Low temperature sintering and magnetic properties of garnet microwave magnetic materials

This study investigated the low temperature sintering for microwave magnetic materials [Bi-incorporated calcium vanadium garnets (Bi-CVG), (Bi0.75Ca1.2Y1.05)(V0.6Fe4.4)O12]. Sintering behavior and magnetic properties of Bi-CVG materials prepared from ultrafine-sized powders were compared with those of materials prepared from micron-sized powders. The activation energy for densification (Ed), derived from temperature and time dependence of materials' density, is markedly reduced by using ultrafine-sized powders as starting materials, i.e., (Ed)ultra = 7.04 kJ mole−1 and (Ed)micron = 39.5 kJ mole−1 for ultrafine and micron powder sintered samples, respectively. The activation energy for densification is further reduced to 4.59 kJ mole−1 by using microwave sintering process with ultrafine powders. Remnant magnetization (Br) of the Bi-CVG materials is similar for samples possessing the same high density, regardless of the microstructures. Conversely, the coercive field (Hc) of the materials is larger for samples containing fine grains and vice versa. While the low frequency magnetic properties of the Bi-CVG materials are microstructure-dependent, the microwave magnetic properties of the materials are not.