Regensburg 2007 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 17: Magnetic Shape Memory Alloys

MA 17.1: Vortrag

Mittwoch, 28. März 2007, 15:15–15:30, H10

First-principles study of the magnetoelastic behavior of magnetic shape memory alloys — •Peter Entel, Markus Gruner, Alfred Hucht, and Georg Rollmann — Physics Department, University of Duisburg-Essen, 47048 Duisburg

We investigate the magnetoelastic properties of magnetic shape memory alloys (MSMA) by large-scale ab initio calculations, which have been performed on massively parallel platforms like the Blue Gene/L at NIC (FZ Jülich). In particular, we focus on the change of elastic properties with composition and, in addition, under the action of uniaxial strain or external magnetic fields close to the magnetic, structural or combined magnetostructural phase transitons in the systems Ni-Mn-Z (Z = Ga, In, Sn). We highlight the atomistic details and origin of the austenitic to martensitic transformation in the MSMA, the latter of which is connected to the anomalous forces acting on the Ni atoms in Ni-Mn-Z. Note that the X atoms in X₂(Y = Mn)Z are usually responsible for the formation of the cubic L2₁ Heusler structure and its stability. However, in case of X = Ni, the high-temperature cubic structure is band-Jahn-Teller instable with respect to tetragonal distortions leading to a modulation of valence electron charges and a more favorable crystal field environment for the Ni atoms. We show how the interplay of Fermi surface nesting (and its change when the structure undegoes a tetragonal distortion) and the impact of anomalous force constants allows to understand most of the physical properties of the MSMA.