Date of Award

8-2025

Document Type

Dissertation

Degree Name

Doctor of Engineering (DEng)

Department

Materials Science and Engineering

Committee Chair/Advisor

Thompson Mefford

Committee Member

Suvra Laha

Committee Member

Thomas Crawford

Committee Member

Dilpuneet Aidhy

Committee Member

Kyle Brinkman

Abstract

This dissertation focuses on understanding how to tune the magnetic properties of nanoparticles through controlling the effective magnetic anisotropy (Keff), which is a key variable in determining a nanoparticle’s Néel relaxation time, which will dictate its magnetic behavior in various applications. In this work, magnetocrystalline anisotropy is tuned by synthesizing tri-metallic substituted ferrite (Fe3-x-yMnxCoyO4) nanoparticles with specific metallic compositions that were informed by computer simulations using density functional theory (DFT) to target magnetocrystalline anisotropy values. A drip synthesis was used to control the size and composition of the tri-metallic ferrites, which were revealed to be monodisperse and compositionally mixed by x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and inductively coupled plasma-optical emission spectroscopy (ICP-OES). Both calorimetric and AC magnetometric specific absorption rate (SAR) measurements suggested that the nanoparticle’s heating capabilities were influenced by their metallic compositions. The tri-metallic nanoparticles were then measured using a physical property measurement system (PPMS) to experimentally measure their Keff values. As the tri-metallic nanoparticles increased in manganese content, the Keff values ranged from 80,000 J/m3 to 115,000 J/m3, showing an opposite trend that was predicted through the DFT simulations and illustrating magnetocrystalline anisotropy can be altered via metallic ion substitution in the nanoparticles’ crystalline lattice. A targeted higher cobalt content tri-metallic nanoparticle series was also synthesized, with a Keff value of 153,162 J/m3. To synthesize a multi-modal nanoparticle for biomedical applications, nanoclusters with a distinct shape resembling flowers were synthesized. The iron oxide nanoflowers (IONFs) were also doped with gadolinium (Gd-IONFs) to improve their magnetic heating, and their magnetic resonance imaging (MRI) capabilities. The nanoflowers showed a large reduction in their Ms when doped with gadolinium. Low temperature relaxation features below 50 K were measured, suggesting polydispersity in the crystallite sizes of the nanoflowers, suggesting that the magnetic properties of the nanoflowers are dictated by the size of the individual nanoparticles that comprise it. To study the effects of dipole interactions on Keff, spherical iron oxide nanoparticles that were 10 nm in diameter were synthesized and coated in silica shells with various shell thicknesses using a reverse microemulsion method. The thicknesses were determined using HRTEM. The Keff values of the nanoparticles at each shell thickness were then determined through finding what temperature that the maximum value for the imaginary susceptibility occurs at different frequencies. Nanoparticles with high heating efficiency were surface functionalized with a polyacrylic acid – polyethylene oxide (PAA-PEO) copolymer with a glycan known as Asialo GM2 ganglioside oligosaccharide (aGM2) attached to the end of the chains using click chemistry, which has been shown to bind to Neisseria Gonorrhoeae. Each modification step for the polymer was characterized using nuclear magnetic resonance (NMR). The functionalized nanoparticles were characterized using Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and zeta potential experiments. They were found to have the glycan bound to their polymer shells, which allows them to be used in experiments for the selective killing of Neisseria Gonorrhoeae through magnetic induction heating.

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