The La <sub> 1-x </ Sub> Sr <sub> The X </ Sub> Of Mno <sub> 3 </ Sub> And Nanotechnology Of Fe Of Ni Powder Composite Microwave Absorption Properties

The microwave absorbing properties of LaMnO₃ system doped by Sr at A site, nano-metal powders and La_0.6Sr_0.4MnO₃ /nano-metal powders were studied systematically.The nano-crystalline powders of La_1-xSr_xMnO₃ were prepared by sol-gel process. The nano-composite materials of La_0.6Sr_0.4MnO₃ /nano-metal powders were prepared by physical blending. DSC-TGA analyzing of dry gelatin and FT-IR analyzing of different heat treatment of La_0.6Sr_0.4MnO₃ showed that the formation of La_0.6Sr_0.4MnO₃ nano-crystalline experienced four stages which were the evaporation of leaving water, the decomposition of EDTA, the decomposition of CH3COO^2- and NH₃^-, the formed of perovskite . XRD analyzing showed that La_1-xSr_xMnO₃ is single perovskite structure. SEM analyzing showed that the shape of La_1-xSr_xMnO₃ was abnormal and the particle size was about 70nm. The shape of Fe-powder and Ni-powder were spherical and the average size was about 40nm and 20nm respectively. The room temperature resistivity of samples was measured by cylinder method. The result showed the resistivity were within semiconductor.The complex permittivity and permeability were measured in the frequency range of 2-18GHz by microwave vector network analyer, the reflection coefficient and the loss tangent were calculated based on measured data. The results showed that the Sr doping contents plays an important role in the effect of microwave absorption. The effective band width more than 10dB of La_1-xSr_xMnO₃(x=0.4) with 2.3mm thickness was 2.15GHz and the highest absorption peak was 13.9dB. The effective band width of nano-Ni powders with 2.4mm thickness was 1.6GHz and the highest absorption peak was 12dB. The effective band width more than 10dB of the nano-Fe powders with 2mm was 1.9GHz and the highest absorption peak was 12.8dB. When the mass proportion of La_0.6Sr_0.4MnO₃ was 40%, the effective band width of La_0.6Sr_0.4MnO₃ /nano-Fe composite with 1.8mm thickness was 5.7GHz and the highest absorption peak was 23.4dB. The effective band width of La_0.6Sr_0.4MnO₃/nano-Ni composite with 1.8mm thickness was 3.9GHz and the highest absorption peak was 38.5dB when the mass proportion of La_0.6Sr_0.4MnO₃was 40%.The study of absorption mechanism showed that both the dielectric loss and the magnetic loss result in the microwave absorption of the sample ofLa_1-xSr_xMnO₃. For nano-metal powders, the magnetic loss plays dominant role. In the La_0.6Sr_0.4MnO₃ /nano-metal powders samples, there were both the dielectric loss and magnetic loss and two losses competed with each other. It was considered that there were ferromagnetic clusters and anti-ferromagnetic clusters in the materials. The ferromagnetic clusters result in magnetic loss and the anti-ferromagnetic clusters result in dielectric loss. The response of them to different frequency gave rise to an alternative effect of dielectric loss and magnetic loss.