Modulated monoclinic crystal structure and large shape memory effect in nickel-rich Ni53.5Mn26.0Ga20.5

We report a seven-layered modulated monoclinic crystal structure in the Ni-rich, Ga-poor Ni53.5Mn26.0Ga20.5 alloy. The present composition exhibits coupled magneto-structural transformation around 350 K. Multi-mode twinning with a predominance of crossing twins, indicative of low residual stresses, is observed. A significant shape memory effect of 1.6% and a high strain recovery ratio of 89% are achieved in the polycrystalline specimen at low stresses, owing to lower twinning energies arising from lattice modulation.