Memory effect of ball-milled and annealed nanosized hematite

P. G. BERCOFF; H. R. BERTORELLO; M. I. OLIVA

PHYSICA B - CONDENSED MATTER

Elsevier

Lugar: Amsterdam; Año: 2007 vol. 398 p. 204 - 207

0921-4526

Fine particles of hematite (mean size 55 nm) were produced by ball-milling a mixture of hematite and pure Fe and annealing at 1000 ºC. XRD and Mössbauer spectroscopy show that only a-Fe2O3 is present in the final product, with lattice and Mössbauer parameters that correspond to bulk hematite. ZFC and FC magnetization measurements were performed from 5 to 300 K, at different applied fields. Two magnetic regimes were observed: one at low temperatures (£100 K) that we ascribe to the magnetic moments in the outer shell of the partcles that couple to the magnetic moments in the core, and another at higher temperature that corresponds to the Morin transition, finding that the Morin temperature is TM = 246 K. The memory effect is clearly observed in magnetic measurements that start from different remanence states and explained as dependent on the ordering of the magnetic moments within the particles.