Crystal Growth and Magnetic Properties of New Ce-T-In and Pr-T-In Compounds (T = Rh, Pd): Sythesis and Characterization of a New Ambient-pressure Superconductor Ce2PdIn8

New single crystals of R2PdIn8 (R = Pr, Ce) and R2RhIn8 compounds have been synthesized by solution growth from In flux and studied with respect to structure and electronic properties. Pr2RhIn8 exhibits van Vleck paramagnetism and strong magnetocrystalline anisotropy attributed to a crystal-field effect on the Pr ion. Ce2PdIn8 compound is paramagnetic down to 0.7 K, superconductivity below 0.7 K has been found. The Sommerfeld coefficient γ = 700–800 mJ/molK links this compound with the heavy-fermion family. Introduction In the Ce-based compounds, the interaction of the Ce ions with the conduction electrons often leads to a large enhancement of the effective electron mass and these are called the heavy-fermion (HF) compounds. They exhibit attractive electronic properties, such as strongly enhanced paramagnetism, non-Fermi liquid behavior, interplay between magnetism and superconductivity (SC), etc. In the last decade, the CenTIn3n+2 series of compounds, where n = 1 or 2 and T = Co, Rh,Ir, attracted attention. These compounds form quasi-two-dimensional tetragonal system with the CeIn3 units and TIn2 layers alternating along the c-axis. All of them perform the HF behavior combined with superconductivity. While CeCoIn5, CeIrIn5 and Ce2CoIn8 [Chen, 2002; Movshovich, 2001; Kim, 2004; Hedo, 2004] are ambient-pressure superconductors, CeRhIn5 and Ce2RhIn8 are tuned to SC by applying pressure or doping [Nicklas, 2003; Hegger, 2000; Ferreira, 2008; Yang, 2008]. Recently, coexistence of antiferromagnetism (AF) and SC in Ce2PdIn8 has been reported [Kaczorowski, 2009]. Following our research of the PrTIn5 compounds revealing indications of the quadrupolar ordered state [Uhlirova, 2008], we commenced a study of the Pr2TIn8 structural variants. In this paper we report on single-crystal preparation and the crystal structure of these Pr compounds and magnetic properties of Pr2RhIn8. Since the preparation of R2PdIn8 was found to be rather complicated, details of sample preparation as a key part of a successful experiment revealing intrinsic electronic properties. First results of electrical-resistivity, ac-susceptibility and specific-heat measurements are presented. Experimental We have prepared single crystals of Ce2TIn8 and Pr2TIn8 compounds listed in Table 1. The solution growth technique from a ternary In-rich flux [Uhlirova, 2008] was used. Pure elements were placed into an alumina crucible with a large amount of In metal, resulting in the total atomic composition R2TIn25-35 and sealed in a silica tube under high vacuum. Then the system was heated up to 950 °C and slowly (4 °C/h) cooled down to 400 °C. After the thermal process the remaining indium was centrifuged through the quartz-wool stopper. Heat capacity (Cp), electrical resistivity (ρ), magnetization (M) and ac susceptibility (χac) were measured with the Quantum Design PPMS and MPMS apparatuses, The χac at low temperatures (0.35 < T <2.5 K) was measured using the custom made extension to PPMS allowing to measure χac using the ACMS option with the 3He insert (including the ACMS preamplifier) [Prokleska, 2009]. Results and discussion The compounds with T = Rh and Ir formed plate like crystals of a size 5×5×2 mm and the c-axis perpendicular to the plate. In case of T = Pd, we obtained a multiphase product, mainly cuboidsshaped single crystals of RIn3 covered by very thin layer (50–100 μm) of R2PdIn8. The rest of Pd formed a cubic phase Pd3In7 (a = 9.436 Å). Thence we assumed that R2PdIn8 grows in a narrow 96 WDS'09 Proceedings of Contributed Papers, Part III, 96–100, 2009. ISBN 978-80-7378-103-3 © MATFYZPRESS