Berlin 2008 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 42: Phase Transitions III

MM 42.6: Talk

Thursday, February 28, 2008, 15:15–15:30, H 0107

Microstructure of epitaxial films of the magnetic shape memory alloy Ni₂MnGa — •Tobias Eichhorn, Michael Kallmayer, Hans-Joachim Elmers, and Gerhard Jakob — Institut für Physik, Universität Mainz, Staudinger Weg 7, 55099 Mainz

Since the first discovery of the magnetic shape memory effect by Ullako et al. interest in this material group has increased continuously. By application of a magnetic field, length changes up to 10 % can be achieved in single crystals of martensitic Ni₂MnGa. However the microscopic mechanism is far from being completely understood. To improve this understanding, single crystalline thin films allow elaborate measuring techniques and form the basis for development of applications on a small length scale.

Thin epitaxial films of Ni₂MnGa and Ni_1.96Mn_1.22Ga_0.82 are grown by dc-magnetron sputtering onto heated Al₂O₃(1120) and MgO(100) substrates. To investigate the structural and magnetic properties of the samples we use temperature dependent x-ray diffraction and magnetometry. To get insight on microscopic magnetism and electronic structure x-ray absorption spectroscopy and magnetic circular dichroism measurements have been performed at the German synchrotron light source BESSY II (Berlin). Concerning technological applications free-standing single crystalline films will be needed. For that purpose water-soluble substrates and suitable sacrificial layers are investigated. To detect the magnetically induced shape memory effect in our films without removal of the substrate we build a setup to measure the magnetostriction by a capacitive method.