Preparation Of BaNd_xFe_12-xO₁₉/Nano-carbon Composites And Study On Their Microwave Absorbing Properties

With the rapid development of modern science and technology,the excessive use of electronic products has brought electromagnetic radiation and pollution to human beings.In order to solve the problems,we need to develop high performance absorbing materials.In this paper,it was proposed to combine the hexagonal M-type barium ferrite with strong magnetic properties and carbon materials with good dielectric properties to obtain a composite material with strong wave absorbing properties.The Nd-doped M-type barium ferrite and its composites mixed with three different carbon materials were mainly prepared,and their microstructure,electromagnetic parameters and wave-absorbing properties were studied.The main results are as follows:BaNd_xFe_12-xO₁₉ nanoparticles were prepared by sol-gel and self-propagating synthesis methods.The grain size of BaNd_xFe_12-xO₁₉ nanoparticles decreased with the increase of Nd doping content in the range of 40-90nm.With the increase of Nd doping amount,the saturation magnetization of nanoparticles first increased and then decreased,and the coercivity increased continuously.The addition of Nd³⁺improved the microwave absorbing properties of barium ferrite.Nd_0.15-BaM had the best microwave absorption performance,the minimum reflection loss was-17.91d B,the frequency was 12.56GHz,and the thickness was 3mm.Nd_0.15-BaM and fullerene（OLC）were mixed through mechanical ball milling to obtain the composite material.OLC was spherical with a diameter of about 5-10 nm.Due to its high electrical conductivity,its addition improved the microwave absorption properties of Nd_0.15-BaM.When the addition of OLC was 8%,its minimum reflection loss at 18GHz was-27.10d B,and the matching thickness was5mm.When the addition of OLC was 10%,its minimum reflection loss at 18GHz was-47.31d B,and the matching thickness was 5mm.But the thickness of its coating was too thick to meet the requirements of light weight.Nd_0.15-BaM and graphene oxide（GO）were mixed through mechanical ball milling to obtain the composite material.GO had a sheet-like structure,and the particles of barium ferrite were attached to the sheet of GO.The addition of GO increased the dielectric constant of the composites.The real part value of Nd_0.15-BaM/3%GO was the largest,which had the best dielectric loss.Its effective absorption bandwidth was 6.67GHz（9.99-16.66GHz）.When the thickness was 2mm,its minimum reflection loss was-82.07d B,and when the thickness was2.5mm,its minimum reflection loss was-53.51d B.Nd_0.15-BaM and carboxylated multi-walled carbon nanotubes（CNTs）were mixed through mechanical ball milling to obtain the composite material.The increase of CNTs content reduced the saturation magnetization and increased the coercivity of the material.The addition of CNTs greatly improved the absorbing properties of Nd_0.15-BaM.The minimum reflection loss of Nd_0.15-BaM/8%CNT was-123.12d B,the frequency at this time was 7.97GHz,the thickness was 2.5mm,and the effective absorption bandwidth was 5.46GHz（5.96-11.42GHz）.When the thickness was 1.5mm,its minimum reflection loss reached-68.83d B at 14.12GHz,and the effective absorption bandwidth was 7.32GHz.In conclusion,the absorbing performance of barium ferrite doped with Nd³⁺has been slightly improved.The absorbing performance of the material after composite with carbon material was obviously improved,which showed that the doping of Nd³⁺and carbon material formed a synergistic effect,which improved the absorbing performance of M-type barium ferrite to a greater extent.