Impact of local magnetism on stacking fault energies: A first-principles investigation for fcc iron

Abstract

A systematic ab initio study of the influence of local magnetism on the generalized stacking fault energy (GSFE) surface in pure fcc iron at 0 K has been performed. In the calculations we considered ferro- and antiferro- (single- and double-layer) magnetic order of local moments as well as their complete disorder, corresponding to paramagnetic (PM) state. We have shown that local magnetism is one of the most important factors stabilizing austenitic structure in iron (with respect to more stable at 0 K hcp) and that the perturbation of magnetic structure by the formation of stacking fault is a short-range effect. Local magnetism also strongly influences the GSFE surface topology and, therefore, the material's plasticity by reducing the energetic barriers that need to be overcome to form the intrinsic stacking fault (ISF) or return from the ISF structure to fcc. The influence of atomic relaxations on such barriers is moderate and does not exceed 15%. In addition, a methodology to evaluate the PM ISF energy using a superposition of the ISF energies obtained for ordered magnetic structures is proposed to overcome computational impediments arising when dealing with disorder in the PM state. The complications of the proposed methodology together with the ways to overcome them are also discussed.