Abstract
The superconducting properties of a series of Zr1+xNi2-xGa and Zr1-xNi2+xGa compounds have been investigated by x-ray diffraction, electrical resistivity, dc magnetization, and ac susceptibility measurements. While the parent compound, ZrNi2Ga, exhibited the cubic L21 Heusler structure, multiple non-cubic structures formed in the Zr and Ni rich doped materials. For x ≤ 0.3, all Zr1-xNi2+xGa compounds demonstrated superconducting behavior, but no superconductivity was observed in the Zr1+xNi2-xGa alloys for x > 0.2. The magnetization data revealed that all materials in both Zr1+xNi2-xGa and Zr1-xNi2+xGa series exhibited type-II superconductivity. With increasing doping concentration x, the paramagnetic ordering were enhanced in both systems while the superconducting properties were found to weaken. The observations are discussed considering the structural disorders in the systems.
Highlights
Ni based Heusler alloys with the cubic L21 structure are well known to exhibit exciting phenomena including martensitic phase transitions,[1,2,3] magnetocaloric effects,[4,5] shape memory effects.[6,7] and superconductivity.[8,9,10] Considering the fact that elemental Ni is ferromagnetic, Ni-rich intermetallic alloys are expected to order magnetically instead of demonstrating superconductivity
It was shown that partial replacement of Zr by Nb resulted in the broadening of the Van Hove singularity and introduced a high degree of disorder in Zr1-xNbxNi2Ga, causing a suppression of TC of the system
The electrical resistivity, dc magnetization and ac susceptibility measurements were performed on a Physical Propriety Measurement System (PPMS) made by Quantum Design Inc
Summary
Ni based Heusler alloys with the cubic L21 structure are well known to exhibit exciting phenomena including martensitic phase transitions,[1,2,3] magnetocaloric effects,[4,5] shape memory effects.[6,7] and superconductivity.[8,9,10] Considering the fact that elemental Ni is ferromagnetic, Ni-rich intermetallic alloys are expected to order magnetically instead of demonstrating superconductivity. Including ZrNi2Ga there are nearly 19 Heusler superconductors that have 27 valence electrons per formula unit with an average of 6.75 electrons per atom.[11] In common, superconductivity in these materials are explained considering the van Hove singularities, which refers to a saddle point in the energy dispersion curves of the electronic structure of the respective material.[12] Among these 19 superconductors, several are rare-earth metal based, like YbPd2Sn and ErPd2Sn, where superconductivity and antiferromagnetic interactions co-exist.[13,14,15] ZrNi2Ga was shown to be a weakly coupled BCS type-II superconductor, with a paramagnetic state above TC.[9] It was shown that partial replacement of Zr by Nb resulted in the broadening of the Van Hove singularity and introduced a high degree of disorder in Zr1-xNbxNi2Ga, causing a suppression of TC of the system. It is interesting to explore the SC properties of these two systems
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