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MM: Fachverband Metall- und Materialphysik

MM 15: Computational Materials Modelling III - Bulk thermodynamics/ Phase Transitions I

MM 15.1: Vortrag

Montag, 31. März 2014, 15:45–16:00, IFW D

Impact of weak and strong magnetic coupling on the thermodynamics of chromium — •Fritz Körmann, Blazej Grabowski, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, D-40237, Düsseldorf, Germany

Chromium is a decisive ingredient for stainless steels and a reliable understanding of its thermodynamic properties is thus indispensable. Parameter-free first-principles methods have nowadays evolved to a state allowing such thermodynamic predictions. For materials such as Cr, however, the inclusion of magnetic entropy and higher order contributions such as anharmonic entropy is still a formidable task. Employing state-of-the-art ab initio molecular dynamics simulations and statistical concepts, we compute a set of thermodynamic properties based on quasiharmonic, anharmonic, electronic and magnetic free energy contributions from first principles [1]. The magnetic contribution is modeled by an effective nearest-neighbor Heisenberg model, which itself is solved numerically exactly by means of a quantum Monte Carlo method. We investigate two different scenarios: a weak magnetic coupling scenario for Cr, as usually presumed in empirical thermodynamic models, turns out to be in clear disagreement with experimental observations. We show that only a mixed Hamiltonian including weak and strong magnetic coupling provides a consistent picture with good agreement to experimental thermodynamic data.

[1] F Körmann, B Grabowski, P Söderlind, M Palumbo, S G Fries, T Hickel and J Neugebauer, J. Phys.: Condens. Matter 25, 425401 (2013).