Adaptive Modulations of Martensites


Modulated phases occur in numerous functional materials like giant ferroelectrics and magnetic shape-memory alloys. For the first time we showed that Ni-Mn-Ga modulated martensite exhibiting the giant magnetically induced strain (magnetic shape memory effect) can be considered as an adaptive phase which profoundly changes the perception of modulated phases in this materials and it is important for understanding of the effect. We investigated the coexistence of austenite, adaptive 14M phase, and tetragonal martensite in Ni-Mn-Ga magnetic shape-memory alloy epitaxial films and showed that the modulated martensite can be constructed from nanotwinned variants of the tetragonal martensite phase. By combining the concept of adaptive martensite with branching of twin variants, we could explain key features of modulated phases from a microscopic view. The work was made in cooperation between IFW Dresden, Institute of Physics and University of Maryland.


Pole figure measurements of the {400}-planes of the pseudo-orthorhombic 14M [(a)–(c)] and the tetragonal NM martensite [(d)-(e)] from ψ=0…10°. The fourfold symmetry verifies epitaxial growth on the MgO(100) substrate. The shift of reflections with respect to the center is due to a misalignment of the sample during measurement.