Crystallization remanent magnetization during the transformation of maghemite to hematite.

Abstract

We have studied crystallization remanent magnetization (CRM) in the gamma Fe2O3 rt arrow alpha Fe2O3 transformation, starting from synthetic, equidimensional maghemite crystals of single-domain size (median diameter of 245 A). Inversion of maghemite to hematite on heating was indicated by an exothermic peak in differential thermal analysis (DTA) at 555oC. In CRM experiments, samples of dispersed maghemite were heated in zero field to temperatures between 300oC and 604oC, held for 3 hours in a 50-mu T field HCRM, and cooled in zero field to 20oC. The intensity of the resulting CRM MCRM increased with increasing conversion to hematite, reaching a maximum of 784 A m-1 (0.0013 emu cm-3) after the 604oC run. -from Authors