On the crystallographic and magnetic structures of nearly stoichiometric iron monoxide

Neutron diffraction experiments have been carried out at room temperature and at 12 K on a polycrystalline three-phase sample of nearly stoichiometric wustite, magnetite, and iron (mole fractions 0.914, 0.080, and 0.006) in order to extend the structural description of wustite to a region were defect clusters should be of less importance, The sample was prepared by controlled disproportionation of a quenched wustite with composition Fe0.9347O. Tetrahedral iron interstitials could not be substantiated from refinement of the room temperature diffraction pattern, hence showing that the number of defect clusters is small. The character of the magnetic order-disorder transition is significantly changed upon going from the highly nonstoichiometric regime to nearly stoichiometric FeO. The transition in near stoichiometric FeO is strongly cooperative, Two components of the low temperature antiferromangetic structure is extracted, the main component (mu(i) = 3.8(4) mu(B)) is along the unique axis [111], while a second smaller (mu(perpendicular to) = 1.3(3) mu(B)) is perpendicular to the unique axis. (C) 1996 Academic Press, Inc.