Magnetism and its impact on atomic arrangements in substitutional alloys: Concentration wave analyses within the KKR-CPA
Date:
Contributed poster at the WE-Heraeus Workshop on ab initio methodologies for complex magnetism and magneto-superconductivity.
Abstract
Alloy phase diagrams—describing the equilibrium phase(s) of mixtures of two or more elements as a function of temperature and composition, usually at ambient pressure—are indispensable in materials science. This is because the nature of atomic arrangements in an alloy plays a key role in determining nearly all physical properties for applications. Considerable effort has been exerted into developing robust theories and computational methodologies capable of predicting the equilibrium phase(s) of an alloy within the framework of first-principles electronic structure calculations. In such models, it is routinely assumed that alloys containing magnetic elements such as Ni, Fe, and Co can be modelled in their (ordered) magnetic ground state. In reality, however, much materials processing takes place at temperatures well above many alloys’ Curie temperatures, meaning this assumption is not well-justified. Here, using a novel analysis technique based on the KKR-CPA and using ‘concentration waves’ to describe atomic-scale chemical fluctuations [1], we demonstrate that the magnetic state of an alloy can have a profound impact on predicted phase diagrams. Using both binary systems such as FeNi [2], as well as multicomponent systems such as CrCoNi [3] as test cases, we compare results of concentration wave analyses performed on the alloys simulated in non-magnetic, ferromagnetic, and paramagnetic states, where the paramagnetic state is described via application of the disordered local moment (DLM) picture. We demonstrate that the nature of predicted chemical ordering, as well as the temperature at which it emerges, is significantly affected by the simulated magnetic state. These results have implications for the materials simulation community, as well as for experimentalists, by suggesting that atomic ordering in some alloys may by ‘tunable’ following application of a magnetic field during the annealing process.
References
[1] C. D. Woodgate and J. B. Staunton, Phys. Rev. B 105, 115124 (2022).
[2] C. D. Woodgate D. Hedlund, L. H. Lewis, J. B. Staunton, Phys. Rev. Mater. 7, 053801 (2023).
[3] C. D. Woodgate, L. H. Lewis, J. B. Staunton, npj Comput. Mater. 10, 272 (2024).