Year: 2026
Type: dissertation
Abstract: Magnetism can be considered not only an inherent property of materials but also an external "knob" to regulate structure-property relationships and dynamic interfacial processes. This dissertation explores magnetic materials from three complementary yet independent perspectives, with the core theme being the functional modulation of solid-state and electrochemical systems through magnetic response and magnetic fields. Firstly, this thesis provides a focused review of magneto-optical Kerr effect (MOKE) microscopy and related magnetic characterization techniques, outlining their physical principles, typical experimental configurations, and practical strengths for probing magnetic states with high sensitivity and spatiotemporal resolution, while summarizing common pitfalls and recommended practices for quantitative analysis. Then, the next part demonstrates a solid-state route to introduce magnetic response into an intrinsically nonmagnetic functional oxide through doping and defect engineering. Using barium titanate (BaTiO3, BTO) as a model ferroelectric perovskite, a series of BaTi0.9M0.1O3 ceramics (M = Fe, Mn, Co, Cr) were synthesized and systematically characterized using X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), Raman spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometer (VSM). The results showed that the perovskite structure was preserved after doping, and no second phase was detected, while the lattice disorder increased after doping. XPS revealed electronic structure reconstruction induced by doping, as well as an increase in the proportion of defects and associated oxygen species. All dopants exhibited weak but discernible room-temperature magnetic hysteresis, indicating that the combination of heterovalent substitution and defect chemistry is a feasible way to induce magnetic responses in ferroelectric materials. Third, this thesis explores magnetic-field regulation of an electrochemical energy-conversion interface. A ZIF-67-derived Co3O4 catalyst modified with iron species was developed for the alkaline hydrogen evolution reaction (HER). Under zero magnetic field, HER performance exhibited a volcano-like dependence on iron loading, with the optimal loading being 2.5% Fe–Co3O4 (η₁₀= 144.3 mV). Applying a vertical magnetic field further enhanced HER kinetics, achieving η10 of 45.1 mV at 100 mT, while simultaneously reducing the fitted charge transfer resistance by an order of magnitude. Control experiments using a glass baffle demonstrated that the field effect is not limited to simple macroscopic convection but is consistent with the coupling between near-electrode transport, bubble kinetics, and interfacial charge transfer processes.
Author: Huang, Tianqi
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7203930574
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