Effect of Mn substitution on structural, magnetic and microwave absorption properties of Co2Y hexagonal ferrite

Efficient microwave absorbing materials are required to solve electromagnetic interference and electromagnetic pollution problems. It has been known that the electromagnetic wave (EMW) absorption properties of ferrites can be improved by element substitution. In this study, the hexagonal Ba2Co2MnxFe12-xO22 (x = 0.0, 0.4, 0.8, 1.2 and 1.6) ferrites were prepared by the solid-phase sintering method, and the effect of Mn substitution on structural, magnetic and microwave absorption performance were investigated in detail. Due to the impact of lattice distortion caused by doping Mn ions in Ba2Co2Fe12O22 ferrites, the concentration of oxygen vacancy increases first and then decreases with increasing Mn substitution. The real part of complex dielectric constant (epsilon') of Ba2Co2MnxFe12-xO22 ferrites decreases with increasing x, which can be attributed to the formation of a stable ion pair (Mn3+ - Fe2+) due to the doped Mn ions entering the octahedral (B) sites. The real part of complex permeability constant (mu') of ferrites increases with the increase of Mn substitution due to the decreased magneto-crystalline anisotropy. The effective absorption bandwidth (EAB) of ferrites increases from 5.5 GHz to 9.1 GHz with the increase of Mn substitution from x = 0 to 1.6, significantly improving microwave absorption performance. The EAB of Ba2Co2MnxFe12-xO22 ferrite at x = 1.2 reaches 8.74 GHz at a thickness of only 1.57 mm, which could be employed as microwave absorbers due to its broad bandwidth, strong absorption, and small thickness. The excellent performance is mainly attributed to the synergy effect of multiple reflections, natural resonance, dipole polarization and good impedance matching.