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°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.