Enhancement of Microwave Absorption Properties of Hexaferrite/Epoxy Composites on the Addition of Non-magnetic Oxides

The effect of non-magnetic oxides such as Al2O3, TiO2 and ZnO on the microwave absorption properties of magnetoplumbite barium hexaferrite (BaFe11.8Co0.2O19) is analyzed. Barium hexaferrite nanoparticles are synthesized through the sol-gel auto-combustion method. BaFe11.8Co0.2O19-Al2O3, BaFe11.8Co0.2O19-TiO2 and BaFe11.8Co0.2O19-ZnO composites are synthesized in a 1:1 ratio through mechanical mixing and heat treatment. The epoxy composites are fabricated with 50% loading of BaFe11.8Co0.2O19-Al2O3, BaFe11.8Co0.2O19-TiO2 and BaFe11.8Co0.2O19-ZnO in epoxy matrix followed by room temperature curing. The powder XRD analyses showed homogeneous distribution of BaFe11.8Co0.2O19 and Al2O3 in BaFe11.8Co0.2O19-Al2O3 composite while TiO2 and ZnO phases dominate in BaFe11.8Co0.2O19-TiO2 and BaFe11.8Co0.2O19-ZnO composites, respectively. Scanning electron microscopy shows the evenly distributed BaFe11.8Co0.2O19 and Al2O3 in BaFe11.8Co0.2O19-Al2O3 composites. The electromagnetic characterization calculated from experimental permittivity and permeability shows reflection loss RL ≤ -10 dB (≥ 90% absorption) for a very small thickness of 0.5 mm over the entire X-band (8-12 GHz) for BaFe11.8Co0.2O19-Al2O3 composites. BaFe11.8Co0.2O19-TiO2 and BaFe11.8Co0.2O19-ZnO show RL < - 8 dB with a thickness of 2.5 mm over the frequency range 8–9.7 GHz and RL < - 8 dB with a thickness of 3.6 mm over 8.7-11.1 GHz, respectively. Further, when compared with BaFe11.8Co0.2O19 alone (RL < -7 dB at 3.2 mm in 8-11 GHz), the BaFe11.8Co0.2O19-Al2O3 composite is superior both in terms of the thickness of the coating as well as the percentage absorption in the X-band.