Twin boundary structure of the modulated variants in a Ni–Mn–Ga alloy

The microstructure of a Ni–Mn–Ga ferromagnetic shape memory alloy has been characterized by transmission electron microscopy. Electron diffraction reveals that the microstructure of the alloy predominately consists of seven-layer modulated martensite. There exists reflection-twinned relation between the martensitic variants. It is found that there are parallel and equidistant fringes at the boundary. The nature of these fringes is discussed and the results show that the boundary fringes are caused by the elastic strains associated with the coherent interface.