Structural and magnetic properties of mechanochemically prepared wüstite (Fe1-xO) nanopowders

Structural and magnetic properties of mechanochemically prepared wüstite (Fe1-xO) nanopowders

Wüstite nanopowders have been prepared by mechanochemical processing (MCP), using high-purity hematite (α-Fe2O3) and iron (Fe) powders as the raw materials. In order to get a single-phase wüstite different mole ratios of (Fe/Fe2O3) were milled. X-ray diffraction studies of the as-milled powders show that a single-phase wüstite was formed for a mole ratio of 0.6. Using the formula a = 4.334-0.478x, for Fe1-xO, where ‘‘a’’ is the lattice parameter of wüstite, a nonstoichiometric composition of Fe0.93O was estimated for the wüstite single phase. Using Scherer’s formula, a mean crystallite size of 13±1 nm was calculated for the single phase wüstite. The morphology of the powders was also checked by TEM. The room-temperature Mössbauer spectra of the samples supported the presence of Fe3+ in octahedral sites of wüstite phase, which is a sign of its nonstoichiomety. Hysteresis loops of the as-milled powders at 5 K and room temperature have been obtained by SQUID and by VSM systems, respectively. In contrast to the bulk wüstite, the loops show non-zero coercivity. The observed magnetizations can be explained by a model based on the spinel-type defect clusters in nonstoichiometry wüstite Room temperature Magnetic measurements showed that nanosized prepared wüstite ferrimagnetic like behavior, which was interpreted according to spinel-like defect clusters