Structure And Magnetic Properties Of Ferrites Sintered By Two-step Sintering Process

Nano-ferrite, as an important non-metallic magnetic material, has been widelyused in telecommunications, electromechanics, transportation, biomedicine etc. Thepreparation and sintering of ferrites have an important influence on the structure andmagnetic properties of ferrites. Up to now, the preparation of ferrites has been fullydeveloped, while the sintering technology as an important factor affecting propertiesof ferrites has caused increasing interesting. Recently, some investigators apply a two-step sintering process to improve the structure and magnetic properties of ferrites.In this dissertation, we used sol-gel auto-combustion to prepare the ferritepowders and sintered the pressed ferrites by single-step sintering process and two-stepsintering process. With the technology of X-ray diffraction (XRD), scanning electronmicroscopy (SEM), vibrating sample magnetometer (VSM) and LCR meter, weinvestigated the effect of calcining temperature and sintering temperature on structureand magnetic properties of NiCuZn ferrite. By changing the content of Cu2+andcomparing the single-step sintering process with the two-step sintering process, weinvestigated the structure and magnetic properties of MgCuZn ferrites.To study the influence of calcining temperature on structure and magneticproperties of Ni0.2Cu0.3Zn0.5Fe2O4ferrite, we chose the temperature range of500~800oC. We obtained the pure spinel phase. With the calcining temperature increasing,the saturation magnetization, sintering density, initial permeability and Curietemperature first increased, and then decreased. The best magnetic properties could beobtained at the calcining temperature650oC.We sintered Ni0.2Cu0.3Zn0.5Fe2O4ferrite by the two-step sintering process inwhich the first sintering temperature THwas between1000oC and1100oC and thesecond sintering temperature TLwas950oC. By comparing the two-step sinteredsamples with the single-step sintered samples at950oC, we found that the two-stepsintering process could improve the structure and soft magnetic properties ofNi0.2Cu0.3Zn0.5Fe2O4ferrite. When THwas1000oC, the highest sintering density,saturation magnetization and uniform grain were obtained. The higher the firstsintering temperature TH, the better the soft magnetic properties were.By two-step sintering process, we fabricated toroid-shaped Mg0.5-xCuxZn0.5Fe2O4samples and investigated the effect of Cu2+content on MgCuZn ferrites. The sinteringdensity and initial permeability were found to be improved comparing with the single- step sintering process. With the Cu2+content increasing, the grain size has no obviouschange, and the initial permeability firstly increased and then decreased. The Curietemperature increased linearly with the Cu2+content.