The low-temperature sintering of M-type hexaferrites

The sintering of the M-type hexaferrites, AFe12O19 (A = Ba, Sr), was studied. The effects of the A cation type, the partial CuO substitution for Fe2O3 and the Fe deficiency on the sintering were examined. Samples with nominal compositions of Ba1−zSrzCuxFey−xO19−δ (z = 0 or 0.5, x = 0-1.0 and y = 11-12) were prepared with a solid-state reaction at 1000 °C. The CuO addition enhanced significantly the sintering rate of the hexaferrites at temperatures below 1100 °C, while a moderate effect on the sintering was caused by a partial substitution of Sr for Ba. The diffusion studies showed that the CuO addition enabled the reactive liquid-phase sintering of hexaferrites at 1000 °C. The relative sintered densities of the Cu-containing hexaferrite ceramics sintered at 1000 °C for 3 h were around 90%. The addition of CuO had a strong effect on the coercivity, but only a moderate effect on the magnetization of the studied ceramics.