Study on Bi3+-Al3+ co-doped YIG for co-firing YIG-Al0.2/NZF ferrite composite substrates

Y 2.5- x Bi 0.5 Al x Fe 5 O 12 (YIG-Al x ) ceramics have been synthesized at 1175 ℃ by the solid-state reaction method. The effects of the co-doped Bi 3+ , Al 3+ ions on the phases, micromorphology, and dielectric and magnetic properties of the yttrium iron garnets (YIG) were investigated. Excessive introduction of Al 3+ ions led to the collapse of the YIG lattice and precipitation of the Bi 3+ and Fe 3+ ions; while moderate Al 3+ doping improved the dielectric properties , but not the saturation magnetization. The YIG-Al 0.2 ceramics proved to have particularly good electromagnetic properties ( ε r = 18.34 ± 0.05@11.19 GHz, tan δ  = 3.09 ± 0.55 × 10 −4 , M s = 19.82 ± 0.55 emu/g). Additionally, tightly bonded Y 2.3 Bi 0.5 Al 0.2 Fe 5 O 12 /Ni 0.8 Zn 0.2 Fe 2 O 4 (YIG-Al 0.2 /NZF) composite substrates were prepared by co-firing at 1175 ℃. The composite substrates exhibited superior electromagnetic properties (YIG-Al 0.2 : ε r = 18.37 ± 0.05@11.15 GHz, tan δ  = 3.08 ± 0.55 × 10 −4 , M s = 21.09 ± 0.55 emu/g; NZF: M s = 67.5 ± 0.55 emu/g), which were slightly affected by the diffusion of Ni and Zn from the NZF. Our findings show that YIG-Al 0.2 /NZF substrates have great potential for use as RF band circulators.