Effects of the grain boundary on the coercivity of barium ferrite BaFe12O19

The magnetic and micro-structural properties of both polycrystalline and single-crystal samples of BaFe12O19 have been investigated to elucidate the relationship between the coercivity and the grain boundary pinning effect. With increasing the sintering temperature of the polycrystalline sample from 1100 to 1300 °C, the grain size gradually increases while the coercivity largely drops from about 4 kOe to a few Oe. The M(H) curve for single-crystal sample, which has little grain boundaries, shows almost negligible coercivity. The difference in the coercivity between the single-crystal and polycrystalline samples is discussed in terms of the pinning of magnetization at the grain boundaries.