Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 32: Postersession II: Spinstruct./Phase Trans. (1-10); Spinelectronics (11-15); Thin Films (16 - 36); Particles/Clusters (37-45); Multiferroics (46-54); Spindynamics/Spin Torque (55 - 76); Post Deadlines (77-79)

MA 32.7: Poster

Freitag, 29. Februar 2008, 11:15–14:00, Poster E

Importance of magnetism for the thermal expansion of transition metals: an ab initio study — •Fritz Körmann, Alexey Dick, Blazej Grabowski, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Postfach 140444, 40074 Düsseldorf, Germany

Recently, extensive efforts have been made to combine density functional theory with thermodynamic concepts. For this purpose the Gibbs free energy has conventionally been calculated employing the quasiharmonic approximation. This method allowed to perform ab initio predictions on, e.g., the thermal expansion of the nonmagnetic system and yielded an excellent agreement with experiment [1]. In magnetic materials the ab initio analysis has also to take into account magnetic excitations and their interplay with the vibronic degrees of freedom. However, most studies treat the magnetic and lattice excitations separately. We therefore performed a systematic investigation of the influence of magnetic configurations on the vibronic degrees of freedom. The calculations have been performed for elementary Fe and Ni in the bcc and the fcc phase. Based on these results, we derived the dependence of the temperature induced magnetic disorder and the change of local magnetic moments on thermodynamic quantities of Fe and Ni, with emphasis on thermal expansion and heat capacities.

[1] B. Grabowski, T. Hickel, and J. Neugebauer, Phys. Rev. B 76, 024309 (2007).