Graduation Semester and Year
Spring 2026
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Physics and Applied Physics
Department
Physics
First Advisor
J. Ping Liu
Second Advisor
Qiming Zhang
Third Advisor
Ali R. Koymen
Fourth Advisor
Joseph Ngai
Sixth Advisor
Qiming Zhang
Fifth Advisor
Yaowu Hao
Abstract
The development of high-performance, rare-earth-free hard magnetic materials is critical for next-generation energy, information, and spin-based technologies. This dissertation investigates structure-property relationships in iron-based magnetic systems, including iron carbides, Fe-Co-B boride alloys, hexaferrites, and FeCo nanostructures, synthesized via chemical and metallurgical routes. Through controlled synthesis and comprehensive structural and magnetic characterization, this work demonstrates that magnetic anisotropy, coercivity, and thermal stability can be systematically controlled through morphology design, compositional tuning, microstructural refinement, and interparticle interaction modulation.
Morphology-driven enhancement of magnetic properties, particularly coercivity and blocking temperature, is established in phase-pure Fe5C2 nanostructures. By precisely controlling particle geometry, the coercivity (Hc) increases systematically from 0.4 to 1.6 kOe, while the blocking temperature rises from ~375 to 507 K as the aspect ratio increases from 1 to 5. A high Curie temperature (~520 K) further identifies Fe5C2 as a thermally stable, rare-earth-free semi-hard magnetic material. In Fe5C2/SiO2 core–shell nanocrystals, SiO2 passivation suppresses dipolar coupling and modifies spin dynamics, leading to enhanced coercivity. The reduction in interparticle interactions is confirmed through zero-field-cooled and field-cooled (ZFC-FC) magnetization, δM analysis, Bloch’s law fitting, and Kneller’s law analysis.
Compositional tuning effects are explored in melt-spun Fe-Co-B-based boride alloys. Minor Zr and Ag incorporation in tetragonal (Fe0.7Co0.3)2B significantly enhances the magnetocrystalline anisotropy field while maintaining saturation magnetization and phase purity. Si substitution in Fe3CoB2 nanocrystallites enables controlled modulation of anisotropy and coercivity through lattice modification and grain refinement. Similarly, Mn-substituted SrFe8-xMnxAl4O19 hexaferrites exhibit substantial coercivity enhancement driven by increased magnetocrystalline anisotropy and modified exchange interactions.
FeCo nanoparticles synthesized via thermal decomposition exhibit exceptionally high saturation magnetization (~230 emu/g) along with strong interparticle dipolar coupling, resulting in interaction-driven anisotropy and enhanced low-temperature coercivity upon magnetic alignment.
Overall, this dissertation explores multiple approaches for tailoring magnetic anisotropy and coercivity in rare-earth-free iron-based materials. By examining morphology, compositional modification, microstructural effects, and interparticle interactions, the results presented here contribute to the understanding of magnetic properties in these systems and provide insight for the development of next-generation rare-earth-free magnetic materials.
Keywords
Rare-earth-free, permanent magnets, coercivity, anisotropy field, maximum-energy-product, Hägg carbide, FeCo nanoparticles, dipolar interactions
Disciplines
Condensed Matter Physics
License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Joshi, Pramanand, "MAGNETIC ANISOTROPY ENGINEERING IN RARE-EARTH-FREE IRON-BASED MAGNETIC MATERIALS" (2026). Physics Dissertations-Archive. 189.
https://mavmatrix.uta.edu/physics_dissertations/189