Preparation Of M-type Barium Ferrite Doped With Rare Earth Elements And Study Of Microwave Absorption Properties

With the booming development of communication technology,the development of integration and miniaturization of electronic devices has become a tendency,though it has also brought about electromagnetic interference and radiation problems.It reduces the quality of information transmission seriously and affects the normal function of living organisms to a certain extent.However,microwave absorbing materials have received widespread attention because they can solve the above-mentioned electromagnetic pollution problems.In particular,the ion doped M-type barium ferrite has become a major research object in microwave absorption because of its excellent dielectric-magnetic loss.It is shown that rare earth elements have good electromagnetic responses in doped microwave absorbing materials due to their unique electronic properties.Therefore,an advanced study of the microstructure of M-type barium ferrite doped with rare earth elements is of great importance to enhance microwave absorption performance.In this thesis,a series of rare earth element doping in M-type barium ferrites were prepared based on the sol-gel self-propagation method.Using X-ray diffractometer,scanning electron microscope,vibrating sample magnetometer,and vector network analyzer,the physical phase,magnetic properties,and electromagnetic properties of Ba_1-xSm_xFe₁₂O₁₉（x=0,0.04,0.08,0.12）,Ba_1-xLa_xFe₁₂O₁₉（x=0,0.04,0.08,0.12）、Ba_1-xY_xFe₁₂O₁₉（x=0,0.04,0.08,0.12）,Ba_1-xLa_xCo_0.4Fe_11.6O₁₉（x=0.04,0.08,0.12）and Ba_1-2xLa_xSm_xFe₁₂O₁₉（x=0.01,0.02,0.03,0.04）ceramic powders were tested,the microstructure and physical phase composition of M-type barium ferrite prepared by different rare earth elements were analyzed,the variation pattern of microwave absorption properties was summarized,and the intrinsic correlation between microwave absorption properties and rare earth element doping was revealed.The results of this thesis are as follows.Firstly,we selected rare earth elements Sm,La,and Y doped M-type barium ferrite,and compared the effects of different doping elements and different concentrations on the cell parameters of M-type barium ferrite.The magnetic properties and microwave absorption properties showed a positive correlation with the radius of rare earth ions through testing.All samples show typical characteristics of hard magnetic materials.We also discuss the influences of Sm³⁺,La³⁺,and Y³⁺on wave absorption properties.In particular,Ba_0.92La_0.08Fe₁₂O₁₉（x=0.08）shows the best microwave absorption performance,reaching a minimum reflection loss of-62.68 d B at a frequency of 13.52GHz with a thickness of 2.0 mm,and the widest effective absorption bandwidth of 5.41GHz with a thickness of 1.9 mm.Firstly,the rare earth elements Sm,La and Y were selected to dope the M-type barium ferrite,and the effects of different doping elements and doping concentrations on the cell parameters of the M-type barium ferrite were compared.The magnetic properties and microwave absorption properties were calculated to show a positive correlation with the radius of the rare earth ions.All samples show typical characteristics of hard magnetic materials.The substitution of barium ions by rare-earth trivalent cations leads to an increase in superexchange interaction,which increases the conductivity of the system and increases the dielectric loss.Ba_0.92La_0.08Fe₁₂O₁₉（x=0.08）shows the best microwave absorption properties,reaching a minimum reflection loss of-62.68 d B at a frequency of 13.52 GHz with a thickness of 2.0 mm,and the widest effective absorption bandwidth of 5.41 GHz with a thickness of 1.9 mm.Based on the above experimental results,the La element with the best composite performance was selected to co-dope Ba Fe₁₂O₁₉with the metallic element Co.It was observed that Co²⁺mainly replaced the 2b and 4f₂and 2b sites of Fe³⁺,resulting in a gradual rising of the coercivity.Meanwhile,with the increasing doping concentration of La³⁺,the material complex permittivity rises and the complex permeability are higher than those of rare-earth single doped M-type barium ferrite.The adding of Co elements enhances the magnetic loss of M-type barium ferrite,and the correlation of La-Co co-doping on the electromagnetic parameters and absorption performance of the material is discussed,where Ba_0.96La_0.04Co_0.6Fe_11.4O₁₉（x=0.04）,RL reaches a peak of-18.54 d B,and the effective absorption bandwidth reaches 1.43 GHz.To further improve the wave absorption performance of rare-earth doped M-type barium ferrite,La-Sm co-doping of rare-earth elements is adopted,which is shown to further increases the lattice distortion and enhance the electron hopping.Compared with the single doping of rare earth elements Sm,La,and Y,the La-Sm co-doping reduce the real part of the dielectric constant and improves the imaginary part of the dielectric constant,and achieves the optimization of impedance matching.Furthermore,the frequency range covered by the impedance matching region is 4-18 GHz,and the optimal balance between impedance matching and energy conservation is obtained.In which,the minimum reflection loss of Ba_0.92La_0.04Sm_0.04Fe₁₂O₁₉（x=0.04）could reach-62.81 d B,and its effective absorption bandwidth could reach 5.62 GHz.The results show that the rare earth double doping expands the microwave absorption performance to higher frequency bands so that it obtains good microwave absorption performance in wider frequency bands.