Berlin 2012 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 41: Joint Session Magnetic Shape Memory Alloys I (jointly with DS, MM)
MA 41.3: Vortrag
Donnerstag, 29. März 2012, 10:45–11:00, H 0106
Modulated martensite and its twin boundaries in Ni-Mn-Ga films — •Anja Backen1,2, Sandra Kauffmann-Weiss1,2, Anett Diestel1,2, Ludwig Schultz1,2, and Sebastian Fähler1 — 1IFW Dresden, Institute for Metallic Materials, P.O. Box 270116, 01171 Dresden, Germany — 2Dresden University of Technology, Institute of Materials Science, 01062 Dresden, Germany
The magnetic shape memory alloy Ni-Mn-Ga has gained much attention due to the high achievable strains of up to 10 % when applying an external magnetic field. The reorientation of martensitic variants is achieved by movement of twin boundaries. An external magnetic field can only overcome a twinning stress of 2 MPa or less, which brings the modulated martensite in the center of research interest. The 14-layer modulated martensite exhibits different generations of twin boundaries. The first generation are nano twin boundaries between non-modulated variants which are formed in order to decrease elastic energy at the austenite-martensite interface. The second generation connects variants of the 14M structure. This second generation is highly mobile and can be moved by an external magnetic field. We analyzed two types of microstructures which represent two cases of the 2nd generation of twinning. Although they appear to be completely different, X-ray diffraction and pole figure measurements reveal that both microstructures are composed of 14M twins. Magnetization measurements show, that only one type of twin boundaries can be moved by a magnetic field which is important for future application in microsystems. This work is funded by DFG via SPP 1239.