Cobalt substitution for iron in BaFe₂As₂ produces a superconducting ground state with indications that antiferromagnetism (AFM) and superconductivity (SC) compete for the same itinerant electrons. Partial cobalt substitution changes the relative sizes of the hole- and electron-like fermi surface pockets responsible for AFM in BaFe₂As₂ with two effects: 1) the magnitude of the ordered moment decreases with increasing cobalt concentration; and 2) beyond a critical concentration commensurate nesting is lost and a small transverse incommensurability appears which maintains long range magnetic order. Magnetic susceptibility and resistivity measurements in applied pressure show suppression of AFM and appearance of SC above 3.5 GPa in BaFe₂As₂ and, similarly, suppression of AFM and enhancement of SC below 2 GPa in Ba(Fe_1–xCo_x)₂As₂. Such measurements could not determine if the suppression of AFM via pressure is due to reduced fermi surface nesting, leaving open the question of whether the mechanisms which produce SC in BaFe₂As₂ and Ba(Fe_1–xCo_x)₂As₂ are the same.
Results of single crystal neutron diffraction measurements which were performed under applied pressure to track the suppression of AFM order and look for IC spin density wave order in Ba(Fe_0.946Co_0.054)₂As₂ will be discussed.