Abstract
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 2O 3 and Sr 7Fe 10O 22 and the reduction of the resultant Fe 2O 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 α-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°C for 1 h under an initial pressure of 1.3 bar followed by re-calcination at 1000°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.
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