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MA: Fachverband Magnetismus

MA 35: Magnetic Oxides and Shape Memory Alloys (jointly with MM)

MA 35.1: Vortrag

Donnerstag, 14. März 2013, 09:30–09:45, H23

Magnetoelastic coupling and the formation of adaptive martensite in magnetic shape-memory alloys — •Markus Ernst Gruner and Peter Entel — Faculty of Physics and CeNIDE, University of Duisburg-Essen, 47048 Duisburg

Efficient magnetic shape-memory alloys undergo a thermoelastic martensitic transformation which is frequently accompanied by structural premartensitic precursor phenomena. The premartensites evolve into modulated martensitic phases which can in several cases be interpreted as nanotwinned representations of the low-symmetry ground state with a more or less regular periodicity of the twin defects. Their presence is related to a pronounced shear anomaly in [110] direction. This is a common signature of magnetic shape memory systems as different as Ni-Mn-based Heusler systems and disordered fcc Fe-based alloys and can be ascribed to an electronic band-Jahn-Teller-type instability which affects the transversal acoustic phonons in [110] direction.

By means of large-scale first-principles total energy calculations, we will demonstrate at the example of Ni-Mn-based Heusler compounds and disordered Fe-Pd alloys, that the presence of a specific magnetic order is an important factor for the (de-)stabilization of nanotwinned or modulated martensites according to the inherently strong magnetoelastic coupling in these systems.