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Orthorhombic intermediate phase originating from {110} nanotwinning in Ni50.0Mn28.7Ga21.3 modulated martensite

L.Straka1,2, J.Drahokoupil1, P.Veřtát1, J.Kopeček1, M.Zelený1,2,3, H.Seiner4, O.Heczko1,2

The temperature evolution of the structure of Ni50.0Mn28.7Ga21.3 single crystals exhibiting magnetic shape memory effect was investigated near the martensitic transformation by X-ray diffraction. Upon heating, five-layered modulated monoclinic martensite (10M) with nm, nm, nm, and at room temperature (297 K) changed to an intermediate (10M′) phase with nm, nm, and at a few tenths of kelvin below the transformation to austenite at K. This previously unreported 10M′ phase between 10M martensite and austenite can be described as orthorhombic using axes diagonal to the original a and b axes derived from the cubic L21 cell...

We discovered intermediate 10M' phase between10M martensite and austenite in Ni-Mn-Ga single crystal. Our experimental and theoretical investigations show that this phase is a {110}-nanotwinned form of 10M.

1Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic
2Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, 12116, Prague, Czech Republic
3Institute of Materials Science and Engineering, NETME Centre, Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, 616 69, Brno, Czech Republic
4Institute of Thermomechanics, Czech Academy of Sciences, Dolejškova 5, 182 00, Prague, Czech Republic