Dresden 2006 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
MM: Metall- und Materialphysik
MM 33: Symposium Materials Modelling II
MM 33.5: Vortrag
Donnerstag, 30. März 2006, 16:00–16:15, IFW A
Temperature dependent properties of Ni2MnGa — •Tilmann Hickel, Blazej Grabowski, Oliver Marquardt, and Jörg Neugebauer — Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 40237 Düsseldorf
The ferromagnetic shape memory compound Ni2MnGa undergoes a martensitic phase transition at 200 K. For temperatures well above this value it has a cubic L21 structure, whereas below the transition temperature the structure is orthorhombic. The resulting deformations drive the shape-memory effect. In order to understand the microscopic processes connected to this phase transition, we have investigated its temperature dependence combining density functional theory in the generalized gradient approximation and thermodynamic concepts. For this purpose, phonon and magnon spectra have been determined. Employing the quasiharmonic approximation we have calculated free energy surfaces as function of key reaction coordinates (lattice constant, c/a-ratio). A detailed analysis of the temperature dependence of the surface minima and the low energy paths allowed to extract direct information regarding the thermodynamic stability of the different phases (austenite, martensite, pre-martensite) and activation barriers. The results are compared with recent experiments.