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We carried out a study of the pressure dependence of the solidification temperature in nine pressure transmitting media that are liquid at ambient temperature, under pressures up to 2.3 GPa. These fluids are 1:1 isopentane/n-pentane, 4:6 light mineral oil/n-pentane, 1:1 isoamyl alcohol/n-pentane, 4:1 methanol/ethanol, 1:1 FC72/FC84 (Fluorinert), Daphne 7373, isopentane, and Dow Corning PMX silicone oils 200 and 60000 cS. We relied on the high sensitivity of the electrical resistivity of Ba(Fe1-xRux)2As2 single crystals to the freezing of the pressure media and cross-checked with corresponding anomalies observed in the resistance of the manganin coil that served as the ambient temperature resistive manometer. In addition to establishing the temperature-pressure line separating the liquid (hydrostatic) and frozen (non-hydrostatic) phases, these data permit rough estimates of the freezing pressure of these media at ambient temperature. This pressure establishes the extreme limit for the medium to be considered hydrostatic. For higher applied pressures, the medium has to be treated as non-hydrostatic. [ABSTRACT FROM AUTHOR]

Pressure is the cleanest way to tune heavy fermion systems to a quantum phase transition in order to study the rich physics and competing phases, and the comparison between ytterbium and cerium systems is particularly fruitful. We briefly review the mechanisms in play and show some examples of expected and unexpected behaviour. We emphasise the importance of the valence changes under pressure and show how modern synchrotron techniques can accurately determine this, including at low temperature. [ABSTRACT FROM AUTHOR]

V6O11 and V7O13 are two members of the VnO2n-1 Magnéli series (n=3-9). At ambient pressure, V6O11 manifests a metal to insulator (MI) transition near TMI=170 K and V7O13 (the exception in the series that does not become insulating at ambient pressure) manifests an antiferromagnetic (AFM) transition with spin density wave character at TN=43 K. Temperature-dependent resistivity data for V6O11 and V7O13 were measured under pressures up to 7.52 and 6.40 GPa, respectively with critical pressures of PcMI=3.8 GPa for V6O11 and PcAFM=3.5 GPa for V7O13. As the MI transition for V6O11 is suppressed no features associated with an AFM transition in the resistivity are seen. Near the critical pressure for V6O11 where the first-order MI transition disappears, a T2 dependence of the low-temperature resistance can be found. On the other hand, in V7O13 as the second-order, antiferromagnetic transition is brought towards T=0, the resistivity shows a vanishing low-temperature region of Fermi-liquid-like behavior, consistent with proximity to a quantum critical point. Improved hydrostaticity of the pressurized sample space enhances the divergence of the T2 coefficient for V7O13 near the AFM critical pressure, 3.5 GPa. [ABSTRACT FROM AUTHOR]

We present temperature dependent resistivity and ac-calorimetry measurements of CeVSb3 under pressure up to 8 GPa in a Bridgman anvil cell modified to use a liquid medium and in a diamond anvil cell using argon as a pressure medium. An initial increase of the ferromagnetic transition temperature Tc with pressures up to 4.5 GPa is observed, followed by decrease of Tc on further increase of pressure and finally its disappearance, in agreement with the Doniach model. We infer a ferromagnetic quantum phase transition around 7 GPa under hydrostatic pressure conditions from the extrapolation to OK of Tc and the maximum of the A coefficient from low temperature fits of the resistivity ρ(T) = ρ0 + ATn. No superconductivity under pressure was observed down to 0.35 K for this compound. In addition, differences in the Tc(P) behavior when a slight uniaxial component is present are noticed and are correlated to the choice of pressure medium. [ABSTRACT FROM AUTHOR]

We present a simple novel technique to adapt a standard Bridgman cell for the use of a liquid pressure transmitting medium. The technique has been implemented in a compact cell, able to fit in a commercial Quantum Design PPMS system, and would also be easily adaptable to extreme conditions of very low temperatures or high magnetic fields. Several media have been tested and a mix of fluorinert FC84:FC87 has been shown to produce a considerable improvement over the pressure conditions in the standard steatite solid medium, while allowing a relatively easy setup procedure. For optimized hydrostatic conditions, the success rate is about 80% and the maximum pressure achieved so far is 7.1 GPa. Results are shown for the heavy fermion system YbAl3 and for NaV6O15, an insulator showing charge order. [ABSTRACT FROM AUTHOR]

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 isoelectronic 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 an approximate rate of ~5 K/% Ru 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 isopentane : 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 to infer their room temperature, hydrostatic limits: 3.5 and 6.5 GPa, respectively. [ABSTRACT FROM AUTHOR]