Detailed microwave loss mechanisms for nanocomposites of La-doped BaFe12O19 and polyaniline

To mitigate the undesirable effects of electromagnetic pollution on the precise instrument, biological health, and human life, high-efficiency microwave-absorbing materials (MAMs) have been pursued by the scientific community. MAMs also have important potential for information security, 5G, energy harvesting, reduced radar cross-section, and military stealth technology. In this work, magnetic/dielectric composites of La-doped BaFe12O19 (La-BaM) and polyaniline (PANI) were developed to be MAMs. Composites with no and 30% of La concentration (named M0-C and M3-C, respectively) showed poor microwave absorption performance with reflection loss (RL) values of about -20 dB, meaning 99% of the incident microwave was absorbed. The effective absorption bandwidths (EABs) were narrow, with values of 0.70 and 1.55 GHz, respectively. In contrast, the microwave absorption performance of composites with 10% and 50% of La concentration (named M1-C and M5C, respectively), reached excellent values in both RL and EAB of -47.83 and -43.53 dB and 3.98 and 3.43 GHz, respectively. These RL values implied that 99.99% of the incident microwave could be absorbed. The superior microwave absorption properties of M1-C and M5-C composites could be attributed to their excellent impedance matching, better natural ferromagnetic resonance, exchange resonance, and better attenuation constant. The loss mechanism of microwave energy in La-BaM/PANI composites could be attributed to interfacial polarization at the interfaces of two phases, dipole polarization and micro-current and conductive loss (from PANI), eddy current (from La-BaM), multiple reflection and scattering (from the dispersion of PANI into La-BaM), as well as thermal energy dissipation (from embedding La-BaM/PANI into the epoxy matrix).