Contents lists available at ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet Superconductivity, Kondo effect, and observation of self-organized pattern formation in intermetallic NiBi 3 thin films Ekta Bhatia a , Abhishek Talapatra b , Jyoti Ranjan Mohanty b , Kartik Senapati a,* a School of Physical Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar, Odisha, 751005, India b Department of Physics, Indian Institute of Technology Hyderabad, Hyderabad, 502285, India ARTICLE INFO Keywords: Reaction diffusion Superconductivity Intermetallic compound ABSTRACT The superconducting properties of the intermetallic compound NiBi 3 have been studied mostly in bulk crystals. In this report we have studied several aspects of NiBi 3 thin films, spontaneously formed at the interface of Ni and Bi multilayers. We have observed superconducting transition around 3.9 K, close to the bulk transition tem- perature of 4.1 K. Due to the diffusive mechanism of formation of NiBi 3 , additional phenomena such as magnetic (Nickel) impurity induced Kondo effect and self organized Turing pattern formation also come into picture. From X-ray diffraction and Magneto-resistance measurements we have established the presence of atomic Ni im- purities in the films. Kondo minima were found to scale with varied concentration of Ni impurities in a series of Ni-Bi multilayer films (with fixed Ni thickness and varied Bi thickness). Similarly, saturation magnetization and superconducting transition temperature were also found to follow the concentration of Ni impurities. In addi- tion, we have also observed signatures of Turing patterns, from magnetic force microscopy, naturally formed with time without any external heat treatment. 1. Introduction Superconductors containing strong ferromagnetic elements such as Fe, Ni, Co are interesting from a fundamental point of view [1–3]. A. Chervenak et al. [4] have shown that ferro-magnetic ions are detri- mental to phonon mediated Bardeen-Cooper-Schrieffer (BCS) pairing mechanism. However, in recent years, Fe based pnictide class of com- pounds have brought a new paradigm to this field where, magnetic (spin) fluctuations have been suggested as the origin of super- conductivity [5]. In general, however, the strong antagonism between superconducting (S) and ferromagnetic (F) orders makes it interesting to explore materials with possible co-existence of S and F orders. In this direction, both intrinsic superconducting materials with ferromagnetic elements [5and6] and heterostructures consisting S and F layers [7] are being studied widely. In this context, we have studied a Ni based intermetallic compound, NiBi 3 , having a bulk T c of ∼ 4.1 K. In fact, the superconducting transi- tion temperature of this compound is highest among the family of Ni based intermetallic compounds. Studies over the last decade have shown some interesting properties of this orthorhombic crystal, which is a type-II superconductor [8–10]. There are reports in favor as well as against the intrinsic nature of ferromagnetism in this compound. Re- ports against intrinsic ferromagnetism ascribe the observed magnetic signal to embedded Ni impurities [11], which inevitably incurs during the crystallization. Although Silva et al. have discarded the possible ferromagnetic behavior of their NiBi 3 crystals due to the observed sig- nature of amorphous Ni, the possibility of a small ferromagnetic con- tribution from NiBi 3 can not be excluded altogether. In single crystal form, there is no direct way of controlling the Ni impurity concentra- tion in NiBi 3 . On the other hand, Martinez et al. [12], based on mag- netization measurements, have claimed that superconductivity and ferromagnetism co-exist in this compound. Almost all studies have fo- cused on bulk properties of this interesting compound. Recently we have shown that very thin films of this compound naturally forms at the interface of Ni-Bi multilayer films [13] by reaction-diffusion me- chanism. In this report we study some of the basic properties of the interfacial NiBi 3 films in a stack of five layer Bi-Ni-Bi-Ni-Bi structure. Magnetization measurements show a gradual decrease in the volume fraction of Ni impurity with increasing Bi thickness while keeping Ni thickness constant. Magnetoresistance measurements of this inter-dif- fused five layer structure showed a weak hysteretic nature below 100 K, confirming absence of bulk Ni behavior. Temperature dependence of resistivity showed a Kondo minimum around 15 K, which varied with Ni impurity concentration, in agreement with the magnetization mea- surements. Superconducting transition temperature also followed the Ni impurity concentration. In addition, we also report a signature of https://doi.org/10.1016/j.intermet.2018.01.005 Received 12 September 2017; Received in revised form 22 December 2017; Accepted 4 January 2018 * Corresponding author. E-mail address: kartik@niser.ac.in (K. Senapati). Intermetallics 94 (2018) 160–164 0966-9795/ © 2018 Elsevier Ltd. All rights reserved. T