Density functional theory calculations were carried out to study magnetic and energetic properties of vacancy, and magnetic and non-magnetic substitutional impurities (respectively Fe and Cu) in the ground state of body-centered cubic Cr, i.e., spin-density wave. The lowest-energy site for all of the defects was found to be around a magnetic node, as compared with the high-spin spin-density wave sites and (100)-layered antiferromagnetic and non-magnetic phases. The corresponding differences for vacancy formation energy were 0.29, 0.32 and 0.23eV, respectively. The migration of a vacancy was revealed to be highly anisotropic in the spin-density wave state, mainly confined in the nodal and adjacent planes. The energy barrier for such a quasi-bidimensional motion was indeed 0.52eV lower than that for migration in perpendicular directions. Regarding magnetic modifications of the spin-density wave introduced by point defects, they were confirmed to be weak and rather local at low defect concentrations (0.27 and 0.55%). Cu behaves similarly to a vacancy-inducing magnetic moment enhancement on neighboring Cr atoms. On the other side, the presence of Fe atoms leads to multiple energy minima with different local magnetic arrangements, particularly around a node, due to competition between neighboring Fe-Cr, Cr-Cr and Fe-Fe magnetic coupling tendencies. The present results strongly suggested that simple antiferromagnetic and non-magnetic phases may not allow an accurate description of defect properties in the ground state of Cr. Instead, an explicit spin-density wave representation was required. In addition, it was pointed out that the presence of vacancy and both Cu and Fe could promote a migration of spin-density wave nodes, which could activate the spin-density wave to antiferromagnetic phase transition via a node-annihilation mechanism, as proposed in previous work.

Vacancy and Substitutional Impurities in the Spin-Density Wave State of Cr from First Principles. R.Soulairol, C.C.Fu, C.Barreteau: Physical Review B, 2011, 83[21], 214103