Regensburg 2019 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 34: Methods in Computational Materials Modelling (methodological aspects, numerics)
MM 34.1: Vortrag
Donnerstag, 4. April 2019, 10:15–10:30, H44
Tight-binding insight in phase stabilities of magnetic iron — •Ning Wang1, Thomas Hammerschmidt1, Tilmann Hickel2, Jutta Rogal1, and Ralf Drautz1 — 1ICAMS, Ruhr-Universität Bochum — 2Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf
Although the phase diagram of iron has been well-established, we still lack a consistent and theoretical understanding. The difficulty lies in the modelling of complex thermal excitations including magnetic, vibrational and electronic excitations and their mutual interactions. Here we present a spin-lattice fluctuation theory by combining the spin-fluctuation theory and the semi-empirical tight-binding model. With this model we perform a thorough investigation of magnetic and structural phase transitions in magnetic iron. A thermodynamic-integration calculation shows a bcc-fcc phase transition driven by magnetic fluctuations. We employ the spin-space averaging scheme and obtain strong magnetic phonon softening in bcc iron. We observe a sign change in the calculated vibrational-entropy difference between bcc and fcc iron, which is atrributed to the transformation back from fcc to bcc iron and in a good agreement with experimental deduction.