SYNTHESIS AND MAGNETIC-PROPERTIES OF HEMATITE WITH DIFFERENT PARTICLEMORPHOLOGIES

Haematite particles of four different morphologies (polyhedral, platel ike, needlelike and diskshape) were synthesized by the hydrothermal me thod. The morphology and average particle diameter (1.4; 7.4; 0.2 and 0.12 mu m, respectively) were determined by transmission electron micr oscopy (TEM) combined with electron diffraction. The haematite samples were studied by transmission Mossbauer spectroscopy in the temperatur e range 4.2-300 K. In all cases, a weak ferromagnetic phase (WF) was p resent above the Morin temperature of 230 K and found to coexist with an antiferromagnetic phase (Ali) below this temperature. However, the populations of the two phases at 230 K were demonstrated to depend on the morphology of the particles. Moreover, the WF and AF phases exhibi t a different dependence of the magnetic texture on temperature and pa rticle morphology. (C) 1998 Elsevier Science S.A. All rights reserved.