Iron and iron-based alloys are widely used as structural components in engineering applications. Under operational temperatures the mechanical and magnetic properties will differ from those of ferromagnetic bcc iron at 0K. We have studied the effect of disordered magnetism on the 1/2<111> screw dislocation core structure in bcc iron. Dislocation cores control the selection of glide planes, cross slip and dislocation nucleation processes. Changes in the magnetic state can lead to modifications in the structure of the core and affect dislocation mobility. We also have also investigated the effect of disordered magnetism on the segregation profile of Cr substitutional impurities, we have obtained the formation energies as a function of position with respect to the dislocation core of Cr solutes. To study the dislocation, we have employed a quadrupolar periodic array of screw dislocation dipoles. To address paramagnetism, we have used the non-collinear disordered local moment approximation (DLM) and performed structural relaxations with density functional theory (DFT). The inherent DFT cell size restriction carries a self-interaction of the solute due to periodicity. To address this effect, we investigate the repulsion energy of the solutes with cells up to 4 Burgers vectors in thickness.