Microwave absorbing properties of W-type Ba_(1-x)La_xCo_2Fe_(16)O_(27)

The samples of La-doped W-type barium ferrite Ba1-xLaxCo2Fe16O27(x=0,0.1,0.2,0.3)were prepared by sol-gel process.The structure,surface morphology and particle size of samples were characterized by XRD and SEM.The complex permittivity and the complex permeability of samples were measured by microwave vector network analyzer in the frequency range from 2 to 18 GHz.The relationship between reflectance and frequency and the relationship between loss tangent and frequency were calculated from the measured data.The microwave absorbing properties and the electromagnetic loss mechanism of samples were studied.The results show that the microwave absorption properties of the samples can be improved by an appropriate doped content of La and the best effect can be attained when x=0.2.If the thickness of the sample is 1.90 mm and x=0.2,the highest absorption peak is 16.2 dB and the effective band width larger than 10 dB reaches 4.0 GHz.The microwave absorption of samples results from both dielectric loss and magnetic loss but the latter is more remarkable.