The effect of ball milling before and after calcination on the magnetic properties of HTR processed strontium hexaferrite powder

HTR process (Hydrogen Treatment and Recalcination) is a very new method in which strontium hexaferrite powder, as produced conventionally from strontium carbonate and iron oxide, has been heated in a hydrogen static atmosphere and then recalcined in air. During the hydrogenation stage, the hard magnetic powder is changed to a soft magnetic material with a low intrinsic coercivity and high saturation magnetisation. However, after recalcination, the saturation magnetisation returns to its initial value, but intrinsic coercivity increases to a value much greater than its amount before hydrogenation. The intrinsic coercivity which has been reported in this regard is about 391 kA/m. In this work this HTR processed powder has been milled in a ball mill and effect of milling before and after calcination on microstructure and particularly magnetic properties has been investigated. The results show a good enhancement in the intrinsic coercivity of material. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)