The Effect Of Sn Or Bi Doping On The Structure And Magnetic Properties Of Li-Zn Ferrites

As a type of magnetic material,soft magnetic ferrite is widely used in many fields,because of the excellent electromagnetic properties such as high saturation magnetization,high permeability,high resistivity and low power loss.In addition,soft magnetic ferrites can adapt to various complex environments due to its high Curie temperature and high chemical stability.Compared with other types of ferrites,spinel soft ferrite has a mature preparation process and lower prices.Hence,it gradually replaces expensive magnetic garnet and other ferrites.All these advantages make spinel soft magnetic ferrite showing bright future and playing vital roles in almost every field of technology,such as isolators,phase shifters,memory core and high-speed digital tapes etc.To obtain excellent magnetic materials,the structure and magnetism of ferrites were modified by changing the occupation of magnetic or non-magnetic cation in lattice.High-performance ferrites are more sensitive to chemical composition,preparation,sintering temperature and sintering time.Compared with other methods,sol–gel auto-combustion method has multiple advantages,i.e.,low costs,absence of high-temperature sintering,easy control and accurate ratio of chemicals.Therefore,sol-gel method is chosen as a suitable way to synthesize Li-Zn ferrites in this work.Li_{（0.2+0.5x）}Zn_0.6Sn_xFe_{（2.2-1.5x）}O₄ and Li_0.2Zn_0.6Bi_xFe_（2.2-x）O₄ ferrites were synthesized successfully.X-ray diffraction（XRD）and scanning electron microscopy（SEM）were carried out to determine the effect of Sn or Bi doping on the structure of Li-Zn ferrites.The magnetic properties of Li-Zn ferrites were charactered by Squid-VSM and LCR impedance analyzer.The diffraction pattern revealed the single-phase spinel structure of the Sn-doped Li-Zn ferrite as x≤0.06.The lattice parameters and the crystallite size increased with Sn⁴⁺doping,which is attributed to larger Sn⁴⁺ion radii compared with host Fe³⁺.With Sn⁴⁺content increasing,the initial permeability increased but the saturation magnetization decreased.The diffraction patterns confirmed the formation of single-phase spinel structure of Bi-doped Li-Zn ferrite as x<0.04.Hybrid phases of Bi₂O₃ and Bi Fe O₃ appeared as x=0.04 and x=0.06,respectively.The lattice constant and grain size of Li-Zn ferrite increased with the Bi³⁺ions introduction.The initial permeability enhanced remarkably with Bi³⁺doping and the saturation magnetization increased as x=0.04.The magnetization curves in the applied field above 800 Oe are fitted using law of approach to saturation.The increasing of the initial permeability can be explained well by the anisotropy constant.