Berlin 2015 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 35: Methods in Computational Materials Modelling IV: Steels

MM 35.1: Talk

Wednesday, March 18, 2015, 11:45–12:00, H 0106

Temperature-dependent magnon-phonon coupling in bcc Fe — •Fritz Körmann, Blazej Grabowski, Biswanath Dutta, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany

An ab initio based framework for quantitatively assessing the non-adiabatic free energy contributions due to magnon-phonon interactions and lattice expansion to phonon energies is developed [1]. Employing the framework of the recently developed spin-space averaging (SSA) procedure provides paramagnetic forces at high temperatures [2]. The full temperature dependence of phonons for arbitrary magnetic temperatures is obtained by relating the ferromagnetic and paramagnetic SSA force constants with energetics from the magnetic subsystem. The latter is derived by means of QMC simulations for an effective Heisenberg model [3]. The theoretical results for bcc Fe are in very good agreement with recent high-quality phonon frequency measurements [1]. For some phonon branches, the impact of magnetic excitations is an order of magnitude larger than the phonon shift due to lattice expansion. The significant role of magnetic short-range order on lattice vibrations above the Curie temperature is demonstrated.

[1] F. Körmann, B. Grabowski, B. Dutta, T. Hickel, L. Mauger, B. Fultz, J. Neugebauer, Phys. Rev. Lett. 113, 165503 (2014).

[2] F. Körmann, A. Dick, B. Grabowski, T. Hickel, J. Neugebauer, Phys. Rev. B 85, 125104 (2012).

[3] F. Körmann, A. Dick, T. Hickel, and J. Neugebauer, Phys. Rev. B 83, 165114 (2011).