Synthesis and microwave absorption properties of Ni-Zn-Mn spinel ferrites

A series of Ni0.5-xZn0.3-xMn0.2+2xFe2O4 ferrites was successfully prepared by the sol-gel autocombustion method. The structure and electromagnetic properties of the powders were characterised by X-ray diffraction, SEM and vector network analysis. The pure powders were formed by heating at 1200 degrees C for 3 h in air, and grain sizes increased as the amount of substitution ranged from x=0.0 to x=0.25. For samples with x=0.1, a minimum reflection loss of -27.57 dB was observed at 11.0 GHz with the less than -10 dB absorption bandwidth at 8.0 GHz with 3.8 mm thickness. The results indicate that substitution with Mn and Zn ions can greatly improve the microwave absorption properties of NiFe2O4 ferrites.