Chemical Correlation of Magnetic Permeability and Microwave Absorption in Spinel Ferrite Nanoparticles

Spinel ferrites (MFe₂O₄, where M = Mn²⁺, Co²⁺, Zn²⁺, etc.) are magnetic nanomaterials with tunable properties that are valuable for wireless communication, memory storage, and electronics. Their complex permeabilities that are governed by composition, particle size, and spin-orbit interactions play a critical role in the determination of their electromagnetic performances. This dissertation explores the effect of chemical doping of nanoscale ferrites of 4 – 12 nm) on the complex permeability and ferromagnetic resonance (FMR) behavior. Size-dependent studies in MnFe₂O₄ and CoFe₂O₄ reveal that increasing particle size enhances both the real (μ′) and imaginary (μ″) parts of permeability due to reduced spin frustration and improved magnetic alignment. Doped CoxMn₁₋ₓFe₂O₄ ferrites show that increasing Co²⁺ lowers permeability, attributed to cobalt’s high magnetic anisotropy and spin-orbit coupling, while simultaneously minimizing its magnetic loss. In contrast, ZnxMn₁₋ₓFe₂O₄ and ZnxCo₁₋ₓFe₂O₄ exhibit rising μ′ and μ″ with increasing Zn²⁺ due to their associated reduced magnetic anisotropy and weakened exchange interactions. Ho³⁺ doping in MnFe₂O₄ leads to decreased permeability, as its large ionic radius and strong spin-orbit coupling disrupt exchange pathways. FMR analysis further highlights how magnetic anisotropy influences absorption. Co-rich ferrites display broader linewidths (FWHM), while Zn-rich variants show increased absorption from reduced damping. Interestingly, Co-containing ferrites demonstrated a unique FMR emission profile, likely resulting from cobalt's strong spin-orbit coupling and dynamic relaxation behavior. Rare-earth doped studies confirmed that such emission is specific to Co²⁺ environments and not solely due to spin-orbit strength. These results clarify how chemical composition modifications and nanoscale tuning governs the electromagnetic response of spinel ferrites, offering a library for high-performance magnetic materials in microwave technologies.

Level thesis:degree_level

Doctoral

Department dc:contributor.department

Chemistry and Biochemistry

Grantor dc:publisher

Georgia Institute of Technology

Year dc:date.issued

2025

Author dc:creator

• Aldama, Edgar

Advisor dc:contributor.advisor

• Zhang, Z. John

Committee members dc:contributor.committeemember

• Wilkinson, Angus
• La Pierre, Henry
• Xia, Younan
• Liu, Meilin

• Complex permeability
• nanoparticles
• spinel ferrites

Language dc:language.iso

en_US

Handle dc:identifier.uri

https://hdl.handle.net/1853/77919

OAI identifier oai:identifier

oai:repository.gatech.edu:1853/77919