Preparation and Magnetic Properties of SrFe₁₂O₁₉ Ferrites Suitable for Use in Self-Biased LTCC Circulators

Strontium ferrites with different Bi₂O₃ content are prepared by the solid phase method, and their magnetic properties are investigated primarily. The Bi₂O₃ additive and sintering temperature separately exhibit a strong effect on the sintering density, crystal structure, and magnetic properties of the ferrites. As to the ferrites with 3 wt% Bi₂O₃, the relatively high sintering density ρ_s, saturation magnetization M_s, and intrinsic coercivity H_ci can be obtained at a low sintering temperature of 900°C even much lower. Furthermore, the effective magnetic anisotropy constant K_eff and magnetic anisotropy field H_a of the ferrites are calculated from the magnetization curve by the law of approach to saturation. It is suggested that the low-temperature sintered SrFe₁₂O₁₉ ferrites with M_s of 285.6 kA/m and H_a of 1564.6 kA/m possess a significant potentiality for applying in the self-biased low-temperature co-fired ceramics circulators from 34 to 40 GHz.