Preparation And Doping Modification Of NiZn Ferrite For NFC Separator

The complex metal environment in the mobile phone leads to the formation of eddy current in the metal of the signals transmitted by the NFC transmitting coil,which greatly interferes with the transmitting and receiving of NFC signals,resulting in the greatly shortened NFC communication distance.The ferrite separator can isolate the electromagnetic signal,weaken the influence of metal environment on the detection signal of NFC transmitting coil,so as to effectively improve the sensitivity of NFC detection and increase the communication distance.Generally speaking,the greater the permeability of the separator,the better the isolation effect,and the greater the communication distance.In order to meet the application requirements of NFC separator and develop ferrite materials with high permeability,this thesis chooses spinel NiZn ferrite as the research object,and adjusts the magnetic properties of NiZn ferrite through nano-ultrafine and component doping.Sol-gel self-combustion method and chemical co-precipitation method were selected to establish the stable synthesis process of NiZn ferrite nano-powder.On this basis,the influence of component doping on NiZn ferrite phase formation,particle structure and magnetic properties was studied in detail.On the basis of systematic research work,the main conclusions are as follows:1)Using citric acid as complexing agent,NiZn ferrite nanoparticles were successfully prepared by sol-gel self-combustion method.The size of NiZn ferrite particles obtained was less than 200 nm,and the powders showed typical soft magnetic magnetization behavior.By adjusting the molar ratio of citric acid to metal ions and the gel oxidation degree,the synthesis process parameters were optimized,and the process conditions for obtaining the stable synthesis of pure NiZn ferrite nano-powder were as follows:the oxidation degree was 60%,the ratio of citric acid to metal ions was 1.5.2)Using NaOH as precipitator and soluble metal nitrate as raw material,the target NiZn ferrite powder can be obtained by chemical co-precipitation method at a temperature above 700℃.The particle size of the obtained NiZn ferrite powder is less than 300 nm,and the magnetic properties are typical soft magnetic materials.The pure phase NiZn nano-ferrite powder can be rapidly synthesized by microwave heat treatment instead of traditional heat treatment under the microwave power of 6000 W and 10 min.Compared with sol-gel self-combustion method,chemical co-precipitation-microwave heat treatment method has higher single product yield and excellent magnetic properties.3)Cu-doped NiZn ferrite was prepared by chemical co-precipitation-microwave heat treatment.The effect of Cu-doped and The absence of Fe on the phase formation,particle size morphology and magnetic properties of NiZn ferrite was studied.The results show that Zn content can significantly affect the size of synthesized particles,and appropriate amount of Zn can improve the saturation magnetization of ferrite.The product with more Cu content has better densification.The Fe content affects the magnetic properties of ferrite and the forming of powder particles.The increase of Fe deficiency can also promote the densification of particles.The magnetic properties of the synthesized NiZn ferrites can be effectively adjusted with the change of doping components.Considering the particle size,phase purity and magnetic properties of the sample,Ni0.40Cu0.20Zn0.40Fe2O4,Ni0.20Cu0.20Zn0.50Fe2O4 and Ni0.15Cu0.15Zn0.50Fe1.94O4 with relatively high saturation magnetization can be used as high quality ferrite powder materials for preparing NFC separator.