Regensburg 2010 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 8: Magnetic Shape Memory Alloys
MA 8.2: Vortrag
Montag, 22. März 2010, 15:30–15:45, H22
Anomalous phonon behaviour in Ni-based Heusler alloys — •Mario Siewert, Markus E. Gruner, Peter Entel, and Alfred Hucht — Faculty of Physics and CeNIDE, University of Duisburg-Essen, 47048 Duisburg, Germany
Ferromagnetic shape memory alloys (FSMAs) are of large scientific interest due to their applicability in actuators and sensors based on magnetic fields. The martensitic transformation in the Ni2MnGa reference system to a modulated low symmetry phase that is responsible for the magnetic shape memory behaviour is preceeded by anomalous temperature dependent phonon softening along the [110] direction in the parent phase. The occurence of the soft mode has been linked to Fermi surface nesting in the past. In this work we report systematic studies of magnetic Ni-Mn-X (X=Al, Si, Zn, Ga, Ge, In, Sn, Sb) based Heusler alloys by means of density functional theory. Our calculations reveal that a phonon softening along the [110] direction up to imaginary frequencies can be found for all compounds in the cubic phase. Furthermore, an inversion of the optical modes can be observed. A systematic investigation of the reconstruction of the Fermi surface as a function of the valence electron number per atom (e/a) allows to predict materials with particular nesting behaviour.