Substitution effect of Me = Al, Bi, Cr and Mn to the microwave properties of polyaniline/BaMeFe11O19 for absorbing electromagnetic waves

Abstract

Polyaniline/substituted barium hexaferrites (abbreviated Pani/BaMeFe11O19, where Me = Al, Bi, Cr and Mn) composites are investigated to be potential electromagnetic wave absorber from 1 to 18 GHz frequency range. Solid-Based Polymerization method is used to prepare the samples with 10% volume fraction of hexaferrite. The effects of iron substitution in hexaferrite composites by trivalent ions Al3+, Bi3+, Cr3+ and Mn3+ on permittivity, permeability and microwave absorption properties are studied. Structural and morphological investigations confirm the presence of Polyaniline and barium hexaferrite phases, which are in interaction in the composites regardless the substitution. Thermogravimetric analysis exhibits an improved thermostability when small ions (Al3+ and Cr3+) are used to substitute Fe3+ in hexaferrite compared to the large cations substitution (Bi3+ and Mn3+), since these latter interfere between the ferrite and intermolecular interaction between Pani macromolecules. Magnetic studies show a ferromagnetic behaviour for all the composites. Saturation magnetization is mainly related to the substituting cations nature in hexaferrite which is determined using measured magnetic data. Coercivity values increase slightly due to the Pani matrix that precludes the movement of the domain wall. The EM parameters ε׳, ε׳׳, μ׳and μ׳׳ are measured using a Vector Network Analyzer. It is found that the dielectric constant increases with the addition of hexaferrite. The maximum of the magnetic losses diminishes and shifts to higher frequencies with Fe3+ doping. These measured EM parameters are used to determine the reflexion loss for different composites. Pani/BaFe12O19 composite shows two minimum reflection losses (RL) in Ku-band. The properties of these ferrites arise from exchange interactions between the oxygen and metallic ions occupying particular positions in its crystalline structure. For the substituted ferrite composites, the minimum RL shifts from in Ku-band to X-band when substituting Fe3+ in hexaferrites by means of the variation of ferromagnetic resonance frequency which influences the microwave absorption properties.