The traditional method of ferrite synthesis is based upon solid-state reaction. The advantages of this approach include simplicity, cost effectiveness, and suitability for commercial process scaling. However, there exist shortcomings in that impurities and defects adversely affect magnetic properties. Here, iron-depleted compositions of bismuth-substituted yttrium iron garnet (ie Bi:YIG) were studied with emphasis placed on the impact of synthesis processing parameters upon the structure and gyromagnetic properties. It was shown that ferrimagnetic resonance linewidth experienced a minimum of 180.3 Oe (X-band) when the sample stoichiometry was 4% depleted in iron (x = 0.2), a reduction of 29.3% from the parent compound. Concomitantly, iron depletion caused a systematic change in lattice parameter that resulted in a dilation of Goodenough-Kanamori-Anderson bond angles increasing exchange energy and magnetization. The substitution of Bi for Y on the dodecahedron sites altered the reaction path and decreased the activation energy effectively reducing sintering temperature. To establish a functional processing protocol, an ion diffusion model is presented to explain the demonstrated processing, structure, and performance paradigm.