Composite films with magnetic nanorods: Fundamentals, processing and applications.

摘要

This dissertation is centered on studying the composite films with magnetic nanorods. In recent years, one-dimensional magnetic nanostructures, such as magnetic nanorods, chains of magnetic nanoparticles, and nanotubes filled with magnetic nanoparticles have caught great attentions due to the breadth of applications. Their unique magnetic and geometrical features open new avenues of studies in medicine, sensors, optofluidics, magnetic swimming, and microrheology. In particular, they offered great opportunities for design of multifunctional devices and for manufacturing of anisotropic nano- and microstructures with unprecedented magnetic and mechanical properties. However, the strategy for nanorod alignment in both Newtonian and complex fluids has not been developed and this remains the main challenge in materials engineering and processing. On the other hand, the basic understanding of the properties of the fabricated composite material is also lacking. These challenges and problems are addressed in this dissertation.;In chapter I, some basic concepts and common terminologies of ferromagnetism such as magnetic anisotropy, domain structure, etc. are introduced. The magnetic hysteresis for a single domain ferromagnetic nanoparticle is also explained. In chapter II, the magnetostatic problems for both single domain magnetic nanosphere and nanorod are solved. The interactions between both spherical nanoparticles and nanorods are also studied based on the solutions of magnetostatics. In chapter III, the synthesis of nickel and cobalt nanorods using electrochemical deposition method is described and various methods are applied to characterize the synthesized nanorods. In chapter IV, the strategies for the alignment of magnetic nanorods in Newtonian and complex fluids are developed. The nanorod alignment in complex fluids is found to be very tricky and deserves further study. In chapter V, the evaporation kinetics and viscosity change of a ceramic precursor (an example of complex fluid) is studied during the sol-gel processing. Together with chapter IV, they provide a basis for the fabrication of ceramic composites containing of magnetic nanorods. In chapter VI, the interactions between magnetic nanorods under magnetic field gradient are studied both theoretically and experimentally. This chapter provides a method of using field gradient to defeat repulsion between nanorods and achieve very high local concentration of nanorods. In chapter VII and VIII, the theory describing the property of composite film is proposed. The ferromagnetic resonance and heating properties of a single domain nanoparticle is studied in chapter VII. In chapter VIII, interactions of electromagnetic waves with magnetic nanocomposite films are discussed. We predict an unusual transmission, reflection, and absorption properties of these films and discuss the Faraday and Kerr effects as well.