MICROSTRUCTURES AND MAGNETIC-PROPERTIES OF CRYSTALLIZED BAO-FE2O3-B2O3 GLASSES WITH FINE BAO.6FE2O3 PRECIPITATES

Crystalline phases and amorphous formation regions for the pseudo-tern ary BaO-Fe2O3-B2O3 system were investigated using melt spinning and wa ter quenching techniques. Specimens were heat treated, examined to det ermine the composition and temperature ranges where the BaO.6Fe2O3 pre cipitated, and the relationship between crystalline phases and magneti c properties was discussed. All as-quenched specimens produced by melt spinning with a composition range of less than 70 mol%Fe2O3 and less than 70 mol%BaO were in an amorphous state, and amorphous formation re gion in the case of water quenching was restricted to the composition range of less than 40 mol%Fe2O3 and more than 20 mol%B2O3. In the pseu do-ternary BaO-Fe2O3-B2O3 system, the composition regions were classif ied according to the kind of precipitated phases. In each region, the relationship between the heat treatment temperature and the relative a mount of the precipitated phases was clarified. The amount of BaO.6Fe2 O3 in the composition region between lines P (the tie-line between BaO .6Fe2O3 and BaO.B2O3) and Q (the tie-line between BaO.6Fe2O3-BaO.Fe2O3 and BaO.B2O3-3BaO.B2O3 eutectics) increased as the BaO/Fe2O3 ratio in a sample became closer to 1/6. In this region, the composition ranges were determined where fine BaO.6Fe2O3 particles of high coercive forc e (higher than 240 kA/m (3 kOe)) precipitated from the amorphous phase s after heating. In the composition region between lines Q and R (the tie-line between BaO.Fe2O3 and 3BaO.B2O3), some ribbon specimens showe d the maximum coercive force of 488 kA/m (6.1 kOe), but they contained very fine BaO.6Fe2O3 particles which indicated superparamagnetism.