Chemistry Has Deep Prepared Manganese Zinc Ferrite And Its Magnetic Studies

With the rapid development of modern electronic industry, electronic equipment are becoming toward the direction of miniaturization, lightweight and thin, so the requirements for the performance of magnetic material are more and more trenchant. As a wildly used soft magnetic materials, MnZn ferrites with higher permeability and lower magnetic loss attrack more and more eyes from researchers. Generally, in order to improve the properities of MnZn ferrites, the composition of the material, the use of additives and the sintering process are studied.On the basis of our research results about chemical co-precipitation in the past few years, MnZn ferrite precursor powders were synthesized by chemical co-precipitation, and two important factors, pH value and the concentration of dispersing agent SDBS were disussd in order to obtain fine and uniform precursor powders. The particle size of the precursor powders were analysed by Laser particle size analyzer, it showed that the average sizes of the particles were1.49～2.12μm in the conditions of pH=9.50～11.00, T=70℃, R=300rpm, V=0.5ml/min, SDBS=0～0.4g/L. After calcining at450℃, the precurosr powders were then pressed into rings, which were followingly sintered at1300℃. X-ray diffraction (XRD) was used to characterize the phase of ferrite, the results indicated that precursor powders prepared at the condition of0.2g/L of SDBS and pH=10.00owned fine particle and intact crystal structure. Magnetic properties of MnZn ferrites were investigated by the vibrating sample magnetometer (VSM) and HP4291A impedance analyzer. It showed that the specific saturation magnetizationσs, coercitive force HC, residual magnetizationσi, initial permeability μi, relative loss factortgδ/μi in100kHz and cut-off frequency fr of the sample were64.09A·m2·kg-1,0.51kA·m-1,3.08A·kg-1,3500,1.52×105and4.2MHz respectively at the optimized technological conditions (pH=10.00, T=70℃, R=300rpm, V=0.5ml/min and SBDS=0.2g/L).The fine and uniform precursors with high activity synthetized via chemical co-precipitation were calcined at different temperature ranged from400to650℃, and then the calcined powders were pressed into rings, which were followingly sintered in air at1200～1350℃and cooled in nitrogen. Thermogravimetric analysis and Differential thermal analysis (TGA-DSC), X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) were used to characterize the variation of the composition and microstructure during the sintering process. The results showed that after calcining at a lower temperature (450℃) and sintering at1300℃, the calcined sample maintains a maintain crystal structure. The calcined samples showed excellent magnetic properties:the saturation magnetization σs firstly arises with the ascending temperature and then decreases to zero, while initial permeability μi of the sintered sample decreases with increasing heat treatment temperature first but rises to apex in the end. After calcining at450℃, the samples were sintered at1300℃, the specific saturation magnetization, coercitive force, initial permeability, relative loss factor and cut-off frequency of the sample were σs≈31.26A·m2·kg-1, Hc≈3.18kA·m-1, and μi≈3200, tgδ/μi≈1.52×10-5(100kHz), fr=4.0MHz respectively.In order to enhance the magnetic properities, SiO2+CaCO3, Bi2O3and MbO5were added to the calcined samples. Fristly, after adding200ppm SiO2, CaCO3with the doping amount of300ppm,600ppm,900ppm and1200ppm was studied. The result shows that the loss of MnZn ferrites were decreased obviously when doping600ppm CaCO3,μi≈2100, tgδ/μi≈6.7×x10-6, and the relative density is95.09%. Secondly, the additive Bi2O3was added with the amount of300ppm,600ppm,900ppm and1200ppm. It shows that Bi2O3can increase the initial permeability μi from2100to2500(at100kHz) at the amount of600ppm, while there is almost no effect on the relative loss factor tgδ/μi. Lastly, Nb2O5was added to improve the magnetic properities of MnZn ferrites. The result is analysed that Nb2O5can improve the loss of MnZn ferrites and relative density, but also can decrease the initial permeability. When doping Nb2O5on MnZn ferrites,μi is decreased from2550(without Nb2O5) to2000(300ppm Nb2O5). From the effect with doping Nb2O5, the initial permeability μi increases from1980to2150with the amount of300ppm Nb2O5, while the relative loss factor tgδ/μi decreases from2.86×10-5to1.09×10-5, and the the relative density is about99.23%.