  The local nuclear and magnetic structure of wustite, Fe1-xO, and the coupling
between them, has been examined using reverse Monte Carlo refinements of
variable-temperature neutron total scattering data. The results from this
analysis suggest that the individual units in a tetrahedral defect cluster are
connected along <110> vectors into a Koch-Cohen-like arrangement, with the
majority of octahedral vacancies concentrated near these defects. Bond valence
calculations indicate a change in the charge distribution on the cations with
the charge on the tetrahedral interstitials increasing on cooling. The magnetic
structure is more complex than previously thought, corresponding to a
non-collinear spin arrangement described by a superposition of a condensed spin
wave on the established type-II antiferromagnetic ordering. This leads to an
architecture with four groups of cations each with different spin directions.
The cations within the interstitial clusters appear to be weakly
ferromagnetically coupled and their spins are correlated to the spins of the
octahedral cations closest to them. This work not only provides further insight
into the local structure of wustite but also a better understanding of the
coupling between defect structures and magnetic and charge-ordering in complex
materials.
