  Superconductivity arises in the layered iron-pnictide compounds when magnetic
long range order disappears. We use first principles density functional methods
to study magnetic arrangements that may compete with long range order near the
phase boundary. Specifically, we study the energetics and charge density
distribution (through calculation of the electric field gradients) for ordered
supercells with varying densities of antiphase magnetic boundaries. We quantify
the amount by which Fe atoms with low spin moments at the antiphase boundaries
have higher energies than Fe atoms with high spin moments away from the
antiphase boundaries. These disruptions in magnetic order should be useful in
accounting for experimental data such as electric field gradients and hyperfine
fields on both Fe and As atoms.
