Berlin 2012 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 53: Joint Session Magnetic Shape Memory Alloys II (jointly with DS, MA)
MM 53.8: Vortrag
Donnerstag, 29. März 2012, 17:00–17:15, H 0112
Blocking effects of twinning microstructure in Ni2MnGa thin films — •Tobias Eichhorn, Richard Hausmanns, Peter Klaer, Hans-Joachim Elmers, and Gerhard Jakob — Institut für Physik, Johannes Gutenberg-Universität Mainz, 55099 Mainz
The Heusler compound Ni2MnGa is one of the rare materials showing a shape memory effect that can be controlled by an external magnetic field. Huge magnetic-field-induced strains (MFIS) of almost 10 % have been demonstrated for bulk single crystals, which makes the compound interesting for actuator applications. Freestanding epitaxial films, as prepared in this work, open up possibilities for miniaturized devices. So far the absence of MFIS in thin film samples at ambient temperature hinders technical implementation. We identify the twinning microstructure, as induced by the film-substrate interaction, to be responsible for blocking effects. The detailed variant configuration and twinning structure for different crystallographic orientation is studied by means of X-ray diffraction and microscopy methods. While (100) oriented samples show an entangled twinning structure, films of (110) orientation possess a promising martensite structure.
Complementary to magnetometry we employ X-ray magnetic circular dichroism measurements to uncover the origin of the magneto-crystalline anisotropy in the system.
This work is part of the DFG priority program SPP 1239.