Effect of Microstructure and Magnetic Properties of Ba-Pb-Hexaferrite Particles on EMI Shielding Behavior of Ba-Pb-Hexaferrite-Polyaniline-Wax Nanocomposites

We report that the microstructure, electrical and magnetic properties of the fillers play a very crucial role in synergistically enhancing absorption dominated electromagnetic interference (EMI) shielding in nanocomposites. We prepared nanocomposites by dispersing of varying microstructure and magnetic properties Barium-Lead hexaferrite (BaxPb1-xFe12O19; x=0.0, 0.4, 0.8 and 1.0) particles and polyaniline (PANI) (light weight conducting species) a in microwave transparent paraffin wax matrix. The EMI shielding behavior of the nanocomposites was studied in the 8-18 GHz frequency band. The hexaferrite powder samples used in the nanocomposites were synthesized by the sol-gel method followed by calcination at 1000 degrees C. The electron micrographs confirm that the pure Pb-hexaferrite sample (x=0) contains well defined hexagonal plate-like particles. With increase in Ba-content in the samples, the hexagonal particles transform to smaller spherical particles, and the magnetic properties such as coercivity and saturation magnetization change. These modifications in the morphology and magnetic properties of the samples facilitate high attenuation of microwave radiation in our developed nanocomposites. The conducting species (PANI) reflects the microwave from its surface but absorbs it through conduction-loss (Ohmic absorption), whereas the (non-conducting) magnetic Ba-Pb hexaferrite particles absorb the microwave through ferromagnetic resonance but scatter it from their surface due to impedance mismatch. The scattered waves normally increase the electromagnetic smog outside the specimen. To reduce this EM-smog, the Ba-Pb hexaferrite-PANI-Wax nanocomposites provide a synergy among all the electrical and magnetic properties, which leads to very high attenuation through absorption of the scattered electromagnetic wave. Our work demonstrates that the nanocomposites containing Ba-Pb hexaferrite particles are not only efficient in shielding microwave radiation but also help in controlling the electromagnetic-smog.