Barium hexaferrites with narrow ferrimagnetic resonance linewidth tailored by site-controlled Cu doping

Abstract

Barium hexagonal ferrites exhibiting unique self-biasing characteristics have great potential for application in planar microwave devices, such as self-biased circulators. Cu doping is an effective method to tailor their anisotropy field and ferrimagnetic resonance (FMR) linewidth to meet the requirements for low-frequency low-loss microwave devices. However, the regulation mechanism of Cu doping is still obscure, and its regulation effect is not optimized. Here, the magnetic and microwave properties of two groups of barium hexaferrites with site-controlled Cu doping are reported. The diffusion dynamics of Cu2+ ions are comprehensively investigated, revealing significant differences in the concentration distribution and polycrystalline morphology, when comparing CuO as a reactant and sintering additive. The accumulation of Cu2+ ions at grain boundaries contributes to the increase in coercivity, whereas the dispersion of Cu2+ ions in crystallites leads to the decrease in the anisotropy field. Moreover, by introducing Cu2+ ions into the interstitial positions of the lattice, barium hexaferrites with a narrow FMR linewidth of 303 Oe and a high remanence ratio of 0.82 are achieved. These results represent the lowest FMR linewidth reported in polycrystalline hexagonal ferrites and prove the great technological value and commercial potential of Cu-doped barium hexaferrites for next-generation planar microwave devices.