Synthesis and characteristics of La3+-Co2+ substituted Sr-hexaferrites for microwave LTCC circulators

The La3+-Co2+ substituted Sr0.7La0.3Fe11.7Co0.3O19 ferrites with 2-5 wt% Bi2O3·B2O3·SiO2·ZnO (BBSZ) glass were synthesized by conventional sintering (CS) method, microwave sintering (MS) method, and hot press sintering (HPS) method at a low sintering temperature of 850 °C compatible with the low temperature co-fired ceramics (LTCC) systems, respectively. These ferrites were chiefly characterized by X-ray diffraction, precision density balance, and vibrating sample magnetometer. It is observed that the addition of BBSZ can promote the low temperature sintering of the ferrites, as well as the formation of M-type phase. But the excessive addition of non-magnetic BBSZ is inclined to reduce the magnetic properties for the ferrites. Detailed effects of the BBSZ amount on their low temperature sintering characteristics are revealed and explained. The proper addition of BBSZ is suggested to be 4, 4, and 5 wt% for the CS ferrites, MS ferrites, and HPS ferrites, respectively. Notably, the obtained MS ferrites can provide relatively high saturation magnetization of 65.3 emu/g, magnetic anisotropy field of 1528.8 kA/m, and intrinsic coercivity of 336.1 kA/m as low temperature sintered M-type hexaferrites for use in microwave LTCC circulators.