Manganese-zinc (MnZn) ferrites are widely employed in electromagnetic interference (EMI) suppression due to their favorable magnetic properties. However, their practical performance is often constrained by the inherent trade-offs among key magnetic properties, such as initial permeability (μ_i), standardized impedance (Z₀), saturation magnetic induction (B_s), and Curie temperature (T_c). Here, we demonstrate a strategy that simultaneously enhances these properties by combining trace Ni doping with precise control of the sintering atmosphere. The low Ni concentration, together with a carefully regulated oxygen partial pressure, suppresses the diffusion driving force of Ni²⁺, leading to its spatially nonuniform distribution and preferential segregation at grain boundaries. This localized Ni enrichment facilitates the formation of transgranular magnetic domains across significant crystallographic misorientation grains. Furthermore, Ni-rich grain boundaries promote the migration of Fe³⁺ from octahedral (B) sites to tetrahedral (A) sites, thereby increasing the A−B and A−A bond angles, shortening the corresponding bond lengths, and strengthening the superexchange interactions within the spinel lattice. As a result of this spatially engineered Ni distribution, the optimized MnZn ferrite exhibits significantly improved properties, including a μ_i of 11,648 at 10 kHz, Z₀ of 43 Ω·mm⁻¹ at 1 MHz, B_s of 524 mT at 1 kHz, 1194 A·m⁻¹, and T_c of 174 °C, outperforming conventional MnZn ferrites. This work highlights spatial compositional engineering as a viable route to advanced soft magnetic materials for next-generation EMI suppression technologies.

Modern wireless communication and radar systems urgently require the application of low-loss and high-permittivity yttrium iron garnet (YIG) ferrite for highly efficient and integrated microwave circulators, isolators, filters, etc. However, achieving a high dielectric constant, low dielectric loss, and narrow ferromagnetic resonance (FMR) linewidth simultaneously is challenging. Here, we synthesized Bi–Ca–Zr co-substituted YIG ferrites and comprehensively investigated the effects of multi-ion substitution on the polycrystalline microstructure and microwave electromagnetic properties of the material. The introduction of Bi³⁺ ions at the crystallographic dodecahedral sites enhances the electronic polarization of single Fe³⁺ ions and the superexchange interaction between them. The substitution ofZr⁴⁺ ions for Fe³⁺ ions at octahedral sites suppresses the FMR linewidth broadening caused by magnetocrystalline anisotropy. Moreover, multi-ion substitution results in competition between liquid phase sintering and grain boundary pinning and influences the densification and grain growth processes, resulting in a non-uniform and dense microstructure composed of crystallites with a bimodal size distribution. This distinctive morphology further contributes to FMR linewidth reduction and permittivity increase. The optimized Bi–Ca–Zr co-substituted YIG ferrite has a narrow FMR linewidth of 33 Oe, high permittivity of 27, and high Curie temperature of 200 °C, making it a promising candidate for next-generation microwave devices.