Dresden 2017 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 7: Analytical Electron Microscopy: SEM and TEM-based Material Analysis
MA 7.7: Vortrag
Montag, 20. März 2017, 12:00–12:15, MER 02
Identification of laminates in 10 M martensite Ni-Mn-Ga magnetic shape memory single crystals — •Jaromír Kopeček1, Ladislav Klimša1, Ladislav Straka1, Jan Drahokoupil1, Petr Veřtát1, Vít Kopecký1, Hanuš Seiner2, Martin Zelený1, and Oleg Heczko1 — 1Institute of Physics of the AS CR, Na Slovance 2, Prague, 182 00, Czech Republic — 2Institute of Thermomechanics ASCR, Dolejškova 5, 182 00 Prague, Czech Republic
Ni-Mn-Ga is the most studied magnetic shape memory alloy and the most effective example of magnetic shape memory effects. Used single crystals with composition Ni50Mn28Ga22 have monoclinic structure at room temperature, nevertheless the monoclinicity is very weak with respect to both monoclinic angle and lattice parameters a and b. Such structure allows two types of mobile twinning boundaries in magnetic field. The Type I with mirror plane symmetry and more complicated, extremely mobile Type II twinning boundary. Generally, thanks to monoclinicity there exists a hierarchy of twinning on different scales: a-c laminate; monoclinic lamellae - compound twinning; a-b laminate. The complex structure of macrotwinning lamellae and monoclinic twinning was observed many times. However, the third level of lamination, i.e. a-b laminate is hard to observe and describe correctly. We observed whole hierarchy of all three types of laminates by particular SEM observation and manage to identify them using our previous knowledge from optical microscopy, X-ray diffraction and theory of martensite. The identification includes the branching of lamellae on twinning boundaries.