Preparation And Sintering Of Ni_xZn_1-xFe₂O₄Ferrites By Solid State Reaction At Low Temperature

Recently, soft magnetic materials become one of the research hotspots for its wideapplications in the fields of electronics, information, and automation and so on. The solidstate reaction at low temperature used to prepare powder materials has attracted muchattention due to its great advantages of low energy consumption, less pollution and timesaving.In this paper, we prepared the Ni-Zn ferrites powder, further used as the raw material ofbulk ferrites, with the chemicals including FeCl₃·6H₂O, ZnCl₂and NiCl₂·6H2O by solid statereaction at low temperature. The microstructures and magnetic properties were characterizedby advanced testing equipments. The influences of sintering temperature, molding pressure,holding time and additives on the relative densities, shrinkages, microstructures andthemagnetism performances of the bulk materials were investigated, and some interestingresults were also obtained.The as-prepared Ni_xZn_1-xFe₂O₄ferrites powder with average grain size of about33nmprepared by the solid state reaction at low temperature appears sphere after sintering at700℃, showing single spinel structure. The Ni_xZn_1-xFe₂O₄ferrite with X=0.5has the maximumsaturation magnetization of59.78emu/g. The lattice parameter decreases gradually with theincrease in Ni content. It is opposite for the coercivity.The average grain sizes of as-prepared Ni_0.5Zn_0.5Fe₂O₄increase with the increase in heattreatment temperature, along with the shapes of particles gradually changing from sphere toregular hexagon. The saturation magnetization increases first and then decreases. The law isopposite for the coercivity. The critical size of Ni_0.5Zn_0.5Fe₂O₄changing from single-domainto multi-domain is about21nm.Appropriate temperature and holding time in the sintering process will promote theincrease in grain size and decrease in porosity. But, the high temperature and long holdingtime will lead to the increase in porosity and volatilization of ZnO, which are not conduciveto improve the initial magnetic permeability and loss reduction. The better sample mold in50MPa is achieved in the case of sintering for4h at1150°C.To improve the magnetic properties Ni_0.5Zn_0.5Fe₂O₄ferrite and especially lower thereduction, we study the influence of the doping of Bi₂O₃, SiO₂and their composite on themicrostructure and magnetic properties. Single doping of Bi₂O₃and SiO₂can both promote the increase in grain size and improve the magnetic property. The co-doping of Bi₂O₃andSiO₂can lead to the increase in grain size and decrease in porosity. The saturationmagnetization decreases dramatically resulting in the deterioration of the initial magneticpermeability and loss reduction.