Electronic structure and effective chemical and magnetic exchange interactions in bcc Fe-Cr alloys

P. A. Korzhavyi* and A. V. Ruban

Department of Materials Science and Engineering, Applied Material Physics, Royal Institute of Technology, SE-100 44 Stockholm, Sweden

J. Odqvist† and J.-O. Nilsson

R&D Centre, Sandvik Materials Technology, SE-811 81 Sandviken, Sweden

B. Johansson

Department of Materials Science and Engineering, Applied Material Physics, Royal Institute of Technology, SE-100 44 Stockholm, Sweden and R&D Centre, Sandvik Materials Technology, SE-811 81 Sandviken, Sweden

Received 21 July 2008; published 9 February 2009

Abstract

Electronic structure calculations are employed in order to investigate the cohesive properties lattice parameter, enthalpy of formation, and bulk modulus of random Fe-Cr alloys as a function of composition and magnetic state, as well as to derive the chemical and magnetic exchange interactions of the constituent atoms. The calculations predict certain anomalies in the cohesive properties of ferromagnetic alloys at a concentration of about 7 at % Cr; these anomalies may be related to the changes in Fermi-surface topology that occur with composition in this alloy system. The obtained interatomic interactions are used as parameters in the configurational Ising and magnetic Heisenberg Hamiltonians for modeling finite-temperature thermodynamic properties of the alloys. We discuss the approximations and limitations of similar modeling approaches, investigate the origin of existing difficulties, and analyze possible ways of extending the theoretical models in order to capture the essential physics of interatomic interactions in the Fe-Cr or similar alloys where magnetism plays a crucial role in the phase stability.

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https://sci-hub.tw/https://journals.aps.org/prb/abstract/10.1103/PhysRevB.79.054202