The effect of hydrogen on composition, microstructure and magnetic properties of strontium hexaferrite

Strontium hexaferrite powder, synthesised conventionally, has been treated in a hydrogen atmosphere and subsequently calcined in air. The phase identification studies showed decomposition of strontium hexaferrite into Fe(2)O(3) and Sr(7)Fe(10)O(22) and the reduction of the resultant Fe(2)O(3) during reaction with hydrogen. The magnetic measurements indicated a substantial increase in the saturation magnetisation and a marked decrease in the remanence and intrinsic coercivity during hydrogenation due to the formation of the alpha-Fe phase. After re-calcination, the hexaferrite phase re-formed and the remanence and saturation magnetisation exhibited values close to the initial ones but there was a significant improvement in the intrinsic coercivity. This was attributed mainly to very fine grains formed as a result of hydrogenation and subsequent re-calcination. The highest intrinsic coercivity obtained in this work was 400 kA/m (5 kOe) which occurred after hydrogenation at 700 degrees C for 1 h under an initial pressure of 1.3 bar followed by recalcination at 1000 degrees C for 1 h, These studies show that strontium hexaferrite powder with an enhanced Value of intrinsic coercivity can be produced from the conventionally synthesised powder. (C) 2000 Elsevier Science Ltd and Techna S.r.l. All rights reserved.