Magnetic Properties Of Nanosize Soft Magnetic Ferrites Synthetized By Sol-gel Auto-combustion

Magnetic nanomaterial is currently the hot topic of the current research. The softmagnetic ferrite is one of the most important soft magnetic materials with a widerange of applications. In this dissertation，the preparation and properties of softmagnetic Mn-Zn ferrites and Ni-Zn ferrites were discussed.The sol-gel auto-combustion preparation technique of ferrite nanocrystal wasinvestigated in this paper. The toroidal specimens were sintered by different sinteringprocesses （including the final-stage sintering process and two steps sintering process）.We designed different stoichiometric composition and studied the influences of ionsubstitution, Co and Cu, on the structure and magnetic properties of Mn-Zn ferritesand Ni-Zn ferrites. The physical and magnetic properties of powder and sinteredcompacts were measured by X-ray diffraction （XRD）, scanning electron microscopy（SEM）, vibrating sample magnetometer （VSM） and LCR meter, respectively.In order to study the influence of different complexing agent （citric acid） contenton magnetic properties of Mn ferrites, we prepared sufficient samples of MnFe2O4ferrites with different ratios of citric acid to metal ion. As proved in the experiments,when the ratio of citric acid to metal ion is1:1, we got pure sample without anyimpurity. The nanosize ferrite power could be magnetized to saturation in a smallermagnetic field and had the maximum saturation magnetization and minimumcoercivity. This is mainly because citric acid content directly affects the hydrolysisreaction and polycondensation reaction. The appropriate citric acid content could fullyreaction with metal ions.The structural characteristics and magnetic properties such as the latticeparameter, grain size, saturation magnetization, as well as initial permeability wereinvestigated for Cu substituted Mn_0.4Zn_0.6-xCo_xFe₂O₄（x=0,0.1,0.2,0.3,0.4） ferrites.The results implied that Co2+ions could be dissolved into the spinel lattice. The latticeparameter and saturation magnetization have a same change trend due to thepreference of ions in specific sites, ion size and magnetic moment. The initialpermeability decreased with the increase of Co content, this mainly because densitydecreased and Co2+ions contributed great and positive magnetocrystalline anisotropy.Moreover, we investigated the structural characteristics and magnetic propertiesof Ni_0.4Cu_xZn_0.6-xFe₂O₄sintered by the final-stage sintering process and two stepssintering process. As proved in the experiments, the sample subjected to the two-step sintering process presented a uniform microstructure with small grain size withoutabnormal grain growth, which benefits to increase density and initial permeability.The two sintering processes didn’t influence Curie temperature which depends on iondistribution and the intensity of exchange effect in Ni-Zn ferrites.