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Evolution of structural, magnetic, and electrical transport properties in Ru‑doped pyrochlore iridate ­Eu2Ir2O7 Yuying Wu1 · Meng Li1 · Xianghu Li1 · Jianfeng Xie2 Received: 19 May 2020 / Accepted: 3 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract We report the evolution of crystal structural, magnetic, and electrical transport properties in the iridates ­Eu2Ir2−xRuxO7 (x = 0.0, 0.1, 0.3, and 0.5). Powder X-ray diffraction measurement indicates the prepared polycrystalline samples retain the cubic pyrochlore-type structure. The evolution of magnetism has been studied using dc magnetic susceptibilities. Although the magnetic irreversibility temperature changes marginally, the magnetic moment increases with progressive Ru doping. A distinct metal-insulator transition is observed for E ­ u2Ir2−xRuxO7 series. The nature of electronic conduction in the low temperature insulating state has been found to follow a power law behavior. Interestingly, we found the resistivity increases with Ru doping in ­Eu2Ir2−xRuxO7. The results may be ascribed to increased electronic correlation and Ir/Ru substitutional disorder, which interrupt direct Ir–Ir hopping in the samples. Keywords  Pyrochlore iridate · Metal-insulator transition · Disorder

1 Introduction The 5d-transition metal oxides have attracted considerable attention due to their fascinating electronic and magnetic properties originating from the interplay between the spin–orbit coupling (SOC) and electronic correlation U [1–3]. Combined with the crystal field interaction, the pyrochlore iridates ­A2Ir2O7 (A = rare earth elements or Y or Bi ion), where the energy scale of SOC and U is comparable in magnitude, are of particular interest. Theoretical studies have clarified that these compounds are

* Yuying Wu [email protected] 1

School of Electrical and Electronic Engineering, Wuhan Polytechnic University, Wuhan 430023, People’s Republic of China

2

Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China



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Journal of Low Temperature Physics

a promising candidate for many exotic topological phases such as Weyl semimetal (WSM) and axion insulator [1, 4–7]. In ­A2Ir2O7, the 5d orbitals of ­Ir4+ are split into two energetically higher eg and three energetically lower t2g levels by the I­ rO6 octahedral environment. SOC further split the t2g levels into two bands with Jeff = 32 quadruplet and Jeff = 12 doublet. The higher Jeff = 12 band is half filled. The effective one-electron bandwidth of I­ r4+ could be finely controlled by the ionic radius of A site, varying from an insulating state for A = Gd-Lu and Y to a metallic state for A = Pr and Bi. For the intermediate members A = Nd, Sm, and Eu, however, they show a distinct metal-insulator transition (MIT) [8]. These three compounds are a promising candidate for the exotic topological phase because it is believed that states near the metal-insulator boundary may have a topologic