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MA: Fachverband Magnetismus
MA 21: Magnetic Shape Memory Alloys I
MA 21.5: Talk
Wednesday, March 25, 2009, 11:15–11:30, HSZ 103
Adaptive martensite phase in constrained epitaxial Ni-Mn-Ga films — •Stefan Kaufmann1,2, Ulrich Rößler1, Robert Niemann1,2, Oleg Heczko1, Jörg Buschbeck1, Ludwig Schultz1,2, and Sebastian Fähler1,2 — 1IFW Dresden, PO Box 270116, 01171 Dresden, Germany — 2Institute for Solid State Physics, Department of Physics, Dresden University of Technology, 01062 Dresden, Germany
Following the concept of Khachaturyan et al. [1] of adaptive martensite we show that the tetragonal, non-modulated (NM) and the orthorhombic 7M modulated phase in Ni-Mn-Ga magnetic shape memory films fulfil all requirements for an adaptive phase formation. By means of epitaxial film growth we could confirm this concept and probe the transformation path in detail. The constraint by the substrate leads to films with austenite, 7M and NM phase coexisting over a very broad temperature range, contrary to the first order phase transformation common for bulk. Since the pole figures for the NM martensite violate the 4-folded symmetry of the cubic austenite, this shows that NM was not formed directly from the austenite but through the adaptive 7M phase. The rigid substrate is used as a reference frame and allows confirmation of the transformation matrix from austenite to 7M martensite by the Wechsler-Lieberman-Read theory. The results prove the orthorhombic 7M phase not to be an intermediate, thermodynamically stable phase but an adaptive phase stabilized due to the constraint by the substrate-film-interface. The resulting complex microstructure is analyzed from a few nm to the µ m range. [1] Khachaturyan A.G. et al., Phys. Rev. B 43, 10832 (1991)