Surfactant-assisted synthesis of polythiophene/Ni0.5Zn0.5Fe2−xCexO4 ferrite composites: study of structural, dielectric and magnetic properties for EMI-shielding applications

Abstract

This work reports the exploitation of nanocrystalline Ni_0.5Zn_0.5Fe_2−xCe_xO₄ ferrite for potential application by designing quasi-spherical shaped polythiophene (PTH) composites via in situ emulsion polymerization. The structural, electronic, dielectric, magnetic, and electromagnetic interference (EMI) shielding properties of PTH/Ni_0.5Zn_0.5Fe_2−xCe_xO₄ composites were investigated. Our results suggest that these properties could be optimized by modulating the concentration of x (composition) in the polymer matrix. Higher values of ε′ and ε′′ were obtained on composite formation, and could be due to the heterogeneity developed in the material. An enhancement in the value of saturation magnetization (123 emu g⁻¹ for x = 0.04) and Curie temperature was obtained with Ce concentration, which is useful for high density recording purposes. A low value of saturation magnetization was obtained for the PTH/Ni_0.5Zn_0.5Fe_2−xCe_xO₄ composite (36 emu g⁻¹ for x = 0.04). This could be attributed to the non-magnetic nature of the polymer. A total shielding effectiveness (SE_T = SE_A + SE_R) up to 34 dB (≈99.9% attenuation) was recorded for PTH/Ni_0.5Zn_0.5Fe_2−xCe_xO₄ composites (x = 0.04) in a frequency range of 8.2–12.4 GHz (X-band), which surpasses the shielding criteria of SE_T > 30 dB for commercial purposes. Such a material with high SE identifies its potential for making electromagnetic shields. The effect of Ce substitution on the microstructure, dielectric, impedance and magnetic properties of PTH/Ni_0.5Zn_0.5Fe_2−xCe_xO₄ ferrite composites was also investigated. X-ray diffraction analysis confirmed cubic spinel phase formation, and the broad reflection peaks indicated the formation of smaller sized particles. The smaller energy band gap (2.53 eV) of the composite indicated that this material could be used for photocatalysis in the visible region. Dielectric and impedance measurements were carried out in a frequency range of 8.2–12.4 GHz. Dielectric properties were improved considerably by the substitution of Ce³⁺ ions in PTH/Ni_0.5Zn_0.5Fe_2−xCe_xO₄ composites. Impedance spectroscopy was used to study the effect of grain and grain boundaries on the electrical properties of PTH/Ni_0.5Zn_0.5Fe_2−xCe_xO₄ composites. Cole–Cole plots showed the formation of single semi-circles for all samples in the measured frequency range. This showed that the composite material was composed of good conducting grains and poorly conducting grain boundaries.