Study of the Morin Transition in Pseudocubic á-Fe2O3 Particles

J. F. BENGOA, M. S. MORENO, S. G. MARCHETTI, R. E. VANDENBERGHE AND R. C. MERCADER

HYPERFINE INTERACTIONS

Springer

Lugar: Berlin; Año: 2005 vol. 161 p. 177 - 183

0304-3843

We have studied the Morin transition in nanostructured pseudocubic a-Fe2O3 particles of about 1.8 mm side. The preparation was carefully chosen to obtain a system with a very narrow crystallite size distribution and particles of homogeneous morphology. Two samples were studied: one without thermal treatment (a-Fe2O3(ap)) and another annealed at 673 K in air for 12h (a-Fe2O3(an)). Both were characterized by XRD, SEM, TGA and Mössbauer spectroscopy. The results indicate that the Morin transition is suppressed for a-Fe2O3(ap), however, a-Fe2O3(an) has a TM » 230 K and the transition is completed over a very narrow temperature range. These results are discussed in connection with the crystallite size, the cell parameters, and the presence of OH- groups (hydrohematite) or incorporated water (protohematite).