Effects of the grain boundary on the coercivity of barium ferrite BaFe ₁₂O₁₉

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.