Impact of vibrations and magnetism on local chemical order in VCoNi and CrCoNi alloys

• Applicant: Dr. Fritz Körmann
• Subject Area: Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569255040

Local chemical order—the local arrangement of elements in an alloy—is crucial in predicting the materials' properties of multicomponent alloys such as VCoNi and CrCoNi. Current models often struggle to accurately predict the stability of local order because they overlook significant thermodynamic contributions from lattice vibrations and magnetism. This project aims to address this gap by developing a comprehensive modeling approach that integrates vibrational and magnetic entropy into chemical local order predictions. Recent studies of VCoNi have revealed a discrepancy of over 300 K between predicted and experimentally observed ordering transition temperatures. Our preliminary results indicate that vibrational entropy significantly contributes to this difference. In the case of CrCoNi, strong magnetic interactions and frustration lead to considerable energy variations and substantial contributions from magnetic entropy, emphasizing the necessity for more accurate magnetic models. The project will develop a computational framework that combines machine-learning interatomic potentials, vibrational free energy calculations, and magnetic model Hamiltonians. Vibrational effects will be captured using thermodynamic integration and free energy perturbation techniques, while magnetic contributions will be modeled with extended Heisenberg Hamiltonians and Monte Carlo simulations. These elements will be integrated into machine-learning low-rank potentials to facilitate efficient sampling of chemical configurations. All methods will be embedded within a modular, python-based workflow. Validation efforts will focus on the VCoNi and CrCoNi alloys and extend the framework to related materials such as CoNiMoAl and VCoNiAl, demonstrating its versatility and relevance for wider alloy design.

• DFG Programme: Research Grants