Suppressed domain wall damping in planar BaM hexaferrites for miniaturization of microwave devices

•CoRu substitution enhanced the permeability of planar BaM ferrite for GHz application.•Bi2O3 doping CoRu-BaM has lower magnetic loss with retaining a high permeability of 3.•Reduced loss arises from domain wall damping suppression by the control of grain size. CoRu-substituted BaM hexaferrites, with additives of Bi2O3, demonstrate low losses and high permeability above 1 GHz. The RuCo- and BiRuCo-doped BaM ferrites were prepared by conventional solid-state reaction methods. Magnetic spectra indicate that there were two peaks in the imaginary part of the permeability spectra which originate from domain wall motion and spin rotation. Compared to the RuCo-BaM sample, BiRuCo-doped BaM samples exhibit slight decreases in permeability (~2.9), but the magnetic loss tangents decrease markedly by 47% to ~0.05 at 1 GHz while retaining a low magnetic loss ~0.1 up to 1.5 GHz. From fitting to experimental data, it’s clear that the reduction of magnetic loss stems predominantly from a suppressed domain wall damping due to the introduction of Bi2O3. It is demonstrated that Bi2O3 can effectively control the microstructure of polycrystalline ferrites, and in turn tailor the contribution of domain wall resonance or spin rotation to permeability and magnetic loss. The results are valuable to the engineering of ferrite materials for use in the miniaturization of wide band microwave antenna at operating frequencies up to 1 GHz.