Combined effects of pressure and Ru substitution on BaFe2As2

The ab-plane resistivity of Ba(Fe1-xRux)2As2 (x = 0.00, 0.09, 0.16, 0.21, and 0.28) was studied under nearly hydrostatic pressures, up to 7.4 GPa, in order to explore the T-P phase diagram and to compare the combined effects of iso-electronic Ru substitution and pressure. The parent compound BaFe2As2 exhibits a structural/magnetic phase transition near 134 K. At ambient pressure, progressively increasing Ru concentration suppresses this phase transition to lower temperatures at the approximate rate of ~5 K/% Ru and is correlated with the emergence of superconductivity. By applying pressure to this system, a similar behavior is seen for each concentration: the structural/magnetic phase transition is further suppressed and superconductivity induced and ultimately, for larger x Ru and P, suppressed. A detailed comparison of the T-P phase diagrams for all Ru concentrations shows that 3 GPa of pressure is roughly equivalent to 10% Ru substitution. Furthermore, due to the sensitivity of Ba(Fe1-xRux)2As2 to pressure conditions, the melting of the liquid media, 4 : 6 light mineral oil : n-pentane and 1 : 1 iso-pentane : n-pentane, used in this study could be readily seen in the resistivity measurements. This feature was used to determine the freezing curves for these media and infer their room temperature, hydrostatic limits: 3.5 and 6.5 GPa, respectively.Comment: 27 pages, 19 figure

Effects of mixed rare earth occupancy on the low temperature properties of (R, R',R''...)Ni2Ge2 single crystals

Temperature and applied magnetic field dependent magnetization measurements on 34 single crystalline samples of (R, R',R''...)Ni2Ge2 compounds (R, R', R'', etc. being primarily Gd-Lu, Y), were made. These measurements reveal that, despite extremes in local moment anisotropy, the average de Gennes parameter is a remarkably good predictor of the paramagnetic to antiferromagnetic ordering temperature. In addition, the pronounced metamagnetic phase transitions seen in the low temperature phase of TbNi2Ge2 are found to be remarkably robust to high substitution levels of Gd and 25% substitutions of other heavy rare earths

Single crystal growth and characterization of the large-unit-cell compound Cu13Ba

Single crystals of Cu$_{13}$Ba were successfully grown out of Ba-Cu self flux. Temperature dependent magnetization, $M(T)$, electrical resistivity, $\rho(T)$, and specific heat, $C_p(T)$, data are reported. Isothermal magnetization measurements, $M(H)$, show clear de Haas-van Alphen oscillations at $T$ = 2 K for applied fields as low as $\mu_0H$ = 1T. An anomalous behavior of the magnetic susceptibility is observed up to $T$ ~ 50K reflecting the effect of de Haas-van Alphen oscillations at fairly high temperatures. The field- and temperature-dependencies of the magnetization indicate the presence of diluted magnetic impurities with a concentration of the order of 0.01at.%. Accordingly, the minimum and lower temperature rise observed in the electrical resistivity at and below $T$ = 15K is attributed to the Kondo impurity effect.Comment: 6 pages, 8 figures, accepted for publication in J. Alloys Comp

Drastic annealing effects in transport properties of single crystals of the YbNi2B2C heavy fermion system

We report temperature dependent resistivity, specific heat, magnetic susceptibility and thermoelectric power measurements made on the heavy fermion system YbNi2B2C, for both as grown and annealed single crystals. Our results demonstrate a significant variation in the temperature dependent electrical resistivity and thermoelectric power between as grown crystals and crystals that have undergone optimal (150 hour, 950 C) annealing, whereas the thermodynamic properties: (c_p(T) and chi(T)) remain almost unchanged. We interpret these results in terms of redistributions of local Kondo temperatures associated with ligandal disorder for a small (~ 1%) fraction of the Yb sites.Comment: 5 pages, 4 figures, submitted to PR

Experimental Setup for the Measurement of the Thermoelectric Power in Zero and Applied Magnetic Field

An experimental setup was developed for the measurement of the thermoelectric power (TEP, Seebeck coefficient) in the temperature range from 2 to 350 K and magnetic fields up to 140 kOe. The system was built to fit in a commercial cryostat and is versatile, accurate and automated; using two heaters and two thermometers increases the accuracy of the TEP measurement. High density data of temperature sweeps from 2 to 350 K can be acquired in under 16 hours and high density data of isothermal field sweeps from 0 to 140 kOe can be obtained in under 2 hours. Calibrations for the system have been performed on a platinum wire and Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ high $T_{c}$ superconductors. The measured TEP of phosphor-bronze (voltage lead wire) turns to be very small, where the absolute TEP value of phosphor-bronze wire is much less than 0.5 $\mu$V/K below 80 K. For copper and platinum wires measured against to the phosphor-bronze wire, the agreement between measured results and the literature data is good. To demonstrate the applied magnetic field response of the system, we report measurements of the TEP on single crystal samples of LaAgSb$_{2}$ and CeAgSb$_{2}$ in fields up to 140 kOe.Comment: 10 pages, 8 figures. accepted in Measurement Science and Technolog