Role of covalent hybridization in the martensitic structure and magnetic properties of shape-memory alloys: The case of Ni_(50)Mn_(5+x)Ga_(35-x)Cu_(10)

摘要

The influence of covalent hybridization on the martensitic structure and magnetic properties of Ni_(50)Mn_(5+x)Ga_(35-x)Cu_(10) shape-memory alloys has been investigated. It is found that the lattice distortion (c - a)/a of Ll_0 martensite linearly increases upon substitution of Mn for Ga, showing a change of slope at Ga = 25 at. %, which is ascribed to a weakened covalent hybridization between main-group and transition-metal atoms. Moreover, due to the competition between the covalent hybridization and the magnetic ordering of the substituted Mn atoms, the magnetic moment per formula unit and the Curie temperature show maxima at Ga = 25 at. % as well. This behavior is closely associated with the corresponding changes of the strength of the covalent hybridization. The results, therefore, suggest that a careful control of the concentration of main-group atoms in Heusler alloys may serve as a tuning parameter for finding multifunctional materials.