Promising shape memory in NiCoMnZ (Z=Si, Ge and Sn) quaternary Heusler alloy from first principles

From the first-principles calculations based on density functional theory with the generalized gradient approximation, electronic structures of NiCoMnZ (Z = Si, Ge and Sn) quaternary Heusler compounds are calculated within the framework to understand the structure stability at the microscopic scale. The structural, electronic and magnetic properties are calculated for the three compounds in both cubic and tetragonally distorted structure. The total energy difference between the cubic and tetragonal structure becomes smaller with increasing the atomic number of Z element, where the tetragonal distortion structure is found to be more stable at a temperature of 0 K, which can be essential due to the Jahn-Teller effect. Through elastic constant calculations, we have proved the stability of the tetragonal structure unlike cubic structure in all studied compounds. The few differences in both energy cohesion and the volume at the equilibrium state between the cubic and the tetragonal distortion phases confirm that the first structure can be found by simple heating of the second one. This tendency suggests the fact that these compounds were promising materials for shape memory applications.