Theoretical investigation on electronic structure, magnetism and martensitic transformation in Ni2Mn1.5Sc0.5 and Mn2Ni1.5Sc0.5 all-d-metal magnetic shape memory alloys

Abstract

Two new all-d-metal Heusler alloys Mn2Ni1.5Sc0.5 and Ni2Mn1.5Sc0.5 are proposed as candidates for magnetic shape memory alloys. In these alloys, the Sc atom prefers occupying the D (0.75, 0.75, 0.75) sites in the Heusler alloy lattice and forms d–d hybridization with its nearest neighbor atoms such as Ni. Martensitic transformation is possible in both Mn2Ni1.5Sc0.5 and Ni2Mn1.5Sc0.5. Differing from the “volume-conserving” character in classic Heusler alloys, a large volume shrinkage of 2.3% and 2.8% occurs in Mn2Ni1.5Sc0.5 and Ni2Mn1.5Sc0.5 during the martensitic transformation, respectively. The magnetization difference between the austenite and martensite is as large as 4.50 μB/f.u. for Mn2Ni1.5Sc0.5 and 4.49 μB/f.u. for Ni2Mn1.5Sc0.5, due to the ferromagnetic–antiferromagnetic magnetic transition coupling with the martensitic transformation. The parallel coupled Mn (B) and Mn (D) spin moments in the austenite become antiparallel in the martensite, which leads to the large decrease of magnetization after the martensitic transformation. The energy difference ΔEM between the martensite and austenite is −45.5 and −25.9 meV/f.u. for Mn2Ni1.5Sc0.5 and Ni2Mn1.5Sc0.5, respectively. The large ΔEM of Mn2Ni1.5Sc0.5 derives from the strong Jahn–Teller effect in its density of states structure and makes it a promising candidate for magnetic shape memory alloys.