Contents lists available at ScienceDirect Solid State Communications journal homepage: www.elsevier.com/locate/ssc Communication Superconducting properties of In doped ZrNi 2 Ga 1-x In x Alex Reigle, Kelly Mason, Jessica Slattery, Scott Lee, Tyler Jamison, Adam Eggert, Vinoin Vincely, Darren Wong, Yuliang Guo, Jeffrey Brock, Mahmud Khan * Department of Physics, Miami University, Oxford, OH 45056, USA ARTICLE INFO Communicated by T. Kimura Keywords: A. Superconductors A. Heusler alloys D. Quantum phase transition ABSTRACT We report on the effect of In doping on the superconducting properties of ZrNi 2 Ga 1-x In x (x = 0.0.05, 0.10, 0.15) Heusler alloys. While the samples with x < 0.1 exhibited the single phase, cubic L2 1 structure, small con- centrations of ZrGa 2 -type orthorhombic secondary phases formed on the samples with x ≥ 0.1. Electrical re- sistivity and dc magnetization measurements showed that the superconducting transition temperature of the compounds decreased with increasing In concentration. All samples showed paramagnetic ordering above their respective superconducting transition temperature. The observations suggest that for x ∼0.45 the ZrNi 2 Ga 1-x In x compound might exhibit a quantum phase transition. 1. Introduction Heusler alloys (generally expressed as XY 2 Z: X and Y are transition metals and Z is a main-group metalloid) [1] are widely known for their ferromagnetic properties [2–4]. A selected group of Heusler alloys based on Pd, Ni, and other metals have also been shown to exhibit Type-II superconductivity [5]. Among the Pd-based Heusler super- conductors that include ZrPd 2 Al, HfPd 2 Al, etc., YbPd 2 Sn has the highest recorded critical temperature (T C ) of 4.9 K [5–7]. Interestingly, certain Pd-based superconductors exhibit both superconductivity and long- range magnetic ordering. For instance, coexistence of superconductivity and antiferromagnetism was found in both YbPd 2 Sn [8,9] and ErPd 2 Sn [10]. Example Ni-based superconductors include NbNi 2 Al, HfNi 2 Al, and NbNi 2 Sn, which have the highest T C of 3.4 K among the series [7,11]. Given that it is conventionally expected for these Ni-rich systems to favor magnetic ordering due to the unpaired d-electrons of Ni, super- conductivity in these compounds remains an active research area. One such Ni-based Heusler superconductor of interest is ZrNi 2 Ga, which has a valence electron per atom concentration (e/a) of 6.75 [12]. This particular e/a value has been linked to the formation of a van Hove singularity in the electronic density of states, facilitating super- conducting behavior [13]. Previous reports have shown this compound to exhibit the L2 1 cubic structure with a lattice parameter of a = 6.093 ± 0.003 Å [12]. The Wyckoff positions of each element are: 4a (0, 0, 0) for Zr, 8c (¼, ¼, ¼) for Ni, and 4b (½, ½, ½) for Ga [12]. ZrNi 2 Ga has a T C of ∼2.9 K, which is relatively higher than other Ni- based Heusler alloys. Electron doping with Nb - which has 5 valence electrons compared to Zr's 4 - to create alloys of the form Zr 1-x Nb x Ni 2 Ga resulted in lower T C and lattice parameter values [12]. In addition, the Zr-rich Zr 1+x Ni 2-x Ga and Ni-rich Zr 1+x Ni 2-x Ga sys- tems have shown that deviation from an e/a of 6.75 results in a strengthened paramagnetic character and weakened superconductivity [14]. Although some work has been done on the effects of elemental doping on the superconducting properties of ZrNi 2 Ga, research on the effects of substituting the constituent elements of ZrNi 2 Ga with elec- tronically similar elements is lacking. Furthermore, since the T C of ZrNi 2 Ga is 2.9 K, doping this material with a fourth element might continuously drive the superconducting phase transition to 0 K, resulting in a quantum phase transition (QPT). This will provide an opportunity to explore and understand the physics that governs the quantum critical point (QCP) [15–19]. Phase transi- tions that occur at finite temperatures above 0 K are caused primarily by thermal fluctuations. On the other hand, a QPT is governed by quantum fluctuations and occur at QCP, T C =0K[17,20]. Keeping the above discussion in mind, we have investigated the superconducting properties of ZrNi 2 Ga 1-x In x (0 ≤ x ≤ 0.15) Heusler alloy system. As both Ga and In are Group 13 isoelectronic elements with 3 valence electrons, substitution of Ga with an equivalent amount of In will not affect the e/a value of ZrNi 2 Ga 1-x In x . Therefore, the goal of this study is to explore the superconducting properties of the ZrNi 2 Ga 1-x In x system where the e/a ratio remains invariant for all samples in the series. 2. Experimental techniques The ZrNi 2 Ga 1-x In x (x = 0.0.05, 0.10, 0.15) compounds https://doi.org/10.1016/j.ssc.2019.01.015 Received 13 November 2018; Received in revised form 30 December 2018; Accepted 16 January 2019 * Corresponding author. E-mail address: khanm2@miamioh.edu (M. Khan). Solid State Communications 291 (2019) 28–31 Available online 17 January 2019 0038-1098/ © 2019 Elsevier Ltd. All rights reserved. T