Aminolytic synthesis and ferromagnetic resonance of cobalt and manganese based spinel ferrite nanoparticles
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Magnetic ferrite nanoparticle is a potential material in a number of fields and designing of such applications requires the fine-tuning of magnetic properties through synthesis by chemical composition and dimensional control. In order to manipulate the specific material performance, the fundamental relationship between the microstructure and magnetic properties is a topic of high interests. Spinel ferrite materials often have a strong coupling to electromagnetic signals due to high permeability and permittivity and thus could be used in a variety of microwave devices, e.g. from military shielding to wireless communication signal enhancement. The purpose of this thesis is to study the magnetic correlations and ferromagnetic resonance (FMR) through different spinel ferrite nanoparticles with systematic size and composition variations, and thus one could design materials that meet the best application properties. Chapter 2 studies the versatility and mechanism of aminolytic method, the nanoparticle synthesis method which has been developed in Zhang group. It is shown that with fine controls of synthesis conditions, a wide range of spinel ferrites with different sizes and compositions can be made successfully. Chapter 3 utilizes aminolytic method and investigates the magnetic property changes with rare-earth elements substitution within spinel ferrite lattices. In Chapter 4, a series of spinel ferrite nanoparticles were made and their physical properties were examed with different techniques including SQUID (superconducting quantum interference device) magnetometry and EPR (electron paramagnetic resonance) spectroscopy. A negative correlation between magnetic susceptibility (χ) and FMR field (H) has been found and it provides a shortcut to foresee H with one single measurable χ without further structural information such as degree of inversion and magnetic structures. Chapter 5 investigates the detailed quantitative correlation between magnetic susceptibility (χ) and FMR field (H) with a series of MnFe2O4 (3-10 nm), ZnxMn1-xFe2O4 and CoxMn1-xFe2O4. This chapter also demonstrates how one could tune FMR absorption profile (both H and ΔH) of the material through synthesis controls. Chapter 6 explores the fabrication of nanomagnetic films and their microwave absorption performance in wireless communication devices. This provides the way to utilize well-designed particles in film forms for actual applications. The thesis ultimate goal is to understand the physical properties of magnetic solids through the systematic studies and further satisfy the need of certain material applications.