Constrained non-collinear magnetism in disordered Fe and Fe-Cr alloys

The development of quantitative models for radiation damage effects in iron, iron alloys and steels, particularly for the high temperature properties of the alloys, requires treating magnetic interactions, which control the phase stability of ferritic-martensitic, ferritic, and austenitic steels. Here, disordered magnetic configurations of pure iron and Fe-Cr alloys are investigated using Density Functional Theory (DFT) formalism, in the form of a constrained non-collinear magnetic model, with the objective of creating a database of atomic magnetic moments and forces acting between the atoms. From a given disordered atomic configuration of either pure Fe or Fe-Cr alloy, a penalty contribution additional to the usual spin-polarized DFT total energy is evaluated by constraining the magnitude and direction of magnetic moments. An extensive database of non-collinear magnetic moment and force components for various atomic configurations has been generated and used for interpolating the spatially-dependent magnetic interaction parameters, for applications in large-scale spin-lattice dynamics and magnetic Monte-Carlo simulations.