Berlin 2012 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 48: Joint Session Magnetic Shape Memory Alloys I (jointly with DS, MA)
MM 48.5: Talk
Thursday, March 29, 2012, 11:15–11:30, H 0106
Adaptive nanostructures in Fe-Pd magnetic shape memory alloys — •Markus Ernst Gruner1, Sandra Kauffmann-Weiß2, Sebastian Fähler2, Ludwig Schultz2, and Peter Entel1 — 1Faculty of Physics, University of Duisburg-Essen, 47048 Duisburg — 2IFW Dresden, P.O. Box 270116, 01171 Dresden
Apart from the prototypical Ni-Mn-Ga Heusler alloy, also Fe-based alloys as Fe70Pd30 exhibit significant magnetic field induced strains in moderate magnetic fields. This is bound to a slightly tetragonal fcc structure (fct) which finds no correspondence on the low temperature binding surface which has been determined from density functional theory (DFT) calculations [PRB 83, 214415 (2011)]. Instead, the energy decreases rather uniformly along the Bain path towards the absolute minimum close to bcc. Recent experiments reveal the possibility of growing Fe70Pd30 films with c/afct = 1.09 extending the Bain path beyond fcc [PRL 107, 206105 (2011)]. XRD spectroscopy reveals that this is accompanied by a novel relaxation mechanism leading to a nanotwinned pattern consisting of fct building blocks. DFT modelling confirms this process showing a second minimum on the binding surface. This owes to the extremely low formation energy of fct twins causing the autonomous evolution of a twinned superstructure in the simulation cell along [110]. This corresponds to the experimentally observed soft transversal acoustic phonon in this direction, which is also a central feature of the Ni2MnGa magnetic shape memory alloy. We demonstrate further that magnetic excitations significantly alter the binding surface and thus potentially influence the transformation.