Disorder-sensitive superconductivity in the iron silicide Lu2_2Fe3_3Si5_5 studied by the Lu-site substitutions

We studied effect of non-magnetic and magnetic impurities on superconductivity in Lu$_2$Fe$_3$Si$_5$ by small amount substitution of the Lu site, which investigated structural, magnetic, and electrical properties of non-magnetic (Lu$_{1-x}$Sc$_x$)$_2$Fe$_3$Si$_5$, (Lu$_{1-x}$Y$_x$)$_2$Fe$_3$Si$_5$, and magnetic (Lu$_{1-x}$Dy$_x$)$_2$Fe$_3$Si$_5$. The rapid depression of $T_c$ by non-magnetic impurities in accordance with the increase of residual resistivity reveals the strong pair breaking dominated by disorder. We provide compelling evidence for the sign reversal of the superconducting order parameter in Lu$_2$Fe$_3$Si$_5$.Comment: 4 pages, 5 figure

Magnetic and electrical properties of (Pu,Lu)Pd3

We present measurements of the magnetic susceptibility, heat capacity and electrical resistivity of Pu$_{1-x}$Lu$_x$Pd$_3$, with $x$=0, 0.1, 0.2, 0.5, 0.8 and 1. PuPd$_3$ is an antiferromagnetic heavy fermion compound with $T_N=24$~K. With increasing Lu doping, both the Kondo and RKKY interaction strengths fall, as judged by the Sommerfeld coefficient $\gamma$ and N\'eel temperature $T_N$. Fits to a crystal field model of the resistivity also support these conclusions. The paramagnetic effective moment $\mu_{\mathrm{eff}}$ increases with Lu dilution, indicating a decrease in the Kondo screening. In the highly dilute limit, $\mu_{\mathrm{eff}}$ approaches the value predicted by intermediate coupling calculations. In conjunction with an observed Schottky peak at $\sim$60~K in the magnetic heat capacity, corresponding to a crystal field splitting of $\sim$12~meV, a mean-field intermediate coupling model with nearest neighbour interactions has been developed.Comment: 13 pages, 13 figure

Competition between Superconductivity and Charge Density Wave Ordering in the Lu5_5Ir4_4(Si1−x_{1-x}Gex_x)10_{10} Alloy System

We have performed bulk measurements such as dc magnetic susceptibility, electrical resistivity and heat capacity on the pseudo-ternary alloys Lu$_5$Ir$_4$(Si$_{1-x}$Ge$_x$)$_{10}$ to study the interplay and competition between superconductivity and the charge density wave (CDW) ordering transition. We track the evolution of the superconducting transition temperature T$_{SC}$ and the CDW ordering temperature T$_{CDW}$ as a function of x (concentration of Ge) ($0.0 \leq x\leq~1.0$). We find that increasing x (increasing disorder) suppresses the T$_{CDW}$ rapidly with the concomitant increase in T$_{SC}$. We present a temperature-concentration (or volume) phase diagram for this system and compare our results with earlier work on substitution at the Lu or Ir site to show how dilution at the Si site presents a different situation from these other works. The heat capacity data in the vicinity of the CDW transition has been analyzed using a model of critical fluctuations in addition to a mean-field contribution and a smooth lattice background. We find that the critical exponents change appreciably with increasing disorder. This analysis suggests that the strong-coupling and non mean-field like CDW transition in the parent compound Lu$_5$Ir$_4$Si$_{10}$ changes to a mean-field like transition with increasing Ge concentration.Comment: 14 pages and 8 figures. Accepted for publication in Phys. Rev.

Stuffed Rare Earth Pyrochlore Solid Solutions

Synthesis and crystal structures are described for the compounds Ln2(Ti2-xLnx)O7-x/2, where Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu, and x ranges from 0 to 0.67. Rietveld refinements on X-ray powder diffraction data indicate that in Tb and Dy titanate pyrochlores, extra Ln3+ cations mix mainly on the Ti4+ site with little disorder on the original Ln3+ site. For the smaller rare earths (Ho-Lu), stuffing additional lanthanide ions results in a pyrochlore to defect fluorite transition, where the Ln3+ and Ti4+ ions become completely randomized at the maximum (x=0.67). In all of these Ln-Ti-O pyrochlores, the addition of magnetic Ln3+ in place of nonmagnetic Ti4+ adds edge sharing tetrahedral spin interactions to a normally corner sharing tetrahedral network of spins. The increase in spin connectivity in this family of solid solutions represents a new avenue for investigating geometrical magnetic frustration in the rare earth titanate pyrochlores.Comment: 25 pages, 7 figures, submitted to J. Solid State Che

Зависимость физико-химических свойств ВТСП-соединений от размера кристаллитов

Керамическим методом с предварительным получением прекурсора синтезированы материалы состава Bi2Sr2Ca1−xLnxCu2Oу (Ln – La, Nd, Y, Ho, Lu) и Bi2Sr2−xLnxCaCu2Oу (Ln – La, Nd, Ho, Lu). Исследованы микроструктура, область гомогенности, электрофизические характеристики, кислородная стехиометрия систем Bi2Sr2Ca1−xLnxCu2Oу (Ln – La, Nd, Y, Ho, Lu) и Bi2Sr2−xLnxCaCu2Oу (Ln – La, Nd, Ho, Lu) в зависимости от степени замещения х и температуры перехода в сверхпроводящее состояние Тсon. Изучено влияние условий термической обработки на размеры кристаллитов, величину кислородного индекса и критическую температуру. Получены наноразмерные частицы (Dср = 0,5—1,5 мкм). Показано, что границы области гомогенности уменьшаются от 0 ≤ x ≤ 0,3 по Lu3+ к 0 ≤ x ≤ 0,05 по La3+.Керамічною методою з попереднім одержанням прекурсору синтезовано матеріяли складу Bi2Sr2Ca1−xLnxCu2Oу (Ln – La, Nd, Y, Ho, Lu) та Bi2Sr2−xLnxCaCu2Oу (Ln – La, Nd, Ho, Lu). Досліджено мікроструктуру, область гомогенности, електрофізичні характеристики й кисневу стехіометрію систем Bi2Sr2Ca1−xLnxCu2Oу (Ln – La, Nd, Y, Ho, Lu) і Bi2Sr2−xLnxCaCu2Oу (Ln – La, Nd, Ho, Lu) залежно від ступеня заміщення х та температури переходу в надпровідний стан Тсon. Вивчено вплив умов термічного оброблення на розмір зерна, величину кисневого індексу та критичну температуру. Одержано нанорозмірні частинки (Dсер = 0,5—0,15 мкм). Показано, що межі гомогенности зменшуються від 0 ≤ x ≤ 0,3 за Lu3+ до 0 ≤ x ≤ 0,05 за La3+.The samples of Bi2Sr2Ca1−xLnxCu2Oу (Ln–La, Nd, Y, Ho, Lu) and Bi2Sr2−xLnxCaCu2Oу (Ln–La, Nd, Ho, Lu) are synthesized using the ceramic technique with precursor. For Bi2Sr2Ca1−xLnxCu2Oy (Ln–La, Nd, Y, Ho, Lu) and Bi2Sr2−xLnxCaCu2Oу (Ln–La, Nd, Ho, Lu) systems, the dependences of microstructure, homogeneity region, electrophysical properties, and oxygen nonstoichiometry on their composition (x) and Tcon value are studied. Influence of heat-treatment conditions on the sizes of crystallites, value of oxygen index, and critical temperature is studied. As shown, the homogeneity region becomes narrower when going from 0 ≤ x ≤ 0.3 for Lu3+ to 0 ≤ x ≤ 0.05 for La3+