Dresden 2014 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 38: Magnetic Materials II
MA 38.10: Vortrag
Donnerstag, 3. April 2014, 12:00–12:15, HSZ 403
Unraveling nanotwinned martensites in Ni2MnGa from first-principles — •Markus Ernst Gruner1,2, Ulrich K. Rössler1, and Sebastian Fähler1,3 — 1IFW Dresden — 2Universität Duisburg-Essen — 3TU Chemnitz
The unique magnetic shape memory properties of the Heusler compound Ni2MnGa are intimately connected with the presence of modulated structures. These were recently interpreted in terms of an adaptive arrangement of [110] aligned nanotwins consisting of nonmodulated tetragonal L10 building blocks, which is considered as the ground state of this compound. This implies, that the energy of the nanotwinned microstructure can be decomposed into the contribution from the L10 volume fraction, the twin interface energy and the interaction between two neighboring interfaces at a given separation. Based on comprehensive total energy calculations in the framework of density functional theory calculations we verify this building principle through a systematic evaluation of twinned microstructures constructed from strained L10 martensite with different c/a. For the equilibrium distortion of martensite, c/a=1.26, we observe indeed nearly perfect additivity of the corresponding contributions. Furthermore, we find that for intermediate distortions specific nanotwinned configurations can be significantly lower in energy than the respective nonmodulated building blocks. In particular, the so-called 4O orthorhombic structure consisting of two double-layer twins becomes energetically comparable to the nonmodulated L10 ground state martensite.