Preparation And Property Study Of Submicrometer-sized NiZn Ferrite Prepared By Spark Plasma Sintering

Ferrite ceramics is one kind of oxide ceramic material which exhibits ferrousmagnetic and Ni-Zn ferrite ceramics with spinel structure is widely used as softmagnetic material. After decades research and exploration, the research of ferrite latticestructure, magnetic source, microstructure, physical properties and the preparationtechnology have reached a very perfect situation. On the other way, along with thedevelopment of electronic products tending to the direction of miniaturization, thepreparation of high density, uniform, fine grain soft magnetic ferrite is particularlyimportant. However, the grain sizes of samples prepared by the traditional preparationmethods are generally very large, the average particle sizes of particles are lesshomogeneous and density is not high. Therefore, seeking an effective new ferritepreparation technology has become the research topic and a hot issue.In the present work high-density submicrometer-sized Ni0.5Zn0.5Fe2O4ferriteceramics were prepared by spark plasma sintering in conjunction with high energy ballmilling. Then the properties of them were evaluated by different characterizationtechniques such as X-ray diffraction, scanning electron microscopy, and dielectric andmagnetic measurements. All samples prepared at sintering temperatures ranging from850to925oC exhibit a single spinel phase and their relative densities and grain sizesrange from90%to99%and~100nm to~300nm, respectively. The dielectric constantincreases with decreasing grain size until~250nm, and then decreases dramaticallywith further decreasing grain size. The saturation magnetization increases continuouslywith increasing grain size/density but the magnetic coercivity decreases. The highestdielectric constant and saturation magnetization at room temperature are approximately1.0×105and84.4emu/g, respectively, while the lowest magnetic coercivity is onlyaround15Oe.For these powders milled for different time by ball milling are sintered900oC and925oC. All samples exhibit a single spinel phase and their relative densities and grainsizes range from86%to99%and~80nm to~350nm, respectively. The dielectricconstant of these samples have the same tendency of these samples prepared at sinteringtemperatures ranging from850to925oC. And the dielectric constant reach the peakvalue at the grain size of~250nm. The saturation magnetization increases continuously with increasing density and the magnetic coercivity decreases with increasing grain size.The highest saturation magnetization at room temperature is approximately86.6emu/g,while the lowest magnetic coercivity is only around15.6Oe.These outstanding properties could be associated with high density and uniformmicrostructure created by spark plasma sintering. Therefore, the spark plasma sinteringis a promising technique for fabricating high-quality NiZn ferrites with high saturationmagnetization and low coercivity.