Impact of magnetism on screw dislocations in body-centered cubic chromium

The influence of magnetism on the properties of screw dislocations in body-centered cubic chromium is investigated by means of ab initio calculations. Screw dislocations having Burgers vectors 1/2 ⟨111⟩ and ⟨100⟩ are considered, following experimental observations showing activity for both slip systems. At low temperature, chromium has a magnetic order close to antiferromagnetism along ⟨100⟩ directions, for which 1/2 ⟨111⟩ is not a periodicity vector. Hence, dislocations with Burgers vectors 1/2 ⟨111⟩ generate magnetic faults when shearing the crystal, which constrain them to coexist and move pairwise, leading to dissociated ⟨111⟩ super-dislocations. On the other side, ⟨100⟩ is a periodicity vector of the magnetic order of chromium, and no such magnetic fault are generated when ⟨100⟩ dislocations glide. Dislocation properties are computed in the magnetically ordered and non magnetic phases of chromium for comparison purposes. We report a marginal impact of magnetism on the structural properties and energies of dislocations for both slip systems. The Peierls energy barrier opposing dislocation glide in {110} planes is comparable for both 1/2 ⟨111⟩ {110} and ⟨100⟩ {110} slip systems, with lower Peierls stresses in the magnetically ordered phase of chromium.