Magnetothermal Characterization of Bi-Ca-Zr-Doped High-Dielectric Garnet Ferrite Materials

Modern wireless communication and radar systems urgently require yttrium iron garnet (YIG) ferrites with low loss, high dielectric constant, and high stability to achieve efficient integration in microwave circulators, isolators, and other devices. However, simultaneously achieving high dielectric constant, low loss, and narrow ferromagnetic resonance (FMR) linewidth remains a challenge. This study investigates Bi-Ca-Zr co-substituted YIG ferrites, systematically examining the effects on crystal structure, magnetoelectric properties, and thermomagnetic characteristics. The introduction of Bi 3+ ions at crystallographic dodecahedral sites enhances electron polarization between Fe 3+ ions, significantly increasing the dielectric constant. Meanwhile, Zr 4+ ions substituting Fe 3+ ions at octahedral sites alter the magnetic moments and super-exchange interactions between sublattices, thereby modulating the material’s saturation magnetization and Curie temperature. Molecular field theory analysis reveals that the super-exchange interaction between Fe 3+ ions at a-sites and d-sites dominates the variation in Curie temperature. Additionally, the material exhibits excellent temperature stability (| α | < 4.5 × 10 –3 /°C) within the range of -55°C to 125°C. Comprehensive results demonstrate that Bi-Ca-Zr-substituted YIG with x = 0.45 achieves optimal performance (saturation magnetization 4π M s = 2024 Gs, coercivity H c = 2.7 Oe, dielectric constant ε’ = 27, FMR linewidth Δ H = 40 Oe, Curie temperature T C = 478 K), making it suitable for low-loss miniaturized microwave devices.