ON THE CRYSTALLOGRAPHIC AND MAGNETIC-STRUCTURES OF NEARLY STOICHIOMETRIC IRON MONOXIDE

Neutron diffraction experiments have been carried out at room temperat ure and at 12 K on a polycrystalline three-phase sample of nearly stoi chiometric 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 sampl e was prepared by controlled disproportionation of a quenched wustite with composition Fe0.9347O. Tetrahedral iron interstitials could not b e substantiated from refinement of the room temperature diffraction pa ttern, hence showing that the number of defect clusters is small. The character of the magnetic order-disorder transition is significantly c hanged upon going from the highly nonstoichiometric regime to nearly s toichiometric FeO. The transition in near stoichiometric FeO is strong ly cooperative, Two components of the low temperature antiferromangeti c 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 Aca demic Press, Inc.