Phase segregation and superconductivity in Cu doped Ni_2-xCu_xNbSn Heusler alloys

Heusler alloys exhibit numerous exotic properties including superconductivity that can be systematically controlled via manipulation of their stoichiometry and elemental doping. It has been reported that partial substitution of Ni by Cu in Ni_2-xCu_xZrGa results in a systematic reduction of T_C.¹ Considering this observation it is interesting to explore the effect of Cu doping on the superconducting properties of other Heusler alloys. Therefore, we have performed an experimental study on the superconducting properties of partially Cu doped Ni_2-xCu_xNbSn materials. Ni₂NbSn has 29 valence electrons per formula unit and 7.25 valence electrons per atom. The material exhibits a superconducting phase transition at T_C = 3.4 K. A series of Ni_2-xCu_xNbSn materials were synthesized by arc-melting and annealing techniques. All materials were characterized by x-ray diffraction, dc magnetization, and transport measurements. Interestingly, a Cu concentration of 2.5% resulted in phase segregation of the system. Two superconducting transitions were observed in all compounds at temperatures near T_C1 = 17.8 K, and T_C2 = 3.4 K. Magnetization data has confirmed type-II superconductivity for each sample at both T_C1 and T_C2.
¹ Dharma Raj Basaula, Jeffrey Brock, Mahmud Khan, AIP Advances 8, 055704 (2018).