-particle angle ?, and results indicate that the different angles ? have effects on the vortex chirality of double EMPs.In a word, this work makes us gain insight into the synthesis of EMPs and its magnetic vortex configuration and the magnetization reversal mechanism, the purpose is to provide the preliminary exploration of magnetic mechanism for using the novel magnetic vortex nanoparticles in various bio-magnetic applications.