Advanced wireless communications demand microwave systems that offer low-loss, narrow linewidth, and large operating frequency range. We have examined the effect of bismuth and gadolinium co-doping in yttrium-iron-garnet (YIG) ferrimagnets through their microstructural, magnetic, and microwave properties for their performance in broad-band high-frequency devices. The GdxBi0.1Y2.9-xFe5O12 (x = 0.0 to 0.3) nanoparticles were prepared using solid-state reaction method. XRD Rietveld-refinements revealed the single-phase YIG structure validating \(Ia\overline{3 }d\) cubic crystal structure. The saturation magnetization decreased by 32% with increasing Gd doping. Magneto-dynamics key parameters such as gyromagnetic ratio, Gilbert damping factor, and extrinsic linewidth, were evaluated to assess the potential of these materials for use in microwave device applications. Microwave device functionalities were demonstrated from S-to-X-band frequencies using Gdx-Bi0.1YIG samples. The fabricated band-pass filter exhibits large tunability of 140%, large bandwidth of 1.97 GHz, and minimal insertion loss of − 1.17 dB with relatively low bias of 0.25–1.95 kOe. The fabricated phase shifter module demonstrated a large differential phase shift of 300 degrees in the frequency range from 3–10 GHz with Gd substitution. The investigated Gd-YIG-based isolator exhibit isolation over 11 dB at low fields for over the frequency span of 3–10 GHz. We have demonstrated that 0.1 formula unit doped Gd- in YIG shows the best results for microwave devices as compared to other samples.
