Synthesis optimization of Zn-Mn ferrites for magnetic fluid applications

• Autor(a) principal: Horta, André Filipe Castanheira
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/29834
• topic: Self-Regulated Heating; Mn-Zn ferrite; Sol-gel auto-combustion method; Hydrothermal method; Curie temperature; Magnetic ordering temperature

Manganese-Zinc ferrite nanoparticles have been the subject of increasing research due to their desired properties for a wide range of applications. These properties include nanometer particle size control, tunable magnetic properties, high saturation magnetization and low toxicity, providing these ferrites with the necessary requirements for cancer treatment via magnetic hyperthermia. During this research, powders of Mn-Zn ferrite were synthesized and characterized, aiming to optimize their structural and magnetic properties for further application in a ferrofluid. Samples with Mn1-xZnxFe2O4 (x=0; 0.5; 0.8; 1) compositions were synthesized via the sol-gel auto-combustion and hydrothermal methods. Synthesized powders were characterized by XRD, SQUID, SEM, TEM and magnetic induction heating techniques. The XRD diffractograms of hydrothermally produced samples presented spinel crystal structure with high single-phase percentage (>88%). Rietveld refinement and Williamson-Hall analysis revealed a decrease of lattice constant (8.50 to 8.46 Å) and crystallite size (61 to 11 nm) with increase of Zn/Mn ratio. TEM images reveals narrow particle size distributions and decrease of the mean particle size (41 to 7 nm) with the Zn/Mn ratio increase. SQUID results showed that the increase of Zn results in a decrease of saturation magnetization (79 to 19 emu/g) and remnant magnetization (5 to approximately 0 emu/g). More noticeably, the M(T) curves present a shift in the samples magnetic ordering temperature towards lower temperatures with the increase of Zn content, from ~556 (estimated) to ~284 K. The magnetic induction heating experiment also unveiled a decrease in the heating rate with the increase of Zn in ferrite. Nanocrystals of Mn-Zn ferrite produced by hydrothermal method present better crystallinity and magnetic properties than the sol-gel auto-combustion samples. The hydrothermally synthesized samples revealed dependence of its structural and magnetic properties with Mn/Zn ratio. The magnetic ordering temperature of these ferrites can be used as a self-controlled mechanism of heating, raising these ferrites to a class of smart materials.