Role of alloying on the shape memory effect in Ni2MnGa

Ni2MnGa undergoes a reversible structural phase transition between a cubic phase and a martensitic phase both of which are ferromagnetic. The large, controlled, shape change associated with the transition is technologically useful in a variety of applications such as actuators and sensors. The transition temperature for the structural transformation is influenced by the stoichiometry of the alloy. In this work we have calculated properties of Ni2MnGa along with several related substitutional alloys. These including substitutions that do not change the electron to atom ratio (e/a) (Al for Ga), as well as additions such as Cu for Ni and Ni for Mn that increase the e/a ratio, and Co for Ni which decreases the ratio. The transition is associated with a soft c(11)-c(12) elastic constant which we have calculated using first principles electronic structure calculations. Changes in structural properties are correlated with changes in the electronic density of states. (C) 2002 American Institute of Physics.