The Influence Of Presintering Temperature And The Two-step Sintering Process On NiMgCuZn Ferrites’ Structure And Magnetic Properties

With the development of electronic industry, multilayer chip inductors（MLCI） as one of the most important surface mount devices（SMD） is widely used in the integrated circuit. NiCuZn ferrite due to excellent magnetic properties has become the main material of laminated chip inductor and become one of the current hot topic in research of ferrite materials. Moreover, MgCuZn ferrite that has good stability, high resistivity and low cost is expected to become a potential magnetic materials of laminated chip inductor. And in the production of multilayer chip inductors the ferrites need to be burned with silver electrode, and silver’s melting point is 961 ℃, so we need to find a method of low temperature sintering. Recently a new method of two-step sintering process was applied to make the properties and structure of ceramics better.In this paper, sol-gel auto-combustion was used to produce the ferrite powders and both the single-step sintering and two-step sintering was used to sinter the pressed ferrites. It was found that the calcining temperature and sintering temperature had very important impact on the NiMgCuZn ferrite.The Ni_0.1Mg_0.1Cu_0.3Zn_0.5Fe₂O₄ ferrites were made by sol-gel auto-combustion with calcining temperature at 550-750 oC. The ferrites had the single phase spinel structure that confirmed by the X-ray diffraction patterns. And with the presintering temperature up the ferrite powder’s crystallite size increased from 16.8 nm up to 37.1 nm. The calcining temperatures had important impact on the structure and magnetic properties of Ni_0.1Mg_0.1Cu_0.3Zn_0.5Fe₂O₄ bulk ferrite sintered in 950 ℃: With the increase of sintering temperature, bulk density, saturated magnetization intensity, initial permeability first increased and then decreased and reached the maximum at 650 ℃.With the increase of sintering temperature, coercive force first decreased and then increased, and reached the minimum at 650 ℃.We sintered Ni_0.1Mg_0.1Cu_0.3Zn_0.5Fe₂O₄ ferrites by the two-step sintering process, in which the first sintering temperature TH is between 1000 oC and 1100 oC, the time of the first sintering temperature ?tH is between 0 minute and 45 minutes, and the temperature TL of the second sintering step is 950 oC. Compared with the single-step sintering between 950 oC and 1100 oC, the results show that the two step sintering process can improve the sintering density and saturation magnetization and initial permeability.