Preparation and properties of barium-ferrite-containing glass ceramics

Magnetic properties of magnetic ceramics are dependent on the magnetisation processes. They are usually dominated by Bloch-wall displacements in multi -domain structures of the sintered magnetic material, even if the starting powder material shows single-domain Stoner-Wohlfarth behaviour. Domain wall motion limits in several cases the quality of magnetic materials for speci al applications like permanent magnets or rf devices. We have developed a n ew type of magnetic powder preparation which permits the fabrication of com pact glass ceramics containing Ba-ferrite maintaining the single-domain beh aviour of the starting powder. This technology is based on the glass crysta llisation method for the precipitation of single-domain Ba-ferrite particle s in a quenched melt of Fe2O3-BaO-B2O3(-SiO2). By milling the crystallized melt or leaching out the borate from the SiO2-containing glass, a glass cer amic powder containing Ba-ferrite can be produced, which can be sintered at moderate temperatures providing a dense compact glass ceramic containing u p to 90 wt% Ba-ferrite. This compact glass ceramic shows the same single-do main behaviour as the starting powders, i.e. it also possesses the high coe rcivities of hard magnetic material. (C) 1999 Elsevier Science Limited. All rights reserved.