Bi-YIG ferrite with high dielectric constant and narrow FMR linewidth and NiCuZn ferrite composite substrates for ultrawideband circulators

In response to the demands for miniaturization and broadband operation in microwave ferrite circulators, high-dielectric Bi 1.2 Y 1. 3 -x Ca 0.5+x Ti x Fe 4.5-x Zr 0.5 O 12 ( x  = 0–0.2) ferrites with a narrow ferromagnetic resonance linewidth were synthesized via the solid-state reaction method. The replacement of Fe 3 + ions with non-magnetic Ti 4+ ions reduces the magnetocrystalline anisotropy and increases the relative density of the ferrite, effectively narrowing the ferromagnetic resonance linewidth. This ion replacement also enhances the rattling effect due to the decrease in bond valence of the ferrite, leading to an increase in the dielectric constant, which is beneficial for the miniaturization of the circulator. The optimized microwave properties are as follows: ε r = 24.5, tan δ = 1.2 × 10 −3 , 4π M s = 1754 G, and ΔH = 57 Oe. When combined with the Ni 0.42–0.08/3 Nb 0.08/3 Cu 0.18 Zn 0.4 Fe 1.9 Mn 0.08 O 4 ferrite, which possesses a high saturation magnetization, the ring composite substrate demonstrates good matching and a tight interfacial connection. The EDS analysis reveals an element diffusion zone of approximately 1 μm at the interface, caused by the diffusion of elements with smaller ionic radii (e.g., Ni, Cu, Zn, Mn, Nb, and Ti). Finally, a microstrip dual-Y junction circulator was simulated, showing an ultrawideband operating frequency range (6–18 GHz), as well as S 11 < −18 dB, S 12 < −18 dB, and S 21 > −0.5 dB. These findings indicate the application potential of the proposed composite substrate in ultrawideband circulators.