Thermally activated exchange narrowing of the Gd3+ ESR fine structure in a single crystal of Ce1-xGdxFe4P12 (x = 0.001) skutterudite

We report electron spin resonance (ESR) measurements in the Gd3+ doped semiconducting filled skutterudite compound Ce1-xGdxFe4P12 (x = 0.001). As the temperature T varies from T = 150 K to T = 165 K, the Gd3+ ESR fine and hyperfine structures coalesce into a broad inhomogeneous single resonance. At T = 200 K the line narrows and as T increases further, the resonance becomes homogeneous with a thermal broadening of 1.1(2) Oe/K. These results suggest that the origin of these features may be associated to a subtle interdependence of thermally activated mechanisms that combine: i) an increase with T of the density of activated conduction-carriers across the T-dependent semiconducting pseudogap; ii) the Gd3+ Korringa relaxation process due to an exchange interaction, J_{fd}S.s, between the Gd3+ localized magnetic moments and the thermally activated conduction-carriers and; iii) a relatively weak confining potential of the rare-earth ions inside the oversized (Fe2P3)4 cage, which allows the rare-earths to become rattler Einstein oscillators above T = 148 K. We argue that the rattling of the Gd3+ ions, via a motional narrowing mechanism, also contributes to the coalescence of the ESR fine and hyperfine structure.Comment: 7 pages, 9 figures, accepted for publication in Phys Rev

Guidelines for Minimizing Salinity Buildup in Groundwaters of Utah

In arid Utah practically all of the replenishable surface water supplies are nearly fully developed. At least some groundwater resources are being used in every basin. Groundwater use is expanding throughout the state and in some areas the draft is nearly equal to the sustained yield. Irrigated agriculture is the major water user. Multiple reuse of water is common in many areas, but as salinity increases with each cycle of usage, salinity also is usually the limiting factor for usefulness. Effective control of salinity buildup will permit more efficient and more extensive use of the state’s waters with potentially large benefits to irrigated agriculture. This report describes physical and chemical processes which contribute to salinity buildup and suggests methods that might be used to control it. Some areas are described where groundwater salinity is becoming a serious problem in the state. Hypothetical cases of salinity buildup are portrayed graphically to illustrate the relationship to time and the effects of the various processes. Emphasis is upon groundwater, but control of surface water salinity is also addressed as these resources are often inextricably interrelated

A Survey and Evaluation of Shallow Groundwater Contamination Hazards in the State of Utah

A survey was made to appraise current man-made contamination of shallow groundwater in Utah. Very little has been published on the subject, and most of the information was obtained by personal observation and through interviews of individuals concerned with water quality protection in Utah. After presenting the relevant physiographic, geologic, and hydrologic characteristics of the various regions of Utah and discussing how these relate to groundwater contamination in general, representative groundwater quality hazards in 32 sites or regions in Utah are presented. A very wide range of hazards to groundwater quality was found to exist. These cases cover the range of situations which need to be covered for an effective shallow groundwater pollution control program. Shallow aquifers with the largest amounts of deleterious contaminations underlie cities and towns. Agricultural areas generate greater quantities of dissolved salts and possible other contaminants, but the contamination is spread over considerably larger areas and thus is more dilute. Improper disposal of oil-field brines is a very serious problem in the state. Leaking disposal ponds, mining operations, and poorly managed solid waste dumps are serious hazards locally. Septic and other wastes from recreational activities in the state are a small but increasing hazard. By law, the State of Utah has the authority and enforcement framework to cope with thee problems of shallow groundwater contamination. More understanding, personnel, guidelines, regulations, and funding are needed to bring the protection of shallow groundwater quality into perspective with the present heavy emphasis upon surface water quality

Superconductivity without Fe or Ni in the phosphides BaIr2P2 and BaRh2P2

Heat capacity, resistivity, and magnetic susceptibility measurements confirm bulk superconductivity in single crystals of BaIr$_2$P$_2$ (T$_c$=2.1K) and BaRh$_2$P$_2$ (T$_c$ = 1.0 K). These compounds form in the ThCr$_2$Si$_2$ (122) structure so they are isostructural to both the Ni and Fe pnictides but not isoelectronic to either of them. This illustrates the importance of structure for the occurrence of superconductivity in the 122 pnictides. Additionally, a comparison between these and other ternary phosphide superconductors suggests that the lack of interlayer $P-P$ bonding favors superconductivity. These stoichiometric and ambient pressure superconductors offer an ideal playground to investigate the role of structure for the mechanism of superconductivity in the absence of magnetism.Comment: Published in Phys Rev B: Rapid Communication

Magnetic, thermal and transport properties of Cd doped CeIn3_3

We have investigated the effect of Cd substitution on the archetypal heavy fermion antiferromagnet CeIn$_3$ via magnetic susceptibility, specific heat and resistivity measurements. The suppression of the Neel temperature, T$_{N}$, with Cd doping is more pronounced than with Sn. Nevertheless, a doping induced quantum critical point does not appear to be achievable in this system. The magnetic entropy at $T_N$ and the temperature of the maximum in resistivity are also systematically suppressed with Cd, while the effective moment and the Curie-Weiss temperature in the paramagnetic state are not affected. These results suggest that Cd locally disrupts the AFM order on its neighboring Ce moments, without affecting the valence of Ce. Moreover, the temperature dependence of the specific heat below $T_N$ is not consistent with 3D magnons in pure as well as in Cd-doped CeIn$_3$, a point that has been missed in previous investigations of CeIn$_3$ and that has bearing on the type of quantum criticality in this system

Site specific spin dynamics in BaFe2As2: tuning the ground state by orbital differentiation

The role of orbital differentiation on the emergence of superconductivity in the Fe-based superconductors remains an open question to the scientific community. In this investigation, we employ a suitable microscopic spin probe technique, namely Electron Spin Resonance (ESR), to investigate this issue on selected chemically substituted BaFe$_{2}$As$_{2}$ single crystals. As the spin-density wave (SDW) phase is suppressed, we observe a clear increase of the Fe 3$d$ bands anisotropy along with their localization at the FeAs plane. Such an increase of the planar orbital content interestingly occurs independently on the chemical substitution responsible for suppressing the SDW phase. As a consequence, the magnetic fluctuations combined with the resultant particular symmetry of the Fe 3$d$ bands are propitious ingredients to the emergence of superconductivity in this class of materials.Comment: 6 pages, 5 figure

The Fermi surface of CeCoIn5: dHvA

Measurements of the de Haas - van Alphen effect in the normal state of the heavy Fermion superconductor CeCoIn5 have been carried out using a torque cantilever at temperatures ranging from 20 to 500 mK and in fields up to 18 tesla. Angular dependent measurements of the extremal Fermi surface areas reveal a more extreme two dimensional sheet than is found in either CeRhIn5 or CeIrIn5. The effective masses of the measured frequencies range from 9 to 20 m*/m0.Comment: 4 pages, 2 figures, submitted to PRB Rapid