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

Abstract

The effect of non-magnetic oxides such as Al₂O₃, TiO₂ and ZnO on the microwave absorption properties of magnetoplumbite barium hexaferrite (BaFe_11.8Co_0.2O₁₉) is analyzed. Barium hexaferrite nanoparticles are synthesized through the sol-gel auto-combustion method. BaFe_11.8Co_0.2O₁₉-Al₂O₃, BaFe_11.8Co_0.2O₁₉-TiO₂ and BaFe_11.8Co_0.2O₁₉-ZnO composites are synthesized in a 1:1 ratio through mechanical mixing and heat treatment. The epoxy composites are fabricated with 50% loading of BaFe_11.8Co_0.2O₁₉-Al₂O₃, BaFe_11.8Co_0.2O₁₉-TiO₂ and BaFe_11.8Co_0.2O₁₉-ZnO in epoxy matrix followed by room temperature curing. The powder XRD analyses showed homogeneous distribution of BaFe_11.8Co_0.2O₁₉ and Al₂O₃ in BaFe_11.8Co_0.2O₁₉-Al₂O₃ composite while TiO₂ and ZnO phases dominate in BaFe_11.8Co_0.2O₁₉-TiO₂ and BaFe_11.8Co_0.2O₁₉-ZnO composites, respectively. Scanning electron microscopy shows the evenly distributed BaFe_11.8Co_0.2O₁₉ and Al₂O₃ in BaFe_11.8Co_0.2O₁₉-Al₂O₃ composites. The electromagnetic characterization calculated from experimental permittivity and permeability shows reflection loss R_L ≤ -10 dB (≥ 90% absorption) for a very small thickness of 0.5 mm over the entire X-band (8-12 GHz) for BaFe_11.8Co_0.2O₁₉-Al₂O₃ composites. BaFe_11.8Co_0.2O₁₉-TiO₂ and BaFe_11.8Co_0.2O₁₉-ZnO show R_L < - 8 dB with a thickness of 2.5 mm over the frequency range 8–9.7 GHz and R_L < - 8 dB with a thickness of 3.6 mm over 8.7-11.1 GHz, respectively. Further, when compared with BaFe_11.8Co_0.2O₁₉ alone (R_L < -7 dB at 3.2 mm in 8-11 GHz), the BaFe_11.8Co_0.2O₁₉-Al₂O₃ composite is superior both in terms of the thickness of the coating as well as the percentage absorption in the X-band.