Studies On Low Temperature Sintering Of YIG Ferrites

Since they exhibit excellent rotating magnetic performance, yttrium iron garnet (YIG) materials have widely applications in microwave communication fields. They are for the use of microwave magnetic components such as circulators, isolators, and phase shifters. But the high sintering temperature(>1450℃) of YIG ferrite does not satisfy the developments of the microwave components, such as miniaturization, chip and integration. In this paper, we tried to reduce the sintering temperature of YIG ferrite by three ways: ionic substitution, synthesizing fine powders, adding the ZnO-B₂O₃-SiO₂ (ZBS) glass as sintering aids. The characteristics of synthetic powders and sintered ferrites were studied by XRD, SEM, laser granularity analyzer, TEM, TG-DTA. And the magnetic properties were also investigated. The results showed that: After ionic substituted, the samples Y_1.05Bi_0.75Ca_1.2Fe_4.4V_0.6O₁₂ could be sintered at 1100℃for 3h by common ceramics method, which exhibited uniform and compact microstructure and were single-phase, without any impurities. The sintering temperature was about 400℃lower than that of common YIG without ionic substitution.Using Y(NO₃)₃·6H₂O and Fe(NO₃)₃·9H₂O as major reactants, YIG nanoparticles with size distribution about 20⁴0nm were synthesized by the solid state reaction at room temperatures with NaOH and C6H8O7·H₂O, respectively. The results showed that the YIG crystallization temperature was lower nearly 100℃when C₆H₈O₇·H₂O was selected as the raw material. The obtained YIG nanoparticles were single-phase by solid state reaction, without any impurities. After pressed the nano-powders could be sintered at 1320℃to form compact sintered pellets with uniform and compact microstructures. The sintering temperature was over 100℃lower than that of samples prepared by conventional ceramic processing. The sintered ferrites exhibited a saturation magnetization (4πMs) of 170mT.ZnO-B₂O₃-SiO₂ (ZBS) glass can significantly reduce the sintering temperature of YIG and YBiCaVIG ceramics. When the doping content was 10wt%, YIG and YBiCaVIG ceramics can be sintered at 1280℃and 950℃respectively by common ceramics method. At the same time, Ca²⁺, V⁵⁺, Bi³⁺ substitution and glass doping lead to the samples saturation magnetization (4πMs) decreased and ferromagnetic resonance linewidth(ΔH) increased. The YBiCaVIG ceramics adding 5% ZBS glass sintered at 950℃, withΔH about 47kA·m^-1, 4πMs about 28mT. While the samples have bigger spin wave linewidth(ΔHk) because of smaller grain size. The YIG ceramics adding 5% ZBS glass sintered at 1350℃, withΔHk about 0.84kA·m^-1, which is conducive to the development of high power devices.