Anomalous magnetic configuration of Mn_2NiAl ribbon and the role of hybridization in the martensitic transformation of Mn_(50)Ni_(50-x)Al_x ribbons

摘要

The magnetic configuration of Mn_2NiAl ribbon has been investigated. In contrast to Ni_2MnAl, the compound Mn_2NiAl with considerable disorder does exhibit ferromagnetism and, due to exchange interaction competition, both ferromagnetic and antiferromagnetic moment orientations can coexist between nearest neighbor Mn atoms. This is unexpected in Heusler alloys. Regarding the mechanism of the martensitic transformation in Mn_(50)Ni_(50-x)Al_x, it is found that increasing the Al content results in an unusual change in the lattice constant, a decrease of the transformation entropy change, and enhancement of the calculated electron localization. These results indicate that the p-d covalent hybridization between Mn (or Ni) and Al atoms gradually increases at the expense of the d-d hybridization between Ni and Mn atoms. This leads to an increased stability of the austenite phase and a decrease of the martensitic transformation temperature. For 11 ≤x≤ 14, Mn_(50)Ni_(50-x)Al_x ferromagnetic shape memory alloys are obtained.