The Performance Study Of Bi-Co Modified Ni-Mg-Cu-Zn Ferrites Synthesized By Sol-gel Method

Multilayer chip inductors?MLCI?is the basic components of high-frequency circuits,which is widely used in industry,information industry,even military industry and other fields.As the main material of MLCI,Ni-Cu-Zn ferrite has good high frequency magnetic properties,low sintering temperature and other advantages.On the other hand,Mg-Cu-Zn ferrite also turns into an important raw material of chip inductors because of its high resistivity and low production costs.Combined with these characteristics of both ferrites,Ni-Mg-Cu-Zn ferrite has become the main research direction as quality raw materials of MLCI.Ni-Mg-Cu-Zn ferrite needs to be sintered at low temperature and maintain good high-frequency performance in order to meet the industrial production needs.Therefore,we studied the effect of doping substitution on improving the structure and magnetic properties of Ni-Mg-Cu-Zn ferrite.In this study,we made metal nitrate solution as raw material occur complex reaction in citric acid,then prepared Ni-Mg-Cu-Zn ferrite powders and bulks by sol-gel method.With the X-ray diffraction?XRD?,vibrating sample magnetometer?VSM?,LCR impedance analyzer,scanning electron microscopy?SEM?and magnetic permeation instrument,we studied the structures and magnetic properties of Ni-Mg-Cu-Zn powders and bulks with Bi³⁺ions,Co²⁺ions,Bi-Co co-doping and different sintering temperature.First of all,the properties of Ni-Mg-Cu-Zn ferrites with Bi³⁺shows that bismuth ions could not only refine the grains,but improve the density of the material and initial permeability.However they had no contribution to the high frequency performance.Doping cobalt ions increases the lattice constant of the material,but decreases the saturation magnetization and initial permeability.In the high frequency environment,with cobalt content increasing the loss tangent significantly reduced,and the Q-factor increased.The parameters of proper Bi-Co co-doping Ni-Mg-Cu-Zn ferrites show that the structure of samples such as sintering density,porosity and particle uniformity can be improved obviously,the initial permeability and quality factor of the material increased with the doping content,and the stability of permeability changes with temperature has also been improved.On the other hand,excessive doping leads to the formation of the heterogeneous phase.Abnormal growth of grain leads to uneven size,which has a relatively unfavorable effect on the structure and magnetic properties of the material.We selected samples with the best doping amount to study the effect of sintering temperature on the parameters of Ni-Mg-Cu-Zn ferrites.The results show that the solid phase reaction has been completely finished due to the doping of bismuth ions.Therefore,the high sintering temperature makes Zn²⁺volatilize,which caused the structure and density of the samples get deteriorated and the grains grow abnormally.The saturation magnetization decreases with sintering temperature,and the coercivity increases.Due to the grain size getting larger at high temperature,the permeability at low and high frequencies increases first and then decreases with sintering temperature.On the other hand,the porosities and impurities produced in the over-burning structure have increased the energy loss at high frequencies and reduce the Q-factor of the materials.